Cracks Loaded by Rolling Contact - Influence of Plasticity around the Crack

2016 ◽  
Vol 258 ◽  
pp. 221-224 ◽  
Author(s):  
Werner Daves ◽  
Michal Kráčalík
Keyword(s):  
Finite Elements ◽  
Driving Force ◽  
Driving Forces ◽  
Crack Tip ◽  
Rolling Contact ◽  
Shear Cracks ◽  
Sliding Contacts ◽  
Crack Driving Force ◽  
Non Linear ◽  
The Common

For the description of cracks in rolling/sliding contacts many overlapping interactions has to be regarded and most of them are non-linear phenomena. This paper emphasis the aspect of plasticity around cyclically loaded shear cracks which is omitted very often in the common literature. It is shown that this plasticity can be calculated and regarded in computed crack driving forces; however, the problem is not solved after doing this. It is a first estimate only to regard the crack driving force calculated in the finite elements surrounding the crack tip as a relevant measure.

A Fatigue Crack Driving Force Parameter

2008 ◽  
Author(s):  
Ying Xiong ◽  
Zengliang Gao ◽  
Junichi Katsuta ◽  
Takeshi Sakiyama
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Driving Force ◽  
Crack Tip ◽  
Force Model ◽  
Crack Driving Force ◽  
R Ratio ◽  
Two Parameter ◽  
Better Than

Most of the previous parameters that utilized as a crack driving force were established in modifying the parameter Kop in Elber’s effective SIF range (ΔKeff = Kmax–Kop). This paper focuses on the physical meaning of compliance changes caused by plastic deformation at the crack tip, the test was carried out for structural steel under constant amplitude loading, and differences of several parameter ΔKeff in literature are analyzed quantificationally. The effect of actual stress amplitude at the crack tip on fatigue crack growth is investigated, and improved two-parameter driving force model ΔKdrive(=Kmax)n(ΔK^)1−n) has been proposed. Experimental data for several different types of materials taken from literature were used in the analyses. Presented results indicate that the parameter ΔKdrive is equally effective or better than ΔK(=Kmax-Kmin), ΔKeff(=Kmax-Kop) and ΔK*(=(Kmax)α(ΔK+)1−α) in correlating and predicting the R-ratio effects on fatigue crack growth rate.

Load and Crack History Effects on Fracture

2007 ◽  
Author(s):  
J. K. Sharples ◽  
P. M. James ◽  
L. A. Higham ◽  
P. M. Wood ◽  
H. Teng ◽  
...  
Keyword(s):  
Residual Stress ◽  
Driving Force ◽  
Driving Forces ◽  
Normal Operation ◽  
Proportional Loading ◽  
Crack Driving Force ◽  
History Effects ◽  
Weld Residual Stress ◽  
Assessment Procedures ◽  
Critical Process

Assessments of the integrity of structures containing defects or cracks require estimates to be made of the elastic-plastic crack driving force (CDF) parameter J. This is the characterising parameter that controls the intensity of the fields of stress and strain close to the tip of a crack. Such estimates of J are inherently made in assessment procedures such as R6, Revision 4 [1]. Engineering components are typically subjected to load cycles, often with significant variations in magnitude. Normal operation cycles or overload (by a proof pressure test for example) may cause a re-distribution of weld residual stresses. A defect can be present at fabrication or develop during operation due to a sub-critical process such as fatigue or stress corrosion cracking. In these two cases, it is reasonable to suppose that the actual crack driving forces are different; since the development of a defect in a region of weld residual stress, in conjunction with additional primary loading, can cause significant non-proportional loading of the crack tip. The objective of the work described in this paper is to provide more accurate estimates of the crack driving force parameter for defects subjected to combined primary and secondary stresses, taking into account the effects of loading hisotory. The eventual aim is to reduce uncertainty in assessments of plant integrity, and to clarify advantage that can be taken from a reduction in crack driving forces due to weld residual stress resulting from overload, operational cycles and the progressive introduction of sub-critical defects. Finite element analyses and R6 calculations are undertaken and compared to examine the effects of inserting a crack at different times during the life of an engineering structure.

