Engineering Material Test 2

In the context of the current chapter, what does the abbreviation HAZ mean? Hazardous Material Heat-Augmented Zone Hexagonal Area Zone Hazardous Anelastic Zone Heat-Affected Zone

Heat-Affected Zone

In the equation τ y = f / b, what is f? Dislocation yield strength Burgers vector Grain boundary density Resistance to dislocation motion Tensile yield strength

Resistance to dislocation motion

What is the criterion for the onset of plastic deformation? σ = σ yσ = σ yσ = σ y Y σ π a = E G cY σ π a = E G cY σ π a = E G c M = M pM = M pM = M p U e l = σ 2 / ( 2 E )U e l = σ 2 / ( 2 E )U e l = σ 2 / ( 2 E ) F / A = HF / A = HF / A = H

σ = σ yσ = σ yσ = σ y

If the survival probability of a sample is x, what is its failure probability? The probabilities are unrelated. − x 1 − x 1 x

1 − x

As shown above, a flat metal plate (H = 40 cm, W = 60 cm) containing an interior hole is loaded in tension. The metal has a fracture toughness of . If the applied stress is 520 MPa and the geometrical correction factor is 1.09, what is the critical crack length in mm?

4

As shown above, a flat metal plate (H = 40 cm, W = 60 cm) containing an interior hole is loaded in tension. The metal has a fracture toughness of . At what stress intensity K will fast fracture occur? Express your answer in units of

45

Which material is the stiffest?

A

Which material quickly necks when it is drawn out?

A

Young's modulus

A

How can work-hardening be reversed? Disperse precipitates in the material. Sinter the material. Create a random substitutional solution. Anneal the material. Plastically deform the material.

Anneal the material.

Which of the following processes is likely to reduce the suitability of a metal for use in a spring? Cold rolling Solid solution hardening Grain refinement Precipitate strengthening Annealing

Annealing

Onset of necking

B

Which material is the strongest?

B

In the beam depicted above, at which of the marked points is the material in tension? (Note that the dashed curve represents the neutral axis.) Neutral Top and Bottom All three points Top None of the points Bottom

Bottom

Which quantity indicates the magnitude and direction of slip in a crystal? Bond angle Ionic radius Burgers vector Line tension Miller index

Burgers vector

n the equation τ y = f / b, what is b? Dislocation yield strength Burgers vector Grain boundary density Tensile yield strength Resistance to dislocation movement

Burgers vector

How is the ideal strength determined? By computing the force required to rupture inter-atomic bonds By measuring the hardness By measuring the proportional limit By directly measuring the tensile strength By measuring the strain after fracture

By computing the force required to rupture inter-atomic bonds

Fracture

C

Which material is the most ductile?

C

Why are ceramic said to be defect-sensitive materials? No one will buy defective ceramic. Ceramics tend to fail by fast fracture before yielding. Ceramics tend to have low elastic moduli. Defects do not cause failure in ductile materials. Defects caused plastic failure in ceramics.

Ceramics tend to fail by fast fracture before yielding.

Which process is likely to occur at a stress concentration where the local stress exceeds the ideal strength of the material? Crack blunting Ductile tearing Necking Cleavage Elastic buckling

Cleavage

In the equation, Y σ π a = E G c what does Y represent? Applied stress Correction factor Toughness Fracture toughness Elastic modulus Crack length (edge crack)

Correction factor

Which the following is a failure mode for pressure vessels? (Choose all that apply.) Corrosion Annealing Fatigue General yield Fast fracture

Corrosion Fatigue General yield Fast fracture

In the equation, Y σ π a = E G c what does a represent? Elastic modulus Fracture toughness Correction factor Applied stress Toughness Crack length (edge crack)

Crack length (edge crack)

What is a glide plane? Amorphous region Crystal plane along with a dislocation moves Extra half-planes of atoms in a crystal {100} plane in f.c.c. structure Tectonic plate

Crystal plane along with a dislocation moves

What is a slip plane? Tectonic plate Extra half-planes of atoms in a crystal {100} plane in f.c.c. structure Crystal plane along with a dislocation moves Amorphous region

Crystal plane along with a dislocation moves

0.1% proof stress

D

Which material fractures before necking?

