This paper is concerned with an application of the homotopy boundary element method originally proposed by Liao and Chwang to the analysis of nonlinear transient heat conduction in anisotropic solids. Usually, domain integrals arise in the boundary integral equation of this formulation. Some ideas are needed to keep the boundary-only feature of BEM. In this paper, the resulting domain integrals are transformed into boundary integrals by the dual reciprocity method using a new set of radial basis functions. The mathematical formulations of this approach for two-dimensional problems are presented in detail. Two schemes are discussed in this paper: the “isotropic” scheme, in which the state before mapping is considered as steady-state heat conduction in isotropic solids; and the “anisotropic” scheme, where the state before mapping is considered as steady-state heat conduction in anisotropic solids. The proposed solution is applied to some typical examples, and the accuracy and other numerical properties of the proposed BEM are demonstrated through discussions of the results obtained.
In a recent experiment, Zhang and co-workers found that a flexible filament in a flowing soap film can exhibit three states; stretched-straight, flapping, and bistability. When this experimental model is regarded as a one-dimensional flag in a two-dimensional fluid flow, their findings contradict the common idea that flags always flap in a wind. In this paper, the flag-in-wind problem is simulated by fluid-structure interaction finite element analysis where Navier-Stokes equations based on the ALE method are strongly coupled with Lagrangian equilibrium equations of the structure. In the simulation the three states are successfully reproduced, and the effects of some representative parameters on the amplitude and frequency of the oscillations are investigated to reveal the underlying mechanism involved in flag flapping.
Thermo-mechanical behavior in a rod subjected to a pulsed heat input was investigated by numerical simulation using the hyperbolic thermo-elasticity theory derived from the thermal dynamics in the present paper. Unlike the classical thermo-elastic theory with the parabolic energy equation and the hyperbolic motion equation, temperature response and thermal stress due to the temperature change exhibit significant wavy characteristics in the hyperbolic thermo-elasticity theory which is based on the non-Fourier heat conduction. The whole region of the rod is split into the heat disturbed region and the heat undisturbed region by the thermal wave front which is determined by the propagating velocity of the heat wave. The heat wave and elastic wave travel in the body at a finite velocity and reflect at the end of the rod. Thermal shock due to the discontinuous jump in thermal condition, and the reflection of thermal stress at the end terminate of the rod are significant during the heating process.
This paper describes the results of our numerical and experimental studies of the nonlinear bending behavior due to domain wall motion in functionally graded piezoelectric actuator under alternating current electric fields. A nonlinear three-dimensional finite element method is employed to simulate the dynamic response of cantilever functionally graded piezoelectric actuator. A phenomenological model of domain wall motion is used in computation, and the effects of ac electric field amplitude and frequency, number of layers, and property gradation on the deflection and internal stresses of the functionally graded bimorphs are examined. It is shown that the predicted deflection results, obtained from the numerical model, agree well with the corresponding experimental results.
The equations for the extended Lord-Shulman (LS) and Green-Lindsay (GL) models are solved for thermoelastic analysis in a semi-infinite medium by employing a finite element method using the theory of virtual displacement and the implicit Newmark algorithm. Simulations for both one-dimensional (1D) and two-dimensional (2D) models are performed to achieve the best approximation under prescribed boundary conditions. The effects of thermoelastic coupling factors and relaxation parameters on thermomechanical behavior of the medium are discussed for the two models. The results are consistent with our previous work using the Laplace transformation method.
PZT piezoelectric thin films can be promising candidates for microactuators or microsensors in MEMS (Micro Electro Mechanical Systems) or NEMS (Nano Electro Mechanical Systems) because of the quick response. In this research, the RF magnetron sputtering method is used for PZT thin films deposition. The sputtering conditions to control the crystalline plane (111) of perovskite structure for PZT to influence the piezoelectric constant can be proposed. Those sputtering conditions such as substrate angle and temperature, Ar/O2 pressure and flow rate were investigated by the heuristic and experimental design method to fabricate optimum PZT perovskite crystal thin film. The condition of substrate temperature was the most important factor to improve piezoelectric constant. The crystalline structure, surface topography and piezoelectric constant of the deposited PZT were observed by X-ray diffraction structural analysis, atomic force microscope and piezoelectric constant evaluation equipment. PZT thin films with only perovskite structure were obtained. PZT (111) was grown with the increase in substrate temperature, and the piezoelectric property was improved. The elastic modulus of 70GPa for the deposited PZT found a good agreement with the quoted value for commercial based bulk PZT. We obtained a piezoelectric constant d31=-28pm/V and a high performance of bimorph actuator.
