bluuebunny/crossref_metadata_2025 huggingface dataset:
Bellows Design Equations Supported by Limit Analysis
Authors: Broyles Robert K.
Published: August 2008

Limit analysis can be used to design metal bellows for pressure capacity. The objective of limit analysis is to prevent gross plastic deformation with an appropriate design margin. The primary advantage of limit analysis over other methods is that it can find the max. allowable limit load for the structure as a whole and not just for the individual parts. In the case of bellows, an allowable limit pressure can be found which assures a specified margin on plastic collapse. In this paper, a parametric FEA study is performed on a series of two-dimensional axisymmetric models of un-reinforced U-shaped bellows with wide ranging dimensions. The non-linear analysis gives the max. allowable limit pressure for each bellows based on limit analysis and a closed form equation is confirmed to accurately describe the FEA results. Combined with existing equations for column instability and external buckling, limiting design pressure equations are presented for bellows design.
Lower Bound Limit Load Determination: The mβ-Multiplier Method
Authors: Seshadri R. , Indermohan H.
Published: August 2008

The existing lower bound limit load determination methods that are based on linear elastic analysis such as the classical and mα-multiplier methods have a dependence on the maximum equivalent stress. These methods are therefore sensitive to localized plastic action, which occurs in components with thin or slender construction, or those containing notches and cracks. Sensitivity manifests itself as relatively poor lower bounds during the initial elastic iterations of the elastic modulus adjustment procedures, or oscillatory behavior of the multiplier during successive elastic iterations leading to limited accuracy. The mβ-multiplier method proposed in this paper starts out with Mura’s inequality that relates the upper bound to the exact multiplier by making use of the “integral mean of yield.” The formulation relies on a “reference parameter” that is obtained by considering a distribution of stress rather than a single maximum equivalent stress. As a result, good limit load estimates have been obtained for several pressure component configurations.
Accelerated Limit Loads Using Repeated Elastic Finite Element Analyses
Authors: Mangalaramanan Prasad
Published: August 2008

This paper demonstrates the limitations of repeated elastic finite element analyses (REFEA) based limit load determination that uses the classical lower bound theorem. The r-node method is prescribed as an alternative for obtaining better limit load estimates. Lower bound aspects pertaining to r-nodes are also discussed.
A Finite Element Study of Friction Effect in Four-Point Bending Creep Test
Authors: Kim Young Suk , Metzger Don R.
Published: August 2008

Creep tests are often performed in four-point bending and the stress distribution in the bending specimen is nonlinear, so creep properties are estimated from bend creep test data. However, getting creep properties from bending creep tests is often doubted because of uncertainties from contact point shift and frictional effect between loading pin and specimen in four-point bending creep tests. Finite element simulations of the four-point bending creep tests were performed with geometric models which include contact conditions. It was found from simulation studies that friction in the bend tests can cause error in the estimation of creep properties, but when no friction was applied in simulations the creep properties were well predicted from bend test data.
Elasto-Plastic Behavior of Polycrystalline Steel at Mesoscopic and Macroscopic Levels
Authors: Kovacˇ Marko , Simonovski Igor , Cizelj Leon
Published: August 2008

An important drawback of the classical continuum mechanics is idealization of inhomogenous microstructure of materials. Approaches, which model material behavior on mesosocopic level and can take inhomogenous microstructure of materials into the account, typically appeared over the last decade. Nevertheless, entirely anisotropic approach towards material behavior of a single grain is still not widely used. The proposed approach divides the polycrystalline aggregate into a set of grains by utilizing Voronoi tessellation (random grain structure). Each grain is assumed to be a monocrystal with random orientation of crystal lattice. Mesoscopic response of grains is modeled with anisotropic elasticity and crystal plasticity. Strain and stress fields are calculated using finite element method. Material parameters for pressure vessel steel 22 NiMoCr 3 7 are used in analysis. The analysis is limited to 2D models. Applications of the proposed approach include (a) the estimation of the minimum component/specimen size needed for the homogeneity assumption to become valid and (b) the estimation of the correlation lengths in the resulting mesoscopical stress fields, which may be used in well-established macroscopical material models. Both applications are supported with numerical examples and discussion of numerical results.
Automated Modeling and Crack Growth Simulation in Pressurized Thin Shell Panels With Multi-Site Damage
Authors: Gopal K. V. N. , Dattaguru B.
Published: August 2008

