bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermohydrodynamic Design Charts for Tilting-Pad Journal
Bearings
Authors: Fillon M. , Khonsari M.
Published: February 2008

Design charts are presented which allow one to predict the maximum temperature and a realistic effective temperature of five-shoe tilting-pad bearings. The charts utilize two dimensionless parameters which characterize the temperature rise in the film based on the ISOADI boundary conditions. A number of examples are presented to illustrate the utility of the design chart where the results are compared to both experimental measurements and full THD simulations.
The Radial and Axial Stiffnesses of Tapered Roller Bearings Under
Combined Load
Authors: Zantopulos H.
Published: February 2008

Equations and their derivations for finding the radial and axial stiffnesses of a single-row tapered roller bearing, assuming a rigid shaft and housing, are given for any case of combined radial and axial loads. This method is extended to include the two-row bearing under certain conditions. Also presented are tables to facilitate these calculations.
Elastohydrodynamic Lubrication by Powder Slurries
Authors: Hua D. Y. , Khonsari M. M.
Published: February 2008

Thermoelastohydrodynamic analysis of a powder slurry containing a mixture of MoS2 particles and a carrier fluid is presented for a line-contact configuration. The constitutive equation of the slurry is a non-Newtonian formulation based on experimental data. The model includes provisions for elastic/plastic deformation of particles in the slurry. Through this deformation, particles are shown to contribute to the load-carrying capacity. The viscosity of the carrier fluid is shown to increase considerably as a result of adding a large amount of particles, thus appreciably affecting the EHL behavior of powder slurries. Performance results are presented for the pressure profile, film thickness, temperature distribution, and traction coefficient for a number of sliding/rolling ratios. The existence of particles in slurry is shown to give rise to a higher temperature field and tends to increase the traction coefficient compared to typical shear thinning fluids.
Fatigue and Fracture Estimation for Metallic Components: Some Current Methods and Future Developments
Authors: Nelson D. V. , Sheppard Sheri D.
Published: February 2008

Current approaches widely used in fatigue and fracture evaluations of mechanical components are summarized. Metallic alloys, and fatigue and fracture behavior in the absence of environmental effects such as corrosion or elevated temperatures, are considered. Certain shortcomings in the approaches are then discussed, followed by samples of recent work to improve the capabilities to make fatigue and fracture assessments. Finally, future developments that could further enhance those capabilities are suggested.
Nonlinear Phenomena in Dynamic Response of Rotors in Anisotropic Mounting Systems
Authors: Ehrich F.
Published: February 2008

In a previous paper (Ehrich, 1994), the author has cataloged a variety of unique rotordynamic responses which have been observed in a computer model of a simple Jeffcott rotor in a nonlinear anisotropic mounting system; that is, operating eccentrically within a clearance and in local intermittent contact with the stator. In addition to the critical synchronous resonant response similar to that found in linear systems, unique responses are found at subcritical operating speeds—superharmonic pseudo-resonances, and regions of chaotic and periodic response in transition zones between successive superharmonic orders. In the transcritical operating regime on both the subcritical and supercritical sides of the critical peak, spontaneous sidebanding is found when the system is very lightly damped. At supercritical operating speeds, subharmonic pseudoresonances, and regions of chaotic response and periodic response in transition zones between successive subharmonic orders are identified. These phenomena are characterized by their unique signature in the response curve, derived from a simple numerical model of a Jeffcott rotor with a bilinear stiffness in the direction normal to the plane of contact. Each phenomenon is further characterized by a typical example of the wave form and the wave form’s spectral analysis. All the waveforms display the tendency of the nonlinear system to have a significant asynchronous response component at its natural frequency irrespective of the rotational or stimulus frequency. In a more recent publication (Ehrich, 1995), recorded observations of rotordynamic response, in the format of “waterfall” or “cascade” charts, of operational high-speed turbomachinery in two typical instances have been compared with equivalent data from the same computer model used to illustrate the cataloged phenomena. The instances are representative of several of the cataloged phenomena. Excellent correspondence between the computed waterfall charts and the data from the actual operational machinery are achieved. The results may be of considerable interest to the community of vibrations engineers who deal with prevention of and remedial action for deleterious asynchronous vibration in operational high speed rotating machinery.
Friction Damping and Isolation Systems
Authors: Ferri A. A.
Published: February 2008

This paper surveys the literature on the use of dry friction in passive damping and vibration isolation. Several analytical techniques are presented followed by applications from various areas. Despite difficulties in the analytical and experimental treatment of friction damped systems, numerous studies have endeavored to predict, measure, and/or enhance the energy dissipation and vibration isolation properties of dry friction in order to improve system performance. Undoubtedly, friction damping will continue to play an important role in many mechanical and structural systems.
Conceptual Developments in Design Components and Machine Elements
Authors: Rivin E. I.
Published: February 2008

