Strain History Effects on Fracture Mechanics Parameters: Application to Reeling

2005 ◽  
Author(s):  
Hugo A. Ernst ◽  
Richard E. Bravo ◽  
Federico Daguerre ◽  
Alfonso Izquierdo
Keyword(s):  
Fracture Mechanics ◽  
Fracture Mechanic ◽  
Fracture Resistance ◽  
Structural Reliability ◽  
Structural Integrity ◽  
Quantitative Measure ◽  
Experimental Program ◽  
Strain History ◽  
History Effects ◽  
Material Fracture

It is now well accepted that welded structures may contain flaws, and that these do not necessarily affect structural integrity or service performance. This is implicitly recognized by most welding fabrication codes that specify weld flaw tolerance, or acceptance, levels based on experience and workmanship practice. However, these levels are somewhat arbitrary and do not provide a quantitative measure of structural integrity, i.e. how “close” a particular structure containing a flaw is to the failure condition. This concept is of special interest in cases in which the pipe is subjected to loads that produce important deformations. In particular the reeling process, used to install offshore lines, produce large cyclic plastic deformation on the pipes. In this work the method to perform a structural reliability analysis (SRA) for a tube subject to reeling is considered in detail. A fracture mechanics based methodology is reviewed and the points that need to be resolved before extending the methods to include reeling are clearly identified. The effect of the strain history on the applied and material fracture mechanics parameters were studied. A theoretical model was developed to describe the crack driving force evolution through strain cycles. A criterion was proposed and corroborated to represent material fracture resistance behavior. An experimental program was carried out. The material analyzed was a X65 - tube 355.4 × 22.2 mm. Monotonic and cyclic fracture mechanic tests were performed on single edge notch in tension (SENT) specimens. The material fracture resistance curve was determined based on the monotonic tests. The cyclic tests were used to determine experimentally the applied fracture mechanic parameters evolution. A very good agreement between predicted and measured CTOD values was obtained for the cases analyzed. A methodology to perform a SRA for tube subjected to reeling is proposed.

Fracture mechanics in design and service: ‘living with defects’ - Statistical aspects of design: risk assessment and structural integrity

1981 ◽  
Vol 299 (1446) ◽  
pp. 111-130 ◽  
Keyword(s):  
Fracture Mechanics ◽  
Structural Reliability ◽  
Structural Integrity ◽  
Product Liability ◽  
Probabilistic Methods ◽  
Statistical Variations ◽  
Engineering Designs ◽  
Recent Developments ◽  
Quantitative Basis ◽  
And Control

Statistical variations in input parameters that affect structural reliability have historically been incorporated approximately in engineering designs by application of safety factors. Increased concerns over the injury potential and costs of licensing, insurance, field repairs or recalls, and product liability claims now demand more quantitative evaluation of possible flaws or unusual usage conditions that might result from statistical variations or uncertainties. This paper describes the basic concepts of probabilistic fracture mechanics that are used to assess and control risk. Recent developments in combined analysis methods are presented that utilize field experience data with probabilistic analysis to improve the accuracy of the structural integrity predictions. Several specific examples are described that illustrate how these probabilistic methods are used to assess risk and to provide a quantitative basis for establishing design, operation or maintenance allowables. These procedures, which realistically model the actual statistical variations that exist, can eliminate unnecessarily conservative approximations and often achieve improved reliability at reduced cost.

An Investigation of the Stress Intensity Factor Along a Corner Crack in Pressurizer Vent Nozzle Penetration Weld

2009 ◽  
Author(s):  
Sang-Min Lee ◽  
Jeong-Soon Park ◽  
Jin-Su Kim ◽  
Young-Hwan Choi ◽  
Hae-Dong Chung
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Plastic Zone ◽  
Structural Integrity ◽  
Operating Conditions ◽  
Corner Crack ◽  
Elastic Plastic ◽  
Material Fracture

Elastic-plastic fracture mechanics as well as linear-elastic fracture mechanics may be applied to evaluate a flaw in ferritic low alloy steel components for operating conditions when the material fracture resistance is controlled by upper shelf toughness behavior. In this paper, the distribution of the stress intensity factor along a corner crack using elastic-plastic fracture mechanics technique is investigated to assess the effect of a structural factor on mechanical loads in pressurizer vent nozzle penetration weld. For this purpose, the stress intensity factor and plastic zone correction of a corner crack are calculated under internal pressure, thermal stress and residual stress in accordance with Electric Power Research Institute (EPRI) equation and Irwin’s approach, respectively. The resulting stress intensity factor and plastic zone correction were compared with those obtained from Structural Integrity Associates (SIA) and Kinectrics, and were observed to be good agreement with Kinectrics results.

