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.

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.

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.

The Fined COD Transform Formula for CT Specimens to Investigate Material Fracture Toughness

2012 ◽  
Vol 188 ◽  
pp. 11-16
Author(s):  
Yao Yao ◽  
Li Xun Cai ◽  
Chen Bao ◽  
Han Jiang
Keyword(s):  
Crack Opening ◽  
Crack Tip ◽  
Compact Tension ◽  
Compact Tension Specimen ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Element Analysis ◽  
Material Fracture ◽  
Crack Tip Opening ◽  
The Relationship

For front-force compact tension specimen (FFCT), based on the refined results of the relationship between crack tip opening displacement and load line crack opening displacement from Finite Element Analysis (FEA), the influences of material properties and plastic deformation near the crack tip have been analyzed. A simplified and accurate transform formula for FFCT specimens is presented in this paper, and the error analysis is conducted.

Estimation of CTOD in the Case of Very Thick Plates by Knowing CVN Value at a Given Temperature

2010 ◽  
Author(s):  
Sylvain Pillot ◽  
Ste´phanie Corre ◽  
Ce´dric Chauvy ◽  
Patrick Toussaint
Keyword(s):  
Mechanical Properties ◽  
Fracture Mechanics ◽  
Tensile Properties ◽  
Material Properties ◽  
Crack Tip ◽  
Heat Treatments ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Thick Plates ◽  
Crack Tip Opening

Material properties assessment at given temperature and thickness is of primary importance for steelmakers. Generally, a list of mechanical properties requirements, namely tensile, Charpy V-Notch (CVN), fracture mechanics, as well as chemical or heat treatments limits are furnished by customers. Subsequently, the best compromise has to be found by the steel producer in order to reach these requirements. Concerning tensile and CVN properties, experience is large and metallurgists are used to determine the best product optimizations so as to reach the requirements’ values. However, optimization is generally more complicated regarding fracture mechanics. Tools are therefore needed in order to evaluate these properties with reference to conventional (i.e. tensile and CVN) properties. The objective of the present paper is to present some rules that can be used to extrapolate Crack Tip Opening Displacement (CTOD) values from CVN and tensile properties. Recent example is given to illustrate this methodology. In addition, special attention will be paid to the comparison of estimated and measured CTOD values.

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