bluuebunny/crossref_metadata_2025 huggingface dataset:
Spray and Combustion Characteristics of Biodiesel∕Diesel Blended Fuel in a Direct Injection Common-Rail Diesel Engine
Authors: Suh Hyun Kyu , Roh Hyun Gu , Lee Chang Sik
Published: April 2008

The aim of this work is to investigate the effect of the blending ratio and pilot injection on the spray and combustion characteristics of biodiesel fuel and compare these factors with those of diesel fuel in a direct injection common-rail diesel engine. In order to study the factors influencing the spray and combustion characteristics of biodiesel fuel, experiments involving exhaust emissions and engine performance were conducted at various biodiesel blending ratios and injection conditions for engine operating conditions. The macroscopic and microscopic spray characteristics of biodiesel fuel, such as injection rate, split injection effect, spray tip penetration, droplet diameter, and axial velocity distribution, were compared with the results from conventional diesel fuel. For biodiesel blended fuel, it was revealed that a higher injection pressure is needed to achieve the same injection rate at a higher blending ratio. The spray tip penetration of biodiesel fuel was similar to that of diesel. The atomization characteristics of biodiesel show that it has higher Sauter mean diameter and lower spray velocity than conventional diesel fuel due to high viscosity and surface tension. The peak combustion pressures of diesel and blending fuel increased with advanced injection timing and the combustion pressure of biodiesel fuel is higher than that of diesel fuel. As the pilot injection timing is retarded to 15deg of BTDC that is closed by the top dead center, the dissimilarities of diesel and blending fuels combustion pressure are reduced. It was found that the pilot injection enhanced the deteriorated spray and combustion characteristics of biodiesel fuel caused by different physical properties of the fuel.
Off-Design Performance Investigation of a Low Calorific Value Gas Fired Generic-Type Single-Shaft Gas Turbine
Authors: Orbay Raik C. , Genrup Magnus , Eriksson Pontus , Klingmann Jens
Published: April 2008

When low calorific value gases are fired, the performance and stability of gas turbines may deteriorate due to a large amount of inertballast and changes in working fluid properties. Since it is rather rare to have custom-built gas turbines for low lower heating value (LHV) operation, the engine will be forced to operate outside its design envelope. This, in turn, poses limitations to usable fuel choices. Typical restraints are decrease in Wobbe index and surge and flutter margins for turbomachinery. In this study, an advanced performance deck has been used to quantify the impact of firing low-LHV gases in a generic-type recuperated as well as unrecuperated gas turbine. A single-shaft gas turbine characterized by a compressor and an expander map is considered. Emphasis has been put on predicting the off-design behavior. The combustor is discussed and related to previous experiments that include investigation of flammability limits, Wobbe index, flame position, etc. The computations show that at constant turbine inlet temperature, the shaft power and the pressure ratio will increase; however, the surge margin will decrease. Possible design changes in the component level are also discussed. Aerodynamic issues (and necessary modifications) that can pose severe limitations on the gas turbine compressor and turbine sections are discussed. Typical methods for axial turbine capacity adjustment are presented and discussed.
Flame Structure and Stabilization Mechanisms in a Stagnation-Point Reverse-Flow Combustor
Authors: Bobba Mohan K. , Gopalakrishnan Priya , Periagaram Karthik , Seitzman Jerry M.
Published: April 2008

A novel combustor design, referred to as a stagnation-point reverse-flow (SPRF) combustor, was recently developed to overcome the stability issues encountered with most lean premixed combustion systems. The SPRF combustor is able to operate stably at very lean fuel-air mixtures with low NOx emissions. The reverse flow configuration causes the flow to stagnate and hot products to reverse and leave the combustor. The highly turbulent stagnation zone and internal recirculation of hot product gases facilitates robust flame stabilization in the SPRF combustor at very lean conditions over a range of loadings. Various optical diagnostic techniques are employed to investigate the flame characteristics of a SPRF combustor operating with premixed natural gas and air at atmospheric pressure. These include simultaneous planar laser-induced fluorescence imaging of OH radicals and chemiluminescence imaging, and spontaneous Raman scattering. The results indicate that the combustor has two stabilization regions, with the primary region downstream of the injector where there are low average velocities and high turbulence levels where most of the heat release occurs. High turbulence levels in the shear layer lead to increased product recirculation levels, elevating the reaction rates and thereby enhancing the combustor stability. The effect of product entrainment on the chemical time scales and the flame structure is quantified using simple reactor models. Turbulent flame structure analysis indicates that the flame is primarily in the thin reaction zone regime throughout the combustor. The flame tends to become more flameletlike, however, for increasing distance from the injector.
Thermohydrodynamic Analysis of Compliant Flexure Pivot Tilting Pad Gas Bearings
Authors: Sim Kyuho , Kim Daejong
Published: April 2008

