scholarly journals DAMAGE AND FRACTURE MECHANICS CONCEPTS IN CALCULATING CYCLICALLY LOADED PRESSURE EQUIPMENT

2016 ◽  
Vol 19 (2) ◽  
Author(s):  
VALI-IFIGENIA IORDĂCHESCU (NICOLOF) ◽  
TEODOR SIMA
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Fracture Mechanics ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Damage And Fracture ◽  
History Of ◽  
Mechanics Concepts ◽  
Crack Tip Opening ◽  
Weld Seams

<p>In the history of technology there occurred many accidents caused by the presence and propagation of cracks in a mechanical structure, especially cracks in weld seams or already existing in the material. The paper evaluates the damage caused by cracks, the superposition of effects by using fracture mechanics concepts (the stress intensity factor, the contour integral and the crack tip opening displacement), while in the case of superposition fracture modes I and II , the relation was checked against the experimental literature data.</p>

The Inelastic Line-Spring: Estimates of Elastic-Plastic Fracture Mechanics Parameters for Surface-Cracked Plates and Shells

1981 ◽  
Vol 103 (3) ◽  
pp. 246-254 ◽  
Author(s):  
D. M. Parks
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Computing Time ◽  
Crack Tip ◽  
J Integral ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Elastic Plastic ◽  
Plates And Shells ◽  
Crack Tip Opening

Recent studies of the mechanics of elastic-plastic and fully plastic crack growth suggest that such parameters as the J-integral and the crack tip opening displacement can, under certain conditions, be used to correlate the initiation and early increments of the ductile tearing mode of crack growth. To date, elastic-plastic fracture mechanics has been applied mainly to test specimen geometries, but there is a clear need for developing practical analysis capabilities in structures. In principle, three-dimensional elastic-plastic finite element analysis could be performed, but, in fact, such analyses would be prohibitively expensive for routine application. In the present work, the line-spring model of Rice and Levy [1-3] is extended to estimate the J-integral and crack tip opening displacement for some surface crack geometries in plates and shells. Good agreement with related solutions is obtained while using orders of magnitude less computing time.

Fracture Mechanics

2012 ◽  
pp. 101-145
Keyword(s):  
Fracture Mechanics ◽  
Strain Energy ◽  
Subsequent Development ◽  
Strain Energy Release ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Linear Elastic ◽  
Energy Release Rates ◽  
Cracked Structures ◽  
Crack Tip Opening

Abstract Fracture mechanics is the science of predicting the load-carrying capabilities of cracked structures based on a mathematical description of the stress field surrounding the crack. The fundamental ideas stem from the work of Griffith, who demonstrated that the strain energy released upon crack extension is the driving force for fracture in a cracked material under load. This chapter provides a summary of Griffith’s work and the subsequent development of linear elastic and elastic-plastic fracture mechanics. It includes detailed illustrations and examples, familiarizing readers with the steps involved in determining strain energy release rates, stress intensity factors, J-integrals, R-curves, and crack tip opening displacement parameters. It also covers fracture toughness testing methods and the effect of measurement variables.

Experimental Investigation of the Mixed-Mode Crack Expanding in Bamboo

2010 ◽  
Vol 146-147 ◽  
pp. 1285-1288
Author(s):  
Jian Ting Zhao ◽  
Shao Peng Ma ◽  
Huan Rong Liu ◽  
Hai Qing Ren
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Outer Layer ◽  
Mixed Mode ◽  
Correlation Method ◽  
Middle Layer ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Gradient Distribution

Bamboo is a typical natural graded material, from the inner layer to the middle layer, and then to the outer layer. The elastic modulus is increasing gradually. The cracks grown on the inner layer and outer layer have different effects on the intensity. In this paper, the influence of the gradient distribution on the fracture behavior of the mixed-mode I and П cracks located in different layers is studied. The displacement measurement of bamboo specimens on asymmetric loading using digital speckle correlation method (DSCM) is performed and the crack tip opening displacement (COD), the stress intensity factor can be obtained. The results show that the COD of the crack in the outer layer is less than that of the crack in the inner layer, the stress intensity factor in the outer layer is greater than that of the crack in the inner layer, that means the property of the gradient distribution of bamboo has the protecting function for the static crack in the inner layer.

The Significance of Low Toughness Areas in the Seam Weld of Linepipe

2004 ◽  
Author(s):  
Robert M. Andrews ◽  
Glyn C. Morgan ◽  
W. Jack Beattie
Keyword(s):  
Fracture Mechanics ◽  
Charpy Impact ◽  
Coarse Grained ◽  
Plastic Collapse ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Seam Weld ◽  
Weld Defect ◽  
T Stress ◽  
Crack Tip Opening

There are concerns that there may be areas of low toughness in the seam welds of submerged are welded linepipe. These areas are typically associated with the Coarse Grained Heat Affected Zone and manifest themselves through low values obtained in Charpy impact and crack tip opening displacement (CTOD) tests. Although it is possible to locate areas of low toughness in linepipe seam welds, it is not clear if these are structurally significant. If it can be shown that low toughness areas in the seam weld HAZ do not affect the fitness for service of the pipe as a structure, these could be accepted for use. Under funding from PRCI, a study has been carried out to investigate this problem quantitatively. Experience in the offshore structural field, where the similar problem of local brittle zones in weld HAZs has received considerable attention, was reviewed. A constraint based fracture mechanics analysis was developed using the T-stress approach. Cracked body finite element analyses were used to obtain the T-stress for a range of surface breaking and buried defects in typical linepipe geometries. The results from these models were used to develop a constraint modified Failure Assessment Diagram for a fracture analysis. Fracture analyses showed that the structural constraint is low and failure will occur by plastic collapse for practical seam weld defect sizes. This shows that even when the seam weld toughness is very low, the dominant failure mode for the structure will be plastic collapse. Hence the low toughness values obtained in fracture mechanics tests are not structurally significant for practical defect sizes likely to occur in linepipe.

