Analysis of Fracture Mechanics Specimens Made of Inconel 600 Based on Assessment Methods of Different Complexity

2009 ◽  
Author(s):  
Tomas Nicak ◽  
Herbert Schendzielorz ◽  
Elisabeth Keim
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Assessment Methods ◽  
Primary Circuit ◽  
Special Focus ◽  
Worst Case ◽  
Local Flow ◽  
Inconel 600 ◽  
Safety Margins ◽  
Micromechanical Models

Fracture mechanics analysis plays an important role in the frame of the safety assessment of nuclear components. Usually the goal of such an analysis is to decide if a given flaw size in the piping (or any component of the primary circuit) is acceptable or not. The word “acceptable” means that structural integrity of the component is guaranteed with sufficient safety margins up to the end of service life or up to the next in-service inspection (considering the worst case loads and lower bound material properties). To fulfil this high-responsible task in practice some useful Engineering Assessment methods (EAM) have been established i.e. Local flow stress concept (Germany), assessment based on J-Integral (France RSE-M), Limit load calculation according to (ASME XI, USA) or Two criteria approach (R6, UK). These EAM are verified by a large number of testscarried out in the past. On a higher level, more advanced assessment methods have been developed during the last years, based on micromechanical models of void nucleation and growth. These advanced micromechanical models are used within the Finite Element Analysis (FEA) and allow to study the whole crack growth process from initiation to final failure in more detail. In the ductile regime, which is the typical case for application of aforementioned methods, the crack growth can be divided into three phases: crack initiation, stable crack growth and unstable crack growth. In this paper methods of different complexity will be applied to analyse fracture mechanics specimens made of Inconel 600. Special focus will be placed on the crack growth modelling based on the Gurson’s porous metal plasticity theory. All performed calculations will be compared with experiments.

A Thermo-Mechanical Fatigue Crack Growth Accumulative Model for Gas Turbine Blades and Vanes

2016 ◽  
Author(s):  
Andrea Riva ◽  
Alessio Costa ◽  
Dalila Dimaggio ◽  
Paolo Villari ◽  
Karl Michael Kraemer ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Propagation ◽  
Gas Turbine ◽  
Crack Growth ◽  
Turbine Blades ◽  
Gas Turbine Blades ◽  
Mechanical Fatigue ◽  
Safety Margins

Heavy duty gas turbine blades and vanes are operated at high temperatures and high stresses, condition where several damage mechanisms can simultaneously be present. For example creep, fatigue and oxidation play an important role in the propagation of existing cracks. Crack growth models are employed for assessment criteria, interpretation of the field feedback and non-conformities management and they are required to be as accurate as possible when predicting crack propagation under the combined effect of all the three phenomena. In this work, a Linear Elastic Fracture Mechanics (LEFM) model based on isothermal experimental tests and validated by Thermo-Mechanical-Fatigue Crack Growth tests (TMFCG), is employed to predict crack propagation of a cast Ni-base superalloy used in gas turbine blades and vanes. When calculating the individual propagation fractions of creep and fatigue crack growth, the model accounts for the instantaneous stress state and temperature in transient regime (i.e. a complete cycle of start-up, base-load and shut-down). The loss of γ’- precipitates at the crack tip due to surface oxidation is interpreted as environmental damage fraction. A complete workflow for the systematic use of the approach, comprising an in-house software, has been defined and developed. Stress intensity factors used for LEFM calculations are determined either using tabulated weight functions or with the aid of Finite Element Analysis (FEA). This flexible approach is consistent with the industrial need of a given fracture mechanics calculation, which might require different levels of accuracy and resources/time consumption case by case. The software identifies the fraction of propagation caused by oxidation, creep crack growth or fatigue crack growth. This allows checking the physical realism of the results by comparing to metallographic analysis of fracture surfaces from broken TMFCG test specimen and/or real component damage information from field. Besides, this feature can be helpful to support the engineer in residual life evaluation under damage tolerant approach because it allows the identification of the type of operational regime that minimizes crack propagation. The software also allows the execution of sensitivity analyses via Monte-Carlo calculations, identifying for a given component and operational condition the more relevant calculation inputs. This feature also quantitatively supports the engineers in the identification of the most appropriate safety margins.

