bluuebunny/crossref_metadata_2025 huggingface dataset:
A Model of Damage and Creep Interaction in a Quasi-Brittle Composite Material Under Axial Loading
Authors: Taha M. M. Reda , Shrive N. G.
Published: May 2011

Creep is the time-dependent, viscoelastic strain observed in materials under constant stress. Creep can increase structural strains/deformations to non-serviceable levels or alter the stress distribution among structural components. While stress redistribution can be helpful in composite materials by relieving the stress on one component, it might have a detrimental effect on another, especially if it leads to overstressing.

A step-by-step in time approach for modeling creep in quasi-brittle materials such as concrete and masonry is utilized, and a new continuum damage model based on Weibull's failure rate distribution is introduced. A multiplicative approach to integrate the creep and damage effects within the step-by-step in time analysis is invoked. The significance of the proposed approach is exemplified through analysis of a clay masonry column filled with grout and subjected to concentric axial load. It is shown that the proposed approach can provide insights on the stress evolution in both components of the composite material that might not be inferred using classical methods of analysis.
A Note on the Transient Solution of Stokes' Second Problem with Arbitrary Initial Phase
Authors: Liu C.-M. , Liu I.-C.
Published: May 2011

The flow of a viscous fluid disturbed by an oscillating plate of arbitrary initial phase is studied in present note. The exact solutions of the velocity and the shear stress are solved using a Laplace transform method. The velocity is derived in terms of complementary error functions and the shear stress on the boundary is given in the form of Fresnel integrals. Since the steady-state solutions are well known, our discussions are focused on the transient solutions. The transient state will disappear faster for the wall stress than that for the velocity field. Comparing the results corresponding to different initial phases, the cosine case reaches to the steady state more rapidly than the sine case.
Anisotropic Strength Characteristics of Composite Soil Specimen Under Cubical Triaxial Conditions
Authors: Lin H.-D. , Chen W.-C.
Published: May 2011

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.
Characterizing the Sound Insulation of a Specially Orthotropic Multi-Layered Medium
Authors: Lin H.-J. , Wang C.-N. , Kuo Y.-M.
Published: May 2011

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.
Finite Element Analysis of Structures with Interval Parameters
Authors: Gao W.
Published: May 2011

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.
Application of Normalized Spectral Acceleration-Displacement (NSAD) Format on Performance-Based Seismic Design of Bridge Structures
Authors: Sung Y.-C. , Chang S.-Y. , Lai M.-C. , Lin T.-W. , Tsai I.-C.
Published: May 2011

For a bi-linear SDOF system subjected to a specific wave form of the ground acceleration, the unique yielding pseudo spectral acceleration and spectral displacement (Say, Sdy) together with various inelastic responses (Sai, Sdi) can be obtained via nonlinear time history analyses, respectively, by tuning the different levels of peak ground acceleration as various input ground motions. Meanwhile, the corresponding elastic responses (Sae, Sde) of a linear SDOF system with the identical mass, viscous damping and elastic stiffness as those of the bi-linear one can also be determined through linear time history analyses under the same excitations. The proposed NSAD format shown on the diagram of the elastic force ratio, Ω=Sae/Say I Say, versus the ductility ratio, (μ= (Sdi/Sdy), is a dimensionless plot of the seismic demands suitable to the engineers who are familiar with the conventional force-based design using linear structural analysis. In this paper, more than two hundred ground motions recorded in the Chi-Chi earthquake, Taiwan (1999) were chosen as the seismic inputs for the establishment of the NSAD format. The characteristics and applications of the NSAD format on the performance-based seismic design of the bridge structures were discussed, and realistic procedures for the methodology were proposed.

The results obtained shows that the NSAD format can help the engineers evaluate the multiple-level seismic demands not only with a well precision but also with a great convenience.
Design and Development of a Piezoelectric Actuator for the Scanning Probe Microscope Used in Ultrahigh Vacuum
Authors: Huang K.-Y. , Lee C.-J.
Published: May 2011

