Evaluating the Rate-Dependent Fracture Toughness of an Automotive Adhesive

Abstract

Adhesives have made significant inroads into structural bonding of automobiles, but concerns remain over the integrity of these bonds under high speed loading conditions that could occur in accidents. A commercial epoxy adhesive is characterized over a wide range of crosshead rates using compact tension fracture specimens made of the neat resin. Measured fracture toughness values at room temperature decreased steadily from 2.5 MPa to roughly 1.7 MPa as crosshead speeds increased from 10−6 to 1 m/s, exhibiting similar behavior as observed in tests of bonded double cantilever beam tests reported elsewhere. Additionally, intermediate rate tests conducted at subambient temperatures showed fracture toughness values that were comparable with the high rate tests conducted at room temperature. Applications of time temperature superposition principle techniques may be suitable for predicting the fracture behavior of the adhesive studied herein. Good correlation was also found between the fracture toughness values measured and the value of tanδ obtained from dynamic mechanical analysis tests conducted at the corresponding reduced test rate.