The residual strength estimation of thin-walled pressurized shell structures is of relevance to pressurized thin piping systems and aged airframes for life extension programs. This requires powerful and efficient computational techniques using finite element method and numerical fracture mechanics for elastic or inelastic stress analysis and crack growth simulation. For this purpose, detailed modeling and finite element mesh generation of built-up structures like stiffened cracked thin shells is necessary and it is a computationally intensive task. Automating the entire process from geometric modeling to stress analysis and crack growth simulation (requires remeshing) vastly improves the efficiency of the computational analysis and reduces the chances of modeling and simulation errors. A geometric primitive based technique has been developed for automated modeling and meshing. The work is carried out primarily on aged fuselage shell panels but the method is applicable to other pressurized thin piping systems. This paper presents a simple and efficient computational procedure using a geometry based logic and surface mesh generation technique for automated modeling and crack growth simulation in pressurized thin-walled shells. The approach has been used to develop a structural integrity evaluator software. Finite element analysis is carried out using a commercial software, and these results are fed to the structural integrity evaluator. Some results of the nonlinear finite element analysis and elastic-plastic stable crack growth simulation in pressurized stiffened fuselage panels using this approach are presented.
Behavior of Embedded Steel Plates in Reinforced Concrete: New Design Basis
Authors: Chakrabarti Sekhar K.
Published: August 2008

The behavior and capacity of embedded steel plates in reinforced concrete structures, are studied using a finite-element model developed for non-linear analysis. Strength interaction diagrams and moment-rotation charts useful for analysis and design of such plates, are developed for eccentric compressive and eccentric tensile loading, at failure and collapse. Capacities for a common class of embedded plates with variation in its thickness are computed for the cases of combined eccentric compression and shear.
Failure Mode of Pipes Containing Circumferential Cracks Under Bending and Its Consequence on the Application of NSCM Criterion
Authors: Milella P. P. , Bonora N. , Gentile D.
Published: August 2008

The results of some 60 tests performed in Italy on 2”, 4”, 6” and 8” pipes of A 106 B and 304 stainless steel, carrying circumferential through-wall cracks of various size under four point bending conditions (FPB), at room temperature and 300° C, have been analyzed using the Net Section Collapse Moment Criterion (NSCM) and the dimensionless plastic zone parameter (DPZP). Most of the test results have shown that the NSCM applies even though the DPZP is lower than unity. This apparent inconsistency is due to the fact that cracked pipes under bending fail by plastic hinge formation of the type occurring in FPB specimens carrying notches, like the Charpy VN ones, as predicted by the slip line theory. Under these conditions, two half circle plastic zones develop at both sides of the notch while the plastic zone straight ahead the notch tip is almost negligible. FE Calculations have confirmed this behavior: the plastic zone underneath the crack tip has not yet reached the neutral axis when the plastic hinge is formed on the sides of the piping, making the NSCM applicable. This, actually, implies that the DPZP as presently used in the screening criteria is not precisely the proper parameter to adopt in the assessment of the NSCM criterion applicability.
Safety Analysis and Risk Assessment for Pressure Systems
Authors: Blyukher Boris
Published: August 2008

There have been many instances where serious injuries and fatalities have resulted from over-pressurization, thermal stress, asphyxiation and other potential hazards associated with testing, handling and storage of compressed gases and pressure facilities at numerous production and research facilities. These hazards are major issues that should be addressed in system design and in materials selection appropriate for high pressure applications. Potential hazards may be mitigated through system analysis and design process which are the major factors in preventing thermal/pressure hazards caused by possible leaks and fragmentation, in the case of rupture. This paper presents a conceptual model and framework for developing a safety analysis which will reduce potential hazards, accidents and legal liabilities. The proposed systematic approach allows to identify hazards provide timely documentation of potential hazards and risks associated with systems, facilities, and equipment. As a result of this hazard analysis process, provisions and actions for hazard prevention and control have been put in place, and all identifiable potential hazards can be reduced to a low risk level.
Limit Load Concepts in Fitness for Purpose Assessment of Flat Endcaps
Authors: Marriott D. L.
Published: August 2008

This paper is a case study in the comparison of different methods of evaluation of components in the creep range. The root of the problem derives from an interesting “fitness-for-purpose” question, in that the component, a header end cap, had only been in service for a few months and it therefore fell between a new part design review and a in-service, fitness-for-purpose analysis. This led to a comparison being made of different methods drawn both from design procedures, and from more recent fitness-for-service methods, initially with a view to developing a plausible and acceptable procedure for validating the design within the roles of the relevant section of the Code, but also as an exercise to explore the applicability of various methods being offered currently in, for instance, recent API guidelines.
Analysis of Non-Uniformly Degraded Pipe Sections
Authors: Smith Amy J. , Dwivedy Keshab K.
Published: August 2008