This paper is to present the design and development of a piezoelectric actuator for SPM in ultrahigh vacuum (10−7∼10−9 Torr). The measuring probe is installed on a precise scanning actuator, which is further driven by a fast approaching actuator. The precise scanning actuator composed of a piezo-tube with segmented electrodes can realize 3-D precise scanning motions at subnanometer level to move the measuring probe over the measured surface. Because of its stable and smooth actuating behavior, the inchworm actuating principle is selected for the fast approaching actuator, which is build up with two controllable clamping devices and an actuating device. Diverse flexure mechanisms are applied in the actuator to attain frictionless guiding and recovery functions. To realize balanced clamping forces on the scanning tube, each clamping device is integrated with a fine regulating mechanism for clamping force. By applying the theoretical model and the finite element analysis, the relations between force and deflection inside the actuator were investigated to validate its function. The developed actuator has sustained the severe baking and pumping process, and their function and performance were verified experimentally in ultrahigh vacuum.
Stability Analysis on Viscous Magnetic Fluid Film Flowing Down Along a Vertical Cylinder
Authors: Cheng P.-J. , Liu K.-C.
Published: May 2011

The paper investigates the hydromagnetic stability theory of a thin electrically conductive fluid film flowing down along the outside surface of a vertical cylinder. The long-wave perturbation method is employed to solve for generalized kinematic equations with free film interface. The normal mode approach is used to compute the stability solution for the film flow. The modeling results display that the degree of instability in the film flow is further intensified by the lateral curvature of cylinder. This is somewhat different from that of the planar flow. It is also observed that by increasing the effect of the magnetic field and increasing the radius of the cylinder the film flow can become relatively more stable as traveling down along the vertical cylinder.
A Material Function of Endochronic Theory and its Application to Test Under Axisymmetrically Cyclic Loading Conditions
Authors: Lin H.-Y. , Yeh W.-C. , Lee W.-J.
Published: May 2011

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].
Time Reversal Processing Effect on Foci Structure in a Dynamic Ocean Waveguide
Authors: Chiu Y. S. , Chen C.-F.
Published: May 2011

Time-reversal mirror (TRM) was recently developed for underwater communication system application. This technique has been introduced as an approach to compensate for signal distortion due to multiple path effect in ocean waveguide. TRM is used in this paper for sending a message signal in ocean waveguide, received at time-reversal-array (TRA), and retransmitted to the dynamic ocean environment with an internal solitary wave. The focal structures obtained from different simulating cases are used for bidirectional transmission expediency, and the TRA is used as the relay-line or trunked radio. Ocean waveguide characteristic effects on acoustical properties are also shown in this paper, and focal structure in different ocean environments is analyzed to provide an optimal approach to underwater communication systems and for physical insight's interests.
A Semi-Analytical Approach for Stress Concentration of Cantilever Beams with Holes Under Bending
Authors: Chen J.-T. , Chen P.-Y.
Published: May 2011

In the paper, the degenerate kernels and Fourier series expansions are adopted in the null-field integral equation to solve bending problems of a circular beam with circular holes. The main gain of using degenerate kernels in integral equations is free of calculating the principal values for singular integrals. An adaptive observer system is addressed to fully employ the property of degenerate kernels for circular boundaries in the polar coordinate. After moving the null-field point to the boundary and matching the boundary conditions, a linear algebraic system is obtained without boundary discretization. The unknown coefficients in the algebraic system can be easily determined. The present method is treated as a “semi-analytical” solution since error only attributes to the truncation of Fourier series. Stress concentration is also our concern. Finally, several examples, including two holes and four holes, are given to demonstrate the validity of the proposed method. The results are compared with those of Naghdi and Bird and Steele. Also, the position where the maximum concentration factor occurs is examined. The present formulation can be extended to handle beam problems with arbitrary number and various positions of circular holes by using the developed general-purpose program.
Propagation of Lamb Waves in Phononic-Crystal Plates
Authors: Hsu J.-C. , Wu T.-T.
Published: May 2011

In this paper, the band structures of Lamb waves in the two-dimensional phononic-crystal plates are calculated and analyzed based on the plane wave expansion method. The phononic-crystal plates are composed of an array of circular crystalline iron cylinders embedded in the epoxy matrix. Square lattice and triangular lattice are analyzed and discussed, respectively. For the square lattice, two complete band gaps exist, and a narrow pass band between the complete band gaps separates them apart. For the triangular lattice, a wide complete band gap existing with the ratio of gap width to midgap frequency Δω/ωm equal to 72% is found. Furthermore, the influence of the plate thickness is crucial for band structures of Lamb waves. Tuning plate thickness can shift the pass bands effectively, and band shifting causes the variation of the width of complete band gap and its opening and closure.
Determination of Mechanical and Electrical Damages of Piezoelectric Material with Periodically Distributed Microvoids
Authors: Yang X. H. , Zeng G. W. , Chen C. Y.
Published: May 2011