STYLE: Mock-Up3 Design—FE Simulation of Crack Growth in a Cladded Ferritic Pipe

2010 ◽  
Author(s):  
Tomas Nicak ◽  
Herbert Schendzielorz ◽  
Elisabeth Keim ◽  
Gottfried Meier ◽  
Dominique Moinereau ◽  
...  
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Large Scale ◽  
Assessment Tools ◽  
Bending Test ◽  
Test Facility ◽  
J Integral ◽  
Material Data ◽  
Porous Plasticity ◽  
Micromechanical Models

This paper describes numerical analyses performed in connection with the design of a large scale mock-up test planned within the European project on structural integrity STYLE. There are three large scale mock-up tests planned in STYLE, each of them dedicated to investigate specific effects. Mock-up3 (cladded ferritic pipe with an outer diameter of 420 mm) is foreseen to investigate transferability of material data, including fracture mechanics properties. Usually, material data are obtained by testing small specimens, which are subsequently used for the assessment of large scale structures (real components). The Mock-Up3 is an original part of a surge line made of low alloy steel 20MnMoNi55 (similar to SA 508 Grade 3, Cl. 1). The test will be performed on a 4 point bending test facility provided by EDF under displacement control at room temperature. The goal of the test is to obtain the stable crack growth of an inner surface flaw until a break through the wall occurs. The range of assessment tools applied within STYLE includes assessment of component failure by fracture mechanics analyses using methods based on fracture mechanics parameters (e.g K1 or J-Integral) as well as methods based on local micromechanical models (e.g. Gurson’s porous plasticity model and its variations). Micromechanical models have some advantages compared to those based on single term fracture parameters, especially if one considers designing a large scale mock-up test. The precise description of the entire damage process, beginning from with initiation on brittle particles, their growth leading to the crack initiation and finally to the macroscopic crack growth, can be seen as the most valuable attribute of these methods. Such methods make it possible to perform a set virtual tests prior to the real one, on which different test conditions can be investigated. A comparison of the common assessment method based on J-Integral with a local approach method, based on the Gurson’s porous plasticity theory, will be presented in this paper. Details on the Gurson model calibration will also be provided. Moreover, influence of boundary conditions on the large scale test will be discussed.

Fracture mechanics in design and service: ‘living with defects’ - Application of fracture mechanics to rubber articles, including tyres

1981 ◽  
Vol 299 (1446) ◽  
pp. 189-202 ◽  
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Strain Energy ◽  
Tensile Failure ◽  
Practical Application ◽  
Complicated Fracture ◽  
Fracture Work

The use of a fracture mechanics approach, based on the rate of release of strain energy, to account for various features of the failure of vulcanized rubbers is outlined. The properties considered include those to which fracture mechanics is often applied — tear, tensile failure, crack growth and fatigue — and others to which its application is less usual — abrasion, ozone attack and cutting by sharp objects. The relation of macroscopically observed properties to the basic molecular strength of the material is also discussed. An example of a quantitative practical application of the rubber fracture work, to groove cracking in tyres, is then considered. Finally, the rather more complicated fracture that can occur in rubber—cord laminates is discussed and it is shown that the energetics approach can be applied to some features, at least, of this.

Effective Modeling of Fatigue Crack Growth in Pipelines

2012 ◽  
Author(s):  
Steven J. Polasik ◽  
Carl E. Jaske
Keyword(s):  
Fatigue Crack ◽  
Stress Intensity ◽  
Fatigue Crack Growth ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Growth Models ◽  
Critical Parameters ◽  
Operating Pressure ◽  
Mechanics Model ◽  
Key Variables

Pipeline operators must rely on fatigue crack growth models to evaluate the effects of operating pressure acting on flaws within the longitudinal seam to set re-assessment intervals. In most cases, many of the critical parameters in these models are unknown and must be assumed. As such, estimated remaining lives can be overly conservative, potentially leading to unrealistic and short reassessment intervals. This paper describes the fatigue crack growth methodology utilized by Det Norske Veritas (USA), Inc. (DNV), which is based on established fracture mechanics principles. DNV uses the fracture mechanics model in CorLAS™ to calculate stress intensity factors using the elastic portion of the J-integral for either an elliptically or rectangularly shaped surface crack profile. Various correction factors are used to account for key variables, such as strain hardening rate and bulging. The validity of the stress intensity factor calculations utilized and the effect of modifying some key parameters are discussed and demonstrated against available data from the published literature.

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