Mechanical Properties of Metals

Question 1

Yield strength

Answer 1

Highest stress that material can sustain before undergoing plastic deformation - either minimum point after elastic region or intersection of stress-strain curve + line parallel to elastic curve offset by certain #

Question 2

Tensile strength

Answer 2

Highest stress that material can sustain before breaking - highest point in stress-strain curve

Question 3

Poisson’s ratio

Answer 3

Ratio of lateral to axial strain of material under axial stress - generally of opposite signs so there’s a negative to make it positive

Question 4

Poisson’s ratio of 0.5

Answer 4

No volume chain with strain (rubber band)

Question 5

Poisson’s ratio of 0

Answer 5

No lateral strain with axial strain (cork)

Question 6

Poisson’s ratio < 0

Answer 6

Positive lateral strain with positive axial strain (foam)

Question 7

Ductility

Answer 7

Measure of degree of plastic deformation that has been sustained at fracture - if fracture strain <5% then brittle

Question 8

Resilience

Answer 8

Capacity of material to absorb energy when deformed elastically

Question 9

Modulus of resilience

Answer 9

Strain energy / unit volume required to stress a material to point of yielding

Question 10

Toughness

Answer 10

Capacity of material to absorb energy up to point of fracture - integral over stress strain curve but function is non-linear

Question 11

Engineering stress and strain

Answer 11

Normalized to initial sample dimensions - when sample deforms the true stress + strain change

Question 12

Hardness test

Answer 12

• Pushing hard object w/round or pointy shape in a material creating indentation - initial stress is always high + plastic deformation occurs
• As point goes in stress decreases + equilibrium reached - shallower mark = harder material