bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy Transfer from High-Frequency to Low-Frequency Modes in Structures
Authors: Nayfeh A. H. , Mook D. T.
Published: February 2008

A perspective of the mechanisms by which energy is transferred from high- to low-frequency modes is presented. The focus is on some recent experiments that reveal how a low-amplitude high-frequency excitation can produce a large-amplitude low-frequency response. Such a phenomenon is potentially harmful, if not catastrophic. Specifically, these experiments clarify the role of internal resonances, combination external and parametric resonances, and the interactions among modes of widely spaced frequencies.
Substructure Methods in Vibration
Authors: Craig R. R.
Published: February 2008

When the response of a structural system to dynamic excitation must be analyzed, a substructure coupling method (or component-mode synthesis method) is frequently employed to reduce the order of the finite element model of the structure. This paper reviews procedures used to formulate component modes for substructures and to assemble substructure models to form reduced-order models of the original system. A brief literature survey covering several applications of substructure coupling is also presented.
Recent Results in Random Vibrations of Nonlinear Mechanical Systems
Authors: Ibrahim R. A.
Published: February 2008

The influence of random vibration on the design of mechanical components has been considered within the framework of the linear theory of small oscillations. However, in some important cases this theory is inadequate and fails to predict some complex response characteristics that have been observed experimentally and which can only be predicted by nonlinear analyses. This paper describes some recent developments in the theory of nonlinear random vibration based on Markov methods and related problems in the design of dynamical systems. Research efforts have been focused on stability/bifurcation conditions, response statistics and reliability problems. Significant progress has been made in developing new analytical methods and conducting experimental testing. These developments have helped to resolve some controversies, and to enhance our understanding of difficult issues. Experimental and numerical simulations have revealed new phenomena that were not predicted analytically. These include on-off intermittency, snap-through phenomena, and the dependence of the response bandwidth on the excitation level. The main results of studying the responses of nonlinear single-and two-degree-of-freedom systems to random excitations obtained by the author and others are discussed in this paper.
Why Do Vortices Generate Sound?
Authors: Powell Alan
Published: February 2008

Emphasizing physical pictures with a minimum of analysis, an introductory account is presented as to how vortices generate sound. Based on the observation that a vortex ring induces the same hydrodynamic (incompressible) flow as does a dipole sheet of the same shape, simple physical arguments for sound generation by vorticity are presented, first in terms of moving vortex rings of fixed strength and then of fixed rings of variable strength. These lead to the formal results of the theory of vortex sound, with the source expressed in terms of the vortex force ρ(u∧ ζ) and of the form introduced by Mo¨hring in terms of the vortex moment (y∧ ζ′), (ρ is the constant fluid density, u the flow velocity, ζ = ∇ ∧u the vorticity and y is the flow coordinate). The simple “Contiguous Method” of finding the contiguous acoustic field surrounding an acoustically compact hydrodynamic (incompressible) field is also discussed. Some very simple vortex flows illustrate the various ideas. These are all for acoustically compact, low Mach number flows of an inviscid fluid, except that a simple argument for the effect of viscous dissipation is given and its relevance to the “dilatation” of a vortex is mentioned.
Imprecision in Engineering Design
Authors: Antonsson E. K. , Otto K. N.
Published: February 2008

Methods for incorporating imprecision in engineering design decision-making are briefly reviewed and compared. A tutorial is presented on the Method of Imprecision (MoI), a formal method, based on the mathematics of fuzzy sets, for representing and manipulating imprecision in engineering design. The results of a design cost estimation example, utilizing a new informal cost specification, are presented. The MoI can provide formal information upon which to base decisions during preliminary engineering design and can facilitate set-based concurrent design.
Axiomatic Design of Mechanical Systems
Authors: Suh N. P.
Published: February 2008

Design is done in many fields. Although the design practices in different fields appear to be distinct from each other, all fields use a common thought process and design principles. Consequently, the true differences between these fields are minor, often consisting of the definitions of words, the specific data, and knowledge. In comparison, larger differences can exist within a given field between simple systems and large systems due to the size and the time dependent nature of functional requirements. The axiomatic approach to design provides a general theoretical framework for all these design fields, including mechanical design. The key concepts of axiomatic design are: the existence of domains, the characteristic vectors within the domains that can be decomposed into hierarchies through zigzagging between the domains, and the design axioms (i.e., the Independence Axiom and the Information Axiom). Based on the two design axioms, corollaries and theorems can be stated or derived for simple systems, large systems, and organizations. These theorems and corollaries can be used as design rules or guidelines for designers. The basic concepts are illustrated using simple mechanical design examples. When design is viewed axiomatically, not only product design but all other designs, including design of process, systems, software, organizations, and materials, are amenable to systematic treatment.
Finite Element Stress Analysis of Tubesheets Perforated by Circular Holes in Square Pitch Pattern
Authors: Ukadgaonker V. G. , Kale P. A.
Published: February 2008

