Comparative Analysis of Two Prosthetic Foot Designs Using Cyclical Load Testing and CAD Simulation
ABSTRACT COMPARATIVE ANALYSIS OF TWO PROSTHETIC FOOT DESIGNS USING CYCLICAL LOAD TESTING AND CAD SIMULATION Under the direction of Dr. Ha Vo One major obstacle in developing lower limb prostheses is the complexity of the ankle complex. The purpose of this study is to test an old prosthetic foot, which provides stability but little movement, and a modified design that sacrifices some stability for improved range of motion at the ankle. To stay within Mercer’s international mission of low-cost prostheses, the design must be entirely mechanical in operation and comprised of easily accessible materials. Both the previous C-Shape model and the new “Spring-Foot” model were fabricated using conventional tools in the College of Engineering machine shop and prosthetic lab. The feet were fatigue tested in an MTS system for 75,000 cycles to simulate walking for one month. C-Shape axial displacement values increased from 2mm at the beginning to 3mm at the end. The Spring-Foot had an initial max displacement of 0.6mm and ended with 0.9mm. Pre-load results from the MTS test were compared against theoretical and ANSYS values. The theoretical and ANSYS values of 231 and 250 N were close while the MTS pre-load of 600 N suggests that there were factors missed in the simulation. ANSYS Static Structural Analysis was used to compare the aluminum loading block with a polypropylene alternative under high loading conditions. Differences in vertical deformation of the two blocks were negligible, reaching only 1 mm under extreme conditions. Solidworks simulation was used to fatigue test the springs for a set displacement to compare to the MTS results. The results proved inconclusive, with the interior coils of the spring surpassing the yield stress of the material. A locked-ankle walking test was generated qualitative feedback as well as pressure and force values through MatScan software. Neither foot had a normal walking pattern, with the peak forces registering 750 N in the C-Shape stance and 650 N in the Spring-Foot stance. Lastly, a formula was derived for future spring selection with varying patient weight. Improving the realism of the testing conditions and creating more secure spring connections will yield more relevant feedback and will better showcase the effect of daily cyclical loading on the plastic pieces and spring connections.