Computational simulations and ballistic verification tests for 7.62mm AP and 12.7mm AP bullet impact against ceramic metal composite armours

摘要

In this study, perforation performance tests of multi layered ceramic-metal composite armours consisting of alumina ceramics (99.5% AI2O3) and aluminium Al 2024-T351 back-up materials against a 7.62mm armour piercing (AP) bullet and a 12.7mm AP bullet impact were numerically simulated and then these simulations were verified by the ballistic tests. Nonlinear dynamics finite element simulations are solved with the LS-DYNA lagrangian solver. In the study, new sets of material constants for appropriate material models, which describe the bullet's steel core and aluminium target material deformation better, are obtained. These new material constants are obtained by evaluating stress-strain curve data and also making Depth of Penetration (DOP) simulations and verification tests for each AP bullet and Al 2024-T351 material before perforation performance simulations of ceramic composite structures. The 3D finite element model is generated and compared with 2D simulations. For DOP simulations, the steel core of the bullet is only modelled, but for perforation simulations a full bullet (copper jacketed and filler material) model is used in simulations for the 12.7mm AP bullet. According to the DOP simulation results, Plastic-Kinematics hardening material model is reasonable enough to describe material damage modelling for both bullets and Al 2024-T351 material. Failure strain (FS), which is the most critical value in the simulations, is obtained from stress-strain curve data and also evaluating DOP test results with some correlation for high strain rate condition. The FS value for Al 2024-T351 against a 12.7mm bullet impact is estimated higher than a 7.62mm bullet impact, which is well expressed by strain hardening due to the increased impact area and energy of the bullet. In perforation simulations, bullets and Al 2024-T351 are simulated with a plastic-kinematics hardening material model, but for the ceramics material, a Johnson-Holmquist (JH2) ceramic material model is selected for a good estimation. Ballistic verification tests performed show that numerical simulations are overlapped successfully with the test results with an acceptable difference. With these appropriate material model constants; the fracture conoid in ceramics, bullet deviation from the line of impact and then stopping, bullet end deformation and aluminium bulging is well shown in the simulations.