Nonlinear fatigue life prediction model based on isodamage curve considering two-block loading

A non-linear life prediction model considering the loading history is proposed based on isodamage curve. The stress-controlled low-high block loading of low cycle fatigue (LCF) at high temperature, with various previous cycles, was performed on a nickel-based superalloy. The damage evolvement of the prior loading was revealed using scanning electron microscopy under the low-high block loading, especially the failure mechanism of coaxing effect. In addition, load history correlation factor was introduced to describe the influence of prior cycle. Based on the Ni-based superalloy, the life prediction model of two-step loading, including the low-high block (LH) and high-low block loading (HL), was proposed, agreeing well with the experimental results for different metals. Compared with other life prediction models, the proposed model demonstrated the higher prediction accuracy and wider applicability. A nonlinear fatigue life prediction model was established considering coaxing effect. No fitted material parameters were included in the new model. A damage exponent of loading history was introduced based on the SEM results. Proposed model performed excellent prediction ability for the two-block loading.