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Modeling The Ductile Brittle Fracture Transition In Reactor Pressure Vessel Steels Using A Cohesive Zone Model Based Approach
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Book Synopsis Modeling the Ductile Brittle Fracture Transition in Reactor Pressure Vessel Steels Using a Cohesive Zone Model Based Approach by :
Download or read book Modeling the Ductile Brittle Fracture Transition in Reactor Pressure Vessel Steels Using a Cohesive Zone Model Based Approach written by and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Fracture properties of Reactor Pressure Vessel (RPV) steels show large variations with changes in temperature and irradiation levels. Brittle behavior is observed at lower temperatures and/or higher irradiation levels whereas ductile mode of failure is predominant at higher temperatures and/or lower irradiation levels. In addition to such temperature and radiation dependent fracture behavior, significant scatter in fracture toughness has also been observed. As a consequence of such variability in fracture behavior, accurate estimates of fracture properties of RPV steels are of utmost importance for safe and reliable operation of reactor pressure vessels. A cohesive zone based approach is being pursued in the present study where an attempt is made to obtain a unified law capturing both stable crack growth (ductile fracture) and unstable failure (cleavage fracture). The parameters of the constitutive model are dependent on both temperature and failure probability. The effect of irradiation has not been considered in the present study. The use of such a cohesive zone based approach would allow the modeling of explicit crack growth at both stable and unstable regimes of fracture. Also it would provide the possibility to incorporate more physical lower length scale models to predict DBT. Such a multi-scale approach would significantly improve the predictive capabilities of the model, which is still largely empirical.
Book Synopsis Stochastic Micromechanical Modeling of Cleavage Fracture in the Ductile-brittle Transition Region by : David I. Auen Stienstra
Download or read book Stochastic Micromechanical Modeling of Cleavage Fracture in the Ductile-brittle Transition Region written by David I. Auen Stienstra and published by . This book was released on 1990 with total page 504 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Local Approach to Fracture by : Jacques Besson
Download or read book Local Approach to Fracture written by Jacques Besson and published by Presses des MINES. This book was released on 2006 with total page 121 pages. Available in PDF, EPUB and Kindle. Book excerpt: Improving the structural integrity together with the performance (weight, time to failure,...) of structures requires a persisting effort in the field of mechanics of materials and structures. This can be achieved by a better understanding of the relationships between microscopic mechanisms and the macroscopic material behavior and structural response with respect to damage and fracture. This improvement strategy of materials, structures and assement methods can be described as local approach to fracture. The local approach to fracture is an active research field. Initially developped in the context of steel structures (pressure vessels), its application domain has become wider and now deals with various kinds of materials (metallic alloys, metal matrix composites, polymers, elastomers, concrete) as well as various physical deformation and damage mechanisms (plasticity, creep, fatigue, ductile fracture, brittle fracture, ...). This volume contains the proceedings on an international conference dedicated to these issues.
Book Synopsis A Mechanism-based Approach to Modeling Ductile Fracture by : Douglas J. Bammann
Download or read book A Mechanism-based Approach to Modeling Ductile Fracture written by Douglas J. Bammann and published by . This book was released on 2004 with total page 82 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ductile fracture in metals has been observed to result from the nucleation, growth, and coalescence of voids. The evolution of this damage is inherently history dependent, affected by how time-varying stresses drive the formation of defect structures in the material. At some critically damaged state, the softening response of the material leads to strain localization across a surface that, under continued loading, becomes the faces of a crack in the material. Modeling localization of strain requires introduction of a length scale to make the energy dissipated in the localized zone well-defined. In this work, a cohesive zone approach is used to describe the post-bifurcation evolution of material within the localized zone. The relations are developed within a thermodynamically consistent framework that incorporates temperature and rate-dependent evolution relationships motivated by dislocation mechanics. As such, we do not prescribe the evolution of tractions with opening displacements across the localized zone a priori. The evolution of tractions is itself an outcome of the solution of particular, initial boundary value problems. The stress and internal state of the material at the point of bifurcation provides the initial conditions for the subsequent evolution of the cohesive zone. The models we develop are motivated by in-situ scanning electron microscopy of three-point bending experiments using 6061-T6 aluminum and 304L stainless steel, The in situ observations of the initiation and evolution of fracture zones reveal the scale over which the failure mechanisms act. In addition, these observations are essential for motivating the micromechanically-based models of the decohesion process that incorporate the effects of loading mode mixity, temperature, and loading rate. The response of these new cohesive zone relations is demonstrated by modeling the three-point bending configuration used for the experiments. In addition, we survey other methods with the potential to provide more detailed information about the near tip deformation fields.