The management of flow assisted corrosion (FAC) has been a part of the maintenance of piping in nuclear power plants for more than 15 years. Programs have been set up to identify vulnerable locations, perform inspections, characterize the degraded configurations, and evaluate the structural integrity of the degraded sections. The section of the pipe is repaired or replaced if the structural integrity cannot be established for the projected degraded section at the next outage. During the past 15 years, significant improvements have been made to every aspect of the program including structural integrity evaluation. Simplified methods and rules are established in ASME Section XI code and in several code cases for verifying structural integrity. The evaluation of structural integrity is performed during the plant outage prior to a decision for repair or replacement. Any improvement in structural integrity evaluation to extend the life of a component by one additional operating cycle can help in performance of repair/replacement of component in a planned manner. Simplified methods and rules provided in the code can be easily used for analysis of pipe sections with degraded area with uniform wall thickness and for non-uniformly degraded sections, provided the degraded portions are modeled with uniform wall thickness equal to the lowest thickness of the section. The representation of a non-uniformly degraded section in this manner is necessarily conservative. The purpose of this paper is to develop methodology to analyze the non-uniformly degraded sections subjected to pressure and moment loading by modeling it in a manner that accounts for the non-uniform cross-section. The formulation developed here is more realistic than the code methodology and is still conservative. The results are presented in form of charts comparing the limit moment capacity of the degraded sections calculated by the formulation in this paper with that using ASME code formulation. The paper concludes that the proposed formulation can be used to supplement the ASME Code method to extend the remaining life of FAC degraded components.
Comparison of Different Methodologies for Stress Analysis of Reinforcing Pads
Authors: Guillot Michael W. , Helms Jack E.
Published: August 2008

Finite element analysis is widely used to model the stresses resulting from penetrations in pressure vessels to accommodate components such as nozzles and man-ways. In many cases a reinforcing pad is required around the nozzle or other component to meet the design requirements of Section VIII, Division 1 or 2, of the ASME Pressure Vessel Code [1]. Several different finite element techniques are currently used for calculating the effects of reinforcing pads on the shell stresses resulting from penetrations for nozzles or man-ways. In this research the stresses near a typical reinforced nozzle on a pressure vessel shell are studied. Finite element analysis is used to model the stresses in the reinforcing pad and shell. The commercially available software package ANSYS is used for the modeling. Loadings on the nozzle are due to combinations of internal pressure and moments to simulate piping attachments. The finite element results are compared to an analysis per Welding Research Council Bulletin 107 [2].
Calculation of Stress Relaxation Properties for 1CrMoV Bolt Material
Authors: Ellis Fred V. , Tordonato Sebastian
Published: August 2008

Analytical life prediction methods have been developed for high temperature turbine and valve bolts. For 1CrMoV steel bolt material, long time creep-rupture and stress relaxation tests were performed at 450°C, 500°C, and 550°C by the National Research Institute for Metals of Japan. Based on analysis of their data, the isothermal creep behavior can be described using a power law: ε=Kσn(t)m+1 where ε is the creep strain, t is the time, σ is the stress, K, n, and m are material constants. The time power is a primarily a function of temperature, but also depends slightly on stress. To obtain the value for the time power typical of low stress, the creep equation constants were found in two steps. The time power was found using the lower stress data and a heat-centered type regression approach with the stress levels taking the place of the heats in the analysis. The heat constants were then calculated at all stress levels and regression performed to obtain the stress dependence. For comparison with the measured uniaxial stress relaxation properties, the relaxed stress as a function of time was calculated using the power law creep equation and a strain hardening flow rule. The calculated stress versus time curves were in good agreement with the measured at initial strain levels of 0.10%, 0.15%, and 0.20% for all temperatures except 500°C. At 500°C, good agreement was found using the creep properties typical of a stronger (within heat variation) material.
A Modified Power Law for Creep Analysis
Authors: Katcher Michael
Published: August 2008

The creep strengths for an annealed Ni-33Fe-25Cr alloy, UNS N08120 (HAYNES® HR-120® alloy) are presented from 1100°F to 2200°F at every 100°F for lives up to 30,000 hours. The creep data is used as a basis for converting the power law method (log stress vs. log time at a defined temperature) to the usefulness of the Larson-Miller method for design creep analysis. A new empirical relationship was developed between stress, temperature and creep rupture life. Power Law equations were generated at each temperature using linear regression of the transformed data to obtain the best-fit constants. The constants were then plotted and a best-fit polynomial of the constants as a function of temperature was determined. The polynomial then replaced the constants in the original power law equation to obtain a single expression of stress as a function of time and temperature. Using this new Modified Power Law (MPL) equation, interpolation or extrapolation to obtain stress becomes possible for any temperature and time.
Fluid-Structure Interaction With S-TRAC and KWUROHR Due to Pressure Waves
Authors: Neumann Ulrich
Published: August 2008

In the last years we have spent a lot of time to improve our programs and procedures, especially on the field of fluiddynamic investigations in piping systems. To get the best design of piping layout the results of fluiddynamic and structural calculations should be realistic as far as possible. In this connection a very important effect is the fluid-structure interaction (FSI) which we have implemented in S-TRAC in connection with our structural dynamic program KWUROHR. On the basis of different calculations we will show the influence of the coupling on the fluid forces and the piping layout.
CFD Modelling of Multiphase Flows: An Overview
Authors: Calay Rajnish K. , Holdo Arne E.
Published: August 2008

The Computational Fluid Dynamics (CFD) is now increasingly being used for modeling industrial flows, i.e. flows which are multiphase and turbulent. Numerical modeling of flows where momentum, heat and mass transfer occurs at the interface presents various difficulties due to the wide range of mechanisms and flow scenarios present. This paper attempts to provide a summary of available mathematical models and techniques for two-phase flows. Some comments are also made on the models available in the commercially available codes.
The Design of Refinement Criteria for Dynamic Grid Adaptation Applied to Airfoil Flow Modeling
Authors: Demir Melih , de With Govert , Holdo̸ Arne E.
Published: August 2008

