bluuebunny/crossref_metadata_2025 huggingface dataset:
Behavior of a Tapered Hub Flange With a Bolted Flat Cover in Transient Temperature Field
Authors: Sawa T. , Hirose T. , Nakagomi Y.
Published: February 2008

An experimental and analytical study was made on a bolted connection subjected to thermal loading. The connection consists of an aluminum alloy tapered hub flange and a flat cover, including a gasket fastened by steel bolts and nuts. Temperature distribution in the connection was measured with thermocouples, and the axial bolt force, the maximum bolt stress, and the hub stress were measured by strain gages under a thermal condition that theinner surface of the flanges was heated and the outer surfaces of the flanges and the cover were held at room temperature. Finite difference analysis was made to obtain the temperature distributions in the connection due to a transient thermal condition. This paper demonstrates the method for obtaining an increment in axial bolt force and the maximum bolt stress. In all cases, the analytical results were fairly consistent with the experimental results.
Uncertainty Analysis in Quantitative Risk Assessment
Authors: Quin S. , Widera G. E. O.
Published: February 2008

Of the quantitative approaches applied to inservice inspection, failure modes, effects,criticality analysis (FMECA) methodology is recommended. FMECA can provide a straightforward illustration of how risk can be used to prioritize components for inspection (ASME, 1991). But, at present, it has two limitations. One is that it cannot be used in the situation where components have multiple failure modes. The other is that it cannot be used in the situation where the uncertainties in the data of components have nonuniform distributions. In engineering practice, these two situations exist in many cases. In this paper, two methods based on fuzzy set theory are presented to treat these problems. The methods proposed here can be considered as a supplement to FMECA, thus extending its range of applicability.
Free Vibration Analysis of Thin Cylindrical Shells by the Differential Quadrature Method
Authors: Bert C. W. , Malik M.
Published: February 2008

By introducing the application of the differential quadrature method (DQM) to the dynamic analysis of thin circular cylindrical shells, the work of this paper makes a step forward in furthering the potential of the DQM in the area of structural mechanics. The problem is identified by an eighth-order system of coupled partial differential equations in terms of the three displacement components. The proposed differential quadrature solution is semi-analytical in that Flu¨gge’s representation of the displacement components by trigonometric sine and cosine functions of the circumferential coordinate is employed. The results of the differential quadrature solutions of the natural frequencies of various shell cases are compared and shown to be in excellent agreement with the published, and also some recalculated, results of exact solutions for freely supported, clamped-clamped, clamped-free, and free-free shells. Comparisons are also made with the published experimental data of clamped-clamped and clamped-free shells.
Use of Stress-Strength Model in Determination of Safety Factor for Pressure Vessel Design
Authors: Quin S. , Widera G. E. O.
Published: February 2008

In pressure vessel design, the values of safety factor are still determined on the basis of engineering experience. Thus, they cannot properly reflect the influence of the consequences of failure and the variabilities in stress and strength. As a result, designsare often excessively conservative, while on the other hand, the possibility of failure still exists. Two approaches for determining the value of the safety factor, which are based on reliability analysis, are presented in this paper. As a result of a comparison, one approach based on a stress-strength model is found to be appropriate for pressure vessel design practice. By transforming the interference parts of the distributions of stress and strength into equivalent normal distributions, the approach allows stress and strength to have arbitrary distributions. Three examples, one in which a vessel is subjected to internal pressure, one in which a tall vessel is subjected to combined loads, and one in which a vessel is subjected to external pressure, are given in the paper. From threexamples, the principles for determining target reliability and the factors affecting the safety factor are discussed. It is concluded that by using the approach presented in this paper for pressure vessel design, different consequences of failure as well as variabilities in stress and strength can be taken into account. The approach yields a value for the safety factor that leads to a design which will be safer and yet more economical.
Dynamic Pulse Buckling of Cylindrical Shells Subjected to External Impulsive Loading
Authors: Gu W. , Tang W. , Liu T.
Published: February 2008

The dynamic plastic buckling of cylindrical shells (rings) subjected to general initial impulsive velocity and subjected to impulsive loading is studied based on the energy criterion. A simple analysis method is given and the formulas of critical mode numbers ncr and critical impulsive velocity νcr are obtained.
Pump and Valve Fastener Serviceability in PWR Nuclear Facilities
Authors: Moisidis N. T. , Ratiu M. D.
Published: February 2008

The results of several studies conducted on corrosion of carbon and low-alloy steels in borated water have shown that impingement of borated steam on ferritic steels or contact with a moist paste of boric acid can lead to high corrosion rates due to high local concentrations of boric acid on the surface. The corrosion process of the flange fasteners of pumps and valves is considered a material compatibility and equipment maintenance problem. Therefore, the nuclear utilities of pressurized water reactor (PWR) power plants can prevent this damage by implementing appropriate fastener steel replacement and extended inspections to detect and correct the cause of leakage. A 3-phase corrosion protection program is presented for implementation based on system operability, outage-related accessibility, and cost of fastener replacement versus maintenance frequency increase. A selection criterion for fastener material is indicated based on service limitation: preloading and metal temperature.
Qualification of Diesel Generator Exhaust Carbon Steel Piping to Intermittent Elevated Temperatures
Authors: Ratiu M. D. , Mosidis N. T.
Published: February 2008