Book Synopsis Fracture and Ductile vs. Brittle Behavior - Theory, Modelling and Experiment: by : Glenn E. Beltz
Download or read book Fracture and Ductile vs. Brittle Behavior - Theory, Modelling and Experiment: written by Glenn E. Beltz and published by Cambridge University Press. This book was released on 2014-06-05 with total page 350 pages. Available in PDF, EPUB and Kindle. Book excerpt: Dramatic progress has been made in the fundamentals of fracture, with special emphasis on the ductile/brittle transition across a broad spectrum of material classes. Unfortunately, however, since these studies are carried out in diverse research communities, communication among the different groups is limited. This book brings these diverse groups together. Contributions generally follow the topical outline upon which the symposium was organized. Part I deals with brittle/ductile behavior of steels and structural metallic alloys. The development of analytical models based on micromechanical models, such as dislocation mechanics and cohesive/contact zone models, is the focus of Part II. Nonmetals, including silicon, are reviewed in Parts III and IV. Fractals, chaos, and scaling theories, with emphasis on fracture in heterogeneous solids, is the basis of Part V. Crystal plasticity and mesoscale dislocation modelling follow in Part VI, with the technologically significant area of interfacial fracture featured in Part VII.
Book Synopsis Investigation of Strain Effect on Cleavage Fracture for Reactor Pressure Vessel Material by : Dr.Kushal Bhattacharyya
Download or read book Investigation of Strain Effect on Cleavage Fracture for Reactor Pressure Vessel Material written by Dr.Kushal Bhattacharyya and published by . This book was released on 2020 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Failure mechanism of 20MnMoNi55 steel in the lower self of ductile to brittle transition (DBT) region is considered as brittle fracture but it has been observed from the experimental analysis of stress-strain diagram that clear plastic deformation is shown by the material before failure. Therefore, strain correction is implemented in the cleavage fracture model proposed by different researchers in the lower self of the DBT region with the help of finite element analysis. To avoid a huge number of experiments being performed, Monte Carlo simulation is used to generate a huge number of random data at different temperatures in the lower self of the DBT region for calibration of the cleavage parameters with the help of the master curve methodology. Fracture toughness calculated after strain correction through different models are validated with experimental results for the different probability of failures.
Book Synopsis Local Approach to Fracture by : Clotilde Berdin
Download or read book Local Approach to Fracture written by Clotilde Berdin and published by Presses des MINES. This book was released on 2004 with total page 91 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents several aspects of the local approach to fracture: damage mechanisms, experimental techniques, damage evolution law and failure criteria, modelling of damage, and numerical simulation -- Back cover.
Book Synopsis A DISLOCATION-BASED CLEAVAGE INITIATION MODEL FOR PRESSURE VESSEL. by :
Download or read book A DISLOCATION-BASED CLEAVAGE INITIATION MODEL FOR PRESSURE VESSEL. written by and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Efforts are under way to develop a theoretical, multi-scale model for the prediction of fracture toughness of ferritic steels in the ductile-to-brittle transition temperature (DBTT) region that accounts for temperature, irradiation, strain rate, and material condition (chemistry and heat treatment) effects. This new model is intended to address difficulties associated with existing empirically-derived models of the DBTT region that cannot be extrapolated to conditions for which data are unavailable. Dislocation distribution equations, derived from the theories of Yokobori et al., are incorporated to account for the local stress state prior to and following initiation of a microcrack from a second-phase particle. The new model is the basis for the DISlocation-based FRACture (DISFRAC) computer code being developed at the Oak Ridge National Laboratory (ORNL). The purpose of this code is to permit fracture safety assessments of ferritic structures with only tensile properties required as input. The primary motivation for the code is to assist in the prediction of radiation effects on nuclear reactor pressure vessels, in parallel with the EURATOM PERFORM 60 project.
