# Shared Flashcard Set

## Details

MATSE 201 Mechanics Quiz Review
Mechanical Properties of Solids
55
Science
11/17/2010

Term
 engineering stress
Definition
 σ = load/Ao     [N/m2]   Ao = initial x-sectional area
Term
 engineering strain
Definition
 ε = (l - lo)/lo   lo = initial length l = length under stress
Term
 basic stress-strain graph for a ductile metal
Definition
 [image]
Term
 For tensile stress, σ and ε are ______.
Definition
 positive
Term
 For compressive stress, σ and ε are ______.
Definition
 negative
Term
 angular stress and strain
Definition
 [image]
Term
 deformation regions graph
Definition
 [image]
Term
 elastic deformation
Definition
 non-permanentfollows Hooke's Law
Term
 Hooke's Law for elastic deformation
Definition
 σ = Eε     E = Young's modulus AKA "elastic modulus" AKA "modulus of elasticity"
Term
 How do bond strength and stiffness vary with Young's modulus?
Definition
 as E ↑, stiffness ↑, bond strength ↑
Term
 elastic energy density
Definition
 given as the area under the stress strain curve
Term
 sample stress-strain curves for material types
Definition
 [image]
Term
 elastic energy density equation
Definition
 elastic energy = ½σE = ½Eε2
Term
 longitudinal and transverse strainand Poisson's ratio
Definition
 [image]
Term
 shear stress and strain equations
Definition
 τ = Gγ E = 2G(1 + ν)   where G = shear modulus AKA modulus of rigidity
Term
 deformation graphyield point (onset of plastic deformation)Tensile strength (maximum of stress-strain curve)
Definition
 [image]
Term
 Why is the regular stress-strain curve of a material misleading?
Definition
 Because of necking (area decrease), engineering stress is artificially low. The "true stress" will show a higher engineering stress.Necking starts after the yield point.
Term
 What is the role of dislocations in ductility?
Definition
 Dislocations can increase ductility by facilitating slip.
Term
 Where does slip most readily occur and why?
Definition
 Slip occurs most readily in high density planes along a high density direction, because denser planes have atoms closer together and denser directions make for shorter slip distances.
Term
 What is the relative susceptibility to slip of FCC, BCC, and HCP crystal structures?
Definition
 FCC - most ductile (12 slip systems)BCC - appreciably ductile (12 slip systems)HCP - least ductile (3 slip systems)
Term
 What is a slip system?
Definition
 # slip systems = (# slip planes)*(# slip directions)
Term
 Why does slip not generally occur in ceramics?
Definition
 -Burger's vector (slip distance) is larger because it involves more than one atom-sliding planes means bringing like charges near each other
Term
 define the phenomenon of viscoelasticity
Definition
 glasses and polymers may behave elastically at low T and flow at high T
Term
 Elastomers can exhibit increasing engineering strain with stress. Why?
Definition
 [image]
Term
 bend test setup diagram
Definition
 [image]
Term
 stress-strain curve from bend test
Definition
 [image]
Term
 Griffith crack model
Definition
 [image]
Term
 Why is σmax greater for compressive stress than for tensile stress?
Definition
 σmax ↑ as r ↓ Because the compressive stress squishes the crack and makers r effectively smaller, σmax can be higher. It's the opposite for tensile stress.
Term
 how does hardness relate to tensile strength and yield strength?
Definition
 as hardness ↑, T.S. ↑, σy ↑, ductility ↓
Term
 interpreting hardness and ductility from stress-strain graph
Definition
 [image]
Term
 list the methods of hardening
Definition
 solution hardeningstrain hardeningcold-workingprecipitation hardeninggrain size size reduction
Term
 solution hardening
Definition
 put a solute atom in the metalthis impedes dislocation movement
Term
 strain hardening
Definition
 create dislocations by bending materialthere get to be too many, and they impede each other's movement
Term
 cold working
Definition
 squish a material, when cold, through rollersthis creates more dislocations
Term
 precipitation hardening
Definition
 [image]
Term
 grain size reduction
Definition
 smaller grain size means more grain boundaries, which impede dislocation movement
Term
 recovering ductility
Definition
 annealing (heat & grains recrystallize) reverses strain-hardening upon annealing, tensile strength ↓, ductility ↑
Term
 creep
Definition
 permanent deformation occurring at high temperature for a material under constant load over a long time
Term
 Why are creep mechanisms diffusion dependent?
Definition
 [image]
Term
 creep testing
Definition
 apply constant load to material and measure long-term deformation
Term
 stages of creep
Definition
 [image]
Term
Definition
 ...................... εs = Kσne(Q / RT)
Term
 fracture morphology ofductile metal
Definition
 "cup & cone"
Term
 fracture morphology ofbrittle metal
Definition
 regular break
Term
 fracture morphology ofceramic
Definition
 "mirror-mist-hackle"
Term
 strength
Definition
 measure of a material's ability to withstand stress or strain
Term
 hardness
Definition
 measure of a material's ability to withstand indentation, distortion, and scratching
Term
 ductility
Definition
 measure of a material's ability to deform under tensile stress
Term
 toughness
Definition
 measure of material's resistance to fracture when stressed
Term
 On a stress-strain curve, the first part is _____ deformation, which is ______ when the load is removed.
Definition
 elasticrecovered
Term
 On a stress-strain curve, the second part is _____ deformation, which is ______ when the load is removed.
Definition
 plasticpermanent
Term
 During elastic deformation, a tensile or compressive strain parallel to the direction of an applied load will induce a strain perpendicular to the load having opposite sign and a magnitude determined by the _____.
Definition
 Poisson ratio
Term
 Why are ceramic materials harder yet more brittle than metals?
Definition
 Ceramics are hard yet brittle because they have strong bonds between atoms with strong ionic/covalent character. Burger's vector is larger because dislocation involves more than one atomsliding planes means bringing like charges close
Term
 Why is Ni more ductile than Co when they both have similar bond strength and melting points?
Definition
 Ni is more ductile because its FCC crystal structure is more ductile than Co's HCP crystal structure
Term
 Metals can be hardened by alloying with other metals. An example of _____ hardening occurs in a system where the Hume-Rothery rules are obeyed.An example of _____ hardening occurs in a system where they aren't.
Definition
 obeyed = solution hardeningnot obeyed = precipitation hardening
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