A new thermohydrodynamic (THD) analysis for compliant flexure pivot tilting pad gas bearings is presented. Unlike many previous THD analyses on oil-lubricated bearings and gas bearings, the new THD analysis solves the rotor and bearing pad temperatures as well as the gas film temperature simultaneously upon adequate thermal boundary conditions on the bearing shell and rotor ends are given. All the previous studies assume that the rotor and bearing temperatures are given as thermal boundary conditions to solve 2D or 3D energy equation in the bearing film. The developed computational method is unique because these boundary conditions are found internally through global energy balance around the bearing. A numerical procedure involves solving the generalized Reynolds equation, 3D energy equation, and heat flux equations around the bearings simultaneously through iterative process. Furthermore, rotor thermal and centrifugal expansions are also considered during the iteration. Parametric studies were performed for the various temperature fields, i.e., rotor temperature, gas film temperature, and pad temperature as a function of nominal clearance, external load, and various thermal boundary conditions. Nominal clearance showed the most significant influence on overall THD behavior. The analyses also show that the rotor-bearing system can go to thermal runaway if adequate cooling mechanism does not exist. Linear perturbation analysis was also performed to investigate the thermal effects on the rotordynamic performance. Rotor thermal growth and increased viscosity increased direct stiffness and damping coefficients compared to the isothermal case.
Three-Dimensional Calculations of Evaporative Flow in Compressor Blade Rows
Authors: Payne R. C. , White A. J.
Published: April 2008

The present paper describes a three-dimensional computational method developed to solve the flow of a two-phase air-water mixture, including the effects of evaporation for a monodispersion of liquid droplets. The calculations employ a fully Eulerian method for the conservation of droplet number and liquid mass and are applicable to multiple blade rows, both stationary and rotating. The method is first tested to ensure that it computes the correct droplet evaporation rate and the correct physical behavior for evaporation within a 1D duct. Results are then presented for flow within a single compressor stage, i.e., a rotor-stator combination.
Combustion Performance of Liquid Biofuels in a Swirl-Stabilized Burner
Authors: Sequera Daniel , Agrawal Ajay K. , Spear Scott K. , Daly Daniel T.
Published: April 2008

Fuels produced from renewable sources offer an economically viable pathway to curtail emissions of greenhouse gases. Two such liquid fuels in common usage are biodiesel and ethanol derived from soybean, corn, or other food crops. In recent years, significant effort has been devoted to identify alternate feedstock sources and conversion techniques to diversify the biofuels portfolio. In this study, we have measured emissions from flames of diesel, biodiesel, emulsified bio-oil, and diesel-biodiesel blends. Experiments are conducted in an atmospheric pressure burner with an air-atomized injector and swirling primary air around it to replicate typical features of a gas turbine combustor. Experiments were conducted for fixed air and fuel flow rates, while the airflow split between the injector and the coflow swirler was varied. Results show a significant reduction in emissions as the fraction of total air fed into the atomizer is increased. Blue flames, reminiscent of premixed combustion, and low emissions of nitric oxides and carbon monoxide were observed for all fuel blends. In general, the emissions from biofuel flames were comparable or lower than those from diesel flames.
Fracture Initiation Due to Asymmetric Impact Loading of an Edge Cracked Plate
Authors: Lee Y. J. , Freund L. B.
Published: April 2008

The two-dimensional elastodynamic problem of a semi-infinite plate containing an edge crack is considered. Initially, the plate is stress-free and at rest. To simulate the asymmetric impact of a projectile on the cracked edge of the plate, a normal velocity is suddenly imposed on the boundary of the plate on one side of the edge crack. The boundary of the plate and the crack faces are otherwise traction-free. Due to the nature of the loading, a combination of transient mode I and mode II deformation fields is induced near the crack tip. The corresponding stress intensity factor histories are determined exactly by linear superposition of several more readily obtainable stress wave propagation solutions, including a fundamental solution arising from a particular problem in the dynamic theory of elastic dislocations. The stress intensity factor histories are determined for the time interval from initial loading until the first wave scattered at the crack tip is reflected at the plate edge and returns to the crack tip. In experiments on fracture initiation in a high-strength steel based on essentially this specimen and loading configuration, Kalthoff and Winkler (1987) reported a fracture grew from the original crack either as a tensile crack inclined to the original crack plane or as a straight-ahead shear fracture, depending on the intensity of the applied velocity. The observations are considered in light of the solution reported here.
Three-Dimensional Solutions for Antisymmetrically Laminated Anisotropic Plates
Authors: Noor Ahmed K. , Burton W. Scott
Published: April 2008

Analytic three-dimensional elasticity solutions are presented for the stress and free vibration problems of multilayered anisotropic plates. The plates are assumed to have rectangular geometry and antisymmetric lamination with respect to the middle plane. A mixed formulation is used with the fundamental unknowns consisting of the six stress components and the three displacement components of the plate. Each of the plate variables is decomposed into symmetric and antisymmetric components in the thickness direction, and is expressed in terms of a double Fourier series in the Cartesian surface coordinates. Extensive numerical results are presented showing the effects of variation in the lamination and geometric parameters of composite plates on the importance of the transverse stress and strain components.
Interactive Bending Behavior of Sandwich Beams
Authors: Hunt G. W. , da Silva L. S.
Published: April 2008

