Despite decades of research, no consensus exists on exactly how material properties affect ballistic performance. This dissertation seeks to advance the understanding of the impact process through a series of impact experiments, microstructural investigations, and analytical and numerical analyses on simple, idealized geometries of an armor alumina and two TiC/Ni cermets. The work begins with an assessment of the predictive capabilities of the recently-developed, mechanism-based Deshpande-Evans constitutive law, through comparisons to impact experiments on a confined, supported armor-grade alumina. Once calibrated, the model accurately predicts the size of the comminuted zone beneath the impact, and provides new insights into the spatial and temporal evolution of subsurface damage and deformation processes during impact.
These experiments and finite element (FE) simulations motivate the development of an analytical framework within which the critical impact velocities required to initiate specific failure mechanisms can be predicted, as a function of material properties and geometry. This is accomplished through a series of FE simulations, coupled with analytical models for the maximum impact pressures and forces, and established initiation criteria for each mechanism. From these analyses failure mechanism maps are generated that provide insight into the sequence and hierarchy of deformation mechanisms during impact as well as the effects of property tradeoffs.
The impact resistance and multi-hit potential of TiC/Ni cermets are evaluated and compared to alumina, tested in the form of plates backed by thin steel sheets. The cermets exhibit ballistic performance comparable to that of the alumina, but suffer significantly less extended cracking and fragmentation, indicating potential for superior multi-hit performance. For both cermets and the alumina, failure is shown to transition from cone cracking at low velocities, to shear plugging at the highest velocities. This transition is accompanied by a decrease in the efficacy of the tiles in spreading the load to the backing sheets, which results in sharper residual deflection profiles of the sheets. FE simulations and in situ observation of impacts on monolithic plates indicate that the shape of the deflection profile provides a useful measure of the effectiveness of the material in spreading the impact load.
|Advisor:||Zok, Frank W.|
|Commitee:||Mackin, Thomas J., McMeeking, Robert M., Pollock, Tresa M.|
|School:||University of California, Santa Barbara|
|School Location:||United States -- California|
|Source:||DAI-B 74/06(E), Dissertation Abstracts International|
|Keywords:||Armor, Ceramics, Cermets, Damage, Impact|
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