bluuebunny/crossref_metadata_2025 huggingface dataset:
A Sensitivity Study of Creep Crack Growth in Pipes
Authors: Wasmer K. , Nikbin K. M. , Webster G. A.
Published: August 2008

Failure of pressure vessels and piping systems that operate at high temperatures can occur by net section rupture, creep crack growth or a combination of both processes. Several design and assessment procedures are available for dealing with this situation. These include the ASME Pressure Vessel and Piping, French RCC-MR (Appendix 16) and British R5 and BS7910 codes. Each of these procedures uses a combination of continuum mechanics and fracture mechanics concepts to make an assessment. Although the procedures adopt the same basic principles, often different formulae are employed to make an assessment. The main parameters that are used are reference stress, σref, stress intensity factor, K, and the creep fracture mechanics term C*. In this paper, an analysis is performed to estimate the sensitivity of the predictions of creep crack growth in a pressurised pipe to the choice of formulae used and materials properties employed. It is shown that most sensitivity is obtained to choice of expression employed for calculating σref and to whether batch specific or more generic materials properties data are selected.
Creep-Fatigue Damage and Life Evaluation for Boiler Header Stub Weldment
Authors: Ito Takuya , Nonaka Isamu , Umaki Hideo , Nishida Hidetaka , Shintani Shizuma
Published: August 2008

In order to clarify the creep-fatigue damage process and to evaluate the creep-fatigue life for boiler 2.25Cr-1Mo header stub welds, a series of creep-fatigue tests were performed on partial mock-up specimens of actual plant under simulated plant loading conditions. Creep voids and micro-cracks occurred along the weld toes at an early stage of life and grew to form many short cracks. These short cracks grew both on the surface and through the wall of the stub tube and later coalesced to form one crack. It was proved that there was a correlation between the maximum crack depth and life ratio and also that there was a correlation between the maximum crack depth and the maximum crack length on the surface. A life prediction method was proposed based on these two correlations.
Material Processing Simulation Using a Meshfree Method
Authors: Park Young H.
Published: August 2008

In this paper, material processing simulation is carried out using a meshfree method. The domain of the workpiece is discretized using the Lagrangian Reproducing Kernel Particle Method (RKPM) where no external meshes are used. The proposed method is formulated for path-dependent material behavior and frictional contact condition. In order to handle large deformation problems, a finite plasticity theory is formulated based on the multiplicative decomposition. The presented formulation is characterized by specifying the elastic domain via any classical yield criterion formulated in terms of Kirchhoff stresses, and a hyperelastic stored energy function relative to the intermediate configuration. A numerical example is demonstrated using the proposed method.
Comparative Study of Adaptive Analysis Processes for Automotive Applications
Authors: Wang Hui-Ping , Botkin Mark E.
Published: August 2008

This paper compares our recently-developed goal-oriented adaptive analysis process with the newly available adaptive capability in Unigraphics (UG) V17 scenario with focus on automotive applications. The error estimators and mesh adaptation procedures employed in both adaptive processes are reviewed. The goal-oriented process incorporates a posteriori error estimator of quantities of interest and a quadrilateral refinement tool so that the adaptivity is done to achieve the specific goal of analysis. The comparisons between the two adaptive processes are demonstrated on several practical problems.
An Efficient Algorithm Based on First Order Reliability Method for Fatigue Reliability Analysis of Mechanical Components
Authors: Tang Jun , Park Young Ho
Published: August 2008

The method for fatigue reliability analysis of mechanical components using the First-Order Reliability Method (FORM) reconciles accuracy and efficiency requirements for random process reliability problems under fatigue failure. However, the algorithm for solving FORM is still complex and time consuming. In this paper, the FORM that utilizes an efficient search algorithm is proposed for reliability assessment of the strain-based fatigue life. Using the proposed method, a family of reliability-defined ε-Nf curves, referred to as R-ε-Nf curves, is constructed. An empirical mean stress modified strain-life equation is also used as the performance function. The primary focus of this effort has been the implementation of the new algorithm of FORM to define reliability factors used in modifying the conventional ε-Nf curve to create a family of R-ε-Nf curves, based on the unique reliability factor rule. The proposed method employs the inverse FORM algorithm to achieve computational results, including reliability and the corresponding fatigue life. The method enables the application of fatigue life design for a given cyclic stress and/or strain history. A numerical example is presented to demonstrate the proposed method.
Large Elastic-Plastic Deformation Analysis of Rectangular Plates
Authors: Naghdabadi Reza , Shahi Mohsen
Published: August 2008

