Simulation-based design of mixed-mode specimens for fracture mechanics tests on fiber-metal laminates

Abstract

Fiber-metal laminates (FMLs), particularly those composed of glass-fiberreinforced polymers (GFRP) and steel, are a promising material combination for applications in wind energy, especially in blade root connections. These laminates exhibit complex fracture behavior that requires advanced modeling techniques to accurately predict crack propagation. This study focuses on the simulation of fracture mechanics tests to identify suitable specimen configurations for experimental validation. The investigated crack interface lies at the GFRP-steel interface. Fibers hereby are oriented exclusively in the 0° direction. Different mode-dependent test configurations were considered to determine the critical strain energy release rates (cERR) under varying mode ratios: Double Cantilever Beam (DCB) for mode I, End-Notched Flexure (ENF) for mode II and SingleLeg Bending (SLB), Cracked-Lap Shear (CLS) as well as mixed-mode bending (MMB) for mixed-mode conditions. The objective is to find specimen configurations allowing to determine critical fracture parameters, including mode I and mode II cERR (GIc, GIIc), as well as the mixed-mode interaction parameter for the BK criterion (eta BK) used to predict crack growth in crack propagation analysis. By simulating multiple mode ratios, a broader range of cERR is assessed to improve the accuracy of crack growth predictions. A key focus of this work are the mixed-mode specimens providing alternatives to the MMB setup as described in ASTM D 6671. Different layup configurations were analyzed for these specimens by varying the GFRP beam thickness. The resulting specimen designs and accomplished mixed-mode ratios are compared to determine configurations that provide reliable fracture parameter identification.