Modeling of void formation during the curing process of paste adhesives

Abstract

In this study, the void formation of the paste adhesives used for bonding of aerospace components is investigated. When high temperatures are applied to accelerate the curing process, volatiles evaporate; therefore the mechanical performance of joints is affected as a result of an increased void content. Today, mass reduction models only consider the degradation of fully cured samples, not taking into account the influence of the curing process on the quality of the paste adhesive. The fundamental idea of this paper is that the amount of mass reduction as a result of evaporation of the paste adhesive decreases with higher curing progression. For quantification, a model is defined approximating the mass reduction in a paste adhesive as a function of temperature, time and the degree of cure. Thermo gravimetric analysis is used to obtain the experimental data of the evaporation process for curing cycles with a single dwell at different temperatures applied to the paste adhesive. These data are used to define a theoretical model, which is validated by comparing the experimental and simulated data for non-isothermal heating processes. Finally, a relation between evaporated mass and void generation during the curing process is established in order to assess the bonding quality of the joint in terms of final void content as a result of the curing cycle.