bluuebunny/crossref_metadata_2025 huggingface dataset:
Lubrication With Micropolar Liquids and Its Application to Short Bearings
Authors: Tipei Nicolae
Published: November 2010

Microscopic effects, generated by micromotions of particles in suspension in a viscous fluid, drastically change the character of the flow between solid walls. To the modified momentum and continuity equations, an equation of angular (spin) particle momentum is added. A vectorial system of equations is presented, for variable material coefficients. General properties of this system are discussed and differential equations for pressure and velocity field are derived. For constant viscosity and micropolar coefficients across the lubricating film, important simplifications lead to easier workable expressions. Under this assumption, the short bearing performance has been analyzed. The fluid pressure increase (compared to Newtonian flow) is represented by a surface depending on two groups of micropolar parameters; the overall bearing characteristics also exhibit larger values with respect to simple Newtonian lubricants. However, for similar gap geometries, the friction coefficient has lower values. Some formulas, regarding the velocity field, friction stresses and side flow, are general and may be applied to any bearing length-diameter ratio.
The Flow Self-Regulating Hydrostatic Screw and Nut
Authors: Bassani R.
Published: November 2010

The new principle of flow self-regulation is applied to hydrostatic screws and nuts. These self-regulating hydrostatic screws and nuts permit a continuous and automatic distribution of the total flow in two half flows in the two recesses merely due to the special shape of the double thread. Formulas are presented and compared with those of ordinary hydrostatic screws and nuts supplied by two pumps. The comparison shows that the self-regulating screws and nuts have a stiffness equal to that of ordinary ones supplied by two pumps, and also that they have pumping and friction dissipated power and therefore a total dissipated power generally equal to those of ordinary ones supplied by two pumps. Their global efficiency is comparable to that of ordinary hydrostatic screws and nuts supplied by two pumps and is consequently better than that of the ordinary ones supplied by only one pump but through two flow regulators. A calculation example is presented, of a self-regulating hydrostatic lead-screw and nut, dissipating minimum pumping power. Finally a prototype of a screw and nut of this kind is shown.
Centrifugal Effects in Hydrostatic Porous Thrust Bearing
Authors: Gupta R. S. , Kapur V. K.
Published: November 2010

In this analysis the customary neglected centrifugal effects on the performance of hydrostatic porous thrust bearing with incompressible lubricant has been studied and the effects of their interaction of pressure distribution and load capacity illustrate the possibility of replacement of the nonporous bearing material by porous one.
Vibration Characteristics of Hollow Symmetrical Blades Based on Thin Shell Theory
Authors: Al Jumaily A. M. , Faulkner L. L.
Published: November 2010

This paper presents the results of investigating the vibrational characteristics of a hollow symmetrical blade based on thin shell theory which allows closed function representation of vibrational characteristics which are inaccessible using beam theory. A modified shell theory is presented and used for the analysis. The hollow blade is considered as a continuous system constructed from two cantilever circular cylindrical shells by matching the continuous boundary conditions. This technique is used to express the results in a continuous function analytical formation. The method presented is clearly for long hollow blades and does not require the computer storage of numerical methods. Comparison is made between the present technique, the beam theory, and experimental data for two laboratory models. The formulation can be extended to most types of blades and still retain the functional representation. This type of analysis may be quite useful when utilized judiciously with other methods such as finite elements.
Residual-Flexibility Corrections for Transient Modal Rotordynamic Models
Authors: Childs D. W. , Bates J. B.
Published: November 2010

An extension is presented to a modal formulation for the dynamics of flexible rotors. To date, rotordynamic modal formulations have retained for integration those modes of vibration whose natural frequencies are within or slightly above the operating speed range of the rotor, with higher-order modes simply discarded. In this study, the residual-flexibility technique is employed to account for the “static” contribution of these higher-frequency modes without requiring their integration. The residual-flexibility technique accounts directly for the static contribution of higher frequency modes due to imbalance and external transient loading, and has been adapted to account for reaction forces which are not accounted for by the nominal rotor/bearing stiffness matrix, e.g., bearing damping forces or speed-dependent bearing stiffnesses. The High-Pressure-Oxygen Turbopump of the Space Shuttle Main Engine (SSME) is analyzed. The maximum operating speed of this turbopump lies between its first and second critical speeds. Comparisons are made without residual-flexibility corrections for two through six modes retained for integration. Simulation runs are made for (a) a deceleration through the first critical speed and (b) a constant speed run at FPL (full power level). The results demonstrate that the residual-flexibility approach yields a significant improvement in accuracy for a comparatively modest increase in computer-time requirements.
Alternative Tuned Absorbers for Steady State Vibration Control of Tall Structures
Authors: Jenniges R. L. , Frohrib D. A.
Published: November 2010