Displacement Consideration for a Ductile Propagating Fracture in Line Pipe

1974 ◽  
Vol 96 (4) ◽  
pp. 318-322 ◽  
Author(s):  
A. K. Shoemaker ◽  
R. F. McCartney
Keyword(s):  
Driving Force ◽  
Driving Forces ◽  
Pipe Wall ◽  
Shear Fracture ◽  
Crack Tip ◽  
Complex Problem ◽  
Empirical Correlations ◽  
Line Pipe ◽  
Velocity Of Propagation ◽  
Propagating Shear

To date, the technically complex problem of arriving at an analysis for a running shear fracture in a gas-transmission line pipe has been primarily viewed by investigators in terms of an energy balance that involves empirical correlations of data. In contrast, in the present paper, the problem is reviewed in terms of the forces, masses, and time involved in the fracturing event and the resultant accelerations, velocities, and displacements with respect to (1) the forces driving the crack, (2) the pipe-wall ductility resisting the driving forces, and (3) the manner in which the crack arrests. Special attention is given to the effects of backfill on these events. On the bases of the data available, it is proposed that the displacements developed by the driving force are the result of the acceleration developed by the pressure acting on the flaps behind the crack. The driving force developed by the flaps results in forces which open the crack. For a constant velocity of propagation, the time for this flap displacement corresponds to the time for the pipe-wall thinning at the crack tip, which is controlled by the pipe-wall ductility. Thus, pipe-wall ductility can limit the speed of the crack. At a low crack speed, sufficient radial displacement of the flaps behind the crack occurs to cause the crack to turn in a helical path and arrest. Finally, the backfill significantly decreases the driving force and thus reduces the pipe-wall ductility necessary for arrest. Therefore, considerations of the displacements which occur during a propagating shear fracture indicate that the time and forces required for thinning the material at the crack tip, which is essentially governed by the ductility of the pipe wall, limit the speed of the crack.

Fitness-for-Service Fracture Assessments of Dissimilar Pipe Girth Welds Incorporating New Crack Driving Force Solutions

2014 ◽  
Author(s):  
Rodolfo F. de Souza ◽  
Claudio Ruggieri
Keyword(s):  
Driving Force ◽  
Large Scale ◽  
Structural Integrity ◽  
Numerical Solutions ◽  
Driving Forces ◽  
Limit Load ◽  
Assessment Procedure ◽  
Crack Driving Force ◽  
Alloy 625 ◽  
Girth Welds

The increasing demand for energy and natural resources has spurred a flurry of exploration and production activities of oil and natural gas in more hostile environments, including very deep water offshore production. Currently, structural integrity of submarine risers and flowlines conducting corrosive and aggressive hydrocarbons represents a key factor in operational safety of subsea pipelines. Advances in existing technologies favor the use of CMn steel pipelines (for example, API X65 grade steel) clad or mechanically lined with a corrosion resistant alloy (CRA), such as Alloy 625, for the transport of corrosive fluids. This work focuses on a fitness-for-service defect assessment procedure for strength mismatched welded components incorporating new crack driving force and limit load solutions. The study broadens the applicability of current evaluation procedures for J and CTOD which enter directly into structural integrity analyses and flaw tolerance criteria to provide a fairly comprehensive body of numerical solutions for crack driving forces in mismatched girth welds with circumferential surface cracks. This investigation also provides mismatch yield load solutions which are central to accurately predict failure load in strength mismatched structures subjected to large scale plasticity and ductile behavior. An approach is utilized to analyze the potential effects of the undermatching girth weld on critical flaw sizes for a typical lined pipe employed in subsea flowlines having a girth weld made of Alloy 625.

Subcritical crack growth and crack tip driving forces in relation to material resistance

2017 ◽  
Vol 35 (4-5) ◽  
pp. 251-265 ◽  
Author(s):  
Kuntimaddi Sadananda ◽  
Kiran N. Solanki ◽  
Asuri K. Vasudevan
Keyword(s):  
Crack Initiation ◽  
Crack Growth ◽  
Driving Force ◽  
Subcritical Crack Growth ◽  
Driving Forces ◽  
Crack Tip ◽  
Crack Arrest ◽  
Internal Stresses ◽  
Continuous Growth ◽  
Elastic Plastic

AbstractBasic concepts, related to the crack tip driving forces in relation to the material resistance, are analyzed for the elastic and elastic-plastic crack growth condition. This defines the crack initiation and growth conditions, as well as for crack arrest. Environment provides an additional driving force, thereby reducing the mechanical driving force required for the crack to grow. It is shown that (a) crack initiation and its growth are inseparable and (b) the magnitude of the applied and/or internal stresses; their gradients are also important for initiation and continuous growth of a crack. Elastic-plastic crack growth is also analyzed using the discrete dislocation models. The results show that its behavior is similar to that of an elastic crack. These concepts are valid for all subcritical crack growth. Mechanical and mechanical equivalent of chemical forces are defined for estimating the life prediction of a component in service. Failure diagrams are defined based on the extension of classical Kitagawa-Takahashi diagram that bridges the behavior of smooth and fracture mechanics specimens. Connections between crack initiation, growth, arrest, and overload fracture are established via these failure diagrams. Application of these diagrams for engineering components in service is outlined for diagnostic and prognostic purposes.

