bluuebunny/crossref_metadata_2025 huggingface dataset:
ANALYSES OF FOUR SYMMETRIC CORNER CRACKS IN ELASTIC PLATES
Authors: Zhao W.
Published: April 2007

Abstract— With the aid of the three‐dimensional weight function method stress intensity factors and crack opening displacements are determined for the problem of four symmetric quarter‐elliptical corner cracks in a rectangular plate or a bar, which is subjected to remote tension. A wide range of configuration parameters is investigated. When the relative crack size is small, the results agree very well with those of a single corner crack determined by the finite element method. The significant difference between four symmetric corner cracks and a single corner crack is also illustrated when the relative crack size is large.
CRACK INITIATION AND PROPAGATION BEHAVIOUR OF A HEAT‐TREATED CARBON STEEL IN CORROSION FATIGUE
Authors: Goto M. , Nisitani H.
Published: April 2007

Abstract— When estimating fatigue damage quantitatively it is important to clarify its physical basis. In this study, rotating bending fatigue tests of a heat‐treated 0.45% carbon steel were carried out in 3% NaCl solution, in order to clarify the physical basis of corrosion fatigue damage from successive observations of plastic replicas. The results show that corrosion pits are generated during the early stages of cycling, then most of them grow with further cycling until a crack is initiated from each corrosion pit. The initiation of corrosion pits from slip bands is observed only in the case when the stress range is relatively large, and in the range of stress for which slip bands are produced in air. After initiation of a crack, the crack propagates by frequent interactions and coalescence with other cracks. The growth rate of an especially small crack in NaCl solution is larger than that in air. However, the growth rate of a comparatively large crack is smaller in NaCl solution than in air.
CRACK PROPAGATION UNDER CYCLIC LOADING
Authors: Carpinteri Andrea
Published: April 2007

Abstract— The crack propagation of a semi‐elliptical surface flaw subjected to cyclic combined axial and bending loadings with constant amplitude is numerically examined according to Paris‐Erdogan law. The critical crack, for which a given number of cycles is necessary to cause fatigue failure, can be determined from interaction between the theoretical results obtained and the experimental data of the Wöhler curves. Some examples are presented for different stress ranges Δσt and loading eccentricities given by e=M/F, where F and M are the axial force and the bending moment, respectively.
THE EFFECT OF INTERMEDIATE HEAT TREATMENTS ON OVERLOAD INDUCED RETARDATIONS DURING FATIGUE CRACK GROWTH IN AN Al‐ALLOY
Authors: Ling M. R. , Schijve J.
Published: April 2007

Abstract— Crack growth fatigue tests were carried out on 2024‐T3 specimens. Constant‐amplitude loading was periodically interrupted by 10 overload cycles. Intermediate heat treatments (T4) were applied to remove the residual stress in the crack tip zone and the crack closure wake behind the crack tip. Retardation effects induced by crack closure due to the previous load history were fully erased by the heat treatments. Overload effects were easily introduced again by new overload cycles afterwards. Crack growth rate results and fractographic observations indicate that primary crack tip plastic deformation (in virgin material) is more effective for crack extension than secondary plastic deformation in an existing plastic zone. This conclusion is significant for cycle‐by‐cycle crack growth prediction models for variable‐amplitude loading.
CRACK GROWTH AND CLOSURE BEHAVIOUR OF SURFACE CRACKS UNDER AXIAL LOADING
Authors: Kim Jong‐Han , Song Ji‐Ho
Published: April 2007

