Analysis of the energy dissipation in multiaxial fatigue tests of AISI 304L stainless steel bars

Abstract

In the recent past, the specific heat loss per cycle (Q parameter) was used to synthesise in a single scatter band approximately 140 uniaxial fatigue test results obtained from constant amplitude, push-pull or torsional, stress- or strain-controlled fatigue tests on plain and notched AISI 304 L stainless steel specimens. It was also demonstrated that the Q parameter can be evaluated during a fatigue test by measuring the cooling gradient after a test stop at the hot spot region of the specimen surface. In the present contribution, the specific heat loss Q has been adopted for the first time to correlate the fatigue strength of AISI 304L specimens subjected to low-cycle multiaxial fatigue loadings. Completely reversed (R = -1) pure bending, pure torsion and combined bending and torsion tests were carried out on hourglass-plain specimens by using two servo hydraulic actuators. In-phase (ϕ = 0°) as well as out-phase (ϕ = 90°) multiaxial fatigue tests were performed by adopting two different biaxiality ratios. In addition, thin-walled tubular specimens were tested under completely reversed tension and torsion fatigue loadings for comparative purposes. Afterwards, all fatigue test results were expressed in term of specific heat loss and compared with the scatter band previously evaluated for plain and notched stainless-steel specimens subjected to uniaxial loading. In the LCF regime the scatter band relevant to uniaxial data correlated well the multiaxial fatigue data.