The diesel generator exhaust piping, usually made up of carbon steel piping (e.g., ASME SA-106, SA-53), is subjected to successive short time exposures at elevated temperatures up to 1000° F (538°C). A typical design of this piping, without consideration for creep-fatigue cumulative damage, is at least incomplete, if not inappropriate. Also, a design for creep-fatigue, usually employed for long-term exposure to elevated temperatures, would be too conservative and will impose replacement of the carbon steel piping with heat-resistant CrMo alloy piping. The existing ASME standard procedures do not explicitly provide acceptance criteria for the design qualification to withstand these intermittent exposures to elevated temperatures. The serviceability qualification proposed is based on the evaluation of equivalent full temperature cycles which are presumed/expected to be experienced by the exhaust piping during the design operating life of the diesel engine. The proposed serviceability analysis consists of: (a) determination of the permissible stress at elevated temperatures, and (b) estimation of creep-fatigue damage for the total expected cycles of elevated temperature exposures following the procedure provided in ASME Code Cases N-253-6 and N-47-28.
Nonaxisymmetric Dynamic Response of Imperfectly Bonded Buried Fluid-Filled Orthotropic Cylindrical Shells
Authors: Dwivedi J. P. , Singh V. P. , Upadhyay P. C.
Published: February 2008

This paper is concerned with the nonaxisymmetric dynamic response of an imperfectly bonded fluid-filled buried orthotropic cylindrical shell excited by a plane longitudinal wave. A thick shell model, including the effect of shear deformation and rotary inertia, has been taken. For the wave propagation in the fluid inside the pipe, linear acoustic equation has been used. The effects of fluid presence on the shell displacements have been studied for different soil conditions and at various angles of incidence of the longitudinal wave. The effects of bond imperfection on the shell response have been compared with the effects realized due to the presence of fluid inside the pipeline. Effects of changes in the fluid density are also discussed. It is found that magnitude of the response of fluid-filled pipeline can become even more than that of an empty pipeline (without fluid), and, hence, it cannot be assumed that a fluid-filled pipeline will always furnish safe and conservative response.
Analysis of Axial Cracks in Hollow Cylinders Subjected to Thermal Shock by Using the Thermal Weight Function Method
Authors: Ma C.-C. , Liao M.-H.
Published: February 2008

In this study, stress intensity factors for axial cracks in hollow cylinders subjected to thermal shock are determined by using the thermal weight function method. The thermal weight function is a universal function for a given cracked body and can be obtained from any arbitrary mechanical loading system. The thermal weight function may be thought of as Green’s function for the stress intensity factor of cracked bodies subject to thermal loadings. Once the thermal weight function for a cracked body is determined, the stress intensity factor for any arbitrary distributed thermal loading can be simply and efficiently evaluated through the integration of the product of the temperature and the correspondent thermal weight function. A numerical boundary element method for the determination of thermal weight functions for axial cracks in hollow cylinders is used in this study to evaluate the transient stress intensity factor. As a demonstration, some examples of axial cracks in hollow cylinders subjected to thermal shock are solved by using the thermal weight function method, and the results are compared with available results in the published literature.
Biaxial Ratcheting and Cyclic Plasticity for Bree-Type Loading—Part II: Comparison Between Finite Element Analysis and Theory
Authors: Nadarajah C. , Ng H. W.
Published: February 2008

In Part I of this two part paper (Ng and Nadarajah, 1996), the results of an extensive program of finite element analyses were described. The problem being considered is the phenomenon of ratcheting and cyclic stress-strain hysteresis loop behavior in a thin-walled cylinder subject to cyclic thermal stress and sustained internal pressure. The purpose of Part II is to compare the finite element results with two analytical solutions and review the applicability of the latter as a design procedure for assessment of these types of structures. The comparison shows that the ratcheting to shakedown boundaries based on F.E. and analytical models are in close agreement. The hoop ratcheting rates predicted by the uniaxial model enveloped the F.E. and biaxial models, while for the axial ratcheting rates, the F.E. results are upper bound.
Buckling of Filament-Wound Cylindrical Vessels Subjected to External Pressure
Authors: Olivas J. D. , Ravi-Chandar K. , Bustillos J. , Craigie L.
Published: February 2008

A study was carried out to evaluate the buckling of anisotropic cylindrical vessels subjected to external pressure. The cylinders were fabricated with filament-wound glass fiber in a vinyl-ester resin matrix and tested using a novel experimental procedure. Characteristic response of each specimen to strain and acoustic emission were compared to the onset of buckling. The measured onset of buckling lobe formation agreed with values predicted by classical calculation methods founded on Donnell kinematic relations and antisymmetric assumptions. Also, two ASME design criteria, Section X and RTP-1, for the design of thin-walled cylindrical vessels made from fiber-reinforced thermosetting plastic, subjected to external pressure were evaluated; RTP-1 was found to be too conservative, while Section X did not provide the professed design factor of 5.
Random Excitation Forces in Tube Bundles Subjected to Two-Phase Cross-Flow
Authors: Taylor C. E. , Pettigrew M. J. , Currie I. G.
Published: February 2008