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.
Intelligent Genetic Algorithm with a Gradient-Based Local Search Applied to Supersonic Wing Planform Optimization
Authors: Liu J.-L. , Chen J.-L.
Published: May 2011

This study proposes an efficiently evolutionary algorithm, termed IGA-LS, which combines an intelligent genetic algorithm (IGA) with a gradient-based local search (LS). The IGA performs a crossover operation and uses a fractional factorial design to determine the optimal combination of design variables. That is, in the proposed IGA, the chromosomes of children are generated via an intelligent crossover process with factorial experiments after the execution of the selection operation of the GA. This gene mating process differs from that of the traditional GA, in which each chromosome of child exchange genes randomly. The gradient-based optimization approach seeks feasible and usable directions in which to minimize a specified objective function. The initial conditions are provided by the IGA in each generation. Therefore, the IGA-LS offers fast convergence and high numerical accuracy. Several multi-modal test functions are introduced herein to examine the algorithmic capacity and efficiency of finding the global optima. Moreover, the proposed IGA-LS algorithm is applied to optimize the design of a supersonic wing planform for supersonic airplane. The objective function is to minimize the drag during supersonic cruising. From the numerical results, the presented algorithm outperforms the traditional GA, the micro-GA and the intelligent GA in terms of convergence rate and value of the optimal function.
Elastic-Plastic Microcontact Analysis of a Sphere and a Flat Plate
Authors: Liou J. L. , Lin J. F.
Published: May 2011

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.
Rheological Characteristics for Thin Film Elastohydrodynamic Lubrication with Non-Newtonian Lubricants
Authors: Chu H.-M. , Chang Y.-P. , Li W.-L.
Published: May 2011

The modified Reynolds equation for power law fluid is derived from the viscous adsorption theory for thin film elastohydrodynamic lubrication (TFEHL). The differences between classical non-Newtonian EHL and non-Newtonian TFEHL are discussed. Results show that the proposed model can reasonably calculate the pressure distribution, the film thickness, the velocity distribution and the average viscosity under thin film lubrication. The thickness (δ), the viscosity (m1), and the flow index (n1) of the adsorption layer influence significantly the lubrication characteristics of the contact conjunction. Furthermore, the film thickness increases with the increase of n1 and the film thickness affected by m1 is greater than that affected by n1, but the effect of n1 produces a very small difference in the pressure distributions. In addition, the greater n1, the smaller the change of velocity distribution in the adsorption layer, and the greater the change of velocity distribution in the middle layer. The larger δ and n1, the larger the deviation on log (film thickness) vs. log (speed) produced in the very thin film regime. In the region of the flow index ratio between 1.0 and 1.3, the difference in film thickness is significant. When the flow index of the adsorption layer is 1.6 times greater than the flow index of the middle layer, the adsorption layer is generally looked upon as a “solid-like”.
Model and Parameters Identification of Non-Linear Joint by Force-State Mapping in Frequency Domain
Authors: Wang J.-H. , Huang H.-Y.
Published: May 2011

Generally, the Force-State Mapping (FSM) is an effective method to identify the parameters of nonlinear joints provided that the joint model is exactly known in advance. However, the variation of the non-linear joints is so large that the mathematical models of non-linear joints generally are not known in advance. Therefore, the model and the parameters of a non-linear joint should be identified simultaneously in practice. In this work, a new identification procedure which was based on the FSM method in frequency domain was proposed to identify the mathematical model and parameters of a non-linear joint simultaneously. Generally, there are many feasible combinations of models and parameters which can satisfy the measurement data within an allowable range of error. In this work, an iteration procedure was used to update the feasible models to result in an optimal model with its parameters. The simulation results show that a proper mathematical model and accurate parameters can be identified simultaneously by the new procedure even that the measurement data are contaminated by noise.
An Experimental Investigation on the Coalescent Behaviors of Colliding Droplets
Authors: Wang C. H. , Pan K. L. , Fu S. Y. , Huang W. C. , Yang J. Y.
Published: May 2011