At present a large number of fluid dynamics applications are found in aerospace, civil and automotive engineering, as well in medical related fields. In many applications the flow field is turbulent and the computational modelling of such flows remains a difficult task. To resolve all turbulent flow phenomena for flow problems where turbulence is of key interest is a priori not feasible in a Computational Fluid Dynamics (CFD) investigation with a conventional mesh. The use of a Dynamic Grid Adaptation (DGA) algorithm in a turbulent unsteady flow field is an appealing technique which can reduce the computational costs of a CFD investigation. A refinement of the numerical domain with a DGA algorithm requires reliable criteria for mesh refinement which reflect the complex flow processes. At present not much work has been done to obtain reliable refinement criteria for turbulent unsteady flow. The purpose of the work is to implement a new refinement technique for the boundary layer in the vicinity of the wall. It is aimed to model the flow around an airfoil with a LES turbulence model and a new DGA algorithm. In addition to that several simulations have been carried out for parametric studies. In these studies the incompressible solver in REACFLOW has been used. This Computational Fluid Dynamics (CFD) code REACFLOW was developed in collaboration with the joint Research Centre (JRC) in Italy. The following aims are aspired: • A new mesh refinement criteria method suitable for boundary layers; • To carry out LES simulations to establish the performance of the refinement criteria. The new criteria which are created in this work are for the near wall region. This criteria uses the wall shear stresses for the refinement technique. For the main flow stream the refinement criteria proposed by de With et al [6] will be used.
The Use of Advanced LES Subgrid Scale Models in Combination With Dynamic Grid Adaptation
Authors: de With Govert , Holdo̸ Arne E. , Peller Nick
Published: August 2008

The use of Large Eddy Simulation (LES) is increasingly investigated. However, the LES simulations are computationally demanding, due to the transient nature of the flow computations and the required mesh resolution. Furthermore, the subgrid scale model used for modeling the unresolved flow motions is normally a-priori selected. In an unstructured mesh where the mesh resolution can vary significantly, subgrid scale models should be applied carefully. The present study is aimed to investigate the use of an advanced approach to reduce mesh size by means of a Dynamic Grid Adaptation (DGA) algorithm and to apply a LES subgrid scale model based on local mesh size and flow structure. In this work the DGA algorithm is coupled with the LES turbulence model and made an integral part of the turbulence model. Furthermore, this work has integrated two different LES subgrid scale models which are locally applied to the element in a dynamic manner, dependent on mesh size and flow structure.
Mixed Mode Loading of an Interface Crack Subjected to Creep Conditions
Authors: Gordon Ali P. , McDowell David L.
Published: August 2008

Interface cracks are seldom subjected to pure Mode I or pure Mode II conditions. Stationary interface cracks between two distinct, bonded elastic-creep materials subjected to remotely applied mixed mode loading are simulated. The finite element method (FEM) is used to examine crack tip fields and candidate driving force parameters for crack growth. Plane strain conditions are assumed. In most cases a functionally graded transition layer is included between the two materials. Examples of such systems include weld metal (WM) and base metal (BM) interfaces in welded or repaired boiler components subjected to elevated temperatures. Numerical solutions based on the asymptotic fields of the homogeneous and heterogeneous Arcan-type specimens are presented. Creep ductility-based damage models are used to predict the initial crack propagation trajectory. The incorporation of functionally graded transition layer regions affects the evolution of time-dependent stress components in the vicinity of the crack tip. The magnitude and direction of crack tip propagation can then be optimized with respect to interface properties.
Integrity Assessment of Ceramic CVD Liners Against Plasma Loading
Authors: Cheng Wing , Kudriavtsev Vladimir , Kolobov Vladimir
Published: August 2008

During the development of aluminum oxide liners for plasma enhanced CVD process, cracking was observed near the bottom and in the mid-section close to the zone of maximum power deposition. Major cracks were observed to run along the circumferential direction across the cylindrical liner and were caused by excessive tensile stresses resulting from temperature gradients or temperature transients induced by different operating conditions. Because of the pre-mature failure, a detailed characterization of the temperature profile was carried out on two ceramic liners using a combination of measurement and numerical modeling. Numerical modeling was performed using CFD-PLASMA and CFD-ACE+ numerical tools, heat transfer and stress finite element analysis (MSC NASTRAN). Results were in turn, used to obtain a better understanding the cause of the pre-mature failure. A probabilistic failure assessment procedure was used to explain the cause of the failure. Temperature gradients or temperature transients could be induced by different operating cycles. Temperature gradients could also occur across the wall thickness of the liner due to heating inside and cooling outside the liner, and along the inside wall in the axial direction due to non-uniform power intensity during normal material processing and cleaning cycles. Design improvement concepts were suggested in terms of more stringent material parameter and better cooling to alleviate any future potential failure.
Study for Sterilization Technology by Underwater Shock Wave
Authors: Watanabe Toshiaki , Harada Kazuki , Takemoto Ayumi , Itoh Shigeru
Published: August 2008