The purpose of this paper is to find a fast and simple solution for the large deformation of rectangular plates considering elastic-plastic behavior. This analysis contains material and geometric nonlinearities. For geometric nonlinearity the concept of load analogy is used. In this method the effect of nonlinear terms of lateral displacement is considered as suitable combination of additional fictitious lateral load, edge moment and in-plane forces acting on the plate. Variable Material Property (V.M.P.) method has been used for analysis of material nonlinearity. In this method, the basic relations maintain the form of stress-strain elastic formula, while material properties are modified to take into account the path-dependency involved in elastic-plastic deformations. Therefore, the solution of a von-Karman plate enduring large elastic-plastic deformations is reduced to that of an equivalent elastic plate undergoing small deformations. The method of solution employed in this study is computationally efficient and can easily be used for various boundary conditions and loadings.
Crack Kinking Criterion for Bimaterial System
Authors: Yao Jianliang , Nishioka Toshihisa , Nozaki Takuma , Fujimoto Takehiro
Published: August 2008

This paper is aimed to find out a suitable criterion for predicting the interfacial crack in the bimaterial system. An investigation was undertaken into the interfacial crack kinking phenomena in a bimaterial specimen of epoxy and aluminum alloy using a combination of experimental method and numerical simulation. It was found that all kinked fractures occurred at loading angles equal to or larger than 120°, so the kinking direction heavily dependeds on the loading mode mixity. Three categories of fracture pattern were identified (A, B and C). In the case of type A fracture, the (J10)kink integrals were generally higher than the homogeneous epoxy Jic at loading angles of 120° and above. In contrast, for types B and C fracture, the J10 integrals were consistently lower than the homogeneous epoxy Jic. Predictions of crack kinking behavior made using the Maximum Energy Release Rate Criterion (MG-criterion) were found to agree well with the observed experimental results. The kinked deformation of crack tip observed by moire´ interferometry, is well agreed with the result of numerical simulation.
Prediction of Fracture and Fatigue Damage in Engineering Structures
Authors: Wei Y. , Chow C. L.
Published: August 2008

This paper presents a method of failure analysis based on the theory of damage mechanics to predict fracture and fatigue failure in engineering structures. Two damage surfaces, the fatigue damage surface and the plastic damage surface, are firstly introduced to characterize material degradation. Then the damage evolution equations are provided. A failure criterion is proposed using the concept of damage accumulation. The model is incorporated into a commercial finite element program ABAQUS, which is used to conduct failure analyses in components made of AL 2024-T3 under both monotonic loading and cyclic loading.
Fatigue Test Plan to Obtain S-N Curves
Authors: Pinto Joa˜o Ma´rio Andrade , Colosimo Enrico A. , Mansur Tanius Rodrigues , Cruz Julio Ricardo Barreto , Palma Ernani Sales , Neto Miguel Mattar
Published: August 2008

S-N curves of structural materials are obtained through fatigue tests. These tests are often performed using five different stress levels, with fifteen test specimens for each stress level. This kind of test plan provides estimates that are less precise compared to other experimental plans, for example, the ones called optimum plan or compromise plan. The main reason for this drawback is the use of the same number of specimens for all stress levels. It has been observed that less precise results are obtained for lower stress levels because failure occurs less frequently. That is why more specimens should be used for lower stress levels as compared to higher stress levels. As long as the number of specimens to be tested at low stress levels is increased, the total number of failures will also increase, which allows one to develop a more precise data analysis. The objective of this work is to present an alternative experimental plan to obtain S-N curves, which intends to provide accurate estimators. A practical application is done for planning a fatigue test, in a flex-rotating machine, to obtain the S-N curve of SAE 8620 steel.
Extending the Local Approach to Fracture: Methods for Direct Incorporation of Microstructural Effects Into Finite Element Models of Fracture
Authors: Beynon J. H. , Das S. , Howard I. C. , Chterenlikht A.
Published: August 2008

The Local Approach to fracture phenomena has been very successful in helping to transfer information derived from testing one geometry on a material (laboratory specimens) to the prediction of the crack growth performance of another (the structure). At least in its most pervasive manifestations, it depends upon constructing finite element models with a ruling element size that is appropriate for the physical scale of the dominant failure mechanism. Since these are primarily of the order of the material microstructure, there is a consequential very strong mesh gradient towards the region of Local Approach interest. When applied to structures of engineering interest, which can be large, the resultant finite element models become very big, sufficiently so that they cannot be run on many computers, if at all. When there is more than one material scale involved, the situation becomes impossible to resolve with conventional finite elements, except through the use of compromise local finite element sizes that blend the requirements from each micro-scale into a smeared cell at the finite element level. Such models have shown considerable success in predicting the performance of a range of components and structures by a number of research groups. Even so, the method is constrained by the excessive computational costs associated with modeling realistic structures, and by other concerns derived from its smearing of possibly incompatible underlying physical effects. CAFE modeling, the coupling of Cellular Automata at the microstructural scale(s) with finite elements that are scaled only for the strain gradients expected at the macro-scale in the structure, offers a way out of these potential problems. The structural level field quantities, held at the element Gauss points, are modified according to information coming from the Cellular Automata with which each Gauss point is associated. Suitable code representing fracture initiation and propagation at the micro-level generates changes incrementally to the Gauss point field variables, which are then brought to equilibrium by the FE modeler (whenever it is an implicit FE system). The method allows a natural representation of the multiple scale interactions typical of the fracture of low alloy steels in the transition region.
Analytical and Numerical Evaluation of the Cyclic Yield Area Criteria for Shakedown Requirements
Authors: Nishiguchi Isoharu , Okamoto Asao , Yamashita Norimichi , Aoki Mitsuru
Published: August 2008