The coalescent behaviors in collisions between two droplets respectively made of different alkanes, water and alkane, methanol and alkane, and ethanol and hexadecane were experimentally studied. The coalescent results between two droplets of different alkanes are qualitatively the same as that with the same material, which simply form a spherical droplet. However, it took time to have the concentration within the droplet to become uniformly distributed. The collision results of water and alkane droplets collision become slightly more complex, in most cases, the water droplet was either inserted into or adhesive to the hexadecane droplet while only insertion was observed if the target droplet was dodecane or heptane. The inserted water droplet tends to partially expose to the environment as the volume fraction of water is sufficiently high, say, ∼0.62 for hexadecane, > 0.70 for dodecane, and > 0.78 for heptane; and the limit is lowered with the decreasing of water or merged droplet size. For the cases of methanol and alkanes, and ethanol and hexadecane, the two colliding droplets were adhesive to each other in all the studies. Furthermore, in most conditions, air bubbles were observed immediately after the collisions, while only few or even none of them might be trapped within the final merged droplet.
Calculations of the Meniscus Force and the Contact Force Formed in the Microcontacts of a Rough Surface and a Smooth, Rigid Surface with a Thin Water Film
Authors: Lin J. F. , Chen S. C.
Published: May 2011

A present model is developed to calculate the adhesion meniscus force due to a rough surface with surface asperity in contact with a smooth, rigid flat covered by a thin water film. The original thickness of this film before surface contacts is dependent upon the relative humidity in the air. Microcontact deformations of surface asperities in the elastic, elastoplastic, and fully plastic regimes are included in the present model under a normal load. The new water film thickness under the condition of microcontact deformations is considered changing with the normal load, and it is obtained from the equation developed on the basis of the volume conservation principle for the new film thickness and the water film volume displaced by the asperities heights dipping in the film. The meniscus profile is also calculated from the balance of the surface tension force and the pressure difference force across the meniscus profile if the new film thickness is available. Water film thickness and the meniscus force are increased by decreasing the mean separation of two contact surfaces, or increasing the relative humidity, or increasing the plastic index. A significant difference in the meniscus force is found between the present model and the model of the literature, which is enhanced by either decreasing the mean separation, or raising the plasticity index, or increasing the relative humidity. The effects of the meniscus force on the load capacity are also evaluated at different mean separations, relative humidity and plasticity indices.
The Mechanics of Cervical Muscle Recruitment on Cervical Spine Stability —A Biomechanical in Vitro Study using Porcine Model
Authors: Cheng C.-H. , Chen T.-Y. , Kuo Y.-W. , Wang J.-L.
Published: May 2011

Cervical muscles are crucial in providing the stability of the cervical spine. Many in vitro studies have investigated the relationship between muscle force and stability directly. However, the effects of different muscle dysfunctions or muscle recruitments on cervical spine stability are not yet clear and therefore, worthy of study. A spine testing apparatus with muscle force replication activated by pneumatic cylinders was developed to find the effect of muscles on spinal stability. Seven porcine cervical spines (C2-T1) were used. Three pairs of cervical muscles, including neck flexors (sternocleidomastoid, SCM) and neck extensors (splenius capitis, SPL; semispinalis capitis, SSC), were simulated. The experimental tests included: 1. no muscle recruitment, 2. full muscle recruitments, 3. SCM dysfunction, 4. SPL dysfunction, and 5. SSC dysfunction. The external pure moment in sagittal plane was applied from 0 Nm to 2 Nm to examine the stability/flexibility of specimens. The spinal stability was evaluated by the neutral zone (NZ), the range of motion (ROM), the reduced NZ (R_NZ), and the reduced ROM (R_ROM). Loading responses of C7-T1 disc were also measured. The results of this study showed: The activation of cervical muscles decreased the NZ and ROM. The degree of decrease among different muscle dysfunctions, however, was not significantly different. The SPL dysfunction induced larger anterior shear force, while the SCM dysfunction exclusively induced extension moment. In conclusion, the muscle forces could stabilize the cervical spine, but significant decrease in spinal stability was not found among dysfunctions of different muscles. The SCM and SPL dysfunction may result in abnormal stress at the C7-T1 disc.
Surface Wave Generation by Buried Forces in a Half Space
Authors: Weaver Richard L
Published: May 2011

The method of explicit expansion in normal modes is applied to derive expressions for the Rayleigh waves generated by distributions of buried transient and harmonic forces. The derived expressions are conceptually clear, and relatively simple.
On Evaluation of Lamb's Integrals for Waves in a Two-Dimension Elastic Half-Space
Authors: Yeh Chau-Shioung , Teng Tsung-Jen , Liao Wen-I
Published: May 2011

