Study Materials for mechanical engineers

Content1. MECHANICAL PROPERTIES! 5

Table 1-2.-Mechanical Properties of Metals/Alloys 6

Strength 6

Hardness 6

Toughness 7

Elasticity 7

Plasticity 7

Brittleness 7

Ductility and Malleability 7

Yield 8

Yield criterion 10

Isotropic Yield criteria 10

Anisotropic yield criteria 11

Factors influencing yield stress 11

Strengthening mechanisms 12

Implications for structural engineering 142. Hardness Testing! 15

Rockwell scale 15

Brinell scale 17

Vickers hardness test 19

Shore Durometer 22

Durometer scales 22

Method of measurement 22

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Test setup for type A & D 22

Durometers of various common materials 233. Wire Rope & Strand! 24

Wire Rope Description 24Size 24Construction 24The main components of a wire rope are shown below. 24Steel Quality Tensile Strength 25EIPS -Extra Improved Plough Strength 25Lay 26

CHARACTERISTICS OF LAY: 27Lubrication 28

Wire Rope Terms 28Minimum Break Force (MBF) 28Diameter 28Design Factor 28Working Load Limit (WLL) 28

CARE AND MAINTENANCE 29Breaking In 29Lubrication 29Inspection 29

EFFICIENCY OF TERMINAL ROPE ATTACHMENTS 30Verope 31Stainless Rope 31Constructions 311 x 19 Strand - Non flexible 327 x 7 Wire Rope - Flexible 327 x 19 Wire Rope - Very Flexible 32Grades 32

Core 344. Notes on Nuts and Bolts! 35

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Bolt Terms 35

Thread Terms 36

Thread Specifications 36

Metric Threads 38

Bolt Strength 39

Preload 395. Fatigue! 43

Fatigue life 43

Characteristics of fatigue 43

Surface fatigue 44

Fretting wear 446. Thermal shock! 46

7. Wear! 47

Adhesive wear 48

Abrasive wear 488. BASIC GASKET DESIGN! 50

Gasket Design Guide 50

Viton 51

Four families of polymers 529. Maraging steel! 54

Properties 54

Heat treatment cycle 54

Uses 55

Physical properties 56

Properties of Maraging Steels 57

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Tempering of maraging steels 57

Variations of Properties in Maraging Steels 5910.Load cell! 61

Load cell types 61

Applications 6211. Inventory! 63

ABC analysis 63

ABC codes 63

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1. MECHANICAL PROPERTIESStrength, hardness, toughness, elasticity, plasticity, brittleness, and ductility and malleability are mechanical properties used as measurements of how metals behave under a load. These properties are described in terms of the types of force or stress that the metal must withstand and how these are resisted.Common types of stress are compression, tension, shear, torsion, impact, 1-2 or a combination of these stresses, such as fatigue. (SeeCompression stresses develop within a material when forces compress or crush the material. A column that supports an overhead beam is in compression, and the internal stresses that develop within the column are compression.Tension (or tensile) stresses develop when a material is subject to a pulling load; for example, when using a wire rope to lift a load or when using it as a guy to anchor an antenna. "Tensile strength" is defined as resistance to longitudinal stress or pull and can be measured in pounds per square inch of cross section. Shearing stresses occur within a material when external forces are applied along parallel lines in opposite directions. Shearing forces can separate material by sliding part of it in one direction and the rest in the opposite direction.Some materials are equally strong in compression, tension, and shear. However, many materials show marked differences; for example, cured concrete has a maximum strength of 2,000 psi in compression, but only 400 psi in tension. Carbon steel has a maximum strength of 56,000 psi in tension and compression but a maximum shear strength of only 42,000 psi; therefore, when dealing with maximum strength, you should always state the type of loading.A material that is stressed repeatedly usually fails at a point considerably below its maximum strength in tension, compression, or shear. For example, a thin steel rod can be broken by hand by bending it back and forth several times in the same place; however, if the same force is applied in a steady motion (not bent back and forth), the rod cannot be broken. The tendency of a material to fail after repeated bending at the same point is known as fatigue.

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Table 1-2.-Mechanical Properties of Metals/Alloys

StrengthStrength is the property that enables a metal to resist deformation under load. The ultimate strength is the maximum strain a material can withstand. Tensile strength is a measurement of the resistance to being pulled apart when placed in a tension load.Fatigue strength is the ability of material to resist various kinds of rapidly changing stresses and is expressed by the magnitude of alternating stress for a specified number of cycles.Impact strength is the ability of a metal to resist suddenly applied loads and is measured in foot-pounds of force.HardnessHardness is the property of a material to resist permanent indentation. Because there are several methods of measuring hardness, the hardness of a material is always specified in terms of the particular test that was used to measure this property. Rockwell, Vickers, or Brinell are some of the methods of testing. Of these tests, Rockwell is the one most frequently used. The basic principle used in the Rockwell testis that a hard material can penetrate a softer one. We then measure the amount of penetration and compare it to a scale. For ferrous metals, which are usually harder than nonferrous metals, a diamond tip is used and the hardness is indicated by aRockwell "C" number. On nonferrous metals, that are softer, a metal ball is used and the hardness is indicated by a Rockwell "B" number. To get an idea of the

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property of hardness, compare lead and steel. Lead can be scratched with a pointed wooden stick but steel cannot because it is harder than lead.A full explanation of the various methods used to determine the hardness of a material is available in commercial books or books located in your base library.ToughnessToughness is the property that enables a material to withstand shock and to be deformed without rupturing. Toughness may be considered as a combination of strength and plasticity. Table 1-2 shows the order of some of the more common materials for toughness as well as other properties.ElasticityWhen a material has a load applied to it, the load causes the material to deform. Elasticity is the ability of a material to return to its original shape after the load is removed. Theoretically, the elastic limit of a material is the limit to which a material can be loaded and still recover its original shape after the load is removed.PlasticityPlasticity is the ability of a material to deform permanently without breaking or rupturing. This property is the opposite of strength. By careful alloying of metals, the combination of plasticity and strength is used to manufacture large structural members. For example, should a member of a bridge structure become overloaded, plasticity allows the overloaded member to flow allowing the distribution of the load to other parts of the bridge structure.BrittlenessBrittleness is the opposite of the property of plasticity. A brittle metal is one that breaks or shatters before it deforms. White cast iron and glass are good examples of brittle material. Generally, brittle metals are high in compressive strength but low in tensile strength. As an example, you would not choose cast iron for fabricating support beams in a bridge.Ductility and MalleabilityDuctility is the property that enables a material to stretch, bend, or twist without cracking or breaking. This property makes it possible for a material to be drawn out into a thin wire. In comparison, malleability is the property that enables a material to deform by compressive forces without developing defects. A malleable material is one that can be stamped, hammered, forged, pressed, or rolled into thin sheets.

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YieldThe yield strength or yield point of a material is defined in engineering and materials science as the stress at which a material begins to deform plastically. Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed. Once the yield point is passed some fraction of the deformation will be permanent and non-reversible.In the three-dimensional space of the principal stresses (1,2,3), an infinite number of yield points form together a yield surface.Knowledge of the yield point is vital when designing a component since it generally represents an upper limit to the load that can be applied. It is also important for the control of many materials production techniques such as forging, rolling, or pressing. In structural engineering, this is a soft failure mode which does not normally cause catastrophic failure or ultimate failure unless it accelerates buckling.Definition

Typical yield behavior for non-ferrous alloys.1: True elastic limit2: Proportionality limit3: Elastic limit4: Offset yield strength

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It is often difficult to precisely define yielding due to the wide variety of stressstrain curves exhibited by real materials. In addition, there are several possible ways to define yielding:[1]True elastic limitThe lowest stress at which dislocations move. This definition is rarely used, since dislocations move at very low stresses, and detecting such movement is very difficult.Proportionality limitUp to this amount of stress, stress is proportional to strain (Hooke's law), so the stress-strain graph is a straight line, and the gradient will be equal to the elastic modulus of the material.Elastic limit (yield strength)Beyond the elastic limit, permanent deformation will occur. The lowest stress at which permanent deformation can be measured. This requires a manual load-unload procedure, and the accuracy is critically dependent on equipment and operator skill. For elastomers, such as rubber, the elastic limit is much larger than the proportionality limit. Also, precise strain measurements have shown that plastic strain begins at low stresses.[2][3]Offset yield point (proof stress)This is the most widely used strength measure of metals, and is found from the stress-strain curve as shown in the figure to the right. A plastic strain of 0.2% is usually used to define the offset yield stress, although other values may be used depending on the material and the application. The offset value is given as a subscript, e.g. Rp0.2=310 MPa. In some materials there is essentially no linear region and so a certain value of strain is defined instead. Although somewhat arbitrary, this method does allow for a consistent comparison of materials.Upper yield point and lower yield pointSome metals, such as mild steel, reach an upper yield point before dropping rapidly to a lower yield point. The material response is linear up until the upper yield point, but the lower yield point is used in structural engineering as a conservative value. If a metal is only stressed to the upper yield point, and beyond, luders bands can develop.[4]

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Yield criterionA yield criterion, often expressed as yield surface, or yield locus, is an hypothesis concerning the limit of elasticity under any combination of stresses. There are two interpretations of yield criterion: one is purely mathematical in taking a statistical approach while other models attempt to provide a justification based on established physical principles. Since stress and strain are tensor qualities they can be described on the basis of three principal directions, in the case of stress these are denoted by , and

.The following represent the most common yield criterion as applied to an isotropic material (uniform properties in all directions). Other equations have been proposed or are used in specialist situations.Isotropic Yield criteriaMaximum Principal Stress Theory - Yield occurs when the largest principal stress exceeds the uniaxial tensile yield strength. Although this criterion allows for a quick and easy comparison with experimental data it is rarely suitable for design purposes.

