I am working on the curing deformation of composite materials, and I use the UMATHT subroutine to define thermal behavior, where U is the internal heat energy per unit mass, and the density of the material should be obtained according to the Abaqus GUI interface input. But I want to account for the non-linear variation of the density with the degree of solidification field, how to do this?

In addition, if multiple field variables are defined in USDFLD, how do field 1, field 2, etc. in the Abaqus GUI interface correspond to the field variables defined by the subroutine?