Page 140 - Mechanical Behavior of Materials

Section 4.4 Trends in Tensile Behavior 141

400
2500
AISI 4142, as quenched
300
2000
σ, Stress, MPa 1500 200 σ, ksi

1000 AISI 1095, hot rolled
100
500 AISI 1020, hot rolled

0
0 0.1 0.2 0.3 0.4
ε, Strain

Figure 4.14 Engineering stress–strain curves from tension tests on three steels.

100

600
7075-T6
80
σ, Stress, MPa 400 2024-T351 60 σ, ksi

40
200
1100
20

0
0 0.05 0.10 0.15 0.20
ε, Strain

Figure 4.15 Engineering stress–strain curves from tension tests on three aluminum alloys.

For metals and ceramics, creep effects become significant around 0.3 to 0.6T m , where T m is
the absolute melting temperature. Thus, creep strains are a factor at room temperature for metals
with low melting temperatures. Strain rate may also affect the tensile behavior of ceramics at room
temperature, but for an entirely different reason unrelated to creep, namely, time-dependent cracking
due to the detrimental effects of moisture.
For engineering metals at room temperature, strain-rate effects due to creep exist, but are not
dramatic. For example, some data for copper are given in Fig. 4.17. In this case, for an increase
in strain rate of a factor of 10,000, the ultimate tensile strength at room temperature increases
about 14%. Larger relative effects occur at higher temperatures as creep effects become more