Maximum Principal Strain Theory - Yield occurs when the maximum principal strain reaches the strain corresponding to the yield point during a simple tensile test. In terms of the principal stresses this is determined by the equation:

Maximum Shear Stress Theory - Also known as the Tresca yield criterion, after the French scientist Henri Tresca. This assumes that yield occurs when the shear stress exceeds the shear yield strength :

Total Strain Energy Theory - This theory assumes that the stored energy associated with elastic deformation at the point of yield is independent of the specific stress tensor. Thus yield occurs when the strain energy per unit volume is greater than the strain energy at the elastic limit in simple tension. For a 3-dimensional stress state this is given by:

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Distortion Energy Theory - This theory proposes that the total strain energy can be separated into two components: the volumetric (hydrostatic) strain energy and the shape (distortion or shear) strain energy. It is proposed that yield occurs when the distortion component exceeds that at the yield point for a simple tensile test. This is generally referred to as the Von Mises yield criterion and is expressed as:

Based on a different theoretical underpinning this expression is also referred to as octahedral shear stress theory.Other commonly used isotropic yield criteria are the Mohr-Coulomb yield criterion Drucker-Prager yield criterion Bresler-Pister yield criterion

Anisotropic yield criteriaWhen a metal is subjected to large plastic deformations the grain sizes and orientations change in the direction of deformation. As a result the plastic yield behavior of the material shows directional dependency. Under such circumstances, the isotropic yield criteria such as the von Mises yield criterion are unable to predict the yield behavior accurately. Several anisotropic yield criteria have been developed to deal with such situations. Some of the more popular anisotropic yield criteria are: Hill's quadratic yield criterion. Generalized Hill yield criterion. Hosford yield criterion.

Factors influencing yield stressThe stress at which yield occurs is dependent on both the rate of deformation (strain rate) and, more significantly, the temperature at which the deformation occurs. Early work by Alder and Philips in 1954 found that the relationship between yield stress and strain rate (at constant temperature) was best described by a power law relationship of the form

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where C is a constant and m is the strain rate sensitivity. The latter generally increases with temperature, and materials where m reaches a value greater than ~0.5 tend to exhibit super plastic behaviour.Later, more complex equations were proposed that simultaneously dealt with both temperature and strain rate:

where and A are constants and Z is the temperature-compensated strain-rate - often described by the Zener-Hollomon parameter:

where QHW is the activation energy for hot deformation and T is the absolute temperature.Strengthening mechanismsThere are several ways in which crystalline and amorphous materials can be engineered to increase their yield strength. By altering dislocation density, impurity levels, grain size (in crystalline materials), the yield strength of the material can be fine tuned. This occurs typically by introducing defects such as impurities dislocations in the material. To move this defect (plastically deforming or yielding the material), a larger stress must be applied. This thus causes a higher yield stress in the material. While many material properties depend only on the composition of the bulk material, yield strength is extremely sensitive to the materials processing as well for this reason.These mechanisms for crystalline materials include:1. Work Hardening - Where deforming the material will introduce dislocations, which increases their density in the material. This increases the yield strength of the material, since now more stress must be applied to move these dislocations through a crystal lattice. Dislocations can also interact with each other, becoming entangled.The governing formula for this mechanism is:

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where y is the yield stress, G is the shear elastic modulus, b is the magnitude of the Burgers vector, and is the dislocation density.2. Solid Solution Strengthening - By alloying the material, impurity atoms in low concentrations will occupy a lattice position directly below a dislocation, such as directly below an extra half plane defect. This relieves a tensile strain directly below the dislocation by filling that empty lattice space with the impurity atom.The relationship of this mechanism goes as:

where is the shear stress, related to the yield stress, G and b are the same as in the above example, C_s is the concentration of solute and is the strain induced in the lattice due to adding the impurity.3. Particle/Precipitate Strengthening - Where the presence of a secondary phase will increase yield strength by blocking the motion of dislocations within the crystal. A line defect that, while moving through the matrix, will be forced against a small particle or precipitate of the material. Dislocations can move through this particle either by shearing the particle, or by a process known as bowing or ringing, in which a new ring of dislocations is created around the particle.The shearing formula goes as:

and the bowing/ringing formula:

In these formulas, rparticle is the particle radius, particle matrix is the surface tension between the matrix and the particle, linterparticle is the distance between the particles.4. Grain boundary strengthening - Where a buildup of dislocations at a grain boundary causes a repulsive force between dislocations. As grain size

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decreases, the surface area to volume ratio of the grain increases, allowing more buildup of dislocations at the grain edge. Since it requires a lot of energy to move dislocations to another grain, these dislocations build up along the boundary, and increase the yield stress of the material. Also known as Hall-Petch strengthening, this type of strengthening is governed by the formula:

where0 is the stress required to move dislocations,k is a material constant, andd is the grain size.Implications for structural engineeringYielded structures have a lower stiffness, leading to increased deflections and decreased buckling strength. The structure will be permanently deformed when the load is removed, and may have residual stresses. Engineering metals display strain hardening, which implies that the yield stress is increased after unloading from a yield state. Highly optimized structures, such as airplane beams and components, rely on yielding as a fail-safe failure mode. No safety factor is therefore needed when comparing limit loads (the highest loads expected during normal operation) to yield criteria.[citation needed]

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2.Hardness Testing Rockwell scaleThe Rockwell scale is a hardness scale based on the indentation hardness of a material. The Rockwell test determines the hardness by measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload.[1] There are different scales, which are denoted by a single letter, that use different loads or indenters. The result, which is a dimensionless number, is noted by HRX where X is the scale letter.

HistoryThe differential depth hardness measurement was conceived in 1908 by a Viennese professor named Ludwig in his book Die Kegelprobe (crudely, "the cone trial").[2] The differential-depth method subtracted out the errors associated with the mechanical imperfections of the system, such as backlash and surface imperfections. The Rockwell hardness tester, a differential-depth machine, was co-invented by Connecticut natives Hugh M. Rockwell (1890-1957) and Stanley P. Rockwell (1886-1940). A patent was applied for on July 15, 1914.[3] The requirement for this tester was to quickly determine the effects of heat treatment on steel bearing races. The Brinell hardness test, invented in 1900 in Sweden, was slow, not useful on fully hardened steel, and left too large an impression to be considered nondestructive. The application was subsequently approved on Feb. 11, 1919, and holds patent number #1,294,171. At the time of invention, both Hugh and Stanley Rockwell (not direct relations) worked for the New Departure Manufacturing Co. of Bristol, CT. New Departure was a major ball bearing manufacturer, that in 1916 became part of United Motors and shortly later, General Motors Corp. After leaving the Connecticut company, Stanley Rockwell, then in Syracuse, NY, applied for an improvement to the original invention on Sept. 11, 1919, which was approved on Nov. 18, 1924. The new tester holds patent #1,516,207.[4][5] Rockwell moved to West Hartford, CT, and made an additional improvement in 1921.[5] Stanley collaborated with instrument manufacturer Charles H. Wilson of the Wilson-Mauelen Company in 1920 to commercialize his invention and develop standardized testing machines.[6] Stanley started a heat-treating firm circa 1923, the Stanley P. Rockwell Company, which still exists in Hartford, CT. The later-named Wilson Mechanical Instrument Company has changed ownership over the years, and was most recently acquired by Instron Corp. in 1993.

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OperationThe determination of the Rockwell hardness of a material involves the application of a minor load followed by a major load, and then noting the depth of penetration, vis a vis, hardness value directly from a dial, in which a harder material gives a higher number. The chief advantage of Rockwell hardness is its ability to display hardness values directly, thus obviating tedious calculations involved in other hardness measurement techniques. Also, the relatively simple and inexpensive set-up enables its installation in college laboratories.It is typically used in engineering and metallurgy. Its commercial popularity arises from its speed, reliability, robustness, resolution and small area of indentation.

