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The present work deals with the dynamic response of structures that are irregular in height, consisting of two parts, a lower part made of concrete and an upper part made of steel. Irregularity is due to different dynamic responses of the two parts, here expressed by their different damping ratios and inelastic material laws. The seismic design of such structures is not satisfactorily covered by current design codes, especially if a decoupled procedure is chosen for the analysis, where the lower part is excited first and its response is used as excitation for the upper part. The present paper aims at contributing toward better understanding of the interaction between the two parts and at proposing improved decoupling criteria for the seismic analysis of inelastic primary-secondary systems. Toward that goal, each part is modeled as a one-degree-of-freedom system, and the maximum responses of coupled and decoupled inelastic time history analyses are compared over a wide range of dynamic characteristics and strength levels of the two parts. The results are presented in the form of error levels between the two alternative analysis procedures. DOI: 10.1061/(ASCE)EM.1943-7889.0000166 CE Database subject headings: Seismic analysis; Inelasticity. Author keywords: Secondary systems; Inelasticity; Decoupling error.

There are two important factors that accompany heat-induced shrinkage of collagenous tissues: mechanical property degradation and partial recovery from the shrunken length (elongation) upon returning to room temperature (defined here as acute recovery). These undesirable factors reduce the efficacy of thermal therapies. We applied chemical cross-linking adjuvant to thermal treatment on New Zealand White rabbit patellar tendon complexes to explore the feasibility of reducing the impact of these undesirable side-effects. Our results have shown that with exposure to 0.5% w/v glutaraldehyde solution during heating, the recovery response of the patellar tendon tissue was decreased, and the mechanical properties of the tissue were significantly improved. [DOI: 10.1115/1.4001924]

As an alternative to purely mechanical methods, optical tracking of passive osmotic swelling was used to assess mechanical properties of the porcine lens capsule. A simple model was developed accounting for the permeability of the lens fiber cells and capsule to water, the concentration of fixed charges in the fiber cells, and the capsule's resistance to the swelling of fiber cells. Fitting the model solution to experimental data provided an estimate of the elastic modulus of the lens capsule under the assumption of linear isotropic elasticity. The calculated elastic modulus at a fixed charge density of 20 mol [m.sup.-3] was 2.0 [+ or -] 0.5 MPa (mean [+ or -] 95% confidence interval; n = 15) for 0.1% saline solution, 0.64 [+ or -] 0.3 MPa (n = 10) for 0.2% saline solution, and 0.28 [+ or -] 0.5 MPa (n =6) for 0.5% saline solution. These values are comparable to previously reported moduli of elasticity for the porcine lens capsule at small strains ( Keywords: modulus of elasticity, lens capsule, osmotic pressure, membrane transport, Donnan equilibrium

In this paper, a node sampling methodology for nonlinear vibration problems of elastic structures involving intermittent contact is proposed. Of particular interest is a vibration problem of platelike elastic structures with a crack, with a large number of degrees of freedom involved on the crack surfaces. Because of the localized nature of such nonlinearity, the number of degrees of freedom on the surfaces greatly affects the computational time of the analysis. Therefore, reducing the number of degrees of freedom on the crack surfaces without significantly sacrificing the accuracy of the results is a critical issue for conducting vibration analysis of such structures in a reasonable amount of time. The focus is placed on the development of an efficient algorithm to select a set of nodes on the crack surfaces, where nonlinear boundary conditions are imposed. The method is developed, based on a procedure for selecting master degrees of freedom for Guyan reduction. The accuracy, efficiency, and optimality of the method are discussed in detail and compared with those aspects of previous methods. The advantages of the new method are demonstrated in terms of the accuracy of the frequency response and the resonant frequencies. DOI: 10.2514/1.J050061

Several aspects of the seismic response of groups containing nonvertical piles are studied, including the lateral pile- head stiffnesses, the 'kinematic' pile deformation, and the 'inertial' soil-pile-structure response. A key goal is to explore the conditions under which the presence of batter piles is beneficial, indifferent, or detrimental. Parametric analyses are carried out using three-dimensional finite-element modeling, assuming elastic behavior of soil, piles, and superstructure. The model is first used to obtain the lateral stiffnesses of single batter piles and to show that its results converge to the available solutions from the literature. Then, real accelerograms covering a broad range of frequency characteristics are employed as base excitation of simple fixed-head two-pile group configurations, embedded in homogeneous, inhomogeneous, and layered soil profiles, while supporting very tall or very short structures. Five pile inclinations are considered while the corresponding vertical-pile group results serve as reference. It is found that in purely kinematic seismic loading, batter piles tend to confirm their negative reputation, as had also been found recently for a group subjected to static horizontal ground deformation. However, the total (kinematic plus inertial) response of structural systems founded on groups of batter piles offers many reasons for optimism. Batter piles may indeed be beneficial (or detrimental) depending on, among other parameters, the relative size of the overturning moment versus the shear force transmitted onto them from the superstructure. DOI: 10.1061/(ASCE)GT.1943-5606.0000337 CE Database subject headings: Piles; Lateral loads; Seismic effects; Numerical models; Kinematics; Soil-structure interactions; Elasticity. Author keywords: Batter piles; Lateral loading; Seismic response; Numerical modeling; Kinematic response; Inertial response; Soil-structure interaction.

Current models to determine the local buckling stress of inelastic plates under in-plane loading are based on plastic deformation theory and semirational or empirical relationships. A successful [J.sub.2] flow theory describing inelastic local buckling of initially perfect plates needs to avoid two well-known pitfalls known as the 'inelastic column buckling paradox' and the 'plastic buckling paradox.' While the former problem, which found its origin in 1895 in Engesser's double modulus approach, was resolved by Shanley in the late 1940s, a convincing solution of the plastic buckling paradox has not yet been presented. This paper proposes a modification to the [J.sub.2] flow theory which hinges on the determination of the shear stiffness from second-order considerations. A differential equation is derived which describes the incremental plate deformations at the inelastic local buckling load. The differential equation is studied for two cases of boundary conditions: a plate simply supported along four edges and a plate simply supported along three edges with one longitudinal edge free. DOI: 10.1061/(ASCE)EM.1943-7889.0000075 CE Database subject headings: Inelasticity; Buckling; Plates; Deformation. Author keywords: Inelastic plate buckling; Non-linear material; Plastic buckling paradox; Plate theory; Local buckling.