Magnitude and Distribution of Retained Residual Stresses in Laboratory Fracture Mechanics Specimens Extracted From Welded Components

2012 ◽  
Author(s):  
R. G. Hurlston ◽  
J. K. Sharples ◽  
A. H. Sherry
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Fracture Mechanics ◽  
Residual Stresses ◽  
Structural Integrity ◽  
Specimen Size ◽  
Finite Element Analyses ◽  
Structural Components ◽  
Stress Partitioning ◽  
Material Fracture

Quantifying material fracture toughness properties is an important step in ensuring structural integrity of industrial components. Welding of structural components can cause large magnitudes of residual stress to be generated, which can be defined as a stress that exists in a material when it is under no primary loading. These stresses can be retained in laboratory fracture mechanics testing specimens removed from non-stress relieved welds, making the quantification of valid material fracture toughness difficult. The aim of this paper is to investigate, analytically, the levels and distributions of residual stresses retained in fracture mechanics specimens taken from welded components. This was achieved using parametric finite element analyses. Furthermore, in order to ensure the validity of fracture toughness measurements derived from components that contain residual stress, a robust method for the design of stress-free fracture mechanics specimens is proposed. Significant weld residual stresses have been shown to be retained in certain laboratory specimens post extraction from non stress-relieved welds. The magnitude and distribution of retained residual stress has been shown to be dependant on material properties, specimen size, specimen type and removal location. In addition, the stress partitioning method has been shown to provide a useful approach for estimating the levels and distributions of residual stresses retained in fracture mechanics specimens extracted in certain orientations.

Structural Integrity Evaluation of Reactor Pressure Vessels During PTS Events Using Deterministic and Probabilistic Fracture Mechanics Analysis

2013 ◽  
Author(s):  
Kazuya Osakabe ◽  
Hiroyuki Nishikawa ◽  
Koichi Masaki ◽  
Jinya Katsuyama ◽  
Kunio Onizawa
Keyword(s):  
Fracture Mechanics ◽  
Structural Reliability ◽  
Structural Integrity ◽  
Probabilistic Approach ◽  
Crack Size ◽  
Initial Crack ◽  
Pressure Vessels ◽  
Probabilistic Fracture Mechanics ◽  
Main Steam Line ◽  
Main Steam

To assess the structural integrity of reactor vessels (RVs) during pressurized thermal shock (PTS) events, a deterministic fracture mechanics (DFM) approach has been widely used such as the procedure in JEAC4206-2007. On the other hand, the application of a probabilistic fracture mechanics (PFM) analysis method for the structural reliability assessment of RV has become attractive recently because uncertainties related to input parameters can be incorporated rationally. The probabilistic approach has already been adopted as the regulation on fracture toughness requirements against PTS events in the U.S. In this paper, in order to verify the applicability of a PFM method to JEAC4206-2007, deterministic and probabilistic analyses have been performed, and the effects of initial crack size defined in JEAC4206-2007 on the temperature margin obtained from DFM and the probability of crack initiation obtained from PFM have been evaluated. With regard to the PTS event variation, a stuck open valve scenario (SO) has been considered in addition to large- and small-break loss of coolant accident (LBLOCA, SBLOCA) and main steam line break (MSLB).

Multiple Plastic Strain Cycles Effects on Structural Reliability Analysis of Pipes

2006 ◽  
Author(s):  
Hugo A. Ernst ◽  
Diego N. Passarella ◽  
Richard E. Bravo ◽  
Federico Daguerre
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Structural Reliability ◽  
Accurate Method ◽  
Experimental Program ◽  
Specific Method ◽  
Defect Assessment ◽  
Edge Notch