Two forms of damped vibration absorbers are evaluated to describe their value in reducing steady state vibration of tall buildings. The first model contains a set of two identical one-degree-of-freedom elements symmetrically mounted in a horizontal plane on either side of the building’s long axis. An alternate model has independent translational and torsional elements mounted at the building’s center. Damping parameters are included for building fundamental bending and torsion modes to evaluate those effects on response. The sensitivity of absorber performance to absorber-building mass ratio μ is of interest to minimize the size of the absorber. Performance of the absorber models was compared based on maximum transmissibility and a quality integral, which is an integrated transmissibility over a frequency spectrum based on amplification at a point on the building top. Small damping in the structure aided absorber performance. Quality is quite insensitive to mass ratio and absorber damping for a building damping ratio in the order of 0.05. Damping is to be reduced in the absorber to improve quality for small absorber-to-building mass ratios when building damping becomes small.
A Boundary Tracking Optimization Algorithm for Constrained Nonlinear Problems
Authors: Moradi J. Y. , Pappas M.
Published: November 2010

A new procedure for numerical optimization of constrained nonlinear problems is described. The method makes use of an efficient “Boundary Tracking” strategy to move on the constraint surfaces. In a comparison study it was found to be an effective method for treating nonlinear mathematical programming problems particularly those with difficult nonlinear constraints.
The Effect of Notches at the Tooth Root Fillet on the Endurance Strength of Gears
Authors: Winter H. , Wirth X.
Published: November 2010

Notches at the tooth root fillet can be caused by shaving or grinding. The influence of different notches at the root fillet on the endurance strength of case hardened spur gears was investigated in back-to-back tests and pulsator tests. Data of the test gears: MnCr and CrNi Steels, module 3 (8 DP) and module 8 (3 DP). Besides the a.m. tests photo elastic investigations were performed. On the basis of some characteristic parameters, it was possible, to find a calculation procedure, to determine the loss of endurance strength due to the effect of various kinds of notches. Moreover it was investigated to what extent the endurance strength of notched gears could be increased by regrinding or shot peening the root fillet. It is known that notches at the tooth root fillet can essentially reduce the endurance strength of gears. This is of special importance for case hardened gears. It is desirable that such notches should be avoided, but sometimes notches are produced by shaving or grinding due to inadequacy of tooling or non-uniform heat distortion. Therefore the influence of geometry and position of notches at the root fillet on the endurance of case hardened spur gears was investigated in back-to-back and pulsator tests. Additionally the extent the endurance strength of notched gears could be increased by regrinding or shot peening the root fillets was studied.
Vibration of an Elastic Beam Subjected to Discrete Moving Loads
Authors: Kurihara M. , Shimogo T.
Published: November 2010

In this paper, vibration problems of a simply-supported elastic beam subjected to randomly spaced moving loads with a uniform speed are treated under the assumption that the input load sequence is a Poisson process. In the case in which the inertial effect of moving loads is neglected, the time history, the power spectral density, and the various moments of the response are examined and the effects of the speed of moving loads upon the beam are made clear.
Experiments on Fluidelastic Vibration of Cantilevered Tube Bundles
Authors: Chen S. S. , Jendrzejczyk J. A.
Published: November 2010

This paper presents the results of three series of experiments on coupled tube/fluid vibration. Natural frequencies and mode shapes of coupled modes as well as steady-state responses are measured for each tube bundle. An analysis is also made for each test. Experimental data and analytical predictions are found to be in good agreement.
Analysis and Experimental Investigation of the Stability of Intershaft Squeeze Film Dampers—Part 2: Control of Instability
Authors: Hibner D. H. , Bansal P. N. , Buono D. F.
Published: November 2010

The results of an analytical and experimental investigation showing the existence of an intershaft viscous damper instability were presented in reference [1]. In the present investigation, a more comprehensive stability analysis is used to study the stability of the test rig which incorporates a modified intershaft bearing support. The analysis is applicable to large multi-mass, rotor-bearing systems and includes the effects of gyroscopic moments, shear deformation, bearing support flexibility, and damping. The results of the stability analysis are presented in the form of system stability maps which clearly indicate the effectiveness of the modification in improving the instability onset speed of the system. Also presented are the results of an experimental investigation which substantiate the analytical predictions.
Torsional Vibrations of a Boiler Feed Pump
Authors: Lees A. W. , Haines K. A.
Published: November 2010