In this paper, a modified version of the method of steepest descent is proposed for the evaluation of Lamb's integrals which can be considered as basis functions dealing with the development of the transition matrix method which can be used to study the wave scattering in a two-dimensional elastic half-space. The formal solutions of the generalized Lamb's problem are studied and evaluated on the basis of the proposed method. After defining a phase function which presents in wavenumber integral, an exact mapping and an inverse mapping can be obtained according to the phase function. Thus, the original integration path can be deformed into an equivalent admissible path, namely, steepest descent path which passed through the saddle point, and then mapped onto a real axis of mapping plane, finally, resulted in an integral of Hermite type. This integral can be efficiently evaluated numerically in spite of either near- to far-field or low to high frequency. At the same time, the asymptotic value can easily be obtained by applying the proposed method. The numerical results for generalized Lamb's solutions are calculated and compared with analytic, asymptotic or other existing data, the excellent agreements are found. The properties of generalized Lamb's solutions are studied and discussed in details. Their possible applications for wave scattering in elastic half-space are also pointed out.
The Method of Generalized Ray-Revisited
Authors: Ziegler Franz , Borejko Piotr
Published: May 2011

In Section 2, ROTATION OF COORDINATES, the Authors derived the emittance functions in the Weyl-Sommerfeld representation of the wave potentials for a horizontal instantaneous single force from those known for a vertical force from conditions of invariance of the phase and amplitude of plane waves under coordinate rotation, Eqs. (10) ∼ (13) and (18) ∼ (20). That transformation implies the validity of the commonly applied identity for the (force) vector components when rotating the vector in the opposite sense to the coordinate rotation. Further, in the three-dimensional case, the vertical force poses an axisymmetric problem which is compatible with the Fourier transformation applied to the coordinates in the horizontal plane.
On the Method of Continuous Analysis
Authors: Ting-Shun Wang James , Lin Chien-Chang
Published: May 2011

The paper, summarizing studies presented in seven journal papers using the method of continuous analysis, is written to honor Professor Y.H. Pao of the Institute of Applied Mechanics at the National Taiwan University on his seventieth birthday for his many significant contributions and leadership in the field of mechanics. These seven papers contain investigations concerning stress, buckling, and vibration analyses of beams and plates having disbonds. The authors feel privileged to have this opportunity to join with Professor Pao's many friends, colleagues and students to participate in this joyous occasion. Being able to appear in this prestigious special issue of the Chinese Journal of Mechanics, the authors believe that the spread of each of the seven papers in the structural mechanics community must at least be increased by ten fold. Hence, the numbering of the reference papers is amplified by a factor of ten which amounts to a total number of seventy as being used in the listing of papers under References. We use this number of seventy to wish Professor Y.H. Pao to have many happy returns on his seventieth birthday.
Effects of a Temperature Cycle on an Elastic-Plastic Shrink Fit with Solid Inclusion
Authors: Mack Werner , Plöchl Manfred , Gamer Udo
Published: May 2011

The stress distribution in a shrink fit with solid inclusion subject to homogeneous heating and subsequent cooling is investigated. It is presumed that both components are in a state of plane stress and exhibit the same elastic-plastic material behavior. Based on Tresca's yield condition and the associated flow rule, the modification of the stress distribution is studied analytically. In particular, the reduction of the interface pressure — and therefore of the transferable moment — caused by the occurrence of plastic deformation is discussed, and the criteria for the avoidance of yielding of the inclusion or full plasticization of the hub are given.
The Method of Generalized Ray-Revisited
Authors: Ziegler Franz , Borejko Piotr
Published: May 2011

Based on a landmark paper by Pao and Gajewski, some novel developments of the method of generalized ray integrals are discussed. The expansion of the dynamic Green's function of the infinite space into plane waves allows benchmark 3-D solutions in the layered half-space and even enters the background formulation of elastic-viscoplastic wave propagation. New developments of software of combined symbolic-numerical manipulation and parallel computing make the method a competitive solution technique.
Dynamic Analysis of Non-Symmetric Cracks Extension
Authors: Chung Yen-Ling , Chen Mei-Rong
Published: May 2011

This paper applies the method of self-similar potentials to analyze the dynamic behaviors of the problems of mode-I, mode-II, and mode-III cracks propagating along the x-axis with constant speed, while the constant speeds of both crack tips are not the same, called nonsymmetric crack expansion. It is assumed that an unbound homogeneous isotropic elastic material is at rest for time t < 0. However, for time t ≥ 0, a central crack starts to extend from zero length along the x-axis. On the crack surfaces of x ≥ 0, there exists uniform distributed load such that the rightmost crack tip propagates with speed ms, while the leftmost crack tip with speed s, where m > 1 and is constant. First, the complete solutions of the mode-I, mode-II, and mode-III problems are obtained. After the complete solutions are found, attention is focused on the crack surface displacements and dynamic stress intensity factors. The results of this study show that the DSIF is equal to the static SIF when the crack-tip speed is zero, and DSIF is zero as the crack-tip speed approaches the Rayleigh-wave speed. Moreover, for the special case m = 1 which indicates that the velocities of both crack tips are the same, the DSIFs of this three modes in this study is the same as those of Ref. [15].
Pragmatical Asymptotical Stability Theorems on Partial Region and for Partial Variables with Applications to Gyroscopic Systems
Authors: Ge Zheng-Ming , Yu Jung-Kui
Published: May 2011

