Theoretical prediction of fatigue strength
| |||||||||||||||
In addition to predict the static strength of implants, it is possible to determine theoretically finite life or fatigue strength using FE-Analysis and the Woehler line of the material.
 FE-Model with boundary conditions
|
The shown proximal femoral nail remains within the human body for several months up to the successful treatment of the fractured bone. Thereafter, the nail will be explanted. This type of implants has to reach a finite life strength at 250.000 load cycles. | Assuming a sinusoidally oscillating load as defined for dynamic tests, the static load cases for maximum and minimum load are determined using the FE-Analysis. From the calculated principal stresses for both load cases the maximum stress amplitude for the critical part of the implant can be determined.
| | ||||||||||||
|
Comparing this value with the Woehler line of the critical part of the implant, the endurable number of load cycles is determined. Repeating this procedure for different minimum and maximum values of loading, the graph below is received.
A comparison of the results with the reached number of load cycles of this implant in a dynamic test (also shown within the graph) confirms the practical applicability of this method. | |||
 Calculated and in test reached number of load cycles |  Principal stress within the bone nail | ||||||
|
An essential benefit of the simulation-based determination is the reproducibility compared to the large deviation of measurement results. Copyright © 1998, ASD Advanced Simulation & Design GmbH  , All rights reserved.last update: webmaster@asd-online.com | |||||||