bluuebunny/crossref_metadata_2025_split huggingface dataset:
MODELLING SHORT CRACK GROWTH BEHAVIOUR IN NICKEL‐BASE SUPERALLOYS
Authors: Grabowski L. , King J. E. 
Published: April 2007

Abstract— This paper provides a description of the features and mechanisms of facetted short crack growth in Ni‐base superalloys, and briefly reviews existing short crack growth models in terms of their application to Ni‐base alloys.The concept of “soft barriers” is introduced to produce a new two‐phase model for local microstructural effects on short crack growth in Waspaloy. This is derived from detailed observations of crack growth through individual grains. The model differs from all previous approaches in highlighting the importance of crack path perturbations within grains. Potential applications of the model in alloy development are discussed.
THE INITIATION AND PROPAGATION BEHAVIOUR OF SHORT FATIGUE CRACKS IN WASPALOY SUBJECTED TO BENDING
Authors: Yates J. R. , Zhang W. , Miller K. J. 
Published: April 2007

AbstractThe fatigue crack growth behaviour of a nickel base superalloy, Waspaloy, has been studied using four point bending specimens in laboratory air. Two groups of tests, for which the span/width ratios were 1 and 2.5, were conducted and the results compared. Surface crack lengths were measured from plastic replicas of the surface. Equations which describe both short and long cracks have been derived and used to predict the fatigue life for the Waspaloy specimens. From plastic replication studies and scanning electron microscope examinations, a physical understanding of the relationship between crack growth and microstructural features was enhanced.
A NORMAL DISTRIBUTION OR A WEIBULL DISTRIBUTION FOR FATIGUE LIVES
Authors: Schijve J. 
Published: April 2007

AbstractThe results of six series of 18 to 30 similar fatigue tests on three types of specimens are used to check the applicability of the normal distribution function and the three‐parameter Weibull distribution function. A least‐square procedure is adopted to obtain the three parameters of the Weibull function. Comments are made on the results obtained.
AN APPROACH TO MEASURE THE SHAPES OF THREE‐DIMENSIONAL SURFACE CRACKS DURING FATIGUE CRACK GROWTH
Authors: Ravichandran K. S. , Larsen J. M. 
Published: April 2007

AbstractThis study presents a technique for measuring shapes of three dimensional surface cracks continuously during fatigue crack growth. The technique uses a laser interferometric system to measure crack compliance and a photomicroscopic system to measure surface crack length. Using a compliance expression for surface cracks, valid for the range of crack aspect ratios (a/c) of 0.2 to 2.0, aspect ratio calculations employing compliance and surface crack length measurements are demonstrated for cracks growing from EDM notches of different geometries (shallow or deep). The experimentally determined aspect ratio variations during cyclic crack growth are shown to be in good agreement with the expected variations in aspect ratio, predicted using the stress intensity factor equations for surface cracks. The effects of deviations in the compliance measurement location from the center of the surface crack due to assymetric crack growth are also accounted for through corrections of compliance measurements for crack‐asymmetry. The fatigue crack growth rates of surface cracks, after incorporating the variations in aspect ratio in the calculations, agreed with the large‐crack growth data for all crack geometries.
EFFECTS OF CRACK LENGTH, NOTCH ROOT RADIUS AND GRAIN SIZE ON FRACTURE TOUGHNESS OF FINE CERAMICS
Authors: Ando K. , Iwasa M. , Kim B. A. , Chu M. C. , Sato S. 
Published: April 2007

AbstractGenerally, fracture toughness and fracture stress of ceramics depend on crack length, notch root radius and grain size. These three parameters are most important when assessing the integrity of structural ceramic members and developing high‐performance ceramics. A new failure criterion called the process zone size failure criterion, has been proposed based on the existence of a crack‐tip process zone. Using this criterion, it is shown that theoretical values are in good agreement with many test results quoted from many papers. It is concluded that this failure criterion is useful when evaluating crack length and notch root radius problems. The effect of grain size on both the fracture toughness and on the toughening mechanism is also considered.
TREATMENT OF FRACTURE TOUGHNESS DATA IN THE TRANSITION REGIME
Authors: Moskovic R. , Neale B. K. 
Published: April 2007