The paper describes an investigation into the dynamic behavior of a large steam turbine-driven boiler feed pump, following the failure of gearboxes, couplings and bearings. The line consists of a 17 MW turbine driving a four-stage high pressure pump directly and a single-stage booster pump via a 2:1 single-reduction gearbox. Flexural vibration was measured using accelerometers at the bearings and eddy current proximity transducers. The torque transmitted to the gearbox was measured using a four-arm strain gauge bridge mounted in a coupling spacer shaft, the signals being obtained via a telemetry system. The observations showed a complex vibration pattern which was compared with predictions from simple analytic models. A lumped mass system accurately predicted the order of magnitude of oscillatory torque as a function of frequency, given the inevitable errors in gear manufacture. It was shown that the choice of flexible coupling has a crucial effect on the response. The methods of calculation have been generalized to give an accurate model of a system with distributed mass. This is achieved formally using the dynamic Green’s function approach or, for detailed results by a finite-element technique. It was shown that a change of coupling alters the dynamic torque of the system. Hence the effects of a number of changes were calculated and a suitable combination of couplings and gearbox were chosen to implement the practical solution to the problem. The basis for the choice is described and the implications for more general design criteria are discussed.
A Computationally Efficient Numerical Algorithm for the Transient Response of High-Speed Elastic Linkages
Authors: Midha A. , Erdman A. G. , Frohrib D. A.
Published: November 2010

A new numerical algorithm, easily adaptable for computer simulation, is developed to approximate the transient response of a single degree-of-freedom vibrating system; governing differential equation is linear and second order with time-dependent and periodic coefficients. This is accomplished by first solving the classical linear single degree-of-freedom problem with constant coefficients. The system is excited by a periodic forcing function possessing a certain degree of smoothness. The integration terms in the solution are systematically expanded into two groups of terms: one consists of non-integral terms while the other contains only integral terms. The final integral terms are bounded. For certain combinations of frequency and damping, within the sub-resonant frequency range, the relative size of the integral terms are demonstrated to be small. The algebraic expansion (non-integral) terms then approximate the solution. The solution to a single degree-of-freedom system with time-dependent and periodic parameters is made possible by discretizing the forcing period into a number of intervals and assuming the system parameters as constant over each interval. The numerical algorithm is then employed to solve an elastic linkage problem via modal superposition. Convergence of the solution is verified by refining the number of intervals of discretization.
Optimization of Crank-and-Rocker Linkages with Size and Transmission Constraints
Authors: Freudenstein F. , Chew Meng Sang
Published: November 2010

An algebraic procedure suitable for pocket calculators is derived for the determination of the proportions of a plane crank-and-rocker linkage in which the ratio of largest to smallest link and the transmission-angle variation are prescribed. A logical analysis of the relative lengths of the links leads to a direct solution without algorithms or iteration. The results are illustrated with tables and numerical examples.
Predicting Acoustical Noise Generation in Complex Mechanical Systems
Authors: Perreira N. D. , Dubowsky S.
Published: November 2010

A fundamental study of noise generation in complex mechanical systems is undertaken. The objective of the study is the development of design guidelines for the prediction of mechanical system noise levels. Recently developed dynamical procedures are used to obtain the motions of linked mechanical systems with elastic elements and connection clearances. An analytical procedure for modeling the acoustical noise generated by complex mechanical systems is applied to a typical linked system, a four-bar mechanism. The far field acoustic pressure distribution is calculated and shown to be a function of many of the parameters under the control of the system designer. To aid the designer in producing quieter systems, acoustic design functions are developed. In particular, the system sound power and modal power efficiencies are found to be promising design tools.
Effects of Disk Flexibility on Shaft Whirl Stability
Authors: Wilgen F. J. , Schlack A. L.
Published: November 2010

The effects of disk flexibility on the critical speeds of flexible shaft-disk systems is investigated by the method of Liapunov. The model consists of a flexible, continuous disk rigidly attached at an arbitrary location along a flexible, continuous shaft which is mounted on short, end bearings. Whirl speed stability boundaries are presented as functions of the disk flexibility parameter. These boundaries reduce to the limiting case of a shaft containing a concentrated mass at the point of disk attachment when the disk’s stiffness is very small, and approach the limiting case of an elastic shaft supporting a rigid disk as the stiffness increases.
A Survey of Cam Manufacture Methods
Authors: Grant B. , Soni A. H.
Published: November 2010

Contained herein is a discussion of the more commonly used methods and hardware available for the production of cams. The text is divided into four areas, including discussion on “original cam” and “copied cam” manufacture methods; numerical control machines, as regards cam manufacture; and finally a brief survey of current industry practice in cam design and manufacture. Listed in tabular form throughout the work are summaries of the various methods of manufacture and also of the various machines available for manufacture. Also, cited are 365 references containing information regarding the various aspects of cam manufacture. These references are categorized by content to facilitate easy access to those of interest.
Joint Displacements in Linkage Synthesis Solutions
Authors: Strong R. T. , Waldron K. J.
Published: November 2010

A comprehensive and unified treatment of the relationship between the displacements, about the joints of a four-bar linkage as it moves through specified design positions is given. The behavior of joint displacements is characteristic of Grashof type, and can be used to help locate solutions of a given type.
Solution Schemes for Problems of Nonlinear Structural Dynamics
Authors: McNamara J. F.
Published: November 2010

