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ANSYS/LS-Dyna Ballistic Impact: Modeling Methods Development

Sphere Penetrating Ballistic Gelatin: Gelatin Modeled with Arbitrary Lagrangian Eulerian Methods

 

The U.S. Army Research, Development and Engineering Center (ARDEC) was looking for a way to predict the response of ballistic gelatin to impacts from various small-caliber projectiles.  The physics of this phenomenon is very difficult to simulate. It requires highly nonlinear, rate-dependent material models for both the projectiles and the gelatin, along with complex failure mechanisms for both media, working simultaneously with eroding contact.

Based on its prior level of expertise in this type of work, CAE Associates was asked to develop modeling methods that would allow projectile designers to simulate impact tests and propose effective designs prior to prototyping.

ANSYS/LS-Dyna was chosen as the most effective tool for simulating these events.  Standard Lagrangian methods and less -common multi-material ALE (Arbitrary Lagrangian Eulerian) methods were proposed.   Multi-material ALE methods were considered primarily because they are capable of retaining material mass upon failure, which was an important modeling consideration for the Army.   Considerable model testing was performed to determine the accuracy and robustness of the multi-material ALE method when combined with failure in different material models.

Numerous material models were evaluated for the gelatin including hyperelastic and viscous fluid models.  Johnson-Cook materials were used for the metal components of the projectiles.  A variety of material failure models were also considered.  Other parameters evaluated in the study were the effects of precession and impact angle, contact algorithms, the inclusion of retained nodes in the Lagrangian methods, friction, and the effects of different ALE parameters.

The extensive body of research produced during the study showed that custom LS-Dyna material model subroutine development is the best approach to capture the unique strain-rate dependent hyperelastic behavior observed in the gelatin.

As part of this work, robust ALE and Lagrangian modeling methods were developed that provide Army analysts with the tools they need for predicting the response of gelatin to ballistic impact.  CAE Associates worked closely with Mr. Mark Minisi, the team leader for the technical modeling and simulation group of the infantry weapon systems division at U.S. Army ARDEC, to identify and satisfy their requirements, obtain test data for comparison and calibration, provide training, and continue to provide support after the project was completed.

Mr. Minisi summarized CAE Associates’ contributions to this project as follows:
"CAE Associates’ assistance was crucial during the first phase of developing gelatin impact models.  Their technical approach was very effective, including an incremental approach from simple Lagrangian to complex Eulerian models. They have repeatedly proven to have outstanding skills in the field of engineering and FEA.  CAE Associates is continuously helpful to the US Army and its efforts."