Page 424 - Biaxial Multiaxial Fatigue and Fracture

408 l ! AUBIN, I! QUAEGEBEUR AND S. DEGAULX

700
600
+ Tension-compression
500
Pmportiona14So
400

300
200

Fig. 8. Cyclic stress-strain responses at the stabilized or quasi-stabilized cycles for seven
different loading paths.

The fatigue lives of the specimens loaded under tension-compression and circle path are
drawn as a function of the equivalent plastic strain amplitude in Fig. 9. This figure confirms the
classical result, extensively studied elsewhere in the present ESIS Special Technical
Publication: non-proportional loadings highly reduce the fatigue life in low-cycle fatigue of
materials. A ratio of up to 7 exists here between the fatigue life obtained for a circle path and
that in tension-compression with a same plastic strain amplitude of 0.25 %.

2 Number of cycles
aeq 0.1 I
10 1000 10000 100000 1000000

0.0001 0

0.00001 0 Circle

Fig. 9. Equivalent plastic strain-life diagram.