Lightweight design of running prosthetic feet using honeycomb sandwich composites: a comparative FEA study

Honeycomb sandwich composites are widely employed in aerospace and structural applications due to their high specific strength and efficient energy storage and return, offering a promising design alternative for running prostheses.

This study investigates the mechanical performance of a running prosthetic foot designed with an aluminum honeycomb core (AMS 3711) and carbon fiber skins, comparing it against a conventional solid epoxy-carbon laminate. A finite element model was developed in ANSYS following ISO 10328 boundary and loading conditions. The analysis evaluated six design configurations, transitioning from a solid reference blade to optimized sandwich structures. Static analyses were performed at two gait-cycle positions defined by ISO 10328 to evaluate mass, deformation, equivalent stress, strain energy, and safety factors across varying core and surface-layer thicknesses under constant total volume.

The results demonstrated that the optimized sandwich design achieved a 63.9% reduction in distal mass (from 1.33 kg to 0.48 kg) compared to the solid counterpart. Contrary to the typical trade-off between lightweighting and energy capacity, the increased compliance of the sandwich structure resulted in a 57.4% increase in strain energy storage. Although the transition to a cellular core initially reduced the safety margin, geometric optimization of the core thickness recovered structural integrity, achieving a safety factor of 1.95, well above the recommended threshold of 1.5.

These findings indicate that honeycomb sandwich architectures offer a superior alternative to solid laminates for running prostheses, simultaneously enhancing energy return efficiency and minimizing structural mass without compromising safety.