In this note it is shown that the combination of conventional laminas (possessing positive Poisson's ratio) and auxetic laminas (possessing negative Poisson's ratio) gives rise to effective in-plane composite laminate Young's modulus that surpasses the rule-of mixture formula. To enable comparison between the developed model with the rule-of-mixture, the former is presented in such a way that two correction functions exist distinctively for multiplication into the two terms of the rule-of-mixture formula. Each of the two correction functions reduces to a minimum of 1 when all laminas possess equal Poisson's ratio, and the correction functions are greater than one when there exists mismatch in the Poisson's ratios among the laminas in the laminate. Plotted results show that the overshooting of the laminate's effective in-plane modulus is significant for semiauxetic laminates but not for conventional and fully auxetic materials. DOI: 10.1061/(ASCE)EM.1943-7889.0000167 CE Database subject headings: Composite materials; Laminates; Stiffness; Young's modulus. Author keywords: Composite laminate; Effective modulus; Rule-of-mixture; Semiauxetics.

A short linear cavity erbium fiber laser is adapted to become a Q-switched laser by using a new and simple loss switching technique. The technique utilizes the inherent flexibility of optical fiber to rapidly drive the fiber end in and out of alignment with a cavity mirror, creating the conditions necessary for Q-switching. We investigate the effectiveness of different Q-switch configurations and analyze the Q-switch opening time of each configuration. [c] 2010 Optical Society of America OCIS codes: 060.2410, 060.3510, 140.3500, 140.3510, 140.3540.

In operating shell-and-tube heat exchangers, tube vibration induced by cross-flow can be a serious problem. The region of concern in steam generators is the upper most U-bend region where the flow crosses a large number of tubes, which also cause significant hydraulic resistance. This hydraulic resistance forces the flow to change direction. From a fluidelastic instability point of view, the tube bundle is excited by oblique cross-flow. A secondary consequence of change in flow direction is a change in the flexibility direction of the tubes relative to the oncoming flow direction at different locations within the U-bend region. It is this somewhat simpler problem that is studied in this work. The effect of array flexibility direction on the fluidelastic instability phenomenon in a rotated-triangular tube bundle is investigated for single phase flow as a starting point. The study consists of both experiments and theoretical analysis of a simplified single-flexible-tube array. Experimental tests are conducted in a wind tunnel on a reconfigurable tube bundle. The results show that fluidelastic instability is strongly dependent on the flexibility angle. The results also show that, generally, the elimination of bundle flexibility in the direction transverse to the flow has a strong stabilizing effect on the tube bundle. The effect is, however, nonlinearly related to flexibility angle. In the second part of this work, the quasi-steady fluidelastic analysis is adapted for a single tube (within a rigid array), flexible in a single but arbitrary direction relative to the flow and subjected to cross-flow. The fluid-force expressions are rewritten to account for an arbitrary tube flexibility direction relative to the approaching flow. In the process, a simplified, flexibility direction dependent, one degree-of-freedom equation is obtained. The model is then evaluated against measured experimental data. This evaluation shows that the predicted critical flow velocity for fluidelastic instability is in qualitative agreement with experimental results, at least in the trend on the effect of varying the flexibility angle. At the same time, the model sheds some light on the role played by the flexibility angle in determining the overall fluid-structure damping underlying the observed stability behavior. [DOI: 10.1115/1.4002181]

This study investigates unsteady flow in tube bundles and fluid forces, which can lead to large tube vibration amplitudes, in particular, amplitudes associated with fluidelastic instability (FEI). The fluidelastic forces are approximated by the coupling of the unsteady flow model (UFM) with computational fluid dynamics (CFD). The CFD model employed solves the Reynolds averaged Navier--Stokes equations for unsteady turbulent flow and is cast in an arbitrary Lagrangian--Eulerian form to handle any motion associated with tubes. The CFD solution provides time domain forces that are used to calculate added damping and stiffness coefficients employed with the UFM. The investigation demonstrates that the UFM utilized in conjunction with CFD is a viable approach for calculating the stability map for a given tube array. The FEI was predicted for in-line square and normal triangle tube arrays over a mass damping parameter range of 0.1-100. The effect of the P/d ratio and the Reynolds number on the FEI threshold was also investigated. [DOI: 10.1115/1.4002112]

This paper presents simulations of a loosely supported cantilever tube subjected to turbulence and fluidelastic instability forces. Several time domain fluid force models are presented to simulate the damping-controlled fluidelastic instability mechanism in tube arrays. These models include a negative damping model based on the Connors equation, fluid force coefficient-based models (Chen, 1983, 'Instability Mechanisms and Stability Criteria of a Group of Cylinders Subjected to Cross-Flow. Part 1: Theory,' Trans. ASME, J. Vib., Acoust., Stress, Reliab. Des., 105, pp. 51-58; Tanaka and Takahara, 1981, 'Fluid Elastic Vibration of Tube Array in Cross Flow,' J. Sound Vib., 77, pp. 19-37), and two semi-analytical models (Price and Paidoussis, 1984, 'An Improved Mathematical Model for the Stability of Cylinder Rows Subjected to Cross-Flow,' J. Sound Vib., 97(4), pp. 615-640; Lever and Weaver, 1982, 'A Theoretical Model for the Fluidelastic Instability in Heat Exchanger Tube Bundles,' ASME J. Pressure Vessel Technol., 104, pp. 104-147). Time domain modeling and implementation challenges for each of these theories were discussed. For each model the flow velocity and the support clearance were varied. Special attention was paid to the tube/support interaction parameters that affect wear, such as impact forces and normal work rate. As the prediction of the linear threshold varies depending on the model utilized, the nonlinear response also differs. The investigated models exhibit similar response characteristics for the lift response. The greatest differences were seen in the prediction of the drag response, the impact force level and the normal work rate. Simulation results show that the Connors-based model consistently underestimates the response and the tube/support interaction parameters for the loose support case. [DOI: 10.1115/1.4001700]

Thermoelastic damping in contour-mode in-plane vibrations of rings, disks, and elliptical plates is investigated on various size scales, using a reduced finite element formulation. The Fourier scheme is applied to the axisymmetric geometries including circular rings and disks, and is found to be remarkably efficient in searching solutions. The numerical accuracy is further improved by the implementation of quadratic interpolation functions. The computational results are validated by comparing with the commercial software packages as well as the existing analytical solutions in literature. For resonators of elliptical shapes, the dominant frequency has a weak dependence on the geometric aspect ratio [gamma], whereas the effect of [gamma] on the quality factor (Q value) is much stronger and the peak Q value of the leading mode consistently occurs in the vicinity of [gamma] = 1.42. [DOI: 10.1115/1.4001506]

Consider a cylinder made of a microstretch thermoelastic material for which one plane end is subjected to plane boundary data varying harmonically in time. On the lateral surface and other base, we have zero body force and heat supply. By using a Toupin type measure associated with the corresponding steady-state vibration, and by assuming that the angular frequency of oscillations is lower than a certain critical frequency, we show that the amplitude of the vibrations decays exponentially with the distance to the base. This decay estimate is similar to that of the Saint-Venant type. [DOI: 10.1115/1.4000971] Keywords: thermoelasticity, microstretch, harmonic, vibrations

