Volume effect of bone utilizing the staircase test method
Jones, Jesse L.
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The focus of this research was to determine if the Staircase Test Method could indeed be utilized in order to quantify the fatigue strength of bovine cortical bone and if by utilizing the Staircase Test Method, the volume effect of cortical bone could be determined based on the Weibull fatigue model in addition to the multiplication factors extracted by literature. The experimental research methods used in this study included a fully-reversible tensile compression loading applied to three volumes of 109, 383 and 1158 cubic millimeters using the Staircase Test Method implementing a constant steep size of 5.5 MPa and various starting stress values. Finally, the mean values were obtained for the posterior section of bovine femur for volumes 109 and 383 cubic millimeters. The fatigue strengths for the initial posterior section utilizing the Staircase Test Method resulted in values of 81.58 and 66.0 MPa for volumes one and two, respectively. These values fell within range of previous studies using similar conditions. The results of the mean values obtained utilizing the Staircase Test Method for the anterior section of bovine femur of volumes one, two and three were calculated as 83.42, 74.25 and 68.75 MPa. These values were then plotted and the average relative error for all three volumes was reported to be 12%. This falls within previous experimental error done by a previous study. Conclusively, the Staircase Test Method was proven valid based on the results of the posterior value for the fatigue strength when compared to previous studies. In regards to the volume effect, the posterior fatigue strength was significantly lower than the predictive values for both volumes groups one and two. A corrected Weibull modulus of (m=5.3) for the posterior section used in order to account for the difference in the fatigue strength (~20%) based on the modified Weibull prediction equation. A corrected Weibull modulus was not needed for the anterior section (m=8.0) based on the results obtained when compared to the predicted values using the modified Weibull equation. Thus, the volume effect was clearly represented for both anterior and posterior portions of the femur for bovine cortical bone with the posterior section resulting in a significantly lower Weibull modulus.