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.

A Standard Approach for Measuring Adhesion Energies in Stiction-Failed Microdevices

2006 ◽  
Author(s):  
Zayd C. Leseman ◽  
Steven Carlson ◽  
Xiaojie Xue ◽  
Thomas J. Mackin
Keyword(s):  
Strain Energy ◽  
Peel Test ◽  
Strain Energy Release ◽  
Piezo Actuator ◽  
Release Rates ◽  
Linear Elastic ◽  
Macro Scale ◽  
Energy Release Rates ◽  
Elastic Fracture ◽  
Strain Energy Release Rates

We present results from a new procedure developed to quantify the pull-off force and strain energy release rates associated with stiction-failure in microdevices. The method is analogous to a standard, macro-scale peel test, but carried out using micro-scale devices. Adhesion is initiated by lowering an array of microcantilevers that protrude from a substrate into contact with a separate substrate. Displacement is controlled by a piezo-actuator with sub-nm resolution while alignment is controlled using linear and tilt stages. An interferometric microscope is used to align the array and the substrate and to record deflection profiles and adhesion lengths during peel-off. This geometry is accurately modeled using linear elastic fracture mechanics, creating a robust, reliable, standard method for measuring adhesion energies in stiction-failed microdevices.

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.

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 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.

Application of Fracture Mechanics to Crack Growth in Rubber-Cord Laminates

2001 ◽  
Vol 74 (3) ◽  
pp. 509-524 ◽  
Author(s):  
G. J. Lake
Keyword(s):  
Fracture Mechanics ◽  
Energy Release Rate ◽  
Energy Release ◽  
Crack Growth ◽  
Release Rate ◽  
Strain Energy ◽  
Fatigue Cracks ◽  
Strain Energy Release ◽  
Energy Release Rates ◽  
Laminated Structures

Abstract The use of a fracture mechanics approach based on the strain energy release rate to assess failure due to the growth of fatigue cracks in rubber—cord laminated structures is discussed. The mechanics of crack propagation is considered for cracking either between the plies or around individual cords, and also for crack initiation and growth near cord ends. Energy release rates can be calculated approximately for each of these cases and enable the laminate results to be related to the independently measured crack growth characteristics of the rubber. Experimental energy release rate determinations, from compliance changes produced by propagating model inter-ply cracks by cutting, provide a check on the accuracy of the calculated energies. The approach identifies material properties relevant to laminate failure and indicates the effects of loading, design and construction parameters on the rate and nature of failure.

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.

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