Comparative Evaluation of Fracture Mechanics Methodologies as Applied to Offshore Structural Design and Integrity Analyses

1985 ◽  
Vol 107 (4) ◽  
pp. 479-484
Author(s):  
H. C. Rhee ◽  
M. M. Salama
Keyword(s):  
Fracture Mechanics ◽  
Structural Design ◽  
Crack Opening ◽  
Resistance Curve ◽  
Opening Displacement ◽  
Design Curve ◽  
Strain Relationship ◽  
Curve Method ◽  
Offshore Industry ◽  
Material Fracture

A comparative study was performed to evaluate the three most widely used elastic-plastic fracture mechanics methodologies. The three methods are the crack opening displacement (COD) design curve, which is widely used in the offshore industry, the British Central Electricity Generating Board (CEGB) R6 method, and the J-resistance curve method. Analyses of various flawed geometries based on these three methods were performed using consistent material fracture properties. The results of both the COD and R6 methods were compared with those of the J-resistance curve, which is the most rigorous of the three methods. The results of the COD concept, following BSI PD 6493 procedures, appear to be conservative at applied stress levels below 60 percent of the material yield strength and unconservative above this value. However, the results of the R6 method appear to be consistently conservative. The behavior of COD design curve solutions can be improved when the structural geometry and the actual stress-strain relationship are properly considered in the analyses.

Fracture mechanics in design and service: ‘living with defects’ - Assessment of defects: the c.o.d. approach

1981 ◽  
Vol 299 (1446) ◽  
pp. 155-167 ◽  
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Crack Opening ◽  
Local Stress ◽  
Concentration Effects ◽  
Opening Displacement ◽  
Widespread Application ◽  
Linear Elastic ◽  
Applied Loading ◽  
Displacement Approach

In welded construction particular problems arise with the application of fracture mechanics for the assessment of the effect of defects on structural performance. In many practical cases the use of plane strain linear elastic fracture mechanics methods is invalidated by the actual material thicknesses of interest, by residual stresses or by local stress concentration effects, and by local yielding. The crack opening displacement approach was originally devised as a means of extending linear elastic methods to more widespread application to welded structures. This required the development of a means of assessing fracture toughness, and a means of relating this fracture toughness to the applied loading conditions, and to sizes and types of defects which might be present. The success of this method of assessing defects over a period of some 10-12 years will be illustrated, together with a discussion of the inherent limitations of the approach and possible improvements resulting from recent research into slow tearing and design curve relationships.

Fracture Mechanics of Periodic Multilayers With Different Microstructural Scales and Moduli Contrast

2008 ◽  
Vol 75 (5) ◽  
Author(s):  
Linfeng Chen ◽  
Marek-Jerzy Pindera
Keyword(s):  
Fracture Mechanics ◽  
Crack Opening ◽  
Strain Energy Release ◽  
Computational Effort ◽  
Mode I ◽  
Preliminary Calculation ◽  
Opening Displacement ◽  
Microstructural Refinement ◽  
Loading Mode ◽  
Microstructural Effects

In a recent investigation of microstructural effects in finite periodic multilayers, we have shown that under Mode I loading, the crack-opening displacement approaches that of the same crack in an equivalent homogenized material as the microstructure comprised of alternating stiff and soft layers becomes increasingly finer. In contrast, Mode I stress intensity factor asymptotically converges to values that depend on the stiffness of the cracked layer. Preliminary calculation of Mode I strain energy release rate as a function of the microstructural refinement suggested that this may be a better fracture mechanics parameter for assessing fracture toughness of periodic layered media. Herein, we extend the above investigation by considering both Mode I and II loading to study the effect of layer modulus ratio on fracture mechanics parameters as a function of microstructural refinement. The previously introduced concept of partial homogenization of the microstructure sufficiently far from the crack is also pursued in order to gauge its efficiency in correctly capturing fracture mechanics parameters with a minimum of computational effort. The fracture mechanics parameters are shown to be influenced by the local microstructure to an extent that depends on the layer modulus mismatch. An accurate calculation of these parameters requires the retention of several layers adjacent to the affected cracked layer whose number depends on the modulus mismatch and loading mode.

A Method of J Testing Based on Crack Opening Displacement for Circumferential Through-Wall Cracked Pipes under Combined Tension and Bending

2006 ◽  
Vol 110 ◽  
pp. 63-70
Author(s):  
Nam Su Huh ◽  
Ludwig Stumpfrock ◽  
Eberhard Roos ◽  
Yun Jae Kim ◽  
Young Jin Kim
Keyword(s):  
Crack Opening Displacement ◽  
Conventional Method ◽  
Crack Opening ◽  
Estimation Method ◽  
Combined Loading ◽  
Resistance Curve ◽  
Opening Displacement ◽  
Load Line ◽  
Load Line Displacement ◽  
Leak Before Break

Application of the leak-before-break concept to nuclear piping requires accurate fracture mechanics assessment on pipes with postulated circumferential through-wall crack subject to combined tension and bending. One important element is determination of relevant J-resistance curve for pipes under combined loading. This paper provides experimental J estimation method for the circumferential through-wall cracked pipe under combined tension and bending, based on the load-crack opening displacement (COD) record to estimate J-resistance curve. To give confidence in the proposed method, the J results from detailed elastic-plastic finite element (FE) analysis are also compared with estimated J based not only on proposed method but also on conventional method using load-load line displacement, which shows that estimated J based on the proposed method provides reliable J estimates regardless of analysis condition, on the other hand, the conventional method using the load-load line displacement record gives erroneous results for shallow cracks.