D

According to the text, the elastic energy per unit volume stored in a block of material stressed uniformly to a stress σ is U e l = σ 2 2 E How can this result be obtained? Measure the tensile strength. Measure the slope of the elastic stress-strain curve Determine the stress at the onset of necking Measure the heat-transfer rate from the spring. Determine the area under the stress-strain curve from 0 to σ.

Determine the area under the stress-strain curve from 0 to σ.

Which processes associated with plastic deformation? Reversible deformation of bonds None of these Unstable propagation of cracks Dislocation glide Stable propagation of cracks

Dislocation glide

In the equation τ y = f / b, what is τ y? Tensile yield strength Grain boundary density Resistance to dislocation movement Dislocation yield strength Burgers vector

Dislocation yield strength

Which of the following causes many metals to yield at stresses far below their ideal strengths? Dislocations Substitutional solutes Vacancies Precipitates Planar defects

Dislocations

How is work-hardening explained? Dislocations pile up at grain boundaries. Solute-generated stresses "roughen" slip planes to hinder dislocation movement. Dislocations obstruct each other. Strong atomic bonds resist dislocation movement. Precipitates obstruct dislocations.

Dislocations obstruct each other.

Which process uses a die to plastically deform a material? Welding Annealing Rolling Forging Drawing

Drawing

Which measure may temporarily halt the growth of an existing crack? Drill a circular hole at the crack tip. Lengthen the crack. Insert a wedge to open the crack. None of these will help. Sharpen the crack tip.

Drill a circular hole at the crack tip.

Which curve might represent a material that forms a stable neck as polymer chains align

E

Yield strength

E

In the equation, Y σ π a = E G c what does E represent? Crack length (edge crack) Correction factor Elastic modulus Fracture toughness Applied stress Toughness

Elastic modulus

What is annealing? Forming by heating and hammering Quenching Heat treatment to remove dislocations Sintering Work-hardening

Heat treatment to remove dislocations

Why are many ductile materials also quite tough? Elastic dispersions act as little springs. Necking does not occur before fracture. Energy is consumed by plastic flow. Necking failure occurs soon after yielding. Cracks retain their sharpness.

Energy is consumed by plastic flow.

What is an edge dislocation? Proof stress Plastic instability Extra half-plane of atoms Elastic instability Neck

Extra half-plane of atoms

Tensile strength

F

How can the addition of glass fibers to a polymer matrix create a tough composite? Chemical reactions create inclusions. Glass fibers cause glass transition. Fibers act as little springs. Glass has a high fracture toughness. Fibers act as crack stoppers.

Fibers act as crack stoppers.

What is a radial force in a cylindrical object? Force directed towards or away from the centerline (r-direction) Force in a plane inclined at 45° to centerline Force in the circumferential direction (θθ-direction) No answer text provided. Force parallel to the centerline (z-direction) Torsional force on the end caps

Force directed towards or away from the centerline (r-direction)

What is a hoop force in a cylindrical object? No answer text provided. Force parallel to the centerline (z-direction) Force in a plane inclined at 45° to centerline Force directed towards or away from the centerline (r-direction) Force on the end caps Force in the circumferential direction (θ-direction)

Force in the circumferential direction (θ-direction)

What is a longitudinal force in a cylindrical object? Force in the circumferential direction (θθθ-direction) Torsional force on the end caps Force parallel to the centerline (z-direction) Force directed towards or away from the centerline (r-direction) Force in a plane inclined at 45° to centerline

Force parallel to the centerline (z-direction)

Which process involves hammering, either with or without heating? Forging Rolling Annealing Welding Drawing

Forging

In which case is large-strain plasticity desirable? Energy storage and recovery by a spring Support of a load by a beam Containment of a high-pressure fluid Support of a load by a column Formation of a metal part

Formation of a metal part

In the equation, Y σ π a = E G c what does E G c represent? Crack length (edge crack) Correction factor Applied stress Toughness Fracture toughness Elastic modulus

Fracture toughness

Elastic energy per unit volume

G

0.1% strain

H

Consider a plate containing an internal crack, as shown above. If fast fracture were to occur, in which direction(s) would the crack propagate? Vertically upward and downward Impossible to predict At a 45-degree angle to the tensile force Horizontally to the left and to the right Both vertically and horizontally

Horizontally to the left and to the right

In a sample subjected to a tensile force, what is the maximum shear stress occur? Tensile forces do not create shear stress In planes inclined at 45° to the force In planes tangent to the force Impossible to generalize In planes normal to the force