Crack Growth Tendency of Surface Shear Cracks in Rolling Sliding Contact

2013 ◽  
Vol 592-593 ◽  
pp. 250-253
Author(s):  
Werner Daves ◽  
Wei Ping Yao ◽  
Stephan Scheriau
Keyword(s):  
Driving Force ◽  
Kinematic Hardening ◽  
Sliding Contact ◽  
Crack Model ◽  
Shear Cracks ◽  
Configurational Force ◽  
Inclined Crack ◽  
Surface Shear ◽  
Crack Driving Force ◽  
Force Concept

Surface cracks arising during rolling sliding contact of a wheel and a rail are investigated. A two-dimensional crack model is proposed which calculates the crack driving force using the configurational force concept. The numerical applicability of the configurational force concept for surface shear cracks under cyclic contact loading is discussed and compared to the J-integral concept. A single inclined crack in a rail loaded by an accelerated wheel is investigated. The material of the rail is described by a cyclic plastic kinematic hardening model. The evolution of the crack driving force during several cycles is investigated.

Fully-Plastic Strain-Based J Estimation Scheme for Circumferential Surface Cracks in Pipes Subjected to Reeling

2013 ◽  
Author(s):  
Luís F. S. Parise ◽  
Claudio Ruggieri ◽  
Noel P. O’Dowd
Keyword(s):  
Driving Force ◽  
Driving Forces ◽  
Fracture Behaviour ◽  
Applied Strain ◽  
J Integral ◽  
Surface Cracks ◽  
Crack Driving Force ◽  
Numerical Assessment ◽  
Estimation Scheme ◽  
J Estimation

Modern installation techniques for marine pipelines and subsea risers are often based on the reel-lay method, which introduces significant (plastic) strains on the pipe during reeling and un-reeling. The safe assessment of crack-like flaws under such conditions requires accurate estimations of the elastic-plastic crack driving forces, ideally expressed in a strain-based formulation to better account for the displacement controlled nature of the reeling method. This paper aims to facilitate such assessments by presenting a strain-based expression of the well-known EPRI estimation scheme for the J integral, which is directly based upon fully plastic descriptions of fracture behaviour under significant plasticity. Parametric finite element simulations of bending of circumferentially cracked pipes have been conducted for a set of crack geometries, pipe dimensions and material hardening properties representative of current applications. These provide the numerical assessment of the crack driving force upon which the non-dimensional factors of the EPRI methodology, which scale J with applied strain, are derived. Finally, these factors are presented in convenient graphical and tabular forms, thus allowing the direct and accurate assessment of the J integral for circumferentially cracked pipes subjected to reeling.

Fracture Margins for Growing Cracks in Weld Repairs

2005 ◽  
Author(s):  
Michael C. Smith ◽  
Peter J. Bouchard ◽  
Martin R. Goldthorpe ◽  
Didier Lawrjaniec
Keyword(s):  
Residual Stress ◽  
Fracture Mechanics ◽  
Driving Force ◽  
Driving Forces ◽  
Linear Elastic Fracture Mechanics ◽  
J Integral ◽  
Residual Stress Field ◽  
Crack Driving Force ◽  
Linear Elastic ◽  
Elastic Fracture

The residual stress field around a single-pass weld filling a slit in a thin rectangular plate has been simulated using both 2D ABAQUS and 3D SYSWELD finite element models, with good agreement between the two codes. Through-wall cracks of varying lengths have been inserted into the plate along the weld centre-line, and the non-linear crack driving force due to residual stress evaluated using three formulations of the J-integral: the standard ABAQUS J, the G-theta approach coded into SYSWELD, and a modified J-integral, Jmod, that retains its path independence under non-proportional loading. Cracks were introduced into the FE meshes either simultaneously (all crack flank nodes released in the same step) or progressively (crack opened in small increments from mid-length to tip). The results were compared with crack driving force estimates made using linear elastic fracture mechanics (LEFM) and the R6 procedure. The crack driving forces predicted by all three J–formulations agree well for simultaneous opening, showing that the crack driving force rises to a peak for a crack length equal to the weld length, and falls for longer cracks. Linear elastic fracture mechanics gives a good estimate of the crack driving force for very short defects (confirming the absence of elastic follow up), but is conservative for longer defects, overestimating the peak driving force by 20%. The R6 estimates, which incorporate plasticity corrections, are more conservative than LEFM, overestimating the peak crack driving force by up to 60%. The crack driving force for a progressively opened crack is much lower than for simultaneous opening, indicating that there may be considerable excess pessimism in conventional assessments of defects of this type.

