Influence of Ductility Ingredients of Structural Adhesives on Fracture Energy under Static Mixed-Mode Loading

In recent years, adhesive bonding is increasingly being applied in the construction of vehicle frames in order to improve body stiffness and crash performance. Regarding crash performance, the behavior of impacted components is affected by the fracture energy value of the adhesive. However, the relationship between the ductility and fracture energy values under mixed-mode loadings has not been sufficiently evaluated. In this paper, the fracture energy of three structural adhesives in a static mixed-mode loading using Double Cantilever Beam (DCB) specimens is presented. To derive the fracture energy values, the Compliance Based Beam Method (CBBM) was used, which allowed for precise determination of fracture energy values. Static mixed-mode loading tests were performed in six configurations of mixed-mode loading, ranging from pure peel mode state to almost pure shear mode state. To study the influence of additives on adhesive performance, three types of structural adhesive were used: one with urethane-modified epoxy additives, another with rubber- particle additives, and finally an additive-free adhesive. In the mixed-mode loading tests, the same effects were observed in all loading modes. The adhesive with rubber- particle additives exhibited a maximum fracture energy value approximately 50% higher than that of the additive-free adhesive, while the adhesive with urethane-modified epoxy additives exhibited a maximum value approximately 100% higher. It was found that fracture energy values under static mixed-mode loading are improved by adding ductility enhancing additives to the adhesive.