CTOD Application to Elastic-Plastic Fracture Mechanics Using Cyclic Ramberg-Osgood Law and HRR Solution

2012 ◽  
Author(s):  
Piotr Bednarz ◽  
Ilya Fedorov ◽  
Jaroslaw Szwedowicz
Keyword(s):  
Cyclic Loading ◽  
Fracture Mechanics ◽  
Crack Closure ◽  
Crack Tip ◽  
Compact Tension ◽  
Loading Conditions ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Crack Tip Opening ◽  
Closure Effect

Very often in the open literature the crack propagation simulation is based on the linear elastic fracture mechanics. This article describes a novel application of the cyclic crack tip opening displacement (ΔCTOD) method for evaluation of the cyclic nonlinear energy release rate under large plasticity and cyclic loading conditions. In order to consider the cyclic loading in the Hutchinson-Rice-Rosengren (HRR) solution, the monotonic plastic deformation of the material behaviour needs to be replaced by its cyclic counterpart. During cyclic loading conditions, a reverse plasticity occurs and leads to a crack closure effect via blunting of the crack tip. As a result, crack flanks are in contact during compression. This effect is determined from the effective difference between the maximum and minimum crack deformation. Then, the cyclic crack tip opening displacement is evaluated by applying the Shih rule. The proposed extension of the HRR solution in application to cyclic loading conditions via stress and strain transformation as well as accounting for the crack closure effect is validated in a good agreement with Dowling and Begley Compact Tension (CT) experiment. Potential crack closure due to crack surface roughness is neglected in current modeling. The proposed methodology extends the existing HRR solution for the reliable lifetime prediction.

A Fracture Mechanics Based Approach to the Assessment of Seismic Resisting Steel Structures

2006 ◽  
Vol 312 ◽  
pp. 89-94 ◽  
Author(s):  
Clark Hyland ◽  
W. George Ferguson
Keyword(s):  
Stress Intensity ◽  
Fracture Mechanics ◽  
Crack Initiation ◽  
Large Scale ◽  
Crack Tip ◽  
Steel Structures ◽  
Constructional Steel ◽  
Small Scale ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement

A method for assessing likelihood of brittle fracture in cyclically loaded steel assemblies subjected to inelastic strains is proposed. The method proposed is based upon relationships between monotonic and cyclic endurance of steel specimens proposed by Kuwamura and Takagi, and analysis of crack tip opening displacement (CTOD), Charpy V-Notch (CVN) and tensile results of pre-strained, fatigue pre-cracked and side-grooved specimens of constructional steel. The proposed method allows the influence of displacement ductility classification (as used in seismic design of structures), notch geometry, and cyclic strain amplitude history on crack initiation to be incorporated into a single design analysis approach. Small scale CTOD testing of steel materials with various levels of pre-strain may be used to identify stress intensity and crack tip displacement at crack initiation for use in the analysis. The integration of a fracture mechanics based approach to analysing stress intensity in conjunction with assembly plastic deformation characteristics derived from finite element modeling offers the promise of an improved approach to steel assembly design for cyclic plastic endurance and should result in more reliable structures and reduced need for large scale testing. This has particular relevance to the structural design of seismic resisting steelwork assemblies which are expected to develop dependable ductile behaviour under high strain variable amplitude cyclic actions.

The Effects of In-Plane and Out-of-Plane Dimensions of a Curved Wide-Plate on Crack-Tip Constraint for Pipeline Fracture Assessment

2014 ◽  
Author(s):  
Hwee-Seung Lee ◽  
Nam-Su Huh ◽  
Ki-Seok Kim
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Crack Tip ◽  
Standard Test ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Out Of Plane ◽  
Dimensional Finite Element ◽  
Crack Tip Constraint ◽  
Crack Tip Opening

One important element of fracture mechanics assessment in pipelines is how to determine the relevant fracture toughness (J-resistance or CTOD-resistance (crack-tip opening displacement)) for nonlinear fracture mechanics analysis. The general practice using a standard fracture mechanics specimen is known to often provide conservative estimates of toughness due to differences in crack-tip constraints between standard specimens and actual components. To improve the accuracy of predicting pipeline failure, various non-standard fracture mechanics specimens have been suggested over the past few decades. Among the several non-standard test specimens, a curved wide-plate in tension is often employed to predict fracture behavior of cracked components, for instance, in gas transportation pipelines. In order to show validity of a curved wide-plate in tension, the fracture toughness values from a full-scale pipeline test have been compared with those from a curved wide-plate in tension, and crack-tip constraints of a curved wide-plate in tension have also been compared with those of actual pipelines or other specimens during last decades. It is well known that a crack-tip constraint of test specimens, including curved wide-plates in tension, depends on many geometric and material parameters, for instance, crack length, thickness and width of specimen and material’s hardening characteristic. Thus, in order to obtain relevant fracture resistance from a curved wide-plate in tension representing accurate crack-tip constraint of pipeline of interest, variations of crack-tip constraints of curved wide-plates in tension according to various in-plane and out-of-plane constraint conditions should systematically be quantified. In the present study, systematic 3-dimensional finite element analyses attempt to investigate the effect of in-plane and out-of-plane parameters on crack-tip constraints of a curved wide-plate in tension.

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