Models for cracking, crack propagation and lifetime

© Fraunhofer IWM

Components in combustion engines, thermal power stations and plants and stationary gas and aircraft turbines under thermomechanical fatigue load are usually exposed to larger plastic deformations, at least locally, as a result of which crack formation of a microstructurally short crack on and in microstructure features (e.g. precipitations, grains, phase boundaries) and defects (e.g. production related pores, cavities and discontinuities) usually play a negligible part in the overall lifetime. Modeling activities have therefore focused for years on the propagation of small cracks of just a few micrometers up to the length of a technical crack (e.g. 0.5 to 1 mm) and on the long crack stage for consideration of remaining lifetime.

Development of models has the aim of applying material (class) specific damage mechanisms for thermomechanical fatigue and creep fatigue to practical models which can subsequently be used for lifetime assessment of components as part of finite element analyses.

What we offer


Methods which employ short crack models in fracture mechanics are mainly used, which are based on an analysis of the time and temperature dependent crack tip fields. The main focal points of research and development include:

  • Handling of variable amplitudes and real operating loads under variable thermocyclic loading
  • Consideration of the crack-length-dependent crack closure effects in areas of both physically short and long cracks
  • Consideration of thermally and mechanically induced stress gradients
  • Consideration of creep fatigue damage in areas of both physically short and long cracks
  • Dealing with manufacturing related defects (e.g. in the case of additively manufactured materials)
  • Evaluation of environmental influences (e.g. hydrogen, oxygen) and extension of the existing lifetime concepts while taking into account the influence of the environmental medium on the fatigue damage
  • Development of lifetime concepts based on the mechanics of materials for evaluations concerning failure probability of components under consideration of microstructure and defect structure