Investigation of high strain rate deformation of tungsten heavy alloys with experimental and numerical methods

Tungsten heavy alloys are widely used as kinetic penetrator material in ballistic applications due to their superior mechanical properties. Therefore, investigating the high strain rate behaviors, deformation types and the interaction with the target have importance in terms of design. In this thesis, deformation behavior and ballistic performance of tungsten heavy alloys at high strain rates were experimentally and numerically investigated. In the study, 93W-3.5Ni-3.5Fe, 93W-4.67Ni-2.33Fe and 93W-5.6Ni-1.4Fe alloys were pressed cold isostatically under 300 MPa and were sintered at 1460, 1480 and 1500ºC for 30 min. under reducing and protective atmosphere. The mechanical properties of the alloys were determined with compression tests at 0.0003, 0.003, 0.03/s strain rates and with microhardness measurements. Microstructural parameters were obtained with the measurements of tungsten grain size, amount of binder phase and contiguity. The deformation types of the samples and the interaction of these samples with the target were determined via Taylor impact and ballistic tests. These tests were performed by single stage gas gun. In Taylor impact tests, cylindirical (8 mm diameter, 24 mm length) tungsten heavy alloy samples were impacted to rigid steel target with velocities of 200, 225 and 250 m/s. In ballistic tests, cylindirical (8 mm diameter, 8 mm length) tungsten heavy alloy fragments were impacted to the 25 mm thick Al 6061-T6 target with appoximately 900 m/s and the interaction between the fragment and the target was investigated. Taylor impact and ballistic tests were numerically modelled and the results were compared with the test results. Numerical studies were performed using Ls-Dyna software. Taylor impact tests were modelled with finite element method and SPH meshfree method. Ballistic tests were modelled with finite element method. The increase in sintering temperature led to increase in the volume fraction of binder phase, tungsten grain coarsening and reduction in contiguity in the microstructures of the alloys. Grain coarsening decreased the yield strengths of the alloys. The increase in Ni/Fe ratio in the alloys enhanced the volume fraction of binder phase in the microstructure. This increase enhanced the solubility of tungsten in the binder phase and the yield strengths of the alloys. In Taylor impact test, the increase in ductility with sintering temperature led to a change of the fracture behavior of fragments from tensile splitting to tensile splitting and shear fracture. The best perforation performance for multiple-component targets was obtained with 93W-4.67Ni-2.33Fe alloy sintered at 1480 °C. The increase in the sintering temperature and plastic deformation of the fragments enhanced the hole diameter and the damage on the single-component target. In the numerical modeling of Taylor impact tests with finite element method, the fracture behaviors were simulated more realistically as the element size was decreased. The modelling of the final dimensions of the test samples with SPH meshfree method was more similar to the test results than the finite element method. The element sizes in the ballistic test modelling have influence on simulating the damage at the fragment and the target.