ASME has accepted the codes for the tubesheets with triangular pitch pattern, but the code standards for the square pitch pattern have not been accepted so far. This is the motivation behind solving the present problem. This paper deals with the finite element stress analysis of a perforated plate or tubesheets with square pitch pattern. For the stress analysis, finite number of holes and in-plane and bending loading are considered. Stress concentration factors are obtained for various ligament efficiencies. The problem of cracks emanating from holes is also considered. Stress intensity factors for various crack lengths and ligament efficiencies are obtained.
A Simple Method for Fluid-Structure Interaction Analysis Under Cavitation Condition
Authors: Baba K. , Fuyama H. , Ochi M.
Published: February 2008

In fluid-structure interaction problems, many studies are done by linear formulations. But severe loading may cause cavitation that shows nonlinear behavior. In handling cavitation phenomena, a displacement potential was introduced or density was used as the variable. Each method loses the conservation of liquid volume that is vital for liquid-filled tanks; mesh size should be the scales of cavitation. This paper proposes a simple method based on Lagrange multiplier method. A numerical example is shown for a one-dimensional problem together with a comparison to an experimental result.
Limit Loads for Pipe Elbows With Internal Pressure Under In-Plane Closing Bending Moments
Authors: Shalaby M. A. , Younan M. Y. A.
Published: February 2008

The purpose of this study is to determine limit loads for pipe elbows subjected to in-plane bending moments that tend to close the elbow (i.e., decrease its radius of curvature), and the influence of internal pressure on the value of the limit load. Load-deflection curves were obtained, and from these curves plastic collapse or instability loads at various values of internal pressure were determined. This was done for different pipe bend factors (h = Rt/r2) using the nonlinear finite element analysis code (ABAQUS) with its special elbow element. The limit load was found to increase and then decrease with increasing pressure for all the elbow geometries studied.
A Unified 3-D Homogenization Model of Beam Bundle in Fluid
Authors: Zhang R. J.
Published: February 2008

A 3-D homogenization model is developed to predict the overall dynamic property of a beam bundle immersed in an acoustic fluid. It is shown that the existing two models, given by Benner and Schumann (1981) and Hammami and Brochard (1991), respectively, are its 2-D application.
An Acetylene Gas Cylinder Explosion
Authors: Price J. W. H.
Published: February 2008

This paper considers the failure of an acetylene gas cylinder which occurred under extreme loading conditions resulting in severe fragmentation of the cylinder. The characteristics of the failure morphology, which is entirely ductile, are discussed. The loading experienced and the fragmentation are put in the context of literature information and events such as failure using explosives and other high-velocity loadings. A model of failure is developed which demonstrates the energies involved in the incident and the explanation for the development of the failure characteristics are discussed.
A Study of Effects of Pipe Geometry on FAD Curves for Austenitic Stainless Steel and Ferritic Steel Piping Materials
Authors: Mohan R. , Wilkowski G. M. , Bass R. , Bloom J. M.
Published: February 2008

A comprehensive study of failure assessment diagrams for circumferentially surface-cracked austenitic stainless and ferritic steel pipes was conducted with the use of the finite element method (FEM). While the majority of the analyses were conducted using the line-spring/shell finite element method, some three-dimensional finite element analyses, conducted independently, are also reported in this paper. Comparison of the predictions of the line-spring/shell and three-dimensional analyses reinforce the validity of the former approach for surface-cracked pipes. The results indicated that the ASME Code Case N-494-2 applicable for ferritic steel piping appears reasonably conservative even for pipes with mean radius-to-wall thickness ratios of 20, whereas the results showed that the newly adopted Code Case N-494-3 for austenitic stainless steel piping requires a limit for pipe with mean radius-to-wall thickness ratios larger than 15. For consistency, the limitation of Rm/t ≤ 15 was incorporated in the approved final version of Code Case N-494-3, and was incorporated in Code Case N-494-2 as well. Because these Code cases are applicable only to Class 1 primary nuclear piping, which typically has values of Rm/t ≤ 15, this is not a significant limitation. It was also shown that the choice of definitions of membrane and bending stresses as well as the choice of F1 function values in calculating the elastic part of the J integral have a profound effect on the resulting FAD curves.
Decoupling Criteria for Multi-Connected Equipment
Authors: Reddy G. R. , Kushwaha H. S. , Mahajan S. C. , Suzuki K.
Published: February 2008

Generally, for the seismic analysis of nuclear power plant structures, requirement of coupling equipment is checked by applying USNRC decoupling criteria. This criteria is developed for the equipment connected to the structure at one location. In this paper, limitations of this criteria and modifications required for application to real life structures such as pressurized heavy water reactor building are discussed. In addition, the authors endeavor to present a decoupling model for multi-connected structure-equipment. The applicability of the model is demonstrated with pressurized heavy water reactor building internal structure and steam generator.
Experimental and Numerical Study of Multi-Pass Welding Process of Pipe-Flange Joints
Authors: Troive L. , Na¨sstro¨m M. , Jonsson M.
Published: February 2008

