bluuebunny/crossref_metadata_2025 huggingface dataset:
A HIGH‐CYCLE FATIGUE CRITERION APPLIED IN BIAXIAL AND TRIAXIAL OUT‐OF‐PHASE STRESS CONDITIONS
Authors: Papadopoulos I. V.
Published: April 2007

A high‐cycle fatigue criterion suitable for multiaxial non‐proportional stress loading is proposed in this paper. The criterion is based on some microscopic considerations related to the crystalline structure of metals. The purpose of the present paper is mainly the application of this criterion in two loading cases: (a) biaxial loads involving two normal stresses or one normal and one shear stress, and (b) triaxial load with two normal stresses and one shear stress. Stress states of these kinds are very common in piping assemblies. Application of the proposed criterion in the case of triaxial loading, where the three stress components are of the same frequency, but out‐of‐phase, leads to a simple analytical formula. This formula is the equation of a bounding surface that delimits in the space of the above three stresses the safety domain against fatigue crack initiation. A remarkable theoretical result concerns the phase difference of the shear stress, which does not appear in the derived formula. Consequently, according to our proposal the safety domain (i.e. the limiting fatigue endurance) under combined out‐of‐phase biaxial normal stress loading and torsion is independent of the phase difference of the torsion. Obviously this result holds also for the simpler case of axial load and torsion. On the contrary the phase difference between the two normal stresses has a strong detrimental effect on the fatigue endurance of a metal. As is shown these theoretical conclusions are in good agreement with fatigue limit test data found in the scientific literature.
COMPENDIUM OF T‐STRESS SOLUTIONS FOR TWO AND THREE DIMENSIONAL CRACKED GEOMETRIES
Authors: Sherry A. H. , France C. C. , Goldthorpe M. R.
Published: April 2007

Conventional theories of fracture assume that the state of stress and strain in the vicinity of a crack tip, and so the onset of failure, is characterised by a single parameter. The physical extent of these single‐parameter fields is determined by the geometry, size and mode of loading of the engineering structure or test specimen containing the crack. It is now recognised that fracture toughness is a material property characterised by a single parameter J only in special circumstances which involve a high degree of constraint at the crack‐tip. In general the apparent toughness of a material changes according to the shape and size of the cracked configuration and the mode of loading imposed.

Recent analytical, numerical and experimental studies have attempted to describe fracture in terms of both J and a second parameter. The reason for the second parameter is to provide further information, which J on its own is unable to convey, concerning how the structural and loading configuration affects the constraint conditions at the crack‐tip. One particular candidate parameter is the elastic T‐stress which is directly proportional to the load applied to the cracked geometry. This paper brings together published solutions for the T‐stress for a range of two and three‐dimensional cracked geometries and presents some new results calculated at AEA Technology.

The application of two‐parameter fracture mechanics is a subject of ongoing development and users of the data in this paper are recommended to seek expert advice regarding applications to specific structural integrity assessments.
ELECTRICAL RESISTANCE VARIATIONS ACROSS A GROWING FATIGUE CRACK AS A FUNCTION OF THE LOAD CYCLE
Authors: Riddell P. J.
Published: April 2007

Greater understanding of fatigue crack growth requires detailed measurements of crack tip plastic flow. A high resolution crack length measurement system based on the electrical potential method has been used to measure the variations in electrical resistance of specimens containing growing fatigue cracks. Crack growth increments caused by individual load cycles could be resolved down to a size of 0.1 μm. The electrical resistance has been found to vary cyclically as a function of the applied load. These variations are consistent with Bowles' observations that the crack initially grows with a very sharp crack tip followed by plastic blunting which is resharpened during unloading. Crack closure effects could be observed in the results generated from tests conducted with stress ratios of 0 and 0.1, but not for a test with a stress ratio of 0.5.
FATIGUE LIFE AND SURFACE CRACK PENETRATION BEHAVIOUR OF AN ALUMINIUM ALLOY
Authors: Nam K. W. , Iwase K. , Ando K.
Published: April 2007

