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This article presents numerical studies on the deformation of particles during dynamic compaction of metal powders. The analysis of the process is based on a micromechanics approach using multiple particle configurations. The material considered is elastoviscoplastic with interparticle friction. Two-dimensional studies on particles in close packed arrangement were carried out using plane strain conditions for deformation and thermal response. The finite element method using an explicit dynamic analysis procedure was used for the simulations. The influence of speed of compaction, strain hardening, strain rate dependency, interparticle friction and size of the powder particles on the final shape and temperature variations within the particles were analyzed. The studies offer useful information on the shape and temperature variations within the particles. The results provide a better understanding of the dynamic compaction process at the micromechanics level.

We propose an optical image security scheme based on polarized light encoding and the photon counting technique. An input image is encoded using the concept of polarized light, which is parameterized using Stokes–Mueller formalism. The encoded image is further encrypted by applying the photon counting imaging technique to obtain a photon limited image. For decryption, the photon limited decrypted image is obtained by using a polarized light decoding scheme with the help of appropriate keys. The decrypted image has sparse representation, which contains sufficient information for verification. This photon counted decrypted image can be verified using correlation filters. The proposed encryption technique offers benefits over the double random phase encoding in that it does not require active elements such as a lens and provides flexibility in the design of encryption keys. The proposed encryption scheme has also been used for hologram watermarking. The computer simulation results for secure image verification and the hologram watermarking scheme have been presented.

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