CHME 361 - Exam 3
At 500 K, the diffusion coefficient for hydrogen in iron is about 3.5 × 10 − 9 m 2 / s. Estimate the distance that iron can diffuse through iron in 7 hours at 500 K. 10^−2 m 10^−1 m 1 m or more 10^−3 m 10^−4 m 10^−6 m or less 10^−5 m
10^−2 m
In general, at what temperature does a metal begin to creep? - 20% to 30% of its melting temperature - 60% to 70% of its melting temperature - 40% to 50% of its melting temperature - 30% to 40% of its melting temperature - 50% to 60% of its melting temperature
30% to 40% of its melting temperature
In general, at what temperature does a ceramic begin to creep? - 40% to 50% of its melting temperature - 50% to 60% of its melting temperature - 60% to 70% of its melting temperature - 30% to 40% of its melting temperature - 20% to 30% of its melting temperature
40% to 50% of its melting temperature
To three significant figures, what is a kilogram-force (kgs) in newtons?
9.81
What creates a stress concentration? - Surface polishing - Shot peening - Roller peening - Abrupt change in cross-section - Annealing
Abrupt change in cross-section
The steady creep rate at constant stress can be represented by the equation ϵss = Aσ^n exp(−Q/RT) What is Q in this equation? - Electric charge - Volumetric flow rate - Steady creep rate - Creep exponent - Activation energy
Activation energy
The steady creep rate at constant stress can be represented by the equation ϵss = Aσ^n exp(−Q/RT) What is Q in this equation? - Steady creep rate - Electric charge - Creep exponent - Activation energy - Volumetric flow rate
Activation energy
How can the fatigue strength of the component be increased? - Remove material to reduce the SCF. - Introduce residual tensile surface stresses. - Remove chamfers. - Avoid abrupt changes in section. - Roughen the surface.
Avoid abrupt changes in section.
Image from Quiz 18 Choose the letter that corresponds to "High-cycle fatigue" region. - A - B - C - D - E
B
Image from Quiz 20 Consider the fracture surface shown above. Identify (by letter) the part of the surface showing unstable crack growth. - A - B - C - D
B
Image from quiz 23 What is most likely to occur at τ = 10 − 4 G and T = 0.3 T m? - Dislocation-core diffusion occurs. - Dislocations glide in response to shear stress. - Dislocation glide and vacancy diffusion occurs - Bonds stretch but do not break. - Dislocations glide and dislocation-core diffusion occurs. - Dislocations glide and dislocation-core diffusion occurs.
Bonds stretch but do not break.
Image from Quiz 20 Consider the fracture surface shown above. Identify (by letter) the part of the surface showing crack growth by fatigue. - A - B - C - D
C
Why does carbon diffuse through iron faster than chromium does? - Iron contains no grain boundaries. - Iron contains very few edge dislocations. - Carbon strengthens the iron crystal lattice more than chromium does. - Carbon atoms are smaller than chromium atoms.
Carbon atoms are smaller than chromium atoms.
Which element is most commonly added to steel to reduce oxidation? - Chlorine - Lithium - Silver - Hydrogen - Chromium
Chromium
Why might compressed water be used instead of air or steam to test pressure vessels? - Water is denser than compressed air or steam. - Compressed water does not cause fracture. - Compressed water does not cause corrosion. - Water is more compressible than air or steam. - Compressed water stores less energy than compressed air or steam.
Compressed water stores less energy than compressed air or steam.
Why is compressed water use instead of gas or steam to test pressure vessels? - Compressed water does not cause fracture. - Water is denser than gas or steam. Compressed water does not cause corrosion. - Compressed water stores less energy then compressed gas or steam. - Water is more compressible than steam.
Compressed water stores less energy then compressed gas or steam.
Which process can cause the formation and growth of cracks at constant loads well below the yield strength? - Necking - Corrosion - Plastic instability - Fast fracture - Elastic buckling
Corrosion
Which is not a characteristic of mild steel? - Easily formed - Cheap - Strong - Dense - Corrosion resistant
Corrosion resistant
What is a possible disadvantage relying on oxide layers for corrosion protection? - Oxide layers are too ductile. - Oxide layers tend to oxidize the underlying metal. - The coatings must be applied and reapplied with the brush. - Oxide layers are too tough. - Cracks can nucleate in the oxide and spread the underlying alloy.
Cracks can nucleate in the oxide and spread the underlying alloy.