The mechanical performance of pavement systems depends on the stiffness of subsurface soil and aggregate materials. The moduli of base course, subbase, and subgrade soils included in pavement systems need to be characterized for their use in the new empirical-mechanistic design procedure (NCHRP 1-37A). Typically, the resilient modulus test is used in the design of base and subbase layers under repetitive loads. Unfortunately, resilient modulus tests are expensive and cannot be applied to materials that contain particles larger than 25 mm (for 125-mm diameter specimens) without scalping the large grains. This paper examines a new methodology for estimating resilient modulus based on the propagation of elastic waves. The method is based on using a mechanistic approach that relates the P-wave velocity-based modulus to the resilient modulus through corrections for stress, void ratio, strain, and Poisson's ratio effects. Results of this study indicate that resilient moduli are approximately 30% of Young's moduli based on seismic measurements. The technique is then applied to specimens with large-grain particles. Results show that the methodology can be applied to large-grained materials and their resilient modulus can be estimated with reasonable accuracy based on seismic techniques. An approach is proposed to apply the technique to field determinations of modulus. DOI: 10.1061/(ASCE)GT.1943-5606.0000329 CE Database subject headings: Resilient modulus; Seismic effects; Base course; Subbases; Granular media; Wave measurement; Elasticity. Author keywords: Resilient modulus; Seismic modulus; Base course; Subbase course; Large-grain materials; Granular materials.

Most of the rock medium possesses intrinsic grain orientation or preferred bedding and joint directions, thus requiring the use of at least transverse isotropy to describe its elastic behavior. This paper presents a series of charts, based on extensive finite element parametric studies along with nonlinear regression analysis of FE simulation results, for estimating the subgrade reaction modulus (or initial tangent to the p-y curve) using five elastic constants of a transversely isotropic rock mass. The proper characterization of subgrade reaction modulus is critical for accurate prediction of the elastic lateral deflection of a rock socketed drilled shaft under the applied lateral loads. The sensitivity of the response of a laterally loaded drilled shaft to the degree of anisotropy and orientation of the plane of anisotropy (bedding plane direction of the rock medium) was demonstrated in this paper for an actual lateral load testing case in Ohio. It is highly recommended to use five elastic constants to estimate subgrade reaction modulus of rock medium exhibiting high degree of cross anisotropy. DOI: 10.1061/(ASCE)GT.1943-5606.0000271 CE Database subject headings: Subgrades; Isotropy; Finite element method; Rock masses; Drilled shafts; Deflection. Author keywords: Subgrade reaction modulus; Transverse isotropy; p-y curve; Finite element; Rock mass; Rock socketed drilled shaft; Lateral deflection.

The analysis of microheterogeneous materials exhibiting eigenstressed and/or eigenstrained phases requires an estimation of eigenstrain influence tensors. Within the framework of continuum micromechanics, we here derive these tensors from extended Eshelby-Laws matrix-inclusion problems, considering, as a new feature, an auxiliary matrix eigenstress. The auxiliary matrix eigenstress is a function of all phase eigenstresses and, hence, accounts for eigenstress interaction. If all material phases are associated with one and the same Hill tensor, the proposed method degenerates to the well-accepted transformation field analysis. Hence, the proposed concept can be interpreted as an extension of the transformation field analysis toward consideration of arbitrarily many Hill tensors, i.e., as an extension toward heterogeneous elastic media comprising inclusion phases with an arbitrary ellipsoidal shape and with arbitrary spatial orientation. This is of particular interest when studying heterogeneous media consisting of constituents with nonspherical phase shapes, e.g., cement-based materials including concrete, or bone. As for polycrystals studied by means of the self-consistent scheme, the auxiliary matrix eigenstress turns out to be equal to the eigenstresses homogenized over the representative volume element (RVE), which is analogous to the self-consistent assumption that the auxiliary stiffness is the average stiffness of the RVE. The proposed method opens the door for micromechanics-based modeling of a great variety of composite phase behaviors characterized by eigenstresses or eigenstrains, e.g., thermoelasticity, poroelasticity, drying-shrinkage, as well as general forms of inelastic behavior, damage, fatigue, and fracture. DOI: 10.1061/(ASCE)EM.1943-7889.0000138 CE Database subject headings: Micromechanics; Inelasticity; Material properties; Transformation. Author keywords: Micromechanics; Homogenization; Transformation field analysis; Generalized Eshelby problem; Thermoelastic moduli; Eigenstrain influence tensor.

Linear consolidation analyses are usually treated either by means of Terzaghi-Rendulic uncoupled theory or Blot's consolidation theory. In this note, the problem of consolidation displacements around an axially loaded sphere was considered. It is demonstrated that both the uncoupled analysis and the coupled analysis give the same governing equation for pore fluid pressure dissipation with time. A simplified procedure for deriving transient strain components is illustrated. A general solution for time-dependent displacements is obtained using uncoupled consolidation analysis. Close agreement is evident between the new approximate uncoupled analysis solution and the existing coupled analysis solution with a maximum error of less than 0.5%. DOI: 10.1061/(ASCE)EM.1943-7889.0000149 CE Database subject headings: Elasticity; Poroelasticity; Spheres; Deformation; Coupling. Author keywords: Elastic analysis; Poroelasticity; Spheres; Deformation.

An experimental investigation on the axial load capacity of fixed-end pretwisted steel bars of rectangular solid cross sections is described in this paper. The fixed-end bar test conducted in this study includes bars with both ends griped and embedded in cylindrical slips. More than 200 specimens are considered in this study containing bars with four different cross sections, widths of 20 mm or 30 mm and thicknesses of 3 mm or 6 mm, and three different lengths of 300, 400, and 500 mm. The samples are twisted beyond their elastic limit using torque machine and then subjected to axial load using a compression MTS machine. A set of twisting angles ranges between 0 and 225[degrees] is considered for each length. Three samples are tested for each angle then the average of the results is calculated. It is proven experimentally that the permanent twists have influenced the axial strength and the static performance of the pretwisted bars. This improvement is supported by the considerable increase in the critical buckling loads of the bars for certain angles of twists. Multiple regression analysis (MRA) is also conducted using the experimental results to develop mathematical models capable of predicting the critical loads of the tested bars. Results indicate that, with a minimal processing of data, MRA could predict well the critical loads of the pretwisted bars within 99% confidence interval. DOI: 10.1061/(ASCE)EM.1943-7889.0000144 CE Database subject headings: Inelasticity; Steel; Bars; Critical loads; Experimentation; Regression analysis. Author keywords: Inelastic pretwisting; Steel bars; Critical load; Experimental investigation; Multiple regression analysis.

