Multilayer materials can exhibit superior toughness and damage tolerance compared to their base materials. However, for flat interlayers with very low stiffness, the in-plane shear stiffness is very low, so that shear forces associated with bending can lead to large deformations. This limitation can be partially overcome by using wavy interlayers, which have been introduced as lithomimetics [1] and are inspired by naturally occurring structures on Earth. But how should the wavy interlayers be designed to retain the toughness advantages of a flat multilayer structure while overcoming the low stiffness in bending? In this study, a numerical analysis is performed on specimens with a thermoplastic matrix and a central thermoplastic elastomer interlayer loaded by three-point bending [2].The propagation of an initial surface crack is studied. In the thermoplastic regions, the crack propagation is analysed based on an incremental evaluation of the energy release rate considering elastic-plastic material behaviour. The crack first propagates in the thermoplastic region and is stopped at the elastomer interlayer. There may be debonding of the matrix-interlayer interface, which is modelled using cohesive zone elements. A parametric study is carried out to evaluate the effect of wave shape and interface toughness on the stiffness and failure behaviour of the specimens. Finally, the simulation results are validated against experimental data using corresponding additively manufactured specimens. The findings of the present study will help to understand the effect of lithomimetic inspired geometry on the toughness enhancement of multilayer materials. Furthermore, understanding the toughening mechanisms of such multilayer structures will allow for improved composite laminate designs with higher delamination resistance. [1] Y. Beygelzimer, R. Kulagin, P. Fratzl, Y. Estrin, The Earth’s Lithosphere Inspires Materials Design, Advanced Materials 33 (2021) 2005473. https://doi.org/10.1002/adma.202005473. [2] C. Waly, R. Höller, T. Griesser, F. Arbeiter, Deformation and fracture of lithosphere-inspired polymeric multi-layer composites, Results in Engineering 24 (2024) 103519. https://doi.org/10.1016/j.rineng.2024.103519.