Macroscopic ferroelectric properties of piezoelectric polycrystals are strongly affected by microscopic inhomogeneous crystal structure. In our previous study, a multi-scale finite element method based on crystallographic homogenization method has been developed to estimate macroscopic properties considering microscopic crystal morphology. In this paper, the crystal orientation distribution of polycrystalline barium titanate has been measured by SEM·EBSD technique, and the measured crystal orientation distribution has been introduced to the microscopic finite element model. As the prediction of macroscopic properties depends on the sampling conditions of the measured crystal orientations, the effects of number of sampling points and sampling area have been investigated. As a result, the effective sampling conditions have been clarified to estimate macroscopic ferroelectric properties.
In order to improve the material characteristics of single and polycrystals of pure aluminum, the relationships between crystallographic orientations and microstructures, and the mechanical properties were examined. Several conventional grain-forming procedures, such as accumulative roll bonding (ARB), equal-channel angular pressing (ECAP) and accumulative forging bonding (AFB), were performed to obtain the ultrafine-grained structure. Furthermore, some analytical results, such as crystal direction maps, inverse pole figure (IPF), and texture, were obtained from the SEM-electron backscattered diffraction pattern (EBSP). As a result, (1) for the ARB method, increases of strength and ductility were shown, since the cube orientation was developed; (2) for the ECAP method, in the extrusion direction (ED) plane at the die angle Ψ=100°, peculiar distributions of microstructure and hardness were obtained; (3) for the AFB method, stratified inclination microstructures were obtained, and thus the typical texture was also observed.
Solder joints between a package and a printed wiring board (PWB) of a portable electronic device sustain heat cycling as a result of power on-off operations, cyclic bending by key pad operation, and impact bending by dropping. Therefore, heat cycling, cyclic bending, and cyclic impact bending tests were conducted on the ball grid array solder joints between a chip scale package and a PWB. The evaluated solders were Sn-3Ag-0.5Cu and Sn-37Pb. The tests showed that the life cycles of the Sn-3Ag-0.5Cu solder joints for the heat cycling and cyclic bending tests were approximately twice those of the Sn-37Pb solder joints. For the cyclic impact bending test, however, the life cycle of the Sn-3Ag-0.5Cu joint under large strain was smaller than that of the Sn-37Pb solder joint because of interfacial crack growth between the solder and the PWB. Finally, fatigue lives of the joints were compared with crack initiation and failure lives of plain specimens by calculating local strain ranges in the joints by elastic-plastic finite element analysis.
The effect of in-situ formation of reinforcing phase on the mechanical properties of FeAl intermetallic alloy was studied. The in-situ FeAl composites containing Al2O3 or Fe3AlC were fabricated by mechanical alloying of elemental powders and mill scale powder followed by vacuum hot pressing. The starting materials were mixed in the appropriate ratio to synthesize 10vol% of the reinforcing phase. FeAl+Al2O3 and FeAl+Fe3AlC alloys showed high hardness value of HV813 and HV524, respectively. The effect of testing temperature on the 0.2% proof stress was evaluated at the temperature range from room to 1273K under compression. FeAl+Al2O3 and FeAl+Fe3AlC alloy showed proof stress of 2240MPa and 1380MPa at room temperature, respectively. At higher temperatures above 773K the proof stress decreased rapidly. The FeAl base in-situ composites including Fe3AlC or Al2O3 showed the high stress exponent and activation energy in the temperatures range of 1073-1273K.
SiC ceramics are expected as oxidation resistant coating material for Carbon/Carbon (C/C) composites. In the present study, SiC ceramics were synthesized through Sol-Gel method with low environmental impact. The gels were synthesized from ethylalcohol, methyltriethoxysilane (MTES), hydrochloric acid (HCl) and purified water (H2O), and it was pyrolyzed at 1000, 1500 and 1700°C. The structures of gels after heat treatment were analyzed by X-ray diffraction (XRD). XRD results indicated that βup-SiC were obtained in the present method and crystallization was increased with increasing heat treatment temperature. There was little weight change in synthesized SiC obtained at 1000°C in air, which results in lower weight changes in SiC coated C/C composites comparing with bare C/C composites. However, SiC coated C/C composites were also oxidized because of the generation of cracks during heat treatment at 1000°C. Residual tensile strength of SiC coated C/C composites were also higher than that of bare C/C composites after 5 minutes oxidation.
