Real Scale Simulation of Ballistic Tests for Multi-Layer Fabric Body Armors

The bottle-neck issues to resolve for numerical simulation of real scale ballistic tests of fabric body armors are computer capacity limitation and prohibitive computational cost. It is not realistic to use micro-level computer simulations for an open end design process. Most numerical simulations are only applicable for small scale parametric analyses, which could facilitate apprehension of fabric failure mechanisms during ballistic impact, but not applicable for the design process. In this paper, a sub-yarn model, the digital element approach, is applied to simulate real scale ballistic tests for soft body armors. In this approach, a yarn is discretized into multiple digital fibers and each fiber is discretized into many digital elements. In order to improve efficiency, two hybrid element mesh concepts are investigated: area based hybrid mesh and yarn based hybrid mesh. The area based hybrid mesh procedure is similar to one utilized in the conventional finite element approach. A fine element mesh is adopted in the area near the impact center; a course element mesh in the area far away. However, numerical simulation results show that the stress wave travels along the principal yarns at the speed of sound immediately after ballistic impact. High yarn stress develops quickly from the impact center to a distance along the principal yarn. As such, the area based hybrid mesh approach fails to obtain improved computer efficiency without loss of accuracy. Because the high stress only develops within principal yarns after a ballistic impact, a yarn based hybrid element mesh procedure is adopted. In this procedure, only principal yarns and yarns near principal yarns are discretized into fine digital fibers; other yarns are discretized into coarse digital fibers. Because only a few principal yarns resist load in a typical ballistic impact, the yarn based hybrid technique could improve simulation efficiency up to 90–95% without sacrificing accuracy. A numerical tool is then developed to generate fabric with a yarn based hybrid mesh. Accuracy of the approach is analyzed. The hybrid mesh technique is applied to simulate real scale ballistic tests of ballistic armors made of 4 to 20 piles of 2-D plain woven fabrics. Numerical results are compared to real scale standard ballistic results.