Applied Numerical Analysis. By C.F. Gerald. Pp. xii, 340. £3·60. 1970. (Addison-Wesley.)

Carbon nanotubes (CNTs) demonstrate remarkable electrical, thermal, and mechanical properties, which allow a number of exciting potential applications. In this article, we review the most recent progress in research on the development of CNT-polymer composites, with particular attention to their mechanical and electrical (conductive) properties. Various functionalization and fabrication approaches and their role in the preparation of CNT-polymer composites with improved mechanical and electrical properties are discussed. We tabulate the most recent values of Young's modulus and electrical conductivities for various CNT-polymer composites and compare the effectiveness of different processing techniques. Finally, we give a future outlook for the development of CNT-polymer composites as potential alternative materials for various applications, including flexible electrodes in displays, electronic paper, antistatic coatings, bullet-proof vests, protective clothing, and high-performance composites for aircraft and automotive industries.

Recent Advances in Research on Carbon Nanotube–Polymer Composites

Review of state of the art in smart rotor control research for wind turbines

This article presents an overview of the up-to-date developments in boron nitride nanotubes (BNNTs), including theory, fabrication, structure, physical properties, chemical functionalization and applications. Soon after the discovery of carbon nanotubes, BNNTs were theoretically predicted, followed by their successful fabrication by arc-discharge in 1995. Subsequently, various methods were developed for the BNNT synthesis, although till now, the growth of highly pure single-walled BNNTs at large quantities remains a challenge. The physical property investigations reveal that BNNTs’ exhibit a stable wide band gap, superb mechanical strength, high thermal conductivity, ultra-violet light emission, etc. All these properties build up the solid basis for their future technological applications. Chemical modification is also a decent approach to adjust the BNNTs properties. In recent years the yield of multi-walled BNNTs has reached the grams level, that can allow their detailed chemical functionalization studies. So far, many kinds of functionalizations through different weak interactions and covalent bonding were developed. These treatments improved BNNT dispersions in solvents and extended their fields of applications. Moreover, some application-related studies on multi-walled BNNTs, such as composites fabrication, hydrogen storage, biocompatibility, and mechanical, and electrical breakdown tests have also been started in recent years.

Boron nitride nanotubes

Knowledge of the elastic properties of Li–Si alloys as a function of Li concentration is crucial in the development of reliable deformation and fracture mechanics models for Si anodes in Li-ion batteries. Here, we have studied these properties using first-principles calculations for both amorphous and crystalline phases observed during lithiation of Si anodes. In the case of crystalline alloys, we present the anisotropic elastic tensors as well as the homogenized Young's, shear, and bulk moduli and the Poisson's ratios. We find that while these moduli decrease in an approximately linear manner with increasing Li concentration leading to significant elastic softening (by about one order of magnitude) in both crystalline and amorphous systems, the Poisson's ratios remain in the range of 0.05–0.20 and 0.20–0.30 in the case of crystalline and amorphous systems, respectively. Further, for a given Li concentration, we find that the amorphous structures are elastically somewhat softer than their crystalline counterparts, the difference being more significant (about 30–40%) in Li-poor phases. Our results underscore the importance of including the concentration dependence of elastic constants in the analysis of stress and deformation fields during lithiation and de-lithiation of Si anodes.

http://ma.ecsdl.org/content/MA2010-02/11/1135.full.pdf

Elastic Softening of Amorphous and Crystalline Li-Si Phases with Increasing Li Concentration: A First-Principles Study

Finite element analysis of the residual stress by cold expansion method under the influence of adjacent holes

Shape memory alloys (SMAs) have demonstrated the potential for various smart structure applications. SMAs undergo a reversible phase transformation from martensite to austenite as temperature increases. This transformation leads to shape recovery and associated recovery strains. If SMA actuators are embedded off the neutral surface and are oriented at arbitrary angles with respect to a beam axis, then the beam bends and twists due to the coupling effects of recovery strains activated. In this study, the shape changes by bending and twisting of a SMA/graphite/epoxy beam controlled by both electric resistive heating and passive elastic tailoring were investigated. Three-dimensional finite-element formulations were derived and validated to analyze the responses of the SMA/composite beam. Numerical results show that the shape of the SMA/graphite/epoxy composite beam can be controlled by judicious choices of control temperatures, SMA angles and elastic tailoring.

Shape changes by coupled bending and twisting of shape-memory-alloy-embedded composite beams

The squeal noise occurring from the disc brakes of passenger cars has been analyzed by using the complex eigenvalue method numerically. The contact between a disc and two pads was analytically modeled as many linear springs and dampers in an effort to develop the improved equation of motion derived on the basis of Lagrange’s equation and the assumed mode method. The finite element modal analysis results for disc brake components constitute an eigenvalue matrix in the analytical equation of motion. The complex eigenvalue analyses based on the equations of motion are able to examine the dynamic instability of a brake system, which is an onset of squeal, by considering the disc rotational effect. Numerical analyses showed that the modes unstable in an undamped analysis became stable in a damped case, which illustrates the important effect of damping on the squeal instability in a brake squeal simulation. Then several modified brake models were suggested and investigated how effectively they suppressed the occurrence of squeal noise. The brake parts such as a pad chamfer and a disc vane were modified and the influence of pad chamfer and vane shapes on squeal occurrence was proved to be significant. The numerical results showed that proper structural modification of a disc brake system can suppress the brake squeal to some extent.

Analysis of automotive disc brake squeal considering damping and design modifications for pads and a disc

The present study investigates the behavior and performance of the recently proposed LIPCA actuator. As such, a reliable finite element program that can predict the behavior of piezoelectric structures is developed based on fully-coupled formulations for piezo electric materials and three-dimensional eight-node incompatible elements. After verifying the proposed code, the actuation displacements of a LIPCA actuator are calculated and compared with experimental results, which were foundto be in goodagreement. Finally, a method for modeling the screw-fixed end condition used in the experimental apparatus is investigated along with effects of the curvature on the actuation displacement and fundamental frequency.

Behaviors and Performance Evaluation of a Lightweight Piezo-Composite Curved Actuator

A new design analysis method based on FEM and a topology optimization for piezoelectric materials was developed for the unimorph cantilevered energy harvesters which can produce the maximum electric power outputs. The optimum topology of a piezoelectric material layer on the harvesting beam has been calculated by considering natural frequencies of beams, electromechanical couplings of piezoelectric materials, tip masses and MMA (method of moving asymptotes). The piezoelectric coefficients such as elasticity, capacitance and piezoelectric coupling were interpolated by element density variables in the topology optimization. The optimum design method was verified by vibration tests and measuring voltage outputs of the harvester and a good correlation between two results has been obtained. The effects of beam geometric parameters and several piezoelectric materials (PZT, PVDF, PMN-PT and piezoelectric fiber composites) on power generation were also investigated. The beam with PMN-PT generated the largest voltage and the next largest is PZT, MFC and PVDF, respectively.

Cheol Kim

Papers

Finite element analysis of the residual stress by cold expansion method under the influence of adjacent holes

Shape changes by coupled bending and twisting of shape-memory-alloy-embedded composite beams

Analysis of automotive disc brake squeal considering damping and design modifications for pads and a disc

Behaviors and Performance Evaluation of a Lightweight Piezo-Composite Curved Actuator

Topology optimization of piezoelectric materials and application to the cantilever beams for vibration energy harvesting