Analysis of the Failure of Bonded Interface between Aluminium Skin and FRP Patch Using Cohesive Zone Model

A single-sided patch of unidirectional carbon fibre-reinforced polymer composite was bonded on a 1.0 mm-thick skin of aluminium alloy 6061-T6 with a centre crack of 25 mm length. Two kinds of patches were studied: (1) 1-ply patch and (2) 2-ply patch. Experiments were conducted to determine the strength of 1-ply patch. It was then simulated using finite element analysis employing a cohesive zone model in ANSYS 15.0. When the repaired specimen was subjected to a quasistatic load, the patch started separating at the crack edge due to the combined action of high peel and the shear stresses at the interface. The rate of separation was slow initially, but grew rapidly at high loads. Separation cracks were also initiated at the leading edges at high loads, leading to catastrophic failure of the specimen. The numerically obtained failure load was compared with that obtained through the experiments, and the effectiveness of using the cohesive zone model for simulating the interface failure was established. The numerical analysis was then applied to predict the failure behaviour of 2-ply patches. The strengths of the 1-ply patch and 2-ply patch for different patch lengths were compared. The strength of 2-ply patch was found to be considerably higher over that of 1-ply patch for short-length patches. However, the difference diminished with the increasing patch length. © 2018, The Institution of Engineers (India).