Finite element application for strength analysis of scarf-patch-repaired composite laminates

The composite scarf joint configuration was utilized to simulate scarf-patch-repaired composite panels. An adhesive bonded scarf (tapered) joint was selected due to less peeling and shear stress over the bondline than with a single-lap or butt joint. The rubber-toughened epoxy film adhesive used had been characterized using ASTM D5656 Standard test (single-lap) incorporated with 2-D plane strain finite element analysis to verify its elastic and plastic properties. In addition to physical test, the ultimate shear strength of the adhesive was predicted using the von Mises and Drucker-Prager plasticity models in conjunction with dynamic shear failure criterion in the commercial finite element software ABAQUS. The numerical analysis provided satisfactory results when compared with experimental data under the relative displacement versus ultimate load level. The revised 4-pinned method more accurately predicted relative displacement than did the 3-pinned method in ASTM D5656 Standard. For composite scarf joint analysis, the 3-D stress analysis with transversely isotropic material properties of composites gave better results than the 2-D plane strain analysis. Regarding the tensile strength of repaired laminates, the finite element dynamic analysis based on the adhesive failure incorporated with the 90-degree ply failure provided the best results, which matched the experimental ultimate loads and the surface strain distributions within the overlap. As expected, the edge effects and longitudinal strain variations across the width of the repaired specimens were only observed in 3-D models and were verified by experimental data. Moreover, the 3-D static and dynamic simulations revealed the relations between laminate strength and the edge effects caused by different stacking sequences. Based on the similar geometry, it was also demonstrated in this study that the balanced and symmetric stacking sequence about mid-plane of the repaired composite panel exhibits higher tensile strength.