The reeling process is one of the most important methods for offshore installations of linepipes. Pipe segments are welded onshore and subsequently bent over a cylindrical rigid surface (reel) in a laying vessel. In a standard cycle the welded pipes are reeled onto a drum, reeled off, aligned and straightened. High plastic deformation is introduced in the pipe. Due to the high loading condition, the high costs of operations and the severe failure consequences, it is necessary to guarantee the integrity of the components during the process. Conventional defect assessment procedures are not explicitly developed for situations with large cyclic plastic strains. In previous work, a fracture mechanics based methodology was developed to obtain an appropriate specific method to assess the structural reliability of reeled pipes. A description of the material resistance toughness and the crack driving force evolution through strain cycles was proposed. This methodology was experimentally verified. In order to expand this model, in this work the case where several reeling cycles are applied is considered. In addition to the fracture mechanics methodology previously developed, a fatigue crack growth (FCG) formulation controlled by ΔJ parameter was developed. This formulation accounts for the crack growth produced during subsequent reeling cycles. Several fatigue laws and methods to calculate ΔJ were evaluated. An experimental program was carried out. Girth welded joints from two different seamless steel pipes were analyzed. Monotonic and cyclic fracture mechanics tests were performed using single edge notch tension (SENT) specimens. Cyclic tests were used to determine experimentally the cyclic crack growth. Experimental measurements were compared to predicted fatigue crack growths for different ΔJ calculation methods and fatigue laws. Comparison between theoretical and experimental results led to the selection of the most realistic fatigue law. A methodology to assess the reliability of pipes during multiple reeling cycles, based on fracture and elastic-plastic fatigue crack growth, was developed. A particular case of interest was presented, tolerable defect sizes were determined for different number of applied reeling cycles. The proposed methodology seems to be an accurate method to assess cases where multiple plastic cycles are taken into account.

Structural Reliability Analysis of Pipes Subjected to Multiple Strain Cycles: Application to Reeling Process

2006 ◽  
Author(s):  
Hugo A. Ernst ◽  
Diego N. Passarella ◽  
Richard E. Bravo ◽  
Federico Daguerre
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Structural Reliability ◽  
Accurate Method ◽  
Experimental Program ◽  
Specific Method ◽  
Defect Assessment ◽  
Edge Notch

The reeling process is one of the most important methods for offshore installations of linepipes. Pipe segments are welded onshore and subsequently bent over a cylindrical rigid surface (reel) in a laying vessel. The pipe is significantly cyclically strained. Due to the high loading condition, the high costs of operations and the severe failure consequences, it is necessary to guarantee the integrity of the components during the process. Conventional defect assessment procedures are not explicitly developed for situations with large cyclic plastic strains. In previous work, a fracture mechanics based methodology was developed to obtain an appropriate specific method to assess the structural reliability of reeled pipes. A description of the material resistance toughness and the crack driving force evolution through strain cycles was proposed. This methodology was experimentally verified. In order to expand this model, in this work the case where several reeling cycles are applied is considered. In addition to the fracture mechanics methodology previously developed, a fatigue crack growth (FCG) formulation controlled by ΔJ parameter was developed. This formulation accounts for the crack growth produced during subsequent reeling cycles. Several fatigue laws and methods to calculate ΔJ were evaluated. An experimental program was carried out. Girth welded joints from two different seamless steel pipes were analyzed. Monotonic and cyclic fracture mechanics tests were performed using single edge notch tension (SENT) specimens. Cyclic tests were used to determine experimentally the cyclic crack growth. Experimental measurements were compared to predicted fatigue crack growths for different ΔJ calculation methods and fatigue laws. Comparison between theoretical and experimental results led to the selection of the most realistic fatigue law. A methodology to assess the reliability of pipes during multiple reeling cycles, based on fracture and elastic-plastic fatigue crack growth, was developed. A particular case of interest was presented, tolerable defect sizes were determined for different number of applied reeling cycles. The proposed methodology seems to be an accurate method to assess cases where multiple plastic cycles are taken into account.

Mismatch Effect on Fracture Driving Force in Mismatched Girth Welded Pipes

2011 ◽  
Author(s):  
Gustavo M. Castelluccio ◽  
S. Cravero ◽  
R. Bravo ◽  
H. Ernst
Keyword(s):  
Fracture Mechanics ◽  
Structural Integrity ◽  
Crack Tip ◽  
J Integral ◽  
Inhomogeneous Materials ◽  
Crack Location ◽  
Unstable Failure ◽  
Edge Notch ◽  
Material Fracture ◽  
Crack Tip Constraint

Elasto-Plastic Fracture Mechanics (EPFM) is a useful tool for analyzing the structural integrity of components. However, EPFM has originally been developed for homogeneous materials and there are some concerns when it is applied to inhomogeneous materials. In the case of welds, the material fracture toughness and the applied fracture mechanics parameter on the structural member (J-integral, CTOD) should be adequately estimated. Furthermore, the mechanic mismatch influences on the local constraint may increase the risk of unstable failure. Hence, to study the effects of weld mismatch and crack locations on fracture behavior, single edge notch under tension (SE(T)) specimens and girth welded pipes under bending containing circumferential cracks were studied by means of finite elements simulations. Different weld widths and locations of cracks over the weld are considered. A study of the opening stresses ahead the crack tip developed in mismatched SE(T) specimens and cracked pipes allows the determination of the most critical combination of weld width and crack location in terms of applied J-integral and crack tip constraint level.