Abstract— Two methods are given in this paper for describing the dependence of fracture toughness on temperature in the transition regime. The first method estimates fracture toughness at, or close to, the onset of stable tearing prior to cleavage fracture. The second method uses a statistical model to describe both initiation and cleavage fracture toughness in terms of stable tearing and specimen thickness.The procedures are illustrated using unirradiated fracture toughness data from the US Heavy Section Steel Irradiation Program 5th Series.
THE MECHANISMS AND DETECTION OF EMBRITTLEMENT IN Cr‐Mo PRESSURE VESSEL STEELS
Authors: Moss C. J. , Kelly P. M. 
Published: April 2007

Abstract— 21/4CrlMo steel and 11/4Cr1/2Mo steel have been widely been used for hydro‐processing units such as hydro‐desulphurising and hydro‐cracking reactors. These reactor pressure vessel steels have a potential for temper embrittlement that leads to toughness degradation and a reduction of the critical flaw size for brittle fracture. These steels are also susceptible to hydrogen embrittlement, especially in aged steels where cracks may propagate in the base metal up to the critical flaw size. A vessel with adequate toughness when originally constructed may therefore embrittle during service and such changes may require pressure restrictions during start‐up and shut‐down.A survey of the literature shows composition to be the controlling parameter for both temper embrittlement (TE) and hydrogen embrittlement (HE), in‐particular the presence of residual impurity elements such as P and the presence of elements such as Mo which nullify the effect of impurity segregation.Much information is available to describe embrittlement phenomena for Cr‐Mo steels. This paper reviews the mechanisms of TE and HE and describes a microstructural characterisation route which subsequently allows the structural integrity of potentially embrittled vessels to be examined for the purposes of remaining life assessment and plant life extension.
A THEORETICAL AND EXPERIMENTAL STUDY OF ENVIRONMENTAL HYDROGEN‐ASSISTED SHORT FATIGUE CRACK GROWTH IN AN Al‐Li ALLOY
Authors: de Los Rios E. R. , Sun Z. Y. , Miller K. J. 
Published: April 2007

Abstract— The initiation and propagation of fatigue cracks in an Al‐Li 8090 alloy in a vapour environment of 0.6 M NaCl solution was investigated. A severe degradation of the resistance to short crack growth was exhibited. Preliminary work carried out to establish the susceptibility of the material to hydrogen embrittlement demonstrated a close correlation between the deformation mode of this alloy and hydrogen absorption. The combination of highly localized slip and highly localized hydrogen fugacity creates a high susceptibility to hydrogen‐assisted crack growth.On the basis of current micro‐mechanical models, it is suggested that hydrogen trapping induces a reduction of the friction stress acting in the crack tip plastic zone. Consequently, enhanced plasticity at the crack tip due to the decrease in friction stress leads to an increase in crack growth rate.An exact solution for a surface crack in a semi‐infinite plane is obtained based on a dislocation crack model. Using this solution a computer method is developed to calculate the time‐dependent short crack growth rate and fatigue lifetime. Both solutions show good correspondence with the experimental results.
MODIFIED CRACK CLOSURE INTEGRAL (MCCI) FOR 3‐d PROBLEMS USING 20‐NODED BRICK ELEMENTS
Authors: Narayana K. B. , George S. , Dattaguru B. , Ramamurthy T. S. , Vijayakumar K. 
Published: April 2007

Abstract— The Modified Crack Closure Integral (MCCI) technique based on Irwin's crack closure integral concept is very effective for estimation of strain energy release rates G in individual as well as mixed‐mode configurations in linear elastic fracture mechanics problems. In a finite element approach, MCCI can be evaluated in the post‐processing stage in terms of nodal forces and displacements near the crack tip. The MCCI expressions are however, element dependent and require a systematic derivation using stress and displacement distributions in the crack tip elements.Earlier a general procedure was proposed by the present authors for the derivation of MCCI expressions for 3‐dimensional (3‐d) crack problems modelled with 8‐noded brick elements. A concept of sub‐area integration was proposed to estimate strain energy release rates at a large number of points along the crack front. In the present paper a similar procedure is adopted for the derivation of MCCI expressions for 3‐d cracks modelled with 20‐noded brick elements. Numerical results are presented for center crack tension and edge crack shear specimens in thick slabs, showing a comparison between present results and those available in the literature.
RELATIONSHIPS BETWEEN THE J‐INTEGRAL AND THE CRACK TIP OPENING DISPLACEMENT FOR STATIONARY CRACKS IN WELDMENTS AT PLASTIC COLLAPSE
Authors: Joch J. , Ainsworth R. A. 
Published: April 2007

