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2020 Research Highlight: Incorporating the UMAT Material Model Interface into the EPIC Code

Incorporating the UMAT Material Model Interface into the EPIC Code

Charles A. Gerlach
Southwest Research Institute

There is a strong desire to ease the process of getting complex material models (developed by others) into computer codes used by the Department of Defense. The MEDE program realized this need and funded Southwest Research Institute (SwRI) to incorporate an interface into the Elastic-Plastic Impact Computations (EPIC) code such to ease the process of using newly developed material models in EPIC1. SwRI incorporated the user material (UMAT) interface into EPIC which allows material models to be easily used within the EPIC framework. This interface is a standard, developed by Abaqus, and requires very few changes to the model if the interface standard is adhered to.

After incorporation of the UMAT interface a thorough checkout was performed to verify the interface was incorporated correctly. The verification used the Tonge-Ramesh (TR) ceramic model2 because this model is included in the native EPIC code3 and there is also a UMAT interface version of the TR model. This allows for a direct comparison of model results; one using the model native in EPIC that has been thoroughly checked and the other using the UMAT interface.

Figure 13 presents a comparison of a single 3D hexahedral element simultaneously subjected to shear and tension (shown on the left) and to shear and compression (shown on the right). Artificial viscosity has been turned off. The results using the TR model through the UMAT interface are shown with black dots and the results using the TR model native in EPIC are shown with the red lines; the two results overlay confirming the UMAT interface is incorporated correctly.

Figure 14 presents a ballistic impact computation of a steel cylinder impacting a boron carbide plate backed by an aluminum plate at 1000 m/s. The computed result on the top uses the TR ceramic model native in EPIC and the result on the bottom uses the UMAT interface; the computed results are nearly identical (the slight differences are a result of temperature which is treated differently between the native model and the UMAT model). This new capability provides the MEDE material model developers with an efficient and simple procedure for using these new models in EPIC. Towards this end, we continue to develop more effective ways to capture and analyze the large, diverse data commonplace in materials today. Direct collaboration with MEDE investigators creates new ways to maximize the impact of their data.