In computational mechanics, strain softening generates ill-posed boundary value problems, which cannot be solved without being regularized, e.g., through the introduction of an internal length scale. This paper investigates how the internal length scale that is introduced by regularization may interact with the external length scale arising from boundary conditions in the particular case of a strain-softening bar of varying cross section and a nonlocal averaging regularization. The interaction of internal and external length scales is examined using an analytical closed-form solution for overnonlocal softening plasticity that derives from a Fredholm equation of the second kind. In the absence of external length (bars of constant section), the analysis shows that the overnonlocal averaging confines and smoothly distributes plastic strain into a localized band. The localization width, plastic strain distribution inside the band, and load-displacement response are controlled by the internal length of the averaging function and the overnonlocal weighting factor. In the presence of external length (bar of varying section), the analytical solution shows that the localization width is controlled by the interaction of external and internal length scales. This interaction is significant when the external and internal lengths are of comparable magnitude, and decreases when the external length becomes large compared to the internal length. The bandwidth is found to depend on the internal and external lengths and stress level while strain localizes, and to relate only to the internal length when the bar collapses. DOI: 10.1061/(ASCE)EM.1943-7889.0000145 CE Database subject headings: Strain; Localization; Plasticity; Bars. Author keywords: Strain localization; Nonlocal material; Strain softening plasticity; Regularization; Analytical solution.

This paper presents an investigation on the dynamic instability of cantilevered nanorods/nanotubes subjected to an end follower force. Eringen's nonlocal elasticity theory is employed to allow for the small length scale effect in the considered dynamic instability problem. The general solution for the governing differential equation is obtained and the dynamic instability characteristic equation is derived by applying the boundary conditions. Exact critical load factors are obtained. These nonlocal solutions are compared with the classical local solutions to assess the sensitivity of the small length scale effect on the critical load factors and flutter mode shapes. It is found that the small length scale effect decreases the critical load and the corresponding frequency parameters as well as reduces the severity of the double-curvature flutter mode shape. DOI: 10.1061/(ASCE)EM.1943-7889.0000135 CE Database subject headings: Dynamic stability; Nanotechnology; Rods; Elasticity; Flutter. Author keywords: Dynamic stability; Follower force; Nanorods/nanotubes; Nonlocal beam theory.

A family of interaction expressions are developed for steel elliptical hollow sections (EHSs) subjected to combinations of axial force, biaxial bending moments, torsion, and bimoments. The formulation is based on kinematically admissible strain fields within the context of the upper bound theorem of plasticity. The interaction relations derived successfully capture the effect of confining radial strains present at welded end sections, as well as sections that are free to deform in the radial direction away from end welded sections. The interaction expressions developed consist of a set of elliptical integrals which are cast in a dimensionless form applicable for EHS of general geometries. An iterative solution technique is developed to solve the resulting nonlinear relations. The applicability of the resulting interaction relations for conducting the cross-sectional check is illustrated through examples. A comparison with shell finite-element analysis results illustrates the validity of the interaction relations derived. DOI: 10.1061/(ASCE)EM.1943-7889.0000141 CE Database subject headings: Steel; Hollow sections; Plasticity; Finite element method. Author keywords: Steel; Elliptical hollow section; Plasticity; Yield surface; Bimoments.

This paper presents a nonlinear thermal buckling analysis of circular shallow pin-ended arches that are subjected to a linear temperature gradient field in the plane of curvature of the arch. The linear temperature gradient produces axial expansion and curvature changes in the arch. The bending action produced by the curvature change and the axial compressive action produced by the restrained axial expansion may lead the arch to buckle suddenly in the plane of its curvature. The end reactions resulting from the restrained axial expansion also produce bending actions that are opposite to that produced by the temperature differential and tend to produce deflections on the convex side of the arch. A geometrically nonlinear analysis for thermoelastic buckling has been carried out based on a virtual work technique, and analytical solutions for the critical temperature gradients for the in-plane limit instability and bifurcation buckling are obtained. It is found that antisymmetric bifurcation is the dominant buckling mode for most shallow arches that are subjected to a linear temperature gradient. The limit instability is possible only for slender and shallow arches. It is also found that a characteristic value of the arch geometric parameter exists and that arches whose geometric parameter is less than this characteristic value show no typical buckling behavior. The formula for this characteristic value of the arch geometric parameter is derived. DOI: 10.1061/(ASCE)EM.1943-7889.0000134 CE Database subject headings: Arches; Bifurcations; Buckling; Closed form solutions; Postbuckling; Temperature effects; Nonlinear analysis. Author keywords: Analysis; Arches; Bifurcation; Buckling; Closed form solutions; Instability; Nonlinear; Postbuckling; Temperature gradient; Thermoelastic; Snap through.

Applications involving highly loaded elastohydrodynamic lubrication (EHL), particularly when the lubricant experiences shear thinning, operating with small film thicknesses may necessitate consideration of surface asperities. A modified Reynolds equation with provision for surface roughness and shear thinning is treated to predict the pressure and surface asperity effect in an EHL line-contact. The unknown in the Reynolds equation is the hydrodynamic pressure instead of the total pressure to ensure that the pressure boundary condition at the outlet is properly posed. The Carreau viscosity model is used for characterizing the shear thinning behavior, Patir and Cheng flow factors for taking into the influence of roughness on the lubricating film, and Greenwood--Trip for determination of pressure at the asperity level. The modified Reynolds equation is solved for the hydrodynamic pressure instead of the total pressure with appropriately defined boundary conditions. [DOI: 10.1115/1.4001787]

Elastohydrodynamic lubrication (EHL) is an important branch of the lubrication theory, describing lubrication mechanisms in nonconformal contacts widely found in many mechanical components such as various gears, rolling bearings, cams and followers, metal-rolling tools, traction drives, and continuous variable transmissions. These components often transmit substantial power under heavy loading conditions. Also, the roughness of machined surfaces is usually of the same order of magnitude as, or greater than, the estimated average EHL film thickness. Consequently, most components operate in mixed lubrication regime with significant asperity contacts. Due to very high pressure concentrated in small areas, resulted from either heavy external loading or severe asperity contacts, or often a combination of both, subsurface stresses may exceed the material yield limit, causing considerable plastic deformation, which may not only permanently change the surface profiles and contact geometry but also alter material properties through work hardening as well. In the present study, a three-dimensional plastoelastohydrodynamic lubrication (PEHL) model has been developed by taking into account plastic deformation and material work-hardening. The effects of surface/subsurface plastic deformation on lubricant film thickness, surface pressure distribution, and subsurface stress field have been investigated. This paper briefly describes the newly developed PEHL model and presents preliminary results and observed basic behavior of the PEHL in smooth-surface point contacts, in comparison with those from corresponding EHL solutions under the same conditions. The results indicate that plastic deformation may greatly affect contact and lubrication characteristics, resulting in significant reductions in lubricant film thickness, peak surface pressure and maximum subsurface stresses. [DOI: 10.1115/1.4001813] Keywords: plasto-elastohydrodynamic lubrication (PEHL), elastohydrodynamic lubrication, plastic deformation, elastic-plastic contact, plastic deformation, tribology