Data from two experimental programs have been analyzed to determine the characteristics of the random excitation forces associated with two-phase cross-flow in tube bundles. Large-scale air-water flow loops in France and Canada were used to generate the data. Tests were carried out on cantilevered, clamped-pinned, and clamped-clamped tubes in normal-square, parallel-triangular, and normal-triangular configurations. Either strain gages or force transducers were used to measure the vibration response of a centrally located tube as the tube array was subjected to a wide range of void fractions and flow rates. Power spectra were analyzed to determine the effect of parameters such as tube diameter, frequency, flow rate, void fraction, and flow regime on the random excitation forces. Normalized expressions for the excitation force power spectra were found to be flow-regime dependent. In the churn flow regime, flow rate and void fraction had very little effect on the magnitude of the excitation forces. In the bubble-plug flow regime, the excitation forces increased rapidly with flow rate and void fraction.
A Case Study of a Proposed Monitor for Industrial Process Fouling
Authors: Becker B. R. , Fricke B. A.
Published: February 2008

Fouling of a piping system refers to the formation of deposits on pipe walls, which can severely impede fluid flow. The food, dairy, and chemical processing industries usually combat the fouling of piping systems through extensive cleaning or complete replacement of the systems, usually on an emergency basis. This paper describes the development of a model which permits real time monitoring of the overall fouling in a piping system and provides insight into the behavior and response trends of piping system fouling to changes in process operating parameters. It facilitates the prediction of both the rate of fouling and the useful life of the piping system, thereby avoiding emergency shutdowns. This paper also describes the implementation of the model in an existing industrial process plant where it was found to accurately monitor actual fouling behavior. The results of the model demonstrate the influence of Reynolds number upon the fouling of this industrial process piping system. This paper also presents a summary of previous fouling research.
A Simple Estimating Method for Reduction of Welding Residual Stresses in Thick Welded Joint From Stress-Relief Annealing—Part I: Development of the Analytical Method for Relaxation Tests and Its Applicability
Authors: Nakacho K. , Ueda Y.
Published: February 2008

Stress-relief annealing (SR treatment) is often applied to relieve welding residual stresses in the fabrication process of pressure vessels, etc. This study aims at development of an efficient method as simple as hand calculation to estimate reduction of residual stresses of very thick welded joint by SR treatment. In this first report, an estimating method is developed for relaxation tests, in uniaxial stress state, at changing and constant temperatures because the stress relaxation phenomenon is very similar to that observed in the SR treatment of a joint. Using the various relations between stress and strains in the relaxation tests, estimating equations are formulated in order to simply calculate the change of the stress. The results obtained by applying the equations are compared with the highly accurate analytical result based on the finite element method. Both results show such a good coincidence that the appropriateness of the adopted method is confirmed. In the next report, this method is extended to SR treatment of a very thick welded joint, of which the stress state and boundary condition are very complex.
Three-Dimensional Interaction Effects in an Internally Multicracked Pressurized Thick-Walled Cylinder—Part II: Longitudinal Coplanar Crack Arrays
Authors: Levy C. , Perl M. , Kokkavessis N.
Published: February 2008

In the first part of this paper, the interaction effects among many radial, internal, semi-circular, and semi-elliptical cracks in a pressurized, thick-walled vessel were quantified. In the present paper, the mode I stress intensity factor (SIF) distribution for numerous longitudinal coplanar, internal, semi-circular, and semi-elliptical arrays of surface cracks in an infinite, pressurized, thick-walled cylinder are evaluated. The 3-D analysis is performed by the finite element (FE) method and the submodeling technique, employing singular elements along the crack front. The effects of dense and sparse interacting longitudinal coplanar crack arrays on the SIFs are studied 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 the crack depth to semi-crack length, a/c, from 0.2 to 2.0. An analysis is performed to determine the influence of the three major parameters—crack density, crack ellipticity, and crack depth—on the interaction effects between adjacent cracks. The results clearly indicate that crack density, and, in some cases, ellipticity have opposing effects on the SIF of longitudinal crack arrays as compared to radial crack arrays. As a result of these contrasting behaviors, thick-walled cylinders having combined longitudinal and radial crack arrays would need further study.
Effects of Crack Depth, Specimen Size, and Out-of-Plane Stress on the Fracture Toughness of Reactor Vessel Steels
Authors: Chao Y.-J. , Lam P.-S.
Published: February 2008