Residual deformations of pipe-flange joints due to thermal strains caused by the multi-pass welding procedure in a manufacturing process are investigated both experimentally and numerically (FEM). To avoid any risk of leakage between two mounted pipes using flange joints, geometrical distortions (twisting) of the flange must be prevented. How the flange is distorted depends both on the groove shape and the weld sequence used. However, to be spared from machine work after the welding process, the distortions have to be minimized. A casting-technique has been developed in order to measure the twisting of the flange after each weld pass. Also, measurements of the residual radial deflection of the pipe have been performed.
New Method for Design of Flat Steel Ribbon-Wound Pressure Vessels
Authors: Zheng J.
Published: February 2008

It has been observed that the degree of contact between layers and the residual stresses caused by pre-tension winding of ribbons does not influence bursting pressure of flat steel ribbon-wound pressure vessels. This suggests the idea that the desirable design criteria for vessels of this type should be based on bursting failure mode, i.e., wall thickness should be determined by bursting pressure which is strongly influenced by friction between layers and laminar effects. It is shown that the probability of bursting failure of vessel for which the bursting pressure is not less than 2.5 design pressure is less than 10−10. An example demonstrates that a design procedure based on this information not only has significant economic advantages, but also can indicate bursting probability.
Effects of Torsional Buckling on the Cleavage Failure of Low-Alloy Steel Tension Pipe Specimens
Authors: Koundy V. , Renevey S. , Marini B. , Combescure A.
Published: February 2008

The local approach criterion of fracture mechanics, initially developed by Beremin for brittle cleavage fracture, is applied here to A508 class 3 low-alloy ferritic steel. This criterion, based on the maximum principal stress and Weibull statistics, has previously been verified in the case of uniaxial tests. In this study, it is extended to multiaxial loading tests, that can lead to more significant levels of plastic strain, and thus permit a study of the effect of plastic strain on cleavage fracture. Uniaxial tests on axisymmetric notched tensile bars (AE2-6) were used to determine Beremin’s model parameters m and σu. The cleavage fracture behavior, described by these parameters, was then verified by multiaxial tension-torsion tests carried out on thin tubular specimens. Numerical simulations of the tension-torsion tests, by the finite element method, were also performed, taking into account the nonlinear geometrical effects and the specimen plastic buckling. The buckling critical loads were calculated and used to ascertain whether fracture was associated with the instability phenomenon. Beremin’s model is shown to correctly describe experimental data which are not affected by buckling.
Probability of Fracture and Life Extension Estimate of the High-Flux Isotope Reactor Vessel
Authors: Chang S.-J.
Published: February 2008

The state of the vessel steel embrittlement as a result of neutron irradiation can be measured by its increase in ductile-brittle transition temperature (DBTT) for fracture, often denoted by RTNDT for carbon steel. This transition temperature can be calibrated by the drop-weight test and, sometimes, by the Charpy impact test. The life extension for the high-flux isotope reactor (HFIR) vessel is calculated by using the method of fracture mechanics that is incorporated with the effect of the DBTT change. The failure probability of the HFIR vessel is limited as the life of the vessel by the reactor core melt probability of 10−4. The operating safety of the reactor is ensured by periodic hydrostatic pressure test (hydrotest). The hydrotest is performed in order to determine a safe vessel static pressure. The fracture probability as a result of the hydrostatic pressure test is calculated and is used to determine the life of the vessel. Failure to perform hydrotest imposes the limit on the life of the vessel. The conventional method of fracture probability calculations such as that used by the NRC-sponsored PRAISE CODE and the FAVOR CODE developed in this Laboratory are based on the Monte Carlo simulation. Heavy computations are required. An alternative method of fracture probability calculation by direct probability integration is developed in this paper. The present approach offers simple and expedient ways to obtain numerical results without losing any generality. This approach provides a clear analytical expression on the physical random variables to be integrated, yet requires much less computation time. In this paper, numerical results on 1) the probability of vessel fracture, 2) the hydrotest time interval, and 3) the hydrotest pressure as a result of the DBTT increase are obtained. Limiting the probabilities of the vessel fracture as a result of hydrotest to 10−4 implies that the reactor vessel life can be extended up to 50 EFPY (100 MW) with the minimum vessel operating temperature equal to 85°F.
Fretting Wear Damage of Heat Exchanger Tubes: A Proposed Damage Criterion Based on Tube Vibration Response
Authors: Yetisir M. , McKerrow E. , Pettigrew M. J.
Published: February 2008

