Establishment of damage estimation rule for brittle fracture after cyclic plastic prestrain in steel

Material damage caused by complicated prestrain like cyclic prestrain and various direction prestrain. It is so important to understand the mechanism of material damage for high-precision lifetime evaluation of steel structure. Material damage depends on not only equivalent plastic strain but the order of pestrain loaded. Also, material damage can be expressed by effective damage strain from back stress uploading and total dislocation density calculated from conventional mechanism based on strain gradient plasticity (CMSGP). These ideas can be extended to multiaxial problems and material damage can be estimated by these parameters as well as uniaxial problems.