Cleavage fracture toughness values for A533-B reactor pressure vessel (RPV) steel at -40°C obtained from test programs at Oak Ridge National Laboratory (ORNL) and University of Kansas (KU) are interpreted using the J-A2 analytical model. The KU test data are from smaller SENB specimens with a/w = 0.1 and 0.5. The ORNL test data are from 1) larger SENB specimens with a/w = 0.1 and 0.5, and 2) a six-point-bend cruciform specimen under either uniaxial or bi-axial loads. The analytical model is based on the critical stress criterion and takes into consideration the constraint effect using the second parameter A2 in addition to the generally accepted loading parameter J. It is demonstrated that the effects of crack depth (shallow versus deep), specimen size (small versus large), and loading type (uniaxial versus biaxial) on the fracture toughness from the test programs can be interpreted and predicted.
Reliability of Steam Generator Tubes With Axial Cracks
Authors: Cizelj L. , Mavko B. , Vencelj P.
Published: February 2008

An approach for estimating the failure probability of tubes containing through-wall axial cracks has already been proposed by the authors. It is based on probabilistic fracture mechanics and accounts for scatter in tube geometry and material properties, scatter in residual and operational stresses responsible for crack propagation, and characteristics of nondestructive examination and plugging procedures (e.g., detection probability, sizing accuracy, human errors). Results of preliminary tests demonstrated wide applicability of this approach and triggered some improvements. The additions to the model are extensively discussed in this paper. Capabilities are demonstrated by results of analysis of steam generator no. 1 in Slovenian nuclear power plant located in Krsˇko after the 1992 inspection and plugging campaign. First, the number of cracked tubes and the crack length distribution were estimated using data obtained by the 100-percent motorized pancake coil inspection. The inspection and plugging activities were simulated in the second step to estimate the efficiency of maintenance in terms of single and multiple-tube rupture probabilities. They were calculated as a function of maximum allowable crack length. The importance of human errors and some limitations of present nondestructive examination techniques were identified. The traditional wall thickness and crack-length-based plugging criteria are compared. The crack-length-based criterion is shown to be more efficient and more safe, especially because of strong suppression effect on probability of multiple-tube rupture. The results are considered to be important for safety and maintenance of existing plants and for further research.
Influence of Internal Pressure on the Impact Behavior of Steel Pipelines
Authors: Jones N. , Birch R. S.
Published: February 2008

This article presents some experimental data recorded from 54 impact tests on pressurized mild steel pipes. The pipes were fully clamped across a span which was ten times the outside pipe diameter of 60 mm. The pipes had a wall thickness of 1.70 mm and were impacted laterally by a rigid wedge indenter at the mid-span and one-quarter-span positions. The impact velocities ranged up to 13.6 m/s and caused large inelastic indentations for the lower values and at higher values a loss of integrity which could occur underneath the indenter and/or at an end support. The critical values for the two failure energies were obtained for a range of internal gas pressures.
The Influence of the Nonhomogeneous Temperature Field on the Optimal Winding Prestress of the Compound Pressure Vessel
Authors: Sucha´nek M. , Vrbka J.
Published: February 2008

The completed ribbon-winding theory, including temperature loading of the high-pressure compound vessel, was proposed. The influence of the bending stress in the wound ribbon is taken into account. Internal core of the compound vessel consists of matrix and ring, made of different materials. The relations were derived in analytical form, describing the radial distribution of necessary tangential prestressing.
Axial Vibrations of Fluid-Filled Bellows Expansion Joints
Authors: Jakubauskas V. F. , Weaver D. S.
Published: February 2008

This paper presents the results of a project undertaken to study the axisymmetric natural vibrations and fluid-added mass of fluid-filled bellows expansion joints. The bellows were modeled using axisymmetric shell finite elements, while the fluid region was discretized using axisymmetric triangular elements. The in-vacuo bellows modes were used as boundary conditions on the potential flow model for the fluid and the added mass determined for each bellows mode. This added mass was then used to determine the in-fluid bellows natural frequencies. Experiments were conducted to verify the theoretical model and agreement was found to be very good. The results were also compared with the frequency predictions of previously developed relatively simple theoretical models.
A Reinforcement Design Method Based on Analysis of Large Openings in Cylindrical Pressure Vessels
Authors: Xue M. D. , Hwang K. C. , Lu¨ W. , Chen W.
Published: February 2008

The analytical solution is given for two orthogonally intersecting cylindrical shells with large diameter ratio d/D subjected to internal pressure. The modified Morley equation is used for the shell with cutout and the Love equation for the tube with nonplanar end. The continuity conditions of forces and displacements at the intersection are expressed in 3-D cylindrical coordinates (ρ, θ, z), and are expanded in Fourier series of θ. The Fourier coefficients are obtained by numerical quadrature. The present results are in good agreement with those obtained by tests and by FEM for ρ0 = d/D ≤ 0.8. The typical curves of SCF versus t/T and d/DT and reinforcement coefficients g, h versus D/T0 for each ρ0 are given on the present method.
Optimum Support Arrangement of Piping Systems Using Genetic Algorithm
Authors: Chiba T. , Okado S. , Fujii I. , Itami K. , Hara F.
Published: February 2008