In orthopedic field, various new treatments of articular cartilage defect, for example autogenous osteochondral grafts, have been developed. With the spread of these treatments, orthopedists began to focus on the mechanical properties of recovered articular cartilage. The quantitative evaluation of articular cartilage before and after these treatments gives orthopedists the important information to improve these treatments and develop new treatments. We have been investigating the non-contact ultrasonic evaluation for articular cartilage under arthroscopy. In this paper, it was hypothesized that the ultrasonic evaluation depended on the collagen fiber in cartilage. The enzymatically degradation of collagen fiber in cartilage surface was performed. The effect of the degradation on sound velocity, attenuation coefficient and signal intensity, which is the index of cartilage stiffness calculated from the proposed method, was measured. The numerical analysis was performed to clear the relation between the cartilage character and ultrasonic parameters. Experimental and numerical results suggest that the present method can be expanded the sensitive evaluation for cartilage disease in clinical field.
In this study, thermal singular stresses in an elastic half-plane containing an infinite row of parallel cracks perpendicular to the boundary is considered. The half-plane is subjected to a uniform heat flux and a uniform mechanical load. The crack surfaces and free surface of the half-plane are maintained at uniform temperatures. The Fourier transform techniques are used to formulate the problem in terms of singular integral equations. The singular integral equations are solved by using the Gauss-Jacobi integration formula. Both the cases of an internal crack and an edge crack are studied. Numerical calculations are carried out, and the effects of the geometric parameters on the temperature-thermal stress distributions and the thermal stress intensity factors are shown graphically.
In this paper a new theoretical method is proposed for calculating the normalized contact duration and indentation depth in elastic, elastic-plastic and plastic collision of circular plates. The contact duration is composed of total loading time and unloading time that are dependent on the relationship between the interaction force and normal indentation. For plastic collision, the contact duration relates to the coefficient of restitution (COR) of the collision. Considering the actual thickness of a circular plate, a coefficient of indentation (COI) is newly introduced in theoretical analyses of the COR. According to experimental results of COR, a hybrid nonlinear model is also proposed to describe the COR of circular plates for obtaining the unloading time of the plastic collision. Contact force history during collision can be expressed approximately by a half-sine wave and the force and contact duration is calculated numerically.
By computer simulation, we examined how a wall or a floor of a container affects the random packing structure of a cubic aggregate of spherical particles. We constructed a model of the aggregate by sequential accumulation of spheres in a cubic box using (A) cyclic boundary conditions only in the y-direction together with random ups and downs of the box floor to estimate the wall effect and (B) the conditions in both of the horizontal directions to extract the floor effect. Using the obtained packing data, we estimated the “area porosities” and cumulative frequencies of the diameters of circles appearing on some cross sections created by cutting the aggregate at different levels, both as functions of distance from the wall/floor. From these results, we found that the surface effect seems to extend as deep as 2.5 particle diameters from the wall and approximately 4.5 diameters from the floor.
A robust optimal design of a bulk-micromachined, decoupled vibratory microgyroscope was carried out to determine geometric dimensions such that the gyroscopic performance is least affected by a fabrication tolerance. Electro-mechanical vibration analysis considering the sensing electrodes and the electronic signal processing were performed to obtain the frequency responses that influence the gyroscopic performance. A statistically distributed lateral over-etching (LOE) developed in the fabrication process was selected as a fabrication tolerance factor. The dimensions of the driving and sensing spring are selected as design variables which are the sum of deterministic mask dimensions and the LOE. To minimize the influence of LOEon the decoupled vibratory microgyroscope performance, the multi-objective function was formulated so as to minimize the sensitivities of the frequency difference with respect to the LOE. As a result, the standard deviation of the frequency difference and the driving natural frequency are reduced to 78% and 8%, respectively, through the Monte Carlos Simulation (MCS).
The objectives of this study are to introduce the use of a photodiode camera for measuring surface strain on soft tissue and to present some representative responses of the tendon. Tendon specimens were obtained from the hindlimbs of canines and frozen to -70°C. After thawing, specimens were mounted in the immersion bath at a room temperature (22°C), preloaded to 0.13N and then subjected to 3% of the initial length at a strain rate of 2%/sec. In tendons which were tested in two blocks of seven repeated extensions to 3% strain with a 120 seconds wait period between, the surface strains were measured with a photodiode camera and near the gripped ends generally were greater than the surface strains in the middle segment of the tendon specimens. The recovery for peak load after the rest period was consistent but the changes in patterns of surface strains after the rest period were not consistent. The advantages of a photodiode measurement of surface strains include the followings: 1) it is a noncontacting method which eliminates errors and distortions caused by clip gauges or mechanical/electronic transducers; 2) it is more accurate than previous noncontact methods, e.g. the VDA and the high speed photographic method; 3) it is a fully automatic, thus reducing labor for replaying video tapes or films and potential errors from human judgement which can occur during digitizing data from photographs. Because the photodiode camera, employs a solid state photodiode array to sense black and white images, scan targets (black image) on the surface of the tendon specimen and back lighting system (white image), and stored automatically image data for surface strains of the tendon specimen on the computer during cyclic extensions.