As a result of the shift in age distribution due to demographic change and the increasing maximum age, especially in the western world, joint and bone diseases such as arthritis and osteoporosis are becoming increasingly common. These diseases require partial or complete joint reconstruction in form of implants and prostheses. The biomaterials used for this purpose originate from different material classes and thus exhibit different behavior towards mechanical and medial stress.
In this study, an adaptable short-time method is being developed to predict the fatigue strength under superimposed loading, which means simultaneous influences of mechanical stress, medium and temperature in order to consider also oxidative or corrosive material’s damage. This method is based on instrumented (in situ) multiple amplitude tests (MAT) and ex situ measurements of materials properties in order to understand the structural changes due to different loading conditions. By evaluating characteristic values recorded during the tests, specific load levels are recognized and carried out in form of constant amplitude tests (CAT) to estimate a Woehler (S-N) curve. The instrumentation of MAT and the choice of medium are adapted to the current implant material. The oxidative processes during the implantation period in the human body take place over years and cannot be reproduced in vitro in real time due to the effort involved. For this reason, a method for accelerating oxidative processes is being researched at the department.
The present short-time method shows, on the one hand, that the superposition through a medium has a significant influence on the fatigue properties and, on the other hand, that the estimation of the fatigue strength by MAT and validation by CAT provides reproducible results.