The support arrangement is one of the important factors in the design of piping systems. Much time is required to decide the arrangement of the supports. We applied a genetic algorithm to find the optimum support arrangement for piping systems. Examples are provided to illustrate the effectiveness of the genetic algorithm. Good results are obtained when applying the genetic algorithm to the actual designing of the piping system.
Effects of Repair Weld Residual Stresses on Wide-Panel Specimens Loaded in Tension
Authors: Dong P. , Hong J. K. , Zhang J. , Rogers P. , Bynum J. , Shah S.
Published: February 2008

As a part of the welding fabrication procedure development for the next generation space shuttle external tank, aluminum-lithium wide-panel specimens were used to assess the interactions between repair weld residual stresses and external loading conditions. The detailed residual stress development in the wide panel specimens with a repair weld was analyzed using an advanced finite element procedure. External tension loading effects were then incorporated in the residual stress model to study the interactions between the residual stress field and external tensile loading. Wide-panel tensile tests were also performed to extract photo strain and strain-gage results. A good agreement between the finite element and experimental results was obtained. The results demonstrate that the presence of high tensile residual stresses within a repair weld has a drastic impact on the stress/strain distribution in the wide panel specimens subjected to external loading. Its implications on structural integrity are discussed in light of the wide-panel results. The effects of post-welding mechanical treatment such as planishing were also examined.
Estimation of Residual Stresses in Hydraulically Expanded Tube-to-Tubesheet Joints
Authors: Allam M. , Chaaban A. , Bazergui A.
Published: February 2008

The knowledge of residual stresses introduced in the tubes of heat exchangers during their expansion in the tubesheet holes is important because of their effect on the structural integrity of components. This paper presents a simplified theoretical method to calculate the maximum residual stresses introduced in the transition zone of expanded tube-to-tubesheet joint. The higher positive values of tensile residual stresses and their corresponding axial locations are determined by using a standard deviation analysis. The validation of the proposed equations was accomplished by comparing their results to those obtained by the finite element method for some arbitrary cases. An upper limit has been imposed on the expansion pressure level, depending on the combination of the geometrical and material parameters that are involved in the design of the tube-to-tubesheet joints.
The Creep Measurement of 475°C Pipeline Using Moire Interferometry
Authors: Huimin X. , Daqing Z. , Fulong D. , Wei Z. , Dietz P. , Schmidt A.
Published: February 2008

In this study, a new experimental method for measuring the creep of pipeline using moire interferometry was proposed. Curved-surface-deformed grating replicating technique was combined with the high-temperature-resistant grating and moire interferometry method, and was applied to measure the creep of a 475°C main steam pipeline in the Qinghe Power Plant for 3600 h. The measuring principle and experimental techniques are described. The measuring error and experimental results are discussed in detail.
Experimental Study on Fatigue Strength of Small-Diameter Socket-Welded Pipe Joints
Authors: Higuchi M. , Nakagawa A. , Iida K. , Hayashi M. , Yamauchi T. , Saito M. , Sato M.
Published: February 2008

The authors conducted fully reversed four-point bending fatigue tests on socket-welded joints 20 to 50 mm in nominal diameter, and rotating bending fatigue tests on socket-welded joints 20 mm in nominal diameter. S-N curves for 33 series of different types of specimens were obtained. Examination was made of the effects of various parameters listed in the forthcoming on fatigue strength such as steel types (carbon and stainless steels), diameter, pipe thickness (Sch), fillet shape, slip-on gap, and root defects. Bending fatigue test results indicated fatigue strength for socket-welded joints to be less for longer life regions than reported in the literature by Markl and George (1950). Fatigue strength for socket joints of 50 mm nominal diameter at 107 cycles of fatigue life was 46 MPa for carbon steel and 60 MPa for stainless steel with nominal bending stress on the pipe surface. Cracks generally originated from the toe when stress amplitude was high with shorter fatigue life and from the root when amplitude was small with longer life. Fatigue strength was greater for smaller diameter, larger Sch (thicker pipe wall), final welding pass on the toe of pipe side, and in the absence of a slip-on gap. From fatigue test results of socket joints with weld defects at the roots, an empirical equation for the relation of defect size with decrease in fatigue strength was established. Fatigue strength was found to decrease to 60 percent the original level for defect size 25 percent of leg length.
Penetration and Perforation of Composite Sandwich Panels by Hemispherical and Conical Projectiles
Authors: Reddy T. Y. , Wen H. M. , Reid S. R. , Soden P. D.
Published: February 2008

The results of penetration and perforation tests carried out on composite sandwich panels with GRP skins and PVC foam cores using hemispherical-ended and conical-nosed indenters/projectiles under quasi-static, drop-weight, and ballistic impact conditions, with impact velocities up to 305 m/s, are described. Load-displacement characteristics under quasi-static loading are presented and the ballistic limits as well as perforation energies are determined. A classification of the sandwich panel responses based on the panel thickness-to-projectile diameter ratio is deduced. General empirical formulas that predict the dynamic perforation energies for FRP laminates and composite sandwich panels loaded by hemispherical-ended projectiles are derived. The empirical equations correlate well with available experimental data. It is shown that, to a first approximation, the formulas obtained for hemispherical-ended projectiles are also applicable to conical-nosed projectiles.
A Simple Upper-Bound Method for Calculating Approximate Shakedown Loads
Authors: Hamilton R. , Boyle J. T. , Shi J. , Mackenzie D.
Published: February 2008