A number of alternative solution schemes for problems of dynamic structural analysis involving large displacements and plastic deformations are compared. The equations of motion, derived from the finite element approximation, are integrated directly using a number of well-known time integration operators; namely, the Houbolt, Newmark, Wilson, and central difference operators. This latter operator serves as a basis for a comparison of accuracy and economy with all methods. Numerical results for nonlinear systems are used to indicate the true worth of integration operators whose properties have been determined theoretically by studying their behavior with linear systems only.
Fluid Elastic Whirling of a Tube Row
Authors: Blevins R. D.
Published: November 2010

An analytical model for flow-induced vibration of a tube row in a cross flow is formulated. A criterion for the onset of instability is developed. The tubes are modeled with different stiffnesses and damping normal and parallel to the free stream to simulate effects which arise in heat exchangers. The critical reduced velocity required for the onset of instability is shown to increase sharply with the separation of natural frequency between tubes. The effect of an adjacent wall and rows composed of a small number of tubes is explored. The model reduces to an experimentally validated criterion for symmetrically supported tubes.
Reactor Coolant Pump Flywheel Overspeed Evaluation
Authors: Riccardella P. C. , Bamford W. H.
Published: November 2010

The overspeed capability of the large steel flywheels used on light water reactor primary coolant pumps has been evaluated through a combined analytical and experimental effort. Limiting speeds of the prototype flywheel design were calculated for the ductile failure mode using the principles of Section III of the ASME Boiler and Pressure Vessel Code, and for the brittle fracture mode using a fracture mechanics approach in which stress intensity factors were determined from finite element computer analysis. The accuracy of the analytical approach was verified by a scale model test program which demonstrates excellent agreement between experiment and analysis. The results of the evaluation are presented in this paper, and they illustrate the kinds of things which can be accomplished through application of modern fracture mechanics technology, including plasticity considerations, to the solution of hardware problems of real engineering interest.
Attitudes Toward Computer Software and Its Exchange in the Pressure Vessel Industry
Authors: Kraus H.
Published: November 2010

A survey of computer software use in the pressure vessel industry was conducted by means of a questionnaire that reached 707 active professionals in the industry. 249 filled-in questionnaires were returned. These were analyzed by standard statistical techniques in order to determine the following: the respondents’ background, the extent of their involvement with computer software in pressure vessel analysis and design, their attitudes toward computer software and their attitudes toward the creation of an active technology transfer effort for that software. The study verifies that a generally positive attitude toward software and its exchange exists among those who actually write and/or use computers. However, it was found that supervisors of those who write and/or use software would be unwilling to share most their programs with an active technology transfer effort for software.
A Technical Basis for Characterizing Flaws Detected by Preservice and Inservice Examinations of Nuclear Power Plant Components
Authors: Maccary R. R.
Published: November 2010

The nondestructive examination procedures specified by the rules of construction of the ASME Boiler and Pressure Vessel Code—Section III, “Nuclear Power Plant Components” require techniques whose flaw detection capabilities are well within the practical limits established for acceptable workmanship and quality of fabrication. The rules of the ASME Section XI, “Inservice Inspection of Nuclear Reactor Coolant Systems”, impose an additional series of examinations. Material or fabrication flaws detected during a preservice examination as well as flaws developed during service must be evaluated to establish the acceptability of the component for initial and continued service. These examination requirements have introduced the need to characterize the flaws detected by the examinations and to set “allowable flaw indication standards.” The principles of fracture mechanics provide an engineering tool which predicts the behavior of materials containing flaws under service loadings. These principles form the underlying basis upon which the allowable flaw indication standards of ASME Section XI were formulated. The development of new rules governing flaw indication characterization and allowable flaw indications standards, as specified in the ASME Code, Section XI, are reviewed.
Elastic Crack Propagation Along a Pressurized Pipe
Authors: Emery A. F. , Love W. J. , Kobayashi A. S.
Published: November 2010

A finite difference shell code which considers transverse shear and rotatory inertia is used to calculate the dynamic behavior of axially running cracks. Short cracks were instantaneously introduced into a static pressurized cylinder and their tips advanced according to a maximum stress criterion. Calculations were made for a range of the critical stress and the terminal velocity of the crack tip was found to be linearly related to the value of the critical stress. Calculations were also made for rapid and slow depressurization of the cylinder to observe the nature of the arrest. In all cases where arrest occurred it did so abruptly.
Effect of Yield Strength Variations on the Inelastic Response of a C-Seal
Authors: Dhalla A. K.
Published: November 2010