Fatigue life and crack retardation behaviour after penetration were examined experimentally using CT specimens and surface pre‐cracked specimens of aluminium alloy 5083‐0. The fatigue crack shape before penetration is almost semicircular, and the measured aspect ratio is larger than the value obtained by calculation using K values proposed by Newman‐Raju. It was found that crack growth behaviour on the back side after penetration is unique, and can be divided into three stages. The Wheeler model retardation parameter was used successfully to predict crack growth behaviour after penetration. By using a crack propagation rule, the change in crack shape after penetration can be evaluated quantitatively.
FATIGUE OF A HIGHLY PRESTRAINED DUAL‐PHASE SHEET STEEL
Authors: Gustavwn A. , Melander A.
Published: April 2007

The effect of prestraining by 15‐30% and ageing on the fatigue properties of a cold‐rolled high‐strength dual phase sheet steel was investigated. Prestraining was performed before machining the fatigue specimens and was carried out in uniaxial as well as biaxial tension. Fatigue testing was carried out under fully reversed strain control and both the cyclic stress‐strain behaviour and the fatigue lives were recorded.

Significant fatigue strength improvements by up to 50% were noted for the prestrained material as compared to the as‐received condition. During fatigue testing in uniaxially prestrained conditions, the occurrence of mean stresses was noted. These mean stresses were persistent when testing at levels corresponding to longer fatigue lives. Taking into account an estimation of these mean stresses and the increase of monotonic strength, modelling of fatigue resistance for the prestrained materials shows fairly good correlation with experimental results.
EFFECT OF SHOT PEENING ON RESIDUAL STRESS AND FATIGUE LIFE OF A SPRING STEEL
Authors: Farrahi G. H. , Lebrijn J. L. , Couratin D.
Published: April 2007

This study describes shot peening effects such as shot hardness, shot size and shot projection pressure, on the residual stress distribution and fatigue life in reversed torsion of a 60SC7 spring steel. There appears to be a correlation between the fatigue strength and the area under the residual stress distribution curve. The biggest shot shows the best fatigue lie improvement. However, for a shorter time of shot peening, small hard shot showed the best performance. Moreover, the superficial residual stresses and the amount of work hardening (characterised by the width of the X‐ray diffraction line) do not remain stable during fatigue cycling. Indeed they decrease and their reduction rate is a function of the cyclic stress level and an inverse function of the depth of the plastically deformed surface layer.
EXTENDING THE FATIGUE LIFE OF MULTI‐LAYER METAL JOINTS
Authors: Finney J. M. , Evans R. L.
Published: April 2007

Abstract The influences of both hole cold expansion and interference‐fit fasteners for extending the fatigue life of multi‐layer aluminium alloy joint specimens under variable‐amplitude loading have been examined experimentally. Improvements in fatigue life were markedly dependent on the degree of load transfer in the specimen joint. Secondary bending in the joint also had a major influence, reducing the effectiveness of these life improvement techniques. Depending on the joint configuration, improvements in fatigue life ranged from nothing at all to a factor of about 40. Fretting appeared to be involved in the initiation of all cracks and where this occurred on faying surfaces only small, if any, improvements in fatigue life were obtained.
TIME‐DEPENDENT FATIGUE CRACK GROWTH IN TITANIUM METAL MATRIX COMPOSITES
Authors: Zhang T. , Ghonem H.
Published: April 2007