A multi-degree-of-freedom nonlinear Rayleigh-Ritz formulation for a sandwich beam is developed and is used to demonstrate the possible sudden destabilizing effects associated with wrinkling on the compressive face. Through-core stretching and core shearing effects are included. Nonlinear load-deflection curves, for various loading conditions including point loads and uniformly distributed loads, are presented.
Dynamics of a Weakly Nonlinear System Subjected to Combined Parametric and External Excitation
Authors: Yagasaki Kazuyuki , Sakata Masaru , Kimura Koji
Published: April 2008

In this paper we study the dynamics of a weakly nonlinear single-degree-of-freedom system subjected to combined parametric and external excitation. The averaging method is used to establish the existence of invariant tori and analyze their stability. Furthermore, by applying the Melnikov technique to the average system it is shown that there exist transverse homoclinic orbits resulting in chaotic dynamics. Numerical simulation results are also given to demonstrate the theoretical results.
The Principle of Asymptotic Proportionality
Authors: Chan H. C. M.
Published: April 2008

The Principle of Asymptotic Proportionality, which is based on the Green’s function method for equilibrium problems, is proposed. Using this principle, the induced far-field variable due to any distribution of applied physical quantities can be approximated. This principle has been verified by considering the induced stresses due to applied tractions and dislocations in two-dimensional linear elastic media, and has been shown to be applicable to other physical phenomena such as electrostatics, gravitation, and electromagnetism.
A Crystallographic Model for the Tensile and Fatigue Response for Rene´ N4 at 982°C
Authors: Sheh M. Y. , Stouffer D. C.
Published: April 2008

An anisotropic constitutive model based on crystallographic slip theory was formulated for nickel-base single crystal superalloys. The current equations include both drag stress and back stress state variables to model the local inelastic flow. Specially designed experiments have been conducted to evaluate the existence of back stress in single crystals. The results showed that the back stress effect of reverse inelastic flow on the unloading stress is orientation dependent, and a back stress state variable in the inelastic flow equation is necessary for predicting anelastic behavior. Model correlations and predictions of experimental data are presented for the single crystal supperalloy Rene´ N4 at 982°C.
Plane-Strain Shear Dislocations Moving Steadily in Linear Elastic Diffusive Solids
Authors: Rudnicki J. W. , Roeloffs E. A.
Published: April 2008

This paper derives the stress and pore pressure fields induced by a plane-strain shear (gliding edge) dislocation moving steadily at a constant speed V in a linear elastic, fluid-infiltrated (Biot) solid. Solutions are obtained for the limiting cases in which the plane containing the moving dislocation (y = 0) is permeable and impermeable to the diffusing species. Although the solutions for the permeable and impermeable planes are required to agree with each other and with the ordinary elastic solution in the limits of V = 0 (corresponding to drained response) and V = ∞ (corresponding to undrained response), the stress and pore pressure fields differ considerably for finite nonzero velocities. For the dislocation on the impermeable plane, the pore pressure is discontinuous on y = 0 and attains values which are equal in magnitude and opposite in sign as y = 0 is approached from above and below. The solution reveals the surprising result that the pore pressure on the impermeable plane is zero everywhere behind the moving dislocation (x < 0). For the dislocation on the permeable plane, the pore pressure is zero on y = 0 and attains its maximum at about (2c/V, 2c/V) where c is the diffusivity, and the origin of the coordinate system coincides with the dislocation. For the impermeable plane, the largest pore pressure change occurs at the origin.
The Response of an Infinite Railroad Track to a Moving, Vibrating Mass
Authors: Duffy Dean G.
Published: April 2008

We examine vibrations that arise when a moving, vibrating load passes over an infinite railroad track lying on a Winkler foundation. Solutions are presented for both moving and stationary vibrating loads as a function of both the mass and driving frequency of the load as well as the physical properties of the track. For a stationary vibrating load, resonance occurs at lower driving frequencies as the mass of the load increases. For a moving vibrating load, resonance occurs at lower driving frequencies when the velocity and/or mass of the load increases.
Surface Waves for Material Characterization
Authors: Rose Joseph L. , Nayfeh Adnan , Pilarski Aleksander
Published: April 2008

Analyses are presented for the propagation of harmonic surface waves on a transversely isotropic layer rigidly bonded to a transversely isotropic substrate of different material. The layer-substrate system is also assumed to be in contact with a liquid and inviscid space. The propagation takes place along an axis of symmetry of both the layer and the substrate. Exact closed-form solutions for the characteristic dispersion relations are presented. Numerical results are presented for material combinations of three classes of centrifugally cast stainless steel material. Results clearly demonstrate the influence of the layer thickness on the propagation speed and, hence, provide a means of material characterization.
A Crack in a Confocal Elliptic Inhomogeneity Embedded in an Infinite Medium
Authors: Wu Chien H. , Chen Chao-Hsun
Published: April 2008