Good practices Cleaning indenter and test-piece to be clear of dirt, grease, rust or paint Measuring on a perpendicular, flat surface ("round work correction factors"

are invoked to adjust for test-piece curvature) Ensuring that the thickness of the test-piece is at least 10 times the depth of

the indentation Maintaining an adequate spacing between multiple indentations Controlling the speed of the indentation.

Scales and valuesThere are several alternative scales, the most commonly used being the "B" and "C" scales. Both express hardness as an arbitrary dimensionless number.Various Rockwell scales[7]

Scale Abbreviation

Load Indenter Use

A HRA 60 kgf 120 diamond cone120 diamond coneB HRB 100 kgf 1/16 in diameter steel

sphereAluminium, brass, and soft steels

C HRC 150 kgf 120 diamond cone Harder steelsD HRD 100 kgf 120 diamond cone120 diamond coneE HRE 100 kgf 1/8 in diameter steel sphere1/8 in diameter steel sphereF HRF 60 kgf 1/16 in diameter steel sphere1/16 in diameter steel sphere

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G HRG 150 kgf 1/16 in diameter steel sphere1/16 in diameter steel sphereAlso called a brale indenterAlso called a brale indenterAlso called a brale indenterAlso called a brale indenterAlso called a brale indenter

Except for one very limited exception,[clarification needed] the steel indenter balls have been replaced by tungsten carbide balls of the varying diameters. Scales using the ball indenter have a "W" suffix added to the scale name to indicate usage of the carbide ball, for example "HR30T" is now "HR30TW".[citation needed]

The superficial Rockwell scales use lower loads and shallower impressions on brittle and very thin materials. The 45N scale employs a 45-kgf load on a diamond cone-shaped Brale indenter, and can be used on dense ceramics. The 15T scale employs a 15-kgf load on a 1/16-inch diameter hardened steel ball, and can be used on sheet metal.Readings below HRC 20 are generally considered unreliable, as are readings much above HRB 100.Brinell scale

The Brinell scale characterizes the indentation hardness of materials through the scale of penetration of an indenter, loaded on a material test-piece. It is one of several definitions of hardness in materials science.Proposed by Swedish engineer Johan August Brinell in 1900, it was the first widely used and standardised hardness test in engineering and metallurgy. The large size of indentation and possible damage to test-piece limits its usefulness.

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The typical test uses a 10 mm diameter steel ball as an indenter with a 3,000 kgf (29 kN) force. For softer materials, a smaller force is used; for harder materials, a tungsten carbide ball is substituted for the steel ball. The indentation is measured and hardness calculated as:

where:P = applied force (kgf)D = diameter of indenter (mm)d = diameter of indentation (mm)The BHN can be converted into the ultimate tensile strength (UTS), although the relationship is dependent on the material, and therefore determined empirically. The relationship is based on Meyer's index (n) from Meyer's law. If Meyer's index is less than 2.2 then the ratio of UTS to BHN is 0.36. If Meyer's index is greater then the ratio increases.[1]

Common valuesWhen quoting a Brinell hardness number (BHN or more commonly HB), the conditions of the test used to obtain the number must be specified. The standard format for specifying tests can be seen in the example "HBW 10/3000". "HBW" means that a tungsten carbide (from the chemical symbol for tungsten) ball indenter was used, as opposed to "HBS", which means a hardened steel ball. The "10" is the ball diameter in millimeters. The "3000" is the force in kilograms force.Brinell hardness numbers

Material HardnessSoftwood (e.g., pine) 1.6 HBS 10/100Hardwood 2.67.0 HBS 1.6 10/100Aluminium 15 HBCopper 35 HBMild steel 120 HB18-8 (304) stainless steel annealed 200 HB[2]Glass 1550 HB

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Hardened tool steel 15001900 HBRhenium diboride 4600 HBNote: Standard test conditions unless otherwise statedNote: Standard test conditions unless otherwise stated

Vickers hardness test

A Vickers hardness tester

The Vickers hardness test was developed in 1924 by Smith and Sandland at Vickers Ltd as an alternative to the Brinell method to measure the hardness of materials.[1] The Vickers test is often easier to use than other hardness tests since the required calculations are independent of the size of the indenter, and the indenter can be used for all materials irrespective of hardness. The basic principle, as with all common measures of hardness, is to observe the questioned material's ability to resist plastic deformation from a standard source. The Vickers test can be used for all metals and has one of the widest scales among hardness tests. The unit of hardness given by the test is known as the Vickers Pyramid Number (HV). The hardness number can be converted into units of pascals, but should not be confused with a pressure, which also has units of pascals. The hardness number is determined by the load over the surface area of the indentation and not the area normal to the force, and is therefore not a pressure.The hardness number is not really a true property of the material and is an empirical value that should be seen in conjunction with the experimental methods and hardness scale used. When doing the hardness tests the distance between

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indentations must be more than 2.5 indentation diameters apart to avoid interaction between the work-hardened regions.The yield strength of the material can be approximated as:

.where c is a constant determined by geometrical factors usually ranging between 2 and 4.

Implementation

Vicker's test scheme

An indentation left in case-hardened steel after a Vickers hardness test.

It was decided that the indenter shape should be capable of producing geometrically similar impressions, irrespective of size; the impression should have well-defined points of measurement; and the indenter should have high resistance to self-deformation. A diamond in the form of a square-based pyramid satisfied these conditions. It had been established that the ideal size of a Brinell impression was 3/8 of the ball diameter. As two tangents to the circle at the ends of a chord 3d/8 long, intersect at 136, it was decided to use this as the included angle of the indenter. The angle was varied experimentally and it was found that the hardness value obtained on a homogeneous piece of material remained constant,

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irrespective of load.[2] Accordingly, loads of various magnitudes are applied to a flat surface, depending on the hardness of the material to be measured. The HV number is then determined by the ratio F/A where F is the force applied to the diamond and A is the surface area of the resulting indentation. A can be determined by the formula

which can be approximated by evaluating the sine term to give

where d is the average length of the diagonal left by the indenter. Hence,

The corresponding units of HV are then kilograms-force per square millimetre (kgf/mm). To convert a Vickers hardness number to SI units (MPa or GPa) one needs to convert the force applied from kilograms-force to newtons and the area from mm2 to m2 to give results in pascals (1kgf/mm = 9.80665106Pa).Vickers hardness numbers are reported as xxxHVyy, e.g. 440HV30, where: 440 is the hardness number, HV gives the hardness scale (Vickers), 30 indicates the load used in kg.

Vickers values are generally independent of the test force: they will come out the same for 500gf and 50kgf, as long as the force is at least 200gf.[3]Examples of HV values for various materials[4]

Material Value316L stainless steel 140HV30347L stainless steel 180HV30Carbon steel 55120HV5Iron 3080HV5

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Shore DurometerDurometer is one of several measures of the hardness of a material. Hardness may be defined as a material's resistance to permanent indentation. The durometer scale was defined by Albert F. Shore, who developed a measurement device called a durometer in the 1920s. The term durometer is often used to refer to the measurement, as well as the instrument itself. Durometer is typically used as a measure of hardness in polymers, elastomers and rubbers.[1]Durometer scalesThere are several scales of durometer, used for materials with different properties. The two most common scales, using slightly different measurement systems, are the ASTM D2240 type A and type D scales. The A scale is for softer plastics, while the D scale is for harder ones. However, the ASTM D2240-00 testing standard calls for a total of 12 scales, depending on the intended use; types A, B, C, D, DO, E, M, O, OO, OOO, OOO-S, and R. Each scale results in a value between 0 and 100, with higher values indicating a harder material.[2]Method of measurementDurometer, like many other hardness tests, measures the depth of an indentation in the material created by a given force on a standardized presser foot. This depth is dependent on the hardness of the material, its viscoelastic properties, the shape of the presser foot, and the duration of the test. ASTM D2240 durometers allows for a measurement of the initial hardness, or the indentation hardness after a given period of time. The basic test requires applying the force in a consistent manner, without shock measuring the hardness (depth of the indentation). If a timed hardness is desired, force is applied for the required time and then read. The material under test should be a minimum of 6.4mm (.25inch) thick.Test setup for type A & D

Durometer Indenting foot Applied mass [kg]

Resulting force [N]

Type A Hardened steel rod 1.1mm - 1.4mm diameter, with a truncated 35 cone, 0.79mm diameter

0.822 8.064

Type D Hardened steel rod 1.1mm - 1.4mm diameter, with a 30 conical point, 0.1mm radius tip

4.550 44.64

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The final value of the hardness depends on the depth of the indenter after it has been applied for 15sec on the material. If the indenter penetrates 2.5mm or more into the material, the durometer is 0 for that scale. If it does not penetrate at all, then the durometer is 100 for that scale. It is for this reason that multiple scales exist. Durometer is a dimensionless quantity, and there is no simple relationship between a material's durometer in one scale, and its durometer in any other scale, or by any other hardness test.Durometers of various common materials

Material Durometer Scale

Bicycle gel seat 15-30 OO

Chewing gum 20 OOSorbothane 40 OO

Sorbothane 0 A

Rubber band 25 A

Door seal 55 A

Automotive tire tread 70 A

Soft skateboard wheel 75 A

Hydraulic O-ring 70-90 A

Hard skateboard wheel 98 AEbonite Rubber 100 A

Solid truck tires 50 D

Hard hat 75 D

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3.Wire Rope & StrandWire Rope Description The properties of a wire rope are derived from its size, construction, quality lay and type of core. Size Ropes are referred to by a diameter size. The correct way to measure wire rope is shown below.

