Crack propagation in mechanical surface treated component areas of Inconel 718

• Applicant: Professor Dr.-Ing. Volker Schulze, since 9/2014
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 251947321

Mechanical surface treatments can notably extend fatigue life of components due to induced compressive residual stresses and strain hardening. Crack propagation is delayed by compressive residual stresses but on the other hand accelerated by strain hardening. Both strain hardening and compressive residual stresses, delay crack initiation. However, the combined effects of these opposing trends are not yet known.This project intends to develop a method for life prediction in the low cycle fatigue regime and high temperature application taking into account the crack propagation behaviour in mechanical treated surface layers. This is essential for a better dimensioning of components. An already available testing technique has to be optimized during the project. For that purpose this behaviour has to be analysed, comprehended and described.Defined residual stress states and strain hardening in inconel718 samples shall be obtained using shot peening and deep rolling as mechanically surface treatment. Residual stress depth distribution and strain hardening state have to be determined and corrected with regard to thermal and cyclic loads. To separate effects of residual stresses and strain hardening some of the crack propagation experiments will be done using work hardened samples. That allows for describing the influence of hardening on crack propagation. These correlations permit a description of crack propagation as function of residual stresses. Considering only the influence of residual stresses is not possible because the creation of residual stresses comes along with a change in the strain hardening state of the material. The challenges of developing a life prediction model are taking account for thermal and cyclic residual stress reduction, weighting of residual stresses and strain hardening and the experimental measuring of crack propagation behaviour in the affected zone.

• DFG Programme: Research Grants
• Participating Person: Dr.-Ing. Theo Fett
• Ehemaliger Antragsteller: Professor Dr.-Ing. Jürgen Hoffmeister, until 9/2014