Analytical and Experimental Methods for Adhesively Bonded Joints Subjected to High Temperatures.

Abstract

Recent advances in material systems have expanded the temperature range over which adhesively bonded composite joints can be used. In this work, several tools are developed for use in modeling joints over a broad range of temperatures. First, a set of dimensionless parameters is established which can be used for analysis of joint performance for an orthotropic symmetric double lap joint. A critical dimensionless ratio of mechanical and thermal loads is identified. The ratio predicts characteristics of the resulting stress distribution. A bonded joint finite element is also developed, wherein a joint-specific finite element is formulated based on an analytical solution. The resulting element allows for mesh-independent joint evaluation and multi-joint simulation at a system or vehicle level. As a mid-level analysis technique, the element has significant predictive and cost advantages over the previously available methods. An advanced analysis technique, the discrete cohesive zone method, is developed and demonstrated in a general element formulation. Initially, the element is examined from the perspective of computational efficiency and robustness. Two efficient traction laws are formulated and are compared to a traction law that is in common use. The element is subsequently used to investigate the interactions of adhesive parameters in standard adhesive characterization experiments. This quantification of experimental sensitivities allows for a deliberate mapping of cumulative experimental results to an appropriate set of model constitutive parameters. With knowledge of the parameter interactions, a set of experimental results are interpreted to determine a set of adhesive constitutive parameters for T650/AFR-PE-4/FM680-1, a high temperature material system of current interest.