Abstract The interaction of fatigue and creep in a titanium metal matrix composite was studied by employing loading frequencies of 10 Hz (in both air and vacuum environment) and 0.1 Hz with and without hold times (in air) at 500°C. It was shown that, for the same loading frequency, the crack growth rate is lower in vacuum than in air. In an air environment, however, where the influence of load‐related creep and environmental effects exist, it was shown that a decrease in the loading frequency leads to a decrease in the crack growth rate. This behavior is interpreted in terms of the redistribution of fiber and matrix stresses occurring in response to the creep‐related relaxation of matrix stresses. The result of this stress redistribution is the generation of a compressive axial residual stress in the matrix phase in the region of the composite ahead of the crack tip. As the crack bridges the fibers in this region, the release of the matrix residual compressive stress leads to the closure of the matrix fractured surfaces at the crack tip, thus leading to a decrease in the crack tip driving force. To support this concept, experimental measurements of the crack opening displacement at different loading frequencies are presented. In addition, a simple model is proposed to describe the nature of the residual stresses developed in the matrix phase during cyclic loading. Results of this model have been examined using finite element analysis. The influence of time‐dependent effects during a fatigue cycle was, furthermore, investigated by carrying out high frequency fatigue tests on specimens which have been previously subjected to creep deformation. Results of these tests in terms of the crack growth rate and associated crack closure, support the conclusion that a predeformed matrix produces a decrease in the crack growth rate of the corresponding composite.
FATIGUE CRACK GROWTH UNDER MODE II LOADING
Authors: Wang M. O. , Hu R. H. , Qian C. F. , Li J. C. M.
Published: April 2007

Abstract— The behavior of fatigue crack growth for low and medium carbon steels, an austenitic stainless steel and an aluminum alloy under pure Mode II loading was investigated experimentally, using cruciform specimens. The results show that under pure Mode II loading, fatigue crack propagation has three possibilities, namely, bifurcation into two branches, propagation along the original Mode II direction, and the mixture of these two situations, depending on the material. The growth rate da/dN vs. ΔKII relation for Mode II propagation is similar to a Pans type law for Mode I growth. Fractographic observations by optical microscopy and SEM were made also on all specimens tested. When a crack branched, striations parallel to the crack front which were often associated with Mode I fatigue crack growth were observed and long marks parallel to the crack propagation direction were also found for slanted fracture surfaces. When a crack propagated along the original Mode II direction, many frictional marks parallel to the crack propagation direction were observed.
PREDICTING FATIGUE LIFE IN COMMERCIALLY PURE ALUMINIUM USING A SHORT CRACK GROWTH MODEL
Authors: Turnbull A. , De Los Rios E. R.
Published: April 2007

Abstract— Advances in manufacturing techniques and improvements in non‐destructive inspection procedures have reduced the size of initial defects in fatigue‐critical components to the scale of the microstructure. Unfortunately, the growth of these so‐called short fatigue cracks is not properly characterised by conventional linear elastic or elastic‐plastic fracture mechanics. However, the Navarro‐de los Rios crack growth model does account for many aspects of their growth and has proved successful in predicting fatigue life of medium carbon and C‐Mn steels. In consequence, the growth of short fatigue cracks in commercially pure aluminium, under fully reversed uniaxial loading, has been studied, using a plastic replication technique and modelled, using the Navarro‐de los Rios crack growth equation. The predicted lifetimes are in good agreement with the actual experimental lifetimes, and compare favourably with predictions based on two previously reported crack growth models.
FATIGUE LIFE DISTRIBUTION AND GROWTH OF CORROSION PITS IN A MEDIUM CARBON STEEL IN 3%NaCl SOLUTION
Authors: Nakajima M. , Tokaji K.
Published: April 2007

Abstract— Statistical fatigue tests have been conducted on a structural medium carbon steel, S45C, in room air and in 3%NaCl solution, using five cantilever‐type rotary bending fatigue testing machines which were specially manufactured for the purpose of the present study. Fatigue life distribution was examined at three and five stress levels in air and in 3%NaCl solution, respectively, and twenty specimens were allocated to each stress level. In room air, it was found that fatigue life distributions followed the three‐parameter Weibull distribution, which were closely related to fracture morphology. In 3%NaCl solution, they also followed the Weibull distribution, but the scatter in fatigue life was smaller in comparison to that in air. It is suggested that the decrease in the scatter of fatigue life may be attributed to a smaller fraction of crack initiation life in 3%NaCl solution. The growth of corrosion pits was investigated using a laser microscope. The distribution of corrosion pit depths followed the log‐normal distribution, and the corrosion pit depths increased with increasing time or the number of cycles. It was found that the growth of corrosion pits was accelerated by stress cycling and the depths increased with increasing stress level. Based on these results, a growth law of corrosion pits, including the effect of stress cycling, is proposed.
FORMATION OF HYDROGEN‐ASSISTED INTERGRANULAR CRACKS IN HIGH STRENGTH STEELS
Authors: Yatabe H. , Yamada K. , de Los Rios E. R. , Miller K. J.
Published: April 2007