A model for the contact area and static friction of nominally flat rough surfaces and rough spherical surfaces is presented. The model extends previously published models, which am limited to plasticity index values below 8, to higher plasticity, index values by accounting for fully plastically deformed asperities based on finite element results by Jackson and Green [2005, 'A Finite Element Study of Elasto-Plastic Hemispherical Contact Against a Rigid Flat,' Trans. ASME, J. Tribol., 127, pp. 343-354]. The present model also corrects some deficiencies of the earlier models at very small plasticity index values below 0.5. [DOI: 10.1115/1.4001555] Keywords: rough surfaces, plasticity index, fully plastic contact

The paper studies the dynamical propagation of star-shaped cracks symmetrically arranged in an elastic thin plate, subjected to the action of instantly applied, comprehensively (uniformly) stretching stresses, which implies a self-similar problem with homogeneous stresses and velocities of particles. Occurrence of such motion patterns is established through experiments. By using the Smirnov--Sobolev functional-invariant solutions method and a careful choice of mappings, the problem is reduced to some boundary value problem of the theory of complex variable functions, and exact analytic solution of the original problem, including a closed-form solution for important stress intensity coefficient near the end of the crack, is derived. We also establish a fundamental theoretical limit imposed on the number of cracks--there has to be at least three cracks. [DOI: 10.1115/1.4000900]

We investigate the problem of an N-phase elliptical inhomogeneity in plane elasticity. The elliptical inhomogeneity is bonded to the unbounded matrix through the intermediate (N - 2) interphases, and the matrix is subjected to remote uniform stresses. We observe that the stress field inside the elliptical inhomogeneity is still uniform when the following two conditions are satisfied: (i) The formed interfaces are (N - 1) confocal ellipses, and (ii) the interphases and the matrix possess the same shear modulus but different Poisson's ratios. In Appendixes A and B, we also discuss an arbitrary number of interacting arbitrary shaped inhomogeneities embedded in an infinite matrix, and an N-phase inhomogeneity with (N - 1) interfaces of arbitrary shape. Here all the phases comprising the composite possess the same shear modulus but different Poisson's ratios. The results in the main body and in Appendixes A and B are further extended in Appendix C to finite plane strain deformations of compressible hyperelastic harmonic materials. [DOI: 10.1115/1.4000929] Keywords: layered elliptical inhomogeneity, uniform stress field, arbitrary shaped inhomogeneity, singularity, analytic continuation

This study addresses the problem of an elastically anisotropic elliptical inhomogeneiiy bonded to an infinite elastically anisotropic matrix through a linear viscous interface. Our results show that uniform, as well as time-decaying stresses, still exist inside the elliptical inhomogeneity when the interface drag parameter, which is varied along the interface, is properly designed, and when the matrix is subjected to remote uniform antiplane shearing. Interestingly, the internal stresses decay with not one but two relaxation times. Some special cases are discussed in detail to demonstrate the obtained solutions. [DOI: 10.1115/1.4000932] Keywords: anisotropic elasticity, elliptical inhomogeneity, time-decaying uniform stress field, viscous interface, relaxation time

Buckling and post-buckling analysis is presented for axially compressed double-walled carbon nanotubes (CNTs) embedded in an elastic matrix in thermal environments. The double-walled carbon nanotube is modeled as a nonlocal shear deformable cylindrical shell which contains small scale effects and van der Waals interaction forces. The surrounding elastic medium is modeled as a tensionless Pasternak foundation. The post-buckling analysis is based on a higher order shear deformation shell theory with the yon Karman--Donnell-type of kinematic nonlinearity. The thermal effects are also included and the material properties are assumed to be temperature-dependent and are obtained from molecular dynamics (MD) simulations. The nonlinear prebuckling deformations of the shell and the initial local point defect, which is simulated as a dimple on the tube wall, are both taken into account. A singular perturbation technique is employed to determine the post-buckling response of the tubes and an iterative scheme is developed to obtain numerical results without using any assumption on the shape of the contact region between the tube and the elastic medium. The small scale parameter [e.sub.o]a is estimated by matching the buckling loads of CNTs observed from the MD simulation results with the numerical results obtained from the nonlocal shear deformable shell model. Numerical solutions are presented to show the post-buckling behavior of CNTs surrounded by an elastic medium of conventional and tensionless Pasternak foundations. The results show that buckling and post-buckling behavior of CNTs is very sensitive to the small scale parameter [e.sub.o]a. The results reveal that the unilateral constraint has a significant effect on the post-buckling response of CNTs when the foundation stiffness is sufficiently large. [DOI: 10.1115/1.4000910] Keywords: buckling, nanotube, nonlocal shell model, higher order shear deformable shell theory, temperature-dependent properties, initial point defects

The subject of the paper is cold-formed thin-walled channel beams with open or closed profile of drop flanges. The geometric properties of two C-sections are described including warping functions and warping inertia moments. The analytical solutions of problems of global and local stability of thin-walled beams are presented. The theoretical solutions of elastic buckling problems of these beams are numerically found using FEM and are experimentally verified. The results of analytical and numerical investigations are compared and presented in the tables and figures. DOI: 10.1061/(ASCE)ST.1943-541X.0000184 CE Database subject headings: Beams; Buckling; Flanges; Finite element method. Author keywords: Thin-walled beam; Global and local buckling; Drop flanges; Channel beams.

The laboratory testing of concrete has shown that elevated temperatures cause air permeability index (API) increase and elastic modulus E decrease. Indeed, the API response typically spans several orders of magnitude making it a sensitive indicator of elastic modulus reduction. However, the API versus E data has been historically assumed to be both event and concrete composition specific, thus limiting its applicability for predictive or modeling purposes. In response, a theoretical model is developed here by (1) establishing that the API is equivalent to the Darcy permeability; (2) developing a microcrack flow model accounting for tortuosity, crack density, and microcrack geometry; and (3) interpreting the Giordano and Colombo elastic modulus damage formulas in terms of the corresponding increase in permeability. The resulting general model depends on stress conditions (plane stress versus plane strain) and a single microcrack flow parameter. For materials with small Poisson's ratios, however, the model becomes independent of stress condition and both equations converge on the same simple solution. The model is verified with both field and laboratory data of concrete response to typical fire elevated temperatures and shown to be comparable in accuracy to previous empirical approaches requiting many more degrees of freedom. Moreover, the data on fire damaged concrete were found to collapse to a single curve suggesting that the microcrack flow parameter is sensitive to elevated temperature but insensitive to concrete composition. The success of the model implies certain limits to microcrack geometry and airflow turbulence in damaged concrete, both of which are discussed. DOI: 10.1061/(ASCE)MT.1943-5533.0000074 CE Database subject headings: Elasticity; Concrete; Material tests; Temperature effects; Fluid dynamics; Fire safety; Fire resistance; Forensic engineering. Author keywords: Air flow; Flow; Analysis; Elastic analysis; Stress analysis; Concrete; Concrete tests; Cracking; Fracture; Fluid dynamics; Elasticity; Fires; Fire safety; Fire resistance; Forensic engineering; Heating; Laboratory tests; Tests; Flow measurement; Nondestructive tests; Permeability; Permeability tests; Physical properties; Plain strain; Strain; Pore water; Microporosity; Portland cements; Thermal resistance; Spalling; Thermal stress; Thermal analysis.