The rules in codes such as the ASME Boiler and Pressure Vessel Code Section III Division 1 and Section VIII Division 2, provide the concept of stress categorization to prevent inelastic failure modes based on the elastic analyses. The categorization of the stresses obtained by the FEM analysis, however, is not always clear and the Three Dimensional FEM Stress Evaluation in JPVRC (TDF committee) has been developed alternative criteria to dispense with the stress categorization. As for the evaluation of the primary plus secondary stress, criteria based on the concept of the Cyclic Yield Area (CYA) have been developed. In this paper, the recent results obtained in the committee are summarized to evaluate the validity and the usability of the criteria.
Mechanism of Fatigue Crack Initiation in Austenitic Stainless Steels in LWR Environments
Authors: Chopra Omesh K.
Published: August 2008

This paper examines the mechanism of fatigue crack initiation in austenitic stainless steels (SSs) in light water reactor (LWR) coolant environments. The effects of key material and loading variables, such as strain amplitude, strain rate, temperature, level of dissolved oxygen in water, and material heat treatment on the fatigue lives of wrought and cast austenitic SSs in air and LWR environments have been evaluated. The influence of reactor coolant environments on the formation and growth of fatigue cracks in polished smooth SS specimens is discussed. Crack length as a function of fatigue cycles was determined in air and LWR environments. The results indicate that decreased fatigue lives of these steels are caused primarily by the effects of the environment on the growth of cracks <200 μm and, to a lesser extent, on enhanced growth rates of longer cracks. A detailed metallographic examination of fatigue test specimens was performed to characterize the fracture morphology. Exploratory fatigue tests were conducted to enhance our understanding of the effects of surface micropits or minor differences in the surface oxide on fatigue crack initiation.
Fatigue Crack Propagation from Notched Specimens of 304 SS in an Elevated Temperature Aqueous Environment
Authors: Wire Gary L. , Mills William J.
Published: August 2008

Fatigue crack propagation (FCP) rates for 304 stainless steel (304SS) were determined in 24°C and 288°C air and 288°C water using double-edged notch (DEN) specimens of 304 stainless steel (304 SS). Tests performed at matched loading conditions in air and water at 288°C with 20–60 cc H2/kg H2O provided a direct comparison of the relative crack growth rates in air and water over a wide range of crack growth rates. The DEN crack extension ranged from short cracks (0.03–0.25 mm) to long cracks up to 4.06 mm beyond the notch, which are consistent with conventional deep crack tests. Crack growth rates of 304 SS in water were about 12 times the air rate. This 12X environmental enhancement persisted to crack extensions up to 4.06 mm, far outside the range associated with short crack effects. The large environmental degradation for 304 SS crack growth is consistent with the strong reduction of fatigue life in high hydrogen water. Further, very similar environmental effects were reported in fatigue crack growth tests in hydrogen water chemistry (HWC). Most literature data in high hydrogen water show only a mild environmental effect for 304 SS, of order 2.5 times air or less, but the tests were predominantly performed at high cyclic stress intensity or equivalently, high air rates. The environmental effect in low oxygen environments at low stress intensity depends strongly on both the stress ratio, R, and the load rise time, Tr, as recently reported for austenitic stainless steel in BWR water. Fractography was performed for both tests in air and water. At 288°C in water, the fracture surfaces were crisply faceted with a crystallographic appearance, and showed striations under high magnification. The cleavage-like facets on the fracture surfaces suggest that hydrogen embrittlement is the primary cause of accelerated cracking.
Development of a Fatigue Strength Database for LWR Water Environment
Authors: Sayano Akio , Higuchi Makoto , Hirano Akihiko , Tsutsumi Kazuya , Yamamoto Yutaka , Sakaguchi Katsumi , Iida Kunihiro
Published: August 2008

A database of fatigue strength in air and high temperature water environments for the materials used in LWR structural components has been developed. It includes the fatigue data acquired in the EFT project entrusted by METI, Japan, as well as public data obtained from domestic and overseas literature. One of the features of the database is that it includes about 2,500 images such as scanning electron micrographs of the fractured surface of the specimen after fatigue test. Another feature is that the program can search data, draw graphs such as S-N curves and hysteresis loops automatically, and make calculations of the hysteresis energy equivalent to the area of hysteresis loop, for example. The structure of the database, the contents of the data compiled, and the functions of the program are presented with actual examples, and the characteristics of the database are discussed.
Japanese Code for Assessment Procedure for Crack-like Flaws in Pressure Equipment
Authors: Konosu Shinji , Tahara Takayasu , Kobayashi Hideo
Published: August 2008

