Fundamentals of Materials Science and Engineering: An Integrated Approach, 3e

GTBL042-07 GTBL042-Callister-v2 August 6, 2007 12:43

206 • Chapter 7 / Mechanical Properties

Stress (10

3 psi)

800

600

400

200

0

Strain

Stress (MPa)

120

100

80

60

40

20

0

0 0.1 0.2 0.3 0.4 0.5

–200°C

–100°C

25 °C

Figure 7.14

Engineering

stress–strain

behavior for iron at

three temperatures.

Incorporation of Equation 7.5 into Equation 7.13b yields

Modulus of resilience

for linear elastic

behavior, and

incorporating

Hooke’s law

Ur=

1

2

σyy=

1

2

σy

(σy

E

)

=

σy^2

2 E

(7.14)

Thus, resilient materials are those having high yield strengths and low moduli of

elasticity; such alloys would be used in spring applications.

Toughness

toughness Toughnessis a mechanical term that is used in several contexts; loosely speaking,

it is a measure of the ability of a material to absorb energy up to fracture. Spec-

imen geometry as well as the manner of load application are important in tough-

ness determinations. For dynamic (high strain rate) loading conditions and when a

notch (or point of stress concentration) is present,notch toughnessis assessed by

using an impact test, as discussed in Section 9.8. Furthermore, fracture toughness is

a property indicative of a material’s resistance to fracture when a crack is present

(Section 9.5).

Stress

0.002 Strain

σy

y

Figure 7.15 Schematic representation showing how modulus

of resilience (corresponding to the shaded area) is determined

from the tensile stress–strain behavior of a material.