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Stijn Hertele - One of the best experts on this subject based on the ideXlab platform.
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Crack Driving Force prediction in heterogeneous welds using vickers hardness maps and hardness transfer functions
Engineering Fracture Mechanics, 2018Co-Authors: Sameera Naib, Nenad Gubeljak, Wim De Waele, Primož Stefane, Stijn HerteleAbstract:Abstract Flawed welds often require an Engineering Critical Assessment (ECA) to judge on the necessity for weld repair. ECA is a fracture mechanics based prediction of the integrity of structural components with defects under operating conditions. Adding to the complexity of a weld ECA is the occurrence of local constitutive property variations in the weldment (‘weld heterogeneity’). Their quantification allows for a more accurate assessment compared to common (standardized) practice, which assumes welds to be homogeneous. Hardness measurements allow to quantify weld strength heterogeneity given their theoretical relation with ultimate tensile strength. However, various standards and procedures report a wide variety of relations (‘transfer functions’) between hardness and strength, and recognize substantial scatter in hardness based predictions of strength. Within this context, this paper investigates the suitability of Vickers hardness mapping to perform an accurate weld ECA for high strength low alloy steel. To overcome the scatter associated with standardized transfer functions, this paper suggests an experimental calibration procedure based on all weld metal tensile tests. Finite Element (FE) analysis has been conducted on welds originating from steels to simulate their Crack Driving Force response in Single-Edge notched Tension (SE(T)) specimens. Vickers hardness maps and hardness transfer functions are combined to assign element-specific constitutive properties to the model. The transfer function calibrated by all weld metal tensile tests yields a better agreement with experimental load-CTOD curves than transfer functions mentioned in standards and codes. Finally, a step-by-step procedure facilitates a practical adoption of the methodology.
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sensitivity study of Crack Driving Force predictions in heterogeneous welds using vickers hardness maps
International NAFEMS Conference on Engineering Analysis Modeling Simulation and 3D-Printing (NAFEMS-3D – 2016), 2016Co-Authors: Sameera Naib, Wim De Waele, Koen Van Minnebruggen, Stijn HerteleAbstract:Weld flaws often require an engineering critical assessment (ECA) to judge on the necessity for weld repair. ECA is a fracture mechanics based prediction of the integrity of welds under operating conditions. Adding to the complexity of an ECA is the occurrence of local constitutive property variations in the weldment (‘weld heterogeneity’). Their quantification is important to allow for an accurate assessment. Hereto, hardness measurements are widely adopted given their theoretical relation with ultimate tensile strength. However, various standards and procedures report a wide variety of different hardness transfer functions and additionally recognize substantial scatter in predictions of strength. Within this context, this paper investigates the suitability of hardness mapping to perform an accurate weld ECA. A finite element analysis has been conducted on welds originating from steel pipelines to simulate their Crack Driving Force response using single-edge notched tension (SE(T)) specimens. Vickers hardness maps and hardness transfer functions are combined to assign element-specific constitutive properties to the model. The resulting Crack Driving Force curves are probed against experimental results. The variable agreement between simulations and experiments highlights the need for further research into the characterization of local constitutive properties of heterogeneous welds. A hardness transfer procedure based on all weld metal tensile testing appears to be particularly promising.
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effects of weld strength heterogeneity on Crack Driving Force in stress and strain based design scenarios
Volume 4: Production Pipelines and Flowlines; Project Management; Facilities Integrity Management; Operations and Maintenance; Pipelining in Northern , 2014Co-Authors: Stijn Hertele, N P Odowd, Matthias Verstraete, Koen Van Minnebruggen, Wim De WaeleAbstract:Weld strength mismatch is a key factor with respect to the assessment of a flawed girth weld. However, it is challenging to assign a single strength mismatch value to girth welds, which are generally heterogeneous in terms of constitutive behavior. The authors have recently developed a method ('homogenization') to account for weld strength property variations in the estimation of Crack Driving Force response and the corresponding tensile limit state. This paper separately validates the approach for stress based and strain based assessments. Whereas homogenization is reliably applicable for stress based assessments, the strain based Crack Driving Force response is highly sensitive to effects of actual heterogeneous weld properties. The sensitivity increases with increased weld width and decreased strain hardening behavior. For strain based design, a more accurate methodology is desirable, and large scale testing and/or advanced numerical modeling remain essential.