There are numerous instances in which in-service flaws due to various kinds of damage and deterioration are found in equipment as a result of in-service inspections. The proper evaluation of such flaws is extremely important. Fitness-for-Service (FFS) codes, such as ASME B&PV Code Sec. XI and JSME S NA1 for nuclear power generation facilities and BS 7910 and API-RP579 for general industrial facilities, are available. In light of such circumstances, the High Pressure Institute of Japan (HPI) has prescribed its code “Assessment procedure for crack-like flaws in pressure equipment” for conducting quantitative safety evaluations of flaws detected in common industrial pressure components such as pressure vessels, piping, storage tanks, and so on designed and fabricated in accordance with Japanese codes and regulations such as JIS B8265 and High Pressure Gas Safety Law. The FFS code consists of Level 1 assessment (whereby assessment can be conducted without extensive knowledge of fracture mechanics) and Level 2 assessment (which enables more detailed fracture mechanics analyses and is currently being studied). The allowable flaw size is specified in accordance with the plate thickness. The required impact absorbed energies based on material strength, whether or not PWHT has been done and the orientation of the flaw in relation to the weld seam, are also specified. An approximated equation of stress intensity factor for an embedded flaw near the surface has been derived. The re-characterization procedure for assessing an embedded flaw has been clarified. The flaw can be judged to be acceptable if its size is less than that of an allowable flaw and the equipment is to be used at temperatures exceeding the temperature (MAT) at which the material absorbed energy meets the required impact absorbed energy.
The Use of the ASME PRA Standard in Pressure Vessel and Piping Work
Authors: Hill Richard A.
Published: August 2008

After several years of intense labor by many industry people, ASME is about to issue its newly approved PRA standard. This standard is for probabilistic risk assessment (PRA) for nuclear power plant applications. It is not a standard on how to build a PRA model; although, that could be inferred from the standard’s technical requirements. This Standard sets forth requirements for PRAs used to support risk-informed decisions related to design, licensing, procurement, construction, operation, and maintenance. It also prescribes a method for applying these requirements depending the degree to which risk information is needed and credited.
A Parametric Study of the Seismic Margins of Piping Components
Authors: Iwan Wilfred D. , Huang Ching-Tung
Published: August 2008

This paper presents an analytical study of frequency effects on seismic margins of piping components. The study is based on response data obtained as part of a joint Electric Power Research Institute (EPRI) and NRC Piping and Fitting Dynamic Reliability (PFDR) Program. The majority of the PFDR component tests were performed using a narrow-banded earthquake excitation input that was tuned to have a frequency slightly lower than the fundamental frequency of the test components. However, the natural frequency of a piping system in an actual plant may vary over a wide range. Therefore the seismic margins at off-resonance conditions are of importance. Two seismic margin definitions are examined. The primary objective of this study was to extrapolate the PFDR test margins to other frequency regions and to investigate the effects of various parameter changes on the margins.
Straight Pipe Cyclic Analyses for Shakedown Verification Code Criteria
Authors: Bhagwagar Tehemton , Gurdal Robert
Published: August 2008

The analyses performed in this paper are exclusively for a straight pipe subject to a constant primary stress and a cyclic secondary stress, as a result of a bending moment on the pipe cross-section. The constant primary stress is, in each analysis, from a CONSTANT dead-weight load and a CONSTANT internal pressure. The cyclic secondary stress is due to cyclic thermal expansion in the pipe, which is the result of a cyclic top-to-bottom linear temperature difference on the pipe cross-section. This temperature cycling produces a secondary stress range C2 ΔM Do / 2 I. This secondary stress range is either higher, or lower than the 3 * Sm stress limit from the ASME-Code. Twenty-four different cyclic elasto-plastic analyses have been performed for this paper. The same elastic perfectly-plastic material model is used for all twenty-four analyses. An attempt has been made to compare the results from the cyclic elasto-plastic analyses with the ASME-Code NB-3600 Rules and with the Efficiency Diagram developed in France for their Code. The main advantage of the Efficiency Diagram is that the decision whether shakedown occurs, or not, is not only a function of the secondary stress RANGE, but also of the CONSTANT primary stress that exists at that time. A relief to the current ASME-Code rules is suggested for the case of a low constant primary stress (less than Sy / 2).
Equi-Biaxial Tension-Compression Low Cycle Fatigue for Type 304 and Cr-Mo-V Cruciform Specimen
Authors: Itoh Takamoto , Sakane Masao
Published: August 2008

