Page 31 - Biaxial Multiaxial Fatigue and Fracture

16 K. DANG VAN, A. BIGNONNET AND JL. FAYARD

Fig. IO. Sonsino’s welded specimen : a tube continuous welded onto a plate.

200

h
k
E 100
v
tJ

0
- 200 -100 0 100 200
P WPa)

Fig. 11. Tube on plate Dang Van’s loading path for out of phase combined torsion and
bending: in this example, p = 102 MPa, T = 112 MPa, and hence the design stress T~ =
0.33~102+112

Figure 12 shows the life duration N versus the parameter TO resulting from these different
fatigue tests. On the same figure, we plot the curve (50 % probability of survival) derived from
the tests on high strength steel elementary structures performed by J.L. Fayard and previously
presented in Fig. 6. This curve presents a linear part of slope -1/3. The upper part of this curve
is nevertheless limited by the yield stress of the material. The curve fits very well the points
resulting from Sonsino’s study. These points are situated slightly above this curve. This is due
to the choice of the failure criterion: the Sonsino’s fatigue life corresponds to a through crack
instead of a crack depth of 0.5e.