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j integral analysis of heterogeneous mismatched girth welds in clamped single edge notched tension specimens
International Journal of Pressure Vessels and Piping, 2014Co-Authors: Stijn Hertele, Matthias Verstraete, Wim De Waele, Rudi Denys, N P OdowdAbstract:Flaw assessment procedures require a quantification of Crack Driving Force, and such procedures are generally based on the assumption of weld homogeneity. However, welds generally have a heterogeneous microstructure, which will influence the Crack Driving Force. This paper describes a stress-based methodology to assess complex heterogeneous welds using a J-based approach. Clamped single-edge notched tension specimens, representative of girth weld flaws, are analyzed and the influence of weld heterogeneity on Crack Driving Force has been determined. The use of a modified limit load for heterogeneous welds is proposed, suitable for implementation in a ‘homogenized’ J-integral estimation scheme. It follows from an explicit modification of an existing solution for centre Cracked tension specimens. The proposed solution provides a good estimate of Crack Driving Force and any errors in the approximation may be accounted for by means of a small safety factor on load bearing capacity.
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sensitivity of plastic response of defective pipeline girth welds to the stress strain behavior of base and weld metal
OMAE2011: PROCEEDINGS OF THE ASME 30TH INTERNATIONAL CONFERENCE ON OCEAN OFFSHORE AND ARCTIC ENGINEERING VOL 2: STRUCTURES SAFETY AND RELIABILITY, 2011Co-Authors: Stijn Hertele, Wim De Waele, Rudi Denys, M VerstraeteAbstract:One of the key parameters influencing the acceptability of a pipeline girth weld defect subjected to remote plastic deformation is the strength mismatch between weld and base metal. However, no single definition exists for weld strength mismatch, as it can be defined either on the basis of yield stress, ultimate tensile stress or any intermediate flow stress. To investigate the relevance of such definitions, the authors have performed a series of analyses of curved wide plate tests, using a validated parametric finite element model. The results indicate that, whereas yield stress overmatch determines Crack Driving Force for small plastic strains, ultimate tensile stress overmatch is the more important parameter for advanced plastic strains and determines the eventual failure mode. Further, the strain capacity and exact Crack Driving Force curve are additionally determined by uniform elongation and Crack growth resistance.
O. Kolednik - One of the best experts on this subject based on the ideXlab platform.
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effect of a single soft interlayer on the Crack Driving Force
Engineering Fracture Mechanics, 2014Co-Authors: Masoud Sistaninia, O. KolednikAbstract:It has recently been shown that a strong spatial variation of the Young’s modulus can improve greatly the fracture resistance and the fracture strength of an inherently brittle material. In this paper, using numerical modeling and application of the concept of the configurational Forces, it is shown that spatial variations of the yield stress can also improve the fracture resistance. The reason is that, when the Crack has crossed a soft interlayer, the Crack Driving Force strongly decreases and the Crack is arrested by the interlayer; this effect appears without previous delamination of the interlayer. From the numerical results, “optimum interlayer configurations” are derived, i.e. for a given matrix material and load, the magnitudes of thickness and yield stress of the soft interlayer are determined so that the Crack Driving Force exhibits a minimum. Such optimum configurations can be used for the design especially fracture resistant materials and components.
