Micromechanical Simulation of Initiation and Propagation of Cleavage Cracks in the Ductile-brittle Transition Region

• Applicant: Privatdozent Dr.-Ing. Geralf Hütter
• Subject Area: Mechanics ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: from 2015 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 269292404

With decreasing temperature typical engineering materials like the most steels become more and more brittle. The reason is the transition of the microscopic failure mode from ductile growth of micro-voids to transgranular cleavage of grains. The drop of the macroscopic fracture toughness caused by the transition from the ductile to the brittle mechanism is a severe problem in engineering applications of body-centered cubic metals since crack-like defects formed during manufacturing or in operation may reduce strength and life-time of a component significantly. In the ductile-brittle transition region the measured fracture toughness values of single crystals and poly-crystals differ by several orders. To the knowledge of the authors no model can explain this discrepancy yet. It is the aim of the present research project to contribute significantly to the understanding of this phenomenon. For this purpose a micromechanical FEM model shall be developed which resolves the microstructure of a ferritic steel at the crack tip discretely in form of particles (segregations, inclusions) and grains. Within different stages of extension of the model the effects of the relevant submechanisms like debonding of particles, fracture of particles, dislocation pile-up at grain boundaries and particles and incompatibility of cleavage planes of neighboring grains shall be investigated and quantified. On this basis the microstructure shall be optimized to increase the fracture toughness.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Meinhard Kuna