Book Synopsis Ductile Crack Growth Analysis Within the Ductile-Brittle Transition Regime by : I. Milne
Download or read book Ductile Crack Growth Analysis Within the Ductile-Brittle Transition Regime written by I. Milne and published by . This book was released on 1983 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: The ductile-brittle transition in ferritic steels is reviewed using data from pressure vessel steels A533B, A508, BS1501-271, and their associated weld metals and heat-affected zones in a variety of conditions. A schematic model is presented which provides a rational basis for understanding the phenomenon and making predictions. This model, which is consistent with the predictions obtained from physical models of cleavage fracture, contains the following important features. 1. If in the transition regime, KIc is defined as the fracture toughness at the onset of the brittle mode of fracture and KIJ is defined as the fracture toughness at the onset of ductile crack growth, then KIc > KIJ. 2. The ductile crack extension obtained between the initiation of ductile crack growth and the onset of brittle fracture is defined by the elastic-plastic crack growth resistance curve. 3. KIc cannot be reached without generating the appropriate amount of ductile crack extension.
Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1989 with total page 410 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis The Role of Cohesive Strength and Separation Energy for Modeling of Ductile Fracture by : T. Siegmund
Download or read book The Role of Cohesive Strength and Separation Energy for Modeling of Ductile Fracture written by T. Siegmund and published by . This book was released on 2000 with total page 13 pages. Available in PDF, EPUB and Kindle. Book excerpt: Barenblatt's idea of modeling the crack process zone by means of a cohesive zone has attracted considerable attention for predicting ductile crack growth. The model allows separation of the energy necessary for material separation from global plastic work. This has been a key problem in ductile fracture when searching for reasons for the geometry dependence of crack growth resistance curves. When using cohesive zone models, the correct determination of the cohesive zone material parameters is of eminent importance. In the past these parameters--the cohesive strength and the separation energy--were assumed to be material constants. However, micromechanical considerations show that this assumption is only an approximation in the case of ductile fracture. Here, the underlying mechanisms of void nucleation, growth, and coalescence are dependent on the stress triaxiality. This effect is accounted for in the new constitutive equation for cohesive zone models as presented here. In this new "triaxiality-dependent cohesive zone model," the cohesive material properties are taken to be dependent on the stress triaxiality in the solid element adjacent to the cohesive element. For low triaxiality, low values of cohesive strength and large values of the separation energy are observed; the opposite holds true for cases of high triaxiality. Ductile crack growth in a mild steel under quasistatic loading was investigated. The results from the use of the triaxiality-dependent cohesive zone model are compared to those of the Gurson-Tvergaard-Needleman (GTN) model as well as to the cohesive zone model with constant material parameters. The dissipation rate is shown to be a favorable measure for the characterization of the crack growth resistance. It allows the description of both the (global) plastic dissipation and the (local) work of fracture.
Book Synopsis Introducing Heterogeneity Into Brittle Fracture Modeling of a 22NiMoCr37 Ferritic Steel Ring Forging by : Xinglong Zhao
Download or read book Introducing Heterogeneity Into Brittle Fracture Modeling of a 22NiMoCr37 Ferritic Steel Ring Forging written by Xinglong Zhao and published by . This book was released on 2008 with total page 22 pages. Available in PDF, EPUB and Kindle. Book excerpt: Microstructural observations of the 22NiMoCr37 "EURO" reactor pressure vessel (RPV) steel ring forging reveal that there is a banded structure along the radial direction, composed of alternate layers rich in bainite and ferrite of wavelength ~1.5 ±0.75 mm. Heterogeneity at this meso (millimetre)-scale as well as at the micro (micrometre)-scale is currently not considered by conventional fracture mechanics. This paper describes the development of two numerical approaches aimed at incorporating such heterogeneity into the Beremin local approach model of cleavage failure, a model that has been used extensively for predicting the brittle fracture of ferritic RPV steels. The approaches developed combine the crystal plasticity finite element method (CPFEM) with continuum finite element analysis (FEA). CPFEM is applied to predict stress distributions at the microscale and to obtain phase-specific yield and flow properties for continuum FEA that derives stresses at the mesoscale. The results confirm that deformation heterogeneity on the micro- and mesoscales influences the local development of stress. At the microscale, the stress distribution within a representative volume of material located within the crack-tip plastic zone is shown to follow a normal distribution with a ratio of mean stress to standard deviation tending towards 0.1. These results indicate local stress levels that are within approximately ±20 % of those derived using continuum FEA. At the mesoscale, a periodic variation of stress is predicted within the larger representative volume. This variation is less dramatic than that observed at the microscale, though it still gives a spatial variation in maximum principal stress of approximately ±7 % between bainite- and ferrite-rich microstructural regions. These results suggest a significant influence of deformation heterogeneity on local stress levels, particularly at the microscale. However, the conventional Beremin cleavage fracture model, modified to account for microscale stress distribution, predicts only a modest influence of deformation heterogeneity on cleavage fracture probability, increasing Pf by just 5 %. This highlights the need to account for both the spatial variation in cleavage initiation sites as well as the distribution in stress throughout the microstructure. The paper describes one approach for this development.