An Investigation of the Stress Intensity Factor Along a Corner Crack in Pressurizer Vent Nozzle Penetration Weld

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Sang-Min Lee ◽  
Jeong-Soon Park ◽  
Jin-Su Kim ◽  
Young-Hwan Choi ◽  
Hae-Dong Chung
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Intensity Factor ◽  
Plastic Zone ◽  
Structural Integrity ◽  
Operating Conditions ◽  
Corner Crack ◽  
Elastic Plastic ◽  
Material Fracture

Elastic–plastic fracture mechanics as well as linear-elastic fracture mechanics may be applied to evaluate a flaw in ferritic low alloy steel components for operating conditions when the material fracture resistance is controlled by upper shelf toughness behavior. In this paper, the distribution of the stress intensity factor (SIF) along a corner crack using elastic–plastic fracture mechanics technique is investigated to assess the effect of a structural factor on mechanical loads in pressurizer vent nozzle penetration weld. For this purpose, the stress intensity factor and the plastic-zone correction of a corner crack are calculated under internal pressure, thermal stress, and residual stress in accordance with Electric Power Research Institute (EPRI) equation and Irwin’s approach, respectively. The resulting stress intensity factor and the plastic-zone correction were compared with those obtained from Structural Integrity Associates (SIA) and Kinectrics Inc., and were observed to be in good agreement with Kinectrics results.

Measurement of the Material State Including the Effects of Recovery and Recrystallization

2000 ◽  
Author(s):  
M. E. Bange ◽  
A. J. Beaudoin ◽  
M. G. Stout ◽  
S. R. MacEwen
Keyword(s):  
Elevated Temperatures ◽  
High Strain ◽  
Quantitative Measure ◽  
Experimental Program ◽  
Strain Rates ◽  
Compression Tests ◽  
State Variable ◽  
Mechanical Threshold ◽  
Material State

Abstract Deformation at elevated temperatures in combination with high strain rates leads to recovery and recrystallization in aluminum alloys. Previous work in recrystallization has emphasized the detailing of microstructural trend in progression from the deformed to the annealed state. In the following, we examine the effect of rate dependence on deformation on AA 5182 and AA 6061. It is demonstrated that identification of underlying microstructural mechanisms is critical. An experimental program is then outlined for characterization of recovery and recrystallization of AA 5182. Instantaneous hardening rate and flow stress are developed from interrupted compression tests. These data are used to establish a quantitative measure of recovery through evaluation of a state variable for work hardening, the mechanical threshold. It is intended that the results serve as a foundation for development of relations for evolution of a mechanical state variable in the presence of recrystallization. Such a framework is necessary for the practical prediction of interstand recrystallization in hot rolling operations.

Verification of Probabilistic Fracture Mechanics Analysis Code for Reactor Pressure Vessel

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Yinsheng Li ◽  
Genshichiro Katsumata ◽  
Koichi Masaki ◽  
Shotaro Hayashi ◽  
Yu Itabashi ◽  
...  
Keyword(s):  
Fracture Mechanics ◽  
Working Group ◽  
Power Plants ◽  
Structural Integrity ◽  
Pressure Vessels ◽  
Irradiation Embrittlement ◽  
Energy Agency ◽  
Probabilistic Fracture Mechanics ◽  
Integrity Assessments ◽  
Reactor Pressure

Abstract Nowadays, it has been recognized that probabilistic fracture mechanics (PFM) is a promising methodology in structural integrity assessments of aged pressure boundary components of nuclear power plants, because it can rationally represent the influencing parameters in their inherent probabilistic distributions without over conservativeness. A PFM analysis code PFM analysis of structural components in aging light water reactor (PASCAL) has been developed by the Japan Atomic Energy Agency to evaluate the through-wall cracking frequencies of domestic reactor pressure vessels (RPVs) considering neutron irradiation embrittlement and pressurized thermal shock (PTS) transients. In addition, efforts have been made to strengthen the applicability of PASCAL to structural integrity assessments of domestic RPVs against nonductile fracture. A series of activities has been performed to verify the applicability of PASCAL. As a part of the verification activities, a working group was established with seven organizations from industry, universities, and institutes voluntarily participating as members. Through one-year activities, the applicability of PASCAL for structural integrity assessments of domestic RPVs was confirmed with great confidence. This paper presents the details of the verification activities of the working group, including the verification plan, approaches, and results.

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