Chapter 2: Mechanical Properties

Question 1

Mechanical properties

Answer 1

Standardized interpretations of a material’s response to stress that compare their response during plastic and elastic deformation.

Question 2

Stress

Answer 2

Measure of what a material feels from externally applied forces.

Question 3

Types of Stress (3)

Answer 3

Tension, compression, shear

Question 4

Stress Formula

Answer 4

σ = P/A

Question 5

Strain

Answer 5

Deformation of a material from stress.

Question 6

Strain formula

Answer 6

ε = ΔL/L

Question 7

Shear Strain Formula

Answer 7

γ = b/h = tanθ = θ for small angles

Question 8

Hooke’s law formulae

Answer 8

σ = Eε
τ = γG

Question 9

Poisson’s ratio

Answer 9

v = - Lateral Strain / Longitudinal (axial) Strain

Question 10

Anisotropic
materials

Answer 10

Mechanical properties depend on the orientation of the material’s body, unsymmetrical crystalline structures.

Question 11

Isotropic materials

Answer 11

Identical material properties in all directions at every given point

Question 12

Poisson’s ratio range

Answer 12

0 - 0.5

Question 13

v = 0.5

Answer 13

Perfectly incompressible isotropic material

Question 14

Elastic deformation

Answer 14

Bonds stretch and shorten as stress is applied, deformations recover quickly.

Question 15

Plastic deformation

Answer 15

Bonds are stretched and/or broken, deformations are permanent.

Question 16

Metallic deformation behavior below the yield point

Answer 16

Elastic

Question 17

Metallic deformation behavior above the yield point

Answer 17

Elastic and plastic

Question 18

Tension testing

Answer 18

Constant rate of elongation applied to a dog bone specimen so that plastic deformation occurs only in the gauge section.

Question 19

Young’s modulus (E)

Answer 19

Slope of the elastic portion of a stress-strain curve

Question 20

Resilience modulus (U)

Answer 20

Measure of material stiffness, area under a stress-strain curve

Question 21

Yield strength, proportional/elastic limit (σy)

Answer 21

Stress on a stress-strain curve that is the limit of elastic behavior and the beginning of plastic behavior.

Question 22

Offset yield strength

Answer 22

When the yield point is difficult to define, stress is measured from ε = 0.002

Question 23

Ultimate yield strength

Answer 23

Highest stress on a stress-strain curve, where a material begins to deform (have a local instability).

Question 24

Reduction in area and length

Answer 24

Measures of ductility

Question 25

Ductility

Answer 25

The measure of plastic strain to fracture, the quality of being flexible.

Question 26

Hardness

Answer 26

Material's resistance to localized plastic deformation, the ability to withstand force without scratching, penetration or indentation.

Question 27

Toughness

Answer 27

Amount of energy a material can absorb before fracturing

Question 28

Reduction in area formula

Answer 28

RA = (Ao - Af)/Ao

Question 29

Brittle fracture

Answer 29

Breakage of a material via rapid crack propagation with low energy release and without significant plastic deformation. Less strain is needed.

Question 30

Ductile fracture

Answer 30

Breaking of a material after extensive plastic deformation. Uses a lot of time and energy and needs an increased load.

Question 31

True stress

Answer 31

Instantaneous stress

Question 32

True stress formula

Answer 32

σT = σ(1+ε)

Question 33

True strain

Answer 33

Instantaneous strain

Question 34

True strain formula

Answer 34

εT = ln(Li/Lo) = ln(1+ ε)

Question 35

Hardness Formula

Answer 35

H = F/A

Question 36

Safety Factor

Answer 36

Ratio of a material's strength to an expected strain.

Question 37

Safety factor formula

Answer 37

FS = σy or uts / σdesign

Question 38

Thermal expansion

Answer 38

Tendency of a material to change its shape, area, volume, and density in response to a change in temperature

Question 39

Thermal expansion formula

Answer 39

ΔL = αLΔT

Question 40

Thermal stress

Answer 40

Stress created by any change in temperature of a material.

Question 41

Thermal stress formula

Answer 41

σt = -EαΔT

Question 42

Thermal stress/strain gradient

Answer 42

Thermal stress/strain between 2 points

Question 43

Thermal stress gradient formula

Answer 43

σ = -E(α1 - α2)ΔT

Question 44

Thermal conductivity

Answer 44

The rate at which heat passes through a material

Question 45

Thermal conductivity formula

Answer 45

q = -k(dT/dx)

Question 46

Thermal conductivity mechanisms (k)

Answer 46

1. Lattice Vibrations/photons in non-metals (kl) 2. Free electrons in metals (ke) k = kl + ke

Question 47

Thermal strain gradient formula

Answer 47

εt = (α1 - α2)ΔT

Question 48

Wiedemann-Franz law

Answer 48

Thermal and electrical properties are related and proportional

Question 49

Thermal shock resistance

Answer 49

The ability of a material to withstand sudden changes in temperature

Question 50

Thermal shock resistance formula

Answer 50

TSR = σk / Eα

Question 51

Heat capacity

Answer 51

Amount of heat energy required to raise the temperature of a material by 1C

Question 52

Heat capacity formula

Answer 52

C = dQ/dT, K/(mol*K)

Question 53

Bond stiffness

Answer 53

Inflection point on a bond-energy curve, above this point, a material will melt.

Question 54

Bond stiffness formula

Answer 54

F = αEΔr

Question 55

Ohm's law

Answer 55

R = V/I

Question 56

Resistivity

Answer 56

Measure of the resisting power of a specified material to the flow of an electric current. Affected by temperature, impurities and deformation. p = RA/l

Question 57

Conductivity

Answer 57

The degree to which a specified material conducts electricity. σ = 1/p

Question 58

Bonding force formula

Answer 58

F = dU/dr

Question 59

Work hardening

Answer 59

Toughening (increase of hardness) of a metal, happens during plastic deformation