Dear SIMULIA community, 

I am working on a project to build an Abaqus model of resistance spot welding process of battery tab and multiple foils. However, I am encountering some convergence issues during the simulation of this model. I would appreciate if you could give some suggestions to solve the problem. I am sharing the description of the problem and the model as much as possible. If you have any additional questions, please let me know.

In this model, I am trying to simulate the resistance spot welding process of a battery tab with two foils. The dimensions of the battery and the tabs and the electrodes are shown in figure no 1. Here, the thickness of the tab is 0.4 mm while the thickness of the foil is 16um. 

The model consists of 1/4th of the whole geometry, having symmetry on x and z faces. The boundary conditions of the model are shown in the figure no 2. 

It can be seen from the figure that the bottom surface of the bottom electrode is pinned and has zero electric potential. The displacement of the top surface of the top electrode is fixed at zero in x and z direction. This model consists of two steps: 1) Squeezing and 2) Apply electric current. A squeezing pressure of 25.4 MPa is applied during squeezing stage and maintained in the next step. 30 kA electric current is applied from the top surface of the top electrode during the apply current step. 

A coupled thermal-electrical-structural model is used here. Q3D8 elements have been chosen for meshes. The interaction properties are defined by tangential and normal behavior, thermal and electrical conductance, heat generation and geometric properties. Based on this surface interactional properties four surface-surface interactions are defined. The master and slave surfaces for these surface interactions are given below: 

Total time for the squeeze steps is 0.3 s where initial increment size is 0.03s. However, the simulation fails to complete the first increment of the squeeze step. The job monitor image is shown in figure no 3. 

In the above snapshot, you can notice from the message file that the maximum penetration error occurs between the foil-1 and foil2 surface-surface Interaction assembly. You have any suggestions or guidance on how to solve the problem, I would highly appreciate it. Please note that, with one battery tab and foil configuration the simulation did not have any convergence issues. However, while adding another foil to this existing model creates this convergence issue.