Comparative Analysis of Cohesive Laws for Predicting Stress Fields in Perforated Fiber Metal Laminates

Fiber-metal laminates (FMLs) are hybrid structures manufactured using alternating layers of aluminium alloy and epoxy-reinforced E-glass fabric, with the stacking sequence [Al/Glass/Al/Glass/Al], offering high specific strength, fatigue resistance, and damage tolerance. However, structural cutouts generate stress concentrations that can significantly affect the mechanical performance and damage behavior of these hybrid polymer-based laminates. This study develops and validates analytical cohesive zone models (CZMs) for predicting stress fields around circular and elliptical cutouts in FML plates, providing a computationally efficient analysis. Tensile specimens with two thicknesses (1.4 and 1.7 mm) were investigated using two cohesive laws: linear, and exponential softening. Model predictions were assessed against experimental results using stress concentration factors. The exponential cohesive law provided the best overall agreement, with Root Mean Square Error (RMSE) values of 24.87 and 20.99 MPa and R² values of 0.281 and 0.311 for the 1.4 and 1.7 mm laminates, respectively. Experimental stress concentration factors ranged from 1.88-3.70 and 2.04-3.51 for the two thicknesses. Elliptical cutouts aligned with the loading direction produced lower stress concentrations, whereas minor-axis alignment resulted in higher concentrations. Increasing laminate thickness improved prediction accuracy. The proposed analytical CZM provides an efficient approach for evaluating stress concentrations and damage-related behaviour in perforated polymer-based FMLs, with potential application in the design and optimization of lightweight composite structures.