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A new view on J-integrals in elastic–plastic materials
International Journal of Fracture, 2014Co-Authors: O. Kolednik, Ronald Schöngrundner, F D FischerAbstract:It is well known that the application of the conventional $$J$$ J -integral is connected with severe restrictions when it is applied for elastic–plastic materials. The first restriction is that the $$J$$ J -integral can be used only, if the conditions of proportional loading are fulfilled, e.g. no unloading processes should occur in the material. The second restriction is that, even if this condition is fulfilled, the $$J$$ J -integral does not describe the Crack Driving Force, but only the intensity of the Crack tip field. Using the configurational Force concept, Simha et al. (J Mech Phys Solids 56:2876–2895, 2008 ), have derived a $$J$$ J -integral, $$J^{\mathrm{ep}} $$ J ep , which overcomes these restrictions: $$J^{\mathrm{ep}} $$ J ep is able to quantify the Crack Driving Force in elastic–plastic materials in accordance with incremental theory of plasticity and it can be applied also in cases of non-proportionality, e.g. for a growing Crack. The current paper deals with the characteristic properties of this new $$J$$ J -integral, $$J^{\mathrm{ep}}$$ J ep , and works out the main differences to the conventional $$J$$ J -integral. In order to do this, numerical studies are performed to calculate the distribution of the configurational Forces in a cyclically loaded tensile specimen and in fracture mechanics specimens. For the latter case contained, uncontained, and general yielding conditions are considered. The path dependence of $$J^{\mathrm{ep}} $$ J ep is determined for both a stationary and a growing Crack. Much effort is spent in the investigation of the path dependence of $$J^{\mathrm{ep}} $$ J ep very close to the Crack tip. Several numerical parameters are varied in order to separate numerical and physical effects and to deduce the magnitudes of the Crack Driving Force for stationary and growing Cracks. Interpretation of the numerical results leads to a new, completed picture of the $$J$$ J -integral in elastic–plastic materials where $$J^{\mathrm{ep}} $$ J ep and the conventional $$J$$ J -integral complement each other. This new view allows us also to shed new light on a long-term problem, which has been called the “paradox of elastic–plastic fracture mechanics”.
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Semi-analytical approaches to assess the Crack Driving Force in periodically heterogeneous elastic materials
International Journal of Fracture, 2012Co-Authors: F D Fischer, J. Predan, P. Fratzl, O. KolednikAbstract:When a Crack propagates in a heterogeneous elastic material, its Crack Driving Force depends strongly on the distribution of the local stiffness near the Crack tip. In materials with periodic spatial variations of the Young’s modulus, shielding and anti-shielding effects appear, i.e. the Crack Driving Force is reduced or enhanced, compared to a homogeneous material. The effect is of great practical relevance, since it may lead to a strong increase of the fracture resistance. The concept of configurational Forces (CCF) offers an established procedure for calculating the Crack Driving Force. A very general relation for the periodic variation of Young’s modulus is applied, allowing the description of both harmonically varying and layered microstructures. Numerical results are presented. Two semi-analytical approximation concepts, based on either the CCF or the moduli perturbation concept, are introduced and discussed. Comparisons are provided and recommendations given.
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a case study on the effect of thermal residual stresses on the Crack Driving Force in linear elastic bimaterials
International Journal of Mechanical Sciences, 2009Co-Authors: Marko Rakin, N K Simha, O. Kolednik, Bojan Medjo, F D FischerAbstract:Abstract The effect of thermal residual stresses in bimaterial structure with initial Crack located near a sharp interface is discussed in this paper. Bimaterial compact tension (CT) specimen is used in the analysis, and the residual stresses are introduced by cooling of the specimen. The residual stresses affect the stress and strain fields near the Crack tip, and the Crack-Driving Force is different compared with that in the homogeneous material without residual stresses. This difference can be quantitatively expressed through an additional Crack-Driving Force term—the material inhomogeneity term, Cinh. In this paper, it is evaluated using the post-processing procedure based on the concept of configurational Forces, following a finite-element analysis. The results indicate that accurate numerical analysis of pre-Cracked bimaterials should include the effect of thermally induced residual stresses. This effect cannot be neglected, even for bimaterials with homogeneous mechanical properties and inhomogeneity in thermal properties only (e.g. welded joints of ferritic and austenitic steel). Based on the obtained results, data from this study can be used in engineering practice to improve integrity and work safety of various inhomogeneous structures.
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j integral and Crack Driving Force in elastic plastic materials
Journal of The Mechanics and Physics of Solids, 2008Co-Authors: N K Simha, F D Fischer, G X Shan, C R Chen, O. KolednikAbstract:Abstract This paper discusses the Crack Driving Force in elastic–plastic materials, with particular emphasis on incremental plasticity. Using the configurational Forces approach we identify a “plasticity influence term” that describes Crack tip shielding or anti-shielding due to plastic deformation in the body. Standard constitutive models for finite strain as well as small strain incremental plasticity are used to obtain explicit expressions for the plasticity influence term in a two-dimensional setting. The total dissipation in the body is related to the near-tip and far-field J-integrals and the plasticity influence term. In the special case of deformation plasticity the plasticity influence term vanishes identically whereas for rigid plasticity and elastic-ideal plasticity the Crack Driving Force vanishes. For steady state Crack growth in incremental elastic–plastic materials, the plasticity influence term is equal to the negative of the plastic work per unit Crack extension and the total dissipation in the body due to Crack propagation and plastic deformation is determined by the far-field J-integral. For non-steady state Crack growth, the plasticity influence term can be evaluated by post-processing after a conventional finite element stress analysis. Theory and computations are applied to a stationary Crack in a C(T)-specimen to examine the effects of contained, uncontained and general yielding. A novel method is proposed for evaluating J-integrals under incremental plasticity conditions through the configurational body Force. The incremental plasticity near-tip and far-field J-integrals are compared to conventional deformational plasticity and experimental J-integrals.