A family of confocal ellipses may be characterized by a single parameter, ρ> 1. In the limit as ρ→1, the ellipse degenerates into a straight line of length 2. It tends to a circle of infinite radius as ρ→ ∞. The geometry of the title problem is fixed by the crack (ρ = 1) and the size of an elliptic inhomogeneity (ρ = ρ0). Both the inhomogeneity and the infinite medium are assumed to be homogeneous and isotropic. Plane and anti-plane solutions associated with remote loading conditions are obtained. The solutions depend, among other parameters, on the size of the inhomogeneity ρ0. Special attention is placed on determining the various limits as ρ0→1.
Elastic-Plastic Analysis of Combined Mode II and III Crack-Tip Fields Under Small-Scale Yielding Conditions
Authors: Pan J. , Shih C. F.
Published: April 2008

Within the context of the small-strain approach, combined mode II and III small-scale yielding solutions of a stationary crack are obtained by finite element analysis. To investigate the behavior of the near-tip fields, the normalized stresses ahead of the crack tip are plotted as functions of the normalized radial distance to the tip for several combinations of prescribed mode II and III elastic K fields. The angular variations of the normalized stresses at a fixed radial distance deep within the plastic zone are also plotted for several combinations of remote mode II and III elastic K fields. These plots show an interesting pattern: Well within the plastic zone, the in-plane stresses can be said to be slightly less singular than r-1/(n+1) while the out-of-plane shear stresses are slightly more singular than r-1/(n+1), where n is the strain-hardening exponent of the material. However, over physically relevant distances ahead of the tip and for the full range of combined mode II and III loadings, the ratio of the in-plane shear stress to the out-of-plane shear stress agrees well with the ratio estimated by linear elastic crack-tip fields.
Analytical Solutions for Circular Bars Subjected to Large Strain Plastic Torsion
Authors: Neale K. W. , Shrivastava S. C.
Published: April 2008

The inelastic behavior of solid circular bars twisted to arbitrarily large strains is considered. Various phenomenological constitutive laws currently employed to model finite strain inelastic behavior are shown to lead to closed-form analytical solutions for torsion. These include rate-independent elastic-plastic isotropic hardening J2 flow theory of plasticity, various kinematic hardening models of flow theory, and both hypoelastic and hyperelastic formulations of J2 deformation theory. Certain rate-dependent inelastic laws, including creep and strain-rate sensitivity models, also permit the development of closed-form solutions. The derivation of these solutions is presented as well as numerous applications to a wide variety of time-independent and rate-dependent plastic constitutive laws.
Kinematics for Bodies Undergoing Residual Stress and its Applications to the Left Ventricle
Authors: Takamizawa Keiichi , Matsuda Takehisa
Published: April 2008

Biological soft tissues are understood to be materials that are residually stressed and nonlinear, and finitely deformed. A generalized continuum kinematics is needed to analyze such materials. Here, we apply Riemann geometry to the analysis of the residual stress and the stress distributions under loading conditions in the left ventricular wall assuming the uniform strain hypothesis. The hypothesis we employ states that the strain is uniformly distributed through the wall thickness at the end diastole. In conventional analyses, in contrast, it has been implicitly assumed that an unloading state gives a stress-free configuration. The steep stress distributions obtained from the conventional assumption are considerably reduced in the present study due to our hypothesis. The results are physiologically more plausible.
The Effect of Contact Generation on the Elastic Properties of a Granular Medium
Authors: Endres Anthony L.
Published: April 2008

Previous models for the elastic properties of a granular medium have assumed that all grain contacts are established in its undeformed configuration. Experimental data for the change in elastic properties as a function of confining pressure cannot be explained by these models. Contact creation is cited as one possible cause for this discrepancy. In this paper a model for a granular material is derived that allows for the creation of grain contacts during hydrostatic compression. This formulation allows for the use of general contact microphysics and a general statistical distribution of gap widths at the near-contact points. Numerical results show that for very small values of the average near-contact gaps (approximately 1/1000 of a sphere radius), there can be significant effects occurring in the range of confining pressures between 106 to 107 Pa. The results of this contact generating model are consistent with published experimental measurements.
The Dynamic Energy Release Rate for a Steadily Propagating Mode I Crack in an Infinite, Linearly Viscoelastic Body
Authors: Walton J. R.
Published: April 2008

