Influence of material properties on pre-embedded adhesion failure and delamination behaviour in curved laminated FRP composite Single Lap Joints

In this paper, the effect of material properties (degree of anisotropy) of the curved laminated Fibre Reinforced Plastic (FRP) composite adherends on the growth of pre-embedded adhesion failure and delamination damage in Single Lap Joint (SLJ), has been investigated. The material properties of the adherends of the SLJ significantly influence the state of stresses (interfacial and inter-laminar stresses) near the pre-embedded damage front, thereby altering the magnitude and distribution of the Strain Energy Release Rate (SERR). The phenomenon becomes more critical when there is a stiffness imbalance between the lap and strap adherends, resulting in increased stress concentrations and accelerated damage growth. To identify materials that minimize SERR and enhance joint integrity, five laminated FRP composites are evaluated as adherend materials for the SLJ: Boron/Epoxy (B/E), Kevlar/Epoxy (K/E), Graphite/Epoxy (Gr/E), Glass/Epoxy (Gl/E), and Carbon/Epoxy (C/E), each with varying anisotropy ratios. A comprehensive three-dimensional (3-D) finite element analysis (FEA) incorporating pre-embedded defects and the Virtual Crack Closure Technique (VCCT) is employed to compute mode-wise and total SERRs. The results show that SLJs made with K/E or Gl/E adherends exhibit superior resistance to both adhesion and delamination failure, provided the strength criteria are met. These findings offer valuable insights into optimal material selection for enhancing the durability and mechanical performance of curved FRP composite-based joints.