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deshayes
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Which material criterion should used to minimize the mass for a given beam stiffness?
Maximize E/p
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Suppose the price per kilogram of material is denoted by Cm. Which criterion should be used to minimize the price for a given beam stiffness?
Maximize E/Cmp
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Equation for stiffness
F/(displacement)
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What kind of loading causes buckling to occur?
Compression
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Which factor from equation Fcrit=(n2pi2EI)/L2 depends on the shape of a structural member and the square of its cross-sectional area?
I
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Which kinds of structural members are most susceptible to buckling?
long columns
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If the geometry of the beam or plate is held constant, how does the vibrational frequency scale with material properties?
f=(E/p)1/2
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A hard diamond indenter is pressed into the surface of a material with force F, creating a permanent indentation of depth l and area A. Suppose the material has modulus E, shear modulus G, and strength sigma. How is the hardness computed from this test?
F/A
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According to the text, what is the approximate relationship between hardness and yield strength for many materials?
H=3(yield strength)
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The tensile strain at fracture is a measure of which property?
Ductility
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Where does the largest shear stress occur in s sample subjected to a tensile load?
Planes inclined at 45 to the tensile load
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What drives dislocation glide?
Shear stress
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What are four ways to strengthen a metal?
- 1. dispersion of small particles
- 2. introduction of solutes
- 3. reduction of grain size
- 4. plastic deformation
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What are four ways to strengthen a polymer?
- reinforcement of fibers like glass
- blending with stronger polymer
- cross-linking
- drawing
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How is work-hardening explained?
Dislocations obstruct each other
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What is intrinsic strength?
Strong atomic bonds resist dislocation movement
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How is solid solution hardening explained?
Solute-generated stresses "roughen" slip planes
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How is dispersion strengthening explained?
Precipitates obstruct dislocation movement
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What occurs during elastic deformation?
Atomic bonds stretch but do not break
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What is annealing?
Heating removes dislocations
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What is cold working of a metal?
Plastic deformation without heating
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How can work-hardening be reversed?
Annealing
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What causes many materials to yield at stresses far below their ideal strength?
dislocations
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What is an edge dislocation?
An extra half plane of atoms
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What is a glide plane?
Plane which a dislocation moves
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Identify each of the quantities in following equation:
Y(sigma)(pi*c)1/2=(EGc)1/2
- Y=correction factor
- sigma=nominal stress
- c=crack length
- Gc=toughness
- E=elastic modulus
- (EGc)1/2=fracture toughness
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Which phenomenon does Y(sigma)(pi*c)1/2=(EGc)1/2 describe?
Fast fracture
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What causes brittle fracture?
long, sharp-tipped cracks
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What can happen at the tip of a crack when local stress exceeds the ideal strength?
Crack propagates by cleavage
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What can happen at the tip of a crack when local stress exceeds the yield strength?
Plastic deformation that blunts the crack tip
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How does ductile fracture occur?
Linking of voids in plastic zone
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How can the addition of glass fiers to a polymer matrix crate a tough composite?
Gibers act as crack stoppers
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Why are many ductile materials also quite tough?
Energy is consumed by plastic flow
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How do cracks start in an uncracked component subject to high-cycle fatigue?
Local plasticity occurs where scratches or section changes concentrate stess
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How do cracks start in an uncracked component subject to low-cycle fatigue?
General plasticity roughens the surface
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What happens during peening?
Residual surface compressive stresses are introduced
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What causes work-hardening?
Dislocations accumulate and hinder each other
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What happens during cyclic loading when Kmax=K1c?
Fails by fast fracture
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In the context of this course, what is fatigue?
Failure of a structure due to cyclic stress
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Which process(es) can cause the formation and slow growth of cracks at loads well below the yield strength?
Corrosion
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Which process generally causes final failure in fatigue?
Fast fracture
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What is the cyclic stress intensity range, delta(K)?
Kmax-Kmin or Y(delta(sigma))(pi*c)1/2
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What is the definition of the mean stress?
(sigmamax+sigmamin)/2
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What is the definition of the stress amplitude?
(Sigmamax-sigmamin)/2
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What is the definition of the cyclic stress range?
sigmamax-sigmamin
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