A viscoelastic-viscoplastic model for adhesives subjected to reversed cyclic load

This study aims to describe a toughened adhesive's ratcheting-recovery behavior under reversed cyclic load using a viscoelastic-viscoplastic model. As most adhesives are based on synthetic polymers, their tensile and compression response can be different. A series of load-Sunload tests were conducted on bulk adhesives and bonded joints involving tension/compression-shear loads to characterize the initial yield surface. The effect of hydrostatic stress was studied by considering the instantaneous response and yield strength under tensile and compression loads. Given the observed modulus degradation and extensive permanent strain during reversed cyclic tests, time-dependent damage factors were considered for both viscoelastic and viscoplastic responses. The model was implemented in a finite element (FE) code and used to model the shear response to reversed cyclic load with varying frequency. Good agreement between the model and experiment was obtained. The consideration of both hydrostatic stress and damage was required to describe the observed adhesive reversed cyclic response.