Many machine elements on the market today have been designed and implemented many decades ago. Some R & D is performed on design optimization. The paper demonstrates directions of conceptual evolution of traditional design components and feasibility of their significant improvements. Role of the “Axiom of Ideality” and of the Prevailing Trends of Evolution of engineering systems in creating novel concepts is emphasized. Descriptions of new concepts of power transmission gears and couplings, key connections, vibration isolators, cantilever design components characterized by high performance parameters are presented.
Design of Tendon-Driven Manipulators
Authors: Tsai Lung-Wen
Published: February 2008

This paper presents an overview of the current state-of-the-art in the design of tendon-driven manipulators. A special characteristic associated with tendon-driven manipulators is that tendons can only exert tension but not compression. Based on this unique characteristic, the fundamental mechanics associated with the design of tendon-driven manipulators are reviewed. The review includes structure classification, kinematics, statics, dynamics and control.
Evaluation of Accumulated Fatigue in Metals Due to Random Oscillating Thermal Stresses
Authors: Klevtsov I. , Crane R.
Published: February 2008

A direct modeling calculation method was developed to improve the accuracy of metal fatigue life estimates. The procedures were developed for the evaluation of once-through steam generator tubes, but were intended to be generally applicable. Random thermal boundary conditions were first simulated, with specific consideration given to the cases of transition boiling and fluctuating coolant inlet temperatures. Subsequently, transient heat transfer rates were determined and wall stresses due to pressure and temperature oscillations were calculated. The resultant wall temperature and stress oscillation data were statistically analyzed to provide the effective parameters used to estimate the metal fatigue.
An Improved Split-Ring Method for Measuring the Level of Autofrettage in Thick-Walled Cylinders
Authors: Perl M.
Published: February 2008

A simple, yet improved, experimental method for measuring the level of autofrettage in thick-walled cylinders, such as gun barrels, is proposed. A representative ring cut from the barrel serves as the test specimen. The ring is split by cutting it radially, while measuring the released hoop strain at the inner and outer surfaces diametrically opposite from the split line. The opening angle resulting from the spring apart from the ring is also monitored. An analysis based on Hill’s residual stress field yields an approximate relation which readily enables the determination of the prevailing level of autofrettage from strain measurements as well as from the value of the opening angle. This relation is found to be practically universal for all relevant cylinder configurations b/a = 1.6–2.2 and all levels of autofrettage of up to φ = 100 percent.
Tensile Plastic Instability of Axisymmetric Pressure Vessels
Authors: Updike D. P. , Kalnins A.
Published: February 2008

This paper examines the calculated pressure at a tensile plastic instability of a pressure vessel and its relationship to burst test results. It is proposed that the instability pressure be accepted as an upper bound to the pressure at which a vessel bursts, and that a strength reduction factor be used to predict the burst. The paper also presents a suitable mathematical model for the calculation of the instability pressures for thin-walled axisymmetric vessels. The proposition is tested by applying the model to a pressurized diaphragm, four cylindrical shells, and two torispherical heads, for which experimental burst data are available. It is found that the ratio of the test burst pressure to the calculated pressure at the tensile plastic instability, expressed in percent, ranges from 71 to 96 percent. The highest ratio occurs for a pressurized diaphragm with no significant defects. The lowest ratios occur for cylindrical shells with longitudinal welds, suggesting that the presence of the welds had a detrimental effect on the burst strength. These results may be useful when designing a pressure vessel with respect to its ultimate strength.
The Effect of Charge Shape on Partially Confined Detonations
Authors: Lind C. A. , Boris J. P. , Oran E. S. , Mitchell W. J. , Wilcox J. L.
Published: February 2008

More than 500,000 tons of obsolete and unwanted conventional weapons exist in the United States. The disposal of these unexploded ordnances, in an environmentally sound and cost-effective way, is of paramount importance. Different types of incinerators and detonation chambers have been proposed to eliminate these unwanted energetic materials. However, questions about the design of such facilities and the environmental consequences of their use must be answered. This paper describes numerical simulations of a large-scale, partially confined detonation facility. Detonation facility designs were evaluated by a series of axisymmetric, time-dependent simulations using FAST3D, a numerical model based on flux-corrected transport coupled to the virtual cell embedding algorithm for simulating complex geometries. The simulations assisted in determining the shape and size of the detonation charge mass that maintained the structural integrity of the facility. Comparisons of the pressure and structural analyses for spherically and cylindrically shaped RDX charges in a fixed volume show that the 50-lb spherically shaped charge resulted in an efficient detonation and maintained the structural integrity of the detonation facility.
Stability of Ring-Stiffened Tubular Members Under External
Pressure
Authors: Karamanos S. A. , Tassoulas J. L.
Published: February 2008

This paper presents results of a rigorous nonlinear finite element technique for the stability analysis of ring-stiffened steel tubes under external pressure. Large deformation, plasticity, as well as residual stresses and imperfections, are taken into account. Both internal and external stiffeners are simulated. A study of various parameters which affect pressure capacity is summarized, along with a comparison with available experimental data.
A Stochastic Analysis for Multiple Supported MDOF Secondary
Systems
Authors: Saudy A. , Aziz T. , Ghobarah A.
Published: February 2008