General purpose nonlinear computer programs are frequently used to satisfy inelastic code criteria. It is important to know the sensitivity of the predicted results to variations in the input parameters. For example, a variation in the material properties may have a significant effect on the response of a structural component. Just how much effect a 20 percent variation in the yield strength of a material would have on the inelastic response of a structural component cannot now be estimated by a rule-of-thumb approach using accumulated prior experience. Because the detailed inelastic analyses are expensive, very limited numerical data are generated in this area. As more information is made available, it may be feasible to arrive at some guidelines for designers similar to those established by experience in the elastic design of structural components. This paper contributes to the available body of experience by examining the effect of the variation in yield strength of the material, and a change in the shell thickness, on the inelastic response of a primary closure seal.
Elastic-Plastic Analysis for Cracked Members
Authors: Hilton P. D.
Published: November 2010

Elastic-plastic finite element analyses are performed for cracked specimens of various geometries and material properties. The calculations are based on the small strain, J2-deformation theory of plasticity; employing a power hardening model for the material behavior under uniaxial tensile loading. The finite element procedure includes the use of a specialized plastic, crack tip singularity element; and, it is applicable to the geometric idealizations of plane stress, plane strain, and axial symmetry. Results are presented for tensile and bending specimens containing exterior cracks and for a hollow cylindrical specimen with a circumferential crack subjected to tensile and pressure loading. Numerical values are reported for the plastic intensity factor, the crack face separation at the exterior surface, and the J-integral. Both the implications of these results to fracture prediction and the limitations on their applicability as a consequence of geometric and material modeling idealizations are discussed.
Effects of Material Parameter Variability on Buckling and Creep Fatigue Interaction at Elevated Temperature
Authors: Berman I. , Gangadharan A. C. , Jaisingh G. H. , Gupta G. D.
Published: November 2010

The effects of variation of elastic-plastic and creep properties of type 304 stainless steel on solutions of two specific inelastic problems are studied in this paper. The problems considered are: 1 – elastic-plastic-creep buckling of a thin cylindrical shell with initial imperfection and sustained external pressure at high temperature; and 2 – creep and fatigue damage in a thin cylindrical shell subjected to cyclic thermal load and constant internal pressure. Some conclusions are drawn as to the relative importance of variations of different material parameters on initial buckling load, creep buckling time and creep and fatigue damage factors.
On the Use of Finite Elements in Fracture Analysis of Pressure Vessel Components
Authors: Reynen J.
Published: November 2010

The paper describes algorithms and their computer implementations to calculate effectively strain energy release rates by means of FEM, making use of substructuring techniques. Numerical examples are given for 2-D and 3-D thermo-elasto crack problems including a corner crack in a pressure vessel nozzle.
The Interface Boundary Conditions for Bolted Flanged Connections
Authors: Thompson J. C. , Sze Y. , Strevel D. G. , Jofriet J. C.
Published: November 2010

In most bolted connections, the unknown interface pressure distribution and the extent of the contact region are essential parameters in any stress analysis. Concerning these parameters, experimental and numerical studies of a model of an isolated single-bolt region show the following. The contact region between the flanges depends almost exclusively on the ratio of the flange thickness to the diameter of the surface region of each flange over which the bolt prestressing force is distributed; the contact zone is virtually independent of both the level of prestressing force and of the size of the bolt hole; and the contact stress distribution for a typical range of parameters is very closely approximated by a truncated conical distribution. The studies also delineate the regions of the flanges around each bolt where the stress state is strongly three-dimensional and regions where simple plate theory is applicable. The relationships established between the contact stress distribution and the various geometric parameters are presented in a form immediately applicable by designers.
Dynamic Analysis as an Aid to the Design of Marine Risers
Authors: Young R. D. , Fowler J. R. , Fisher E. A. , Luke R. R.
Published: November 2010

This paper describes a computer program for economically predicting the dynamic response of marine risers to lateral forces from waves (regular and random) and currents (vortex shedding). Present emphasis of riser design appears to be on long drilling risers, deep ocean mining systems, and petroleum production risers. The latter encompasses a wide range of depths, applications, and configurations. Therefore, in addition to a technical description of the model, the paper discusses the differences in response between long and short risers and which physical parameters should be scrutinized in analyzing each of these. Also included is a method for estimating minimum tension requirements along with a discussion of “effective tension” in conjunction with the significance of buoyancy and mud weight.
A Finite-Element Model for Residual Stresses and Deflections in Girth-Butt Welded Pipes
Authors: Rybicki E. F. , Schmueser D. W. , Stonesifer R. W. , Groom J. J. , Mishler H. W.
Published: November 2010

Computational models for predicting transient temperature distributions, residual stresses, and residual deflections for girth-butt welds are described. Comparisons of predicted and measured temperatures for a two-pass welded pipe show agreement to within 9 percent and 17 percent of the measured values for passes one and two, respectively, the model for predicting residual stresses and residual deflections is based on a finite-element representation recognizing individual passes, temperature dependent elastic-plastic constitutive behavior, elastic unloading for material in the nonlinear stress-strain range, and changes in geometry due to the deformation of each weld pass. Load incrementation and incremental stress-strain relations are also used. Results for a two-pass girth-butt welded pipe show good correlation between residual stresses and residual deflections obtained from the computational model and data obtained from a welded 304 stainless steel pipe.
Mechanical Behavior of Nonlinear Visco-Elastic Celluloid Under Superimposed Hydrostatic Pressure
Authors: Nishitani T.
Published: November 2010

