Multi-material and thickness optimization of sandwich structures subject to failure criteria

Sandwich structures are essential for lightweight design, but their multi-material composition introduces complexities, particularly additional failure modes that must be addressed during design. Structural optimization provides an efficient means to manage these complexities and accelerate development of high-performance designs. Discrete Material and Thickness Optimization (DMTO) enables such optimization of general multi-material and multi-layered structures with varying thickness. The objective of this work is to extend the DMTO framework for sandwich structure design by incorporating sandwich failure criteria. The problems are parametrized using the Discrete Material and Direct Thickness Optimization (DMDTO), a variant of DMTO, allowing the layer thickness to vary independently in each sandwich face sheet and core. A sandwich failure analysis approach that includes key sandwich failure criteria is presented in this context, particularly shear crimping and face wrinkling criteria — novel additions within multi-material and thickness optimization. These criteria are formulated to allow utilizing efficient gradient-based solvers with adjoint design sensitivity analysis to compute problem gradients. Several numerical examples are solved to demonstrate the approach, including a simplified wind turbine blade main spar that highlights the potential for industrial application of the approach.