An analysis is presented for the dynamic, steady-state propagation of a semi-infinite, mode I crack in an infinite, linearly viscoelastic body. For mathematical convenience, the material is assumed to have a constant Poisson’s ratio, but the shear modulus is only assumed to be decreasing and convex. An expression for the Stress Intensity Factor (SIF) is derived for very general tractions on the crack faces and the Energy Release Rate (ERR) is constructed assuming that a fully developed Barenblatt type failure zone with nonsingular stresses exists at the crack tip and the loadings have a simple exponential form. For comparative purposes, expressions for the ERR are derived for the special cases of dynamic steady-state crack propagation in elastic material and quasi-static crack propagation in viscoelastic material, both with and without a failure zone. Sample calculations are included for power-law material and a standard linear solid in order to illustrate the combined influence of inertial effects, material viscoelasticity, and a failure zone upon the ERR.
Interface Crack Between Two Dissimilar Half Spaces Subjected to a Uniform Heat Flow at Infinity—Open Crack
Authors: Kuo An-Yu
Published: April 2008

The thermal stress problem of an “open” crack situated at the interface of two bonded, dissimilar, semi-infinite solids subjected to a uniform heat flow is studied. Heat transmission between adjacent crack surfaces is assumed to be proportional to the temperature difference between the crack surfaces with a proportional constant h, which is defined as the contact coefficient or interface conductance. Temperature distribution of the problem is obtained by superimposing the temperature field for a perfectly bonded composite solid and the temperature fields for a series of distributed thermal dipoles at the crack location. The distribution function of the dipoles is obtained by solving a singular Fredholm integral equation. Stresses are then expressed in terms of a thermoelastic potential, corresponding to the temperature distribution, and two Muskhelishvili stress functions. Stress intensity factors are calculated by solving a Hilbert arc problem, which results from the crack surface boundary conditions and the continuity conditions at the bonded interface. Thermal stress intensity factors are found to depend upon an additional independent parameter, the Biot number λ = (ah/k), on the crack surface, where a is half crack length and k is thermal conductivity. Dipole distribution and stress intensity factors for two example composite solids, Cu/Al and Ti/Al2O3, are calculated and plotted as functions of λ. Magnitude of the required mechanical loads to keep the interface crack open is also estimated.
Torsional Response of Rectangular Composite Laminates
Authors: Tsai C.-L. , Daniel I. M. , Yaniv G.
Published: April 2008

The torsional response of a composite laminate of rectangular cross-section was analyzed by the Mindlin-Reissner theory. The analysis takes into account separately the shear properties of each layer. A general closed-form relationship was derived between torque and angle of twist in terms of the geometric parameters and shear properties of the laminae. In the case of unidirectional laminates, relations can be expressed involving the three principal shear moduli, G12, G13, and G23. An experimental method was also developed for determining these moduli by measuring surface and edge strains with strain gages. Results for a typical graphite/epoxy composite show the validity of the usual assumption of transverse isotropy.
On Randomly Excited Hysteretic Structures
Authors: Cai G. Q. , Lin Y. K.
Published: April 2008

Approximate probability distributions of certain response variables are obtained for hysteretic systems under Gaussian white-noise excitations. The approximate method used is a generalization of a dissipation-energy-balancing procedure, developed previously for nonlinear but basically nonhysteretic systems. Some new issues related particularly to hysteresis models are explained and resolved. The method is applicable to either bilinear or smooth-type hysteresis without the restriction that the response be a narrow-band process or the energy dissipation be small. Comparison of computed results with available simulation results indicates that the proposed method is accurate for wide ranges of excitation levels and system parameters.
Analysis of Inclined Wall Plume by the k-ε Turbulence Model
Authors: Fukushima Yusuke , Hayakawa Norio
Published: April 2008

The similarity solution of inclined wall plume is obtained analytically. The mathematical model used herein consists of the continuity equation of flow, the momentum balance equation in the flow direction, the diffusion equation of concentration, the equation of kinetic energy of turbulence and the equation of viscous dissipation rate of turbulence. It is shown that this set of equations has the similarity solution which can be solved numerically for each angle of the inclined wall. This numerical model is applied to the wide range of the slope angle, which includes the vertical wall plume as the special case and the nearly horizontal wall plume. The velocity and concentration profiles of the inclined wall plume are explained well by the similarity solutions.
Limit Analysis of a Stochastically Inhomogeneous Plastic Medium With Application to Plane Contact Problems
Authors: Nordgren R. P.
Published: April 2008

The lower and upper bound theorems of plastic limit analysis are extended to a stochastically inhomogeneous medium. The extended theorems provide bounds on the mean safety factor against plastic collapse. A three-parameter yield function is treated by introducing a spatial correlation function for uniaxial yield strength. Application of the stochastic upper-bound theorem is made to the plane problem of a truncated wedge under contact pressure. The results apply to the design of arctic structures against local ice pressure.
Numerical Analysis of Plane-Strain Tension Test for Rate-Dependent Solids
Authors: Tugˇcu P.
Published: April 2008