In planes inclined at 45° to the force

Plastic strain after fracture

J

What is the criterion for deciding which material is the most ductile? Largest strain after fracture Largest yield strength Largest Young's modulus Largest tensile strength Little plastic deformation before fracture

Largest strain after fracture

Which are generally more likely to cause a sudden failure? Impossible to generalize Long, blunt-tipped cracks Short, sharp-tipped cracks Short, blunt-tipped cracks Long, sharp-tipped cracks

Long, sharp-tipped cracks

What is the modulus of rupture for a beam that fails in bending? Maximum tensile stress in the surface of the beam Maximum compressive stress Maximum tensile stress along the neutral axis Maximum shear stress in the surface of the beam. Maximum compressive stress along the neutral axis.

Maximum tensile stress in the surface of the beam

Which materials tend to have both the highest toughness and the highest fracture toughness? Glasses Ceramics Polymers Metals Impossible to generalize

Metals

What is the tensile strength? Nominal stress at the onset of plastic flow None of these Nominal stress at the high point of the stress-strain curve Nominal stress at fracture Nominal stress at a permanent strain of 0.1%

Nominal stress at the high point of the stress-strain curve

What is the yield strength? None of these Nominal stress at fracture Nominal stress at the onset of plastic flow Nominal stress at a permanent strain of 0.1% Nominal stress at the high point of the stress-strain curve

Nominal stress at the onset of plastic flow

The equation d σ / d ϵ = σ is the criterion for which process? Fast fracture Buckling Onset of necking Surface indentation Onset of yielding

Onset of necking

The equation d σ n / d ϵ n = 0 is the criterion for which process? Onset of yielding Onset of necking Buckling Surface indentation Fast fracture

Onset of necking

The Weibull distribution for a brittle sample of volume V subjected to a tensile stress σ may be represented by, P s ( V ) = exp ⁡ { − V V 0 ( σ σ 0 ) m } where V 0, σ 0, and m are empirical constants. If the volume of the sample is increased, what does this equation predict about P s? P s decreases. Impossible to tell. It depends on the sign of m. P s remains unchanged. P s increases.

P s decreases.

Which process occurs by dislocation glide in metals? Fast fracture Plastic deformation Corrosion Buckling Elastic deformation

Plastic deformation

What is likely to happen at the tip of a crack where the local stress σ m a x exceeds the yield strength σ y ? Precipitates hinder dislocation glide. Necking occurs. The crack propagates by cleavage. Plastic deformation blunts the crack tip. Bonds stretch but do not break.

Plastic deformation blunts the crack tip.

Why do most polymers have intermediate toughness but low fracture toughness? Polymers tend to be nonlinearly elastic. Polymers tend to be amorphous. Ballmer displayed anelastic behavior. Cracks cannot occur in polymers. Polymers tend to have low elastic moduli.

Polymers tend to have low elastic moduli.

The Weibull distribution for a brittle sample of volume V subjected to a tensile stress σ may be represented by, P s ( V ) = exp ⁡ { − V V 0 ( σ σ 0 ) m } where V 0, σ 0, and m are empirical constants. What is the meaning of P 0 ( V )? Pressure at which the sample fails Probability a sample will fail Pressure at which critical shear stress occurs Pressure at which the sample fails Probability a sample will survive

Probability a sample will survive

What causes fast fracture? Vacancies Dislocation movement Plastic instability Anelastic deformation Rapid crack growth

Rapid crack growth

Which process deforms the material plastic lead by compressing it between rotating cylinders? Forging Drawing Rolling Annealing Welding

Rolling

What kind of defect converts a plane of atoms into a helical surface? Edge dislocation Vacancy Free surface Screw dislocation Precipitate

Screw dislocation

What causes the movement of dislocations? Grain boundaries Annealing Compressive stress Shear stress Tensile stress

Shear stress

What is the mechanism for fracture in a brittle solid loaded in compression? General plastic deformation Stable propagation of a single crack Rapid propagation of a single crack Debonding Slow extension of many cracks to form a crushed zone

Slow extension of many cracks to form a crushed zone

What is the effect of grain size on yield strength? Large grades tend to increase yield strength. Small grains tend to increase yield strength. Grain size has no effect on yield strength. The effect of grain size cannot be predicted.

Small grains tend to increase yield strength.