The behavior of polymers is significantly influenced by hydrostatic pressure. In this paper, the effects of hydrostatic pressure and the third invariant of the deviatoric stress tensor on the nonlinear visco-elastic deformation of celluloid are first discussed in connection with experiments of torsion of tubular specimens and tension of uniaxial specimens. The distinctive features of the deformation behavior in creep and for proportional loading (namely, uniform rate of stress increase with time) under superimposed hydrostatic pressure are investigated by using the nonlinear visco-elastic celluloid. The stress-strain relation of the nonlinear visco-elastic media with regard to the effect of the hydrostatic pressure is deduced from the invariant theory with an hypothesis of creep potential. The deduced relation gives fairly good agreement with the actual observations.
Growth Characteristics of Part-Through Cracks in Thick-Walled Plates and Tubes
Authors: Sommer E. , Hodulak L. , Kordisch H.
Published: November 2010

The extension of part-through cracks in thick-walled plates and tubes under fatigue loading has been investigated. Growth characteristics have been determined by analyzing the fracture surfaces. For this purpose artificial markings were induced on the fracture surfaces by an overload technique. The crack extension in the direction of the semiaxes as well as the crack growth along the whole front has been evaluated and interpreted in terms of the parameters: crack depth, ratio of crack width to crack depth, yield stress and the ratio of the stress intensity factor to the yield stress.
Characterization of Fracture in Vessels and Piping
Authors: Adams N. J. I.
Published: November 2010

A two-parameter fracture criterion previously applied to flat plates has been extended to cylindrical and spherical shells. It is applicable to all modes of fracture including net section stress levels above yield. The predictive capability is such that the calculated stress at failure for 85 percent of the data examined, was within 10 percent of the experimental values. Furthermore, 96 percent were within 15 percent of the experimental values.
A Mechanical Model for Permafrost Thaw Subsidence
Authors: Mitchell R. F.
Published: November 2010

A mechanical model describing permafrost subsidence has been developed and correlated with a full scale field test performed by the Atlantic Richfield Company and Exxon Company, USA at Prudhoe Bay. The permafrost mechanical response is modeled with a linear stress-strain relation that incorporates pore pressure reduction as the subsidence loading mechanism. The pore pressure reduction is due to the phase change of pore ice upon thaw and was verified by field test measurements. The mechanical response of the well casing is included in the model with no slip assumed between casing and permafrost. The thaw subsidence model explains several features observed in the field test. The pore pressure reduction mechanism produces an upward rebound of the permafrost base, resulting in compressive casing strains above the base and tensile strains below. The pore pressure loading also produces an inward lateral motion of the thawed-frozen interface. The inward motion, together with layers of different soil types, produce the alternating compressive and tensile strains measured in the field test. These alternating strains can be significant, depending on permafrost lithology.
Consistent Treatment of Extensional Deformations for the Bending of Arches, Curved Beams and Rings
Authors: Fettahlioglu O. A. , Mayers J.
Published: November 2010

A consistent treatment of the extensional deformations of thin circular rings subjected to general distributed and concentrated loadings is presented. Coupled Euler equations and consistent boundary condition combinations in terms of the radial and tangential midsurface displacements are obtained for the dynamical problem using Hamilton’s principle. Discontinuity conditions corresponding to discrete application of generalized forces are also provided. For static analysis, the governing equations are transformed into two uncoupled sixth-order differential equations in the radial and tangential displacements, respectively, and the complete solutions are obtained for general loading. Closed-form solutions for displacements and stress resultants are developed for illustrative and comparative purposes relative to specific full ring, curved beam, and arch examples. The results confirm that extensional deformations can play a significant role in the bending of thin curved beams, and arches and that such structures are more readily and consistently analyzed by the present treatise than by Winkler curved-beam theory with its potential for inconsistent approximations toward thinness and resulting possible violation of static equilibrium by the stress resultants calculated from the stress-displacement state.
Instability Analysis of Torispherical Pressure Vessel Heads with Triangular Thin-Shell Finite Elements
Authors: Kanodia V. L. , Gallagher R. H. , Mang H. A.
Published: November 2010