Abstract— Slip line field and finite‐element analyses for J and crack tip opening displacement, δt, at plastic collapse are performed for an idealised weldment. The relationship between these two quantities is shown to depend on the nature of the loading (tension or bending), the ratio of yield stresses in weld and base materials, and on the width of the weld compared to the remaining ligament ahead of the crack. Cases where the weldment behaves as a single weld material are determined. However, it is also shown that there is a significant range of cases where the base material yield stress governs the relationship between J and δt, at collapse, even when the crack is located in weld metal.It is shown that the relationship between J and δt, at plastic collapse only occurs at loads very close to the collapse load unless the crack is located close to the weld/base boundary or the weld width is small compared to the remaining ligament ahead of the crack. More generally, the weldment behaves as a single weld material in terms of the relationship between J and δt, and conventional fracture assessments using J or δt, are equivalent.
INTERACTION OF HIGH CYCLE FATIGUE AND CREEP IN 9%Cr‐1%Mo STEEL AT ELEVATED TEMPERATURE
Authors: Vašina R. , Lukáš P. , Kunz L. , Sklenička V. 
Published: April 2007

AbstractHigh‐cycle‐fatigue/creep experiments were performed on a 9%Cr‐1%Mo temperered marten‐site ferritic steel at 873 K in air. The stress ratio R=σmin/σmax ranged from‐1 (“pure” fatigue) to 1 (“pure” creep). The maximum stress σmax was kept constant at 240 MPa. The lifetime depends on the stress ratio R in a non‐monotonic way.In the stress ratio interval 0.6 < R < 1.0 both the creep strain rate and the lifetime are controlled by mean stress σmassof the stress cycle. In the stress ratio interval — 1 < R < 0.2 the lifetime is controlled by the stress amplitude na. The fatigue/creep interaction occurs in between these intervals.The fatigue/creep loading induces transformation of the tempered martensite ferritic structure into an equiaxed subgrain structure. The resulting subgrain size depends strongly on the stress ratio.
FATIGUE DAMAGE IN AUSTENITIC‐FERRITIC DUPLEX STAINLESS STEELS
Authors: Degallam S. , Sedwuki A. , Degallaix G. , Kruml T. , Polák J. 
Published: April 2007

AbstractFatigue damage in two austenitic‐ferritic duplex stainless steels, with the structure of a natural composite and different levels of nitrogen content, was studied in low‐cycle fatigue. Both steels show initial cyclic hardening followed by softening and a long stabilisation period. The cyclic stress‐strain curve increases with the nitrogen content while Manson‐Coffin curves of both steels intersect at medium fatigue lives. The study of the surface relief reveals intensive slip markings both in ferrite and in austenite. Their density is influenced by the nitrogen content. Both the intensity and density of the persistent slip band (PSB) markings are higher in the ferrite. Crack initiation was found to appear predominantly in PSBs in the ferritic grains at the low strain amplitudes, and in the ferritic and austenitic grains at the highest strain amplitudes. The level of the cyclic stress‐strain response and the fatigue lives are discussed in terms of the cyclic strain localisation and of the effect of texture and nitrogen content on the strength and fatigue damage. The increased strength of the austenitic phase, due to high nitrogen alloying, results in cyclic slip localisation in the ferrite, and the decrease of fatigue life, compared with the steel with the lower nitrogen content.
FATIGUE CRACK INITIATION LIFE PREDICTION IN HIGH STRENGTH STRUCTURAL STEEL WELDED JOINTS
Authors: Tricoteaux A. , Fardoun F. , Degallaix S. , Sauvage F. 
Published: April 2007