A simple criterion is proposed to estimate fretting wear damage in heat exchanger tubes with clearance supports. The criterion is based on parameters such as vibration frequency, midspan vibration amplitude, span length, tube mass, and an empirical wear coefficient. It is generally accepted that fretting wear damage is proportional to a parameter called work rate. Work rate is a measure of the dynamic interaction between a vibrating tube and its supports. Due to the complexity of the impact-sliding behavior at the clearance supports, work rate calculations for heat exchanger tubes require specialized nonlinear finite element codes. These codes include contact models for various clearance support geometries. Such nonlinear finite element analyses are complex, expensive and time consuming. The proposed criterion uses the results of linear vibration analysis (i.e., vibration frequency and mid-span vibration amplitude due to turbulence) and does not require a nonlinear analysis. It can be used by nonspecialists for a quick evaluation of the expected work rate, and hence, the fretting wear damage of heat exchanger tubes. The proposed criterion was obtained from an extensive parametric study that was conducted using a nonlinear finite element program. It is shown that, by using the proposed work rate criteria, work rate can be estimated within a factor of two. This result, however, requires further testing with more complicated flow patterns.
Life Assessment of 1 1/4 Cr-1/2 Mo Steel Catalytic Reformer Furnace
Tubes Using the MPC Omega Method
Authors: Ibarra S. , Konet R. R.
Published: February 2008

Remaining life assessments were conducted on in-service catalytic reformer furnace tubes that had been operating 21 yr. These assessments were made with both API RP 530 (Appendix E) and the new Project Omega method. Small sections from the furnaces were removed and creep rupture tests conducted using the Omega methodology, and the remaining life was determined. These tests showed that the furnace tubes had negligible damage.
A Procedure to Predict Solid Particle Erosion in Elbows and
Tees
Authors: Shirazi S. A. , Shadley J. R. , McLaury B. S. , Rybicki E. F.
Published: February 2008

A semi-empirical procedure has been developed for predicting erosion rates in pipe geometries, such as elbows and tees. The procedure can be used to estimate safe operating conditions and velocities in oil and gas production where sand is present. In the proposed procedure, a concept is introduced that allows determination of erosion rate for different pipe geometries. In the procedure, based on empirical observations, the erosion rate is related to the impact velocity of sand particles on a pipe fitting wall. A simplified particle tracking model is developed and is used to estimate the impact velocity of sand particles moving in a stagnation region near the pipe wall. A new concept of equivalent stagnation length allows the simplified procedure to be applicable to actual pipe geometries. The “equivalent stagnation regions” of an elbow and a tee geometry of different sizes are obtained from experimental data for small pipe diameters, and a computational model is used to extend the procedure to larger pipe diameters. Currently, the prediction method applies to mild steel and accounts for the effects of sand size, shape, and density; fluid density, viscosity, and flow speed; and pipe size and shape. The proposed method has been verified for gas and liquid flows through several comparisons with experimental data reported in the literature. The results of the model accurately predict the effects of sand size and fluid viscosity observed in the experiments. Furthermore, predicted erosion rates showed good agreement with experimental data for gas, liquid, and gas-liquid flows in several 50.8-mm (2-in.) elbows and tees.
A Constitutive Model for High Damping Rubber Bearings
Authors: Sano` T. , Di Pasquale G.
Published: February 2008

Some simplified 1-degree-of-freedom (1-dof) constitutive models suitable for the simulation of high damping rubber bearings are analyzed. The well-known equivalent elastic and bilinear models are compared with a version of the Davidenkov-Martin law modified by the authors. The seismic behavior of an isolated structure is analyzed using the different models and the results are compared. The predictions obtained by means of the proposed law are also compared with experimental snap-back test results.
Yield-Before-Break Fracture Mechanics Analysis of High-Strength Steel Pressure Vessels
Authors: Underwood J. H. , Farrara R. A. , Audino M. J.
Published: February 2008

Case study examples of fracture mechanics testing and analysis of Ni-Cr-Mo high strength steel cannon tubes are presented. The testing and analysis include the situation of significant plastic deformation accompanying fracture, which often occurs when high pressure is applied to high-toughness steel pressure vessels. analysis is based on a comparison of the size of the Irwin crack-tip plastic zone the remaining ligament of the tube in the area of the critical fatigue crack which causes final failure. The results of the study show that the type of final failure can be predicted—as either a relatively safe, yield-before-break failure or a less safe running-crack type of failure—for a variety of material, configuration, and loading conditions.
ASME Code Safety Valve Rules—A Review and Discussion
Authors: Bernstein M. D. , Friend R. G.
Published: February 2008

Safety valve rules, i.e., rules for overpressure protection by the use of various pressure-relieving devices, vary somewhat among the five book sections of the ASME Boiler & Pressure Vessel Code which require such protection. This paper reviews those rules by discussing the following topics: Pressure relief device terminology and function. The problem of overpressure protection. Code rules for overpressure protection: rules for determining required relieving capacity; for allowable overpressure; for set pressure and set pressure tolerance; for blowdown. The various pressure relief devices permitted by the Code. Design of pressure relief valves. How relieving capacities are established and certified. The qualification of pressure relief device manufacturers. Installation guidelines. Concluding remarks.
Robust Approximate Methods for Estimating Inelastic Fracture Parameters
Authors: Seshadri R. , Kizhatil R. K.
Published: February 2008

