Implementation of periodic boundary conditions for loading of mechanical metamaterials and other complex geometric microstructures using finite element analysis

The implementation of periodic boundary conditions (PBCs) is one of the most important and difficult steps in the computational analysis of structures and materials. This is especially true in cases such as mechanical metamaterials which typically possess intricate geometries and designs which makes finding and implementing the correct PBCs a difficult challenge. In this work, we analyze one of the most common PBCs implementation technique, as well as implement and validate an alternative generic method which is suitable to simulate any possible 2D microstructural geometry with a quadrilateral unit cell regardless of symmetry and mode of deformation. A detailed schematic of how both these methods can be employed to study 3D systems is also presented.

     

Composites with needle-like inclusions exhibiting negative thermal expansion: A preliminary investigation

In this work a simple cylindrical structure with a stiff needle-like inclusion embedded within a much softer matrix is presented and analysed with the aim of obtaining a system with tunable thermal expansion properties. It is shown that by the correct combination of the thermal and mechanical properties of the matrix and inclusion, it is possible to design a system which can be tailor-made to exhibit particular values of the coefficient of thermal expansion (CTE) in the radial direction and also negative thermal expansion (NTE). In particular an analytical model to quantify the radial strain with changes in temperature is derived and verified through finite element analysis. The model is used to find correct property combinations which lead to particular values of thermal expansion which could also be negative or zero.     

Regenerator research, development and applications in Australia - 1978 status

Energy and cost savings by regenerative heat recovery in air-conditioning systems in Australia are potentially greatest in the humid tropical regions using total heat regenerators, while sensible heat regenerators are satisfactory for use in southern regions.A sensible heat regenerator with a matrix made from polyester film was evolved by CSIRO, and is being manufactured commercially in Melbourne and used in southern Australia. A total heat regenerator with a matrix made from wool-nylon ribbon is being developed by CSIRO. Satisfactory performance has been obtained, but carry-over and face area for given capacity are excessive at this stage.     

The analysis of warpage in wafer-level compression molding

Advanced 3D MEMS packaging technologies involving the encapsulation of devices at wafer-level are being developed in order to achieve further minimization and cost reduction of consumer electronic devices. Compression molding using epoxy molding compounds is one technique being considered for wafer-level encapsulation. Excessive out-of-plane deformation has been reported in wafer-level compression molding trials using blank wafers which would negatively impact device reliability and the implementation of successive processes to the molded wafer. This paper presents finite element models of the molded wafer, with and without embedded dies which simulate the observed multi-state warpage characteristics. Molded wafer warpage measurements were also carried out in order to verify the applicability of the small and large deformation theories for layered plates and to verify the finite element model of the molded blank wafer. Possible factors (non-planar mold layer thickness and anisotropic wafer elastic properties) leading to asymmetric warpage in molded blank wafers were also investigated. From the molded wafer model with embedded dies the effects of flip-chip die dimensions and wafer thickness on the out-of-plane deformation together with possible reliability issues were analyzed.

     

A new design of the esophageal Wallstent endoprosthesis resistant to distal migration

OBJECTIVE: Because plastic-covered metallic stents used in the palliation of patients with unresectable esophageal cancer are associated with significant rates of migration, particularly when the lower end of the stent projects into the gastric fundus, the purpose of this study was to establish whether two new prototype designs of the Wallstent esophageal endoprosthesis are prone to migration. SUBJECTS AND METHODS: A cylindrical stent and a conical stent were studied. Both designs included plastic covering inside the metallic mesh. In addition, the conical device incorporated a variation in the braiding angle between the upper and lower parts of the endoprosthesis. Ten conical stents and eight cylindrical stents were inserted in 18 patients with tumors involving the gastroesophageal junction who were followed up with esophagography and endoscopy. RESULTS: All insertions of stents were successful. Two cylindrical stents (25%) migrated distally. Two conical stents (20%) migrated proximally. One perforation occurred that was associated with distal migration of a cylindrical stent. CONCLUSION: The frequency of distal migration of cylindrical stents is unacceptably high. Conical stents are resistant to distal migration, although improvements in design are required to deal with the problem of proximal migration.     

Experimental investigation of N-MOS inversion layers in the electric quantum limit

In this paper we report on the experimental determination of inversion electron charge density, silicon surface potential, and effective electron mobility vs oxide electric field, for NMOSFETs with gate oxide thickness Tox = 2.2 nm operating far beyond the limit of applicability of Boltzmann relationships in the inversion layer. We find that such oxides have the same values of destructive breakdown electric field, dielectric constant, and trap density at the silicon-oxide interface as “thick” oxides.     

Morphology and continuity development in highly reactive nanoscale polymer blends

This work examines the effect of the extent of reaction on morphology, continuity development and cocontinuity in highly reactive nanoscale blends of brominated poly(isobutylene-co-p-methylstyrene) (BIMSM) and polyamide (PA) containing different amounts of plasticizer. The reactive melt blending protocol used is shown to be very effective in generating fine droplets in the 50-80 nm range scale, as observed by atomic force microscopy, and producing high amounts (about 46%) of graft copolymer. The amount is even higher (about 57%) for plasticized blends. It can be seen that the reaction between the elastomer and PA shifts the percolation thresholds and overall continuity development in the system to higher concentrations, but no effect is observed on the concentration region of dual-phase continuity.When a plasticizer is added to the PA, and it is the matrix phase, elastomer continuity development and cocontinuity shifts to higher concentrations. This is a result of both the increased extent of reaction in the presence of a plasticizer and the lower viscosity of the PA phase. When plasticized PA is the dispersed phase, however, these two phenomena oppose each other. The increased extent of reaction shifts plasticized PA continuity development to even higher concentrations in the blend, but the lower viscosity of the plasticized PA phase shifts the continuity development to lower PA phase concentrations. The net effect is that no change is observed on PA phase continuity with addition of plasticizer in an elastomer matrix.It is found, overall, that the dominant factor in controlling the dispersion of higher concentrations of elastomer into the PA phase is the extent of reaction between BIMSM and polyamide.