In our recent work (Grujicic et al., Int. J. Impact Eng., 2008), various open-literature experimental findings pertaining to the ballistic behavior of soda-lime glass were used to construct a simple, physically based, high strain rate, high-pressure, large-strain mechanical model for this material. The model was structured in such a way that it is suitable for direct incorporation into standard commercial transient non . In general, a good agreement was found between the computational and the experimental results relative to: (a) the front shapes and the propagation velocities of the longitudinal and transverse waves generated in the target during impact and (b) the front shapes and propagation velocities of a coherent-damage zone (a zone surrounding the projectile/target contact surface which contains numerous micron and submicron-size cracks). However, substantial computational analysis/experiment disagreements were found relative to the formation of crack centers, i.e. relative to the presence and distribution of isolated millimeter-size cracks nucleated ahead of the advancing coherent-damage zone front. In the present work, it was shown that these disagreements can be substantially reduced if the glass model (Grujicic et al., Int. J. Impact Eng., 2008) is advanced to include a simple macrocracking algorithm based on the linear elastic fracture mechanics.

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Molecular-level modeling and simulations are employed to study room-temperature micro-structural and mechanical response of soda-lime glass when subjected to high (i.e., several giga-Pascal) uniaxial-strain stresses/pressure. The results obtained revealed the occurrence of an irreversible phase-transformation at ca. 4 GPa which was associated with a (permanent) 3-7% volume reduction. Close examination of molecular-level topology revealed that the pressure-induced phase transformation in question is associated with an increase in the average coordination number of the silicon atoms, and the creation of two-to fourfold (smaller, high packing-density) Si-O rings. The associated loading and unloading axial-stress versus specific-volume isotherms were next converted into the corresponding loading Hugoniot and unloading isentrope axial-stress versus specific-volume relations. These were subsequently used to analyze the role of the pressure-induced phase-transformation/irreversible-densification in mitigating the effects of blast and ballistic impact loading onto a prototypical glass plate used in monolithic and laminated transparent armor applications. The results of this part of the study revealed that pressure-induced phasetransformation can provide several beneficial effects such as lowering of the loading/unloading stress-rates and stresses, shock/release-wave dispersion, and energy absorption associated with the study of phase-transformation.

A fully coupled thermomechanical finite element analysis of the friction-stir welding (FSW) process developed in the authors' previous work is combined with the basic physical metallurgy of Ti-6Al-4V to predict/assess the structural response of FSW joints. A close examination of the experimental results reported in the open literature reveals that in most cases the heat-affected zone (HAZ) of the weld possesses the most inferior properties and tends to control the overall structural performance of the weld. Taking this observation into account, a microstructure evolution model is developed and parameterized for the Ti-6Al-4V material residing in the HAZ. Specifically, this model addresses the problem of temporal evolution of the globular a-phase particles located within prior b-phase grains (the dominant microstructural parameter in the HAZ) during the FSW process. Next this model is combined with the wellestablished property versus microstructure correlations in Ti-6Al-4V in order to predict the overall structural performance of the weld. The results obtained are found to be in reasonably good agreement with their experimental counterparts, suggesting that the present computational approach may be used to guide the selection of FSW process parameters in order to optimize the structural performance of FSW joints (at least while they are controlled by the HAZ-material microstructure/properties).