AXIAL-TORSIONAL FATIGUE - A STUDY OF TUBULAR SPECIMEN THICKNESS EFFECTS

A room-temperature experimental program was conducted on AISI type 316 stainless steel to determine the effect of wall thickness on the cycl ic deformation behavior and fatigue life of thin-wall, tubular, axial- torsional fatigue specimens. The following experimental variables were examined in this study: the depth of the surface work-hardened layer produced in specimen machining, and the effects of strain range and ax ial-torsional strain phasing. Tubular fatigue specimens were fabricate d with wall thicknesses of 1.5, 2.0, and 2.5 mm. One as-fabricated spe cimen from each wall thickness was sectioned for microstructural exami nation and microhardness measurement. A specimen of each wall thicknes s was tested at each of three conditions-high strain range in-phase, l ow strain range in-phase, and low strain range out-of-phase-for a tota l of nine axial-torsional fatigue experiments. Little or no variation in the fatigue life or deformation behavior as a function of wall thic kness was observed. The machining-induced work-hardened zone, as a per centage of the gage section material, was found to have a minimal effe ct on both deformation behavior and fatigue life. Out-of-phase fatigue tests displayed shorter fatigue lives and more cyclic hardening than in-phase tests.