Construction The main components of a wire rope are shown below.

In the above example, each individual wire is arranged around a central wire to form a 7-wire strand. Six of these strands are formed around a central core to make a wire rope. The rope is specified at 6 x 7 (6/1) i.e., six strands each of seven wires.

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The actual range of wire rope constructions is wide and varied but the number could be limited to approximately twenty-five. The size and number of wires in each strand, as well as the size and number of strands in the rope greatly affect the characteristics of the rope. In general, a large number of small-size wires and strands produce a flexible rope with good resistance to bending fatigue. The rope construction is also important for tensile load (static, live or shock) abrasive wear, crushing, corrosion and rotation.Steel Quality Tensile Strength Production Methods, equipment and quality control in steelmaking and wire drawing ensure that wire rope conforms to Australian and International specifications.

Wire ropes are usually supplied in the following tensile ranges:

Minimum Tensile Abbreviated DescriptionBlack (bright, non-galvanised) wire

1770 MPa 1770 grade

Galvanised wire 1570MPa G1570 grade

NOTE : G1770 (Galvanised 1770 MPa) is the preferred grade for galvanized ropes other than standard multiple operation ropes of 6 x 7, 6 x 19, 6 x 24, and 6 x 37 construction. However, other than special tensile ranges can be supplied in both galvanized and black as follows:-

1220 MPa

1420 MPa

1970 MPa

2070 MPa

2250 MPa

EIPS -Extra Improved Plough StrengthGalvanised ropes and Strand are made of zinc coated (galvanised) wire rope for protection against corrosion.

With the increasing use of heavy-duty and more compact equipment (e.g. power winches on mobile cranes and mine winding) there is a gradual upward trend in the required rope wire tensile range. However, as factors other than strength influence the life of wire rope, the specific application must be kept in mind when the tensile strength of the wire is selected.

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LayThis refers to the way the wires in the strands, and the strands in the rope are formed into the completed rope. The wire strands are essentially laid up in a planetary motion with controlled twist being imparted to produce a tightly formed rope.

The term "lay" is used in three ways:

1. To describe the direction in which the strands are laid in the rope right or left. In a Right Hand lay strands are laid around the rope core in a clockwise direction see illustration below. In a Left Hand lay, the strands are laid anti-clockwise see illustrations below. Steel Wire Ropes are conventionally produced Right Hand lay unless special circumstances require Left Hand lay.

2. To describe the direction in which the wires are stranded in relation to the direction of the strands in the completed rope, e.g. Ordinary lay or Langs lay. Ordinary lay means the wires in a strand are laid in a direction opposite to the direction in which the strands are laid in the final rope. Langs lay ropes have superior properties in resistance to wear, abrasion, fatigue and scuffing. This is illustrated below, where it can be seen that wear on an outer wire is distributed over a far greater area than in Ordinary lay.

3. "Lay" is also a measure of the pitch of a strand in a rope.

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CHARACTERISTICS OF LAY: The direction of rope lay does not affect the breaking force of a rope. However, the combination of strand lay and rope lay will greatly affect the rope characteristics and this factor must be taken into consideration when choosing a rope. Although the lay length can slightly affect rope behavior the dominant aspect that influences performance is the direction of lay and whether it is Langs lay or Ordinary lay . For example, the importance of rope lay is evident in a four-part highlift grab where rotation of the grab is prevented by the use of alternate right-hand and left-hand ropes.

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Lubrication When a rope is operated over a drum or sheave, the strands and wires move relative to one another. To reduce the resultant friction within the rope as well as the friction between the rope and drum or sheave, ropes are lubricated in manufacture. In addition this lubrication also retards corrosion and inhibits possible rotting of the fibre core. In special applications a combination of lubricants may be called for example, the core and inner wires of the strands may be heavily lubricated while the lighter lubrication may be applied to outer wires and strands. Wire rope cores are normally heavily lubricated irrespective of the outer strand lubrication. Regular lubrication is more beneficial than applying large amounts infrequently. Wire Rope Terms Minimum Break Force (MBF) MBF of a strand or rope is that shown in maker catalogues or Standard Specifications. It is based on the use of wires of nominal size and the minimum tensile strength. This is the figure which should be used for design of rope equipment. Diameter The measurement across the centre line of the circle circumscribing the outer wires of a strand or the outer strands of a rope. Design Factor Term applied to the required ratios of rope breaking force to total rope force due to load. Normally set by Statutory bodies, e.g. Mines Department, Navigation Departments, Lifts and Scaffolds Departments.Working Load Limit (WLL) The WLL is the safe load that a rope can carry on a particular service. The WLL should bebased on the minimum breaking force, not the actual breaking force, which can vary depending on construction and size. The WLL for wire rope is calculated as per AS1666.1 The recommended minimum design factors for steel wire ropes under general conditions are as per AS2759. Rope that are used on appliances complying with any of the Parts of the AS1418 or AS1735 series of Standards shall be subject to design factors specified by those Standards. AS1666 Series of standards specifies the design factors for wire rope used in wire rope sings. Design factors less than the above may be used, subject to the appropriate risk assessment being done by a competent person for a particular application.

Due account should be taken of the number of parts and the efficiency whenever the design factor of a system is being determined. Regulatory authorities or other Standards may require other design factors.

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CARE AND MAINTENANCE Breaking In A wire rope may be looked upon as a machine composed of a large number of moving parts. As such it should be broken in as soon as it is installed, by loading it very lightly for a few cycles and then gradually stepping up the load, to enable both wires and strands to bed down into the working positions, with the load distributed as uniformly as possible. With the standard 6 and 8 stranded ropes, the torque can be greatly diminished after breaking-in by releasing the connection and allowing the torque to run out. This procedure may have to be repeated until the constructional stretch has been worked out of the rope and it has become neutral. The use of spinners or swivels should be avoided whenever possible. All ropes should be reeled onto winch drums as tightly and uniformly as possible during the initial installation. Lubrication Lubrication impregnated into the rope during manufacture is not sufficient to last the life of the rope. Additional lubrication should be added to the rope during service. The frequency of lubrication in the field is determined by the operating conditions of the rope e.g., high-speed heavy duty operation calls for more frequent lubrication, as do wet and/or corrosive conditions. For general purpose applications medium viscosity black oil is considered suitable. For corrosive conditions a high penetrating, water-repellant rust-inhibiting oil should be used.Inspection Wire rope is tough and durable, but nonetheless expendable and eventually reaches the end of its safe service life. Rope deterioration becomes noticeable through the presence of broken wires, surface wear, corrosion, wire or strand distortion due to mechanical abuse, or drastic reduction in diameter and lengthening of the lay. Also deterioration can be detected by the use of modern non-destructive testing techniques. Wire ropes should periodically be inspected for signs of deterioration. While Statutory Regulations govern the inspection and discarding of certain ropes, the same rules cannot be applied to all ropes. The proper frequency and degree of inspection depends largely on the possible risk to personnel and machinery in the event of rope failure. The determination of the point at which a rope should be discarded for reasons of safety requires judgment and experience in rope inspection, in addition to knowledge of the performance of previous ropes used in the same application.

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Where Statutory Regulations are laid down for the inspection and discarding of wire ropes and their attachments, wire rope users should become fully acquainted with the regulations and see that they are carried out.

Sufficient records should be kept to provide reliable history of the ropes under their control.

Inspection of both operated and discarded ropes frequently indicates equipment faults that have a large bearing on the services life and safety of the rope. It is therefore essential to inspect the equipment on which the rope is used as well as the rope. EFFICIENCY OF TERMINAL ROPE ATTACHMENTS When calculating the working load limit of a wire rope sling an allowance is made for the terminations the table below (extracted from AS 2759) gives the percentage that should be applied to a WLL calculation involving a particular rope fitting.

Efficiency of Terminal Rope AttachmentsEfficiency of Terminal Rope AttachmentsEfficiency of Terminal Rope AttachmentsEfficiency of Terminal Rope AttachmentsEfficiency of Terminal Rope Attachments

hen calculating the working load limit of a wire rope sling an allowance is made for the terminations the table below (extracted from AS2759) gives the percentage that should be applied to a WLL calculation involving a particular rope fitting.