AbstractThe local approach method is used to calculate the fatigue crack initiation/early crack growth lives (Ni) in high strength structural steel weldments. Weld‐toe geometries, welding residual stresses and HAZ (heat affected zone) cyclic mechanical properties are taken into account in the Ni estimation procedure. Fatigue crack initiation lives are calculated from either a Basquin type or a Manson‐Collin type equation. The local (HAZ) stress and strain amplitudes and the local mean stress are determined from an analysis based on the Neuber rule and the Molski‐Glinka energy approach. The accuracy of the different methods is evaluated and discussed. Finally the previous methods are used with HAZ cyclic mechanical properties estimated from hardness measurements.
COMPARISON OF ANALYTICAL, NUMERICAL AND EXPERIMENTAL SOLUTIONS TO PROBLEMS OF DEEPLY CRACKED WELDED JOINTS IN BENDING
Authors: Burstow M. C. , Ainsworth R. A. 
Published: April 2007

AbstractThis paper presents analytical and numerical solutions to the analysis of welded specimens when loaded in three‐point bending, and compares the results with those obtained experimentally. In each case the crack is located within the weld material, and runs parallel to the weld. Two analytical models are presented for deriving limit loads using slip‐line field theory. Due to the welding process, the material behaviour in the weld‐base interface is complex, and this is described in the analytical solutions using a number of material zones. The analytical solutions also provide the η and d∞ coefficients which are used to determine the J and crack tip opening displacement (CTOD) parameters. These solutions are then compared with numerical results obtained using the finite element method.Good agreement is obtained between the numerical and analytical results, and it is shown that for overmatched specimens a better analytical solution can be obtained by using a slip‐line field geometry which passes predominantly through the base material. When the analytical η solutions are applied to the experimental results it is shown that, in the case of undermatched weldments, J can be used as a fracture characterising parameter, but it cannot be used in the case of an overmatched specimen.
NON‐PROPORTIONAL CYCLIC HARDENING OF POLYCRYSTALLINE MATERIALS
Authors: Sun S.‐G. , Hwang K.‐C. 
Published: April 2007

AbstractA previously proposed single crystal hardening law is applied to the prediction of responses of polycrystalline material under non‐proportional cyclic loading. In this paper, the Kroner, Budiansky and Wu model is adopted and the relevant numerical schemes for both the iteration related to the non‐proportional loading paths and the search of active slip systems are established. Two typical engineering materials: oxygen‐free, high‐conductivity (OFHC) copper and 316 stainless steel, which differ greatly from each other in microstructure, are used for predictions and comparisons with experiments. Loading paths include the symmetric tension‐compression cycle, the circular cycle and the rectangular cycle. The behaviour of 316 stainless steel, at both room and elevated temperature is modelled. Comparisons show that the predictions are in quantitative agreement with the corresponding experiments for all the cases mentioned above. In addition, comparisons of different single crystal hardening laws are also presented.
CONSTRAINT EFFECTS ON DUCTILE CRACK GROWTH IN CLADDED COMPONENTS SUBJECTED TO UNIAXIAL LOADING
Authors: Sattari‐Far I. 
Published: April 2007

Abstract A two‐parameter approach based on the J‐integral and the parameter h, the ratio of the hydrostatic stress to the effective stress, was examined for ductile crack growth in cladded specimens. A series of cracked specimen configurations were tested and analysed by FEM to study the crack‐tip constraint in different geometries. The test program consisted of homogeneous SEN specimens of a base material (A533‐B steel), homogeneous SEN specimens of a cladding material (stainless steel weldment) and cladded specimens containing surface cracks through the cladding. Some issues concerning the cladding/base interface were also discussed from the basis of metallographical and fractographical examinations.While the crack growth initiation of the investigated materials appeared to be insensitive to the crack‐tip constraints, the propagation of ductile crack growth was significantly influenced by crack‐tip constraints. The crack‐tip constraints in different specimen configurations could successfully be characterized by the parameter h. Prediction of crack growth along the crack fronts in two cladded specimens using the developed resistance laws accounting for constraint effects gave promising results.
THE INFLUENCE OF PLASTIC PRESTRAINING ON BRITTLE FRACTURE RESISTANCE OF METALLIC MATERIALS WITH CRACKS
Authors: Pokrovsky V. V. , Troshchenko V. T. , Kopcmsky G. A. , Kaplunenko V. G. , Fiodorov V. G. , Dragunov Yu. G. 
Published: April 2007

