Fatigue life and strength of two composite materials used for below knee prosthesis

Introduction. The composite materials (4P+2C) and (4P+4C) that are used in manufacturing the below knee prostheses socket were subjected to mechanical tests tensile and bending constant and variable loading at stress ratio R = -1 and room temperature (RT25-30°C ). During the gait cycles, fatigue tensile and compression stress are induced. Methodology. The thickness and weight of the fatigue samples were 2 and 2.7 mm, 2.954 and 3.42 (gm) respectively. The increase in thickness and weight showed an increase in (UTS)tensile (UTS) bending, ET modulus of elasticity in tensile and Eb modulus of elasticity in bending by 18.84% 7.72%, 36.36% and 15.06% respectively. Results: While this increase improved the fatigue strength at 106 cycle and fatigue life at 60 MPa applied stress by 82.9% and 78.88% respectively. Increasing and decreasing fatigue variable program was carried out for the two composites. Discussion. Applying Miner rule to the obtained experimental results showed that Miner theory is not capable to predict safe fatigue life and its overestimated the fatigue properties. Conclusions. Proposed non-linear fatigue model was suggested and it applied to the experimental data. The fatigue results obtained from this model have a good agreement with those obtained experimentally