A hybrid modeling concept for ultra low cycle fatigue of metallic structures based on micropore damage and unit cell models

The paper presents a concept for life-time predictions of metallic structures subjected to ultra low cycle fatigue. The proposed hybrid strategy is characterized by a combination of unit cell analyses on a microstructural level and a micropore damage model used for structural analyses on the macroscopic level. To account for the large plastic deformations evolving during cyclic loading, an advanced elasto-plastic model using a Bari–Hassan-type kinematic hardening rule based on a superposition of several kinematic hardening laws according to Armstrong-Frederick is employed. Micromechanically oriented unit cell analyses are used for a calibration of the model parameters of a macroscopic Gurson-type model. Numerical results include the validation of the macroscopic Gurson model based on laboratory test results on steel specimens as well as a prototype application to a life-time prediction of a metallic spherical pressure vessel subjected to earthquake loading.