Fast Fatigue Properties Identification by “Self-heating” Method: Application to Automotive Welded Joints

Abstract

The welded assemblies’ high cycle fatigue properties identification for the automotive industry is a long and expensive process which has to be very efficient to perform both safety and lean design. Fatigue properties determination is a time and cost consuming process, it requires several days and specimens to be performed. The self-heating method offers the possibility to dramatically shorten the test duration. It consists in measuring the temperature of the structure under cyclic loading, and then linking it to fatigue properties. Only one specimen and few hours are required for fatigue properties identification providing important cost and time reduction. Thus, an experimental protocol is proposed to measure the rise of temperature of a lap joint welded specimen, with the use of infra-red thermography. Assuming that only self-heating and thermoelastic phenomena are responsible of the temperature evolution, self-heating temperature is extracted from experimental data. A 1D thermal model is proposed to describe the evolution of the temperature of the specimen due to self-heating. The welded joint concentrates dissipative phenomena, which corresponds to a concentrated heat source. This heat source field is then identified by fitting the model to experimental results, and its evolution with the applied loading is used to determine the welded assembly endurance limit. Self-heating method results are proven to be consistent to those obtained by classical fatigue tests.