# A Modified Fatigue Life Prediction Model for Cyclic Hardening/Softening Steel

## TL;DR

This paper introduces a new model to predict how long steel can withstand repeated stress before breaking, improving accuracy for both high and low stress cycles.

## Contribution

A novel fatigue life prediction model is proposed by modifying flow stress and plastic deformation equations using hysteresis loop data.

## Key findings

- The model achieved prediction errors within a factor of two for 310S stainless steel and 1045 carbon steel.
- It reliably predicts both high-cycle and low-cycle fatigue life across the entire ε-N curve.
- The model incorporates strain amplitude effects through modified stress–strain hysteresis loop relationships.

## Abstract

The accumulation of fatigue damage is primarily caused by cyclic plastic deformation. In low-cycle fatigue, cyclic plastic deformation is the dominant deformation mode. In high-cycle fatigue, although most deformation is elastic, plastic deformation may still occur in localized regions of stress concentration and plays a critical role in the initiation of fatigue cracks. Considering that cyclic plastic deformation can be characterized by hysteresis loops, this study modifies the flow stress equation and the cyclic plastic deformation relationship based on stress–strain hysteresis loops at half-life cycles under different strain amplitudes. An improved model for life prediction that incorporates the effects of strain amplitude is proposed. The results of experiments on 310S stainless steel and 1045 carbon steel demonstrate that the model achieved prediction errors within a factor of two and provided reliable predictions for both high-cycle and low-cycle fatigue life across the entire ε-N curve.