Page 83 - Biaxial Multiaxial Fatigue and Fracture

68 h! ISOBE AND S. SAKURAI

g 100

f 80 0.2 0.4 0.6 0.8 1.0
Mises' eq. strain amplitude Af42 (%)
Fig. 6. von Mises'equivalent stress-strain relationship between base metal and weldment.

0.4- SUS304 Welded joint. RT

4 0.1 - Front surface side

0.2r
0.3 -

0.4
Fig. 7. Longitudinal strain range distribution near the weld line at room temperature [7].

In the case of carbon and stainless steels, the reduction in fatigue life of weldment has been
also observed. The fatigue strength reduction factors were determined through the discussion
on the effect of joint configuration, welding process, cyclic plasticity, metallurgical factors, and
so on [2]. For a metallugical aspect, the effect of a nongeometric metallurgical notch effect
which is the hardness changes locally around the heat affected zones within the multi-pass
weldment and causes larger strain within the softened regions, had been reported [6]. Figure 7
shows an example of strain distribution around the weld joint in a bending test of a large plate
of 304 stainless steel [7]. This strain increasing has been considered as the reason of the life
reduction in the weldment of stainless steels. On the other hand, such a distinct change in
hardness was not observed in the weldment of Hastelloy-X, so the life reductions of weldment
were not caused by the strain concentration.