A new stochastic analysis is developed to estimate the response of multiple supported mdof secondary systems to dynamic loading. In the proposed stochastic analysis, the effect of the dynamic interaction between the secondary and primary systems is included. An outline for the theoretical formulation of the proposed stochastic analysis is presented. The assumptions adopted in the formulation are discussed. The dynamic interaction is shown to comprise two effects: the effect of the interaction forces arising at the attachment points, and the effect of the changes in the primary system properties resulting from the attachment of the secondary system. In addition, numerical examples are provided to demonstrate the validity of the proposed analysis.
Deformation Plasticity Failure Assessment Diagram (DPFAD) for Materials With Non-Ramberg-Osgood Stress-Strain Curves
Authors: Bloom J. M.
Published: February 2008

This paper presents a brief history of the evolution of the Central Electricity Generating Board’s (CEGB) R-6 failure assessment diagram (FAD) procedure used in assessing defects in structural components. The reader is taken from the original CEGB R-6 FAD strip yield model to the deformation plastic failure assessment diagram (DPFAD), which is dependent on Ramberg-Osgood (R-O) materials to general stress-strain curves. An extension of the DPFAD approach is given which allows the use of material stress-strain data which do not follow the R-O equation such as stainless steel or carbon manganese steel. The validity of the new approach coined piecewise failure assessment diagram (PWFAD) is demonstrated through comparisons with the J-integral responses (expressed in terms of failure assessment diagram curves) for several cracked configurations of non-R-O materials. The examples were taken from both finite element and experimental results. The comparisons with these test cases demonstrate the accuracy of PWFAD. The use of PWFAD requires the availability of deformation plasticity J-integral solutions for several values of the strain-hardening exponent as well as uniaxial tensile stress-strain data at the temperature of interest. Lacking this information, the original R-O DPFAD approach using known engineering yield and ultimate strengths would give the best available approximation. However, it is strongly recommended that actual uniaxial tensile stress-strain data be used when available.
Axisymmetric Elastic-Plastic FE Analysis of Pressurized
Elbows
Authors: Boussaa Dj. , Dang Van K. , Labbé P. , Tang H. T.
Published: February 2008

A variational formulation for the pure in-plane bending problem of pressurized elbows with arbitrary cross section, written in the 3-D infinitesimal displacement continuum mechanics framework, and particularly appropriate when a refined elastic-plastic local response is needed (e.g., in the presence of ratcheting), is presented. The similarity between this problem and an axisymmetric analysis is underlined and turned to account to solve the former using existing FE routines devoted to the latter. Some applications are given to illustrate the potentialities of the model.
Preliminary Design of Tubular Composite Structures Using Netting
Theory and Composite Degradation Factors
Authors: Tew B. W.
Published: February 2008

Tubular products and process vessels built using fiber-reinforced composite materials provide significant advantages in applications that require corrosion resistance, high strength, and light weight. A design approach based on netting theory is presented which enables engineers to develop preliminary structural designs for these structures using composite materials. The integration of creep, cyclic loading, and environmental degradation factors into initial design calculations is also discussed and illustrated.
Multiaxial Stress Concentration in an Externally Pressurized Cylinder
With an External Circumferential Groove
Authors: Tipton S. M. , Hickey K. A. , Rawson M. S. , Sorem J. R.
Published: February 2008

A thick-walled cylindrical specimen containing an external circumferential groove was subjected to external pressure. To investigate the maximum pressure sustainable by the reduced wall thickness, strain gage measurements were taken during external pressurization tests. For comparison to experimental results, an elastic-plastic notch stress-strain analysis was conducted based on Neuber’s rule. The analysis utilized multiaxial elastic finite element results along with elastic-plastic tensile test data for the cylinder material. Based on experimental observations, it was necessary to supplement the approach with an additional relation between elastic and elastic-plastic multiaxial strains for the axisymmetric geometry under investigation. Assuming an invariant hoop to radial strain ratio rather than an invariant hoop to axial strain ratio provided better agreement with experimental results. It is demonstrated that the boundary conditions used to model the specimen had a substantial effect on the finite element results, even though the boundary was somewhat removed from the region of concentrated stress. Biaxial strain measurements are presented versus pressure over the elastic and into the plastic regime, and deformation plasticity theory was used to compute stress and radial strain components corresponding to measured strains. It is demonstrated that in order to apply a multiaxial Neuber’s rule to accurately estimate the elastic-plastic stress-strain response (using elastic stress concentration information and elastic-plastic material data), it is necessary to utilize an experimental observation that the ratio of the hoop to radial strain remains invariant from the elastic to the elastic-plastic regime. This differs from published assumptions about invariant hoop-to-axial strain ratios based on analysis of circumferentially grooved solid shafts. The predictions are accurate for moderate plastic strains, but correlation breaks down for bulk plastic deformation.
Stochastic Response of Piping Systems With Flexible Supports
Authors: Soliman H. O. , Datta T. K.
Published: February 2008

