We use discrete element method (DEM) simulations to study the evolution of defects during sintering. In DEM, the particulate nature of the sintering powder is taken explicitly into account because each particle is modeled as a discrete entity interacting with its neighbors. This allows to treat naturally the gain or the loss of contacts between particles, and to explicitly take particle rearrangement into account. These effects are particularly important when looking for the nucleation, growth or healing of local heterogeneities such as defects. We first study the evolution of a crack (generated, e.g., during ejection or drying processes) when no geometrical constraint is imposed. We then investigate how constrained sintering between two parallel planes may lead to crack initiation and growth. We show that the extent of interparticle rearrangement plays a major role in the evolution of the crack under such conditions. The main conclusion of these simulations is that some geometrical constraint is necessary for a defect to grow into a crack and that the presence of an initial defect is not a necessary condition to initiate cracks.

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The purpose of the present work is to determine the magneto-electroelastic effective properties of reinforced piezoelectric composite materials with unidirectional cylindrical fibers periodically distributed in a square array through the Asymptotic Homogenization Method (AHM). The case when mechanical displacement is in-plane and electric and magnetic fields are out-of-plane is studied. Each periodic cell of the medium is a binary composite wherein both constituents are homogeneous magneto-electroelastic materials with transversely isotropic properties. Closed-form expressions for the overall properties are obtained. Numerical calculations are carried out for the BaTiO 3 /CoFe 2 O 4 composite. A good match is obtained between AHM and other calculations reported in the literature. These results may be considered as congruent with the experimental experience.

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In the search of lead-free piezoelectric materials, ceramic processing techniques offer potential tools to increase the piezoelectric and ferroelectric properties in addition to new chemical compositions. Powders of pure BNKT16 (Bi 0.5 (Na 0.84 K 0.16 ) 0.5 TiO 3 ) phase were synthesized by sol-gel method with a low crystallization temperature (750 ℃ ). Ceramic samples were sintered by pressureless sintering (PLS), sinter-forging (SF), and spark plasma sintering (SPS) techniques. Structural, morphological, and chemical characterizations were performed by XRD, Raman, EDS, and SEM. Sintered samples by PLS and SF exhibit rod-like grains associated to bismuth volatility. The highest remanent polarization (11.05 µC/cm 2 ), coercive field (26.2 kV/mm), and piezoelectric coefficient (165 pC/N) were obtained for SF sample. The piezoresponse force microscopy (PFM) analysis shows that the crystallites at the nanoscale exhibit piezoelectric phenomenon and the highest piezoelectric response is reported for PLS sample. The presence of the rhombohedral phase, the increase in grain and crystallite size, and the oriented rod-like inclusions favoring the crystallographic texture are facts that enhance the piezoelectric coefficient for BNKT16 piezoceramics.