Evaluating residual stresses in bonded lap joints through experiments and numerical modeling

Structural adhesive joining is considered to be an excellent route to achieve both light weighting and dissimilar material joining for automotive structures While adhesive joining eliminates the needs for drilling holes and distributes the load over larger areas; the processing/curing conditions, especially the thermal shock (rapid cooling) can create residual stresses that significantly reduce the strength of the resulting joints, in most cases prior to application of mechanical/service loads. These residual stresses can lead to dimensional instability, increased stress corrosion and reduced fatigue life. In this study, adhesively bonded single lap joints were manufactured using Acrylonitrile Butadiene Styrene (ABS) adhesive and glass fiber reinforced epoxy (Garolite, G-10) substrates. The joints were processed at a constant temperature of 240℃ maintained via oven-heating and subsequently allowed to cool under natural convection in ambient air. The residual strains generated in the adhesive layer were measured experimentally using an embedded high-resolution fiber-optic strain sensor. The results were compared against a coupled thermo-mechanical finite element (FE) model. Initial results show good agreement between the experiments and numerical models for the elastic behavior.