Fracture mechanics characterisation of crack growth under creep conditions

1988 ◽  
Vol 23 (2) ◽  
pp. 87-96 ◽  
Author(s):  
T Hollstein ◽  
R Kienzler
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Crack Opening ◽  
Three Dimensional ◽  
Creep Crack Growth ◽  
Constant Load ◽  
Opening Displacement ◽  
Creep Crack ◽  
Incoloy 800 ◽  
Three Dimensional Finite Element

Creep crack growth rates in the 32%−Ni−20%−Cr alloy Incoloy 800 H at 800°C are correlated with the fracture mechanics parameter C∗ integral. This was done by experimental and numerical investigations of different specimen sizes and geometries under constant load, constant rate of crack opening displacement or crosshead displacement, or slow cyclic loading. In the numerical simulations plane and three-dimensional finite element calculations have been performed without consideration of creep crack growth.

Yielding fracture mechanics

1975 ◽  
Vol 10 (4) ◽  
pp. 207-216 ◽  
Author(s):  
C E Turner
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Crack Opening ◽  
Stable Crack Growth ◽  
Significant Degree ◽  
Crack Size ◽  
Simple Criterion ◽  
Opening Displacement ◽  
A Value ◽  
Structural Configurations

Yielding fracture mechanics seeks to find a relationship between applied stress, crack size and material toughness that is independent of the geometry of a component when fracture occurs after significant degree of yielding. The crack opening displacement, Δ, and the J contour integral are two proposals for describing the stresses and deformation at the tip of a sharp crack embedded in a region of yielding material. The concepts can be related in the form J = M σ YΔ where σ Y is the uniaxial yield stress, and M a factor with a value between about 1 and 2.5. The concepts are still under development. Either term can be chosen as a measure of the severity of crack tip deformation in a given material with the onset of crack growth in monotonic loading occurring at a critical value, Δ c or Jc, for a given thickness. Experimental evidence so far is in broad support of this picture but there remains uncertainty over the degree to which Δ c or Jc is independent of geometry and the extent to which stable crack growth prevents the usage of one simple criterion of fracture for all structural configurations.

Fracture Mechanics

1983 ◽  
pp. 269-293
Author(s):  
R. L. Tobler ◽  
H. I. McHenry
Keyword(s):  
Fracture Mechanics ◽  
Crack Opening Displacement ◽  
Low Temperatures ◽  
Fracture Behavior ◽  
Crack Opening ◽  
J Integral ◽  
Cryogenic Temperatures ◽  
Testing Methods ◽  
Opening Displacement ◽  
The Many

Abstract This chapter reviews the concepts of fracture mechanics and their application to materials evaluation and the design of cryogenic structures. Emphasis is placed on an explanation of technology, a review of fracture mechanics testing methods, and a discussion on the many factors contributing to the fracture behavior of materials at cryogenic temperatures. Three approaches of elastic-plastic fracture mechanics are covered, namely the crack opening displacement, the J-integral, and the R-curve methods. The chapter also discusses the influence of thermal and metallurgical effects on toughness at low temperatures.

Plastic Limit Loads for Slanted Circumferential Through-Wall Cracked Pipes Based on Finite Element Limit Analysis

2011 ◽  
Author(s):  
Hyun-Min Jang ◽  
Doo-Ho Cho ◽  
Jae-Boong Choi ◽  
Young-Jin Kim ◽  
Nam-Su Huh ◽  
...  
Keyword(s):  
Finite Element ◽  
Fracture Mechanics ◽  
Crack Opening Displacement ◽  
Crack Opening ◽  
Limit Load ◽  
Correction Factors ◽  
Plastic Limit ◽  
Opening Displacement ◽  
Limit Loads ◽  
Plastic Limit Load

Based on detailed three-dimensional (3-D) finite element (FE) limit analyses, the plastic limit load solutions for pipes with slanted circumferential through-wall cracks (TWCs) subjected to axial tension, global bending and internal pressure are reported. The FE model and analysis procedure employed in the present numerical study were validated by comparing the present FE results with existing solutions for plastic limit loads of pipes with idealized TWCs. To quantify the effect of slanted crack on plastic limit load, the slant correction factors for calculating plastic limit loads of pipes with slanted TWCs from pipes with idealized TWCs were newly proposed via extensive 3-D FE calculations. These slant correction factors are presented in a tabulated form for practical ranges of geometry and each loading conditions. Moreover, the present FE plastic limit loads were also compared with the existing solutions of pipes with slanted TWCs. These FE plastic limit load solutions can be applied to estimate elastic-plastic fracture mechanics parameters and creep fracture mechanics parameters, such as elastic-plastic J–integral and crack opening displacement, creep C*-integral and creep crack opening displacement, based on the reference stress concept considering more realistic crack shape.

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