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.