A simple approach for calculating upper-bound shakedown loads is described. The method is based on a series of iterative elastic finite element analyses (the elastic compensation procedure) applied to Koiter’s upper-bound shakedown theorem. The method is demonstrated for a typical pressure vessel application; an axisymmetric nozzle in a spherical shell. Several geometrical configurations are investigated. The calculated upper-bound shakedown loads are compared with lower-bound results obtained by the authors, simple shakedown criteria, and various results given in the literature.
Automated System for Analyzing Stress Intensity Factors of Three-Dimensional Cracks: Its Application to Analyses of Two Dissimilar Semi-Elliptical Surface Cracks in Plate
Authors: Yoshimura S. , Lee J.-S. , Yagawa G.
Published: February 2008

This paper describes a new automated system for analyzing the stress intensity factors (SIFs) of three-dimensional cracks. A geometry model containing one or several three-dimensional cracks is defined using a commercial CAD system, DESIGNBASE. Several local distributions of node density are chosen from the database of the present system, and then automatically superposed on one another over the geometry model by using the fuzzy knowledge processing. Nodes are generated by the bucketing method, and ten-noded quadratic tetrahedral solid elements are generated by the Delaunay method. A user imposes material properties and boundary conditions onto parts of the geometry model such as loops and edges by clicking them with a mouse and by inputting values. For accurate analyses of the stress intensity factors, finer elements are generated in the vicinity of crack tips, thanks to the fuzzy knowledge processing. The singular elements such that the midpoint nodes near crack front are shifted at the quarter-points are automatically placed along the three-dimensional crack front. The complete finite element model generated is given to a commercial finite element code, MARC, and a stress analysis is performed. The stress intensity factors are calculated using the displacement extrapolation method. To demonstrate practical performances of the present system, two dissimilar semi-elliptical surface cracks in a plate subjected to uniform tension are solved, and their interaction effects are discussed in detail. It is shown from the results that ASME Boiler and Pressure Vessel Code, Section XI, Appendix A gives a conservative stress intensity factor for two identical adjacent surface cracks and for two dissimilar adjacent surface cracks.
Evaluation of the Method for Lowering Stress Concentration at the Thread Root of Bolted Joints With Modifications of Nut Shape
Authors: Fukuoka T.
Published: February 2008

Many studies have been devoted to investigate how the maximum stress occurred in the bolted joint could be reduced. Patterson and Kenny suggest that a modified nut with a straight bevel at the bearing surface is effective. However, they only dealt with M30, and estimations on the nut geometry had not been necessarily sufficient. In this study, an extensive finite element approach for solving general multi-body contact problem is proposed by incorporating a “regularization method” into stiffness matrices with singularity involved; thus, numerical analyses are executed to accurately determine the optimal shape of the modified nut for various design factors. A modified nut with a curved bevel is also treated, and it is concluded that the modified nuts are significantly effective for bolts with larger nominal diameter and fine pitch, and are practically useful compared to pitch modification and tapered thread methods.
Elastic, Plastic, and Creep Buckling of Imperfect Cylinders Under Mechanical and Thermal Loading
Authors: Eslami M. R. , Shariyat M.
Published: February 2008

Based on the concept of secant and tangent modulus, the nonlinear equilibrium and stability equations of thin cylindrical shells under axial compression, external pressure, or external fluid pressure are derived. The resulting equations are applicable to shells without length limitation as the rotations and transverse shears are included in the derivations. The reduction factors for plastic and creep buckling are then obtained. A procedure for determining secant and tangent modulus in the very general case of elastic, plastic, or creep stress in the presence of temperature gradient is proposed. Then, using Donnell’s nonlinear theory of shells, the effect of initial imperfection on the strength of the elastic shell is discussed. The foregoing results are extended to plastic and creep buckling of cylindrical shells of arbitrary length and temperature gradient. Some design curves are proposed using the obtained equations. Finally, the present results are compared with available results in the literature and the accuracy of the method is examined.
Fracture Analysis of the NESC-1 Spinning Cylinder Experiment
Authors: Keeney J. A. , Bass B. R.
Published: February 2008