F D Fischer - One of the best experts on this subject based on the ideXlab platform.
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Crack Driving Force in twisted plywood structures
Acta Biomaterialia, 2017Co-Authors: F D Fischer, Otmar Kolednik, Jožef Predan, Hajar Razi, Peter FratzlAbstract:Abstract Twisted plywood architectures can be observed in many biological materials with high fracture toughness, such as in arthropod cuticles or in lamellar bone. Main purpose of this paper is to analyze the influence of the progressive rotation of the fiber direction on the spatial variation of the Crack Driving Force and, thus, on the fracture toughness of plywood-like structures. The theory of fiber composites is used to describe the stiffness matrix of a twisted plywood structure in a specimen-fixed coordinate system. The Driving Force acting on a Crack propagating orthogonally to the fiber-rotation plane is studied by methods of computational mechanics, coupled with the concept of configurational Forces. The analysis unfolds a spatial variation of the Crack Driving Force with minima that are beneficial for the fracture toughness of the material. It is shown that the estimation of the Crack Driving Force can be simplified by replacing the complicated anisotropic twisted plywood structure by an isotropic material with appropriate periodic variations of Young’s modulus, which can be constructed based either on the local stiffness or local strain energy density variations. As practical example, the concepts are discussed for a specimen with a stiffness anisotropy similar to lamellar bone. Statement of Significance Twisted plywood-like structures exist in many natural fiber composites, such as bone or insect carapaces, and are known to be very fracture resistant. The Crack Driving Force in such materials is analyzed quantitatively for the first time, using the concept of configurational Forces. This tool, well established in the mechanics of materials, is introduced to the modeling of biological material systems with inhomogeneous and anisotropic material behavior. Based on this analysis, it is shown that the system can be approximated by an appropriately chosen inhomogeneous but isotropic material for the calculation of the Crack Driving Force. The spatial variation of the Crack Driving Force and, especially, its local minima are essential to describe the fracture properties of twisted plywood structures.
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A new view on J-integrals in elastic–plastic materials
International Journal of Fracture, 2014Co-Authors: O. Kolednik, Ronald Schöngrundner, F D FischerAbstract:It is well known that the application of the conventional $$J$$ J -integral is connected with severe restrictions when it is applied for elastic–plastic materials. The first restriction is that the $$J$$ J -integral can be used only, if the conditions of proportional loading are fulfilled, e.g. no unloading processes should occur in the material. The second restriction is that, even if this condition is fulfilled, the $$J$$ J -integral does not describe the Crack Driving Force, but only the intensity of the Crack tip field. Using the configurational Force concept, Simha et al. (J Mech Phys Solids 56:2876–2895, 2008 ), have derived a $$J$$ J -integral, $$J^{\mathrm{ep}} $$ J ep , which overcomes these restrictions: $$J^{\mathrm{ep}} $$ J ep is able to quantify the Crack Driving Force in elastic–plastic materials in accordance with incremental theory of plasticity and it can be applied also in cases of non-proportionality, e.g. for a growing Crack. The current paper deals with the characteristic properties of this new $$J$$ J -integral, $$J^{\mathrm{ep}}$$ J ep , and works out the main differences to the conventional $$J$$ J -integral. In order to do this, numerical studies are performed to calculate the distribution of the configurational Forces in a cyclically loaded tensile specimen and in fracture mechanics specimens. For the latter case contained, uncontained, and general yielding conditions are considered. The path dependence of $$J^{\mathrm{ep}} $$ J ep is determined for both a stationary and a growing Crack. Much effort is spent in the investigation of the path dependence of $$J^{\mathrm{ep}} $$ J ep very close to the Crack tip. Several numerical parameters are varied in order to separate numerical and physical effects and to deduce the magnitudes of the Crack Driving Force for stationary and growing Cracks. Interpretation of the numerical results leads to a new, completed picture of the $$J$$ J -integral in elastic–plastic materials where $$J^{\mathrm{ep}} $$ J ep and the conventional $$J$$ J -integral complement each other. This new view allows us also to shed new light on a long-term problem, which has been called the “paradox of elastic–plastic fracture mechanics”.
