Numerical simulation for stress and failure of functionally graded adhesively bonded tee joint of laminated FRP composite plates

Three Dimensional (3D) stress analyses of functionally graded adhesively bonded tee joint made of laminated Fiber Reinforced Polymeric (FRP) composite are carried out using geometrically non-linear Finite Element Analysis (FEA). The FE model of the tee joint is validated by comparing the stresses with the results available in literature. Effects of material anisotropy and fiber orientation angle on 3D stress components of the validated model of the tee joint are studied in this paper. The tee joint is analyzed to determine 3-D stress components with rigid base boundary condition. The out-of-plane stresses (σzz and τyz and τxz) and von-Mises stress (σe) components on mid-surface of adhesive layer are determined for different FRP composite plates made of Graphite/Epoxy (Gr/E), Glass/Epoxy (Gl/E) and Boron/Epoxy (B/E) materials with varied laminate stacking sequence viz. unidirectional [0]8, cross-ply [(0/90)s]2 and angle ply [(+45/−45)s]2 when it is subjected to an out-of-plane loading through the right angled plate of the tee joint. Suitable design recommendations of the tee joint in terms of appropriate material with specific lamination scheme have been made based on stress and failure analysis. Further, an attempt has been made to improve the strength of recommended tee joint structure by reducing the stress concentration at the ends of overlap. This has been achieved by distributing stresses uniformly over the entire bond line by employing Functionally Graded Adhesive (FGA) material instead of using conventional single adhesive. Linear and exponential material gradation function profiles have been used to grade the adhesive layer in the tee joint. Effect of both the material gradation profiles with different modulus ratios on out-of-plane and von-Mises stresses have been studied. Numerical simulation based on Finite Element Analysis indicates that out-of-plane and von-Mises stress levels reduce significantly.