The plane-strain tension test is analyzed numerically for a material with strain and strain-rate hardening characteristics. The effect of the prescribed rate of straining is investigated for an additive logarithmic description of the material strain-rate sensitivity. The dependency to the imposed strain rate so introduced is shown to have a significant effect on several features of the load-elongation curve such as the attainment of the load maximum, the onset of localization, and the overall engineering strain.
The Influence of Inclusion Shape on the Overall Viscoelastic Behavior of Composites
Authors: Wang Y. M. , Weng G. J.
Published: April 2008

The Eshelby-Mori-Tanaka method is extended into the Laplace domain to examine the linearly viscoelastic behavior in two types of composite materials: a transversely isotropic one with aligned spheroidal inclusions and an isotropic one with randomly oriented inclusions. Though approximate in nature, the method offers both simplicity and versatility, with explicit results for the sphere, disk, and fiber reinforcements in the transformed domain. The results coincide with some exact solutions for the composite sphere and cylinder assemblage models and, with spherical voids or rigid inclusions, the effective shear property also lies between Christensen’s bounds. Consistent with the known elastic behavior, the inverted creep compliances in the time domain indicate that, along the axial direction, aligned needles or fibers provide the most effective improvement for the creep resistance of the aligned composite, but that in the transverse plane the disk reinforcement is far superior. For the isotropic composite disks are always the most effective shape, whereas spheres are the poorest. Comparison with the experimental data for the axial creep strains of a glass/ED-6 resin composite containing 54 percent of aligned fibers indicates that the theory is remarkably accurate in this case.
Regular Pyramid Punch Problem
Authors: Bilodeau G. G.
Published: April 2008

An approximate solution is found for a regular pyramidal punch indenting, without friction, an elastic half-space. The method is based on the reasonable assumption of the stress distribution and of the region of contact. The force-indentation relationship is obtained for a regular pyramidal punch. The results compare well with direct numerical results.
Analysis of Thermal Conduction Effects on Thermoelastic Temperature Measurements for Composite Materials
Authors: Dunn S. A.
Published: April 2008

Measurement of the temperature changes which occur as a body undergoes a change in stress is becoming a widely used technique for the analysis of surface stress fields. In this paper, an investigation into the effects of thermal conduction on surface thermoelastic temperature changes for composite materials is reported. A mathematical model which shows the effects of thermal conduction is developed, and the results from this model are compared with experimental data. The mathematical model is then extended to solve for heat transfer between two thermally dissimilar materials. It is shown how this model can be used to account for the effects of a surface epoxy layer on the observed thermoelastic temperature changes.
Scattering of an Impact Wave by a Crack in a Composite Plate
Authors: Datta S. K. , Ju T. H. , Shah A. H.
Published: April 2008

The surface responses due to impact load on an infinite uniaxial graphite/epoxy plate containing a horizontal crack is investigated both in time and frequency domain by using a hybrid method combining the finite element discretization of the near-field with boundary integral representation of the field outside a contour completely enclosing the crack. This combined method leads to a set of linear unsymmetric complex matrix equations, which are solved to obtain the response in the frequency domain by biconjugate gradient method. The time-domain response is then obtained by using an FFT. In order to capture the time-domain characteristics accurately, high-order finite elements have been used. Also, both the six-node singular elements and eight-node transition elements are used around the crack tips to model the crack-tip singularity. From the numerical results for surface responses it seems possible to clearly identify both the depth and length of this crack.
Eigenvalue Inclusion Principles for Distributed Gyroscopic Systems
Authors: Yang B.
Published: April 2008

In his famous treatise The Theory of Sound, Rayleigh enunciated an eigenvalue inclusion principle for the discrete, self-adjoint vibrating system under a constraint. According to this principle, the natural frequencies of the discrete system without and with the constraint are alternately located along the positive real axis. Although it is commonly believed that the same rule also applied for distributed vibrating systems, no proof has been given for the distributed gyroscopic system. This paper presents several eigenvalue inclusion principles for a class of distributed gyroscopic systems under pointwise constraints. A transfer function formulation is proposed to describe the constrained system. Five types of nondissipative constraints and their effects on the system natural frequencies are studied. It is shown that the transfer function formulation is a systematic and convenient way to handle constraint problems for the distributed gyroscopic system.
Lyapunov Exponents and Stochastic Stability of Coupled Linear Systems Under Real Noise Excitation
Authors: Ariaratnam S. T. , Xie Wei-Chau
Published: April 2008

The almost-sure asymptotic stability of a class of coupled multi-degrees-of-freedom systems subjected to parametric excitation by an ergodic stochastic process of small intensity is studied. Explicit asymptotic expressions for the largest Lyapunov exponent for various values of the system parameters are obtained by using a combination of the method of stochastic averaging and a well-known procedure due to Khas’minskii, from which the asymptotic stability boundaries are determined. As an application, the example of the flexural-torsional instability of a thin elastic beam acted upon by a stochastically fluctuating load at the central cross-section of the beam is investigated.
Scattering of Water Waves by a Pair of Semi-infinite Barriers
Authors: McIver P. , Rawlins A. D.
Published: April 2008

