From Earth’s Crust to Composite Design: A Numerical and Experimental Study of Lithosphere-Inspired Polymeric Multi-Layer Composites

Compliant flat interlayers (IL) embedded into a cracked stiff matrix improve damage tolerance in polymeric systems, but typically at the cost of reduced stiffness and lower crack-initiation forces. To mitigate these limitations, a design approach originating from the Earth’s lithosphere was adopted. In particular, a symmetric wavy compliant IL was embedded into a stiff matrix, and a numerical model was established in ABAQUS to identify promising geometries via a systematic variation of wave height, wavelength, and the relative position of the wave to the initial crack. Numerical results demonstrate that stiffness, crack-initiation force, and total energy dissipation strongly vary with IL geometry. Compared to the flat IL, wavy ILs continuously enhance stiffness and crack-initiation force, albeit with reduced energy absorption. The crack position relative to the wavy IL shows only minor influence on the global fracture response. Based on the numerical results, seven variants were selected and fabricated using PolyJet technology and experimentally examined. The experimental results confirm the numerical predictions, demonstrating good agreement in the initial force–displacement regime, which validates the numerical model as an efficient tool for preliminary design screening. Beyond crack initiation, linear-elastic assumptions lead to deviations, limiting the models applicability to the early fracture stage.