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The ability of light-weight all fiber-reinforced polymer-matrix composite armor and hybrid composite-based armor hard-faced with ceramic tiles to withstand the impact of a non-ArmorPiercing (non-AP) and AP projectiles is investigated using a transient non-linear dynamics computational analysis. The results obtained confirm experimental findings that the all-composite armor, while being able to successfully defeat non-AP threats, provides very little protection against AP projectiles. In the case of the hybrid armor, it is found that, at a fixed overall areal density of the armor, there is an optimal ratio of the ceramic-to-composite areal densities which is associated with a maximum ballistic armor performance against AP threats.The results obtained are rationalized using an analysis based on the shock/blast wave reflection and transmission behavior at the hard-face/air, hard-face/backing and backing/air interfaces, projectiles' wear and erosion and the intrinsic properties of the constituent materials of the armor and the projectiles.

The material model for a Multi-Walled Carbon Nanotube (MWCNT) reinforced poly-vinyl-ester-epoxy matrix composite material (carbon nanotube reinforced composite mats, in the following) developed in our recent work [1], has been used in the present work within a transient non-linear dynamics analysis to carry out design optimization of a hybrid polymer-matrix composite armor for the ballistic performance with respect to the impact by a Fragment Simulating Projectile (FSP). The armor is constructed from E-glass continuous-fiber poly-vinyl-ester-epoxy matrix composite laminas interlaced with the carbon nanotube reinforced composite mats. Different designs of the hybrid armor are obtained by varying the location and the thickness of the carbon nanotube reinforced composite mats. The results obtained indicate that at a fixed thickness of the armor, both the position and the thickness of the carbon nanotube reinforced composite mats affect the

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New soil models for a tire-soil interaction are developed and compared. A rigid tire model is used to perform an extensive sensitivity study on the previously used Finite Element Analysis (FEA) soft soil (dense sand) to determine the importance of mesh size, soil plot size, and edge constraints. Furthermore, parameters for Smooth Particle Hydrodynamics (SPH) particles are determined for either complete or partial replacement of FEA elements in the soil model. Rolling resistance tests are then conducted for different FEA, SPH, and FEA/SPH soil models. Replacement of FEA elements with SPH particles is isolated as a variable and it is found that using a deeper amount of SPH particles increases rolling resistance while increasing the SPH particle density has little effect on rolling resistance.

A study is described that evaluated the effect of the mode mix used to create a precrack on the perceived delamination toughness of laminated composites. Mode I double cantilever beam, mode II end-notched flexure, and mixed-mode symmetrically delaminated single leg bending tests were first performed on unidirectional graphite/epoxy specimens with mode I precracks. The tests were then repeated on new unidirectional specimens with mode II precracks. Through an examination of the mechanisms involved, it is shown that toughness values for materials that do not exhibit fiber bridging will be most accurate, at all mode mixities, if test specimens are precracked at the same mode mix as the test itself.