Robust approximate methods to estimate the inelastic energy release rate J, and the creep crack-growth parameter, C*, for cracked components are described in this paper. These methods use linear elastic finite element analysis in conjunction with the concepts of the generalized local stress strain (GLOSS) analysis and redistribution nodes (r-nodes), and are readily applicable to complex geometries and loadings. J-estimates obtained by the use of robust methods are found to be in good agreement with the results of elastic-plastic finite element analysis.
Effect of Reinforcement on the Strength of Junctions Between
Cylindrical and Conical Shells
Authors: Kalnins A. , Updike D. P.
Published: February 2008

Two failure modes are addressed for cylinder-cone junctions under internal or external pressure: axisymmetric yielding and low-cycle fatigue. If the junction fails to meet the failure criterion of any one of the two modes, then it must be strengthened by reinforcement. It is shown in the paper that the degree to which a junction is strengthened depends on the distribution of the reinforcement. A placement of reinforcement on the cylinder alone, leaving the actual connection between the cylinder and cone unreinforced, adds strength with regard to axisymmetric yielding, but may not strengthen the junction sufficiently with regard to low-cycle fatigue. This means that the junction may appear reinforced, but is not strengthened. It is pointed out that the design rules of Section VIII, Div. 1 of the ASME B & PV Code (1992) set the need for reinforcement according to the failure criterion of low-cycle fatigue, while the distribution of the reinforcement is guided by the criterion of axisymmetric yielding. There is no assurance that the reinforced junction will meet the failure criterion of low-cycle fatigue. This means that the safety margin on the number of allowed cycles is less than that which is expected and that the junction may be unfit for cyclic service. It is also shown in the paper that a reinforcement distribution that requires minimum thicknesses for sections of both the cylinder and cone near the junction can satisfy criteria for both failure modes. This approach is already used in Code Case 2150 of Section VIII, Div. 1, for half-apex cone angles from 30 to 60 deg, and required in Div. 2 for cone angles from 0 to 30 deg. Its extension to angles from 0 to 60 deg for both internal and external pressure is recommended.
The Prediction of Wear in Fluidized Beds
Authors: Rogers W. A.
Published: February 2008

A procedure is formulated to model impact and abrasion wear of surfaces exposed to a fluidized bed. A methodology adapting a single-particle wear model and the kinetic theory of gases to granular flows is used to develop a model accounting for impact wear from all possible particle collisions. Abrasive wear is modeled using a single-particle abrasion model adapted to describe the effects of many abrading particles. Parameters describing granular flow are necessary for evaluation of the resulting wear expressions. They are determined by numerical solution of the conservation equations describing fluidized-bed hydrodynamics. Additional parameters appear in the wear expressions which describe the contact between individual fluidized particles and the wearing surface. These are determined by an optimization procedure which minimizes error between predicted and measured wear rates. The modeling procedure was used to analyze several bubbling and turbulent fluidized bed experiments with single-tube and tube bundle configurations. Quantitative agreement between the measured and predicted wear rates was found, with some exceptions for local wear predictions. This work demonstrates a methodology for wear predication in fluidized beds.
Response and Damping of Fabricated Branch Pipe Junctions Subjected to
Internal Pressure and Simulated Seismic Bending
Authors: Yahiaoui K. , Moreton D. N. , Moffat D. G.
Published: February 2008

This paper presents some of the results obtained from fifteen tests performed to investigate the ratcheting behavior of fabricated piping branch junctions subjected to steady internal pressure and dynamic resonant run pipe in-plane bending imposed to simulate seismic events. The experimental evidence confirms that the dynamic stresses are self-limiting, and thus secondary in nature. The logarithmic decrement method is used to estimate the percentage damping ratios from the steadily decaying free vibration data at the end of a forcing event. It is demonstrated that the percentage damping, measured after the component had experienced cyclic strain ranges as high as 1 percent, is rather low (1–2 percent of critical). These results are contrasted with those from the general literature, and ASME III recommended values from which it is shown that the use of higher damping ratios for similar components and loadings may underestimate the actual dynamic responses.
One-Way Buckling of Circular Rings Confined Within a Rigid
Boundary
Authors: Sun C. , Shaw W. J. D. , Vinogradov A. M.
Published: February 2008

The stability of a ring confined by a rigid boundary, subjected to circumferential end loads, is investigated both theoretically and experimentally. The effect of initial geometric imperfections on the buckling load is determined by assuming an initial deflection configuration as a simple sine form and the critical condition was derived from equilibrium analysis. An experimental approach was designed to verify the analytical results. Comparison with other theoretical results are also made.
Alternate Design Charts for Fixed Tubesheet Design Procedure Included
in ASME Boiler and Pressure Vessel Code, Section VIII, Division
1
Authors: Kuppan T.
Published: February 2008

