Characterization of adhesively bonded joints using bulk adhesive properties

Though using bulk adhesive properties to predict adhesively bonded joint response has yet to be proven infallible, based upon the success of previous works, this effort attempts to shed some light on the stresses present in a typical automotive bonded joint. Adhesive material properties obtained in previous works were used in a finite element analysis of a simulated automotive joint to predict the stresses in that joint.

The automotive joint analyzed was a simplified representation of a joint provided by General Motors. The specifications included the rate or stiffness of the joint and the materials to be used. The basic design of the joint is a rectangular solid section steel frame to which an SMC panel is bonded using Ashland Chemical urethane based adhesives.

Due to computer time constraints and problem complexity, a complete analysis including a time dependent, viscoelastic analysis was not possible. The linear elastic case analyzed gave important insight into the magnitudes of stresses to be expected in a typical joint. It was found that for an applied load to produce a 1 degree deflection in the steel frame, the stresses in the adhesive were below 20% of the ultimate tensile strength of the adhesive. This low stress state is significant because the adhesive behaves as a linear viscoelastic material in that range, making further analysis less complicated and time consuming.