What is meant by creep damage? - Unstable crack propagation - Glass transition - Necking - Creation and growth of internal cavities - Stress relaxation
Creation and growth of internal cavities
In the context of fatigue calculations, what is N f? - Stress amplitude - Mean stress - Reversals to failure - Cycles to failure - Cyclic strain range - Cyclic stress range
Cycles to failure
In the context of fatigue calculations, what is σ max − σ min? - Mean stress - Cycles to failure - Stress amplitude - Mean strain - Cyclic stress range - Cyclic strain range
Cyclic stress range
Image from Quiz 20 Consider the fracture surface shown above. Identify (by letter) the likely origin of the initial crack. - A - B - C - D
D
Which equation accounts for the temperature dependence of diffusion? Δx = √(DΔt) ϵss = Aσ^n exp(−Q/RT) J = D (dc/dx) D = D0 exp(−Q/RT)
D = D0 exp(−Q/RT)
What is an advantage of directional solidification (DS) for creating turbine blades? - DS can produce long grains aligned with stress to minimize creep. - DS can produce exceptionally fine grains to increase diffusion rates. - DS eliminates substitutional solutes. - DS is cheaper than other methods. - DS eliminates precipitates.
DS can produce long grains aligned with stress to minimize creep.
Consider the equation, J = D (dc/dx) Why is the negative sign included in this equation? - The negative sign ensures that the flux will be positive. - Diffusion occurs from high concentrations to low concentrations. - Increasing the activation energy decreases the diffusion coefficient. - Diffusion occurs from low concentrations to high concentrations. - Increasing the temperature decreases the diffusion rate.
Diffusion occurs from high concentrations to low concentrations.
What is the mechanism by which climb occurs? - Ductile rupture. - Bond breaking and reforming at an age dislocation - Cleavage. - Cyclic stress. - Diffusion of atoms away from a dislocation
Diffusion of atoms away from a dislocation
Which process for casting a turbine blade involves the gradual withdrawal of the mold from the furnace? - Directional solidification - Blow molding - Blade cooling - Investment casting - Extrusion
Directional solidification
Image from Quiz 23 What is most likely to occur at τ = 10 − 3 G and T = 0.95 T m? - Dislocation-core diffusion occurs. - Dislocations glide and diffusion concurs through dislocations. - Dislocations glide in response to shear stress. - Dislocation glide and vacancy diffusion occurs - Bonds stretch but do not break.
Dislocation glide and vacancy diffusion occurs
In the context of the current chapter, what is climb? - Dislocation slip on a slip plane. - Dislocation movement on a glide plane. - Dislocation movement perpendicular to the glide plane. - Dislocation locking or pinning by an obstacle such as a precipitate.
Dislocation movement perpendicular to the glide plane.
Image from Quiz 23 What is most likely to occur at τ = 5 × 10 − 3 G and T = 0.7 T m? - Dislocations glide and dislocation- core diffusion occurs. - Dislocation-core diffusion occurs. - Dislocations glide and vacancy diffusion occurs - Dislocations glide in response to shear stress. - Bonds stretch but do not break.
Dislocations glide and dislocation- core diffusion occurs.
Image from Quiz 23 What is most likely to occur at τ = 10 − 1 G and T = 0.1 T m? - Dislocation-core diffusion occurs. - Bonds stretch but do not break. - Dislocation glide and vacancy diffusion occurs - Dislocations glide in response to shear stress.
Dislocations glide in response to shear stress.
What is the stroke of a piston engine? - Ratio of maximum volume to minimum volume - Design power output - Cerebrovascular incident - Diameter of the cylinders - Distance of piston travel
Distance of piston travel
When is an adherent oxide film undesirable? - During joining operations such as brazing - When the surface is to be polished - When electrical insulation is required - During high-temperature operation - During exposure to oxidizing environments
During joining operations such as brazing
Image from Quiz 18 Choose the letter that indicates "Plastic strain amplitude". - A - B - C - D - E
E
What results from the presence of an extra half-plane of atoms in a crystal? - Grain boundary - Edge dislocation - Void - Planar defect - Vacancy
Edge dislocation
When applied to dry oxidation of a material, what does the following equation describe? k = A exp(−Q/RT) - Oxidation if a volatile oxide forms - Effect of temperature on the oxidation rate - Oxidation if a protective oxide film forms - Oxidation if a nonproductive oxide film forms
Effect of temperature on the oxidation rate
In what form does a so-called "native" metal occur in nature? - Isotope - Oxide - Halide - Carbonate - Element
Element
What does a negative Energy mean in the following equation? Material + Oxygen + Energy ⟶ Oxide of Material - Energy is released when the oxide is formed - The rate of oxidation is low - The rate of oxidation is low - Energy must be added to the material in the presence of oxidation for the oxide to form
Energy is released when the oxide is formed
What do "clam-shell" or "beach" marks indicate on a fracture surface? - Lack of corrosion - Fast crack propagation - Treansgranular cleavage - Aqueous corrosion - Fatigue crack propagation
Fatigue crack propagation
Why is diffusion more rapid in fine-grained silver than in coarse-grained silver? - Fine-grained silver contains more grain boundaries. - Fine-grained silver contains more edge dislocations. - Fine-grained silver contains more vacancies. - Fine-grained silver contains more interstices.