Abstract— Crack growth and closure behaviour of surface cracks in 7075‐T6 aluminium alloy are investigated under axial loading, noting the difference in fatigue growth behaviour at the maximum crack depth point and at the surface intersection point and also with through‐thickness crack growth behaviour. The plane strain closure response at the point of maximum depth of a surface crack is monitored using an extensometer spanning the surface crack at the midpoint of its length. The plane stress closure at the surface intersection point is observed by multiple strain gauges placed at appropriate intervals ahead of the crack tip and continuously monitored without interrupting the fatigue test. The crack opening ratio is found to be about 10% greater at the maximum depth point than at the surface intersection point. Under axial loading, the difference in plane strain crack closure behaviour between the surface crack and the through‐thickness crack is relatively small. Growth rates of surface cracks can be well described by the effective stress intensity factor range based on the closure measurements made in this study. The growth rates in terms of the effective stress intensity factor range seem to be slightly slower in surface cracks than in through‐thickness cracks.
FATIGUE LIFE ESTIMATION IN RESISTANCE SPOT WELDS: INITIATION AND EARLY GROWTH PHASE
Authors: Sheppard Sheri D. , Strange Michael
Published: April 2007

Abstract— The main objective of this research is to develop a model of fatigue crack initiation and early crack growth in resistance spot welds that is specimen independent. This objective is achieved by examining the stress state around a resistance spot weld. A general expression for the structural stress around the weld is formulated that is dependent only on the loading immediately surrounding the weld. As such, it is specimen independent.

An additional objective is to explore the feasibility of applying this fatigue crack initiation model of life estimation using structural response data from finite element analysis (FEA). This numerical technique is often used for evaluating structural integrity of assemblies. Limited verification examples show that the structural stress range as calculated from FEA reaction load data is capable of describing fatigue crack initiation and early crack growth in cyclically loaded resistance spot welds.
SOME OBSERVATIONS ON CREEP CRACK INITIATION FROM NOTCHES
Authors: Ellison E. G. , Kobayashi M.
Published: April 2007

Abstract— Tests have been carried out on a 1 Cr‐Mo‐V steel at 565°C to describe creep crack initiation in two notched geometries. From metallographic observation the initiation times were observed to be approx. 8 and 13% of rupture lives for the sharp slit and blunter notch shapes, respectively. Based on only a few tests a relationship between the initiation time ti and the creep crack parameter J* was found to be of the form ti(J*)0.67= constant.
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

The 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.
THE EFFECT OF STRESS RATIO ON THE FATIGUE THRESHOLD CONDITION OF PHYSICALLY SMALL CRACKS
Authors: Lal D. N.
Published: April 2007

An approach is proposed to predict the intrinsic threshold of physically small cracks without invoking crack closure considerations. The basic assumption invoked is that a ΔK representation is valid for short cracks, hence the lower‐bound threshold value, ΔK0(s)(min) for short cracks can be numerically equated with the lower‐bound threshold value of long cracks, ΔK*0(l)(min), s of the same material. Several experimental observations provide a basis for this rationalization. The approach allows a quantitative prediction of stress ratio and crack length dependence of ΔK0(S) which provides good agreement with experimental data for several low‐strength steels and aluminium alloys. This alternative procedure may be found useful in design applications.
FATIGUE CRACK GROWTH UNDER BIAXIAL LOADING
Authors: Lam Y. C.
Published: April 2007

Fatigue crack growth under biaxial loading for long cracks subjected to low cyclic stress levels was investigated. The biaxial stress ratio λ ranging from ‐0.5 to + 1.0 was considered. The strain energy density factor range was used as the criterion for predicting the crack growth rates and crack path. The agreement between prediction and experimental results was reasonable for crack growth rates and marginal for crack paths. The investigation highlighted the inherent difficulties for crack path prediction and indicated the increased sensitivity to initial crack angle and biaxial stress ratio when the biaxial stress ratio approaches unity.
FATIGUE STRENGTH EVALUATION FROM SURFACE YIELDING DATA
Authors: He J. , Wang H. , Nan J.
Published: April 2007