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Semi-analytical approaches to assess the Crack Driving Force in periodically heterogeneous elastic materials
International Journal of Fracture, 2012Co-Authors: F D Fischer, J. Predan, P. Fratzl, O. KolednikAbstract:When a Crack propagates in a heterogeneous elastic material, its Crack Driving Force depends strongly on the distribution of the local stiffness near the Crack tip. In materials with periodic spatial variations of the Young’s modulus, shielding and anti-shielding effects appear, i.e. the Crack Driving Force is reduced or enhanced, compared to a homogeneous material. The effect is of great practical relevance, since it may lead to a strong increase of the fracture resistance. The concept of configurational Forces (CCF) offers an established procedure for calculating the Crack Driving Force. A very general relation for the periodic variation of Young’s modulus is applied, allowing the description of both harmonically varying and layered microstructures. Numerical results are presented. Two semi-analytical approximation concepts, based on either the CCF or the moduli perturbation concept, are introduced and discussed. Comparisons are provided and recommendations given.
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a case study on the effect of thermal residual stresses on the Crack Driving Force in linear elastic bimaterials
International Journal of Mechanical Sciences, 2009Co-Authors: Marko Rakin, N K Simha, O. Kolednik, Bojan Medjo, F D FischerAbstract:Abstract The effect of thermal residual stresses in bimaterial structure with initial Crack located near a sharp interface is discussed in this paper. Bimaterial compact tension (CT) specimen is used in the analysis, and the residual stresses are introduced by cooling of the specimen. The residual stresses affect the stress and strain fields near the Crack tip, and the Crack-Driving Force is different compared with that in the homogeneous material without residual stresses. This difference can be quantitatively expressed through an additional Crack-Driving Force term—the material inhomogeneity term, Cinh. In this paper, it is evaluated using the post-processing procedure based on the concept of configurational Forces, following a finite-element analysis. The results indicate that accurate numerical analysis of pre-Cracked bimaterials should include the effect of thermally induced residual stresses. This effect cannot be neglected, even for bimaterials with homogeneous mechanical properties and inhomogeneity in thermal properties only (e.g. welded joints of ferritic and austenitic steel). Based on the obtained results, data from this study can be used in engineering practice to improve integrity and work safety of various inhomogeneous structures.
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j integral and Crack Driving Force in elastic plastic materials
Journal of The Mechanics and Physics of Solids, 2008Co-Authors: N K Simha, F D Fischer, G X Shan, C R Chen, O. KolednikAbstract:Abstract This paper discusses the Crack Driving Force in elastic–plastic materials, with particular emphasis on incremental plasticity. Using the configurational Forces approach we identify a “plasticity influence term” that describes Crack tip shielding or anti-shielding due to plastic deformation in the body. Standard constitutive models for finite strain as well as small strain incremental plasticity are used to obtain explicit expressions for the plasticity influence term in a two-dimensional setting. The total dissipation in the body is related to the near-tip and far-field J-integrals and the plasticity influence term. In the special case of deformation plasticity the plasticity influence term vanishes identically whereas for rigid plasticity and elastic-ideal plasticity the Crack Driving Force vanishes. For steady state Crack growth in incremental elastic–plastic materials, the plasticity influence term is equal to the negative of the plastic work per unit Crack extension and the total dissipation in the body due to Crack propagation and plastic deformation is determined by the far-field J-integral. For non-steady state Crack growth, the plasticity influence term can be evaluated by post-processing after a conventional finite element stress analysis. Theory and computations are applied to a stationary Crack in a C(T)-specimen to examine the effects of contained, uncontained and general yielding. A novel method is proposed for evaluating J-integrals under incremental plasticity conditions through the configurational body Force. The incremental plasticity near-tip and far-field J-integrals are compared to conventional deformational plasticity and experimental J-integrals.
