Ratchetting Deformation of SUS316 Steel Thin Tube under Combind Axial-Torsional Loading at Elevated Temperature

Abstract

Biaxial loading tests were carried out by subjecting a thin tube of SUS316 steel to cyclic torsional straining at 923K under a constant axial load. The aim of the tests was to observe and characterize the ratchetting deformation at elevated temperature under multiaxial loading. The results obtained were as follows:
(1) The ratchetting strain ε_a was proportional to the constant axial stress σ and the power of the number of cycles N, in such a way as ε_a=C·σ·N^α.
(2) The effect of the cyclic torsional strain rate γ on the ratchetting strain ε_a was approximately represented by ε_a=C'·γ^β.
(3) The growth rate of the ratchetting strain slowed down with decreasing strain amplitude, and the shakedown behavior was observed at Δγ/√3=0.5%.
(4) The classical plastic analysis of the ratchetting deformation predicted an overestimation of accumulation of the ratchetting strain. A simplified ratchetting analysis method based on the effective primary stress concept gave good correlation with the experimental results.