Page 444 - Mechanical Behavior of Materials

444 Chapter 9 Fatigue of Materials: Introduction and Stress-Based Approach

50
σ = σ 7075-T6 Al
300 a ar k = 1, axial 40
t
σ , Stress Amplitude, MPa 200 138 0 –138 30 σ a

ksi
276
a
100 σ = 414 MPa 20
m
10

0 0
10 4 10 5 10 6 10 7 10 8 10 9
N , Cycles to Failure
f
Figure 9.26 Axial loading S-Ncurves at various mean stresses for unnotched specimens
of an aluminum alloy. The curves connect average fatigue strengths for a number of lots of
material. (Data from [Howell 55].)

radius, ρ 1.59 mm
2024-T4 Al
400 d d = 7.62 mm 60 S a
S , Nom. Stress Amplitude, MPa 300 d 40 ksi

200

ρ = 1.59 mm
100
a
ρ = 0.25 mm 20
S = 0
m
0 0
10 4 10 5 10 6 10 7 10 8
N , Cycles to Failure
f
Figure 9.27 Effects of notches having k t = 1.6 and 3.1 on rotating bending S-N curves of an
aluminum alloy. (Adapted from [MacGregor 52].)