Page 248 - Biaxial Multiaxial Fatigue and Fracture

232 C. GAIER AND H. DANNBAUER

The reason is the critical plane criterion: The stress amplitude in the critical plane is almost the
same for combined load with 90 degree phase shift as for uniaxial bending load. The difference
is, that for the combined load case the stress vector is rotating, whereas for the bending one it
changes only its sign. This vector rotation is not considered by the critical plane criterion. The
test results show, that for ductile materials there must be an interaction between planes, which
could be taken into account e.g. by integral methods, where an average damage value is
calculated over all planes.

10 mo 103mO 1 mom, IOmOmo
worcydes

Fig. 12. Computed S/N-curves for cast aluminium and comparison to tests

-m- Bending Test - .B - Bending Fernfat
--.t. Torsion Test - + - Torsion Fernfat
+I
-A- Comb. 0" Test - - Comb. 0" Fernfat
---t. Comb. 90" Test - e - Comb. 90" Femfat

Fig. 13. Computed S/N-curves for tempering steel and comparison to tests