Field and laboratory testing programs were conducted to develop an efficient methodology for estimating resilient modulus ([M.sub.r]) values of subgrade soils for use in the design of pavement structures. The field testing program consisted of obtaining Shelby tube samples of subgrade soils from different pavement projects throughout Louisiana. The laboratory program included conducting repeated load triaxial M,. tests as well as physical property tests on the collected samples. The validity of the correlation equations developed by the long-term pavement performance (LTPP) to predict the Mr was examined. In general, the LTPP model underestimated the values of M,. coefficients obtained in this study. A comprehensive regression analysis was conducted to develop models that predict the M,. coefficients of different subgrade soils in Louisiana using different physical properties. A good agreement was observed between the measured and predicted Mr coefficient values. Furthermore, the developed models had a better prediction of measured Mr coefficient values than the LTTP models. Finally. a catalog of resilient modulus of subgrade soils at different moisture content levels was developed. DOI: 10.1061/(ASCE)MT.1943-5533.0000073 CE Database subject headings: Resilient modulus; Subgrades; Pavements; Design. Author keywords: Resilient modulus; Subgrade soils; Pavement design; MEPDG; Regression models.

Shock-wave interaction with an elastic structure is investigated using a coupled numerical analysis approach, which considers solid-fluid interaction within an arbitrary Lagrangian-Eulerian framework. The analysis is performed considering a compressive shock wave, where the shock front is followed by constant pressure. An analysis procedure, which considers the change in the fluid domain due to the deformation of the solid and changes in the overpressure due to the movement of the elastic structure, is developed. Approximate numerical procedures for solving the Riemann problem associated with the shock are implemented within the Godunov finite volume scheme for the fluid domain. The influences of parameters such as structural stiffness and mass of the system on the displacement, velocity, and energy of the elastic structure following the shock-wave incidence are investigated. Immediately after the contact of the shock wave with the solid surface the pressure at the face of the elastic solid rises to a value which is equal to that obtained off of a fixed rigid wall. Subsequently, the motion of the piston produces changes in the applied pressure. The overpressure applied to the elastic system does not have a fixed profile but it depends on its elastic stiffness and structure mass. It is shown that there is a continuous exchange of energy between the air and the moving elastic structure, which produces a damped motion of the solid. The effect of damping is considerable for the cases of low elastic stiffness and low structural mass, where the resulting motion of the solid is nonoscillatory. The conventional analysis procedure, which ignores the energy exchange between the air and the moving solid, predicts an undamped oscillatory response of the structure for all cases considered. It is shown that neglecting the interaction between the air and solid can produce significant error in the total energy of the structure and the dynamic load factor when the resulting motion is nonoscillatory. DOI: 10.1061/(ASCE)AS.1943-5525.0000022 CE Database subject headings: Blasting; Elastic structures; Structural response; Fluid-structure interactions. Author keywords: Shock; Blast; ALE; Riemann; Overpressure; Transient; Dynamic; Structure.

The results of research initiated in the early 1980s led to the replacement of plasticity-based design guidelines for the load-carrying capacity of headed anchors embedded in concrete with those developed using fracture mechanics. While provisions are available in the design codes that account for the presence of tensile fields causing concrete cracking, no provisions are available for anchors embedded in prestressed concrete. This paper presents the results of linear elastic fracture mechanics (LEFM) analyses and of a preliminary experimental investigation of the progressive failure of headed anchors embedded in a concrete matrix under compressive or tensile prestress. The model predicts an increase (decrease) in load-carrying capacity and ductility with increasing compressive (tensile) prestress. It is shown that despite neglecting the dependence on size of concrete fracture toughness, LEFM predicts with remarkable accuracy the functional dependence of the ultimate capacity on prestress. DOI: 10.1061/(ASCE)EM.1943-7889.0000120 CE Database subject headings: Anchors; Axisymmetry; Finite element method; Prestressed concrete; Cracking; Tensile strength. Author keywords: Headed anchors.

This paper presents a micromechanical finite-element (FE) model for predicting the viscoelastic properties (dynamic modulus and phase angle) of asphalt mixtures, typical stone-based composites. The two-dimensional (2D) microstructure of asphalt mixtures was captured by optically scanning the surface image of sectioned specimens. FE mesh of image samples was generated within each aggregate and asphalt mastic. Along the aggregate boundary, the FEs share the nodes to connect the deformation. The micromechanical FE model was accomplished by incorporating specimen microstructure and ingredient properties (viscoelastic asphalt mastic and elastic aggregates). The generalized Maxwell model was applied for viscoelastic asphalt mastic with calibrated parameters from nonlinear regression analysis of the mastic test data on dynamic modulus and phase angle. The displacement-based FE simulations were conducted on the numerical samples under sinusoidal cyclic loading. The predicted dynamic modulus and phase angle were compared favorably with the mixture test data over a frequency range. The simulation results of the asphalt mixture samples have good correlations with the numerical calibration of asphalt mastic specimens. These results indicate that the developed micromechanical FE model can provide a computational tool for predicting the global viscoelastic properties of asphalt mixtures with captured microstructure and ingredient properties. Additionally, this study can increase the mechanistic understanding of global viscoelastic properties of asphalt mixtures by linking their microstructure. DOI: 10.1061/(ASCE)MT.1943-5533.0000062 CE Database subject headings: Micromechanics; Composites; Aggregates; Asphalts; Mixtures; Finite element method; Viscoelasticity; Microstructures. Author keywords: Micromechanics; Composites; Aggregates; Asphalts; Mixtures; Finite-element method; Viscoelasticity; Dynamic modulus; Phase angle.