This paper describes high temperature multiaxial low cycle fatigue lives of type 304 stainless steel and 1Cr-1Mo-1/4V steel cruciform specimens at 823K and 923K in air. Strain controlled multiaxial low cycle fatigue tests were carried out using cruciform specimens at the principal strain ratios between −1 and 1. The principal strain ratio had a significant effect on low cycle fatigue lives. Fatigue lives drastically decreased as the principal strain ratio increased. Multiaxial low cycle fatigue strain parameters were applied to the experimental data and the applicability of the parameters was discussed. The equivalent strain based on crack opening displacement (COD strain) developed in the paper and Γ*-plane parameter successfully predicted multiaxial low cycle fatigue lives. The crack morphology was also extensively discussed from not only the surface crack direction but also the crack inclination into the specimen.
Probabilistic Analysis of 60-Year Environmental Fatigue Effects for Reactor Components
Authors: Deardorff Arthur F. , Dedhia Dilip , Rosinski Stan T. , Harris David O.
Published: August 2008

In NUREG/CR-6674, a probabilistic fracture mechanics analysis was conducted to assess the effects of light water reactor environmental effects on the probability of fatigue initiation and subsequent crack growth leading to leakage and possible core damage. The results were based on stresses for typical locations in BWR and PWR reactors as determined from an analysis reported in NUREG/CR-6260. Although environmental effects were shown to have an insignificant effect on core damage frequency, the study concluded that there could be a significant increase in probability of leakage. A detailed review of the methodology and input conditions used in NUREG/CR-6674 has been completed, including use of an altered probabilistic fatigue curve with more representative high-cycle stress variance and consideration of results from more recent environmental fatigue testing. This revised analysis indicates that environmental effects on the probability of leakage and core damage frequency in an extended nuclear plant operating period are significantly less than previously reported in NUREG/CR-6674. This paper summarizes the analysis performed and the results obtained.
Section XII of the ASME Code—Transport Tanks
Authors: Selz Allen
Published: August 2008

In December 1996, the United States Department of Transportation requested that ASME create a new code for transport tanks. ASME formed Subcommittee XII to fulfill this request. The scope of the subcommittee is the development of codes and standards covering the construction, in-service inspection, alteration and repair of transport tanks used for the carriage of dangerous goods by all means of transport; to develop criteria for accreditation of manufacturers of these tanks; and to develop codes and standards that are suitable for reference by regulatory authorities and safety organizations world-wide. Some significant code issues are the separation of technical and administrative requirements, third-party inspection, minimal impact on the industry’s current way of doing business, and the technical issues associated with pressure relief for vessels that can overturn. The first edition is in the hands of ASME Technical Publications and is scheduled to be issued in late 2003.
New Developments in API 579
Authors: Osage David A.
Published: August 2008

New developments in API 579 Recommended Practice For Fitness-For-Service [1] is presented in this paper. This document was initially released in January of 2000 and since that time has become the de facto international fitness-for-service standard for the refining and petrochemical industry. A discussion of the changes planned for the next release of API 579, efforts to validate the fitness-for-service technology incorporated in API 579, and a discussion of a new API document pertaining to damage mechanisms are provided. Plans for a joint API and ASME standard and future directions of the API in-service inspection codes relative to API 579 and equipment integrity are also covered.
Reactor Water Environmental Fatigue
Authors: O’Donnell William J.
Published: August 2008

Existing nuclear plants were designed based on fatigue data obtained entirely in air environments. We now seek to extend the life of these plants, recognizing that many conservatisms were included in the fatigue stress calculations, stress concentration factors and lumped transients. Since we know how these plants were operated, we can quantify the cyclic rates and coolant chemistry. This makes it feasible to use environmental fatigue life evaluation technology which takes credit for the reduced corrosion fatigue damage which occurs during more rapid transients and for reduced dissolved oxygen levels which produce lesser corrosion fatigue damage in carbon and low alloy steels. Accordingly, the use of Fen environmental fatigue life reduction factors which depend on the cyclic rates, coolant chemistry and temperature are quite useful for evaluating the safe fatigue life of aging plants and for license renewal.
Changes Needed to Address Current Institutional Problems
Authors: Hedden Owen F.
Published: August 2008

The voluntary support of ASME boiler and pressure vessel Code-writing activity began with the boiler manufacturer leaders getting together to address the problem of catastrophic failures of boilers and pressure vessels. Even into the 1970s, many companies sent their V-P level engineering people to the “Boiler Code”. Not just the major manufacturers, but also the architect-engineers, material suppliers, and inspection/insurance companies had staffs devoted to ASME codes and standards activities. In 1969 I was assigned to a group of four engineers whose full-time responsibility was to the work of the Boiler and Pressure Vessel Committee. And there were many others in the company who were also heavily involved in these and other ASME standards committees. The companies were also making other related contributions, such as designing, manufacturing, and donating test vessels to industry R&D groups. All of this meant that we had a great deal of technical support, as well as the usual secretarial support. And six Code meetings per year.
A Common Approach to Risk Analysis Methodology
Authors: Sims J. Robert
Published: August 2008