The method of the sterilization is divided into the thermal sterilization, the chemical sterilization and the other non-thermal sterilization, roughly. Recently, as for the food industry, it pays attention to the non-thermal sterilization, which little makes the quality of food, a taste, and so on change. Especially, in the seafood industry, non-thermal sterilization that provides raw food is very important technology. Therefore, we consider sterilization by the underwater shock wave. This technology is thought that it can be applied to not only food industry but also the medical field. The final aim of this study is in confirming the technique of the sterilization by the underwater shock wave. At first, we carried out experiments, which use detonating cord and coriform (E. coli.) We estimate for a suitable set of explosives and the quantity.
Cell Ruptures of Microorganisms by Shock Wave and Ultrasonic Wave
Authors: Fujiwara Kazuhito , Hiroe Tetsuyuki , Asakawa Makio
Published: August 2008

A sterilization and a cell rupture using the shock wave generated by a wire explosion was tested and the effect of the impulsive load on the mortality of microorganism. This technique enables the sterilization of foods, juice or chemical agents without heating them. Microorganism cells were broken by shock waves and ultrasonic waves and different fracture patterns were shown in the SEM image. In the shock the efficiency was depended on the size of bacteria, although that was depended on the strength of the cell membrane in the ultrasonic. It was also found that the shock is effective for spores of bacteria that are superior to normal cells in the endurance and the resistibility. Numerical simulations demonstrated the size effect in the shock cell rupture.
Evaluation of Fracture Toughness From Instrumented Charpy Impact Tests for a Reactor Pressure Vessel Steel
Authors: Parrot A. , Forget P. , Dahl A.
Published: August 2008

The monitoring of neutron induced embrittlement of nuclear power plants is provided using Charpy impact test in the surveillance program. However structural integrity assessments require the fracture toughness. Some empirical formulas have been developed but no direct relationship was found. The aim of our study is to determine the fracture toughness of a Reactor Pressure Vessel steel from instrumented Charpy impact test using local approach to fracture. This non-empirical method has been applied in the brittle domain as well as in the ductile to brittle transition for an A508 C1.3 steel. In the brittle domain, fracture occurs by cleavage and can be modeled with the Beremin model. Fracture toughness has been successfully determined from Charpy impact tests results and the influence of several parameters (mesh design, Beremin model with one or two parameters, number of Charpy impact tests results) on the results was considered. In the ductile to brittle transition, cleavage fracture is preceded by ductile crack growth. Ductile tearing has been accounted for in the simulations with the Rousselier model whereas cleavage fracture is still described with the Beremin model. The determination of fracture toughness from Charpy impact tests gave encouraging results but finite element simulations have to be refined in order to improve predictions.
Stress Intensity Factor Solutions for Part-Throughwall Pipe Flaws
Authors: Kidwell Kerry M. , Rush Phillip
Published: August 2008

The need to quantify crack tip stress intensity solutions for complex stress states and geometries has forced the development of theoretical stress intensity solutions by numerical methods, such as finite element analysis (FEA). Using FEA, we developed a stress intensity handbook solution to the previously analyzed geometry of part-throughwall pipe flaws. This paper presents the results of this effort for infinitely long, axial internal flaws in cylinders. We also examined the mesh parameters that need to be considered to obtain reasonably accurate elastic mode I stress intensity solutions using the ANSYS finite element program.
Assessment of Potential Damage to Ductile Cast Iron Cask as a Result of Exceptional Impact Loading
Authors: Bonora Nicola , Ruggiero Andrew
Published: August 2008

Safety of shipping cask for nuclear spent fuel is always a reason of concern for the designers, regulators and public opinion. Even though safety requirements are already outstanding for this kind of structure, additional worries about its vulnerability have been expressed, especially after the terrorist attack of September 11th, 2001. During the 1970s and 1980s, U.S. National Regulatory Commission (NRC) evaluated the consequences of an hypothetical terrorist attacks and in 1984, came to the conclusion that the use of explosives would not result in a serous threat and, subsequently, proposed lessened security requirements for shipments. The recent public release of a footage of a 1998 test at the Army’s Aberdeen Proving Ground in Maryland, showing an anti-tank missile breaching the cast iron wall of a CASTOR cask, re-opened the discussion about the effective safety and resistance of these container to exceptional impact events. In this paper the preliminary results of a research program in progress at the University of Cassino on ductile cast iron structural integrity and impact protection evaluation are presented. The exceptional impact event of an airplane crash onto a cask has been re-analyzed by means of an extensive numerical simulation using hydrocode and developing a specific damage modeling for failure in ductile cast iron.
The Energy Approach of Elastic-Plastic Fracture Mechanics Applied to the Analysis of the Warm Pre-Stress Effect
Authors: Wadier Yves , Bonnamy M.
Published: August 2008