Book Synopsis Micromechanical Prediction of Fracture Toughness for Pressure Vessel Steel Using a Coupled Model by : MR. Goldthorpe
Download or read book Micromechanical Prediction of Fracture Toughness for Pressure Vessel Steel Using a Coupled Model written by MR. Goldthorpe and published by . This book was released on 1999 with total page 23 pages. Available in PDF, EPUB and Kindle. Book excerpt: A method of analyzing the ductile to brittle transition region of a ferritic steel using a coupled micromechanical model of ductile damage, stable crack growth and cleavage fracture has been developed to improve the definition of upper shelf behavior for actual structures. Ductile damage is modelled using the Gurson model as modified by Tvergaard, along with a specially developed crack growth user element. The probability of cleavage fracture is predicted by post-processing the finite element results using the Beremin model of cleavage fracture. Predictions are made of ductile tearing and cleavage fracture in test specimen and wide plate configurations of A533B steel for a range of temperatures. The coupled model is capable of predicting transition toughness and transition temperature shifts for different levels of structural constraint. An analytically-based definition of the onset of upper shelf temperature (OUST) is the temperature at which the coupled ductile damage/cleavage fracture model predicts a probability of failure by cleavage fracture of 5%. Estimates of the shift in the OUST due to different levels of in-plane crack tip constraint are made using the elastic T-stress as a measure of constraint. There is potential for using the T-stress as a measure of structural constraint in order to determine shifts in transition temperature for materials with degraded toughness.
Book Synopsis INVESTIGATION ON THE EVALUATION OF CLEAVAGE FRACTURE TOUGHNESS USING PCCv SPECIMENS IN THE DUCTILE-BRITTLE TRANSITION RANGE OF REACTOR PRESSURE VESSEL STEELS - (CONTRACT RESEARCH) by : Kunio Onizawa
Download or read book INVESTIGATION ON THE EVALUATION OF CLEAVAGE FRACTURE TOUGHNESS USING PCCv SPECIMENS IN THE DUCTILE-BRITTLE TRANSITION RANGE OF REACTOR PRESSURE VESSEL STEELS - (CONTRACT RESEARCH) written by Kunio Onizawa and published by . This book was released on 1997 with total page 36 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis A Scalable Computational Approach for Modeling Dynamic Fracture of Brittle Solids in Three Dimensions by : Andrew Nathan Seagraves
Download or read book A Scalable Computational Approach for Modeling Dynamic Fracture of Brittle Solids in Three Dimensions written by Andrew Nathan Seagraves and published by . This book was released on 2010 with total page 140 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis a new parallel computational method is proposed for modeling threedimensional dynamic fracture of brittle solids. The method is based on a combination of the discontinuous Galerkin (DG) formulation of the continuum elastodynamic problem with Cohesive Zone Models (CZM) of fracture. In the proposed framework, discontinuous displacement jumps are allowed to occur at all element boundaries in the pre-fracture regime in a manner similar to "intrinsic" cohesive element methods. However, owing to the DG framework, consistency and stability of the finite element solution are guaranteed prior to fracture. This in stark contrast to the intrinsic cohesive element methods which suffer wave propagation and stability issues as a result of allowing discontinuous displacement jumps in the pre-fracture regime without properly accounting for them in the weak statement of the problem. In the new method, a fracture criterion is evaluated at all element boundaries throughout the calculation and upon satisfaction of this criterion, cracks are allowed to nucleate and propagate in the finite element mesh, governed by a cohesive tractionseparation law (TSL). This aspect of the method is similar to existing "extrinsic" cohesive element methods which introduce new fracture surfaces in the mesh through the adaptive insertion of cohesive elements subsequent to the onset of fracture. Typically this requires the mesh topology to be modified on-the-fly, a process which is highly complex and hinders the scalability of parallel implementations. However, for the DG method, discontinuities exist at element boundaries from the start of the calculation and so modifications of the mesh topology are unnecessary for introducing new fracture surfaces. As a result, the parallel computational framework is highly scalable and algorithmically simple. In this thesis, the formulation and numerical implementation of the method is described in detail. The method is then applied to simulate two practical problems. First a ceramic spall test is simulated. In this example, the DG method is shown to accurately capture the propagation of longitudinal elastic waves and the formation of a spall plane. Mesh dependency of the predicted spall plane and the dissipated cohesive energy is investigated for refined meshes resolving the size of the fracture process zone and the results are shown to be highly mesh-sensitive for the range of mesh sizes used. The spall test is also simulated using an existing intrinsic cohesive approach which is shown to alter the propagation of elastic stress waves, leading to the spurious result that no spallation occurs. In a second numerical example, the proposed DG method is applied to simulate high-velocity impact of an unconfined ceramic plate with a rigid spherical projectile. The method is shown to capture some of the basic fundamental aspects of the impact response of unconfined ceramics including the formation of conical and radial cracking patterns.