A frequency domain spectral analysis of piping systems with flexible supports is presented for uniformly modulated nonstationary support excitations. The support points are idealized by spring-dashpot arrangements. The equations of motion of the resulting nonclassically damped, multipoint excitation system are written and solved in terms of the absolute displacements of the dynamic DOF. This facilitates a direct computation of the dynamic stresses induced at various cross sections of the pipe segments. The method of analysis provides a quasi-stationary response based on the assumption that the modulating function varies slowly with time; the exact response analysis in frequency domain for such systems with nonstationary support excitation is difficult to determine. Using the method of analysis presented, the response of a piping system is obtained for a set of important parametric variations related to the flexibility, damping, and excitation of the supports.
Elastoplastic Analysis of Layered Metal Matrix Composite Cylinders—Part II: Numerical Results
Authors: Salzar R. S. , Pindera M.-J. , Barton F. W.
Published: February 2008

Part I (Salzar et al, 1996) of the paper presented an exact elastic-plastic analytical solution for an arbitrarily laminated metal matrix composite tube subjected to axisymmetric thermo-mechanical and torsional loading. In Part II, this solution strategy is first validated by comparison with available closed-form solutions, as well as with results obtained using the finite-element approach. Subsequently, examples are presented that illustrate the utility of the developed solution methodology in predicting the elastic-plastic response of arbitrarily layered metal matrix composite tubes. In particular, optimization of the response of composite tubes under internal pressure is considered through the use of functionally graded architectures.
Nonlinear Effects on the Stiffness of Bolted Joints
Authors: Lehnhoff T. F. , Wistehuff W. E.
Published: February 2008

Axisymmetric finite element modeling of bolted joints was performed to show the effects of the magnitude and position of the external load, member thickness, and member material on the bolt and member stiffnesses. The member stiffness of the bolted joint was found to decrease 10 to 42 percent for the 20-mm to 8-mm bolts, respectively, as the magnitude of the external load was increased. Member stiffness appears to be independent of the radial location of the external load and increases as the member thickness decreases. Member stiffness decreased by a factor of 2.5 to 3 with a change in the member material from steel to aluminum. The cast iron members had a decrease in member stiffness of a factor of 1.7 to 1.9. The aluminum over cast iron combination had a member stiffness between the aluminum and cast iron alone. Bolt stiffnesses varied by less than two percent for changes in the magnitude of the external load for all bolt sizes and member materials, except for the 8-mm bolt where stiffness increased by approximately 11 percent. Changes in radial position of the external load had no effect on the bolt stiffness. A 3 to 13-percent decrease in the bolt stiffness was found when changing from steel to aluminum members. A 2 to 3-percent bolt stiffness decrease resulted when the member material was changed from steel to cast iron and similarly from steel to the aluminum over cast iron combination
Analysis of Flange Joints Under External Loads
Authors: Koves W. J.
Published: February 2008

Flange joint leakage is one of the common maintenance problems in refineries and chemical plants. This paper studies the effect of external loads on the strength and leakage behavior of flanged joints. Finite element and analytical methods are compared, and the proposed method is compared with leakage data. The common “equivalent pressure” method is shown to be very conservative, and a method of evaluating external loads is recommended.
Low-Velocity Perforation of Punch-Impact-Loaded Metal Plates
Authors: Wen H.-M. , Jones N.
Published: February 2008

An approximate quasi-static theoretical analysis is presented for the behavior of punch-impact-loaded metal plates. Based on the principle of virtual work, load-deflection relationships are first obtained and then used to predict the energy-absorbing capabilities of plates subjected to low-velocity impacts that cause perforation. It is demonstrated that the theoretical predictions are in good agreement with experimental observations on fully clamped steel plates when material strain rate sensitivity is taken into consideration and provided that perforation does not occur by adiabatic shear plugging.
NDE of a Crack by Using Closely Coupled Probes for DCPD Technique
Authors: Saka M. , Oouchi A. , Abe´ H.
Published: February 2008

In order to enhance the sensitivity of the d-c potential drop technique, the principle of a technique using the closely coupled probes is proposed. A calibration equation for this technique is derived, where the path-independent integral je for electric crack problems is utilized. Experiments on laboratory specimens are discussed which validate the use of the calibration equation for the nondestructive evaluation of cracks. It is shown that the sensitivity of the present method using closely coupled probes is higher than that of the usual method using a uniform current flow in the region far from the crack.
Stress Intensity Factors for Cracks in Conventional S-N Fatigue Specimens
Authors: O’Donnell T. P.
Published: February 2008