Abstract The purpose of the present work was to study the influence of different regimes of overloading of pressure vessel steels in different states which correspond to the steel properties at the beginning of a reactor operation and at different degrees of embrittlement (simulated by heat treatment). The experiments were performed on 25, 50 and 150 mm thick specimens with short and long cracks of various shape in the temperature range from 293 to 623 K corresponding to the service temperature range of those steels.The following factors were investigated contribution of different effects (residual stresses, strain hardening, crack tip blunting) into the enhancement of the brittle fracture resistance of steels after warm prestressing, stability of the positive warm prestressing effect during subsequent exposure of the steels to different service loading conditions; size effect on optimal regimes of thermo‐mechanical prestressing and on the brittle fracture resistance characteristics of the steels studied after warm‐prestressing. An approach is proposed to predict the increase in the brittle fracture resistance of steels with cracks after warm prestressing.
FRACTOGRAPHY AND ITS ROLE IN FRACTURE INTERPRETATION
Authors: Thompson A. W. 
Published: April 2007

AbstractFundamental understanding of fracture requires accurate interpretation of fractography. Examples are drawn from recent work on titanium aluminide alloys based on both Ti3Al and TiAl. Although the fracture mode in these alloys is often characterized as “cleavage”, in reality the fracture surfaces are neither entirely cleavage‐like, nor do the “cleavage” regions generally correspond to the classical description of cleavage. Implications of such fractographic observations, and of model fracture calculations, are discussed. Needs for further work to clarify fracture processes are also identified.
DYNAMIC CRACK PROPAGATION AND CRACK ARREST INVESTIGATED WITH A NEW SPECIMEN GEOMETRY: PART II: EXPERIMENTAL STUDY ON A LOW‐ALLOY FERRITIC STEEL
Authors: Iung T. , Pineau A. 
Published: April 2007

AbstractThe novel experiment developed in our Institute to investigate crack initiation, rapid crack propagation and crack arrest with one specimen, the ring test, was applied to a ferritic HSLA pipeline steel. The maximum crack speed achieved in these experiments was between 230 m/s and 1165 m/s. The fracture toughness at crack arrest, KIa, was determined by a static analysis of this specific test. In all cases, it was found that KIa was much lower than KIc. The values of KIa decrease when the maximum crack speed increases, the results being largely scattered. The fracture toughness at crack arrest is therefore not an intrinsic parameter of the material for a given temperature. Cleavage fracture obtained under these conditions is characterized by the existence of numerous cleavage microcracks, mechanical twins and unbroken ligaments. The decrease in fracture toughness when crack speed increases is related, using the Beremin or the RKR model, to the high strain rates at the tip of a rapid propagating crack. A model which takes into account the effect of unbroken ligaments left in the wake of a propagating crack is developed to account for the large values of KIa which were occasionally measured.
UNIFIED CORRELATIONS IN TRANSITION TEMPERATURES OF LOW ALLOY STEELS AND WELD METALS OF VARIOUS TOUGHNESSES
Authors: Ma H. , Zhu L. , Wang Z. 
Published: April 2007

AbstractFour types of toughness were measured over a range of temperatures using CVN, COD, 4PB and PCI specimens made of low alloy steels and weld metals. It was found that there were unified correlations in transition temperatures among the various toughness parameters which could be realized by the dependence of the yield strengths of the test materials on both temperature and strain rate.The intrinsic reason for the correlations could be attributed to local cleavage conditions, which control the ductile‐to‐brittle transition during ductile fracture processes, whether the specimens were notched or precracked, under static or dynamic loading conditions. It is suggested that the ductile fracture process itself was independent of test temperature, but the local cleavage condition remains to be more fully understood in future work.
SHORT FATIGUE CRACK GROWTH BEHAVIOUR IN WASPALOY AT ROOM AND ELEVATED TEMPERATURES
Authors: Smith R. A. , Liu Y. , Grabowski L. 
Published: April 2007

AbstractShort fatigue crack growth tests have been carried out at room and elevated temperatures using the nickel‐based superalloy known as Waspaloy. A fully automated computer controlled system has been developed and employed for controlling the testing and monitoring of the growth of freely initiated surface short cracks on smooth specimens. Surface cracks as small as 10 um in length have been detected and recorded at temperatures up to 700°C. Anomalous short crack propagation behaviour was observed when comparisons were made with the corresponding long crack behaviour. Some aspects of mechanical, microstructural and environmental effects on the short fatigue crack growth behaviour of the material are discussed.