The elastic instability of an internally-pressurized cylindrical tank with a torispherical head is investigated using a triangular, doubly curved, thin-shell finite element. The formulation of the finite element, which is based upon cubic displacement functions and a modified principle of potential energy, is first described. Then, the element is verified by comparing numerical results for the linear, stable analysis to alternative solutions for the same problem. The subsequent instability investigation includes the solution of the linearized problem of equilibrium bifurcation, that is, of the classical eigenvalue problem, and a general nonlinear analysis, based on tracing the nonlinear load-displacement path. The critical pressure, obtained with use of the general nonlinear analysis, agrees closely with an experimental result as well as with a numerical solution stemming from an axisymmetric formulation.
The Effect of Specimen Thickness Upon the Fatigue Crack Growth Rate of A516-60 Pressure Vessel Steel
Authors: Sullivan A. M. , Crooker T. W.
Published: November 2010

Fatigue crack growth rate studies on A516-60 pressure vessel steel indicate no effect of specimen thickness in stress-relieved specimens ranging in thickness from 0.25 to 2.0 in. (6.35 to 50.8 mm). A regression curve equation for all thicknesses relating cyclic crack growth rate (da/dN) to crack-tip stress-intensity factor range (ΔK) is obtained. The significance of these results is discussed in the light of current engineering practice and previous studies on size effects in fatigue crack propagation.
Creep Analysis of Metallic Structures in the Presence of Thermal Gradients Using Newer Constitutive Relations
Authors: Kumar V. , Mukherjee S.
Published: November 2010

Several newer constitutive relations have recently been proposed for describing the mechanical behavior of metals and alloys under elevated temperature creep conditions. A salient feature of the mathematical structure of many of these relations is that they typically express the nonelastic strain rates as functions of the current values of stress, temperature, and some other suitably defined state variables. A computational scheme is presented in this paper for the inelastic analysis of metallic structures subjected to both mechanical and thermal loadings and obeying constitutive relations of the type described before. Several numerical examples for the creep of thick-walled spheres, cylinders, and rotating disks in the presence of thermal gradients are presented. The particular constitutive relations used in these calculations are due to Hart. The proposed computational scheme is found to be very efficient from the view point of both computational time and effort. The effects of previous cold work on the stress redistribution and creep of these structural elements are discussed.
Fatigue Design Criteria for Pressure Vessel Alloys
Authors: Jaske C. E. , O’Donnell W. J.
Published: November 2010

Fatigue design criteria for pressure vessel steels are developed herein based on analysis of available material data between room temperature and 427 C (800 F). Strain-controlled low-cycle and high-cycle fatigue data for austenitic steels, alloy 800, alloy 600, and alloy 718 were evaluated. The effects of mean stresses were considered and design curves were proposed for use in Sections III and VIII of the ASME Boiler and Pressure Vessel Code.
The Influence of Drying and Stress on the Permeability of Texas Lignite
Authors: Thompson T. W. , Sen S. , Gray K. E. , Edgar T. F.
Published: November 2010

Tests have been carried out to quantify the variation in permeability of Texas lignite with drying and with applied stress. It has been shown that the matrix permeability of lignite may be increased from effectively zero to the order of 10 darcies by removing about 20 percent by weight of water. In addition, an increase of confining pressure after drying will reduce the permeability, but only by about one order of magnitude. Drying of the matrix thus may produce matrix permeabilities of the same order as the undried field fracture permeability. The permeability increase of the matrix is initially greater parallel to the bedding than perpendicular, but after further drying the two orientations show similar final permeabilities. This drying effect could have a significant influence on the operation of an in-situ gasification process by increasing the transmissivity and injectivity of the producing seam. Drying of the seam could occur by the flow of unsaturated gas and will be enhanced by combustion.
Layered Cylindrical Pressure Vessels
Authors: Widera G. E. O. , Logan D. L.
Published: November 2010

The validity and range of applicability of a specialized shell theory for nonhomogeneous, anisotropic elastic materials is tested by comparison with a uniformly valid theory. The comparison is carried out for the problem of an edge beam reinforced, pressurized composite cylinder. Included in the comparison is a study of the influence of such design parameters as degree of anisotropy, fiber orientation, thickness and length to radius ratios, and extensional and bending stiffness of the edge beam.
The Application of ASME Code Case 1828
Authors: Schneider R. W. , Waters E. O.
Published: November 2010

ASME Code Case 1828: “A Simplified Method of Analyzing Flat Face Flanges with Metal-to-Metal Contact Outside the Bolt Circle” provides rules for the analysis and design of a wide variety of identical and nonidentical flange pairs. Although the method is based on certain simplifying assumptions, a designer may lose confidence in his solution of a problem because of the multiplicity of steps which are involved. Accordingly, the purpose of this paper is to demonstrate the application of Code Case 1828 by means of four illustrative problems and supporting discussion.
Comparison of ICEPEL Predictions With Single-Elbow Flexible Piping System Experiment
Authors: A-Moneim M. T. , Chang Y. W.
Published: November 2010