Why is brass stronger than pure copper? Solute-generated stresses "roughen" slip planes to hinder dislocation movement. Precipitates obstruct dislocations. Dislocations hinder each other. Dislocations pile up at grain boundaries. Strong atomic bonds resist dislocation movement.

Solute-generated stresses "roughen" slip planes to hinder dislocation movement.

Why is it difficult to perform tensile test on brittle materials? Specimens tend to break where gripped by the machine. Brittle materials yield before breaking. Machines measure the yield strength only for ductile materials. It is difficult to make brittle specimens the right size for tensile testing. Testing machines are not powerful enough.

Specimens tend to break where gripped by the machine.

How is intrinsic strength explained? Dislocations pile up at grain boundaries. Strong atomic bonds resist dislocation movement. Precipitates obstruct dislocations. Solute-generated stresses "roughen" slip planes to hinder dislocation movement. Dislocations hinder each other.

Strong atomic bonds resist dislocation movement.

What is likely to happen at the tip of a crack where the local stress σ m a x exceeds the ideal strength σ ~ ? Plastic deformation blunts the crack tip. Necking occurs. Bonds stretch but do not break. Precipitates hinder the dislocation glide. The clock propagates by cleavage.

The clock propagates by cleavage.

What is meant by the "unstable" propagation of a crack? The crack grows slowly as stress increases. The crack does not grow at all. The crack grows slowly at a constant stress. The crack grows rapidly after reaching a critical size. The crack grows slowly after reaching a critical size.

The crack grows rapidly after reaching a critical size.

What is meant by the "stable" propagation of a crack? The crack does not grow at all. The crack grows slowly after reaching a critical size. The crack grows slowly as stress increases. The crack grows slowly at a constant stress. The crack grows rapidly after reaching a critical size.

The crack grows slowly as stress increases.

Why do brittle materials appear stronger in bending that intention? The largest flaw may not belocated where the tensile stress is highest in a beam. It is difficult to make brittle specimens the right size for tensile testing. Cracks twist out of their original orientation to propagate parallel to the compressive stress. The largest flaw may straddle the neutral axis. Bending tends to reduce or eliminate surface flaws.

The largest flaw may not belocated where the tensile stress is highest in a beam.

What causes many metals to yield stress is far below their ideal strength? Plastic instability Cross linking Elastic instability Glass transition The movement of dislocations

The movement of dislocations

The maximum elastic energy per unit volume stored in a block of material stressed uniformly occurs when σ = σ y. Hence, U e l = σ y 2 2 E (Maximum energy density) Why is this the maximum? The spring will be damaged at higher stress. Excessive heating can occur at higher energy densities. Springs should be stiff to avoid fracture. Slip-plane roughening can occur at higher energy densities. Stiffer materials can store more energy.

The spring will be damaged at higher stress.

What happens to many BCC metals like steels at low temperature? They become glassy. They become anelastic. They become more ductile. They become more tough. They become more brittle.

They become more brittle.

n the beam depicted above, at which of the marked points is the material in compression? (Note that the dashed curve represents the neutral axis.) Neutral Top Bottom None of the points All three points Top and Bottom

Top

In the equation, Y σ π a = E G c what does G c represent? Applied stress Elastic modulus Toughness Crack length (edge crack) Fracture toughness Correction factor

Toughness

What happens at the saturation pressure, p s a t? Stress corrosion is arrested. HAZ is created. Trends granular cleavage occurs. Vapor-liquid equilibrium is established. Polymers behave as elastic-brittle solids.

Vapor-liquid equilibrium is established.

What is ductile tearing in a metal? Local separation of the matrix and fibers Ductile-to-brittle transition Voids linking up in the plastic zone. Transgranular cleavage. Intergranular cleavage.

Voids linking up in the plastic zone.

What is the criterion for the onset of fast fracture? M = M p U e l = σ 2 / ( 2 E ) F / A = H Y σ π a = E G c σ = σ y

Y σ π a = E G c

Which property is a measure of the stiffness of a material? Proof stress Young's modulus Toughness Yield strength Tensile strength

Young's modulus

Let p a b s = absolute system pressure p a t m = local atmospheric pressure p s a t = saturation pressure What is the definition of the system's gauge pressure, p g a u g e? p a t m − p a b s ( p a b s − p a t m ) / p s a t p a b s + p a t m p a b s − p s a t p a b s − p a t m

p a b s − p a t m