A procedure to develop a true geometric finite element (FE) model of a Berkovich indenter using fused silica as a reference material is proposed. 2D and 3D models of the indenter tip were evaluated based on the delimiting factors such as the indenter true geometry, elastic modulus, yield stress and hardening modulus, and compared with the experimental results. The true geometry of the Berkovich indenter paying special attention to the tip end was determined by a non-linear regression of the indentation data at small indentation depths using the equation of a sphere, and by image analysis of AFM micrographs. The tip bluntness was described with a so-called rounding radius and incorporated into the 3D FE model, which was in fact the most important parameter considered for a better representation of the load–displacement curves obtained experimentally. The advantages of using 3D models instead of 2D models are described and discussed here. Finally, different methods were used to determine the yield stress of fused silica, including the analysis of the load–penetration data transformed to ‘stress–strain’ indentation curve as well as by the analysis of the von Mises equivalent stress distribution obtained with the 3D FE models. The results show that the yield stress of fused silica is 4.5–4.6 GPa.

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Room temperature p-type conductivity and coexistence of ferroelectric order in ferromagnetic Li doped ZnO nanoparticles

Structure and mechanical properties of electroless nickel-boride (Ni−B) thin film coatings on S7 steel substrate were studied in as-plated and annealed samples. The electroless bath does not contain Pb, Cd, or Ta in the stabilizer agents. The mechanical properties of the Ni−B coatings were obtained from nanoindentation measurements. Models by Korsusky and King were used to obtain hardness and elastic modulus, respectively. The structure of the coatings was observed by atomic force and scanning electron microscopy and XRD. Bath composition, plating time, annealing temperature, and time were considered in order to prepare coatings with optimal mechanical properties.

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