The ICEPEL Code for coupled hydrodynamic-structural response analysis of piping systems is used to analyze an experiment on the response of flexible piping systems to internal pressure pulses. The piping system consisted of two flexible Nickel-200 pipes connected in series through a 90-deg thick-walled stainless steel elbow. A tailored pressure pulse generated by a calibrated pulse gun is stabilized in a long thick-walled stainless steel pipe leading to the flexible piping system which ended with a heavy blind flange. The analytical results of pressure and circumferential strain histories are discussed and compared against the experimental data obtained by SRI International.
Computation of Residual Stresses due to Multipass Welds in Piping Systems
Authors: Rybicki E. F. , Stonesifer R. B.
Published: November 2010

In this paper, a computational model is developed to calculate the magnitude and distribution of residual stresses for multipass girth-butt welded pipes. The model consists of two parts, a temperature analysis model and a finite element stress analysis model. Elastic-plastic temperature dependent mechanical properties and unloading due to stress reversals are included in the model. While computational models for predicting residual stress distributions due to one- and two-pass welds have been developed, there are certain difficulties associated with predicting the behavior of multipass welds in an economical way. An approach for handling these types of problems is described. Residual stresses obtained with the model for a seven-pass weld and a thirty-pass weld are compared with residual stresses obtained from laboratory measurements. Good agreement is found between the computed and measured values of residual stresses for for both welds.
Part-Circular Cracks at Various Openings Under Complex Loading Conditions
Authors: Bhandari S. K. , Barrachin B. , Picou J. L.
Published: November 2010

It is shown that the problem of evaluating the stress-intensity factor of a part-circular crack at the base of any through opening in a three-dimensional solid under general external planer loading conditions can be reduced to the resolution of three problems: 1) Analysis of the three-dimensional uncracked solid with the given opening shape under given loading conditions; 2) analysis of a two-dimensional solid with the given opening shape and a line crack under the given loading conditions; 3) analysis of a semi-infinite solid with the given crack shape under uniform stress. In fact, the given problem, identical to that of a pressurized crack at the edge of an opening, is reduced to the solution of an embedded circular crack with suitable pressure distribution which takes into account the presence of the opening. This pressure distribution is postulated as a product of initial pressure due to the application of external load on the uncracked geometry (Problem 1) with a function resulting from the analysis of a 2-D problem (Problem 2). Finally, the K values calculated using this modified pressure distribution on the circular crack, are corrected for the 3-D nature of the crack front through the solution of Problem 3. The methodology has been applied to part-circular cracks at elliptical openings in a 3-D solid under traction and moment loading. The method has been extended to treat corner cracks in quarter solids. A circular crack at a BWR-nozzle corner has been treated as an illustrative example. Finally, some generalizations of the method have been suggested.
Verification of Specimens for Low-Cycle Fatigue and Cyclic Plasticity Testing
Authors: Schultz C. C. , Zien H. M.
Published: November 2010

The results of inelastic finite element analyses of several uniaxial specimens used for low-cycle fatigue and cyclic plasticity testing are presented. The test specimens studied include both hourglass and uniform gage-type geometries. These results indicate that normally used hourglass specimens may significantly underestimate the strain for a given stress. Uniform gage specimens with commonly used length-to-diameter ratios are shown to provide adequate stress-strain data. Two extensively strain-gaged uniform gage specimens were tested to provide data to confirm the acceptability of the inelastic analysis methods.
An Engineered Methanogenic Pathway Derived from the Domains
Bacteria
and
Archaea
Authors: Lessner Daniel J. , Lhu Lexan , Wahal Christopher S. , Ferry James G.
Published: November 2010

A plasmid-based expression system wherein
mekB
was fused to a constitutive
Methanosarcina acetivorans
promoter was used to express MekB, a broad-specificity esterase from
Pseudomonas veronii
, in
M. acetivorans
. The engineered strain had 80-fold greater esterase activity than wild-type
M. acetivorans
. Methyl acetate and methyl propionate esters served as the sole carbon and energy sources, resulting in robust growth and methane formation, with consumption of >97% of the substrates. Methanol was undetectable at the end of growth with methyl acetate, whereas acetate accumulated, a result consistent with methanol as the more favorable substrate. Acetate was consumed, and growth continued after a period of adaptation. Similar results were obtained with methyl propionate, except propionate was not metabolized.

IMPORTANCE
The fragile interactions of multispecies food chains converting complex biomass to methane are easily disrupted, a major impediment to efficient and reliable conversion of renewable biomass as an alternative to fossil fuels. The hybrid pathway, derived by combining catabolic pathways from a methanogen of the domain
Archaea
and a strictly aerobic species of the domain
Bacteria
, catalyzes the complete conversion of an industrial solvent that is also a naturally occurring compound to methane and carbon dioxide. The engineered pathway expands the exceptionally narrow range of substrates utilized by methanogens, exemplifying the simplification of food chains leading to the more-efficient conversion of complex biomass to methane.