Surface yielding was detected by X‐ray diffraction. The surface yield strength s̀sy was significantly less than the bulk yield strength, and depends on the physical state and roughness of the surface. However s̀sy does not change with changes in surface residual stress. Determination of surface yielding, measured under static loading, indicates that a remarkable number of grains have been plastically deformed at the s̀sy stress level, which will result in damage accumulation under cyclic loading. Crack initiation predominates at the level of the fatigue endurance life for smooth parts and experiments indicate that s̀sy equals the smooth specimen fatigue limit, particularly that associated with a high survival probability.
CREEP‐FATIGUE CRACK GROWTH AND FRACTOGRAPHY OF METALLIC MATERIALS IN AIR AND VACUUM AT ELEVATED TEMPERATURES
Authors: Koterazawa Ryoichi
Published: April 2007

Creep‐fatigue crack growth behaviour of a Type 304 stainless steel, a quenched 21/4Cr‐1Mo steel, Hastelloy X, a Ti‐6242 alloy, and a low carbon steel under different reversed loading patterns (P‐P, C‐P and C‐C) were investigated in air and a vacuum environment. The results are discussed in the light of fracture mechanics and fractography. Crack growth rates for all of the materials tested were successfully correlated in terms of the cyclic J integral range (ΔJ) irrespective of the loading patterns. In the low growth rate region, where fatigue fracture was predominant, crack growth rates of all the materials were about the same for the same value of ΔJ. On the other hand, growth rates were somewhat different, depending on the creep ductility of the material in the region of high growth rate, where creep fracture was predominant. Materials with lower ductility exhibited higher growth rates for the same ΔJ values. Differences were insignificant between the crack growth rates in air and vacuum and were consistent with the small differences observed in the fracture surface morphology in the two environments.
A NORMAL DISTRIBUTION OR A WEIBULL DISTRIBUTION FOR FATIGUE LIVES
Authors: Schijve J.
Published: April 2007

The 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

This 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

Generally, 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.
A PATH‐INDEPENDENT PARAMETER FOR FATIGUE UNDER PROPORTIONAL AND NON‐PROPORTIONAL LOADING
Authors: Wang C. H. , Brown M. W.
Published: April 2007

Abstract— A path‐independent multiaxial fatigue damage criterion is proposed based on critical plane concepts: fatigue crack growth is controlled by the maximum shear strain, and an important secondary effect is due to the normal strain excursion over one reversal of the maximum shear strain. The effect of loading path on fatigue endurance is quantified by the normal strain excursion. Only one multiaxial material constant is required in the model which can be determined from uniaxial test data plus one torsional result. The parameter can be easily integrated with a shear strain‐life relationship to predict low cycle fatigue lifetime. Experimental data of four different materials: En15R steel, 1% Cr‐Mo‐V steel, 304 stainless steel, and 316 stainless steel at two temperatures were used to verify the criterion. It is shown that the proposed parameter can satisfactorily correlate test results for various proportional and non‐proportional straining paths.
DETECTING SMALL FATIGUE CRACKS BY ACOUSTIC MICROSCOPY
Authors: Pan J. Z. , Jenkins P. J. , de los Rios E. R. , Miller K. J.
Published: April 2007

Abstract— The acoustic microscope has shown great potential for use in fatigue experiments. A comparison between acoustic and optical images of fatigued Aluminium Lithium alloy specimens shows that the acoustic microscope has the ability to monitor very small cracks. Since it is easy (a) to find cracks and to locate their tips, (b) to detect damage ahead of a crack tip, (c) to distinguish cracks from slip bands and (d) to monitor the coalescence of cracks, the acoustic microscope can now be used with increasing confidence for obtaining data and understanding the mechanisms involved in metal fatigue.
SHORT FATIGUE CRACK GROWTH IN PLAIN AND NOTCHED SPECIMENS OF AN 8090 Al‐Li ALLOY
Authors: Pan Jia Zhen , de Los Rios E. R. , Miller K. J.
Published: April 2007

