A material function of endochronic theory is proposed for investigating the plastic behaviors of material. Depending on the material parameters properly chosen, the present model can be classified into four categories, and is appropriate for describing various materials behaving cyclic strain hardening inherently with respect to the deformation history. Experimental verification of the theory was demonstrated using the experimental results of Shiao [1] and Lamba and Sidebottom [2]. The theory is in good agreement with experimental results obtained by Shiao [1] through comparing the stress-strain hysteresis loops of SAE 4340 steel under axisymmetrically cyclic loading condition with various amplitudes. In addition, the present model is shown to be capable of describing the behavior of erasure of memory of materials, as experimentally observed by Lamba and Sidebottom [2].

The problem of a semi-infinite propagating crack in the piezoelectric material subjected to a dynamic anti-plane concentrated body force is investigated in the present study. It is assumed that between the growing crack surfaces there is a permeable vacuum free space, in which the electrostatic potential is nonzero. It is noted that this problem has characteristic lengths and a direct attempt towards solving this problem by transform and Wiener-Hopf techniques [1] is not applicable. This paper proposes a new fundamental solution for propagating crack in the piezoelectric material and the transient response of the propagating crack is determined by superposition of the fundamental solution in the Laplace transform domain. The fundamental solution represents the responses of applying exponentially distributed loadings in the Laplace transform domain on the propagating crack surface. Exact analytical transient solutions for the dynamic stress intensity factor and the dynamic electric displacement intensity factor are obtained by using the Cagniard-de Hoop method [2,3] of Laplace inversion and are expressed in explicit forms. Finally, numerical results based on analytical solutions are calculated and are discussed in detail.

Based the previously published model on the two-dimensional micromechanical fiber interaction framework of two-phase composites, effective transverse elastic properties of composites containing two types of randomly located yet unidirectionally aligned circular fibers are studied in this paper. Approximate local solutions for the interaction problem of two randomly located circular fibers of different elastic properties are presented. A fiber-reinforced composite material containing two extreme types of inclusions, voids and rigid fibers, is also investigated. Comparison with Hashin's variational bounds and Mori-Tanaka method, the current approach provides reasonably accurate predictions for three-phase composites. Finally, numerical simulation examples are implemented to demonstrate the capability of the proposed model.

This paper provides 41 cubical triaxial test results to examine the influence of the stress path angle and the improvement ratio on the anisotropic strength of the composite soil specimens consisting of remolded soft clay and grout columns. Pictures of failed samples shown in this paper are especially enlightening in demonstrating failure mechanisms. Results from this study can be summarized as follows. The composite soil specimens exhibited different failure patterns depending on the stress path angle, axial compression failure for 0°, 30° and 60°; lateral compression for 120° and 150°; and axial extension for 90° and 180°. Consistently, diagonal shear cracks through the grout column were observed for axial compression failure samples. On the other hand, tension cracks were observed for samples which failed due to lateral compression and axial extension. The composite soil specimens exhibited apparent anisotropic behavior. In general, the anisotropic strength ratio increased with the improvement ratio. The equivalent strength formula commonly used in practice may give erroneous results, especially when the stress paths are those of tension failure. In such a case, the anisotropic strength ratio suggested in this paper can significantly improve its accuracy.

Practically all retaining walls may rotate, yet movements of the wall could be restricted, particularly under working conditions. Since the earth pressure on the retaining wall often deviates from the fully active state, there is a need for predicting the earth pressure at any wall movement. The shearing behavior of backfill behind the wall plays an essential role for predicting the redistributions of earth pressure for different wall movements. This paper studies 25 sets of test for analyzing the drained lateral extension behaviors of saturated Ottawa sand. Three methods are used to interpret the active state of specimens and it is found that the monotonic increasing property of the σ'cs – εrp plot obtained by using the (q')max method is more obvious than those obtained by the other two methods. Where σ'cs is an initial confining stress of specimen for lateral extension test, and εrp is a radial strain of specimen developed at the active state. The specimens, with the relative density between 15% ∼ 90% and with the confining stress between 80kPa ∼ 280kPa, range their values of εrp from −1.18% to −2.99%. The magnitude of εrp can be used to judge the secure level of deformation for a retaining structure. Subsequently, this study derives a formula to predict the redistribution of earth pressure on a retaining wall when the wall moving outwards based on the results of those lateral extension tests. This prediction method is a new approach to study the problems of earth pressure. Comparisons of predicted results from numerical solutions technique and observations from model tests show that the performance of this method is reasonable.

