Investigation of modified single lap joints for aerospace applications

In today's aerospace industry, the utilization of composite materials is increasingly prevalent due to their advantages in structural efficiency, weight reduction, and high specific strength. Particularly in primary load-bearing components such as fuselage and wing structures, the preference for composite materials has encouraged the adoption of adhesive bonding techniques over traditional mechanical fasteners. Adhesives not only reduce the number of fasteners thereby lowering the structural weight but also enable more aerodynamically integrated designs. However, this method may present certain strength-related disadvantages, especially in areas where holes must be drilled, leading to stress concentrations and limited axial load-carrying capacity of the adhesive. In this context, the development of alternative or hybrid joining techniques to enhance structural performance has gained significant importance. This study comparatively evaluates the mechanical performance of single lap joints (SLJs) with identical geometric configurations, assembled either exclusively with adhesive and using modified bonding designs. Each joint was manufactured by bonding two composite structures, each consisting of eight symmetrical and balanced stacked prepreg layers arranged in a 2×2 Twill woven configuration, using HYSOL EA9394 epoxy-based adhesive. The modified joint design was realized by introducing two additional holes of 3 mm diameter into the structure and filling them with adhesive to enhance the bonding characteristics. The study is supported by experimental tensile tests and numerical simulations conducted using the ABAQUS/FEA software. Based on these analyses, the effects of different joining approaches on load-bearing capacity, deformation behavior, and failure mechanisms are examined in detail. The findings aim to contribute to the literature by offering optimized joint solutions for composite structures.