Size Effect on Strength of Hybrid Metal-Composite Joints

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Metal-composite joints are common in composite structures made up of conventional steel parts and advanced polymer composite parts, e.g., in hybrid ship hulls. Correct prediction of the size effect on the strength of the joints is important for the extrapolation of the small-scale laboratory testing results to full size joints, for ensuring an efficient and reliable design. In this study, the size effect on the strength of metal-composite joints is analyzed theoretically, numerically and experimentally. The analytical formulation of the size effect is asymptotically anchored at the large size limit by the linear elastic fracture mechanics (LEFM), which exhibits a singularity with a complex exponent. Numerical analysis with cohesive fracture model is used to design the specimens to be tested, and also to analyze the experimental results to be reported at the conference. Preliminary results from the ongoing experimental studies are also presented. Both computational and analytical methods indicate that the fracture must initiate from the inner steel-composite edges. The experimental findings confirmed that indeed the fracture initiates in the inner steel-composite edges. To determine the size effect law that spans all sizes, the energy release rate is determined numerically and used in the sense of equivalent LEFM. Initial findings indicate that the size effect on the strength of hybrid joints is of the LEFM type.