This paper emphasizes on determining the mechanical and electrical damages of piezoelectric ceramics with periodically distributed ellipsoidal or spherical microvoids. Based on the unit cell method, detailed three-dimensional finite element analyses are carried out to acquire the effective electromechanical properties of voided PZT-7A materials, and then the mechanical and electrical damages are determined through the relations between the damage variables and the effective properties in the continuum piezoelectric damage constitutive theory. The quantitative connections between the damages and microstructure parameters, including the microvoid volume fraction and the microvoid aspect ratio, are analyzed in detail. Some interesting conclusions are obtained.

In this paper, a locally implicit scheme on unstructured dynamic meshes is presented to study transonic turbulent flows over vibrating blades with positive interblade phase angle. The unsteady Favre-averaged Navier-Stokes equations with moving domain effects and a low- Reynolds-number k-ε turbulence model are solved in the Cartesian coordinate system. To treat the viscous flux on quadrilateral-triangular meshes, the first-order derivatives of velocity components and temperature are calculated by constructing auxiliary cells and Green's theorem for surface integration is applied. The assessment of accuracy of the present scheme on quadrilateral-triangular meshes is conducted through the calculation of the turbulent flow around an NACA 0012 airfoil. Based on the comparison with the experimental data, the accuracy of the present approach is confirmed. From the distributions of magnitude of the first harmonic dynamic pressure difference coefficient which include the present solution and the related experimental and numerical results, it is found that the present solution approach is reliable and acceptable. The unsteady pressure wave, shock wave and vortex-shedding phenomena are demonstrated and discussed.

Coal pyrolysis and gasification incorporating synthesis gas (syngas) combustion are investigated experimentally in the present study. Two different coals are considered; one pertains to high-volatile bituminous and the other low-volatile one. For the pyrolysis, using thermogravimetry in association with mass spectrometry reveals that the concentrations of CO and CO2 increase with increasing temperature, whereas those of H2 and CH4 undergo increase followed by decrease. Regarding the gasification, the formations of the four gases between the two different coals are similar. However, when the reaction temperature is relatively low such as 800°C, carbon reactivity of the low-volatile coal decays in a significant way. Furthermore, with the reaction temperature of 1000°C the entire gasification histories of the two coals can be divided into five periods in accordance with syngas combustion. They are initiated, growing, rapidly decaying, progressively decaying, and frozen periods, sequentially. The flame is wrinkled in the growing and rapidly decaying periods where the reaction strength is much higher than that near extinction. When the reaction temperatures are 800 and 900°C, the growing and rapidly decaying periods tend to wither. Recognizing the syngas combustion characteristics, one is capable of figuring out the coal gasification process in more detail.

This work explores the sound transmission loss provided by the orthotropic multi-layers to elucidate the sound insulation of FRP (Fiber Reinforced Plastics). Mat is the major material considered in the numerical works. The transfer matrices of a single layer of the orthotropic laminate and the fluid are determined. Further, the boundary conditions on the various interface planes are arranged into matrix form. Combining the transfer matrixes and the boundary conditions and applying the transfer matrix method (TMM) yields the surface impedance and the sound transmission loss. The sound-propagation characteristics are studied. Additionally, the STC (Sound Transmission Class) of FRP and steel are compared and discussed.

This paper presents a complete approach to characterize physical aging in long term creep of composite laminates using short term creep test. Carbon/epoxy composite IM7/977−3 was use to make the coupon specimens of unidirectional fiber orientation and symmetrical laminates. Creep tests were conducted on the specimens to obtain momentary compliances at isothermal conditions. Physical aging in elastic and in creep compliances were modeled respectively. Momentary creep compliances in various aging times were shifted to superpose a reference curve by introducing shift factors for both relaxation time and shape factor of a power law model. Linear relations between shift factors and aging time in log-log scale were found and defined as shift rates. By using reference curve associated with the shift rates, momentary creep compliance in any given aging time can be predicted. By introducing a time dependent shift factor, momentary creep compliance can be modified and turned into an effective time model, which can successfully predict the long term creep of composite laminates at isothermal aging. This approach only requires the test data of momentary creep, and no material properties in each lamina are needed.

