An influence of cyclic loading on the form of constitutive relationship for DP500 steel

• New constitutive model including influence of prior fatigue was proposed.
• Three basic mechanisms influencing stress–strain curves were identified.
• Micro-damages and dislocation rearrangement are included into new model.
• Developed model uses cumulative fatigue damage coefficient.
• Cumulative fatigue damage is determined on the basis of inelastic strain value.

Fatigue loading induces a microstructure evolution leading to the change of macroscopically observed mechanical behavior of a dual phase DP500 steel. It was assumed that stress–strain characteristic of a pre-fatigued material may be determined using constitutive equation taking into account damage parameter. To estimate development of the fatigue damage in specimen a variation of the inelastic strain component was applied.The flat “dog-bone” specimens were initially loaded using stress controlled cycles. When the strain reached a given value the fatigue process was stopped. Subsequently, the specimens with introduced fatigue damage were subjected to tensile tests. Next, the Johnson-Cook's constitutive equation was calibrated separately for each pre-fatigue case. Finally, a new constitutive relationship, based on the Johnson-Cook's model was proposed. It reflects the hardening and softening effects by taking into account both a change in the dislocation structure and development of fatigue microdamage. Proposed model shows a very good agreement with experimental data.

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