Predicted and Measured Bond-Line Read-Through Response in Composite Automotive Body Panels Subjected to Elevated Temperature Cure

Abstract

Visible distortions in automotive Class “A” surfaces, while being merely cosmetic defects, are unacceptable to customers. One type of surface distortion, referred to as bond-line read-through (BLRT), can occur due to the elevated temperature cure of an adhesive in bonded panel assemblies. The severity of these distortions can be measured by the local curvature of the surface. A finite element (FE) model capable of predicting the occurrence and severity of BLRT-induced surface distortions is being developed and validated. FE model predictions for the surface curvature of the outer panel in a bonded, laboratory scale assembly subjected to a simulated cool-down from the adhesive cure temperature to room temperature were compared with measured results. FE model predictions based on linear elastic material properties for the adhesive and substrate over-predicted the magnitude of the curvature in the outer panel as compared with the measured results. FE model predictions based on viscoelastic material properties for the adhesive and linear elastic material properties for the substrate resulted in substantially better correlation between predicted and measured distortions.