Abstract— Fatigue tests on notched and plain specimens were carried out under a combined acoustic and optical microscope. Crack initiation in plain specimens occurs invariably at inclusions which act as sites of stress concentration. Short crack propagation behaviour shows the usual pattern of accelerations and retardations associated with microstructural variations. Growth can only be sustained if the applied stress is sufficiently high to overcome the microstructural barriers. For the notched specimens the extent of the notch tip and crack tip plastic zone sizes control crack propagation. A short crack will continue to propagate only if its own plastic zone can sustain growth as the crack tip extends beyond the notch zone, otherwise it becomes non‐propagating. Notch plastic zones are calculated using both approximate and accurate solutions. Some microstructural effects are discussed.
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.
HIGH TEMPERATURE ELASTIC‐PLASTIC SMALL CRACK GROWTH BEHAVIOR IN A NICKEL‐BASE SUPERALLOY
Authors: Rosenberger A. H. , Ghonem H.
Published: April 2007

Abstract— An experimental study of the elastic‐plastic fatigue behavior of small surface cracks in Alloy 718 at 650°C was conducted under conditions of total strain control. During cycling, the crack growth was continuously monitored using a direct current potential drop technique while the influence of crack closure was monitored using a laser interferometry technique measuring the crack mouth opening displacement. The crack tip plastic zone size was also measured using a post‐test delta phase decoration technique. Results show that the growth rates of the small cracks correlate well with long crack LEFM data when using an appropriate elastic‐plastic driving force parameter. The anomalous crack growth rates observed in some experiments were found to be experimental transients dominated by the crack initiation fracture and do not represent an intrinsic behavior of Alloy 718. No contribution to the anomalous small crack growth could be attributed to either crack closure or enhanced crack tip plasticity.
A CRITERION FOR INTERGRANULAR BRITTLE FRACTURE OF A LOW ALLOY STEEL
Authors: Kantidis E. , Marini B. , Pineau A.
Published: April 2007

Abstract— The intergranular brittle fracture behaviour of a A533 B Cl 1 steel was investigated by applying a temper embrittlement heat treatment to simulate the presence of local brittle zones (ghost lines) in the as‐received material. This heat treatment produced an embrittled material that failed by an intergranular mode at low temperature. An increase in the Charpy transition temperature and a significant decrease in fracture toughness were observed in the embrittled steel as compared to the as‐received material. Tensile tests on smooth specimens and on notched bars were carried out to determine the critical stress corresponding to brittle intergranular fracture and to investigate the scatter in the results. It is shown that the mean value of the critical stress seems to be an increasing function of temperature. A statistical model, the Beremin model, initially proposed to describe brittle cleavage fracture was applied to intergranular fracture. Modifications are introduced in this model to take into account the temperature dependence of the critical stress. It is shown that this modified model is able to predict the temperature dependence of fracture toughness and the scatter in the experimental results.
AN ELASTIC‐PLASTIC MODEL FOR FATIGUE CRACK GROWTH AT NOTCHES
Authors: Ahmad H. Y. , Yates J. R.
Published: April 2007

Abstract— The development of an elastic‐plastic fracture mechanics model for predicting fatigue crack growth rates in notched specimens is presented in this paper. The model is based on experimental short and long crack growth results from un‐notched specimens and the distribution of strain ahead of the notch root. This approach may be applied to the assessment of the lifetime of many high technology engineering components.
ANALYZING DUCTILE FRACTURE USING DUAL DILATIONAL CONSTITUTIVE EQUATIONS
Authors: Zhang Z. L. , Niemi E.
Published: April 2007

Abstract— By adopting a suggestion made by Thomason, a new failure criterion for the Gurson‐Tvergaard model has been recently introduced by the authors. In this study, a method based on the Gurson‐Tvergaard constitutive model and the new failure criterion is applied to the analysis of ductile fracture. The main features of the method are that the material failure is a natural process of the development of Thomason's dual dilational constitutive responses, and the void volume fraction corresponding to the failure by void coalescence is not necessarily a material constant and is not needed to be fitted beforehand. Furthermore, void nucleation parameter(s) can be numerically fitted from experimental tension results. This method has been implemented into the ABAQUS finite element program via a user material subroutine and is applied to the prediction of tension problems conducted by the authors. In the analyses, two strain‐controlled void nucleation models have been studied and compared. The void nucleation parameters corresponding to the two models have been calibrated. The crack initiation of both smooth and notched axisymmetric tensile specimens are well predicted by the method. Finally, several critical issues in the analysis of ductile fracture are discussed.
RELIABILITY OF METAL COMPONENTS IN FATIGUE: A SIMPLE ALGORITHM FOR THE EXACT SOLUTION
Authors: Bargmann H. , Rüstenberg I. , Devlukia J.
Published: April 2007

