Page 204 - Biaxial Multiaxial Fatigue and Fracture

188 1: LAGODA ET AL.

the stress gradient under torsion and let us bring that kind of loading to pure shearing so as to
obtain equivalence between the both loading.

-0.004--1
-800

C)
1 .000
MJ/m3 MJ/m

0.500 0.500

0.000 1 ' 1 ' 1 ' 0.000

-0.500
-0.500

-1 .ooo
-1.000

Fig.2. Fragments of the variable amplitude histories of a) stress, b) strain and c) energy pa-
rameters W(t) and d) W(t)

Transform the Eq. (2) of regression for pure torsion to the following form

zat = ztft (2Nf )bt (9)

Then, coefficient f, and exponent b, of fatigue strength under torsion are equal to

1
b =--,
mt