Fatigue testing of GFRP materials for the application in automotive leaf springs

Abstract

Due to their high specific properties, fiber reinforced plastics are ideal candidates for the substitution of steel parts in the automotive sector enabling high weight savings and increasing the efficiency of automobiles. One possible application are leaf springs made of glass fiber reinforced plastics. Due to the simple bending load case, the fiber orientation can be aligned with the main stress direction. In real life such components as leaf springs are loaded under stochastic loads originated from different driving maneuvers. To replicate those fatigue load case, a high number of component tests are required. Aim of the present work (as a result of a joint research project between the Institute for Plastics Processing and Ford Motor Company) is to develop a simplified testing program that is able to reproduce the damage and the fatigue behavior which occurs in real composite components. For this purpose, three point bending experiments on unidirectional specimens made of glass fiber reinforced epoxy pre-preg material are performed. However, since the loading of the real component introduces additional transverse stresses in the region of the clamping group, the results on specimen level are not transferable to component level. For this purpose, a special clamping group is developed on specimen level to enable a better prediction of fatigue life and the transferability of the results of the fatigue tests to component level. This results in a more realistic representation of the leaf spring stress state in the fatigue experiments. As a result of this research, a higher safety margin in the design phase of such components and less testing time is achieved.