Experimental and numerical failure analysis of SLJ and SSLJ CFRP joints using the LaRC05 criterion within a combined XFEM-CZM

This study presents an experimental and numerical investigation of single-stepped-lap joints (SSLJs) and single-lap joints (SLJs) made from carbon/epoxy composites (CFRP), focusing on the combined effects of joint geometry and substrate thickness (2.0 and 4.0 mm) on joint strength and failure mechanisms. The main contribution of this work lies in the systematic assessment of these two parameters and in the use of a coupled LaRC05/XFEM-CZM framework to provide a comprehensive description of damage evolution by simultaneously accounting for adhesive failure and damage initiation in the composite substrates. CFRP plates were CNC-machined to obtain the required joint geometries, adhesively bonded using a structural epoxy, and subjected to tensile testing. A three-dimensional finite-element model was developed in Abaqus, incorporating cohesive zone modeling (CZM) for the adhesive and the LaRC05 criterion coupled with the extended finite element method (XFEM) for the composite substrates. The numerical predictions showed very good agreement with the experimental results. The SSLJ consistently outperformed the conventional SLJ, with the 2.0 mm configuration reaching an ultimate failure load of 7584 N compared with 6852 N for the SLJ, corresponding to an improvement of 10.7%. This improvement is attributed to improved load-path alignment and reduced secondary bending effects. Conversely, increasing the substrate thickness from 2.0 to 4.0 mm reduced the ultimate failure load by 4.13% for the SSLJ and 6.76% for the SLJ. Although the thicker substrate increases the overall flexural stiffness, the associated modification of load-path eccentricity intensifies secondary bending and combined stresses near the overlap ends. The coupled numerical framework successfully reproduced the global experimental response and predicted the progression of adhesive and localized substrate damage. Overall, the 2.0 mm SSLJ exhibited the best mechanical performance among the investigated configurations.