Wim De Waele - One of the best experts on this subject based on the ideXlab platform.
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Crack Driving Force prediction in heterogeneous welds using vickers hardness maps and hardness transfer functions
Engineering Fracture Mechanics, 2018Co-Authors: Sameera Naib, Nenad Gubeljak, Wim De Waele, Primož Stefane, Stijn HerteleAbstract:Abstract Flawed welds often require an Engineering Critical Assessment (ECA) to judge on the necessity for weld repair. ECA is a fracture mechanics based prediction of the integrity of structural components with defects under operating conditions. Adding to the complexity of a weld ECA is the occurrence of local constitutive property variations in the weldment (‘weld heterogeneity’). Their quantification allows for a more accurate assessment compared to common (standardized) practice, which assumes welds to be homogeneous. Hardness measurements allow to quantify weld strength heterogeneity given their theoretical relation with ultimate tensile strength. However, various standards and procedures report a wide variety of relations (‘transfer functions’) between hardness and strength, and recognize substantial scatter in hardness based predictions of strength. Within this context, this paper investigates the suitability of Vickers hardness mapping to perform an accurate weld ECA for high strength low alloy steel. To overcome the scatter associated with standardized transfer functions, this paper suggests an experimental calibration procedure based on all weld metal tensile tests. Finite Element (FE) analysis has been conducted on welds originating from steels to simulate their Crack Driving Force response in Single-Edge notched Tension (SE(T)) specimens. Vickers hardness maps and hardness transfer functions are combined to assign element-specific constitutive properties to the model. The transfer function calibrated by all weld metal tensile tests yields a better agreement with experimental load-CTOD curves than transfer functions mentioned in standards and codes. Finally, a step-by-step procedure facilitates a practical adoption of the methodology.
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sensitivity study of Crack Driving Force predictions in heterogeneous welds using vickers hardness maps
International NAFEMS Conference on Engineering Analysis Modeling Simulation and 3D-Printing (NAFEMS-3D – 2016), 2016Co-Authors: Sameera Naib, Wim De Waele, Koen Van Minnebruggen, Stijn HerteleAbstract:Weld flaws often require an engineering critical assessment (ECA) to judge on the necessity for weld repair. ECA is a fracture mechanics based prediction of the integrity of welds under operating conditions. Adding to the complexity of an ECA is the occurrence of local constitutive property variations in the weldment (‘weld heterogeneity’). Their quantification is important to allow for an accurate assessment. Hereto, hardness measurements are widely adopted given their theoretical relation with ultimate tensile strength. However, various standards and procedures report a wide variety of different hardness transfer functions and additionally recognize substantial scatter in predictions of strength. Within this context, this paper investigates the suitability of hardness mapping to perform an accurate weld ECA. A finite element analysis has been conducted on welds originating from steel pipelines to simulate their Crack Driving Force response using single-edge notched tension (SE(T)) specimens. Vickers hardness maps and hardness transfer functions are combined to assign element-specific constitutive properties to the model. The resulting Crack Driving Force curves are probed against experimental results. The variable agreement between simulations and experiments highlights the need for further research into the characterization of local constitutive properties of heterogeneous welds. A hardness transfer procedure based on all weld metal tensile testing appears to be particularly promising.
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effects of weld strength heterogeneity on Crack Driving Force in stress and strain based design scenarios
Volume 4: Production Pipelines and Flowlines; Project Management; Facilities Integrity Management; Operations and Maintenance; Pipelining in Northern , 2014Co-Authors: Stijn Hertele, N P Odowd, Matthias Verstraete, Koen Van Minnebruggen, Wim De WaeleAbstract:Weld strength mismatch is a key factor with respect to the assessment of a flawed girth weld. However, it is challenging to assign a single strength mismatch value to girth welds, which are generally heterogeneous in terms of constitutive behavior. The authors have recently developed a method ('homogenization') to account for weld strength property variations in the estimation of Crack Driving Force response and the corresponding tensile limit state. This paper separately validates the approach for stress based and strain based assessments. Whereas homogenization is reliably applicable for stress based assessments, the strain based Crack Driving Force response is highly sensitive to effects of actual heterogeneous weld properties. The sensitivity increases with increased weld width and decreased strain hardening behavior. For strain based design, a more accurate methodology is desirable, and large scale testing and/or advanced numerical modeling remain essential.