Abstract— An efficient and accurate method for computing the fatigue‐life distribution of metal structures is presented. The problem is governed by the basic equations of the Coffin‐Manson‐Neuber local‐strain fatigue theory for notched components. The coefficients of fatigue strength and fatigue ductility, the fatigue notch factor as well as the nominal‐stress amplitude may be random variables with an arbitrary joint distribution. In order to arrive at a direct solution for the fatigue‐life distribution, hence an assessment of the reliability of a component, a collocation method has been developed which gives the total‐strain amplitude as an explicit function of the stress amplitude and the fatigue notch factor. This explicit equation has very close conformity to the corresponding, true, implicit equation. The fatigue‐life distribution is finally expressed in a multiple‐integral closed form. A simple algorithm termed the “complete‐probability fast integration” (CPFI) is developed which gives the exact solution, to any desired accuracy, for the entire ranges of fatigue‐life and reliability. CPFI is superior when compared to the results and procedures of the approximate methods currently employed.
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.
ELASTIC BRIDGING FOR MODELING FATIGUE CRACK PROPAGATION IN A FIBER‐REINFORCED TITANIUM MATRIX COMPOSITE
Authors: Nguyen T.‐H. B. , Yang J.‐M.
Published: April 2007

Abstract— A model based upon linear elastic bridging and fiber crack tip shielding is proposed for predicting fatigue crack growth in a SCS‐6/Ti‐6–4 composite. The model is characterized by the fiber/matrix debond length rather than the fiber/matrix interfacial frictional shear strength used in most current fatigue models. Finite elements combined with fracture mechanics are applied for computing the local stress intensity. The local stress intensity in the matrix is then utilized to predict crack growth in the composite via comparison to monolithic fatigue crack propagation data for a similar Ti‐6–4 matrix material.
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.
FATIGUE LIFE PREDICTION OF HEAT‐TREATED CARBON STEELS AND LOW ALLOY STEELS BASED ON A SMALL CRACK GROWTH LAW
Authors: Goto M. , Nisitani H.
Published: April 2007

Abstract— Since heat‐treated high strength steels are often used as materials for machines and structures that operate under severe service conditions, it is important to evaluate their fatigue life. Hence the growth law of a small fatigue crack must be known in order to estimate the fatigue life of machines and structures since the life of such members is controlled mainly by the behaviour of a small crack. The growth rate of a small crack can not be predicted usually by linear elastic fracture mechanics, but can be determined uniquely by the term σnal, where σa is stress amplitude, l is crack length and n is a material constant. In this paper, the small‐crack growth law of heat‐treated carbon steels and low alloy steels was studied. An effective and convenient method based on a small‐crack growth law, dl/dN=C3(σa/σa)nl is proposed, where σu is the ultimate tensile strength, for predicting the small crack propagation life of heat‐ treated steels with different tensile strength levels, together with a method for determining the fatigue life of plain members.
THE INFLUENCE OF NOTCH PLASTICITY ON SHORT FATIGUE CRACK BEHAVIOUR
Authors: Ahmad H. Y. , de los Rios E. R. , Yates J. R.
Published: April 2007

Abstract— A study has been made of fatigue crack formation and growth at the root of different notch profiles in a structural steel subjected to fully reversed tension‐compression loading. The scale of stage I microstructural crack growth at notches decreased with increasing notch root strain and was comparable to the size of stage I cracks in shallow hourglass profile specimens at the same strain. Stage II crack growth rates were faster within the notch plastic field than in the elastic stress field of the bulk material.
CYCLIC PLASTICITY IN TYPE 316L AUSTENITIC STAINLESS STEEL
Authors: POLÁK J. , OBRTLÍK K. , HÁJEK M.
Published: April 2007

