On the hysteretic response of mechanical strain induced by thermal stress in fastened metal-composite hybrid structures during a temperature cycle

Abstract

As the use of composite materials in aerospace is growing fast, more metal-composite hybrid structures come into being and thermal stress becomes increasingly a concern that may affect structural safety. In this paper, experimental and numerical studies are conducted on the mechanical strain induced by thermal stress in an AL/CFRP hybrid structure subjected to a heating–cooling–heating cycle. The studied hybrid structure consists of a metal plate and a composite laminate fastened by three bolts. The experimental results show that the mechanical strain in either metal or composite exhibits a hysteresis as the structure undergoes the temperature cycle, which implies the existence of structural nonlinearities. Finite element analysis, which incorporates details of the bolt joint, reproduces the hysteretic responses that reach a reasonable agreement with the experimental ones. Numerical studies disclose the effects of the structural parameters, i.e., friction coefficient, clamping force, fastener-hole clearance and bolt spacing, on the hysteresis and provide insights into the physical events during the thermal cycling. The reported work reveals that the movement of the bolts inside the surrounding holes is the key mechanism that drives the hysteretic thermal stress in the tested structure and sheds light on further investigations of structural safety of such hybrid structures under cyclic thermomechanical conditions.