Chapter 6 - Mechanical Properties of Metals

Question 1

ASTM

Answer 1

American Society for Testing and Materials

Question 2

ways that loads are applied (3)

Answer 2

1. tension
2. compression
3. shear/torsional

Question 3

tension tests

Answer 3

a specimen is deformed, usually to fracture, with a gradually increasing tensile load that is applied along the long axis of a specimen, standard diameter is 0.505”, recorded as load or force vs elongation

Question 4

engineering stress

Answer 4

σ = F/Ao, measured MPa or psi

Question 5

1 MPa

Answer 5

10^6 N/m^2

Question 6

engineering strain

Answer 6

ϵ = (li-lo)/lo = ∆l/lo, unitless

Question 7

compression tests

Answer 7

force is compression and the specimen contracts along the direction of the stress, negative stress and strain, used when a materials behavior under large and permanent strains is desired or when the material is brittle in tension

Question 8

shear stress

Answer 8

τ = F/Ao

Question 9

plastic deformation

Answer 9

nonrecoverable deformation, corresponds to the breaking of bonds with original atom neighbors and then re-forming bonds with new neighbors

Question 10

yielding

Answer 10

when plastic deformation occurs

Question 11

proportional limit

Answer 11

(P) the location on the graph where the stress-strain curve departs from linearity

Question 12

yield strength

Answer 12

(σy) the stress corresponding the intersect of a line offset by 0.002 from the original curve and the stress-strain curve, measure of a metals resistance to plastic deformation

Question 13

fracture point

Answer 13

(F) point of fracture

Question 14

tensile strength

Answer 14

(TS) the stress at the maximum on the engineering stress-strain curve, maximum stress that can be sustained by a structure in tension

Question 15

necking

Answer 15

occurs at TS, when the subsequent deformation begins to be at one point

Question 16

ductility

Answer 16

measure of the degree of plastic deformation that has been sustained at fracture, indicates to a designer the degree to which a structure will deform plastically before fracture, specifies the degree of allowable deformation during fabrication operations, generally increases with temperature

Question 17

brittle

Answer 17

a metal that experiences very little or no plastic deformation upon fracture

Question 18

resilience

Answer 18

(Ur) the capacity of a material to absorb energy when it is deformed elastically and then, upon unloading, to have this energy recovered, computed by finding the area under the engineering stress-strain curve taken to yielding

Question 19

resilient materials

Answer 19

those having high yield strength and low moduli of elasticity, used in spring applications

Question 20

toughness (2)

Answer 20

the area under the σ-ϵ curve up until the point of fracture

1. fracture toughness: indicative of a material’s resistance to fracture when a crack is present
2. notch toughness: the ability to absorb energy and plastically deform before fracturing

Question 21

true stress

Answer 21

σ = F/Ai

Question 22

true strain

Answer 22

ϵ = ln[(li/lo]

Question 23

strain-hardening exponent

Answer 23

(n) constant used in predicting where necking may begin