Fine-grained silver contains more grain boundaries.
What causes thermal fatigue? - Fluctuating temperature - Dislocation climb - Strain hardening - Quenching - Annealing
Fluctuating temperature
How do cracks form in low-cycle fatigue? - General plasticity roughened the surface. - Cleavage occurs where the stress exceeds the ideal strength. - Energy dissipation causes local heating. - Stress concentrations cause local plasticity. - Dislocations pileup at grain boundaries.
General plasticity roughened the surface.
How do cracks form in low-cycle fatigue of components that initially contain no cracks? - Elastic deformation roughens the surface. - Cleavage occurs where the stress exceeds the yield strength. - Energy dissipation generates heat. - Dislocations pileup at grain boundaries. - General plasticity roughens the surface.
General plasticity roughens the surface.
Which phenomenon is described by the following equation: da/dN = A (ΔK)^m - Failure by fast fracture - Yielding - Growth of fatigue crack - Buckling - Necking
Growth of fatigue crack
What is the first requirement for creep-resistant metal or ceramic? - High melting temperature - High modulus - Low yield strength - High density - Low modulus
High melting temperature
What is a tapped hole? - Shot-peened hole - Hole having internal threats - Drilled hoe - Punched and expanded hole - Expanded hole
Hole having internal threats
What does a positive Energy mean in the following equation? Material + Oxygen + Energy ⟶ Oxide of Material - In the presence of oxygen, the material is more stable than its oxide. - The oxide will form rapidly. - In the presence of oxygen, the material is less stable than its oxide. - The oxide will form slowly.
In the presence of oxygen, the material is more stable than its oxide.
Where does interstitial diffusion occur? - In the spaces between atoms in the crystal - Along grain boundaries - Through dislocations - Into vacancies in the crystal
In the spaces between atoms in the crystal
How can the Carnot efficiency of a heat engine be increased? - Increase the heat-sink temperature. - Increase the heat-source temperature. - Increase friction in the engine. - Burn more fuel. - Burn less fuel.
Increase the heat-source temperature.
Consider the equation, D = D0 exp(−Q/RT) Why is the negative sign included in this equation? - Increasing the activation energy decreases the diffusion coefficient. - Diffusion occurs from high concentrations to low concentrations. - Diffusion occurs from high concentrations to low concentrations. - The negative sign ensures that the flux will be positive. - Increasing the temperature decreases the diffusion rate.
Increasing the activation energy decreases the diffusion coefficient.
Which is a heat engine? - Internal combustion engine - Electrochemical fuel cell - Photovoltaic cell - Flux capacitor - Wind turbine
Internal combustion engine
Which process for casket turbine blade involves the formation of a mold around the wax pattern? - Investment casting - Directional solidification - Blade cooling - Blow molding - Extrusion
Investment casting
Which equation represents Fick's first law of diffusion? Δx = √(DΔt) ϵss = Aσ^n exp(−Q/RT) J = D (dc/dx) D = D0 exp(−Q/RT)
J = D (dc/dx)
Which defects cause materials to yield at stresses far below their theoretical strengths at ordinary temperatures? - Volume defects - Point defects - Planar defects - Line defects - Cracks
Line defects
In general, what is the correlation between the energy of oxidation and the rate of oxidation? - Energy greater than 10 implies a high rate. - Energy greater than one implies a high rate. - The more negative the energy, the higher the rate. - Little or no correlation exists between energy and rate. - The more positive the energy, the higher the rate
Little or no correlation exists between energy and rate.