In comparison with the transverse vibrations of rectangular plates, far less attention has been paid to the in-plane vibrations even though they may play an equally important role in affecting the vibrations and power flows in a built-up structure. In this paper, a generalized Fourier method is presented for the in-plane vibration analysis of rectangular plates with any number of elastic point supports along the edges. Displacement constraints or rigid point supports can be considered as the special case when the stiffnesses of the supporting springs tend to infinity. In the current solution, each of the in-plane displacement components is expressed as a 2D Fourier series plus four auxiliary functions in the form of the product of a polynomial times a Fourier cosine series. These auxiliary functions are introduced to ensure and improve the convergence of the Fourier series solution by eliminating all the discontinuities potentially associated with the original displacements and their partial derivatives along the edges when they are periodically extended onto the entire x-y plane as mathematically implied by the Fourier series representation. This analytical solution is exact in the sense that it explicitly satisfies, to any specified accuracy, both the governing equations and the boundary conditions. Numerical examples are given about the in-plane modes of rectangular plates with different edge supports. It appears that these modal data are presented for the first time in literature, and may be used as a benchmark to evaluate other solution methodologies. Some subtleties are discussed about corner support arrangements. [DOI: 10.1115/1.4000777]

In this paper, the classic coupled thermoelasticity model of hollow and solid spheres under radial-symmetric loading condition (r, t) is considered. A full analytical method is used and an exact unique solution of the classic coupled equations is presented. The thermal and mechanical boundary conditions, the body force, and the heat source are considered in the most general forms, where no limiting assumption is used. This generality allows to simulate a variety of applicable problems. [DOI: 10.1115/1.4001198] Keywords: coupled thermoelasticity, hollow sphere, exact solution

This paper presents a new analytical method that can calculate the load distribution on the thread teeth in cylindrical pipe threaded connection. The new method was developed by analyzing each male and female thread tooth from the connection on the basis of elastic mechanics. By using this method, the load distribution on each thread tooth can be calculated with the tightening torque and thread numbers. By applying the new method on the sample of AP1 88.9 mm round threaded connection, the obtained results show that the load on thread tooth mainly concentrates on the last four or five threads engaged. By using the finite element analysis method to the same sample validates the new method. The new method proposed in this paper is practical and convenient because it can be applied to calculate the load and deformation on each thread tooth just with tightening torque and thread numbers, which is easier to implement in practice. [DOI: 10.1115/1.4000729] Keywords: cylindrical pipe threaded connection, analytical method, elastic mechanics, load distribution, FEA method

The generalized minimal residual (GMRES) method is a common choice for solving the large nonsymmetric linear systems that arise when numerically computing solutions of incompressible nonlinear elasticity problems using the finite element method. Analytic results on the performance of GMRES are available on linear problems such as linear elasticity or Stokes' flow (where the matrices in the corresponding linear systems are symmetric), or on the nonlinear problem of the Navier--Stokes flow (where the matrix is block-symmetric/block-skew-symmetric); however, there has been very little investigation into the GMRES performance in incompressible nonlinear elasticity problems, where the nonlinearity of the incompressibility constraint means the matrix is not block-symmetric/block-skew-symmetric. In this short paper, we identify one feature of the problem formulation, which has a huge impact on unpreconditioned GMRES convergence. We explain that it is important to ensure that the matrices are perturbations of a block-skew-symmetric matrix rather than a perturbation of a block-symmetric matrix. This relates to the choice of sign before the incompressibility constraint integral in the weak formulation (with both choices being mathematically equivalent). The incorrect choice is shown to have a hugely detrimental effect on the total computation time. [DOI: 10.1115/1.4000414]

In this paper: a low dimensional model is constructed to approximate the nonlinear ferroelastic dynamics involving mechanically and thermally-induced martensite transformations. The dynamics of the first order martensite transformation is first modeled by a set of nonlinear coupled partial differential equations (PDEs), which is obtained by using the modified Ginzburg--Landau theory. The Chebyshev collocation method is employed for the numerical analysis of the PDE model. An extended proper orthogonal decomposition is then carried out to construct a set of empirical orthogonal eigenmodes of the dynamics, with which system characteristics can be optimally approximated (in a specified sense) within a range of different temperatures and under various mechanical and thermal loadings. The performance of the low dimensional model is analyzed numerically. Results on the dynamics involving mechanically and thermally-induced phase transformations and the hysteresis effects induced by such transformations are presented. [DOI: 10.1115/1.4000381] Keywords: ferroelastic dynamics, phase transformations, coupled dynamic thermoelasticity, optimal approximation, extended proper orthogonal decomposition, Galerkin projection, multiphase solids, smart materials and structures, shape memory alloys, metastable phases, low dimensional models, multiscale problems, model reduction

This paper describes various viscoelastic magnetic silicone gel bodies developed to create a new type of viscoelastic magnetic material. This material is capable of undergoing substantial changes in mechanical properties due to the large deformation caused by magnetic traction force under the application of a moderate strength magnetic field. This study performed tensile tests for various viscoelastic magnetic silicone gel bodies under a uniform steady magnetic field. The elastic moduli of the gel bodies were measured under different controlled experimental conditions. The experimental results showed that, under the applied magnetic field, the elastic moduli of the viscoelastic magnetic silicone gel bodies increased and were largely dependent upon the magnetic properties of the magnetic particles. The magnetic particle size and the material properties of the dispersant and the silicone gel also had significant effects on the moduli of the gel bodies. This paper also discusses the most appropriate combination of the materials used in this study from the standpoint of gaining a large magnetic traction force. POLYM. ENG. SCI., 50:857-862, 2010. [C] 2009 Society of Plastics Engineers, INTRODUCTION It was recently discovered that flow rate control can be performed by magnetic fluid membranes that are capable of freely changing the cross section of a pipe under a [...]

A finite-element-method-based micromechanics has been used for predicting the orthotropic properties of open-cell foams that have tetrakaidecahedral unit cells. Foams with equisided and Kelvin-elongated tetrakaidecahedron as unit cells are studied. The results for elastic constants from the finite element models agree well with those of available analytical models. The struts were modeled using both Euler--Bernoulli and Timoshenko beam elements. It is found that classical beam theory overpredicts the elastic moduli when the struts have smaller length-to-thickness ratios. The effect of varying strut cross section on the elastic constants is studied. The variation is assumed to be such that the strut cross section gradually decreases from maximum value at the support ends to minimum value at the beam midsection. It is found that for the same relative density, foams with varying cross sections have much lower elastic moduli than foams with uniform cross sections. DOI: 10.2514/1.J050022

In this study, the finite-element method is used to investigate the seismic behavior of rectangular liquid tanks in two-dimensional space. This method is capable of considering both impulsive and convective responses of liquid-tank system. Two different finite-element models corresponding with shallow and tall tank configurations are studied under the effects of both horizontal and vertical ground motions using the scaled earthquake components of the 1940 El-Centro earthquake record. The containers are assumed fixed to the rigid ground. Fluid-structure interaction effects on the dynamic response of fluid containers are taken into account incorporating wall flexibility. The results show that the wall flexibility and fluid damping properties have a major effect on seismic behavior of liquid tanks and should be considered in design criteria of tanks. The effect of vertical acceleration on the dynamic response of the liquid tanks is found to be less significant when horizontal and vertical ground motions are considered together. The results in this study are verified and compared with those obtained by numerical methods and other available methods in the literature. DOI: 10.1061/(ASCE)ST.1943-541X.0000123 CE Database subject headings: Dynamic response; Finite element method; Storage tanks; Ground motion; Liquids. Author keywords: Sloshing; Rectangular tank; Dynamic analysis; Tank flexibility; Finite element; Liquid containing.