Stress intensity values for cracks growing in conventional fatigue specimens are determined, with emphasis on the end constraint conditions associated with S-N fatigue testing. Three-dimensional finite element analysis methods are used to analyze thumbnail-shaped cracks in cylindrical geometries. Crack front straightening due to the increased bending introduced as crack growth progresses is included in the models. Because relatively stiff fatigue test machines prevent rotation at the clamped ends of test specimens, uniform axial displacement boundary conditions are imposed. Results for uniformly applied axial stress end conditions are also obtained for comparison. For crack-depth-to-specimen-diameter ratios over one-third, bending restraint induced in the specimens under applied axial displacement significantly reduces the resulting stress intensity relative to values computed for uniform end tension. The results are useful for evaluating crack growth in fatigue specimens within the limits of linear elastic fracture mechanics.
Robust Stress-Classification of Pressure Components Using the GLOSS and GLOSS R-Node Methods
Authors: Seshadri R.
Published: February 2008

The GLOSS and GLOSS r-node methods are used to classify stresses in pressure components. The classification scheme is akin to the prevailing ASME Boiler and Pressure Vessel Code procedures. The proposed method is applied to a cylinder flat-head configuration for thin as well as thick heads, and the stress classification methodology is outlined. The methods described in this paper can be readily applied to a general three-dimensional pressure component configuration.
Analyses of Possible Failure Mechanisms and Root Failure Causes in Power Plant Components Using Neural Networks and Structural Failure Database
Authors: Yoshimura S. , Jovanovic A. S.
Published: February 2008

This paper describes analyses of case studies on failure of structural components in power plants using hierarchical (multilayer) neural networks. Using selected test data about case studies stored in the structural failure database of a knowledge-based system, the network is trained: either to predict possible failure mechanisms like creep, overheating (OH), or overstressing (OS)-induced failure (network of Type A), or to classify a root failure cause of each case study into either a primary or secondary cause (network of Type B). In the present study, the primary root cause is defined as “manufacturing, material or design-induced causes,” while the secondary one as “not manufacturing, material or design-induced causes, e.g., failures due to operation or mal-operation.” An ordinary three-layer neural network employing the back propagation algorithm with the momentum method is utilized in this study. The results clearly show that the neural network is a powerful tool for analyzing case studies of failure in structural components. For example, the trained network of Type A predicts creep-induced failure in unknown case studies with an accuracy of 86 percent, while the network of Type B classifies root failure causes of unknown case studies with an accuracy of 88 percent. It should be noted that, due to a shortage of available case studies, an appropriate selection of case studies and input parameters to be used for network training was necessary in order to attain high accuracy. A collection of more case studies should, however, resolve this problem, and improve the accuracy of the analyses. An analysis module for case studies using the neural network has also been developed and successfully implemented in a knowledge-based system.
On the Seismic Behavior of Unanchored Liquid Containers
Authors: Natsiavas S. , Begley C. J. , Peterson P. J.
Published: February 2008

This work presents a combined analytical/numerical methodology, predicting the behaviorof unanchored liquid storage tanks subjected to seismic excitation. First, the dynamic response of the system and the resulting hydrodynamic loads are determined by employing a simplified dynamic model. According to this model, the base uplift of the container isrepresented by an equivalent nonlinear rotational spring, placed between the foundation and the base plate of the tank. The characteristics of this spring are determined from static considerations, by applying standard finite element methodologies. Taking into account the form of the uplift spring stiffness, comprehensive parametric studies on the dynamics of unanchored liquid containers are first performed, in a systematic way. The results of these studies provide valuable insight into the role of the system parameters on its response. Once the dynamic loads are determined, a stress and buckling analysis can be performed, by employing finite element modeling again. The validity of the findings of the present work is checked through comparisons with experimental results.
Wear Studies of Materials for Tubes and Antivibration Bars in Nuclear Steam Generators
Authors: Ko P. L. , Taponat M.-C. , Zbinden M.
Published: February 2008

Wear occurs as a result of relative motion at the interface of two contacting bodies. In nuclear power steam generators, high flow rates can induce vibration of the tubes resulting in wear damage due to impact and sliding contacts between the tubes and their supports. A research project aiming to gain better understanding of the mechanisms and mechanics involved in vibratory wear and to develop a more versatile predictive wear model was carried out. Combinations of Inconel tubes against flat antivibration bars of 403 SS and electrolytic-chrome plated Inconel 600 were tested under conditions of reciprocating sliding and impacting in water at room temperature and at 250°C. The results show that, depending on the material combinations and he loading conditions, distinctively different wear mechanisms and often drastically different wear rates can occur.
Energy Method for Base Uplifting Analysis of Liquid-Storage Tanks
Authors: Malhotra P. K. , Veletsos A. S.
Published: February 2008

A solution, based on Ritz energy method, is presented for the uplifting analysis of a uniformly loaded semi-infinite beam supported on a rigid foundation. Motivated by a need to understand the effects of earthquake-induced base uplifting in unanchored liquid-storage tanks, the solution accounts for the nonlinearities associated with large displacements and material yielding in the base plate, and considers the constraining action of the tank wall. The results are in close agreement with those from the “exact” analysis.
Three-Dimensional Interaction Effects in an Internally Multicracked Pressurized Thick-Walled Cylinder— Part I: Radial Crack Arrays
Authors: Perl M. , Levy C. , Pierola J.
Published: February 2008