Type of Rope fitting or end attachment

Typical tensile efficiency percentage

(Note 1)

Resistance to vibration

Ease of fitting in field

Reference to Note below

Turnback eye with pressed aluminium alloy ferrule: 80mm rope diameter 90 Good -

Flemish eye with pressed sleeve: 80mm rope diameter 90 Good -

Hand spliced eye: >=8 20 60mm rope diameter 75 Good - 1

Open swaged socket 100 Good Fair 2 and 3

Close Swaged socket 100 Good Fair 2 and 3

Open poured socket 100 Fair Good 2

Close poured socket 100 Fair Good 2

Wedge grip capel 100 Fair Good 2

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Wedge-type socket 80 Fair Excellent -

Eye with wire rope grips 80 Good Very Good 4 and 5

Eye with fist grips 80 Good Very Good 4 and 5

Notes:

1. Where Lang's lay rope is used, the efficiency is up to 15% less than that given.

2. Fitting in the field is not uncommon, but specialised equipment is necessary.

3. Fitting in the field is generally restricted to ropes with a diameter of not more than 20mm.

4. Not to be used for lifting.

5. When fitted with the required number of wire rope grips, refers to AS2076 or the manufacturer's recommendation.

VeropeBullivants continually review the special needs of our customers and we are now pleased to offer our customers Verope. Verope can offer innovative and cost effective solutions.

Verope is a Joint Venture company between Kiswire from South Korea and Pierre Verreet, head and founder of Verope. The concept of Verope AG is to provide affordable high quality special steel wire ropes for crane applications to the world market.

The products featured in this catalgoue have been approved by leading crane manufacturers.

Stainless Rope Stainless steel wire rope has many varied uses in various industries. The main characteristics which make stainless steel wire rope such a popular product are its resistance to corrosion, attractive long lasting appearance, comparative inexpensiveness and the full range of accessories available.

Stainless steel has a lower resistance to bending stresses than galvanised rope. Failure due to work hardening and fatigue is to be avoided by using:

Sheaves 25 times rope diameter

Bending angles over 90 degrees

Please note Stainless steel is not recommended for lifting purposes.

Constructions Three constructions are commonly available:

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1 x 19 Strand - Non flexible

Suitable for standing rigging, mast stays, applications where the strand will not be subjected to bending stresses, i.e. should not be run over sheaves. Smooth surface.

7 x 7 Wire Rope - Flexible

Suitable for hand rails, hang glider struts, luff wires in sails, trapeze wires.

7 x 19 Wire Rope - Very FlexibleSuitable for running rigging, control cables, fishing nets, cranes and winches. Grades Bullivants stock a full range of stainless steel wire ropes and strand for use in marine and general engineering applications. There are two common grades available, Grade 304 (AISI) and Grade 316 (AISI). Grade 304: 304 stainless steel will provide good results in most applications. It will resists organic chemicals and a wide range of inorganic chemicals. Grade 304 has good fatigue properties in engineering applications where rope is sound on a drum or passes over

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sheaves. Grade 304 is not recommended in environments of high temperatures or high chloride or sulphate concentrations. Grade 316: 316 Stainless steel has a higher corrosion resistance than Grade 304 and has improved properties at higher temperatures and chloride and sulphate resistance. It is the recommended grade for any standing applications particularly in marine environments.

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Core

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4.Notes on Nuts and BoltsA screw thread is a helical groove on a shaft. When used for delivering power, it is called a drive screw. Drive screws aren't really all that efficient, as they loose a significant amount of power to friction. However, this friction can be put to use in the case of threaded fasteners. You might say that a drive screw is an inclined plane wrapped around a post, while a fastener is a wedge wrapped around a post.Bolt Terms

A 1/2-13UNC-2A-3 bolt, with a 2" thread and a 1" shank.As nuts and bolts are not perfectly rigid, but stretch slightly under load, the distribution of stress on the threads is not uniform. In fact, on a theoretically infinitely long bolt, the first thread takes a third of the load, the first three threads take three-quarters of the load, and the first six threads take essentially the whole load. Beyond the first six threads, the remaining threads are under essentially no load at all. Therefore, a nut or bolt with six threads acts very much like an infinitely long nut or bolt (and it's a lot cheaper).

Stress on bolt threads. Note how the majority ofthe stress is on the first thread to the left.Image from Spiralock.

Thread % %Sum


1 34% 34%


2 23% 55%


3 16% 71%Stress on bolt threads. Note how the majority ofthe stress is on the first thread to the left.Image from Spiralock.



6 7% 98%

There is little point in having more than six threads in anything. Nuts with National Coarse threads typically have 5 threads in them, whereas nuts with National Fine threads

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have about 8 threads. Nuts are usually stronger than the bolts they are on, which is to say that the bolt will usually break before the nut strips.It is often said that two threads must be exposed above a nut. The reason for this is that the first two threads of a bolt are often poorly formed, and may not engage the nut properly. If they're not doing their share, the other threads in the nut will be overloaded, and the nut may strip.Thread TermsMetric and American threads both conform to the same profile, a series of equilateral triangles with the crests chopped off and the roots rounded.

External Standard Thread ProfileThe depth of the threads is 54.127% of the distance between threads, and the radius of the rounded root is 14.434% of the distance between threads. Another way of looking at it would be to say that 1/8 of the height of each equilateral triangle is chopped off the top, and 1/4 of the height off the bottom, leaving only 5/8 of the height available. (The height of an equilateral triangle is equal to the width times half of the square root of three; 5/8 of this is 0.54127.)The root diameter of the thread is the nominal diameter minus 108.3% of the pitch of the thread. This means that fine threads have larger root diameters than coarse threads, and thus larger tap drill sizes. For threading using a tap or die, most threads are not cut to full depth, but to 75% or so. The resulting threads are not quite as strong, but full depth threading is very hard on the tap or die. Threading on a lathe presents no difficulty cutting to full depth.Thread SpecificationsThread specifications are written thus:1/2-13UNC-2

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which means: bolt diameter threads per inch thread type fit class

There are four Fit Classes, ranging from falling-off-loose to scientific-instrument-tight. Class 1= Loose Class 2= Free Class 3= Medium Class 4= Close

The class is followed by an A for external (screw) threads and a B for internal (nut) threads. Most are class 2. 3 is for precision assembly, and 4 is used for things like lathe lead screws and measuring instruments.In November 1948, NATO issued a new standard for threads, the Unified National system. American bolts had flat-bottomed groves between threads, which interfered with British round-topped threads. Likewise, British bolts wouldn't fit American nuts. The Unified system uses a round-bottom grove to fit the British threads, and a flat-topped thread to fit the American threads, so it not only fit itself, but both existing systems.

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Metric ThreadsMetric threads use the same thread profile as SAE threads. The biggest difference is that the thread pitch (distance between consecutive threads) is given instead of threads per unit distance.

Diameter CoarsePitchmm

FinePitchmm

Root Dia.Coarse

mm

HexHeadSizemm

ISOWasher

IDmm

ISOWasher

ODmm

ISOWasher

Thicknessmm

1 0.25 0.7294 1.1 0.25 0.8294 1.2 0.25 0.9294 1.4 0.30 1.075 1.6 0.35 1.221 3.2 1.8 0.35 1.421 2 0.40 1.567 4

2.2 0.45 1.713 2.5 0.45 2.013 5 3 0.50 2.459 5.5 3.4 7.0 0.6

3.5 0.60 2.850 4 0.70 0.50 3.242 7 4.5 9.0 0.9

4.5 0.75 0.50 3.688 5 0.80 0.50 4.134 8 5.5 10 11

5.5 0.50 6 1.00 0.50 4.917 10 6.7 12.5 1.87 1.00 0.75 5.917 8 1.25 0.75 6.647 13 8.7 17 1.89 1.25 0.75 7.647

10 1.50 0.75 8.376 16 10.9 21 2.211 1.50 0.75 9.376 12 1.75 0.75 10.11 18 13.4 24 2.7

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14 2.00 1.00 11.83 21 16 2.00 1.00 13.83 24 17.4 30 3.318 2.50 1.00 15.29 20 2.50 1.00 17.29 30 21.5 37.9 3.3

Bolt StrengthThe Society of Automotive Engineering has issued standard J429, which sets forth standards for both strength. The SAE grade of a bolt is marked on it's head in the form of short radial lines, the number of lines being two less than the SAE grade (i.e.. 3 lines for grade 5).