For a long time, all stability theorems are concerned with the stability of the zero solution of the differential equations of disturbed motion on the whole region of the neighborhood of the origin. But for various problems of dynamical systems, the stability is actually on partial region. In other words, the traditional mathematical model is unmatched with the dynamical reality and artificially sets too strict demand which is unnecessary. Besides, although the stability for many problems of dynamical systems may not be mathematical asymptotical stability, it is actual asymptotical stability — namely “pragmatical asymptotical stability” which can be introduced by the concept of probability. In order to fill the gap between the traditional mathematical model and dynamical reality of various systems, one pragmatical asymptotical stability theorem on partial region and one pragmatical asymptotical stability theorem on partial region for partial variables are given and applications for gyroscope systems are presented.
Frequency Discrimination Characteristics of Cochlear Basilar Membrane Using a Fluid/Structure Model
Authors: Wo Andrew M. , Chen Chi-Fang , Hsu Yi-Feng , Liang Jeffrey
Published: May 2011

This paper addresses the vibratory mechanics associated with frequency discrimination of basilar membrane within the cochlear of the inner ear. Periodic excitation is provided to the oval window, which results in generation of waves within the fluid-filled cochlear traveling towards the apex. These waves interact with the compliant basilar membrane structure causing its vibratory motion. Solution procedure of the fluid/structure model consists of a two-step process. First, a finite element calculation (ANSYS) solves for the membrane vibration with an initial harmonic pressure distribution. Second, a control volume analysis links the resultant vibratory motion with the fluid pressure acting on the basilar membrane, thus a pressure feedback loop is accomplished. Results show that dominant factors affecting vibratory characteristics of the basilar membrane are its structural geometry and attenuation of pressure wave as it travels away from the oval window. Calculations clearly capture the designed function of the basilar membrane, principally its frequency discrimination behavior.
Thermal Stress Analysis of Thermally-Enhanced Plastic Ball Grid Array Electronic Packaging
Authors: Yeh Meng-Kao , Chiang Kuo-Ning , Su Jiann-An
Published: May 2011

The thermally enhanced ball grid array (TEBGA) electronic packaging under thermal cycling and thermal loading was investigated numerically. Two-dimensional finite element analysis by ANSYS was used for calculating the temperature distribution and thermal stress on the symmetric and diagonal cross sections of TEBGA. The thermal failure based on the peel and shear stresses at interfaces of TEBGA took place at the interface between the heat sink and epoxy moulding compound. The Tasi-Hill failure criterion was modified to predict the failure at various interfaces in TEBGA package. The TEBGA geometric parameters, including the thickness of the heat sink, the thickness of the adhesive layer between the heat sink and the die, and the thickness of the reinforcing copper ring, were varied to assess their effects on the failure mode of TEBGA. The results showed that for a TEBGA under thermal cycling, the stress values were reduced for thicker adhesive layers and thinner heat sinks; for a TEBGA under thermal loading, the die-to-ambient thermal resistance of TEBGA decreased for thinner adhesive layers and thicker heat sinks. The slimmer heat sink of extruded plate type can dissipate more heat and can reduce the stress values. Proper choice of geometric parameters of TEBGA package can prevent its failure at interfaces and furthermore, improve the reliability of electronic packaging.
Optimal Distal Screw Alignment in the Gamma Nail
Authors: Chao Ching-Kong , Hsiao Chun-Ching , Chen Po-Quang
Published: May 2011

