We present an analytical approach for the penetration and perforation processes of concrete targets by rigid projectiles. We first derive an empirical relation for the penetration resistance (R t ) of thick concrete targets to rigid projectiles, in terms of their unconfined compressive strength (f c ) and the projectile's diameter (D). We then develop an analytic model for the perforation process of concrete slabs by accounting for their back surface, through a reduced resisting stress (R eff ) which the slab exerts on the rigid projectile. With these values of R eff , we calculate the ballistic limit velocity (V bl ) for a given projectile/slab configuration, as well as the residual velocities (V r ) of a perforating projectile. Predictions from our model are compared with several sets of published data, showing good agreement.

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Nanowires and nanoparticles are envisioned as important elements of future technology and devices, owing to their unique mechanical properties. Metallic nanowires and nanoparticles demonstrate outstanding size-dependent strength since their deformation is dislocation nucleation-controlled. In this context, the recent experimental and computational studies of nucleation-controlled plasticity are reviewed. The underlying microstructural mechanisms that govern the strength of nanowires and the origin of their stochastic nature are also discussed. Nanoparticles, in which the stress state under compression is nonuniform, exhibit a shape-dependent strength. Perspectives on improved methods to study nucleation-controlled plasticity are discussed, as well the insights gained for microstructural-based design of mechanical properties at the nanoscale.

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