This paper presents finite-element analyses of the cylinder specimen being used in the international Network for Evaluating Steel Components (NESC) large-scale spinning-cylinder project (NESC-1). The objective of the NESC-1 project is to focus on a complete process for assessing the structural integrity of aged reactor pressure vessels. A new cylinder specimen was reconstituted from segments of the previously tested SC-4 and SC-6 specimens because the relatively high fracture toughness of the original specimen might preclude achieving the test objectives. The wall thickness is greater for the reconstituted specimen when compared with the previous specimen geometry (175 versus 150 mm). Also, the initial and coolant temperatures for the proposed thermal shock may be reduced as much as 25°C to increase the probability of achieving cleavage initiation. Analyses were carried out to determine the combined effects of increasing the wall thickness and lowering the initial and coolant temperatures in the experiment. Estimates were made of the change in hoop strain on the clad inner surface directly above a subclad crack due to initiation and axial propagation of the crack. Three-dimensional finite-element models of the cladded cylinder were generated with 6:1 and 2:1 semi-elliptical 70-mm-deep subclad cracks. The cylinder specimen was subjected to thermal-shock and centrifugal loading conditions and analyzed with a thermo-elastic-plastic material model. The analytical results indicate that lowering the initial and coolant temperatures by 25°C will not significantly change the peak driving force, but will shift the stress-intensity factor (KI) versus temperature curves so that the crack will become critical at an earlier time in the transient. The peak KI value occurs at a lower temperature (after the crack becomes critical), which increases the probability of achieving cleavage initiation. Also, the calculated hoop strains for the two crack aspect ratios (simulation of 2:1 crack propagating axially) provide an estimated change in hoop strain in the range of 3 to 4 percent on the clad inner surface.
Determination of Sample Size in Service Inspection
Authors: Qin S. , Widera G. E. O.
Published: February 2008

When performing inservice inspection on a large volume of identical components, it becomes an almost impossible task to inspect all those in which defects may exist, even if their failure probabilities are known. As a result, an appropriate sample size needs to be determined when setting up an inspection program. In this paper, a probabilistic analysis method is employed to solve this problem. It is assumed that the characteristic data of components has a certain distribution which can be taken as known when the mean and standard deviations of serviceable and defective sets of components are estimated. The sample size can then be determined within an acceptable assigned error range. In this way, both false rejection and acceptance can be avoided with a high degree of confidence.
Weight Functions for an External Longitudinal Semi-Elliptical Surface Crack in a Thick-Walled Cylinder
Authors: Kiciak A. , Glinka G. , Burns D. J.
Published: February 2008

Mode I weight functions were derived for the deepest and surface points of an external radial-longitudinal semi-elliptical surface crack in a thick-walled cylinder with the ratio of the internal radius to wall thickness, Ri/t = 1.0. Coefficients of a general weight function were found using the method of two reference stress intensity factors for two independent stress distributions, and from properties of weight functions. Stress intensity factors calculated using the weight functions were compared to the finite element data for several different stress distributions and to the boundary element method results for the Lame´ hoop stress in an internally pressurized cylinder. A comparison to the ASME Pressure Vessel Code method for deriving stress intensity factors was also made. The derived weight functions enable simple calculations of stress intensity factors for complex stress distributions.
Vibration and Stability of Two Tubes in Cross-Flow
Authors: Zhu S. , Chen S. S. , Cai Y.
Published: February 2008

Two tubes in tandem and normal to flow were studied on the basis of the unsteady-flow theory. Motion-dependent fluid forces were measured in a water channel, and the pitch-to-diameter ratio was 1.35. From the measured fluid forces, fluid damping and stiffness were calculated as a function of reduced flow velocity and several Reynolds numbers. Once the fluid-damping and fluid-stiffness coefficients are known, coupled vibration and stability of the two tubes in cross-flow can be predicted.
Prevention of Nonductile Fracture in 6061-T6 Aluminum Nuclear Pressure Vessels
Authors: Yahr G. T.
Published: February 2008

The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Committee has approved rules for the use of 6061-T6 and 6061-T651 aluminum for the construction of Class 1 welded nuclear pressure vessels for temperatures not exceeding 149°C (300°F). Nuclear Code Case N-519 will allow the use of this aluminum in the construction of low-temperature research reactors such as the Advanced Neutron Source. The rules for protection against nonductile fracture are discussed. The basis for a value of 25.3 MPam (23 ksi in.) for the critical or reference stress intensity factor for use in the fracture analysis is presented. Requirements for consideration of the effects of neutron irradiation on the fracture toughness are discussed.
Interaction Effects in Combined Arrays of Radial and Longitudinal Semi-Elliptical Surface Cracks in Pressurized Thick-Walled Cylinder
Authors: Perl M. , Levy C. , Wang J.
Published: February 2008

In two previous papers, the interaction effects for two separate cases of large arrays of semi-elliptical, internal, surface cracks in a thick-walled, cylindrical pressure vessel were studied. First, arrays of radial cracks were considered followed by the study of longitudinal-coplanar crack arrays. Circumferential crack density and longitudinal crack spacing were found to have opposing effects on the prevailing stress intensity factors (SIFs). Consequently, in the present paper, combined arrays of both radial and longitudinal cracks are considered, and their interaction effects are studied. The mode I stress intensity factor (SIF) distribution for numerous configurations of combined semi-circular and semi-elliptical crack arrays are evaluated. The 3-D analysis is performed by the finite element (FE) method and the submodeling technique, employing singular elements along the crack front. The effects of crack density in the circumferential direction and of relative spacing in the longitudinal direction on the SIFs are studied for combined arrays of up to 32 circumferentially equispaced, radial cracks and having longitudinal relative spacing of 2c/d of 0.25 to 0.99; for a wide range of crack depth to wall thickness ratios, a/t, from 0.05 to 0.4; and for various ellipticities of the crack, i.e., the ratio of crack depth to semicrack length, a/c, from 0.2 to 1.5. The results clearly indicate that the SIFs are considerably affected by the interaction among the cracks, and that the SIF values depend upon the circumferential density and longitudinal spacing, the crack depth and ellipticity, as well as the three-dimensional nature of the problem.
Effects of Compressibility on Flow Characteristics and Dynamics of Swing Check Valves—Part I
Authors: Botros K. K. , Jones B. J. , Roorda O.
Published: February 2008