What is the stress concentration factor (SCF)? - Safety factor applied to avoid failure - Spring constant for elastic deformation - Degree of work- hardening - Maximum local stress divided by background stress - Degree of cold-working
Maximum local stress divided by background stress
In the context of fatigue calculations, what is (σ max + σ min) / 2? -Stress amplitude -Cyclic strain range - Mean stress - Cyclic stress range - Cycles to failure - Mean strain
Mean stress
When applied to the dry oxidation of a material, what does the following equation describe? Δ m = kL t , kL > 0 - Effect of temperature on the oxidation rate - Oxidation if a nonproductive oxide film forms - Oxidation if a volatile oxide forms - Oxidation if a protective oxide film forms
Oxidation if a nonproductive oxide film forms
When applied to the dry oxidation of a material, what does the following equation describe? (Δm)^2 = kp t , kp > 0 - Oxidation if a volatile oxide forms - Effect of temperature on the oxidation rate - Oxidation if a protective oxide film forms - Oxidation if a nonprotective oxide film forms
Oxidation if a protective oxide film forms
When applied to the dry oxidation of a material, what does the following equation describe? Δm = kL t , kL < 0 - Oxidation if a protective oxide film forms - Oxidation if a volatile oxide forms - Oxidation if a nonproductive oxide film forms - Effect of temperature on the oxidation rate
Oxidation if a volatile oxide forms
Why might a metal gain mass when it oxidizes? - The metal forms oxide films that are less dense than the original metal. - Oxidation proceeds by the addition of oxygen to the surface. - The metal's crystal structure changes. - The metal forms oxide films that are more dense than the original metal. - The metal forms volatile oxides.
Oxidation proceeds by the addition of oxygen to the surface.
What property of pure refractory metals such as Nb, Ta, Mo, and W make them unsuitable for turbine blades? - Low yield - High modulus - Tendency to creep - High toughness - Rapid oxidation
Rapid oxidation
What is nitriding of silicon? - Reaction with nitrogen-bearing compounds - Quenching by immersion in liquid nitrogen - Elimination of stress concentrations - Elimination of cracks - Surface abrasion
Reaction with nitrogen-bearing compounds
In the context of oxidation, what is the meaning of volatile? - Trending to erupt violently - Readily vaporizable at low temperatures - Characterized by rapid or unexpected change - Explosive - Fluent or having a ready flow of speech
Readily vaporizable at low temperatures
What is creep relaxation? - Recovery from tertiary creep - Reduction of stress near crack services - Stress relief after creep rupture - Strain reduction by creep - Replacement of elastic strain by creep strain
Replacement of elastic strain by creep strain
What is creep relaxation? - Replacement of elastic strain by creep strain - Reduction of stress near crack services - Recovery from tertiary creep - Stress relief after creep rupture - Strain reduction by creep
Replacement of elastic strain by creep strain
What property of a fluid is measured by its viscosity? - Resistance to elastic deformation - Resistance to fatigue - Resistance to corrosion - Resistance to fracture - Resistance to flow
Resistance to flow
In the context of the current chapter, what is the meaning of refractory? - Bristol - Resistant high temperatures - Tough - Ductile - Resistant to medical treatment
Resistant high temperatures
In the context of fatigue calculations, what is 2 Nf? - Mean stress - Stress amplitude - Cyclic strain range - Cyclic stress range - Cycles to failure - Reversals to failure
Reversals to failure
What does stud mean in the current chapter? - Metal or rubber cleats in a snow tire - Upright piece in the framing of the building - Linear precipitate - Rod or pin, often threaded on both ends - Something cut short
Rod or pin, often threaded on both ends
In the context of this course, what is a fillet? - Rounded, concave junction - Narrow strip of fabric uses a headband - Stress concentrator - Square-mesh fabric with a geometric design - Longitudinal slice
Rounded, concave junction
What is an advantage of a single crystal alloy (SX) for creating turbine blades? - SX reduces diffusion rates by eliminating grain boundaries. - SX is cheaper to produce than polycrystalline alloys. -X contains exceptionally fine grains to increase diffusion rates. - SX contains no solutes. - SX contains no dislocations.
SX reduces diffusion rates by eliminating grain boundaries.
Which of the following (if any) will not increase the creep resistance of metals or ceramics? - Small grains - They all will increase creep resistance. - Solutes - Precipitates - High melting point
Small grains
What is the effect of grain size on yield strength? - Small grains tend to increase yield strength. - The effect of grain size cannot be predicted. - Large grades tend to increase yield strength. - Grain size has no effect on yield strength.
