Thermo-mechanical properties prediction of Ni-reinforced Al2_2O3_3 composites using micro-mechanics based representative volume elements

For effective cutting tool inserts that absorb thermal shock at varying temperature gradients, improved thermal conductivity and toughness are required. In addition, parameters such as the coefficient of thermal expansion must be kept within a reasonable range. This work presents a novel material design framework based on a multi-scale modeling approach that proposes nickel (Ni)-reinforced alumina (Al$_2$O$_3$) composites to tailor the mechanical and thermal properties required for ceramic cutting tools by considering numerous composite parameters. The representative volume elements (RVEs) are generated using the DREAM.3D software program and the output is imported into a commercial finite element software ABAQUS. The RVEs which contain multiple Ni particles with varying porosity and volume fractions are used to predict the effective thermal and mechanical properties using the computational homogenization methods under appropriate boundary conditions (BCs). The RVE framework is validated by the sintering of Al$_2$O$_3$-Ni composites in various compositions. The predicted numerical results agree well with the measured thermal and structural properties. The properties predicted by the numerical model are comparable with those obtained using the rules of mixtures and SwiftComp, as well as the Fast Fourier Transform (FFT) based computational homogenization method. The results show that the ABAQUS, SwiftComp and FFT results are fairly close to each other. The effects of porosity and Ni volume fraction on the mechanical and thermal properties are also investigated. It is observed that the mechanical properties and thermal conductivities decrease with the porosity, while the thermal expansion remains unaffected. The proposed integrated modeling and empirical approach could facilitate the development of unique Al$_2$O$_3$-metal composites with the desired thermal and mechanical properties for ceramic cutting inserts

SEM assessment of the nature of the interface between molloplast-B and denture base materials

Silicone resilient liners possess most of the required properties of denture liners, however they poorly bond to denture bases. It was the purpose of this investigation to microscopically assess the nature of the interface between a denture liner and three acrylic bases as affected by some parameters. A heat-cured silicone liner (Molloplast-B) and three commercially available acrylic denture base materials were used in this study. Each test specimen composed of Molloplast-B that was bonded to both sides of a denture base blank. Prior to packing the liner, the surfaces of each denture base blank were treated. The surface treatment included either application of a primer or roughening. In other test specimens, the liner was packed against "uncured" resin. In addition, the interfaces of "precured" specimens were examined in both wet and dry conditions. SEM examination revealed that the three denture base materials varied in the nature of their interfaces with the denture liner. Satisfactory junction was observe when the liner was packed against "uncured" acrylic bases. After aging in water, the liner/denture base interface displayed numerous wide gaps with slight changes in Molloplast-B surface texture. This could be attributed to water sorption by the liner and subsequent swelling of its structure.King Saud Universit

Experimental and Computational Analysis of Low-Velocity Impact on Carbon-, Glass- and Mixed-Fiber Composite Plates

One of the problems with composites is their weak impact damage resistance and post-impact mechanical properties. Composites are prone to delamination damage when impacted by low-speed projectiles because of the weak through-thickness strength. To combat the problem of delamination damage, composite parts are often over-designed with extra layers. However, this increases the cost, weight, and volume of the composite and, in some cases, may only provide moderate improvements to impact damage resistance. The selection of the optimal parameters for composite plates that give high impact resistance under low-velocity impact loads should consider several factors related to the properties of the materials as well as to how the composite product is manufactured. To obtain the desired impact resistance, it is essential to know the interrelationships between these parameters and the energy absorbed by the composite. Knowing which parameters affect the improvement of the composite impact resistance and which parameters give the most significant effect are the main issues in the composite industry. In this work, the impact response of composite laminates with various stacking sequences and resins was studied with the Instron 9250G drop-tower to determine the energy absorption. Three types of composites were used: carbon-fiber, glass-fiber, and mixed-fiber composite laminates. Also, these composites were characterized by different stacking sequences and resin types. The effect of several composite structural parameters on the absorbed energy of composite plates is studied. A finite element model was then used to find an optimized design with improved impact resistance based on the best attributes found from the experimental testing

Sensing and Control of Thermally Induced Vibrations of Stationary Blades Using Piezoelectric Materials

Vibration sensing and control of stationary blades (beam/plate-type structures) using piezoelectric materials subjected to thermal loads are considered in this work. Thermal effects are imposed on these blades, which are assumed to be mounted with piezoelectric patches for vibration sensing and control. Effects of the temperature field on the piezoelectric media are treated through the phenomenon of thermopiezoelectricity where electrical, mechanical, and thermal fields are all coupled. First, static blades are considered without control using the finite element method and analytical equations for verification of the finite element model. The finite element program ANSYS is utilized to implement the finite element method in all cases. Negative velocity feedback is then applied for the control of thermally induced vibrations of these stationary blades using the piezoelectric materials. It is concluded that the finite element model is accurate and that the use of the piezoelectric materials in the roots of stationary blades for the purpose of controlling thermally induced vibrations via a negative velocity feedback scheme is possible