SAE Grade Size Range Strength (psi)1 1/4" to 1-1/2" 60,0002 1/4" to 3/4" 74,0002 7/8" to 1-1/2" 60,0005 1/4" to 1" 1,20,0005 1-1/8" to 1-1/2" 1,05,0007 1/4" to 1-1/2" 1,33,0008 1/4" to 1-1/2" 1,50,000

ASTM standards are sometimes used as well; A325 bolts are the equivalent of SAE 5, and A490 bolts are the equivalent of SAE 8.PreloadA very misunderstood part of bolting stuff together is preload, which is the tension placed on the bolt by the nut (as opposed to the load). A sufficiently high preload will protect the bolt from fatigue as the load changes, as the varying load will change the clamping force on the bolted components, rather than the tension on the bolt. (This is not strictly true, but for a tinkerer like me, it's adequate.) As a rule of thumb, the preload should exceed the maximum load by 15% or so.In order for this to work, however, the joint must be stiffer than the bolt. For this reason, the shank of high-tech bolts are often necked down to the same diameter of the root of the thread. As long as it isn't thinner than the root of the thread, it isn't any weaker than the thread, and therefore doesn't effect overall bolt strength, but it is significantly less stiff than the original shank.There are two ways to measure preload on a bolt; a torque wrench, and by measuring the angle the nut has turned. Of the two, the latter is more accurate, as friction plays a significant - and more importantly, indeterminate - role when using a torque wrench.Torque = K preload diameterK, the so-called Nut Factor, usually varies between 0.3 and 0.1, and is very sensitive to a number of factors, ranging from temperature to thread condition, even to how fast the bolt is tightened.

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Measuring the angle the nut has turned is simply measuring how much the bolt is stretching, equal to the pitch (distance between threads) times the number of turns. Using this requires that the components being bolted don't compress much (or compress a known amount), and that the "spring rate" of the bolt be known.Turns = preload (spring rate pitch)For example, if the "spring rate" of a 1/2-13 bolt is 50,000 pounds per inch (note that I made that up, and that most bolts will yield long before stretching an inch), and you need 500 pounds of preload, you'll need to stretch the bolt 500 50000 = 0.01 inch. At 13 threads per inch (0.0769 inches per thread), this would equate to 0.13 turns, or about 45 past snug.If more than one bolt is used in a joint, and those bolts are closer together than about four diameters, the preload on one bolt will effect the preload on the other bolts by compressing the joint. This effect is called "crosstalk", and then all bets are off. Joints that are significantly less stiff than the bolts, such as joints involving gaskets, suffer much worse from crosstalk. The best way to control crosstalk is to use a carefully thought out tightening sequence (usually a spiral starting at the center, or for circular patterns, alternating bolts), and to tighten the bolts in small steps. Even so, it's a crap shoot. CreepCreep is the tendency of a solid material to slowly move or deform permanently under the influence of stresses. It occurs as a result of long term exposure to levels of stress that are below the yield strength of the material. Creep is more severe in materials that are subjected to heat for long periods, and near the melting point. Creep always increases with temperature.The rate of this deformation is a function of the material properties, exposure time, exposure temperature and the applied structural load. Depending on the magnitude of the applied stress and its duration, the deformation may become so large that a component can no longer perform its function for example creep of a turbine blade will cause the blade to contact the casing, resulting in the failure of the blade. Creep is usually of concern to engineers and metallurgists when evaluating components that operate under high stresses or high temperatures. Creep is a deformation mechanism that may or may not constitute a failure mode. Moderate creep in concrete is sometimes welcomed because it relieves tensile stresses that otherwise may have led to cracking.Unlike brittle fracture, creep deformation does not occur suddenly upon the application of stress. Instead, strain accumulates as a result of long-term stress. Creep deformation is "time-dependent" deformation.

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The temperature range in which creep deformation may occur differs in various materials. For example, Tungsten requires a temperature in the thousands of degrees before creep deformation can occur while ice formations will creep in freezing temperatures.[1] As a rule of thumb, the effects of creep deformation generally become noticeable at approximately 30% of the melting point for metals and 4050% of melting point for ceramics. Virtually any material will creep upon approaching its melting temperature. Since the minimum temperature is relative to melting point, creep can be seen at relatively low temperatures for some materials. Plastics and low-melting-temperature metals, including many solders, creep at room temperature as can be seen markedly in old lead hot-water pipes. Planetary ice is often at a high temperature relative to its melting point, and creeps.Creep deformation is important not only in systems where high temperatures are endured such as nuclear power plants, jet engines and heat exchangers, but also in the design of many everyday objects. For example, metal paper clips are stronger than plastic ones because plastics creep at room temperatures. Aging glass windows are often erroneously used as an example of this phenomenon: measurable creep would only occur at temperatures above the glass transition temperature around 900F/500C. While glass does exhibit creep under the right conditions, apparent sagging in old windows may instead be a consequence of obsolete manufacturing processes, such as that used to create crown glass, which resulted in inconsistent thickness. [2][3]An example of an application involving creep deformation is the design of tungsten light bulb filaments. Sagging of the filament coil between its supports increases with time due to creep deformation caused by the weight of the filament itself. If too much deformation occurs, the adjacent turns of the coil touch one another, causing an electrical short and local overheating, which quickly leads to failure of the filament. The coil geometry and supports are therefore designed to limit the stresses caused by the weight of the filament, and a special tungsten alloy with small amounts of oxygen trapped in the crystallite grain boundaries is used to slow the rate of coble creep.In steam turbine power plants, pipes carry steam at high temperatures (566C/1050F) and high pressures of 24.1 MPa (3500 psi) or greater. In jet

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engines, temperatures can reach up to 1400C (2550F) and initiate creep deformation in even advanced-coated turbine blades. Hence, it is crucial for correct functionality to understand the creep deformation behavior of materials.

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5.FatigueIn materials science, fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading. The maximum stress values are less than the ultimate tensile stress limit, and may be below the yield stress limit of the material.Fatigue lifeASTM defines fatigue life, Nf, as the number of stress cycles of a specified character that a specimen sustains before failure of a specified nature occurs.[1]Characteristics of fatigue

Fracture of an aluminium crank arm. Dark area: slow crack growth. Bright area: sudden fracture. The process starts with dislocation movements, eventually forming

persistent slip bands that nucleate short cracks. Fatigue is a stochastic process, often showing considerable scatter

even in controlled environments. The greater the applied stress range, the shorter the life. Fatigue life scatter tends to increase for longer fatigue lives. Damage is cumulative. Materials do not recover when rested. Fatigue life is influenced by a variety of factors, such as temperature,

surface finish, microstructure, presence of oxidizing or inert chemicals, residual stresses, contact (fretting), etc.

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Some materials (e.g., some steel and titanium alloys) exhibit a theoretical fatigue limit below which continued loading does not lead to failure.

In recent years, researchers (see, for example, the work of Bathias, Murakami, and Stanzl-Tschegg) have found that failures occur below the theoretical fatigue limit at very high fatigue lives (109 to 1010 cycles). An ultrasonic resonance technique is used in these experiments with frequencies around 1020kHz.

High cycle fatigue strength (about 103 to 108 cycles) can be described by stress-based parameters. A load-controlled servo-hydraulic test rig is commonly used in these tests, with frequencies of around 2050Hz. Other sorts of machineslike resonant magnetic machinescan also be used, achieving frequencies up to 250Hz.

Low cycle fatigue (typically less than 103 cycles) is associated with widespread plasticity; thus, a strain-based parameter should be used for fatigue life prediction. Testing is conducted with constant strain amplitudes typically at 0.015Hz.

Surface fatigueSurface fatigue is a process by which the surface of a material is weakened by cyclic loading, which is one type of general material fatigue.Fretting wearFretting wear is the repeated cyclical rubbing between two surfaces, which is known as fretting, over a period of time which will remove material from one or both surfaces in contact. It occurs typically in bearings, although most bearings have their surfaces hardened to resist the problem. Another problem occurs when cracks in either surface are created, known as fretting fatigue. It is the more serious of the two phenomena because it can lead to catastrophic failure of the bearing. An associated problem occurs when the small particles removed by wear are oxidised in air. The oxides are usually harder than the underlying metal, so wear accelerates as the harder particles abrade the metal surfaces further. Fretting corrosion acts in the same way, especially when water is present. Unprotected bearings on large structures like bridges can suffer serious degradation in behaviour, especially when salt is used during winter to deice the highways carried by

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the bridges. The problem of fretting corrosion was involved in the Silver Bridge tragedy and the Mianus River Bridge accident.