Design formulas and calculation procedure for the design of fixed tubesheets of shell and tube heat exchangers are included in Appendix AA—Nonmandatory of ASME Boiler and Pressure Vessel Code, Section VIII, Division 1. To minimize the number of calculations, charts are provided as part of the design procedure. This article provides alternate charts for certain parameters and the original version of the charts are extended for larger values of tubesheet design parameter. Numerical values are given in tabular form for certain functions used in plotting the design charts. This will help to do design calculations without referring to the charts.
Development of the MPC Omega Method for Life Assessment in the Creep Range
Authors: Prager M.
Published: February 2008

A methodology for characterizing and assessing the behavior of materials after service in the creep range has been developed and used on a broad range of materials and components. It incorporates the results of relatively short-term tests and improved databases on materials properties. The essence of the method is the definition of a material performance characteristic which the author refers to by the symbol Ωp. This coefficient effectively describes the rate at which a material’s ability to resist stress is degraded by strain. While Ωp is a function of stress, temperature, and mode of loading, it is amenable to parametric representation and is, therefore, useful in predicting life and strain accumulation. Time to failure and total accumulated strain are shown to be consequences of a characterizing strain rate, as defined herein, and an appropriate Ωp for the operating conditions and geometry of interest. Accumulated strain, future strain, current creep rate, remaining life, total damage, and damage rate are among the quantities which are easily calculated. The development of the method employs and extends the concepts of Larson-Miller, Monkman-Grant, Robinson, Theta Projection, Kachanov, and Norton.
Stress-Intensity Factors for an Internal Semi-Elliptical Surface Crack in Cylindrical Pressure Vessels
Authors: Chen D.-H. , Nisitani H. , Mori K.
Published: February 2008

In this paper, the surface crack problem in a cylinder subjected to internal pressure is solved. The analysis is based on the body force method, but it is different from the conventional body force method in the following point. That is, the body forces to be distributed continuously on the assumed boundaries in an infinite body are approximated by some discrete point forces acting on the outside of the assumed boundaries. By using this method combined with the resultant force boundary conditions, solutions with high accuracy are obtained.
Failure Investigation of a Low Chrome Long-Seam Weld in a
High-Temperature Refinery Piping System
Authors: Buchheim G. M. , Osage D. A. , Brown R. G. , Dobis J. D.
Published: February 2008

The results of an investigation of a long-seam welded low chrome pipe that failed in a high-temperature refinery piping system are presented in this paper. Based upon the results of a metallurgical investigation, which included a creep testing program and a detailed finite element stress analysis, the cause of the failure has been attributed to creep damage at the weld seam. The metallurgical investigation and creep testing program indicated that the 1-1/4 Cr-1/2 Mo pipe material was normalized and exhibited greater than average creep strength and creep ductility. The results of a piping stress analysis indicated that all pressure, weight, and thermal stresses were in compliance with the ASME B31.3 Piping Code (ASME, 1993a). Nonetheless, the pipe failed after only 100,000 h at a nominal hoop stress of 6 ksi (41.4 MPa) with an operating temperature range of 970°F (521°C) to 1000°F (538°C). Results from subsequent detailed finite element stress analyses of the failed pipe indicated that very high localized bending stresses were present in the pipe due to peaking at the long-seam weld. These stresses partially relax by creep, but after 100,000 h they were still approximately 38 percent higher than the nominal hoop stress. The creep strains resulting from stress relaxation and those associated with the long-term value of the sustained stresses cause severe creep damage at the weld seam. As a result of this damage, cracks initiated at the inside of the pipe and primarily grew through the HAZ/fusion line until an 18-in. through-wall crack developed. The pipe was produced to ASTM A691, Grade 1-1/4 Cr, Class 41 (ASTM, 1989), and the peaked geometry was found to satisfy the fabrication tolerances of this standard. The need for the development of an acceptable tolerance for peaking in addition to the outside diameter and out-of-roundness fabrication tolerances currently included in this standard is highlighted for long-seam welded pipe that is to operate in the creep range.
Experimental Study on Seismic Responses of Piping Systems With
Friction—Part 1: Large-Scale Shaking Table Vibration Test
Authors: Suzuki K. , Watanabe T. , Mitsumori T. , Shimizu N. , Kobayashi H. , Ogawa N.
Published: February 2008

This report deals with the experimental study of seismic response behavior of piping systems in industrial facilities such as petrochemical, oil refinery, and nuclear plants. Special attention is focused on the nonlinear dynamic response of piping systems due to frictional vibration appearing in piping and supporting devices. A three-dimensional mock-up piping and supporting structure model wherein piping is of 30-m length and 200-mm diameter is excited by a large-scale (15 m × 15 m) shaking table belonging to the National Research Institute for Earth Science and Disaster Prevention in Tsukuba, Ibaraki. Power spectra of the response vibration and the loading-response relationship in the form of a hysteresis loop under several loading conditions are obtained. The response reduction effect caused by frictional vibration is evaluated and demonstrated in terms of “response reduction factor.”
Collinear Internal Cracks and Edge Crack in a Semi-Infinite Sheet
Subjected to Arbitrary Tractions
Authors: Nishimura T.
Published: February 2008