Small grains tend to increase yield strength.
Why is brass stronger than pure copper? - Dislocations hinder each other. - Precipitates obstruct dislocations. - Strong atomic bonds resist dislocation movement. - Dislocations pile up at grain boundaries. - Solute-generated stresses "roughen" slip planes to hinder dislocation movement.
Solute-generated stresses "roughen" slip planes to hinder dislocation movement.
How do cracks form in high-cycle fatigue? - Energy dissipation causes local heating. - Stress concentrations cause local plasticity. - Cleavage occurs where the stress exceeds the ideal strength. - Dislocations pileup at grain boundaries. - General plasticity roughened the surface.
Stress concentrations cause local plasticity.
How does a crack grow in a pure metal or polymer subjected to cyclic loads? - Substitutional solutes roughen the slip planes, hindering dislocation - Compressive stress causes crack closure. - Tensile stress produces a plastic zone, which folds forward as stress is removed. - Grain boundaries prevent dislocation glide.
Tensile stress produces a plastic zone, which folds forward as stress is removed.
During which stage does creep damage accumulate? - Initial elastic strain - Tertiary creep - Primary creep - Secondary creep
Tertiary creep
Image from Quiz 20 Consider the growth of a crack subjected to an alternating load: Why does Δ K increase even though Δ σ is constant? - The crack grows longer with each cycle. - The modulus increases as the material is subjected to cyclic stress. - The toughness G c increases as the crack grows with each cycle. - The fracture toughness K c increases with each cycle. - The correction factor Y increases with each cycle.
The crack grows longer with each cycle.
What happens during the creep relaxation time? - The material fails by creep. - The stress decreases to half its original value. - The stress is reduced by half near crack surfaces. - Tertiary creep is reversed. - The strain decreases to half its original value.
The stress decreases to half its original value.
One kind of linear oxidation may be described by Δm = kL t , kL > 0 What explains this behavior? - An oxide film adheres to the surface. - The surface oxide film breaks down. - The rate of oxidation is temperature - dependent. - Volatile oxides are formed. - The material is immune to oxidation.
The surface oxide film breaks down.
What does a large negative energy of oxidation imply about the rate of oxidation? - An energy of oxidation less than -1 implies a high rate. - The more negative the energy of oxidation, the lower the rate of reaction. - The more negative the energy of oxidation, the higher the rate of reaction. - There is little or no correlation between the energy and the rate.
There is little or no correlation between the energy and the rate.
Where in the material does core diffusion occur? - At crack tips - Inside precipitates - Through dislocations - In the space between adjacent grains - Through the bulk of the crystal
Through dislocations
What is the purpose of stable precipitates in a nickel-based super-alloy intended for high-temperature use? - To hinder dislocation glide - To increase the elastic modulus - To increase the density - To blunt crack tips - To increase diffusion
To hinder dislocation glide
What is the purpose of substitutional solutes in a nickel-based super-alloy intended for high-temperature use? - To hinder dislocation glide - To increase the elastic modulus - To increase the density - To blunt crack tips - To increase diffusion
To hinder dislocation glide
Which practice will reduce the likelihood of the fatigue failure of a bolted connection? - Tighten the bolts just enough to hold the connection together. - Torque the bolts to produce a large preload. - Use studs instead of conventional bolts. - Use short, stiff, large-diameter bolts. - Loosen the bolts.
Torque the bolts to produce a large preload.
How does cyclic stress cause a crack to grow in an engineering alloy containing small conclusions? -Compressive stress causes the inclusions to fragment. -Inclusions hinder dislocation glide. -Voids form around the inclusions and link up with each other. -Inclusions concentrate the stress.
Voids form around the inclusions and link up with each other
In some cases, linear oxidation may be described by Δm = kL t , kL < 0 What explains this behavior? - The rate of oxidation is temperature -dependent. - The surface oxide film breaks down. - The material is immune to oxidation. - Volatile oxides are formed. - An oxide film adheres to the surface.
Volatile oxides are formed.
What is generally true of welded joints? - Welds tend to have low SCFs. - Welds contain residual tensile stresses. - Welds contained residual compressive stresses. - Wells tend to have smooth surfaces. - Welds increase fatigue resistance.
Welds contain residual tensile stresses.
