Fatigue Behavior of Mechanical Joining for HSS Grades

Weight reduction and economy in the use of materials are the most important aim of automotive industries. Steel manufacturers develop high strength steel in order to increase mechanical properties. Fatigue behavior of assemblies is an important issue to consider, and in the case of thin steel sheet spot welding is the widely technique used. Is this paper, other techniques have been studied such as clinching and riveting.

Fatigue tests were performed on different steel grades and several sheet thickness on a single spot specimen subjected to shear-tension loading. Results show that the fatigue strength of these assemblies is strongly dependant of the steel grade on the contrary of spot welds. Some tests on two spots specimens confirm that the fatigue strength is proportional to the number of spots. Then relationships in order to predict the fatigue strength from plate thickness are proposed from experimental results. Finally, in order to predict fatigue property from the fatigue behavior of the steel and including the assembling parameters, a modeling has been developed using finite element calculations. Good results are obtained and will enable to optimize the spot geometry.