Abstract— The fracture behaviour of high strength steels under the influence of hydrogen was studied, with special emphasis on the critical condition for the formation of intergranular (IG) cracks. Mechanical tests were carried out on cathodically charged specimens subjected to both a constant load and a constant displacement under a variety of hydrogen‐charging conditions. Experimental analyses show that a high local hydrogen concentration plus a high stress intensity at a quasi‐cleavage (QC) crack tip are required to initiate intergranular cracking. The condition for continued intergranular crack propagation, leading to micro‐void coalescence (MVC), is determined by the combined effect of the speed of crack propagation together with the rate of hydrogen diffusion. A quasi‐cleavage crack triggers the onset of intergranular crack growth irrespective of the test control parameters, i.e. constant loading or constant displacement conditions.

A fracture map is proposed relating to the boundary conditions between QC, IG and MVC cracking, which will assist further research.
FATIGUE CRACK GROWTH FROM TWO‐DIMENSIONAL SURFACE DEFECTS
Authors: Shuter D. M. , Geary W.
Published: April 2007

Abstract The growth of semi‐elliptical cracks emanating from single surface defects under cyclic bending loading conditions has been investigated. Experiments to determine crack shape development during fatigue have been conducted on specimens containing spark‐machined starter defects of various shapes and sizes. The results appear to indicate that the size and shape of the initial starter defect only affects the developing crack shape until the crack depth is approximately 20% of the specimen thickness; upon reaching this depth, all crack shapes (independent of initial size and shape) appear to be very similar. A mathematical model, based on the Newman and Raju stress intensity solution for semi‐elliptical cracks, has been utilised to predict effectively the shape of the cracks developing from the various single starter defects with aspect (a/c) ratios as large as 3.
PASSIVATION EFFECTS ON CRACK CLOSURE IN THE FATIGUE CRACK PROPAGATION OF A PEAK‐AGED Al‐Li‐Zr ALLOY IN NaCl AND Na2SO4 SOLUTIONS
Authors: Chun Y.‐G. , Pyun S.I.
Published: April 2007

Abstract Fatigue cracking of a peak‐aged Al‐Li‐Zr alloy was investigated by measuring crack closure as a function of applied anodic potential in 0.6 M NaCl and 0.5 M Na2SO4 solutions with an unloading elastic compliance technique, and by comparison with crack closure in dry air. The present work involves complementary anodic behaviour of the Al‐Li‐Zr alloy in both solutions by potentiodynamic polarization and potentiostatic current transient experiments. From the repassivation rates in the passivation potential range in both solutions, it is indicated that a more stable passive film is formed at lower applied anodic potential than at higher applied anodic potential. The intrinsic fatigue crack propagation (FCP) rates under unstable passivation potential in both solutions were significantly larger than those obtained in dry air. Under stable passivation potential in both solutions, however, the intrinsic FCP rates in the low ΔKeff range were slightly lower than those obtained in dry air. The crack closure in the low ΔKeff range increased under stable passivation potential, in dry air and under unstable passivation potential. The high crack closures appearing in the low ΔKeff range were characterized by a tortuous fracture surface in dry air, and the occurrence of various crack paths such as rolling plane delamination under unstable passivation potential. The difference between environmental crack closures under stable and unstable passivation conditions is discussed in terms of environment‐assisted crack‐tip damage processes.
EFFECT OF STRESS STATE ON THE FAILURE MECHANISM AND FRACTURE OF AUSTENITIC STEEL UNDER THERMAL CYCLING CONDITIONS
Authors: Krajczyk A. , ŻUchowski R.
Published: April 2007