A soil-structure system associated with a semi-infinite structure such as tunnel or pavement is usually investigated by finite element analysis. If the boundary of the finite element model selected is not far enough from the excitation source or does not have an appropriate energy-absorption mechanism, it may introduce a significant error induced by reflected waves. This study develops a structural transmitting boundary to absorb the transmitting energy at the boundary of the analytical model. The structure is divided into finite and semi-infinite regions. The stiffness of the semi-infinite region is established by the principle of virtual work and applied at the transmitting boundary. The comparisons of the structural displacements induced by vertical harmonic excitations show that the analytical model size can be significantly reduced, if the proposed transmitting boundary is used to simulate the semi-infinite structural region.

Since a long-term oscillation of a tuned mass damper (or TMD) in vibration control may impair the spring stiffness of the TMD, this phenomenon will directly down-tune the target frequency of the TMD. For this reason, this study intends to present a string-type tuned mass damper (or STMD) with an adjustable tuning frequency to mitigate the resonant response of a simple beam due to moving loads. The STMD device is installed inside the inner room of a bridge box girder and is composed of a distributed spring-dashpot-mass with a stretched string. Considering a linear beam-STMD model, a generalized two-degrees-of-freedom system is employed to determine the optimum tuning frequency condition and parameters of the STMD in vibration control. Compared with a traditional TMD device, the proposed STMD has the advantage of being adjustable in tuning frequency. From the numerical examples, the results indicate that the proposed STMD is a potential vibration control device in suppressing the train-induced vibration of railway bridges. Even though the tuning frequency of the STMD down-deviate from the target one by 10%, the control effectiveness of such a detuning STMD can still achieve about 90% as that of an optimal STMD by tuning its frequency to fit the optimum tuning frequency condition presented in this study.

Finite Element Modeling was used to compare the efficacy of common screw-plate configurations used for fixation of parasymphyseal fractures of the mandible. Measures of Von Mises stress on the screw bone interface, as well as principal strain in the reduced fracture region, were used in this comparison. This study also explored differences between orthotropic and isotropic modeling practices and compared the effect of mastication forces on both the fractured and intact halves of the mandible. The results of this analysis showed no major differences between configurations from a mechanistic point of view. This suggests that the use of any of the studied screw-plate configurations will not increase chances for post-operative complications. Furthermore, little difference is seen between analyses with either orthotropic or isotropic material properties. The inclusion of orthotropic properties can thus be avoided in future studies with similar boundary and plating conditions. Mastication ipsilateral to the fracture increases Von Mises stress 2 to 4 times, and should be avoided during early healing periods. These recommendations only apply to patients whose fractures mimic the finite-element model.

An analytical model for determining the shear strength of concrete pile caps under the failure mode of diagonal-compression originally based on the softened strut-and-tie model is proposed. The failure probabilities of reinforced concrete pile caps are investigated by Monte Carlo method. The results indicate that the proposed model can accurately predict the shear strength of the pile caps. The distribution of the failure probabilities for pile caps designed to ACI 318-02 Appendix A and the proposed design method are more uniform than that designed to the ACI 318-99. The ACI 318-99 is very conservative and cannot provide a consistent safety for pile caps design. It is suggested that the procedures in the ACI 318-02 Appendix A should be moved to the main body of ACI 318-02 and the proposed design method should be incorporated into the current reinforced concrete pile cap design methods.