Book Synopsis Prediction of the Shape of the KJ Ductile-to-Brittle Transition Temperature Curve for Ferritic Pressure Vessel Steels Using the Material's Resistance to Crack Extension KJ Versus ?a Curve by : G. Wardle
Download or read book Prediction of the Shape of the KJ Ductile-to-Brittle Transition Temperature Curve for Ferritic Pressure Vessel Steels Using the Material's Resistance to Crack Extension KJ Versus ?a Curve written by G. Wardle and published by . This book was released on 2007 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fracture toughness (KJ (cleavage) ) measurements made within the ductile-to-brittle transition region for ferritic pressure vessel steels are not always described by the shape of the Master Curve currently given in ASTM Standard E 1921. The objective of this paper is to show how the shape of the transition toughness curve may be related to the shape of the material's resistance to crack extension curve (KJR) once the crack tip starts to blunt and ductile crack extension precedes cleavage failure. Using an empirical relationship between the mean ductile crack extension (?a) prior to the onset of cleavage failure and temperature (?a=?exp(?T)), then the relationship between KJ and T may simply be given by KJ=KA+?[?exp(?T)]?, where KA, ?, and ? are simply the coefficients to an offset power law to KJ versus ?a data given by KJR=KA+?(?a)?. For specimens of different sizes, a reference temperature TK may be defined for a given reference level of ?a or equivalent KJ. Unique curves may be defined for materials with differing crack extension resistance curves through plots of KJ versus (T-T?a(ref)) or (T-TK(ref)). The generalized form of the transition curve may be given by KJ=KA+??a(ref)exp[?(T-T?a(ref))]?, or KJ=KA+(K(ref)-KA)exp[?(T-TK(ref))]?. Experimentally, ? has been estimated as approximately 0.08 for nuclear pressure vessel materials such as A533B/A508. Using a specific situation wherein the value of KA=30 MPa ?m, K(ref)=100 MPa ?m, and ?=0.25 then, for a B=25-mm specimen, within experimental scatter this provides an almost exact match to the Master Curve given by KJ=30+70exp[0.019(T-TK100)]. The predictions of transition curve shape using the material's resistance to crack extension curve are believed to be complementary to the Master Curve method, and may describe the shape of the transition curve when there is ductile crack extension prior to cleavage failure. Further work is recommended to investigate the relationship between the predicted ductile-to-brittle transition curve and the Master Curve for probabilities of cleavage failure post-initiation.
Book Synopsis Dislocation Mechanics Basis and Stress State Dependency of the Master Curve by : M. Wagenhofer
Download or read book Dislocation Mechanics Basis and Stress State Dependency of the Master Curve written by M. Wagenhofer and published by . This book was released on 2000 with total page 10 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Master Curve approach to characterizing fracture toughness transition behavior of pressure vessel steels is based on statistical analysis of empirical data and not on a physics-based understanding of the fracture behavior of these steels. While there is an over-abundance of empirical data that supports the idea of a single curve shape for all pressure vessel steels, this cannot replace the need for solid physical modeling. The lack of fracture toughness data for a considerable proportion of the nuclear fleet suggests that a purely empirical argument cannot validate the Master Curve for all conditions of interest. In order to validate the Master Curve approach research has been undertaken to provide a physical understanding of the fracture behavior of pressure vessel steels. This will provide the basis for defining the limits of the Master Curve as well as for enabling extrapolation of the Master Curve model to other material conditions with only limited testing. A previous paper [1] detailed a dislocation mechanics-based constitutive model approach to describe the link between microstructure and temperature dependence of flow and fracture toughness behavior. In this paper, the strain to fracture under the appropriate stress state will be discussed in terms of the dislocation mechanics-based constitutive models and the effect on the shape of the Master Curve.