Under certain conditions, numerous internal surface cracks develop in pressurized thick-walled cylinders, both in the radial and longitudinal directions. For fatigue life assessment of such vessels, the 3-D interaction effects among these cracks on the prevailing stress intensity factors (SIFs) need evaluation. In Part I of this paper, radial crack arrays are considered exclusively. The mode I SIF distribution for a wide range of semi-circular and semi-elliptical cracks are evaluated. The 3-D analysis is performed via the finite element method with the submodeling technique, employing singular elements along the crack front. SIFs are evaluated for arrays of up to n = 180 cracks; for a wide range of crack depth to wall thickness ratios, a/t, from 0.05 to 0.6; and, for various ellipticities of the crack, i.e., the ratio of crack depth to semicrack length, a/c, from 0.2 to 2. Using a least-squares fit, two simple expressions for the most critical (n = 2) SIFs are obtained for sparse and dense crack arrays. The formulas, which are functions of a/t and a/c, are of very good engineering accuracy. The results clearly indicate that the SIFs are considerably affected by the interaction among the cracks in the array as well as the three-dimensionality of the problem. In Part II of this paper, the interaction effects between longitudinal coplanar cracks will be analyzed.
Analysis of Preloaded Bolted Joints Under Exponentially Decaying Pressure
Authors: Esmailzadeh E. , Chorashi M. , Ohadi A. R.
Published: February 2008

Dynamic properties of joints must be considered when designing complex structures. A good deal of investigation has been carried out for a better understanding of the dynamic behavior of mechanical joints. It is suitable initially to identify the parameters of a mechanical joint by using either experimental modal analysis or accurate finite element model, and then predicating the behavior of closure bolting system by means of spring-mass-damper model. The effect of bolt prestress on the maximum bolt displacement and stress has been treated. The loading is assumed to be initially peaked, exponentially decaying internal pressure pulse acting on the closure. The dependence of peak bolt stresses and deflections on the bolt prestress level and system damping is investigated. It has been shown that the derived formulas, if damping is neglected, reduce to those reported in the literature. Furthermore, the damping effect is shown to be most important, especially for large natural frequencies, longer loading duration, and lower levels of prestress. Existence of damping, which results in the reduction of maximum bolt displacement and stress, was shown to be beneficial, especially for longer loading duration. The importance of bolt displacement reduction from the viewpoint of fatigue life, vibration loosening, and sealing, especially for lower values of prestress, has been fully emphasized.
Fatigue Life Measurements and Analysis for Overstrained Tubes With Evacuator Holes
Authors: Underwood J. H. , Parker A. P. , Corrigan D. J. , Audino M. J.
Published: February 2008

Sections of cannon tubes with inner radius of 53, 60, and 78 mm were cycled from near zero to 100–300 MPa internal pressure until fatigue failure occurred. The failure locations were along 2-mm holes cut through the cannon wall at a 30-deg angle to the tube axis, for the purpose of evacuating combustion gases from the cannon after firing. The cannons had various amounts of autofrettage by overstraining, including 0, 30, 50, and 100 percent. The amount of overstrain affected both the initiation position of the fatigue crack along the evacuator hole and the measured fatigue life. Increasing the amount of overstrain moved the crack initiation from the tube inner radius toward a mid-wall position and significantly increased fatigue life. Fracture mechanics and solid mechanics-based calculations of fatigue life were performed for comparison with the measured lives. The calculations gave a good description of the measured life, taking account of tube configuration, applied pressure, amount of overstrain, stress concentration of the hole, crack size and shape, material fatigue crack rate behavior and yield strength, and pressure in the hole and on the crack surfaces. As with measured fatigue life, the calculated life was significantly affected by the amount of autofrettage of the tube. The ratio of outer to inner radius of the tube and the presence of pressure in the evacuator hole also had substantial effects on the calculated fatigue life.
Limit Analysis of a Spherical Shell Under Axial Loading on Central Boss
Authors: Yeom D. J. , Robinson M.
Published: February 2008

The purpose of this study is to investigate the collapse load of a spherical shell under axial loading on a central boss. The investigation was carried out using an existing lower-bound plastic limit analysis package and the ABAQUS finite element code. Results are obtained for various geometrical parameters and compared with previous analytical and experimental results.
Creep Buckling of Ovalized Tubes Under External Pressure
Authors: Koundy V. , Forgeron T. , Hivroz J.
Published: February 2008

In order to get a better understanding of the role of various parameters on the creep collapse phenomenon of long circular tubes, an experimental and numerical program has been undertaken. It mainly aims at studying the influence of the behavior of the material composing the circular tubes and their geometrical characteristics on the flattening time. This paper presents the results of numerical simulations performed with a specific computer program using an analytical approach. They have been compared with the data obtained from creep tests performed in various conditions on preovalized tubes as well as with the solutions obtained from the finite element method. It is shown that a good agreement is achieved between experimental results and calculation results.
Accelerated Stress Rupture Testing for Creep Life Prediction—Its Value and Limitations
Authors: Viswanathan R. , Foulds J.
Published: February 2008

