Date of this Version
Wheeler, AK. 2020. Geometric Iteration of a Knee Prosthetic and Static Stress-Bearing Capacity. Undergraduate Honors Thesis. University of Nebraska -Lincoln.
The purpose of this study was to improve a prosthetic knee model in terms of size, weight, and biocompatibility. Several tests were run to determine its effectiveness in supporting static and quasistatic loads. The positions in which these tests were run include static upright standing, static one-knee 90 degree kneeling, static squatting at maximum flexion, and quasistatic midstride. These simulations were conducted to find areas of high stress and strain. These patterns were used to determine the maximum body weight a physical prosthetic could support. The material used to create the prosthetic was changed from AISI 316 stainless steel to 6061-O aluminum alloy, resulting in a 55% strength reduction with a 73.8% weight decrease. This tradeoff was acceptable as the user would benefit more from the reduced weight than the increased strength. After the tests were conducted, the knee was found to support a 217 pound user without failure. This value was limited by the kneeling test, which produced the steepest stress-to-weight curve (m=41.1 psi/lbf). This maximum weight exceeds nearly 100% of the adult population in the United States. The lower 50% of men and women could utilize the prosthetic at factors of safety of 1.079 and 1.272, respectively. The lower 26.6% and 51.8% of Indian men and women could utilize the prosthetic at a factor of safety of 2. While this iteration improved on the initial design, further geometric design changes and dynamic testing would yield more optimized results.