Abstract— The cyclic stress‐strain response of two heats of austenitic stainless steel 3 16L was experimentally studied under a wide range of cyclic plastic strain amplitudes. Three domains on the cyclic stress‐ strain curve were found. In the middle domain the plateau behaviour corresponds to fatigue softening. The domain at low plastic strain amplitudes is characterized by stabilized behaviour and the domain of the highest plastic strain amplitudes by continuous hardening. Individual domains were correlated with observed dislocation structures. The existence of the plateau can be related to the localization of the cyclic strain into persistent slip bands. A Manson‐Coffin plot of the material over a wide cyclic amplitude range is curved and can be approximated by a double logarithmic dependence.
REPRESENTATION OF CYCLIC PROPERTIES AND HYSTERESIS ENERGY IN α‐BRASS USING A CERTAIN CLASS OF ELASTIC‐PLASTIC MODELS
Authors: Kaleta J. , Ziętek G.
Published: April 2007

Abstract— The paper deals with the analytical representation of the cyclic stressstrain curve, the hysteresis loop and the hysteresis energy for a single‐phase α‐brass. The one‐ and two‐parameter elastic‐plastic models that were used were so chosen as to produce compatible representation of both the stress‐strain relationship and the hysteresis loop. The models were checked with experimental data. The specimens were tested in uniaxial tension‐compression (Rε=−1) under total strain amplitude control. The experiments covered a broad spectrum of lives from the low‐cycle region through to the high‐cycle regime, i.e. up to lives of N= 1 × 106 cycles. The adopted measurement method enabled the cyclic deformation curve, hysteresis loop and hysteresis energy to be determined independently. It was shown that the modifed Ramberg‐Osgood model is a good approximation to actual cyclic behaviour of α‐brass.
APPLICATION OF ENERGY DISSIPATION RATE ARGUMENTS TO STABLE CRACK GROWTH
Authors: Turner C. E. , Kolednik O.
Published: April 2007

Abstract—Energy dissipation rate,D, and crack tip opening angle (CTOA) have been related for large amounts of ductile crack growth in a fully plastic two‐dimensional model of real elastic plastic material. SeveralJ‐type risingR‐curves have been constructed and related, some based on the cumulative energy dissipated and some as a characterising term that relates closely to the far‐fieldJcontour value. These two meanings co‐exist but the relationship is geometry dependent. For deep notch bend (DNB) cases the non‐dimensional groupLα/r* (whereLis normalised load, α is CTOA andr* defines the position of the instantaneous centre of rotation) governs the value of dJ. Certain DNB cases whereR‐curves vary with size are resolved by this group rather than by CTOA itself whereas for centre‐cracked tension there is a higher value of CTOA than for DNB.
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.
AN ENGINEERING ASSESSMENT OF FATIGUE CRACK GROWTH OF IRREGULARLY ORIENTED MULTIPLE CRACKS
Authors: Tu S.‐T. , Dai S.‐H.
Published: April 2007

Abstract— Knowledge of the behaviour of interacting and irregularly oriented multiple cracks is very limited. The recharacterisation rules for such cracks are usually empirical. In order to provide more reasonable rules for an engineering assessment of fatigue growth of irregularly oriented multiple cracks, this paper first studies the mechanics of fatigue growth of two‐dimensional non‐coplanar cracks. Uniaxial and biaxial fatigue testing on specimens with various multiple cracks are then carried out. Possible errors in the assessment of the cracks using the current rules are discussed. An improved procedure for the fatigue life assessment is developed.
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

High‐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

Fatigue 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

The 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

This 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

A 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.
NOTCH EFFECT ON TWO‐LEVEL CUMULATIVE LOW‐CYCLE FATIGUE LIFE UNDER DIFFERENT BIAXIAL LOADING MODE SEQUENCES
Authors: Yip M.‐C. , Jen Y.‐M.
Published: April 2007