An experimental program was recently carried out in the context of a MPA-EDF collaboration, in order to study the “Warm Pre-Stress” effect on CT25 side-grooved specimens made of 18MND5 (equivalent to A508) ferritic steel. At EDF, an energy approach has been developed and an energy release rate, called Gp, has been defined. Conversely to the J-approach, this energy approach is, in principle, valid in all situations, and can be used in particular to study the “Warm Pre-Stress” effect in RPV structural integrity assessment. For the WPS cycle called “LCF” (Loading + Cooling + Fracture), the comparison to the experimental results and to the results obtained with the Beremin model is very satisfactory, all the results being in a good agreement. For the WPS cycle called “LUCF” (Loading + Unloading + Cooling + Fracture) the results obtained with the energy method, compared to experimental results, show a conservatism which is not very important, anyway smaller than the conservatism obtained with the Beremin model.
The Behaviour of a Process Zone at the Root of a Deep Sharp Flaw for Mode I Loading
Authors: Smith E.
Published: August 2008

The process zone representation of non-linear behaviour at the root of a flaw or crack is frequently used to quantify fracture initiation scenarios. In a paper presented at the 2002 PVP Conference, the author showed that with regard to a process zone at the root of a deep sharp flaw for Mode III loading conditions, its behaviour can be described, to a good degree of accuracy, by inputting the stress distribution ahead of the actual flaw root into an analysis of a process zone at the root of a semi-infinite crack in an infinite solid. The present paper describes an analysis of the analogous Mode I loading situation, with the results being compared with those obtained by a procedure which blends the small and large s/ρ behaviours where s is the process zone size and ρ is the flaw root radius of curvature.
Tests and Calculations of Thermomechanical Shocks in the Brittle/Ductile Transition Zone of a Pressure Vessel Steel
Authors: Reytier M. , Chapuliot S. , Ne´de´lec M.
Published: August 2008

In order to study the effects of a sudden cooling in a thick hot structure, such as the vessel of a pressurised water reactor, a specially-adapted compact tension specimen has been developed. It consists of a CT50 (2T-CT specimen) with holes through the specimen to cool the crack tip locally by liquid nitrogen. Therefore, this new test allows to study in details different loading-temperature histories near the brittle/ductile transition zone which may put the classical crack intiation criteria in the wrong. First, this article describes in details two tests for which a cleavage rupture has been obtained during the thermal shock on this 16MND5 steel. Either the Crack Mouth Opening Displacement was maintained during the test or the applied load. Then, numerical calculations have been realised in order to estimate the local mechanical fields at the crack tip and to evaluate the global fracture mechanics parameters. Thanks to these tests and these thermal and mechanical simulations, a work is done on rupture criteria under thermal shocks by using either the “Master Curve” approach or the Beremin model.
The Toughness-Induced Crack Deceleration Mechanism on Ultra-High Pressure Steel Gas Pipelines
Authors: Zhuang Z. , You X. C.
Published: August 2008

Failure incident investigations and laboratory experiments of high toughness pipeline rupturing indicate that current methods used to predict arrest are not reliable when applied to high toughness pipelines. The current methods neglect the heat dissipation caused by plastic work unloading for high toughness pipelines, leading to large errors when small-scale test results are compared with full-scale fractures. The cause of the phenomenon is analyzed in this paper with a macroscopic and phenomenological method which uses the energy balance equation to develop an iterative algorithm used in a Finite Element Method (FEM) simulation of toughness induced deceleration. This simulation, in combination with the two-specimen drop weight tear test (DWTT), which determines the heat dissipation rate, provides a broad prediction of the dynamic fracture process. In addition, the crack tip opening angle (CTOA) criterion is verified by comparing the CTOA in FEM simulations and the critical value of (CTOA) obtained in the two-specimen DWTT. Thus, the avoidance of both the dimensional effect and the dissipation of irrelevant energy common in small-scale tests are achieved.
Influence of the Yield-to-Tensile Strength Ratio on the Failure Assessment of Corroded Pipelines
Authors: Zhu Xian-Kui , Leis Brian N.
Published: August 2008

It is well known that both the yield strength and the tensile strength of a material have significant effect on the failure behavior of pipelines. Thus it can be anticipated that the yield-to-tensile strength (Y/T) is closely related to the strain hardening behavior of the material, and it also influences the failure behavior. This paper theoretically explores the influence of T/Y (the inverse of Y/T) ratio on the failure pressure of pipelines with or without corrosion defects. Based on the instability of deformation and finite strain theory, a plastic collapse criterion for close-ended pipes without corrosion defects is developed first. The constitutive behavior of line pipes is characterized by a power-law strain hardening relation, while the plastic deformation obeys the Mises yield criterion and the associated deformation theory of plasticity. An approximate relationship between the T/Y ratio and the strain hardening exponent n is obtained, and a closed-form solution to the limit pressure of pipe based on T/Y is derived. This plastic instability model is extended to predict the failure pressure of pipelines with corrosion defects, and validated by the PCRI experimental database. The results show that (a) the T/Y ratio is simply proportional to the strain hardening exponent n, which is almost independent of the yield strain and affected by the definition of the yield stress; (b) the failure pressure predicted by the present plastic instability model increases as the T/Y ratio decreases; and (c) as T/Y → 1, the present solution approaches to that predicted by the Mises strength criterion based on the nominal hoop and axial stresses.
Increased Temperature Margins Due to Constraint Loss
Authors: Bezensek Bostjan , Hancock John W.
Published: August 2008