Fully-Plastic Strain-Based J Estimation Scheme for Circumferential Surface Cracks in Pipes Subjected to Reeling

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
Luís F. S. Parise ◽  
Claudio Ruggieri ◽  
Noel P. O'Dowd
Keyword(s):  
Finite Element ◽  
Driving Force ◽  
Driving Forces ◽  
Finite Element Simulations ◽  
J Integral ◽  
Crack Driving Force ◽  
Numerical Assessment ◽  
Estimation Scheme ◽  
The Given ◽  
J Estimation

Modern installation techniques for marine pipelines and subsea risers are often based on the reel-lay method, which introduces significant (plastic) strains on the pipe during reeling and unreeling. The safe assessment of cracklike flaws under such conditions requires accurate estimations of the elastic–plastic crack driving forces, ideally expressed in a strain-based formulation to better account for the displacement controlled nature of the reeling method. This paper aims to facilitate such assessments by presenting a strain-based expression of the well-known Electric Power Research Institute (EPRI) estimation scheme for the J integral, which is directly based upon fully plastic descriptions of fracture behavior under significant plasticity. Parametric finite element simulations of bending of circumferentially cracked pipes have been conducted for a set of crack geometries, pipe dimensions, and material hardening properties representative of current applications. These provide the numerical assessment of the crack driving force upon which the nondimensional factors of the EPRI methodology, which scale J with applied strain, are derived. Finally, these factors are presented in convenient graphical and tabular forms, thus allowing the direct and accurate assessment of the J integral for circumferentially cracked pipes subjected to reeling. Further results show that crack driving force values estimated using the proposed methodology and the given g1 factors are in very close agreement to those obtained directly from the finite element simulations.

Significance of HAZ Softening on Strain Concentration and Crack Driving Force in Pipeline Girth Welds

2005 ◽  
Author(s):  
Ming Liu ◽  
Yong-Yi Wang ◽  
David Horsley
Keyword(s):  
Driving Force ◽  
Crack Tip ◽  
Functionally Graded ◽  
Weld Strength ◽  
Heat Affect Zone ◽  
Crack Driving Force ◽  
Strain Concentration ◽  
Symmetric Deformation ◽  
Girth Welds ◽  
The Impact

Modern micro-alloyed, control-rolled TMCP steels generally have good strength, high toughness, and good weldability. However, these valuable properties come along with certain undesirable features, such as low strain hardening (high yield to tensile ratio), low ductility as measured by uniform elongation (elongation at ultimate tensile strength), and possible heat-affect-zone (HAZ) softening due to reduced hardenability. These undesirable features are particularly detrimental in strain-based design of pipelines. Although the phenomenon of HAZ softening has been known for a long time, the impact of the HAZ softening on the integrity of pipeline girth welds was not well understood. The objective of this work was to understand the impact of HAZ softening on girth weld integrity. Finite element analysis was conducted to investigate the effects of HAZ softening on crack driving force and strain concentration in girth welds under longitudinal tensile loading. The material properties of WM and BM were obtained from an X100 girth weld. The HAZ was modeled as a functionally graded material based on its measured hardness. The models contained surface-breaking defects located at the fusion boundary simulating lack-of-sidewall fusion defects. The analysis results showed that increased CTOD driving force can be expected due to HAZ softening. The extent of increase is positively related to the width and degree of softening of the HAZ. On the other hand, weld strength overmatch reduces the total CTOD driving force. The strain concentration in the softened HAZ circumferentially remote from a surface-breaking defect was small. However, high strain concentration existed over the circumference covering the length of the defect. This concentration was primarily attributable to the existence of the defect and secondarily to the HAZ softening. One significant result from this work was that the relative increase in CTOD driving force and strain concentration due to HAZ softening was independent of defect size. In other words, on a relative basis, HAZ softening was no worse on large defects than on smaller defects. This result should be helpful in rationalizing the effects of HAZ softening for defects of various sizes that exist in field applications. Non-symmetrical crack-tip deformation occurred with softened HAZ. A large proportion of the crack-tip deformation was located in the HAZ. The magnitude of non-symmetric deformation increased with the increase of HAZ width and degree of softening. Even higher degree of non-symmetric deformation occurred with the increase of weld overmatching level. The structural significance of reduced total CTOD driving force and increased un-symmetric deformation at the crack tip due to weld strength overmatch warrants further study. The reduction in total CTOD driving force alone does not necessarily results in a higher level of weld integrity if the “intrinsic” toughness of the HAZ is substantially lower than the weld metal.

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