The stress intensity factors are calculated for collinear internal cracks and an edge crack in a semi-infinite sheet subjected to arbitrary tractions. Analysis is conducted by formulating the integral equations of tractions along the plate edge and crack surfaces. The accuracy is checked with known results in the literature. Then, the numerical analysis is used to establish the stress intensity factors for various sizes of the edge crack and internal cracks in tension. Also, the stress intensity factors are calculated for the edge crack and internal crack subjected to typical distributed loadings, and the effects of mutual interaction between the cracks are presented.
Constraint in the Failure Assessment Diagram Approach for Fracture
Assessment
Authors: Ainsworth R. A. , O’Dowd N. P.
Published: February 2008

This paper presents a framework for including constraint effects in the failure assessment diagram approach for fracture assessment. As parameters for describing constraint are still the subject of development, the framework is illustrated using both the elastic T-stress and the hydrostatic Q-stress. It is shown that constraint effects can be treated by modifying the shape of the failure assessment curve. In their simplest form, the modifications involve only two parameters: one quantifying the magnitude of structural constraint which depends on geometry and crack size; and the second quantifying the influence of constraint on fracture toughness.
Sloshing Analysis Method Using Existing FEM Structural Analysis
Code
Authors: Tokuda N. , Sakurai T. , Teraoku T.
Published: February 2008

A fluid analysis method using an analogy relating the pressure wave equation of fluid to elasticity equations is applied to sloshing analysis, where existing FEM structural analysis codes are available. It is seen from theoretical consideration that the present method is equivalent to the classical FEM formulation of linear sloshing analysis. The numerical analyses of liquid sloshing in a rigid cubic tank and of vibration of tubulous fluid under gravitational force are performed by using the present method. The results are shown to be in excellent agreement with the theoretical values.
Enhancement of Pressurizer Safety Valve Operability by Seating Design
Improvement
Authors: Moisidis N. T. , Ratiu M. D.
Published: February 2008

Operating conditions specific to pressurizer safety valves (PSVs) have led to numerous problems and have caused industry and NRC concerns regarding the adequacy of spring-loaded self-actuated safety valves for reactor coolant system (RCS) overpressure protection. Specific concerns are: setpoint drift, spurious actuations, and leakage. Based on testing and valve construction analysis of a Crosby model 6M6 PSV (Moisidis and Ratiu, 1992), it was established that the primary contributor to the valve problems is a susceptibility to weak seating. To eliminate spring instability, a new spring washer was designed, which guides the spring and precludes its rotation from the “reference” installed position (Figs. 6 and 7). Results of tests performed on a prototype PSV equipped with the modified upper spring washer has shown significant improvements in valve operability and a consistent setpoint reproducibility to less than ±1 percent of the PSV setpoint (testing of baseline, unmodified valve, resulted in a setpoint drift of ±2 percent). Enhanced valve operability will result in a significant decrease in operating and maintenance costs associated with valve maintenance and testing. In addition, the enhanced setpoint reproducibility will allow the development of a nitrogen to steam correlation for future in-house PSV testing which will result in further reductions in costs associated with valve testing.
Peak Stress and Fatigue Assessment at the Saddle Support of a
Cylindrical Vessel
Authors: Ong L. S.
Published: February 2008

The maximum stress in a saddle-supported cylindrical storage vessel is often the circumferential stress developed at the tips (or horns) of the saddle support. Although the peak stress at the support is not immediately detrimental to the integrity of a vessel, it would have a long-term effect on the fatigue life of the vessel. This article provides a parametric equation to determine the peak circumferential stress at the support. To assist calculations, a worksheet procedure has been proposed. The parametric equation is accompanied by four graphs, each graph provides values for a geometric variation of the problem. An example has been shown on the application of the parametric equation. A fatigue assessment is also made on the example vessel and comparison is made between ASME and British design codes. The parametric curves can be also used as a set of design curves for specifying support dimensions.
Vibration of a Tube Bundle in Two-Phase Freon
Cross-Flow
Authors: Pettigrew M. J. , Taylor C. E. , Jong J. H. , Currie I. G.
Published: February 2008

Two-phase cross-flow exists in many shell-and-tube heat exchangers. The U-bend region of nuclear steam generators is a prime example. Testing in two-phase flow simulated by air-water provides useful results inexpensively. However, two-phase flow parameters, in particular surface tension and density ratio, are considerably different in air-water than in steam-water. A reasonable compromise is testing in liquid-vapor Freon, which is much closer to steam-water while much simpler experimentally. This paper presents the first results of a series of tests on the vibration behavior of tube bundles subjected to two-phase Freon cross-flow. A rotated triangular tube bundle of tube-to-diameter ratio of 1.5 was tested over a broad range of void fractions and mass fluxes. Fluidelastic instability, random turbulence excitation, and damping were investigated. Well-defined fluidelastic instabilities were observed in continuous two-phase flow regimes. However, intermittent two-phase flow regimes had a dramatic effect on fluidelastic instability. Generally, random turbulence excitation forces are much lower in Freon than in air-water. Damping is very dependent on void fraction, as expected.
A Crack Arrest Test Using a Toughness Gradient Steel
Plate
Authors: Okamura H. , Yagawa G. , Hidaka T. , Urabe Y. , Satoh M. , Sano J.
Published: February 2008