Enhanced levels of toughness associated with constraint loss are related to temperature shifts in the ductile-brittle transition curve. An argument to quantify the temperature shift is developed using self-similarity of near-tip stress fields under small-scale yielding combined with scaling techniques developed by Dodds and co-workers [1,2] for cleavage. The change in the yield stress and hence temperature that give the same stress field at failure in constrained and unconstrained fields has been determined. The procedure is illustrated using the data of Sherry et al [3] for A533B pressure vessel steel. The results are consistent with the empirical expressions proposed by Wallin [4], and enable a discussion of the physical implications for the micro-mechanics of cleavage.
Statistical Model for Prediction of Plate-Specific Fracture Toughness Properties of ASTM A285 Steel
Authors: Subramanian K. H. , Wiersma B. J. , Duncan A. J. , Harris S. P.
Published: August 2008

A materials test program was developed to measure mechanical properties of A285 carbon steel under conditions relevant to waste storage tanks at the Savannah River Site. Fracture toughness and tensile testing were performed on ASTM Type A285 steels that span tank plate compositions. Variables relevant to the material and load conditions for Type I and Type II tanks were defined and a statistical test matrix was designed for fracture toughness testing. The test matrix consisted of eight variables expected to influence mechanical properties. The independent variables were carbon content, manganese content, sulfur content, thickness, pearlite fraction, and grain size. The responses were the fracture toughness JIc, and a figure-of-merit at J3mm to allow for sub-critical ductile crack growth. A total of 85 J-R curves were compiled. The full data set was used to construct statistical models to predict fracture properties as a function of metallurgical properties and operating conditions. Eight independent models resulting from combinations of loading rate (quasi-static, dynamic) and orientation (T-L, L-T) were developed. The statistical significance of terms was determined for each of the models. Thickness and grain size were found to be of statistical significance in the models developed for the dynamic strain rate testing data. Compositional variables were found to be of statistical significance for the quasi-static loading rate fracture toughness data.
Improved Failure Assessment Diagrams to Describe Delayed Hydride Cracking Initiation at a Blunt Flaw
Authors: Scarth Douglas A. , Smith Ted
Published: August 2008

Delayed Hydride Cracking (DHC) in Zr-2.5 Nb alloy material is of interest to the CANDU (CANada Deuterium Uranium) industry in the context of the potential to initiate DHC at a blunt flaw in a CANDU nuclear reactor pressure tube. The material is susceptible to DHC when a hybrided region forms at the flaw tip. The hydrided region could then fracture to the extent that a crack forms, and is able to grow by the DHC crack growth mechanism. A process-zone based methodology for evaluation of DHC initiation at a blunt flaw that takes into account flaw geometry has been developed. In a paper presented at the 2000 ASME PVP Conference, the process-zone methodology was used to develop failure assessment diagrams in such a way that the geometry dependence of the failure assessment curves was minimized. This was achieved by defining the ordinate of the failure assessment diagrams in terms of the ratio of the applied elastic peak stress divided by the threshold peak stress for DHC initiation at the tip of a deep flaw. However, the resultant failure assessment curves for Mode I loading did not have the simple form as the curves for Mode III loading, where the Mode III case was modelled in order to clearly see the interplay between material and geometry parameters. The present paper demonstrates that the irregular shapes of the Mode I curves were due to the relation for the threshold peak stress for the deep flaw that was used in the Mode I failure assessment curves. In the 2000 ASME PVP Conference paper an exact relation for the threshold peak stress was used for Mode III loading, while an approximate relation was used for Mode I. In the present paper a more accurate relation for the threshold peak stress for a deep flaw was used for Mode I loading, and the resultant Mode I failure assessment curves have a simpler form, which leads to more practical applications of the approach. Agreement between the improved Mode I failure assessment diagram predictions and experimental results is reasonable.
Fracture Toughness Transferability Study Between the Master Curve Method and a Pressure Vessel Nozzle Using Local Approach
Authors: Laukkanen Anssi , Nevasmaa Pekka , Keina¨nen Heikki , Wallin Kim
Published: August 2008

