Influence of the cure state on mechanical properties of an epoxy‐based adhesive: Experimental characterization and numerical simulation

Abstract Heat curing epoxy‐based adhesives are extensively used in primary bonded structures. The manufacturing process of joints with heat curing adhesives is commonly made with isothermal processes where a large curing time is set to guarantee the complete curing of the adhesive. The aim of the current study is to investigate the influence of the curing state on the tensile mechanical properties of a structural one‐component epoxy based adhesive. To achieve this, tensile tests on bulk adhesive dog‐bone coupons with incomplete curing were performed. The process cycle was adjusted to achieve the desired curing degree for testing. The curing process was simulated by using the Kamal kinetics model calibrated with differential scanning calorimetry (DSC) tests. The results show that the curing process is very sensitive to the curing temperature, requiring a low curing temperature to control process duration. A good correlation between the estimated curing degree and the final obtained curing measured with the Fourier‐transform infrared spectroscopy FTIR was found. Regarding the mechanical properties, the elastic modulus and the tensile strength are reduced at lower curing degrees making the material softer and more ductile. The loss in the mechanical properties shows to be consistent with the measurements performed with dynamical mechanical analyses (DMA) by measuring the evolution of the elastic modulus with the curing degree. In this way, the numerical simulation of the curing process seems to be a valuable tool to predict the final performance of adhesive, and design the curing cycle.