Risk analysis has been used extensively to inform decisions throughout government and industry for many years. Many methodologies have been developed to perform these analyses, resulting in differences in terminology and approach that make it difficult to compare the results of an analysis in one field to that in another. In particular, many approaches result only in a risk ranking within a narrow area or field of interest, so the results cannot be compared to rankings in other areas or fields. However, dealing with terrorist threats requires prioritizing the allocation of homeland defense resources across a broad spectrum of possible targets. Therefore, a common approach is needed to allow comparison of risks. This presentation summarizes an approach that will allow the results of risk analyses based on using current methodologies to be expressed in a common format with common terminology to facilitate resource allocation decisions.
Fatigue Effect of RCS Branch Line by Thermal Stratification
Authors: Youm Hag-Ki , Kim Kwang-Chu , Park Man-Heung , Jin Tea-Eun , Lee Sun-Ki , Kim Tae-Ryong , Kim Jong Hyun
Published: August 2008

Recent events reported at a number of nuclear power plants worldwide have shown that thermal stratification, cycling, and striping in piping can cause excessive thermal stress and fatigue on the piping material. These phenomena are diverse and complicated because of the wide variety of geometry and thermal hydraulic conditions encountered in reactor coolant system. Thermal stratification effect of re-branched lines is not yet considered in the fatigue evaluation. To evaluate the thermal load due to turbulent penetration, this paper presents a fatigue evaluation methodology for a branch line of reactor coolant system with the re-branch line. The locations of fatigue monitoring and supplemented inspections are discussed as a result of fatigue evaluations by Interim Fatigue Management Guideline (ITFMG) and detail finite element analysis. Although the revised CUF was increased less than 50 %, the CUF values for some locations was greater than the ASME Code limits.
Residual Stress Induced by Waterjet Peening: A Finite Element Analysis
Authors: Kunaporn Sawalee , Ramulu Mamidala , Jenkins Michael G. , Hashish Mohammed
Published: August 2008

The concept of multiple droplet impacts resulting from ultra high-pressure waterjet (UHPWJ) was used to develop a mathematical model to describe the effect of interfacial pressure on the underlying workpiece material. A non-linear elastic-plastic finite element analysis (FEA) was carried out in this study using the interfacial pressure model to predict residual compressive stresses. This three-dimensional FEA model was based on quasi-static considerations to provide prediction of both magnitude and depth of residual stress fields in a 7075-T6 aluminum alloy (A17075-T6). Results of the FEA modeling were in good agreement with experimental measurements. Effects of applied pressures on the residual stress fields are also presented and discussed as a method of estimating high-pressure waterjet induced compressive stresses under varying process conditions for peening.
Power Actuated Pressure Relief Valve for High Pressure Vessels
Authors: Tra¨ff Anders C. , Jansson Peter C.
Published: August 2008

The pressure required for treatment of food ranges from 300 to 600 MPa, depending on the food being processed and the desired results, higher pressure giving better and more economical results. However, there are currently no predictable, reliable, and repeatable safety devices available for very high pressures like 600 MPa. Rupture disks have a short life at these pressures, and pressure relief valves for very high pressure are not repeatable. Thus the possibility of using a system design is an attractive alternative that will make the overpressure protection more reliable and controllable. In current applications, high-pressure vessels normally operate from a few MPa to 200 MPa, for example when extracting substances, compacting powder materials, or healing defects in materials. The pressure medium is typically a pure gas or a liquid. Here existing devises serve their purpose. The request for mild treatment of food to enhance safety and quality has created a niche for very high pressure. With this new technique the food is treated at low temperature and high pressure for a short time. The treatment inactivates micro organisms but maintains the nutritional and organoleptic values of the food, achieving a food with high quality and increased safety throughout its commercial shelf life.
Guided Wave Propagation Mechanics Across a Pipe Elbow
Authors: Hayashi Takahiro , Kawashima Koichiro , Sun Zongqi , Rose Joseph L.
Published: August 2008

Wave propagation across a pipe elbow region is complex. Subsequent reflected and transmitted waves are largely deformed due to mode conversions at the elbow. This prevents us to date from applying guided waves to the nondestructive evaluation of meandering pipeworks. Since theoretical development of guided wave propagation in a pipe is difficult, numerical modeling techniques are used. We have introduced a semi-analytical finite element method, a special modeling technique for guided wave propagation, because ordinary finite element methods require extremely long computational times and memory for such a long-range guided wave calculation. In this study, the semi-analytical finite element method for curved pipes is developed. A curved cylindrical coordinate system is used for the curved pipe region, where a curved center axis of the pipe elbow region is an axis (z′ axis) of the coordinate system, instead of the straight axis (z axis) of the cylindrical coordinate system. Guided waves in the z′ direction are described as a superposition of orthogonal functions. The calculation region is divided only in the thickness and circumferential directions. Using this calculation technique, echoes from the back wall beyond up to four elbows are discussed.
Tightening Sequence for Bolted Flange Joint Assembly
Authors: Kumakura Susumu , Saito Kumiko
Published: August 2008

