Structural integrity and failure of transfemoral prosthetic socket fabricated using carbon prepreg technique: Influence of fiber orientation and curing conditions

Abstract

This study provides valuable guidance for simplifying fabrication procedures and enhancing the structural integrity and safety of carbon fiber (CF) laminate transfemoral (TF) prosthetic sockets. While the high specific strength of CF laminate sockets offers advantages over conventional plastics, essential production data—their orientation-dependent strength and optimal cure conditions—are lacking, often requiring complex, costly cure cycles. This study investigated (i) the influence of fiber orientation on TF prosthetic CF socket strength via finite element analysis (FEA) during standing, and (ii) optimal single-step Vacuum-Bag-Only (VBO) cure conditions for prepreg in a low-cost conventional oven. Three distinct CF laminates ((45/−45/45/−45), (0/90/0/90), (0/45/−45/90)) were implemented in TF socket finite element (FE) models. Tensile and flexural tests validated FE results and assessed laminate failure modes. Differential Scanning Calorimetry (DSC) investigated cure temperatures, while surface voids were inspected to identify optimal single-step cure conditions. A 1-h isothermal cure at 90°C facilitated resin flow and yielded minimal surface voids. FEA revealed ply orientations insignificantly influenced residual limb pressure. Most plies in the (45/−45/45/−45) CF laminate favorably aligned with oblique deformation for TF socket stabilization during standing. Experimentally, it exhibited the lowest stiffness (10.86 GPa) and strength (161.49 MPa). Nevertheless, its strength is superior to other socket materials and enhances safety through clear pre-fracture signs from ductile failure. Maximum pressure of up to 32.2 kPa at the medial-distal site during standing was insufficient to cause discomfort. These findings provide guidelines for high-quality TF sockets using prepreg by simplifying the fabrication process.