Constant load with changing material model in ABAQUS

Hi,

 

I am trying to define a simple model in ABAQUS with a changing material model and constant load, something similar to creep. I define multiple steps and achieve changing material behavior (e.g., different Young's modulus in linearly elastic model) with UMAT over the steps. The load is applied in the first step and keeps constant afterwards. However, the stress and deformation field only changes in the first step and keeps constant in following steps even if the material behavior is changing. I think it is due to the reason that there is no further change in the load and thus, the deformation will also not change if we implicitly solve the equation group in the solver. So generally, how should we define the model for such cases as creep? Thanks!