Fatigue life prediction of Polymethyl methacrylate (PMMA) polymer under random vibration loading

Abstract

The objective of this paper is to develop a robust numerical fatigue life prediction model for Polymethyl Methacrylate (PMMA) polymer material of automotive lamp components subjected to random vibration loading, with consideration for material non-linearity to reduce number of iterations in the design cycle. The fatigue life based on initial elastic modulus and secant modulus is predicted using ANSYS software and compared to the experimentally obtained fatigue life. Three fatigue life prediction models, Steinberg, Narrow-Band and Wirsching were used. Twelve specimens cut-out from injection moulded optical blades of PMMA were tested to obtain the fatigue life using electrodynamic shaker. The average experimental fatigue life was obtained from the twelve specimens tested. The use of initial elastic range based modulus gives fatigue life that is 43% lower than the experimental result, while for the secant modulus based analysis, the fatigue life accurately matches the experimental result with only 1% difference. Hence, a complete non-linear finite element model may not be necessary to estimate the fatigue life. The numerical result is based on Wirsching fatigue model, which provides a more accurate prediction than Steinberg and Narrow-Band models.