 The stage of fatigue crack propagation is usually divided into a short and a long crack period. Depending on the material, up to 90% of cyclic lifetime are spent on short crack propagation. During this phase microstructural obstacles have a strong influence and the application of LEFM (linear elastic fracture mechanics) is not appropriate. Models are favourable which describe both, long and short crack propagation and hence provide a realistic lifetime prediction. This project is an interdisciplinary study including detailed experimental investigations on short crack growth and its simulation applying dislocation theory. A crack propagation model takes crack closure and grain orientation effects into account.
The model used is based on that proposed by Navarro and de los Rios. This model was used in earlier studies and a satisfactory agreement with the experimental data could be found. The metastable beta titanium alloy LCB (low cost beta), a promising candidate for applications in automotive industries, is studied with emphasis on crack initiation and short crack propagation. The characterisation of the microstructure of the material was performed after different heat-treatments. Crack initiation and short crack propagation were measured by means of replica technique and an ISDG system. |
