I have Force-Displacement values of a tensile test that undergoes uniaxial loading. Please find attached the stress strain curve of the loading.

Sigma1 denotes the Equivalent stress of the element at current time increment and Sigma0 denotes Peak equivalent stress of the element reached at the end of the loading stage. I need to calculate a stress ratio Sigma1/Sigma0 at each time increment.

In order to calculate the stress ratio, the time increment of the peak stress has to be reached after which the field variables (of USDFLD) in the previous time increments has to be modified to calculate the stress ratio. This stress ratio has to be applied to the material model of the same simulation.

Is it possible/recommended to achieve this using USDFLD? Or is there a better alternative in ABAQUS?