Assessment of an Improved Multiaxial Strength Theory Based on Creep-Rupture Data for Type 316 Stainless Steel

A new multiaxial strength theory incorporating three independent stress parameters was developed and reported by the author in 1984. It was formally incorporated into ASME Code Case N47-29 in 1990. In the earlier paper, the new model was shown to provide significantly more accurate stress-rupture life predictions than the classical theories of von Mises, Tresca, and Rankine, for type 304 stainless steel tested at 593°C under different biaxial stress states. Further assessments for other alloys are showing similar results. The current paper provides additional results for type 316 stainless steel specimens tested at 600°C under tension-tension and tension-compression stress states and shows 2–3 orders of magnitude reduction in the scatter in predicted versus observed lives. A key feature of the new theory, which incorporates the maximum deviatoric stress, the first invariant of the stress tensor, and the second invariant of the deviatoric stress tensor, is its ability to distinguish between life under tensile versus compressive stress states.