The effect of stress distribution due to the changes of the distal screw alignment in relation to the Gamma nail and the femoral shaft is thoroughly studied in this paper. Failure of the Gamma nail composite occurs through the cranial aperture of the distal screws and the insertion hole for the lag screw due to nonunion, delayed-union and continued weight-bearing. A three-dimensional finite element model was used to study the fractured femur, the Gamma nail, the lag screw and the distal locking screws. The first and the second distal screws were inserted into the Gamma nail in four different configurations. We found that the stress of the Gamma nail composite was substantially reduced with the two screws configured in the anterior to posterior direction. This alignment can bear greater loading in the more demanding fracture types. In the subtrochanteric fracture or the comminuted fractures at the proximal femur, the optimal alignment of the two distal screws was in the anterior to posterior direction.
In-Plane Bending Fracture of a Large Beam Containing a Circular-Arc Crack
Authors: Shiah Y. C. , Fang Jiunn , Wei Chin-Yi , Liang Y.C.
Published: May 2011

In this paper, the crack problem of a large beam-like strip weakened by a circular arc crack with in-plane bending moments applied at both ends is approximately solved using the complex variable technique. Complex stress functions corresponding to the applied bending moments are superposed with those due to the disturbance of the crack to satisfy the governing boundary equation. The conformal mapping function devised to transform the contour surface of a circular arc crack to a unit circle is then substituted in the boundary equation to facilitate the evaluation of Cauchy integrals. In this way, the complex stress functions due to the crack disturbance are determined and the stress intensity factors are calculated through a limiting process to give their explicit forms. Eventually, the geometric functions for the variation of the stress intensity factors on account of the crack shape are plotted as a function of the curvature of a circular-arc crack.
The Unsteady Viscous Flow Generated by an Oscillating Porous Plate
Authors: Liu C.-M. , Hwung H.-H. , Kong C.-H.
Published: May 2011

The flow of a viscous still fluid disturbed by an oscillating porous plate with an arbitrary initial phase is investigated. Using the Laplace transform, the exact solution of the velocity profile is revisited. Subsequently, the wall stress implying the required driving force is derived in this study. The solutions are valid not only for large times but also for small times. Four special cases are discussed to investigate the influences of four parameters on the development of the flow. A dimensionless analysis for general cases is also provided. Our analyses significantly stress on the following subjects. Firstly, the porous velocity and the decay factor affecting the development of the flow are studied. Secondly, the occurrence time of separation and the corresponding critical condition are investigated. The period of the transient velocity influenced by the Reynolds number and the initial phase is discussed. Present study includes many existing solutions as special cases. Results can be also applied to many engineering problems with the same PDE form and boundary conditions. In conclusion, this study presents the detailed discussions and the magnitude of the required driving force which were missed in previous works.
Molecular Dynamic Simulation of Escape of Hydrogen Atoms from (5, 5) Carbon Nanotubes
Authors: Wang C. S. , Chen J. S. , Wang Y. C. , Lee J. , Chyou Y. P.
Published: May 2011

In this article the mass and heat transfer between fluid molecule and carbon tube is studied via molecular dynamic simulation based on Lennard-Jones Potentia and Bernner-Tersoff Potential model. Some valve holes are formed by removing different numbers of molecules from flank of (5, 5) armchair carbon tube (the hole area = 17.3 ∼ 116.9Å2). The results indicate that only diffusion behavior is not able to describe the phenomena, otherwise the atom release rate and valve hole size are interdependent. Meanwhile the variation of potential energy barrier, work function, energy gap arose from different valve geometrical size are observed. These variations can influence the dynamic behavior such as flow rate and velocity by molecule penetration.
Nonlinear Panel Flutter of Composite Sandwich Plates with Thermal Effect
Authors: Shiau L.-C. , Kuo S.-Y.
Published: May 2011

By considering the total transverse displacement of a sandwich plate as the sum of the displacement due to bending of the plate and that due to shear deformation of the core, a high precision higher order triangular plate element is developed for the nonlinear panel flutter analysis of thermally buckled sandwich plates. Von Karman large deformation assumptions and quasi-steady aerodynamic theory are employed for the analysis. Newmark numerical time integration method is applied to solve the nonlinear governing equations in time domain. Results show that temperature will increase both the maximum displacement and motion speed of the plate. But the maximum displacement and velocity of the plate will not vary much with the aerodynamic pressure. Buckle pattern change phenomenon occurred in some specific case will increase the flutter boundary and change the flutter motion type of the plate. Temperature gradient increases the overall stiffness of the plate, which in turn stabilizes the sandwich panel and increases the flutter boundary of the plate.
Shear Horizontal Piezoelectric Waves in a Piezoceramic Plate Imperfectly Bonded to Two Piezoceramic Half-Spaces
Authors: Chen Z. G. , Hu Y. T. , Yang J. S.
Published: May 2011

