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.

Quantitative Decisions Relative to Structural Integrity

1980 ◽  
Vol 102 (1) ◽  
pp. 56-63 ◽  
Author(s):  
C. A. Rau ◽  
P. M. Besuner
Keyword(s):  
Failure Modes ◽  
Structural Integrity ◽  
Product Liability ◽  
Turbine Rotor ◽  
Recent Developments ◽  
Quantitative Basis ◽  
Strong Motivation ◽  
Definition Of ◽  
And Control ◽  
Liability Claims

The injury potential and increased cost of licensing, insurance premiums, product liability claims, and field repairs or recalls provide strong motivation to quantitatively evaluate and control the risk of various products. Risk analysis involves the definition of the probable failure modes and the assessment of failure probability, failure severity and the corresponding risks and costs. Basic concepts are reviewed and recent developments in methods to quantify the risk of structural failure when limited failure experience is available are presented. An example involving a turbine rotor is described which illustrates how the conventional and, new methods provide a quantitative basis for assessing structural integrity and risk and for making decisions regarding future operation, repair, or replacement.

The Potential for Non-Conservative Results From the Probabilistic Fracture Mechanics Analyses Is Assessed Based on the Collected Observation of Fatigue Cracks in Offshore Steel Structures

2017 ◽  
Author(s):  
Ole Tom Vårdal
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Structural Integrity ◽  
Fatigue Cracks ◽  
Steel Structures ◽  
Lessons Learned ◽  
Probabilistic Methods ◽  
Growth Potential

In structural integrity management, it is essential to know the fatigue crack growth potential. The lessons learned from use of refined fatigue analyses, fracture mechanics and probabilistic methods for platforms in-service are presented. For ageing offshore units of semi-submersible design, the inspection history of more than 20 000 NDT inspections and detection of close to 1000 fatigue cracks, are used in this study. These experience data are used to assess the potential for Non-conservative estimate for the fatigue crack growth potential.

Rosenhain Centenary Conference - 3. Materials development present and future 3.7. Recent developments in ultra high strength steels and their applications

1976 ◽  
Vol 282 (1307) ◽  
pp. 377-387 ◽  
Keyword(s):  
Fracture Mechanics ◽  
High Strength Steels ◽  
High Strength ◽  
Unstable Fracture ◽  
Materials Development ◽  
Stable Crack Propagation ◽  
Recent Developments ◽  
Ultra High Strength Steels ◽  
Mechanics Concepts ◽  
And Control

As far as the development of new classes of ultra high strength steels is concerned the past decade has seen little progress apart from a few notable exceptions such as the trip steels. However, the introduction of fracture mechanics concepts to the evaluation of material properties has been responsible for an enormous breakthrough in the understanding of the factors which influence the fracture processes in conventional high strength steels. This approach has concerned not only the resistance of these materials to unstable fracture under rising load but also the stable crack propagation which can occur in aggressive environments under static load and in both aggressive and inert environments under cyclic loading conditions. Utilization of fracture mechanics has demonstrated the improvement which can be obtained in the properties of high strength steels through the use of thermomechanical treatments, hardening by intermetallic compounds and control of inclusions. Though much still remains to be learned in each of these fields, this paper highlights some aspects of the progress which has been made in the understanding of the fracture, fatigue and stress corrosion cracking of high strength steels.

Reliability Analysis for the Feeder Subject to Wall Loss

2012 ◽  
Author(s):  
Min Wang ◽  
Xianxun Yuan ◽  
Xinjian Duan ◽  
Michael J. Kozluk
Keyword(s):  
Reliability Analysis ◽  
Wall Thickness ◽  
Structural Reliability ◽  
Structural Integrity ◽  
Degradation Mechanism ◽  
Linear Regression Analysis ◽  
Probabilistic Methods ◽  
Piping System ◽  
Wall Thinning ◽  
Reliability Method

Wall thinning is one of the most common degradation mechanisms experienced in piping system. Gradual wall thinning can cause the pipe to leak or in the worst scenario, to rupture. Wall thinning due to FAC of feeder pipe in CANDU® reactors has been identified as an active degradation mechanism, and local thinning has been observed in various locations such as elbows/bends and Grayloc. The assessment of structural integrity is important for the fitness-for-service of those feeders whose wall thickness is predicted to be lower than the required minimum wall thickness before their design life and therefore subject to costly repair or replacement. Among various probabilistic methods, the first-order reliability method (FORM) is adopted in this paper to evaluate the structural reliability of feeders subject to wall thinning, while the wall thickness, one of the key parameters in the reliability analysis, is modeled by three methods based on the wall thickness measurements. They are linear regression analysis, random thinning rate analysis and gamma process modeling. The difference and limitation of the methods for reliability analysis are addressed.

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).

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.

Structural Life Expectancy of Marine Vessels: Ultimate Strength, Corrosion, Fatigue, Fracture, and Systems

2015 ◽  
Vol 1 (1) ◽  
Author(s):  
Bilal M. Ayyub ◽  
Karl A. Stambaugh ◽  
Timothy A. McAllister ◽  
Gilberto F. de Souza ◽  
David Webb
Keyword(s):  
Structural Reliability ◽  
Failure Modes ◽  
Structural Integrity ◽  
Structural Response ◽  
Probabilistic Methods ◽  
Life Assessment ◽  
Operational Environment ◽  
Stiffened Panels ◽  
Factors Affecting ◽  
Marine Vessels

This paper provides a methodology for the structural reliability analysis of marine vessels based on failure modes of their hull girders, stiffened panels including buckling, fatigue, and fracture and corresponding life predictions at the component and system levels. Factors affecting structural integrity such as operational environment and structural response entail uncertainties requiring the use of probabilistic methods to estimate reliabilities associated with various alternatives being considered for design, maintenance, and repair. Variability of corrosion experienced on marine vessels is a specific example of factors affecting structural integrity requiring probabilistic methods. The Structural Life Assessment of Ship Hulls (SLASH) methodology developed in this paper produces time-dependent reliability functions for hull girders, stiffened panels, fatigue details, and fracture at the component and system levels. The methodology was implemented as a web-enabled, cloud-computing-based tool with a database for managing vessels analyzed with associated stations, components, details, and results, and users. Innovative numerical and simulation methods were developed for reliability predictions with the use of conditional expectation. Examples are provided to illustrate the computations.

Nanoscale transistors

2017 ◽  
Author(s):  
Sandip Tiwari
Keyword(s):  
Field Effect Transistors ◽  
Ballistic Transport ◽  
Dimensional Change ◽  
Real Space ◽  
Operational Characteristics ◽  
Statistical Variations ◽  
Channel Transport ◽  
And Control ◽  
Long Channel ◽  
Detailed Nature

This chapter brings together the physical underpinnings of field-effect transistors operating in their nanoscale limits. It tackles the change in dominant behavior from scattering-limited long-channel transport to mesoscopic and few scattering events limits in quantized channels. It looks at electrostatics and a transistor’s controllability as dimensions are shrunk—the interplay of geometry and control—and then brings out the operational characteristics in “off”-state, e.g., the detailed nature of insulator’s implications or threshold voltage’s statistical variations grounded in short-range and long-range effects, and “on”-state, where quantization, quantized channels, ballistic transport and limited scattering are important. It also explores the physical behavior for zero bandgap and monoatomic layer materials by focusing on real-space and reciprocal-space funneling as one of the important dimensional change consequences through a discussion of parasitic resistances.

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