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6.Thermal shock Thermal shock is the name given to cracking as a result of rapid temperature change. Glass and ceramic objects are particularly vulnerable to this form of failure, due to their low toughness, low thermal conductivity, and high thermal expansion coefficients. However, they are used in many high temperature applications due to their high melting point.Thermal shock occurs when a thermal gradient causes different parts of an object to expand by different amounts. This differential expansion can be understood in terms of stress or of strain, equivalently. At some point, this stress overcomes the strength of the material, causing a crack to form. If nothing stops this crack from propagating through the material, it will cause the object's structure to fail.Thermal shock can be prevented by:

2. Reducing the thermal gradient seen by the object, by1. changing its temperature more slowly2. increasing the material's thermal conductivity

3. Reducing the material's coefficient of thermal expansion4. Increasing its strength5. Decreasing its Young's modulus6. Increasing its toughness, by

1. crack tip blunting, i.e., plasticity or phase transformation2. crack deflection

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7.Wear In materials science, wear is the erosion of material from a solid surface by the action of another substance. The study of the processes of wear is part of the discipline of tribology. There are five principal wear processes:

7. Adhesive wear8. Abrasive wear9. Surface fatigue10. Fretting wear11. Erosion wear

The definition of wear does not include loss of dimension from plastic deformation, although wear has occurred despite no material removal. This definition also fails to include impact wear, where there is no sliding motion, cavitation, where the counterbody is a fluid, and corrosion, where the damage is due to chemical rather than mechanical action.Wear can also be defined as a process in which interaction of the surfaces or bounding faces of a solid with its working environment results in dimensional loss of the solid, with or without loss of material. Aspects of the working environment which affect wear include loads (such as unidirectional sliding, reciprocating, rolling, and impact loads), speed, temperature, type of counterbody (solid, liquid, or gas), and type of contact (single phase or multiphase, in which the phases involved can be liquid plus solid particles plus gas bubbles).In the results of standard wear tests (such as those formulated by the respective subcommittees of ASTM Committee G-2), the loss of material during wear is expressed in terms of volume. The volume loss gives a truer picture than weight loss, particularly when comparing the wear resistance properties of materials with large differences in density. For example, a weight loss of 14 g in a sample of tungsten carbide + cobalt (density = 14000 kg/m) and a weight loss of 2.7 g in a similar sample of aluminium alloy (density = 2700 kg/m) both result in the same level of wear (1 cm) when expressed as a volume loss.The working life of an engineering component is over when dimensional losses exceed the specified tolerance limits. Wear, along with other aging processes such as fatigue, creep, and fracture toughness, causes

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progressive degradation of materials with time, leading to failure of material at an advanced age. Under normal operating parameters, the property changes during usage normally occur in three different stages as follows:- Primary or early stage or run-in period, where rate of change can be

high. Secondary or mid-age process where a steady rate of aging process is

maintained. Most of the useful or working life of the component is comprised in this stage.

Tertiary or old-age stage, where a high rate of aging leads to rapid failure.

With increasing severity of environmental conditions such as higher temperatures, strain rates, stress and sliding velocities, the secondary stage is shortened and the primary stage tends to merge with the tertiary stage, thus drastically reducing the working life. Surface engineering processes are used to minimize wear and extend working life of material. [1][2]Adhesive wearAdhesive wear is also known as scoring, galling, or seizing. It occurs when two solid surfaces slide over one another under pressure. Surface projections, or asperities, are plastically deformed and eventually welded together by the high local pressure. As sliding continues, these bonds are broken, producing cavities on the surface, projections on the second surface, and frequently tiny, abrasive particles, all of which contribute to future wear of surfaces.Abrasive wearAbrasive wear occurs when a hard rough surface slides across a softer surface[3]. ASTM (American Society for Testing and Materials) define it as the loss of material due to hard particles or hard protuberances that are forced against and move along a solid surface[4].Abrasive wear is commonly classified according to the type of contact and the contact environment [5] The type of contact determines the mode of abrasive wear. The two modes of abrasive wear are known as two-body and three-body abrasive wear. Two-body wear occurs when the grits, or hard particles, are rigidly mounted or adhere to a surface, when they remove the

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material from the surface. The common analogy is that of material being removed with sand paper. Three-body wear occurs when the particles are not constrained, and are free to roll and slide down a surface. The contact environment determines whether the wear is classified as open or closed. An open contact environment occurs when the surfaces are sufficiently displaced to be independent of one anotherThere are a number of factors which influence abrasive wear and hence the manner of material removal. Several different mechanisms have been proposed to describe the manner in which the material is remove. Three commonly identified mechanisms of abrasive wear are:

12. Plowing13. Cutting14. Fragmentation

Plowing occurs when material is displaced to the side, away from the wear particles, resulting in the formation of grooves that do not involve direct material removal. The displaced material forms ridges adjacent to grooves, which may be removed by subsequent passage of abrasive particles. Cutting occurs when material is separated from the surface in the form of primary debris, or microchips, with little or no material displaced to the sides of the grooves. This mechanism closely resembles conventional machining. Fragmentation occurs when material is separated from a surface by a cutting process and the indenting abrasive causes localized fracture of the wear material. These cracks then freely propagate locally around the wear groove, resulting in additional material removal by spalling[6].Abrasive wear can be measured as loss of mass by the Taber Abrasion Test according to ISO 9352 or ASTM D 1044.

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8.BASIC GASKET DESIGNThe gasket is only one component of a sealing system. The other components are the mating surfaces, the clamping method, the internal and external environments. First we need to consider the general function of a gasket:Prime FunctionTo allow two surfaces to be adequately mated and sealed.Provide easy separation of the mated parts at service intervals.Prevent escape or ingress of fluids (gas or liquid) even at extreme pressures and temperatures.Major Requirement Impermeable: Must not allow leakage through the material, even under pressure.Resilience and Strength: Must conform and mould itself into all irregularities on flange surfaces whilst having sufficient tensile strength to resist blow-out under operating conditions.Recovery: Must seal when tightened down (and often crushed) but recover to maintain a seal when the flanges move under mechanical, temperature or pressure forces.Creepage: Must not creep, spread or extrude under conditions of high bolt pressure or high contained fluid pressure - even at high temperatures.Chemicals: Must not be attacked or weakened by a wide range of fluids even when exposed for extended periods at high temperatures.Temperature: Must remain resilient for long periods of time at low or high temperatures.Contamination: Must not contaminate the sealed fluids - especially important in the pharmaceutical and food industries.Gasket Design GuideStep 1: Material SelectionEvaluate the application, the likely temperatures, pressures, and any chemicals.For dust sealing with low bolt loading consider a foam rubber.Lids and sumps can be sealed with cork.At low temperatures and pressures select a rubber suitable for the environment.Uses above 100 centigrade but at low pressures could be accommodated by a specialist rubber.For aggresive chemicals below about 240 centigrade PTFE can often help.Various non-asbestos jointings are available for conditions up to 450 centigrade and 160 bar.Consider graphite for steam with a variable process cycle and mica for extreme temperatures.Step 2: The Flange and the GasketOnce the material is chosen the flange and bolting need to be designed to ensure the following:

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The gasket is compressed evenly over the whole surface area. Thin flanges or excessive distance between bolt holes can result in some portions of the gasket being crushed whilst other areas are not sufficiently loaded to prevent leakage or blow-out.The flange and gasket will appear thus;

Vary the width of narrow flanges. If the bolts are widely spaced and the flange width is constant then excessive loading will occur on the limited material around the bolts.For example;

This design will even the loading;

Note: Sheet metal flanges can be stiffened by forming a lip. Soft materials can be protected by using compression stop (could be a washer).Additional requirements for dynamic sealing(Typically "O" rings and other shaft seals).Fitting: Often must flex or compress during assembly of parts and then maintain a seal with no means of assistance to provide post assembly pressure.Friction: Must not burn or wear when in contact with rotating or sliding components.Sealing: Always a compromise. Most dynamic seals must leak to function. It is the leaking fluid which provides the buffer between the moving parts and acts as a lubricant.VitonViton is a brand of synthetic rubber and fluoropolymer elastomer commonly used in O-rings and other moulded or extruded goods. The name is a registered trademark of DuPont Performance Elastomers L.L.C..

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Viton fluoroelastomers are categorized under the ASTM D1418 & ISO 1629 designation of FKM. This class of elastomers is a family comprising copolymers of hexafluoropropylene (HFP) and vinylidene fluoride (VDF or VF2), terpolymers of tetrafluoroethylene (TFE), vinylidene fluoride (VDF) and hexafluoropropylene (HFP) as well as perfluoromethylvinylether (PMVE) containing specialties. The fluorine content of the most common Viton grades varies between 66 and 70%.

Four families of polymers A(Dipolymers of VF2/HFP): General purpose sealing. Automotive, Aerospace

fuels & lubricants B(Terpolymers of VF2/HFP/TFE): Chemical Process plant, Power Utility Seals

& Gaskets F(Terpolymers of VF2/HFP/TFE): Oxygenated Automotive fuels.

