C. G. Fountzoulas

Highly anisotropic CoPt and FePt nanoparticles have been prepared and embedded in a C and BN matrices using the tandem deposition mode. The as-made multilayer CoPt(FePt)/C(BN) films show a disordered face centered cubic (fcc) structure, which is magnetically soft and have low coercivity (<20 Oe). Magnetic hardening occurs after a heat treatment at elevated temperatures (<550/spl deg/C), which results in the formation of the nanoparticles leading in an increase of coercivity with values up to 15 kOe at room temperature. Transmission electron microscope studies showed FePt particles embedded in C matrix with a size increasing from below 3 nm in the as-made state to about 8 nm in the optimum annealed state. The hardening is due to the high anisotropy of the face centered tetragonal (L1/sub 0/) phase with a bulk anisotropy K>10/sup 7/ erg/cm/sup 3/. The coercivities obtained are much below those expected for noninteracting single-domain particles and the difference is attributed mainly to a smaller anisotropy in the nanoparticles associated with a lower degree of atomic ordering of the L1/sub 0/ phase.

Abstract 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-linear dynamics finite element-based software packages like ANSYS/Autodyn (Century Dynamics Inc., 2007) or ABAQUS/Explicit (Dessault Systems, 2007). To validate the material model, a set of finite element analyses of the edge-on-impact tests was conducted and the results compared with their experimental counterparts obtained in the recent work of Strassburger et al. ( Proceedings of the 23rd International Symposium on Ballistics , Spain, April 2007; Proceedings of the 22nd International Symposium on Ballistics , November 2005, Vancouver, Canada). 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.