Local approach methods are to greater extent used in structural integrity evaluation, in particular with respect to initiation of an unstable cleavage crack. However, local approach methods have had a tendency to be considered as methodologies with ‘qualitative’ potential, rather than quantitative usage in realistic analyses where lengthy and in some cases ambiguous calibration of local approach parameters is not feasible. As such, studies need to be conducted to illustrate the usability of local approach methods in structural integrity analyses and improve upon the transferability of their intrinsic, material like, constitutive parameters. Improvements of this kind can be attained by constructing improved models utilizing state of the art numerical simulation methods and presenting consistent calibration methodologies for the constitutive parameters. The current study investigates the performance of a modified Beremin model by comparing integrity evaluation results of the local approach model to those attained by using the constraint corrected Master Curve methodology. Current investigation applies the Master Curve method in conjunction with the T-stress correction of the reference temperature and a modified Beremin model to an assessment of a three-dimensional pressure vessel nozzle in a spherical vessel end. The material information for the study is extracted from the ‘Euro-Curve’ ductile to brittle transition region fracture toughness round robin test program. The experimental results are used to determine the Master Curve reference temperature and calibrate local approach parameters. The values are then used to determine the cumulative failure probability of cleavage crack initiation in the model structure. The results illustrate that the Master Curve results with the constraint correction are to some extent more conservative than the results attained using local approach. The used methodologies support each other and indicate that with the applied local approach and Master Curve procedures reliable estimates of structural integrity can be attained for complex material behavior and structural geometries.
Calculating Crack Opening Area for the Limited Plasticity Situation
Authors: Smith E.
Published: August 2008

When formulating a leak-before-break case for a component in a pressurized system, it is essential to quantify the opening area associated with a crack that is subjected to the tensile stresses that are appropriate to normal operating situations. In a paper presented at the 2002 PVP Conference, the author presented a simple and exact method, based on the strip yield representation of plastic deformation, for calculating the area. The method was validated against the known result for the case of an isolated two-dimensional crack in a uniformly stressed infinite solid, but the method has general applicability. Special consideration was given to the case where plastic deformation is limited, as is usually appropriate for normal operating situations, and the method then simplifies considerably. This paper shows that the method, as it is applied to the limited plastic deformation situation, gives results which are the same as those obtained by use of the equivalent crack procedure, where an actual crack is replaced by an effective elastic crack, which is longer than the actual crack by an amount which is related to the flow properties of the material and the applied loadings. To illustrate the usefulness of the author’s method, it is applied to a specific stress distribution as might arise from a combination of pressure induced and weld residual tensile stresses.
Allowable Axial Flaw Sizes for Stainless Steel Pipes Derived From Limit Load Criteria and Failure Assessment Diagram Procedure
Authors: Hasegawa Kunio , Miyazaki Katsumasa , Wilkowski Gery M. , Scarth Douglas A.
Published: August 2008

Piping containing flaws that exceed the Acceptance Standards of Section XI of the ASME Code is evaluated using analytical procedures described in Section XI to determine plant operability for the evaluated time period. Subarticle IWB-3640 of Section XI provides allowable axial and circumferential part-through-wall flaws determined from limit load criteria. ASME Section XI Code Case N-494-3 also provides evaluation procedures based on use of a failure assessment diagram to determine allowable flaw sizes. To understand the allowable flaw sizes determined by the limit load criteria and the failure assessment diagram procedure, anstenitic stainless steel pipes with axial part-through-wall flaws with a wide range of pipe diameters were analyzed. The allowable flaw depth based on limit load from Code Case N-494-3 was determined to be very close to that determined from IWB-3640 of Section XI, when the predicted failure mode is elastic-plastic fracture. It was found that the allowable flaw depths derived from the failure assessment diagram procedure of Code Case N-494-3, are lower, but are not significantly different, from those determined from the limit load criteria of IWB-3640. This is due to the relatively high fracture toughness that was used for the austenitic stainless steel.
Developments in the Flaw Assessment Procedures of R6 Revision 4 and BS7910
Authors: Ainsworth R. A. , Budden P. J. , Dowling A. R. , Sharples J. K.
Published: August 2008

The British Standards flaw assessment procedure BS7910 was issued in 1999 and combined and updated the previous published documents PD6493 and PD6539 for components operating at temperatures where creep was negligible and important, respectively. A major revision, Revision 4, of the R6 defect assessment procedures was released about a year later. Both BS7910 and R6 are under active development. This paper describes updates to the BS7910 and R6 Revision 4 documents since they were first issued. Ongoing developments which will lead to future revisions to the documents are also described.
A New Combined Deterministic and Probabilistic Flaw Evaluation Procedure
Authors: Dillstro¨m Peter
Published: August 2008

The Swedish handbook and computer program SACC, Safety Assessment of Components with Cracks, has recently been revised. The major differences compared to the last revision are within the following areas: • It is now a combined deterministic and probabilistic flaw evaluation procedure. • A new deterministic safety evaluation system is included. The main purpose is to more realistically handle large secondary stresses within the procedure. • It is now possible to include J-dominated stable crack growth. • New KI and limit load solutions are also included. • The appendices on material data to be used for nuclear applications and on residual stresses are revised. This paper provides an overview on the new handbook, with an emphasis on the probabilistic flaw evaluation procedure.