We analyze the propagation of shear horizontal (SH) piezoelectric waves guided by a plate of polarized piezoceramics between two piezoceramic half-spaces with imperfectly bonded interfaces. The interfaces are described by the so-called shear-lag model with an elastic constant characterizing the interface physical behavior. Exact dispersion relations are obtained. It is found that the waves are sensitive to the physical nature of the interfaces. The results are useful for acoustic wave devices.
Failure Mechanism and Bearing Capacity of Shallow Foundation on Poorly Cemented Sandstone
Authors: Chang J.-C. , Liao J.-J. , Pan Y.-W.
Published: May 2011

This paper aims to investigate the failure mechanism of a shallow foundation on poorly cemented sandstone and to propose an upper bound solution for the bearing capacity of the foundation. A series of laboratory material and load-bearing model tests with specimens made of artificial rock mimic undisturbed natural poorly cemented sandstone.

Based on a series of load-bearing model tests, bearing behavior and progressive failure mechanisms are investigated. It was found that the bearing behavior on poorly cemented sandstone is distinct from the cases on hard rock or on soil, and exhibits both plasticity and brittle characteristics. It is noted that the bearing capacity formulas for a shallow foundation commonly used for soil or hard rock are not appropriate for the case of poorly cemented soft sandstone. Based on the observed failure mechanism, a simplified plastic collapse mechanism is proposed and an upper-bound solution on the basis of a multi-block translation mechanism is formulated. It is shown that the upper bound solution agrees well with the experimental bearing capacity as long as a proper non-associated flow rule is adopted.
Vortex Simulations of the Flow-Field of a Flat Plate with a Non-Zero Angle of Attack
Authors: Hsu C.-C. , Huang C.-I
Published: May 2011

A Lagrangian style vortex simulation technique is used to study the flow fields past a stationary flat plate at various angles of attack in the range 1° to 90°. Time mean values of oscillating lift and drag coefficients, and the Strouhal number versus angle of attack are computed and compared with experimental results. Time-mean and root-mean-square values of stream-wise and transverse velocities in the wake region are also calculated. Self-similar defect velocity distribution is obtained far downstream. Owing to the interaction of free shear layers, highly root-mean-square values of velocities appear at the downstream vertex of the triangular low velocity region, which exits behind an inclined flat plate.
Heat Transfer of Confined Circular Jet Impingement
Authors: Hsieh Shou-Shing , Huang Jung-Tai , Tsai Huang-Hsiu
Published: May 2011

Experiments for heat transfer characteristics of confined circular single jet impingement were conducted. The effect of jet Reynolds number, jet hole-to-plate spacing and heat flux levels on heat transfer characteristics of the heated target surface was examined and presented. The local heat transfer coefficient along the surface is measured and correlations of the stagnation point, local and average Nusselt number are developed and discussed. Finally, comparisons of the present data with existing results were also made.
The Endochronic Approach for Structural Steel Subjected to Cyclic Loading
Authors: Lu Jun-Kai , Ji Nai-Kuan
Published: May 2011

The A36 structural steel shows significant Baushinger effect under cyclic loading. Present paper modifies the anisotropic endochronic model to describe the behaviors of the A36 structural steel subjected to cyclic loading. The deformation induced anisotropy has been considered to modify the definition of the intrinsic time. Also, the different hardening functions are used with respect to the mechanical behavior under loading and unloading condition, respectively. Then, the presented constitutive equations are used to describe the mechanical behaviors of the A36 structural steel under different cyclic strain paths. The theoretical results are compared with the experimental data. The test investigated includes several different cyclic uniaxial and axial-torsional loading experiments from Hong and his co-workers. It is shown that the present model is capable of describing the anisotropic behaviors of A36 structural steel well.
Thermal Stress in Discretely Layered Structures with Functional Graded Materials
Authors: Hwang S.-F. , Liao W.-T.
Published: May 2011

Functional graded materials are generally provided in discretely layered structures to reduce the abrupt mismatch and to improve failure performance. To investigate the thermal stress singularity occurring at the intersection of an interface and a free end, two-dimensional and three-dimensional finite element analyses are performed for titanium and aluminum layers with or without functional graded materials. The results indicate that once the functional graded material is added, the stress singularity around the intersection of an interface and a free end could be significantly relieved. If more FGM layers are used, the stress singularity could be further reduced to a very small value. If the longitudinal normal stresses and interlaminar shear stress are considered, two-dimensional finite element analysis may be enough, while three-dimensional analysis is necessary for the interlaminar normal stress. Otherwise, one may underestimate its stress singularity.