Transcript
KCC INST. OF TECH. & MGMTGr. Noida
Presentation Theme :-
Mechanical Properties of MaterialsPr@tik Rawat 2012 me batch 1
Theme Outline
Engineering Materials Properties of Materials - Hardness,Toughness, Strength,
Malleability, Elasticity, Plasticity, Ductility
The Tensile Test: Stress-Strain Diagram Properties Obtained from a Tensile
Test True Stress and True Strain
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Materials
Metals Plastics
Steel
Stainless steel
Die & tool steel
Cast iron
Ferrous Non-ferrous
Aluminum
Copper
Zinc
Titanium
Tungsten
Thermosets
Phenolic
Polymide
Epoxies
Polyester
Engineering Materials
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Materials
Metals Plastics Composites
Reinforced plastics
Metal-Matrix
Ceramic-Matrix
Laminates
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Properties of Materials
Mechanical Properties
Yield strength
Ultimate strength
Ductility
Hardness
Toughness
Fatigue (cyclic load)
Creep (temp / time)
Physical & chemicalProperties
Thermal conductivity
Thermal expansion
Electrical conductivity
Magnetic properties
Corrosion
Density
Melting point
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Hardness
• The ability of a material to resist scratching, wear and tear and indentation.• Large hardness means: --resistance to plastic deformation or cracking in compression. --better wear properties.
e.g., 10mm sphere
apply known force (1 to 1000g)
measure size of indent after removing load
dDSmaller indents mean larger hardness.
increasing hardness
most plastics
brasses Al alloys
easy to machine steels file hard
cutting tools
nitrided steels diamond
Adapted from Fig. 6.18, Callister 6e. (Fig. 6.18 is adapted from G.F. Kinney, Engineering Properties and Applications of Plastics, p. 202, John Wiley and Sons, 1957.)
Hardness
Hardness is the property of material in which material opposes some acts such as rubbing, scratching, penetrating , marking.
The depth or size of the indentation is measured, and corresponds to a hardness number.
The softer the material, the larger and deeper the indentation (and lower hardness number).
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Toughness
Lower toughness: ceramics
Higher toughness: metals
Toughness is the ability to absorb energy up to fracture (energy per unit volume of material).
A “tough” material has strength and ductility.
Approximated by the area under the stress-straincurve.
• Energy to break a unit volume of material• Approximate by the area under the stress-strain curve.
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smaller toughness- unreinforced polymers
Engineering tensile strain, ε
Engineering tensile stress, σ
smaller toughness (ceramics)
larger toughness (metals, PMCs)
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Toughness
Malleability -> The ability of a material to be reshaped in all directions without cracking.
Strength -> The ability of a material to stand up to forces being applied without it bending , breaking, shattering or deforming in any way.
Elasticity -> The ability of material to absorb force and flex in all direction returning to its original position.
Plasticity -> The ability of material to be change in shape permanently.
Ductility -> It is a property of material by virtue of which materials can be drawn in wires. ( stretch without breaking or snapping)
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Stress-Strain Test
specimen
machinePr@tik Rawat 2012 me batch 11
Tensile Test
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(c)2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning™ is a trademark used herein under license.
• Localized deformation of a ductile material during a tensile test produces a necked region. • The image shows necked region in a fractured samplePr@tik Rawat 2012 me batch 14
Terminology
Load - The force applied to a material during testing.
Strain gage or Extensometer - A device used for measuring change in length (strain).
Engineering stress - The applied load, or force, divided by the original cross-sectional area of the material.
Engineering strain - The amount that a material deforms per unit length in a tensile test.
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Stress-Strain Diagram (cont) • Elastic Region (Point O–A) - The material will return to its original shape after the material is unloaded( like a rubber band). - The stress is linearly proportional to the strain in this region.
εEσ = : Stress(psi)E : Elastic modulus (Young’s Modulus) (psi) : Strain (in/in)
σ
ε- Point B : Permanent Deformation Starts - a point where permanent deformation occurs. ( If it is passed, the material will no longer return to its original length.)
ε
σE =or
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Yield Point (Point C & D )
Point C is called UYP . At this point there is an increase in strain even though there is no increase in stress (load)
A formation of creep from this point , makes the specimen plastic and the material begin to flow.
The value of stress corresponding to point C is called yield stress or yield strength.
The yield stress is defined as that unit stress which will cause an increase in length without an increase in load.
D is lower yield point
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• Tensile Strength (Point E) - The largest value of stress on the diagram is called Tensile Strength(TS) or Ultimate Tensile Strength (UTS) - It is the maximum stress which the material can support without breaking.• Fracture (Point F) - If the material is stretched beyond Point 3, the stress decreases as necking and non-uniform deformation occur. - Fracture will finally occur at Point 5.
Stress-Strain Diagram (cont)
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Stress-Strain Diagram (cont)
Strain Hardening is when a metal is strained beyond the yield point.
An increasing stress is required to produce additional plastic deformation and the metal apparently becomes stronger and more difficult to deform.
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Typical stress-strain behavior for a metal showing elastic and plastic deformations, the proportional limit P and the yield strength σy, as determined using the 0.002 strain offset method (where there
is noticeable plastic deformation). P is the gradual elastic to plastic transition.
THANKS !!!!! Pratik Rawat
Section - A
ME – 3rd year
R.No. - 094
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