Accelerated stress rupture testing has become a common method for determination of the remaining life of in-service components subject to creep damage at elevated temperatures. Stress and temperature increases have both been used to cause accelerated test failures, although the temperature accelerated tests have been preferred during the last decade. Remaining life estimation schemes have essentially involved extrapolation of results of the accelerated tests to the operating conditions. The accelerated test approach has found such widespread acceptance that most users today are unaware of its limitations and have started using the results in a definitive and quantitative way as a direct prediction of the remaining life of the component. EPRI (Electric Power Research Institute) investigators have examined the application and validity of a number of aspects of accelerated testing, as well as the underlying assumptions in the extrapolation procedures. This paper reviews the current practice, describes results from a number of research activities, and provides general guidelines for accelerated rupture testing.
Effects of LWR Coolant Environments on Fatigue Lives of Austenitic Stainless Steels
Authors: Chopra O. K. , Gavenda D. J.
Published: February 2008

Fatigue tests have been conducted on Types 304 and 316NG stainless steels to evaluate the effects of various material and loading variables, e.g., steel type, strain rate, dissolved oxygen (DO) in water, and strain range, on the fatigue lives of these steels. The results confirm significant decreases in fatigue life in water. Unlike the situation with ferritic steels, environmental effects on Types 304 and 316NG stainless steel are more pronounced in low-DO than in high-DO water. Experimental results have been compared with estimates of fatigue life based on a statistical model. The formation and growth of fatigue cracks in air and water environments are discussed.
Flexural Rigidity of Annular Flange Connections
Authors: Kimura H. , Nonaka S.
Published: February 2008

In order to analyze the vibration of a structure whose elements are connected with bolts, it is necessary to estimate the flexural rigidity of bolted connections. Some studies have been reported on annular flange connections subjected to external bending moments. In these studies, the bolt axial force and the sealing performance are examined in detail, but their flexural rigidity is not sufficiently discussed. This paper deals with a calculation method to estimate the flexural rigidity of bolted annular flange connections subjected to external bending moments. In the analysis, a model for estimating the flexural rigidity is proposed, taking account of the dispersiveness of bolt disposition and the rigidity of flange-shell junction. That is, the annular flange is replaced with a plate and the hub with a cylindrical shell. For verification, experiments are performed. Calculated results are in fairly good agreement with experimental ones.
Riser-Relief Valve Dynamic Interactions (Extension to a Previous Model)
Authors: Botros K. K. , Dunn G. H. , Hrycyk J. A.
Published: February 2008

Further investigation of the dynamic stability behavior of a typical pilot-operated relief valve is reported. The present study is an extension to Botros et al. (1997) model, which includes mapping of the oscillating frequencies and amplitudes with riser dimensionless length L/D; inclusion of the effects of a wedge-O-ring seal in the model; detailed analyses of the field tests revealing unknown values for model parameters. These model refinements resulted in a better agreement between simulation results and field measurements. Analysis of piston oscillation frequencies and amplitudes indicates that the piston oscillation frequency mirrors the riser’s one-quarter-wave resonance frequency for lower values of L/D. At L/D = 20 and higher, two modes of oscillations started to emerge with two distinct frequencies. Maximum oscillation amplitudes occurred at L/D corresponding to one-quarter wave. Wedge-O-ring seal mechanism helps in suppressing piston oscillations; but it must be used in conjunction with a proper lubricant, otherwise the piston may jam partway during the upward stroke.
An Accurate Method of Evaluating Relaxation in Bolted Flanged Connections
Authors: Bouzid A. , Chaaban A.
Published: February 2008

Bolted flanged joint assemblies may begin to leak some time following a successful hydrostatic test. One of the reasons is that the gasket experiences a drop in its initial compressive stress due to creep, thermal dilatation, and thermal degradation. The need to pay attention to the relaxation behavior of bolted joints for high-temperature applications is recognized by the ASME Code, but no specific guidelines are given to help engineers, neither at the design nor maintenance levels. This paper deals with the basic analytical tools that have been used to develop a computer program “SuperFlange” that can be used to make accurate predictions of the relaxation of bolted flanged joints, and hence be able to provide a reasonable leakage assessment over time. A simplified analytical method of relaxation analysis will also be presented. These proposed methods are supported by test results obtained on a real bolted joint fixture and by FE modeling. A strong emphasis will be put on flanged joint rigidity, which is one of the major controlling parameters of relaxation besides the material properties involved.
ASME Task Group Report on Primary Stress
Authors: Pastor T. P. , Hechmer J.
Published: February 2008

