A New Experimental Method for the Introduction of a Predetermined Amount of Residual Stresses in Fatigue Test Specimens

A new experimental method for the incorporation of residual stresses (RS) in standard fatigue steels specimens was developed. RS were introduced by means of high frequency (360 kHz) induction heating. Surface tensile RS resulted from cooling down the specimen subjected to a high thermal gradient. To preserve the mechanical properties of the steel, it was necessary to circulate a coolant at the center of the specimen. The 304L austenitic stainless steel does not undergo phase transformation nor micro structural changes in the solid state and was thus selected for this purpose. Multiphysics finite element (FE) analysis was used to calculate the distributed RS in the fatigue samples. These calculations were compared to XRD measurements and a very good agreement was obtained. It was therefore demonstrated that RS induced with induction heating could be numerically assessed. This conditioning method was then proved efficient to study the only influence of a predetermined amount of RS on the fatigue properties of austenitic 304L steel without undergoing influences of other parameters such as microstructure, surface finish and geometry.