Unraveling the puzzle of the mechanical degradation: shear behavior of nickel foam/polyurethane composites under different loading paths

Mechanical performance of foam metals degrades when loaded in multi-direction, so similar behaviour exists in foam metal/polymer. Therefore, using strength obtained from uniaxial tests as the basis for design is unsafe. Degradation of mechanical properties of nickel foam/polyurethane (NF/PU) under biaxial loading has been investigated. Monotonic and cyclic shear tests were performed under different biaxial loading paths. A fine-scale finite element model was established using X-ray CT. Shear behavior and performance under various paths were quantitatively evaluated. Microstructural evolutions of cells were analyzed to elucidate mechanisms. The results indicate that damage in one-direction simultaneously affects behavior in orthogonal-direction, contributing to reduction in performance. Energy dissipation may increase with the distance of the path. Integration of PU enhances force transmission pathways while simultaneously altering deformation mechanisms and failure modes of the embedded NF skeleton. Edge degradation in NF skeleton is less pronounced than in standalone NF under biaxial loading at equivalent strain levels. A correlation between the load-carrying capacities of NF/PU under biaxial and uniaxial loading has been established, and a method for evaluating performance under biaxial loading has been proposed. These insights provide theoretical foundations to support the application of NF/PU in vibration control, civil engineering, and other domains.