In the design of natural gas compressor stations, a check valve is a critical element which is commonly placed on the discharge side of the compressor to prevent reverse flow that can cause serious damage to the compressor itself and other components such as seals and bearings. One of the selection criteria of the check valve for this particular application is the valve flow characteristics in steady flow, and its dynamic characteristics in unsteady flow operation. With regards to steady flow valve Characteristics, current models for the determination of the check valve open angle versus mean flow velocity are based on semi-empirical data obtained from water tests, which were found to deviate from measurements involving fluids of relatively higher compressibility. This paper presents results of steady flow testing of an NPS 4 swing type check valve in air. Mean flow velocities versus disk angles were measured together with several local pressure measurements at the back side of the valve disk. Comparison of these results with the EPRI model and Rahmeyer’s model revealed that these two models underestimate the mean flow velocity for a given disk angle in air. A model was thus developed based on further refinement of Rahmeyer’s model, but more suitable for fluids of relatively higher compressibility, and accounts for both torque contributions: (i) from jet velocity impingement (Kv), and (ii) from back pressure distribution (Kp). The work presented here points out the need for better design of the disk shape, particularly at the lower lip, and/or the valve body in order to create a lower disk back pressure to improve the disk lifting torque at lower mean flow velocity.
The Significance of Crack Depth (a) and Crack Depth-to-Width Ratio (a/W) With Respect to the Behavior of Very Large Specimens
Authors: Smith J. A. , Rolfe S. T.
Published: February 2008

Previous studies have shown that there is an increase in cleavage fracture toughness of laboratory specimens with shallow flaws compared with those laboratory specimens having deep flaws. Typical crack depths in real structures generally are very small relative to the member width. Therefore, the crack depth to structural member width (a/W) ratios are very small (less than 0.1). Accordingly, the effect of this observation on the behavior of larger structures that actually represent typical engineering applications could be significant. Using experimental and analytical results from previous studies on A533-B steel specimens, the effect of the shallow flaw behavior with respect to very large specimens was examined. Using the Dodds and Anderson constraint correction, predictions of the cleavage fracture toughness of large-scale wide-plate tests and full thickness clad beams from an actual reactor pressure vessel were shown to compare favorably with actual test results. The results of these studies suggest the possibility of predicting the increase in fracture toughness for low constraint structural geometries using high-constraint laboratory test specimen results. The ability to take advantage of this increase in toughness in analysis of actual structures could be very useful in estimating the actual safety and reliability of existing structures with service cracks.
Proposal for Calculations of Flat Oval Pipes Under Internal Pressure Under Consideration of Material Plastification
Authors: Jekerle J.
Published: February 2008

In the wall of an oval pipe, additional to the circumferential forces, shear forces and bending moments occur under internal pressure load. Under this condition, the bending stresses in certain cross sections reach a figure many times that of normal stresses so that yield strength of the material can be exceeded. The usual stress calculation method is based on the calculation of the bending moments with the use of the elastic bending equation. The use of the part-plastic equation presented in the paper gives more accurate values for the bending moments sought in the cross sections being checked. This paper shows that even though the new calculation method leads to a smaller wall thickness of the flat oval pipe, the design of the flat oval pipe is nevertheless safe.
Modeling of Multiaxial Creep Behavior for Incoloy 800 Tubes Under Internal Pressure
Authors: Koundy V. , Forgeron T. , Le Naour F.
Published: February 2008

In order to validate the long-term behavior of fast breeder reactor steam generator tubes, a creep test monitoring program has been undertaken. A series of over one hundred tests was performed on small specimen tubes which were cut from the as-received tube material of Incoloy 800, similar to those used in generator applications. In contrast to uniaxial conditions in which constant load conditions usually apply, multiaxial experiments were performed assuming constant stress conditions. Thin walled tube approximation was used to estimate the stresses across the tube wall thickness required for given internal tube pressures. This paper deals with a refined numerical modeling of stresses and strains in the pressurized test specimens, taking into account: internal pressure changes, nonlinear geometrical effects, and creep deformation during all the test procedure cycles. Comparison of the numerical results with the experimental measurements shows a good agreement which validates the multiaxial generalization of the RCC-MR strain creep laws which were used in the calculations. A multiaxial creep rupture criterion is discussed.