Concentrated aqueous inorganic acids, water, steam Viton Extreme(Copolymers of TFE/Propylene and Ethylene/TFE/PMVE):

Automotive, Oil Exploration, Special Sealing, Ultra Harsh EnvironmentsThe performance of fluoroelastomers in aggressive chemicals depends on the nature of the base polymer and the compounding ingredients used for moulding the final products (e.g. O-rings). This performance can vary significantly when end-users purchase Viton polymer containing rubber goods from different sources. Viton is generally compatible with hydrocarbons, but incompatible with ketones such as acetone and organic acids such as acetic acid. O-rings made of Viton are typically color coded as black but new gaskets, seals and O-rings should be green FKM or black FKM but with a green mark on the outer edge.Viton O-rings have been used safely for some time in the SCUBA diving world for divers who dive with gas blends referred to as Nitrox. Viton is used because it has a lower probability of catching fire, even with the increased percentages of oxygen found in Nitrox. It is also less susceptible to decay under increased oxygen conditions.Viton tubing or Viton lined hoses are commonly recommended in automotive and other transportation fuel applications when high concentrations of biodiesel are required. Studies indicate that types B and F

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(FKM- GBL-S and FKM-GF-S) are more resistant to acidic biodiesel. (This is Biodiesel fuel that is unstable and oxidising)

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9.Maraging steelMaraging steels (a portmanteau of martensitic and aging) are iron alloys which are known for possessing superior strength and toughness without losing malleability. These steels are a special class of low carbon ultra-high strength steels which derive their strength not from carbon, but from precipitation of inter-metallic compounds. The principal alloying element is 15 to 25% nickel.[1] Secondary alloying elements are added to produce intermetallic precipitates, which include cobalt, molybdenum, and titanium.[1] Original development was carried out on 20 and 25% Ni steels to which small additions of Al, Ti, and Nb were made.The common, non-stainless grades contain 1719% nickel, 812% cobalt, 35% molybdenum, and 0.21.6% titanium. Stainless grades rely on chromium not only to prevent their rusting, but to augment the hardenability of the alloy as their nickel content is substantially reduced. This is to ensure they can transform to martensite when heat treated, as high-chromium, high-nickel steels are generally austenitic, and unable to undergo such a transition.PropertiesDue to the low carbon content maraging steels have good machinability. Prior to aging, they may also be cold rolled to as much as 8090% without cracking. Maraging steels offer good weldability, but must be aged afterward to restore the properties of heat affected zone.[1]When heat treated the alloy has very little dimensional change, so it is often machined to its final dimensions. Due to the high alloy content the alloys have a high hardenability. Since ductile FeNi martensites are formed upon cooling, cracks are non-existent or negligible. They can also be nitrided to increase case hardness. They can be polished to a fine surface finish.Non-stainless varieties of maraging steels are moderately corrosion resistant and resist stress corrosion and hydrogen embrittlement. More corrosion protection can be gained by cadmium plating or phosphating.Heat treatment cycleThe steel is first annealed at approximately 820 C (1,510 F) for 1530minutes for thin sections and for 1hour per 25mm thickness for heavy sections, to ensure formation of a fully austenitized structure. This is

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followed by air cooling to room temperature to form a soft, heavily-dislocated iron-nickel lath (untwinned) martensite. Subsequent aging (precipitation hardening) of the more common alloys for approximately 3hours in the 480 to 500C range produces a fine dispersion of Ni3(X,Y) intermetallic phases along dislocations left by martensitic transformation, where X and Y are solute elements added for such precipitation. Overaging leads to a reduction in stability of the primary, metastable, coherent precipitates, leading to their dissolution and replacement with semi-coherent Laves phases such as Fe2Ni/Fe2Mo. Further excessive heat-treatment brings about the decomposition of the martensite and reversion to austenite.Newer compositions of maraging steels have revealed other intermetallic stoichiometries and crystallographic relationships with the parent martensite, including rhombohedral and massive complex Ni50(X,Y,Z)50 - usually simplified to Ni50M50.UsesMaraging steel's strength and malleability in the pre-aged stage allows it to be formed into thinner rocket and missile skins, allowing more weight for payload while still possessing sufficient strength for the application. Maraging steels have very stable properties, and even after overaging, due to excessive temperature, only soften slightly. These alloys retain their properties at mildly elevated operating temperatures and have maximum service temperatures of over 400C (752F).[citation needed] They are suited to engine components, such as crankshafts and gears, and the firing pins of automatic weapons that cycle from hot to cool repeatedly while under substantial loads. Their uniform expansion and easy machinability, carried out before aging makes maraging steel useful in high wear components of assembly lines and dies. Other ultra-high strength steels, such as Aermet alloys, are not as machinable because of their carbide content.In the sport of fencing, blades used in competitions run under the auspices of the Fdration Internationale d'Escrime are often made with maraging steel. Maraging blades are required in foil and pe because the crack propagation in maraging steel is 10 times slower than in carbon steel. This results in less blade breakage and fewer injuries. The thought that such blades break flat is actually a fencing urban legend. Testing has shown that

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the blade breakage patterns in carbon steel and maraging steel blades are identical[citation needed]. Stainless maraging steel is used in bicycle frames and golf club heads. It is also used in surgical components and hypodermic syringes, however it is not suitable for scalpel blades, because the lack of carbon prevents it from holding a good cutting edge.Maraging steel production, import, and export by certain states is closely monitored by international authorities because of their use in gas centrifuges for uranium enrichment. Very few other materials will work for this task, and its other uses are very specialized.Physical properties Density: 8.1 g/cm (0.29 lb/in) Specific heat, mean for 0100 C (32212 F): 813 J/(kgK) (0.108 Btu/

(lbF)) Melting point: 2575 F, 1413 C Thermal conductivity: 25.5 Wm/(mK) Mean coefficient of thermal expansion: 11.3106 Yield tensile strength: typically 10302420 MPa (150,000350,000

psi)[2] Ultimate tensile strength: typically 16002500 MPa (230,000360,000

psi). Grades exist up to 3.5 GPa (500,000 psi) Elongation at break: up to 15% KIC fracture toughness: up to 175 MPa-m Young's modulus: 210 GPa[3] Shear modulus: 77 GPa Bulk modulus: 140 GPa Hardness (aged): 50 HRC (grade 250); 54 HRC (grade 300); 58 HRC

(grade 350)[citation needed]

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Properties of Maraging Steels

Abstract: The 18% Ni-maraging steels, which belong to the family of iron-base alloys, are strengthened by a process of martensitic transformation, followed by age or precipitation hardening. Precipitation hardenable stainless steels are also in this group. Maraging steels work well in electro-mechanical components where ultra-high strength is required, along with good dimensional stability during heat treatment.

The 18% Ni-maraging steels, which belong to the family of iron-base alloys, are strengthened by a process of martensitic transformation, followed by age or precipitation hardening. Precipitation hardenable stainless steels are also in this group.Maraging steels work well in electro-mechanical components where ultra-high strength is required, along with good dimensional stability during heat treatment. Several desirable properties of maraging steels are:

Ultra-high strength at room temperature Simple heat treatment, which results in minimum distortion Superior fracture toughness compared to quenched and tempered

steel of similar strength level Low carbon content, which precludes decarburization problems Section size is an important factor in the hardening process Easily fabricated Good weldability.

These factors indicate that maraging steels could be used in applications such as shafts, and substitute for long, thin, carburized or nitrided parts, and components subject to impact fatigue, such as print hammers or clutches.

Tempering of maraging steelsTempering as an operation of heat treatment has been well known from the Middle Ages. It is used with martensite-quenched alloys. The processes of tempering will be considered here for steels only, sinse steels constitute an overwhelming majority of all marensite-hardenable alloys.

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Maraging steels are carbonless Fe-Ni alloys additionally alloyed with cobalt, molybdenum, titanium and some other elements. A typical example is an iron alloy with 17-19% Ni, 7-9% Co, 4.5-5% Mo and 0.6-0.9% Ti. Alloys of this type are hardened to martensite and then tempered at 480-500C. The tempering results in strong precipitation hardening owing to the precipitation of intermetallics from the martensite, which is supersaturated with the alloying elements. By analogy with the precipitation hardening in aluminum, copper and other non-ferrous alloys, this process has been termed ageing, and since the initial structure is martensite, the steels have been called maraging.The structure of commercial maraging steels at the stage of maximum hardening can contain partially coherent precipitates of intermediate metastable phases Ni3Mo and Ni3Ti. Ni3Ti phase is similar to hexagonal -carbide in carbon steels. Of special practical value is the fact that particles of intermediate intermetallics in maraging steels are extremely disperse, which is mainly due to their precipitation at dislocations.The structure of maraging steels has a high density of dislocations, which appear on martensitic rearrangement of the lattice. In lath (untwined) martensite, the density of dislocations is of an order of 1011-1012 cm-2, i.e. the same as in a strongly strain-hardened metal. In that respect the substructure of maraging steel (as hardened) differs appreciably from that of aluminum, copper and other alloys which can be quenched without polymorphic change.It is assumed that the precipitation of intermediate phases on tempering of maraging steels is preceded with segregation of atoms of alloying elements at dislocations. The atmospheres formed at dislocations serve as centers for the subsequent concentration stratification of the martensite, which is supersaturated with alloying elements.In maraging steels the dislocation structure that forms in the course of martensitic transformation, is very stable during the subsequent heating and practically remains unchanged at the optimum temperatures of tempering (480-500C). Such a high density of dislocations during the whole course of tempering may be due to an appreciable extent, to dislocation pinning by disperse precipitates.

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A long holding in tempering at a higher temperature (550C or more) may coarsen the precipitates and increase the

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