EFFECTS OF PROPORTIONAL AND NONPROPORTIONAL STRAINING SEQUENCES ON THE HARDENING SOFTENING BEHAVIOR OF IN 738-LC AT ELEVATED-TEMPERATURES

The temperature dependence of multiaxial cyclic behaviour on IN 738 LC was elucidated experimentally. Cyclic proportional and non-porportion al tension/torsion strain paths, as well as proportional and non-propo rtional straining sequences were applied to thin- walled tubular speci mens. The specimens were subjected to various temperatures, several ef fective strain rates and an effective strain of 0.6%. It was shown tha t IN 738 LC did not exhibit any additional hardening or softening unde r non-proportional loads. Furthermore, the stress loci at a given effe ctive strain of 0.6% are circular in the sigma - square-root3tau stres s space, indicating that the J2-theory can be used to describe the mul tiaxial behaviour of IN 738 LC. Changes in straining direction from pr oportional loading to non-proportional loading (and vice versa) do not effect the cyclic deformation behaviour at temperatures greater-than- or-equal-to 600-degrees-C. Stress relaxation during biaxial strain hol d in a circular path has been found to lead to non-proportional unload ing paths. There are some similarities between stress relaxation under strain control and ratchetting under stress control.