There are many investigations on surface acoustic wave (SAW) filters with interdigitated interdigital transducers (IIDT) in the last two decades; however, the same is not true for the case of IIDT SAW filters fabricated on layered piezoelectric substrates. Therefore, the aim of this study is to explore the characteristics of the IIDT structures on layered piezoelectric media and further, to improve the frequency response of layered IIDT SAW filters with the unique dispersive properties of a layered piezoelectric structure. A method based on the effective permittivity approach, the coupling of modes (COM) model, and the H-matrix is utilized to analyze the characteristics of IIDT on the ZnO/Diamond/Si layered structure. In this study, it is shown that by optimizing the ratio of input to output IDT pairs, the side-lobe level of frequency responses on the ZnO/Diamond/Si layered structure could be suppressed, similar to that on the half-space substrate. In addition, it is also proved that the notched pass-band could be flattened out by designing the center frequency on the local maximum of the electromechanical coupling coefficient dispersion curve.

The elastic-plastic microcontact model of a sphere in contact with a flat plate is developed in the present study to investigate the effect of surface roughness on the total contact area and contact load. From the study done by the finite element method, the dimensionless asperity contact area, average contact pressure, and contact load in the elastoplastic regime are assumed to be a power form as a function of dimensionless interference (δ/δec). The coefficients and exponents of the power form expressions can be determined by the boundary conditions set at the two ends of the elastoplastic deformation regime. The contact pressures evaluated by the present model are compared with those predicted by the Hertz theory, without considering the surface roughness and the reported model, including the roughness effect, but only manipulating in the elastic regime. The area of non-zero contact pressure is enlarged if the surface roughness is considered in the microcontact behavior. The maximum contact pressure is lowered by the presence of surface roughness if the contact load is fixed. Under a normal load, both the contact pressure and the contact area are elevated by raising the plasticity index for the surface of the same surface roughness.

This paper present a new method called the interval factor method for the finite element analysis of truss structures with interval parameters. Using the interval factor method, the structural parameters and loads can be considered as interval variables, and the structural stiffness matrix can then be divided into the product of two parts corresponding to its deterministic value and the interval factors. The computational expressions for lower and upper bounds, mean value and interval change ratio of structural placement and stress responses are derived from the static governing equations by means of the interval operations. The effect of the uncertainty of the structural parameters and loads on the structural static responses is demonstrated by truss structures.

This work focuses on studying the effect of flow velocity on microcantilever-based biosensor by numerical simulation. The microcantilever sensors used in detecting biomolecules have attractive advantages like cost efficiency, real-time and ability of fabricating in array. Both rectangular and triangular shapes of a general model of microcantilever beam are considered. Several important physical phenomena are obtained. Comparing with the first order Langmuir theory, we have calculated the effect on the reactive rate, produced concentration, the distribution of concentration and deflection in the z axis by solving these physical coupled problem involving flow field, concentration field and chemical reaction on the reaction surface. It is found numerically that the transportation of analyte, reactive rate, the distribution of concentration and deflection in the z axis are all effected by changing the flow velocity. The result has shown that flow velocity is an important factor for this biosensor.

The aim of this paper attempts to apply the differential quadrature (DQ) method for solving two-dimensional natural convection in an inclined cavity. The velocity-vorticity formulation is used to represent the mass, momentum, and energy conservations of the fluid medium in an inclined cavity. We employ a coupled technique for four field variables involving two velocities, one vorticity and one temperature components. In this method, the velocity Poisson equation, continuity equation, vorticity transport equation and energy equation are all solved as a coupled system of equations so as to we are capable of predicting four field variables accurately. The main advantage of present approach is that coupling the velocity and the vorticity equations allows the determination of the boundary values implicitly without requiring the explicit specification of the vorticity values at the boundary walls. A natural convection in a cavity with different angle of inclinations for Rayleigh number equal to 103, 104, 105 and 106 and H/L aspect ratios varying from 1 to 3 is investigated. It is shown that with the use of the present algorithm the benchmark results for temperature and flow fields could be obtained using a coarse mesh grid.

In this paper, an exergetic efficiency optimization method that combines the concept of exergy and finite-time thermodynamic theory is developed to analyze an irreversible heat engine. With the total thermal conductance constraint, the analytical solutions of optimal allocation of thermal conductance and the corresponding maximum exergetic efficiency, thermal efficiency, as well as operating temperatures of hot and cold sides are obtained under a fixed overall heat supply rate. The results show that the exergetic efficiency optimization method can effectively analyze an irreversible heat engine.