Thermal conductivity measurement is a quick and easy test for compacted soils. This study presents the results of thermal conductivity testing on silt compacted under standard and modified Proctor efforts. A comparison of moisture content measurements from both lab oven and field oven is also presented and discussed. Measured thermal conductivity was correlated to the bulk density and water content. It is further correlated to Young's modulus and Shear modulus of the compacted silt, which were determined through ultrasonic pulse velocity measurements. Several trends were observed which may be used to correlate soil thermal conductivity of the compacted silt to compaction and elastic moduli for quality control/quality assurance of compacted soil. DOI: 10.1061/(ASCE)MT.1943-5533.0000035 CE Database subject headings: Fiber reinforced polymer; Composite materials; Sustainable development; Silts; Elasticity; Compacted soils. Author keywords: Thermal conductivity; Compacted silts; Elastic modulus.

This paper provides tractable solutions for elastic crack opening displacement (COD) of slanted through-wall cracks in plates and cylinders. The solutions were developed via detailed three dimensional elastic finite element analyses. The COD values were calculated along the thickness at the center of the crack. As for the loading conditions, only remote tension was considered for the plates, whereas remote tension, global bending moment, and internal pressure were considered for the cylinders. The finite element model employed in the present analysis was verified by using existing solutions for a cylinder with an idealized circumferential through-wall crack. The present results can be used to evaluate leak rates of slanted through-wall cracks, which can be used as a part of a detailed leak-before-break analysis considering more realistic crack shape development. [DOI: 10.1115/1.4000200] Keywords: elastic crack opening displacement, idealized through-wall crack, leak-before-break, leak rate, slanted through-wall crack

A simple and systematic procedure is proposed for shakedown analysis using a combination of linear and nonlinear finite element analysis (FEA). The method can identify the boundary between the shakedown and ratcheting domains directly and does not require a cyclic analysis (noncyclic). The proposed method performs an elastic-plastic FEA to determine the reduction in load carrying capacity due to the cyclic secondary loads. An elastic modulus adjustment procedure is then used to generate statically admissible stress distributions and kinematically admissible strain distributions under the applied primary loads. By modifying the local elastic moduli it is possible to obtain inelastic-like stress redistribution. The method is demonstrated with a 'two-bar structure' model based on analytical routine. The analysis is then applied to some typical shakedown problems including the 'classical Bree problem,' the 'bimaterial cylinder,' and the 'plate with a hole subjected to radial temperature gradient.' [DOI: 10.1115/1.4000506] Keywords: shakedown, ratcheting, elastic modulus adjustment procedure (EMAP)

A compliance operator is often utilized to evaluate the elastic displacement of surfaces in the simulation of transient and steady-state elastohydrodynamic lubrication of conformal-contact systems. The values of the compliance operator represent the elastic responses of all nodes when only one node is under a unit load. The accuracy of compliance operator values, computational cost, and storage size are important issues. Our study of steady-state conformal-contact elastohydrodynamic lubrication analyses suggests a method of selective-fine-mesh with selective-storage, as well as a special technique of the combined selective-fine-mesh with selective-storage mapping. These two techniques enable an efficient elasticity procedure for the simulation of steady-state and transient conformal-contact elastohydrodynamic lubrication systems by means of the finite element method. [DOI: 10.1115/1.4001120] Keywords: conformal-contact elastohydrodynamic lubrication, finite element, transient

The static and dynamic properties of tilting-pad journal bearings with controllable radial oil injection are investigated theoretically. The tilting pads are modeled as flexible structures and their behavior is described using a three-dimensional finite element framework and linear elasticity. The oil film pressure and flow are considered to follow the modified Reynolds equation, which includes the contribution from controllable radial oil injection. The Reynolds equation is solved using a two-dimensional finite element mesh. The rotor is considered to be rigid in terms of shape and size, but lateral movement is permitted. The servovalve flow is governed by a second order ordinary, differential equation, where the right hand side is controlled by an electronic input signal. The constitutive flow-pressure relationship of the injection orifices is that of a fully developed laminar velocity profile and the servovalve is introduced into the system of equations by a mass conservation consideration. The Reynolds equation is linearized with respect to displacements and velocities of the nodal degrees of freedom. When all nodal points satisfy static equilibrium, the system of equations is dynamically perturbed and subsequently condensed to a 2 x 2 system, keeping only the lateral motion of the rotor. As expected, bearing dynamic coefficients are heavily influenced by the control parameters and pad compliance. [DOI: 10.1115/1.4000721] Keywords: tilting-pad journal bearings, control, elastohydrodynamics, vibration

This paper presents a study of the spinning influence on film thickness and friction in EHL circular contacts under isothermal and fully flooded conditions. Pressure and film thickness profiles are computed with an original full-system finite element approach. Friction was thereafter investigated with the help of a classical Ree--Eyring model to calculate the longitudinal and transverse shear stresses. An analysis of both the velocity and shear stress distributions at every point of the contact surfaces has allowed explaining the fall of the longitudinal friction coefficient due to the occurrence of opposite shear stresses over the contact area. Moreover in the transverse direction spinning favors large shear stresses of opposite signs, decreasing the fluid viscosity by non-Newtonian effects. These effects have direct and coupled consequences on the friction reduction that is observed in the presence of spinning. They are expected to further decrease friction in real situations due to shear heating. [DOI: 10.1115/1.4001104] Keywords: elastohydrodynamic lubrication, point contact, spinning, film thickness, traction, non-Newtonian behavior, complex kinematics, shear stress distribution

An elastic contact model for three-dimensional layered or coated materials under coupled normal and tangential loads, with consideration of partial slip effects, has been developed in this paper. The response functions for calculating the displacements and stresses were determined in the frequency domain by using the Papkovich--Neuber potentials. The partial slip contact problem was solved by a numerical procedure based on the conjugate Gradient method and fast Fourier transform technique. The contact pressure, surface shear tractions, stick ratios, rigid body displacements, and subsurface stresses are analyzed under different conditions with variations in the material properties and coating thickness. Results show that stiffer coatings tend to decrease the stick ratios and the rigid ball tangential displacements in comparison to those with compliant coatings under the same contact conditions. For stiffer coatings, the values of the yon Mises stress and compressive surface stress increase and the positions of maximum von Mises stress move up to the surface; meanwhile, the distributions of the compressive stress become asymmetric due to the action of the tangential load. [DOI: 10.1115/1.4001011] Keywords: partial slip, coating, dry. contact, CGM