I am modeling the Laser Powder Bed Fusion (LPBF) additive manufacturing process in ABAQUS. My goal is to simulate the irreversible transition from powder to solid material using a user-defined field variable (FIELD(1)) in a USDFLD subroutine.

Model Overview:

FV=1: Represents the initial, unmelted powder material.

FV=2: Represents the consolidated solid material after melting and solidification.

The transition from FIELD(1)=1 to FIELD(1)=2 is triggered when the integration point temperature (TEMP) exceeds the material's melting point. This is implemented with a SMOOTH transition in the subroutine.

Crucially, this transition must be irreversible. Once powder becomes solid, it cannot revert.

The Problem: The material transition works correctly within the first analysis step (simulating the first layer). However, when the second analysis step begins (simulating the second layer), the field variable in the elements of the first layer reverts from 2 back to a less value (1.6 for example).

I have implemented a check in the subroutine to "lock" the field variable, but this lock does not persist between steps. The state is lost when the new step starts.



Has anyone faced such an issue on using user's material subroutine in layer-wise additive manufacturing simulation