Bolted flange joint assembly has been widely used in chemical and nuclear plants. Insufficient bolt loads in the bolted flange joints lead to serious accidents. The insufficient bolt loads are due to inappropriate bolt tightening methods in many cases. In order to obtain target bolt loads by the torque control method, it is especially important to know a torque coefficient and an appropriate tightening sequence. Another problem exists because where mating flanges are tightened by multiple bolts. It is known that it is extremely difficult to obtain a uniform bolt loads among the multiple bolts. In this study, new and any experimentally examined, tightening sequences for the bolted flange joints using multiple bolts are proposed. As a result, the proposed tightening method was proved to be more effective than that by the ASME method.
Methodical Guideline for Bolt-Up Operation of Pipe Flange Connections: A Case Using Sheet Gasket and Spiral Wound Gasket
Authors: Takaki Tomohiro , Fukuoka Toshimichi
Published: August 2008

The purpose of this study is the proposal of guidelines for bolt-up operation of pipe flange connections with joint sheet gasket or spiral wound gasket. Numerical calculations are systematically executed for pipe flanges with wide variety of nominal size by using finite element analysis, which can simulate the bolt-up process of a pipe flange connection, because the tightening performance of the pipe flange connection largely depends on the bolt-up process. Gaskets also have dominant effects on the tightening performance. It is, however, impossible to determine the number of tightening passes to get uniform bolt preloads for all kinds of gaskets. A simplified modeling method of nonlinear stress-strain relationship of gasket is, therefore, evaluated and a representative material property of gasket is selected to develop the bolt assembly guideline. The bolt-up procedure, in which four bolts located 90 degrees from each other are tightened with the same magnitude of preload at the installation process, is investigated.
Web-Enabled Database for Gasket Parameters
Authors: Over H.-H. , Igelmund A. , Zerres H. , Gue´rout Y. , Kockelmann H.
Published: August 2008

The available technique of a Web-enabled material database was adapted to a new Gasket Data Bank (Gasket-DB) in the frame of an European research project PERL (Pressure Equipment, Reduction of Leak rate: gasket parameters measurements). Main content are gasket characteristics determined on all gasket types defined in the new European gasket standard series EN 1514, part 1 to 7: • actual gasket parameters in ENV 1591-2 (public access), • proposed gasket parameters to define more reliable values (restricted access), • certified manufacturers gasket data (restricted access), • gasket parameter ranges (public access). Data retrieval is providing intelligent user guidance. Data entry is carried out by Joint Research Centre (JRC) Petten, NL, by means of standardized format (Excel file with different sheets, reflecting the table structure of the database). The prototype database and the user interface can easily be extended and customized to the needs and requirements of the engineering gasket society, e.g. link to customer documentation, databases, services like design calculation tools.
On the Constraint-Based Failure Assessment for Surface Cracked Welded Plates Under Tension
Authors: Wang X. , Reinhardt W.
Published: August 2008

Conventional failure assessment schemes (CEGB-R6, BS-7910) use a lower bound toughness obtained from highly constrained test specimens. A lower crack tip constraint leads to enhanced resistance to both cleavage and ductile tearing. The cracks in many real engineering structures are not highly constrained, which makes failure predictions using conventional failure assessment schemes based on the lower bound fracture toughness overly conservative. Too much conservatism in the structural assessment can lead to unwarranted repair or decommissioning of structures, and thus cause unnecessary cost and inconvenience. Due to recent developments in constraint-based fracture mechanics, it is important to include the constraint effect in the practical assessment of defective components. For example, the recent revision of R6 and the newly developed structural integrity assessment procedures for European industry (SINTAP) have suggested a framework for failure assessments that can take the constraint effect into account. In this paper, the constraint-based failure assessment of a surface cracked welded plate under uniaxial tension load is presented. A constraint-based failure assessment diagram and a method for combining primary and the secondary loads are discussed. Finite element based correlations are used to calculate the stress intensity factors, and constraint parameters, while the limit loads are derived from existing closed form approximations. It is demonstrated that when the lower constraint effect is properly accounted for, the maximum allowable tensile stress level can increase 15% or more.
Methods, Models, and Assumptions Used in Finite Element Simulation of a Pilger Metal Forming Process
Authors: Martin John
Published: August 2008

