Multiscale Computational Design of Ti-6Al-4V/SiC Composite Femoral Stems: SIMP Topology Optimisation, Functionally Graded TPMS Lattices

Abstract

Aseptic loosening driven by stress shielding remains the principal long-term failure mode of total hip arthroplasty (THA), affecting 10-15% of implants within 15 years and generating annual revision costs exceeding USD 8 billion globally. This study presents an integrated multiscale computational framework for the design of functionally graded femoral stems using Ti-6Al-4V/SiC whisker-reinforced composite materials. The framework systematically couples seven sequential modules: (M1) Halpin-Tsai micromechanical characterisation of three material systems  Ti-6Al-4V, Ti/SiC 20 vol%, and Ti/SiC 40 vol%; (M2) analytical beam stress analysis under ISO 7206-4 oblique cantilever loading; (M3) SIMP topology optimisation at V* = 0.70 achieving 30% mass reduction (C/C₀ = 0.37), (M4) TPMS lattice homogenisation for four architectures (Gyroid, Diamond, Cubic, Octet) with a corrected stress shielding index (SSI_Gyroid = +11.1%) representing an 87% reduction from monolithic Ti-6Al-4V (SSI = 82.5%), (M5) multiaxial fatigue analysis combining Rainflow cycle counting, modified Goodman criterion, and dual Miner damage reporting (D_ISO = 0.001-0.018; D_full = 0.117-1.426. The Ti/SiC 20 vol% composite in a functionally graded Gyroid architecture emerges as the optimal clinical configuration, uniquely satisfying all biomechanical, osseointegration, and SLM fabricability requirements simultaneously.