A previously published solution by the method of matched asymptotic expansions for scattering of long water waves by a pair of semi-infinite barriers is known to be incorrect. Here the reasons for this are examined and a revised procedure given that recovers the long-wave expansion of the known exact solution.
Small Vibrations of Rotating Ring Segments and Full Rings Under External or Internal Pressure
Authors: Pelchen Christoph , Wauer Jo¨rg
Published: April 2008

The combined effect of a radial pressure load and a centrifugal field on the vibrations of an inextensible, circular, slender ring structure is treated. First, the stationary pre-buckling state of the segment or the full ring is specified. Then small oscillations about this configuration are investigated. The variations of vibration frequencies with the pressure load and the speed rate are examined and possible buckling loads are determined.
Singular Plastic Fields in Steady Penetration of a Rigid Cone
Authors: Durban David , Fleck Norman A.
Published: April 2008

The essential features of the active plastic zone at the tip of a penetrating rigid cone are investigated for a rigid/perfectly plastic solid. An exact solution is suggested for the plastic zone. A rigid zone exists ahead of the cone and is separated from the plastic zone by a conical surface of discontinuity. It is assumed that the material yields instantaneously by going through a “shear shock” across the rigid/plastic interface. The orientation of the interface is determined by an ad hoc requirement for minimum shear strain jump at the shear shock. Results are presented for different cone angles and friction factors. The stresses within the plastic zone admit a logarithmic singularity whose level increases with cone angle and wall friction.
Chaotic Responses of a Two-Degree-of-Freedom Elastic-Plastic Beam Model to Short Pulse Loading
Authors: Lee J.-Y. , Symonds P. S. , Borino G.
Published: April 2008

The paper discusses chaotic response behavior of a beam model whose ends are fixed, so that shallow arch action prevails after moderate plastic straining has occurred due to a short pulse of transverse loading. Examples of anomalous displacement-time histories of a uniform beam are first shown. These motivated the present study of a two-degree-of-freedom model of Shanley type. Calculations confirm these behaviors as symptoms of chaotic unpredictability. Evidence of chaos is seen in displacement-time histories, in phase plane and power spectral diagrams, and especially in extreme sensitivity to parameters. The exponential nature of the latter is confirmed by calculations of conventional Lyapunov exponents and also by a direct method. The two-degree-of-freedom model allows use of the energy approach found helpful for the single-degree-of-freedom model (Borino et al., 1989). The strain energy is plotted as a surface over the displacement coordinate plane, which depends on the plastic strains. Contrasting with the single-degree-of-freedom case, the energy diagram illuminates the possibility of chaotic vibrations in an initial phase, and the eventual transition to a smaller amplitude nonchaotic vibration which is finally damped out. Properties of the response are further illustrated by samples of solution trajectories in a fixed total energy plane and by related Poincare section plots.
On the Identification of a Harmonic Force on a Viscoelastic Plate From Response Data
Authors: D’Cruz J. , Crisp J. D. C. , Ryall T. G.
Published: April 2008

The problem of determining the force acting on a structure from measurements of the response of the structure to the force is an inverse problem. Presented is a method for determining the location, magnitude, and phase of a harmonic point force acting on a simply-supported classical viscoelastic rectangular plate from a number of displacement readings at discrete points on the plate. Presented also is a demonstration of the robustness of the solution technique to the effects of measurement noise as well as a means by which problems involving more general structural and loading configurations may be solved.
Three-Dimensional Solutions for the Free Vibrations and Buckling of Thermally Stressed Multilayered Angle-Ply Composite Plates
Authors: Noor Ahmed K. , Burton W. Scott
Published: April 2008

Analytic three-dimensional elasticity solutions are presented for the free vibration and buckling of thermally stressed, multilayered, angle-ply composite plates. Sensitivity derivatives are also evaluated and used to study the sensitivity of the vibration and buckling responses to variations in the different lamination and material parameters of the plate. The plates are assumed to have rectangular geometry and an antisymmetric lamination with respect to the middle plane. The temperature is assumed to be independent of the surface coordinates, but has an arbitrary symmetric variation through the thickness of the plate. A linear, Duhamel-Neumann type constitutive model is used, and the material properties are assumed to be independent of temperature. The thermal plate response is subjected to time-varying perturbation displacements, strains, and stresses. A mixed formulation is used with the fundamental unknowns consisting of the six perturbation stress components and the three perturbation displacement components of the plate. The initial thermal deformations are accounted for. Each of the plate variables is decomposed into symmetric and antisymmetric components in the thickness direction, and is expressed in terms of a double Fourier series in the Cartesian surface coordinates. Numerical results are presented showing the effects of variations in material characteristics and fiber orientation of different layers, as well as the effects of initial thermal deformations on the vibrational and buckling responses of the plate, as well as their sensitivity derivatives.
Elastodynamic Response of a Unidirectional Composite Laminate to Concentrated Surface Loads: Part I
Authors: Mal Ajit K. , Lih Shyh-shiuh
Published: April 2008