The pilger process is a cold-worked mechanical process that combines the elements of extrusion, rolling, and upsetting for the formation of thin-walled tubes. This complex manufacturing process relies on the results of trial and error testing programs, experimental parameter sensitivity studies, and prototypical applications to advance the technology. This finite element modelling effort describes the methods, models, and assumptions used to assess the process parameters used to manufacture thin-walled tubing. The modelling technique breaks down the manufacturing process into smaller computer generated models representing fundamental process functions. Each of these models is linked with the overall process simulation. Simplified assumptions are identified and supporting justifications provided. This work represents proof of principle modelling techniques, using large deformation, large strain, finite element software. These modelling techniques can be extended to more extensive parameter studies evaluating the effects of pilger process parameter changes on final tube stress and strain states and their relationship to defect formation/propagation. Sensitivity studies on input variables and the process parameters associated with one pass of the pilger process are also included. The modelling techniques have been extended to parameter studies evaluating the effects of pilger process parameter changes on tube stress and strain states and their relationship to defect formation. Eventually a complex qualified 3-D model will provide more accurate results for process evaluation purposes. However, the trends and results reported are judged adequate for examining process trends and parameter variability.
Study of Effective Elastic Moduli of Cracked Solid
Authors: Park Young H. , Morgan Wesley
Published: August 2008

In this paper, effective moduli of cracked solid material were investigated. An analytical approach is discussed for a cracked solid containing randomly oriented inclusions by using elastic potential and a standard tensorial basis. A numerical simulation of the testing of mechanical responses of samples of cracked solid material (porous material) is also carried out. The numerical scheme in this work will focus mainly on numerical modeling of the observed behavior, in particular, the dependence of the macroscopic material properties on the porocity.
Study About Real-Time Finite Element Method Using CNN
Authors: Gao JingBo , Xu MinQiang , Wang RiXin
Published: August 2008

The paper presents cellular neural network (CNN) for real-time finite element method, useful as calculating temperature field and thermal stress field for rotor of turbine and so on. The comparability between template of CNN and the stiffness matrix of finite element is analyzed, and the conception of finite element template (FMT) of CNN is discussed. The FMT can be suitable for finite element grid with arbitrary shape. In this paper, the FMT is simulated by temperature field of rotor of turbine, the result is right.
Crack Shape Development of Two Interacting Surface Elliptical Cracks
Authors: Patel S. K. , Dattaguru B. , Ramachandra K.
Published: August 2008

The issue of assessing residual life of an aged structure based on damage tolerance concepts attained significance in high technology fields such as aerospace, piping and pressure vessels and nuclear engineering. Computational fracture analysis of these structures in the presence of single or multi-site surface flaws is essential for life estimation and life extension. In this paper development of accurate post-processing technique (Modified Virtual Crack Closure Integral) to estimate strain energy release rates, and simple numerical method to simulate crack shape development in single and multiple interacting cracks (till they merge into single dominant crack) is presented. Crack shape development in single surface elliptical cracks was carried out earlier in literature using 2 degree of freedom model wherein fatigue crack growth is estimated along the major and minor axis of the ellipse and new crack shape was derived by fitting an ellipse to these points. A special three-degree of freedom model is proposed and presented in this paper for interacting and coalescing cracks. The crack shape development was checked with experimental work on coupons with multi-site surface cracks tested under fatigue loading. In safety critical aerospace and thick piping structures this work is significant in predicting the remaining life of aged components with multi-site damage.
DQEM Analysis of In-Plane Deflection of Curved Beam Structures
Authors: Chen Chang-New
Published: August 2008

The development of differential quadrature element method in-plane deflection analysis model of arbitrarily curved nonprismatic beam structures was carried out. The DQEM uses the extended differential quadrature to discretize the differential eigenvalue equation defined on each element, the transition conditions defined on the inter-element boundary of two adjacent elements and the boundary conditions of the beam. Numerical results solved by the developed numerical algorithm are presented. The convergence of the developed DQEM analysis model is efficient.
Periodic Symmetry for Explicit Methods for Large Deformation Twisting and Stretching
Authors: Metzger Don R.
Published: August 2008

The presence of repetitive symmetry in continua and structures allows for the modeling of a single symmetric cell. Typically, the symmetry conditions are enforced with homogeneous kinematic constraints, but these may preclude some otherwise admissible response. Also, in large deformation situations, the original symmetric boundaries can distort significantly. The objective of this work is to provide a means for explicit finite element methods to ensure periodic symmetry while resultant loads may be prescribed on the symmetric boundaries. A method is devised to determine external forces that concurrently maintain dynamic equilibrium of the system with compatible deformations at the boundaries. The method requires only internal forces and nodal positions, which are accessible in an explicit finite element formulation.
Enhancing Probabilistic Risk Assessment Methodology for Solving Reactor Safety Issues
Authors: Cho F. L.
Published: August 2008

This paper reveals a paradigm of analyzing the consequential effects of severe nuclear reactor accident, radionuclides fraction and source terms release, that will influence the MACCS2 codification [1], by coupling with the results of SAPHIA-PSA Levels l & 2 quantification process [2], MELCORE [3], STCP [4], PST [5], and XSOR [6]. Those codes are mutually exclusive and useful. However, it lacks of the closed interface and linkage for addressing Plant Damage States (PDS), Severe Accident Sequences, and Risk Consequence. Thus, it is imperative to formulate the consistent baseline information for MACCS2, PSA Levels 1, 2 and 3, and then linking to a new algorithm of NCM.