Abstract Two‐level cumulative low‐cycle fatigue lives of AISI 316 stainless steel notched specimens with different biaxial loading mode sequences were experimentally analyzed in this paper. Forty‐eight cases were conducted in the experimental program by considering the loading level sequence effect, the biaxiality of two levels and the cycle ratios. Results show that interlock effect caused by the characteristic fracture surfaces of the different biaxial states is beneficial to the cumulative fatigue lives. On the other hand, the tensile loading of the second level will accelerate the opening of cracks and decrease fatigue strength. Miner's rule predicts most fatigue lives within 30% error bands, and the loading level sequence effect was not found in this research involving complex fracture modes. Fractography of specimens in the cumulative fatigue tests is reported and discussed in this paper.
THE EFFECT OF ECCENTRIC LOADING ON THE STRESS DISTRIBUTION IN THREAD ROOTS
Authors: Burguete R. L. , Patterson E. A.
Published: April 2007

Abstract Three‐dimensional photoelasticity has been used to examine the effect of eccentric loading on the stress distribution along the helix of the roots of threaded fasteners. In the investigation the ratios of axial to bending stress were similar to those found commonly in engineering components. The results showed that, as the level of eccentricity increased, the maximum stress in helix of the thread root did not change significantly, but there was an increase in the length of helix which experienced high stress. This will lead to an increase in the probability of crack initiation and propagation in the presence of eccentric loading.
CRACK GROWTH MORPHOLOGY AND MICROSTRUCTURAL CHANGES IN 316 STAINLESS STEEL UNDER CREEP‐FATIGUE CYCLING
Authors: Gao N. , Brown M. W. , Miller K. J.
Published: April 2007

Abstract— A study into microstructural effects and crack growth behaviour of AISI type 316 stainless steel under creep‐fatigue conditions at 550°C within the high strain ranges of 0.9–2.5%, including a 60min hold time, was undertaken on a high‐temperature reverse‐bending rig. Throughout the tests, surface cracks on both the tensile‐hold and the compressive‐hold sides were monitored by means of a plastic‐strip replication technique. Additional investigations were conducted on failed specimens to examine the crack morphology in the depth direction, and to examine the function of oxidation; also to study changes of fracture surface morphology, changes in dislocation structures and precipitate configurations corresponding to the different strain ranges. These detailed analyses revealed that the predominantly intergranular long cracks on the tensile‐hold side and transgranular short cracks on the compressive‐hold side are dominant aspects of the investigation. The dislocation structures under creep‐fatigue conditions are strain‐range dependent, with a clearly defined cell structure at the higher strain ranges and dense dislocation tangles at lower strain ranges. The large reduction in creep‐fatigue endurance can be attributed to early crack growth and grain boundary cracking caused by stress relaxation, oxidation, precipitation and, most importantly, the coalescence of the many minor surface short cracks.
SHORT CRACK COALESCENCE AND GROWTH IN 316 STAINLESS STEEL SUBJECTED TO CYCLIC AND TIME DEPENDENT DEFORMATION
Authors: Gao N. , Brown M. W. , Miller K. J.
Published: April 2007

Abstract— A study has been undertaken into short crack growth behaviour of AISI type 316 stainless steel under creep‐fatigue conditions at 550°C within the high strain range of 0.9 to 2.5% and including a 60 min hold‐time. During the high‐temperature, reverse‐bending tests, surface crack initiation and growth on both the tensile‐hold and the compressive‐hold sides of circular‐section specimens were monitored by means of a plastic replication technique. Detailed analysis revealed that under creep‐fatigue conditions, the initiation and growth behaviour of many individual cracks and their subsequent coalescence to form a major Stage II (tensile) crack was the dominant feature in the failure process. A life prediction model is proposed which incorporates the process of short crack coalescence. Satisfactory predictions of creep‐fatigue lifetimes are derived from the model.