Multi-material topology optimisation considering interfacial tension-compression asymmetry in additive manufacturing

In multi-material additive manufacturing (MMAM) structures, interfaces are prone to failure due to inherent tension-compression asymmetry. Achieving fully compressive interface designs is crucial for enhancing load-bearing capacity. Inspired by the similarity between interfacial tension-compression asymmetry and composite laminate anisotropy, this paper for the first time links multi-material interfaces to composite failure theory. Leveraging this connection, a novel multi-material topology optimisation (MMTO) method based on the Tsai-Wu criterion is proposed to provide full-compression interface designs. Firstly, an improved double-filter strategy extracts the interface phase field and constructs graded finite element models. Secondly, an interfacial tension-compression coefficient (ITCC) derived from the gradient field and Tsai-Wu criterion characterises interfacial tensile-compressive states. Subsequently, an adaptive constraint method is established, which constructs a global constraint through a Heaviside projection-based integral (HPI) and adaptive threshold strategy. Then, this constraint is embedded into the MMTO model to minimise structural compliance, and sensitivity analysis guides the interface configuration toward compression. The method is validated through 2D and 3D numerical examples. Finally, its engineering applicability is demonstrated through material characterisation, design, manufacturing, and testing. Three-point bending test results show a 55.4% load capacity increase over traditional designs, confirming significant interface stress improvement and application potential.