The quantitative features of the elastodynamic field produced in a unidirectional graphite/epoxy composite laminate by surface loads are studied. The material of the composite is modeled as a transversely isotropic dissipative medium with its symmetry axis parallel to the laminate surface. The surface displacement produced by a transient concentrated point load on the surface of a uniform half-space and a plate of finite thickness is calculated by means of a multiple transform technique followed by inversion through numerical integration. The two-dimensional (plane-strain) line load problems for the plate are also solved as special cases. In addition, an approximate solution based on the classical plate bending theory which includes transverse shear and rotary inertia is obtained and the range of validity of the approximate solution is determined through comparison with the exact results. The multiple transform technique is shown to be a viable alternative to finite element and other numerically intensive computational schemes for wave field calculations in composite laminates. Part I of the paper contains the formulation, and a discussion of the general features of the response, the numerical treatment and results are given in Part II.
Nonlinear Dynamics of In-Plane Loaded Imperfect Rectangular Plates
Authors: Bhimaraddi Alavandi
Published: April 2008

This paper deals with the nonlinear vibrations of composite laminated plates using the generalized formulation of which the von Karman-type formulation is a special case. The two-dimensional plate theory used is that of a parabolic shear theory in which the transverse shear strain distribution is parabolic across the plate thickness. The resulting governing equations of this formulation are nonlinear is all the plate displacement parameters unlike the von Karman model in which they are nonlinear in the lateral displacement only. Because of this complex nature of the equations the usual approach for nonlinear plate analysis cannot be used, and hence a regular perturbation technique has been adopted to obtain the solution of these equations. All the complexities like the initial imperfections and in-plane applied edge loads have also been included in the analysis. Numerical examples for simply-supported plates indicate that for in-plane loaded imperfect plates, the von Karman formulation differs slightly when compared with the present more general formulation.
The Effect of Compressibility on the Stress Distributions in Thin Elastomeric Blocks and Annular Bushings
Authors: Lai Yeh-Hung , Dillard D. A. , Thornton J. S.
Published: April 2008

The effect of the bulk compressibility of elastomers on the response of rubber blocks and bushings bonded to platens is in vestigated. Closed-form solutions for the stresses and deformations within the elastomer are presented for the case of rigid adherends. It is shown that even with relatively small shape factors, the compressibility can significantly affect the apparent stiffness. A finite element analysis shows that the closed-form solution accurately predicts the stress distribution for rigid adherends, but also reveals that platen deformations in realistic systems may significantly alter the distributions.
On the Proper Boundary Conditions for a Beam
Authors: Fan H. , Widera G. E. O.
Published: April 2008

Employing the asymptotic expansion approach, the boundary conditions of a beam are reconsidered in the present paper. Gregory and Wan’s (1984) decay analysis technique is extended here to formulate the boundary conditions for the outer expansion. Among the various prescribed boundary data, most of the attention is focused on the displacement case because engineering beam theories employ incorrect conditions for these data. Numerical calculations are carried out for the displacement prescribed beam having a circular cross-section.
Coefficients of Restitution
Authors: Smith Charles E. , Liu Pao-Pao
Published: April 2008

Simplified procedures for predicting post-collision motion in a mechanical system usually incorporate a “coefficient of restitution,” a ratio that must be estimated before the prediction can be completed. Two such ratios have been widely used for some time and a third has been introduced recently by W. J. Stronge. The dependence of these ratios on parameters that characterize various collisions is examined here, using simplifying assumptions about the contact mechanism and with a finite element code. For some collisions all three coefficients of restitution are identical, while significant distinctions can result from other combinations of system configuration, direction of approach velocity, and coefficient of friction.
A Second-Order Approximate Analytical Solution of a Simple Pendulum by the Process Analysis Method
Authors: Liao S. J.
Published: April 2008

In this paper, a new kind of analytical method of nonlinear problem called the process analysis method (PAM) is described and used to give a second-order approximate solution of a simple pendulum. The PAM does not depend on the small parameter supposition and therefore can overcome the disadvantages and limitations of the perturbation expansion method. The analytical approximate results at the second-order of approximation are in good agreement with the numerical results. They are compared with perturbation solutions, and it appears that even the firstorder solutions are more accurate than the perturbation solutions at second-order of approximation.
Node Control of Uniform Beams Subject to Various Boundary Conditions
Authors: Weaver L. , Silverberg L.
Published: April 2008

This paper introduces node control, whereby discrete direct feedback control forces are placed at the nodes of the N+1th mode (the lowest N modes participate in the response). Node control is motivated by the node control theorem which states, under certain conditions, that node control preserves the natural frequencies and natural modes of vibration of the controlled system while achieving uniform damping. The node control theorem is verified for uniform beams with pinned-pinned, cantilevered, and free-free boundary conditions, and two cases of beams with springs on the boundaries. A general proof of the node control theorem remains elusive.