Structure and Properties of Metals (l.u. 2/8/10).

Structure and Structure and Properties of Metals Properties of Metals (l.u. 2/8/10) (l.u. 2/8/10)

General Material QuestionsGeneral Material Questions

What is passivation? What causes passivation? Is this good or bad? What is passivation? What causes passivation? Is this good or bad? Have you ever seen passivation?Have you ever seen passivation?

What material has a higher stiffness, AL or carbon fiber?What material has a higher stiffness, AL or carbon fiber?

What material has a higher tensile strength, carbon fiber or diamond?What material has a higher tensile strength, carbon fiber or diamond?

How would you describe the behavior of lead when compressed at How would you describe the behavior of lead when compressed at room temperature versus zinc?room temperature versus zinc?

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Strength ProblemStrength Problem

What pulling force (in lbs) will cause a HS steel rod (1 inch DIA) to What pulling force (in lbs) will cause a HS steel rod (1 inch DIA) to begin to fail? How many tons is this?begin to fail? How many tons is this?

What is the pulling force if the rod DIA = .5?What is the pulling force if the rod DIA = .5?

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Strength ProblemStrength Problem

What pulling force (in lbs) will cause a HS steel rod (1 inch DIA) to What pulling force (in lbs) will cause a HS steel rod (1 inch DIA) to begin to fail? How many tons is this?begin to fail? How many tons is this?

F=pAF=pA 1 lb = 4.448 N1 lb = 4.448 N 1 m = 39.37 in1 m = 39.37 in 1 Pa = 1 N/m1 Pa = 1 N/m22

A = A = ππ rr22

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DensityDensity

Material weight per unit volume, related to atomic weight, radius and Material weight per unit volume, related to atomic weight, radius and packing.packing.

Sometimes expressed in proportion to the density of water (specific Sometimes expressed in proportion to the density of water (specific gravity = Sg).gravity = Sg).

SI: kg/m³, USCS: lb/in³ SI: kg/m³, USCS: lb/in³

Specific Strength (strength-to-weight ratio)Specific Strength (strength-to-weight ratio)

Specific Stiffness (stiffness-to-weight ratio)Specific Stiffness (stiffness-to-weight ratio)

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Sg H2O (seawater) = 1.03Sg H2O (seawater) = 1.03Sg oil (SAE grade) = .87-.89Sg oil (SAE grade) = .87-.89

Density QuestionsDensity Questions

What has a higher specific gravity, lead or tungsten? What has a higher specific gravity, lead or tungsten?

Determine the density of copper in lb/inches cubed? How many ounces Determine the density of copper in lb/inches cubed? How many ounces per cubic inch is this? What percentage more is the density of per cubic inch is this? What percentage more is the density of Tungsten?Tungsten?

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Thermal PropertiesThermal Properties

Temperature: ”Temperature: ”the tendency of an object to absorb or dissipate energy the tendency of an object to absorb or dissipate energy in the form of heatin the form of heat""

““Heat is simply another form of energy that can be measured only in Heat is simply another form of energy that can be measured only in terms of the effect it produces” (Tippens, 1992, p. 321)terms of the effect it produces” (Tippens, 1992, p. 321)

Heat is not a substance – it is energy that is given up or absorbedHeat is not a substance – it is energy that is given up or absorbed

Molecules move differently in different materialsMolecules move differently in different materials

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Temperature Conversions (Scales)Temperature Conversions (Scales)

Relative: referenced to physical phenomena (freezing-boiling point of Relative: referenced to physical phenomena (freezing-boiling point of water)water)

SI: Celsius (°C), USCS: Fahrenheit (°F) SI: Celsius (°C), USCS: Fahrenheit (°F) scales coincide at -40°scales coincide at -40°

Thermal PropertiesThermal Properties

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Thermal PropertiesThermal Properties

Temperature Conversions (Scales)Temperature Conversions (Scales)

Absolute: referenced to minimal achievable temperature (atomic motion Absolute: referenced to minimal achievable temperature (atomic motion ceases)ceases)

SI: Kelvin (°K), USCS: Rankine (°R)SI: Kelvin (°K), USCS: Rankine (°R)

°K=(°C+273)°K=(°C+273) °R=(°F+460)°R=(°F+460)

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Melting Point: “Melting Point: “energy required to separate the atomsenergy required to separate the atoms””

Pure Metals: one defined melting point.Pure Metals: one defined melting point.

Alloys: wide range of temperatures. Alloys: wide range of temperatures.

Mercury’s melting point = -39 degrees CMercury’s melting point = -39 degrees C

Thermal PropertiesThermal Properties

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Thermal PropertiesThermal Properties

where: Q = heat capacity m = mass cp = specific heatT = change in temperature

Material

AluminumGlassIronCopperWater

0.210.200.110.091.00

S. Heat (SI)

Specific Heat: “Specific Heat: “energy required to change the temperature of a unit of energy required to change the temperature of a unit of mass by 1mass by 1°” (amount)°” (amount)

The lower the specific heat, the faster the temperature will rise in The lower the specific heat, the faster the temperature will rise in material.material.

