FATIGUE LIFE ASSESSMENT OF GFRP FOR LONGITUDINAL LEAF SPRINGS

摘要

Due to the 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 application are composite leaf springs made of glass fiber reinforced plastic (GFRP). Because of the simple bending load case, the fiber direction can be aligned with the loading direction. For longitudinal leaf springs, the axle is clamped in the center to the leaf spring component leading to a different stress state compared to pure bending. The aim of the research presented (in a cooperation between Institute for Plastics Processing and Ford Research and Innovation Center) is to develop a testing method on specimen level that is able to determine the fatigue life including the complex stress state in the clamping section. For this purpose, three point bending experiments on unidirectional specimens made of GFRP epoxy prepreg material are performed including a miniaturized clamping system. This results in a more realistic representation of the leaf spring stress state in the fatigue experiments. The applied force in the clamping section is measured during experiments and reveals the creeping behavior of the composite material. Fatigue testing also shows a significant change in damage evolution compared with the pure bending stress state resulting in shorter fatigue lives. With the results of this research, higher safety in the design of this component and less testing time is achieved.