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Multiferroic ceramics with the general formula (x)MgFe2O4–(1−x)BaTiO3 (x=0.4, 0.5, and 0.6) were synthesized by solid-state sintering process. From the x-ray diffraction analysis, it was observed that almost no chemical reaction occurs between the ferrite and the ferroelectric materials used to form the diphase composite systems. No impure phase was observed in all the sintered composite systems. Leakage current density, ferroelectric properties and dielectric properties were found to improve with the addition of the ferroelectric phase. For the composite with the least amount of ferrite, the values of remnant polarization (2Pr) before and after dc magnetic poling at 7kOe for 1h were found to be 1.35 and 2.12μC∕cm2, respectively. This showed marked improvement as high as 57% and confirmed the coupling of the electrical dipoles with the magnetic field applied. All the studied composite systems proved to be multiferroic in nature. The highest magnetoelectric coupling coefficient of 50.2mV∕cmOe was measured at dc magnetic field of 10kOe along with ac frequency of 50Hz at room temperature for the 0.6MgFe2O4–0.4BaTiO3 composite system. Magnetoelectric effect at resonance frequency increases by a factor of 80 compared to the other frequencies for such composite systems.

In order to develop more rational design and damage tolerance approaches, there is a need for more accurate, realistic, and practical modeling of damage progression in composite structures at the component level, and not just at the laboratory specimen level. This presents a considerable challenge because experimental and analytical results at the specimen level do not always translate to observations of damage at the component or structural levels. In this article, a simple but novel finite element-based method for modeling progressive damage in fiber-reinforced composites is proposed. The element-failure method (EFM) is based on the idea that the nodal forces of an element of a damaged composite material can be modified to reflect the general state of damage and loading. The EFM, when employed with suitable micromechanics-based failure criteria, may be a practical method for mapping damage initiation and propagation in composite structures. This concept is especially useful because the nature of damage in composite laminates is in general complex and diffused, characterized by multiple matrix cracks, fiber pullout, fiber breakage, and delaminations. It is therefore not practical or even possible to identify and model the multitude of cracks in the fashion of traditional fracture mechanics. Currently, progressive damage in composites is most commonly modeled using material property degradation methods (MPDM). Unfortunately, MPDM often employs rather arbitrary and restrictive degradation schemes that, in some cases may result in computational problems. In contrast, computational convergence and stability is always assured in EFM because the stiffness matrix is never altered. Furthermore, no contact algorithm to prevent nonphysical solutions involving interpenetration of delamination and crack surfaces is necessary, because the failed elements are not removed from the model. It is shown in this article that the EFM is a more general method than the MPDM. A comparison study of damage progression and delamination in a composite laminate subjected to three-point bend using a recently proposed failure criterion called the strain invariant failure theory (SIFT) is presented. The results show that the EFM is able to predict the damage pattern more accurately than the MPDM.

The purpose of this in vitro study was to investigate the effect of polishing systems on the microleakage of conventional and resin-modified glass-ionomer cements. Class V cavities were prepared at the cemento-enamel junction of 80 freshly extracted posterior teeth. The prepared teeth were randomly divided into two groups and restored with conventional or resin-modified glass-ionomer cements. The restored teeth were stored in distilled water at 37 degrees C for 1 week after removal of excess restorative with diamond finishing burs. The restored teeth were then divided into four groups of 10 and finished and polished using the following systems: Two Striper MFS; Sof-Lex XT; Enhance Composite Finishing and Polishing System; Shofu Composite Finishing Kit. The finished restorations were subjected to dye penetration testing. Results showed that the microleakage at dentin margins of conventional glass-ionomer cements and enamel margins of resin-modified glass-ionomer cements are significantly affected by the different polishing systems.

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