Effects of infrared radiation on the mechanical properties of an epoxy-amine adhesive using a Central Composite Design method

Recently, the aerospace industry has been facing many challenges, including an increase in the production rates to meet the market needs. In the context of adhesives and liquid shim applications, this means the possibility of on-demand curing. In other words, adhesives must cure slowly at room temperature and this process must be accelerated at any time to allow for the fastest polymerization possible. However, while on-demand curing is possible in several ways (ultraviolet radiation, induction, or microwave), the route chosen in this study is infrared (IR) radiation. This is because this method allows curing at low temperatures (i.e., around 50°C) and is universal, hence requiring no modification in the adhesive formulation. Given that the acceleration of polymerization using thermal (temperature) and nonthermal (radiation–matter interaction) effects has been demonstrated in another study, it is now important to study the properties of such an adhesive after curing under IR radiation. In this study, we measured the following properties: adherence on aluminum 2024-T3 via three-point bending, tensile strength and modulus, and flexural strength and modulus. We also studied the parameters of the IR lamp, including the lamp–adhesive distance and the rate and temperature of polymerization. For this purpose, a composite design of experiments was used, which generally has two main advantages: screening and response surface methodology. On the one hand, screening allows determining the factors, among those selected, that have a significant influence on the studied responses. At the same time, it allows determining the interactions (synergistic effects) between the influencing parameters. On the other hand, response surface methodology allows quantifying the influence of the parameters and determining the optimal ones