This paper considers the subject of primary stress as applied in pressure vessel design carried out in accordance with the ASME Boiler and Pressure Vessel Code (1992). The paper is the result of discussions held by members of the Task Group on Primary Stress. Specific subjects discussed include methods for calculating primary stresses, the ASME limits on primary stresses and their meaning, use of the Code stress classification table in pressure vessel design, and commentary on the use of state-of-the-art analysis techniques to design pressure vessels and satisfy Code primary stress limits. A modified definition for primary stress is given, and examples for evaluating primary stresses for different geometries is provided.
Dynamic Response of Cross-Ply Laminated Shell Panels
Authors: Li N. , Mirza S.
Published: February 2008

Fiber-reinforced composites are being widely used in the aircraft and aerospace industry, as well as in other field such as automobile, electronics, etc. In this work, a method based on the superposition and state-space techniques is developed to study the free vibration of cross-ply laminated composite shell panels with general boundary conditions. An example problem of a shell panel with two adjacent edges clamped and the others simply supported is investigated. Convergence tests have been carried out to demonstrate the veracity of the approach. Accurate fundamental frequencies of the shell are presented for various shell parameters.
An Analysis of the Two-Bar Ratcheting Behavior Using the Viscoplasticity Theory Based on Overstress (VBO)
Authors: Nakamura T. , Krempl E.
Published: February 2008

The ratcheting behavior of the “unsymmetric two-bar system” was investigated by numerical experiments. The two bars are restrained to the same length and are subjected to a constant load. One bar sees cyclic temperature variations, while the other bar is kept at constant temperature. The material models employed are rate independent plasticity (kinematic hardening) and the viscoplasticity theory based on overstress (VBO) matched to represent the cyclic neutral 6061 T6 aluminum alloy elastic and inelastic deformation behavior. For simplicity, temperature-independent material properties were assumed. Numerical analyses were performed to investigate the effects of rate of thermal loading and temperature range. Elastic-inelastic shake down is ultimately achieved due to work hardening. There is a strain range increase until it reaches a steady value. Kinematic hardening and VBO predict almost the same strain range, which, for the case of VBO, is nearly rate-independent. The behavior for both material models is very different for the mean strain. For VBO, the number of cycles to shakedown is rate-dependent and is considerably larger than for kinematic hardening. Finally, the steady-state mean strain and strain range are computed directly for VBO.
Biaxial Fatigue of A533B Pressure Vessel Steel
Authors: Nelson D. V. , Rostami A.
Published: February 2008

The low-to-intermediate cycle fatigue behavior of A533B steel is investigated using solid round bar specimens tested in combined bending and torsion. Loadings are applied in-phase and 90 deg out-of-phase to produce cases of proportional and nonproportional biaxial fatigue. Out-of-phase loadings are found to be more damaging than in-phase loadings. Two equivalent strain criteria similar to those in the ASME Boiler and Pressure Vessel Code and a newer approach based on cyclic plastic work are used to correlate fatigue lives. The equivalent strain criteria are found to underestimate the fatigue damage in out-of-phase tests, but to provide reasonably good correlations overall. The plastic work approach provides a conservative treatment of the out-of-phase data and somewhat better overall correlation. Cracking behavior observed during the tests is also summarized.
Response and Failure of Ductile Circular Plates Struck by a Mass
Authors: Jones N. , Kim S.-B. , Li Q. M.
Published: February 2008

A theoretical analysis is presented in this paper to predict the dynamic plastic response of aluminium alloy and mild steel circular plates when struck normally by blunt solid cylindrical masses at the center. Reasonable agreement is obtained with experimental results for the permanent transverse displacements. Different failure mechanisms, which have been found in previous experimental studies on aluminium alloy and mild steel plates, are also illustrated by the proposed theory.
Experimental Study of Mechanical Pipe Snubber Seismic Behavior
Authors: Nims D. K. , Kelly J. M.
Published: February 2008

A series of seismic tests of mechanical snubbers on a full-scale model piping system provided a unique opportunity for detailed scrutiny of snubber seismic behavior on an actual piping system. The observed snubber behavior is a complicated pattern of braking and releasing, drag and drift, and the dynamic characteristics of the snubber, as well as the input motion, play a role in the response of the snubber. The snubbers were effective in limiting pipe displacements. Relative accelerations across the snubber were larger than expected. Snubber hysteretic behavior was irregular. Results from this testing are important in understanding snubber behavior, evaluating snubber performance, and in assessing alternatives to snubbers.
The Influence of Support Hardware and Piping System Seismic Response on Snubber Support Damping
Authors: Lay C. , Abu-Yasein O. A. , Pickett M. A. , Madia J. , Sinha S. K.
Published: February 2008

The damping coefficients and ratios of piping system snubber supports were found to vary logarithmically with pipe support nodal displacement. For piping systems with fundamental frequencies in the range of 0.6 to 6.6 Hz, the support damping ratio for snubber supports was found to increase with increasing fundamental frequency. For 3-kip snubbers, damping coefficient and damping ratio decreased logarithmically with nodal displacement, indicating that the 3-kip snubbers studied behaved essentially as coulomb dampers; while for the 10-kip snubbers studied, damping coefficient and damping ratio increased logarithmically with nodal displacement.