Evaluation of Numerical Methods to Model Structural Adhesive Response and Failure in Tension and Shear Loading

Abstract

Improved energy efficiency in transportation systems can be achieved with multi-material lightweight structures; however, joining often requires the use of adhesive bonding and design efforts are challenged by the paucity of data required to represent adhesives in numerical models. The data for three epoxy structural adhesives tested in tension and shear over a range of strain rates (0.001–1000 s−1) is reported. The range of experimentation addresses regular operation and extreme conditions (crash scenarios) for vehicles. The data was implemented with cohesive and solid elements; and the models were assessed on their ability to reproduce adhesive material response. Good agreement was achieved using both approaches. In average the coefficients of determination (r2) between measured experimental response and simulations were 0.81 for tension and 0.59 for shear, with 2 % difference in the prediction of stress at failure. The cohesive formulation was computationally efficient and reproduced rate effects, but was limited in representing the response of the non-toughened epoxy. The solid element formulation required longer simulation times, but yielded similar accuracy for tension (2 % difference in stress to failure and r2 values of 0.98, on average). However, the shear response accuracy (r2 = 0.53) was reduced by coupling between shear and tension strain rate effects. Numerical simulation of structural adhesives requires constitutive models capable of incorporating uncoupled deformation rate effects on strength. The results of this study indicate that a cohesive model can provide adequate representation of an adhesive joint for tensile and shear loading across a range of deformation rates.