A crack arrest test was carried out using a toughness gradient steel plate with three layers to study the concept of crack arrest toughness. Four-point bending load with thermal shock was applied to the large flat plate specimen with a surface crack. Five crack initiations and arrests were observed during the test and the propagated crack bifurcated. Finally, cracks were arrested at the boundary of the first and the second layer, except for a small segment of the crack. The first crack initiation took place slightly higher than the lower bound of KIc data obtained by ITCT specimens. That is, the KIC concept for brittle crack initiation was verified for heavy section steel plates. The first crack arrest took place within the scatter band of KIa and KId data for the first layer. That is, the KIa concept appears applicable for crack arrest of a short crack jump.
A New Constitutive Model in the Theory of Plasticity—Part I:
Theory
Authors: Jiang W.
Published: February 2008

By proposing two rules to regulate the movement of the yield surface, this paper develops a new kinematic hardening model in the theory of plasticity. A closed-form general solution is obtained in the case of linear stress paths, material response under cyclic loadings is discussed, and various tube problems are solved to demonstrate the model.
A New Constitutive Model in the Theory of Plasticity—Part II:
Examples
Authors: Jiang W.
Published: February 2008

This part of the paper presents several examples to further demonstrate the hardening model proposed in the first part of the paper. Closed-form solutions are achieved for a thin-walled tube subjected to linear, rectangular, and circular loading paths, and the corresponding yield center loci and plastic strain trajectories are illustrated. The features of this model are further discussed.
Weight Functions and Stress Intensity Factors for Longitudinal
Semi-Elliptical Cracks in Thick-Wall Cylinders
Authors: Zheng X. J. , Glinka G.
Published: February 2008

Weight functions for the surface and the deepest point of an internal longitudinal semi-elliptical crack in a thick-wall cylinder (Ri/t = 1) were derived from a general weight function and two reference stress intensity factors. For several linear and nonlinear crack face stress, fields, the weight functions were validated against finite element data. Stress intensity factors were also calculated for the Lame´ through the thickness stress distribution induced by internal pressure. The weight functions appear to be particularly suitable for fatigue and fracture analysis of surface semi-elliptical cracks in complex stress fields. All stress intensity factor expressions given in the paper are valid for cylinders with the inner-radius-to-wall-thickness ratio, Ri/t = 1.
New Post-Yield Fracture Toughness Parameters for Engineering
Materials
Authors: Wang T.-J. , Kuang Z.-B.
Published: February 2008

Micromechanics approach is employed to investigate the constraint effect on post-yield fracture toughness. Relationships between the conventional post-yield fracture toughness values, J1c and δc, and crack tip constraint characterized by the crack tip stress triaxiality are derived on the basis of an improved micromechanics criterion for ductile fracture. Then, new crack tip parameters Jmc and δmc (and associated new criteria for ductile fracture) are proposed, in which the effects of crack tip deformation and constraint are taken into account. Experiments show that both Jmc and δmc are material constant independent of stress state or specimen geometry. They can serve as new post-yield fracture toughness parameters to differentiate the fracture toughness of engineering materials, which provide new approaches for fracture assessments of engineering structures.
Cumulative Detection Probability as a Basis for Pressure Vessel
Inspection Intervals
Authors: Garic G.
Published: February 2008

This work discusses use of the cumulative flaw detection probability as the basis for establishing pressure vessel inspection intervals. The method is based on the accumulated probability of detecting a flaw over several inspections. It explicitly incorporates a user decision as to the acceptable level of failure risk. A four-step approach is outlined including fracture mechanics flaw growth calculations with probabilistic treatment of detection probability. It is concluded that (a) inspection intervals based on the cumulative probability of detection provide significant advantages over traditional cycle-based methods, (b) pressure vessel recertification inspections should rely on high percentage inspections conducted on a relatively infrequent basis.
Cylindrical Shells Under Partially Distributed Radial Loading
Authors: Yi W. , Basavaraju C.
Published: February 2008

The elastic solution to the fundamental problem of a cylindrical shell subjected to a symmetric, partially distributed, and self-balanced radial pressure loading acting on the external surface is obtained under plane strain condition. A dual series approach based on Airy’s stress functions is employed yielding an exact solution to an auxiliary composite cylindrical assembly problem. The solution for the problem under study is then derived as a limit case of the auxiliary composite cylinder problem. It is proven that the more generalized solution presented here may be used to recover several well-known classical results. The solutions also agree very well with the numerical results obtained from a finite element analysis performed for one sample hollow shell problem. The rigorous expressions found in this analysis for the stress and displacement fields are applicable to both thin and thick-walled shells, including piping.