SI: cal/(g °C), USCS: BTU/(lb °F)SI: cal/(g °C), USCS: BTU/(lb °F)

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Thermal Conductivity: “Thermal Conductivity: “heat flow within the materialheat flow within the material” (how fast)” (how fast)

Through convection (e.g. ac), conduction (e.g. boil water), and Through convection (e.g. ac), conduction (e.g. boil water), and radiation (e.g. sunlight)radiation (e.g. sunlight)

Metals: high conductivityMetals: high conductivity

Non-Metals: poor conductivity (e.g. insulators)Non-Metals: poor conductivity (e.g. insulators)

SI: cal/s or W, USCS: BTU/sSI: cal/s or W, USCS: BTU/s

Thermal PropertiesThermal Properties

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Using Thermal ConductivityUsing Thermal Conductivity

Thermal PropertiesThermal Properties

where: Q = energy transfer rate (BTU) k = thermal conductivity constant

(1 W/m K = 6.94 BTU in/ft2 h F) A = area (sq ft) t = time (hr)T = change in temperature (F)L = thickness (in)

•

Q = kAtQ = kAt TL Material k (BTU)

Silver 1451Brass 750Copper 2660Silver 2870Steel 320Brick 5Concrete 5.6

Thermal ProblemsThermal Problems What is the r-value of aluminum? What is the r-value of aluminum?

A 1 inch thick cooler separates an inside temperature of 8° C and outside A 1 inch thick cooler separates an inside temperature of 8° C and outside temperature of 36° C. How much heat (in BTU’s) is lost through a 10 fttemperature of 36° C. How much heat (in BTU’s) is lost through a 10 ft22 area over the course of an hour?area over the course of an hour?

Let A represent the area in square feetLet A represent the area in square feet Let Let ۲۲ represent the time of 1 hourrepresent the time of 1 hour Let L be the thickness of the wall in inchesLet L be the thickness of the wall in inches Let k be the thermal conductivity constant, for styrofoam = .033 (W/m K)Let k be the thermal conductivity constant, for styrofoam = .033 (W/m K)

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Thermal Expansion: “Thermal Expansion: “atomic motion linked to temperature gradientatomic motion linked to temperature gradient””

Constant Mass, Increase in VolumeConstant Mass, Increase in Volume

Thermal Stresses, Fatigue, and ShockThermal Stresses, Fatigue, and Shock

Dimensional AccuracyDimensional Accuracy

Modulus of ElasticityModulus of Elasticity

Thermal PropertiesThermal Properties

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Thermal ExpansionThermal Expansion

Thermal PropertiesThermal Properties

where: L = change in length = coefficient of expansion L = lengthT = change in temperature

TLL

www.concrete.org

Material α (Alpha) 10-5/°C

Aluminum 2.4

Brass 1.8

Concrete .7-1.2

Copper 1.7

Glass/Pyrodex .3

Iron 1.2

Lead 3

Silver 2.0

Steel 1.2

Zinc 2.6

Thermal Expansion QuestionsThermal Expansion Questions

What has a higher rate of expansion, steel or tungsten?What has a higher rate of expansion, steel or tungsten?

Calculate the linear expansion (in inches) of a bar of aluminum at 30 Calculate the linear expansion (in inches) of a bar of aluminum at 30 degrees C if the initial length of the bar is 10 m at 10 degrees C. What degrees C if the initial length of the bar is 10 m at 10 degrees C. What are the equivalent Fahrenheit temperatures for this expansion? are the equivalent Fahrenheit temperatures for this expansion?

Let ∞ represent alpha (coefficient of linear expansion) for aluminum = Let ∞ represent alpha (coefficient of linear expansion) for aluminum = 23.6x1023.6x10-6-6/° C/° C

∆∆L is the respective change in length in metersL is the respective change in length in meters ∆∆t is the change in temperature to cause length changet is the change in temperature to cause length change

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Electric and Magnetic PropertiesElectric and Magnetic Properties

Conduction: electric flow within the materialConduction: electric flow within the material

SI: 1/ohm-m, USCS: 1/ohm-ft SI: 1/ohm-m, USCS: 1/ohm-ft 1/ohm = mho1/ohm = mho

Resistivity (dielectrics/insulators)Resistivity (dielectrics/insulators) Superconductors: near zero resistivity at certain temperaturesSuperconductors: near zero resistivity at certain temperatures Semiconductors: solid state devices (impurities/conductivity control)Semiconductors: solid state devices (impurities/conductivity control)

Common Magnetic metals: Iron, cobalt, nickelCommon Magnetic metals: Iron, cobalt, nickel

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Material DeteriorationMaterial Deterioration Corrosion: deterioration of metals and ceramicsCorrosion: deterioration of metals and ceramics Degradation: plastics (thermal aging/degradation)Degradation: plastics (thermal aging/degradation) Passivation: protective hard oxide film – chromium in metalsPassivation: protective hard oxide film – chromium in metals Rust: oxidation of steels or cast ironRust: oxidation of steels or cast iron

(magickcanoe.com)

(www.landerholm.us)

Copper OxidationCopper Oxidation

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