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j integral analysis of heterogeneous mismatched girth welds in clamped single edge notched tension specimens
International Journal of Pressure Vessels and Piping, 2014Co-Authors: Stijn Hertele, Matthias Verstraete, Wim De Waele, Rudi Denys, N P OdowdAbstract:Flaw assessment procedures require a quantification of Crack Driving Force, and such procedures are generally based on the assumption of weld homogeneity. However, welds generally have a heterogeneous microstructure, which will influence the Crack Driving Force. This paper describes a stress-based methodology to assess complex heterogeneous welds using a J-based approach. Clamped single-edge notched tension specimens, representative of girth weld flaws, are analyzed and the influence of weld heterogeneity on Crack Driving Force has been determined. The use of a modified limit load for heterogeneous welds is proposed, suitable for implementation in a ‘homogenized’ J-integral estimation scheme. It follows from an explicit modification of an existing solution for centre Cracked tension specimens. The proposed solution provides a good estimate of Crack Driving Force and any errors in the approximation may be accounted for by means of a small safety factor on load bearing capacity.
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sensitivity of plastic response of defective pipeline girth welds to the stress strain behavior of base and weld metal
OMAE2011: PROCEEDINGS OF THE ASME 30TH INTERNATIONAL CONFERENCE ON OCEAN OFFSHORE AND ARCTIC ENGINEERING VOL 2: STRUCTURES SAFETY AND RELIABILITY, 2011Co-Authors: Stijn Hertele, Wim De Waele, Rudi Denys, M VerstraeteAbstract:One of the key parameters influencing the acceptability of a pipeline girth weld defect subjected to remote plastic deformation is the strength mismatch between weld and base metal. However, no single definition exists for weld strength mismatch, as it can be defined either on the basis of yield stress, ultimate tensile stress or any intermediate flow stress. To investigate the relevance of such definitions, the authors have performed a series of analyses of curved wide plate tests, using a validated parametric finite element model. The results indicate that, whereas yield stress overmatch determines Crack Driving Force for small plastic strains, ultimate tensile stress overmatch is the more important parameter for advanced plastic strains and determines the eventual failure mode. Further, the strain capacity and exact Crack Driving Force curve are additionally determined by uniform elongation and Crack growth resistance.
Jinghua Xiao - One of the best experts on this subject based on the ideXlab platform.
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effect of a laser pre quenched steel substrate surface on the Crack Driving Force in a coating steel substrate system
Acta Materialia, 2007Co-Authors: Banquan Yang, Gengxing Luo, Kun Zhang, Guangnan Chen, Jinghua XiaoAbstract:A mechanical model of a coating/laser pre-quenched steel substrate specimen with a Crack oriented perpendicular to the interface between the coating and the hardened layer is developed to quantify the effects of the residual stress and hardness gradient on the Crack Driving Force in terms of the J-integral. It is assumed that the Crack tip is in the middle of the hardened layer of the pre-quenched steel substrate. Using a composite double cantilever beam model, analytical solutions can be derived, and these can be used to quantify the effects of the residual stress and the hardness gradient resulting from the pre-quenched steel substrate surface on the Crack Driving Force. A numerical example is presented to investigate how the residual compressive stress, the coefficient linking microhardness and yield strength and the Young's modulus ratio of the hardened layer to the coating influence the Crack Driving Force for a given Crack length. (C) 2007 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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a quantitative analysis of the effect of laser transformation hardening on Crack Driving Force in steels
Surface & Coatings Technology, 2006Co-Authors: Banquan Yang, Kepeng Zhang, Guangliang Chen, Gengxing Luo, Jinghua XiaoAbstract:A mechanical model of a laser transformation hardening specimen with a Crack in the middle of the hardened layer is developed to quantify the effects of the residual stress and hardness gradient on Crack Driving Force in terms of J-integral. It is assumed that the Crack in the middle of the hardened layer is created after laser transformation hardening. Using a Double Cantilever Beam model, the analytic solutions, which can be used to quantify the effects of the residual stress and the hardness gradient resulting from laser transformation hardening on Crack Driving Force, are obtained. A numerical example shows the Crack Driving Force decrease is very sensitive to the residual compressive stress increase.