Abstract This study was aimed at assessing the influence of stress state upon the life of specimens as well as on the failure mechanisms under thermal cycling. The experiments were carried out on thin‐walled tubular specimens (made of austenitic steel). They were loaded in pure tension and in pure torsion as well as under complex loading. A constant value of an equivalent stress was obtained in each case. The influence of stress state on both the specimen life and the equivalent steady strain rate has been found. The Monkman—Grant failure criterion was used as a relationship between time to failure and equivalent steady strain rate. The analysis of the results obtained showed that the low proportion of the shear stress component in the equivalent stress does not change the values of constants in that failure criterion as is also the case for the Norton‐Bailey law. The prevalence of the shear stress component is a cause of a significant change in the coefficient of the Monkman‐Grant failure criterion while the exponent remains constant for all examined stress states. Initiation and propagation of cracks as well as their surface character were found to be affected by the stress state.
IN SITU SEM MEASUREMENTS OF CRACK CLOSURE FOR SMALL FATIGUE CRACKS IN ALUMINIUM 2024‐T351
Authors: Hallday M. D. , Poole P. , Bowen P.
Published: April 2007

Abstract Crack closure has been measured for a range of small, self‐initiated fatigue cracks using in situ SEM loading. Cracks were grown at positive R ratios in the aluminium alloy 2024‐T351 and at nominal ΔK levels that extend substantially below the corresponding long crack threshold. The crack closure stress of the small cracks decreased and the Kcl level increased with increasing crack size until the long crack value near threshold was reached. For cracks of depth larger than about one grain size, a good correlation was obtained between small and long crack growth rate data in terms of ΔKeff
PROPAGATION BEHAVIOUR OF SHORT FATIGUE CRACKS IN Q2N STEEL
Authors: Wu X. J. , Akid R.
Published: April 2007

Abstract— The work described in this paper characterizes short fatigue crack growth behaviour of Q2N steel having a complex microstructure and designated for pressure vessel and offshore structure applications. Short and long fatigue crack growth tests for this steel were conducted under three point bend loading conditions. It was found that, in the initial stages of growth, short cracks propagate much faster than those of long cracks when correlated with the linear elastic fracture mechanics (LEFM) parameter ΔK. A period of crack growth retardation was observed at crack lengths of approx 50 μm. The theory of the interaction between short cracks and grain boundaries fails to predict the occurrence of this deceleration minima. A new short crack deceleration mechanism is proposed based on experimental observation. Observation of the characteristic behaviour of short cracks allowed the development of a short crack growth model based on microstructural fracture mechanics analyses.
FRACTOGRAPHIC ANALYSIS OF FATIGUE CRACK GROWTH IN ENGINE COMPRESSOR DISKS OF Ti‐6Al‐3Mo‐2Cr TITANIUM ALLOY
Authors: Shanyavsky A. A. , Stepanov N. V.
Published: April 2007

Abstract—Fractographic features related to fatigue crack growth in a Ti‐6Al‐3Mo alloy are studied using compressor disks tested on a hydraulic test bed and which simulate operational multiaxial cyclic loading conditions. The hold‐time of a cycle results in the formation of a fracture relief which reflects mainly the two‐phase (α+β) lamellar structure of the titanium alloy and a fragmentary fatigue striation formation. Correlation between the number of fatigue striations on the fracture surface and the number of applied blocks of loading (imitating the service conditions of compressor disks) has been obtained. The hold‐time duration of the cycle does not affect the crack growth rate and the formation of the fracture relief in this material. An analytic expression is suggested to describe the relationship between fatigue striation spacing, δ, and the stress intensity factor KcI as applied to quarter‐ellipse‐shaped cracks; it is of the form δ= C[f(τ, FCi)KcI]4, where f(τ, FCi) accounts for the hold‐time, τ, and the programmed loading together with their influence on the fatigue crack growth behaviour. The particular threshold value of stress intensity factor (KcI) is established at 20 MPa m. The work indicates that the role of τ manifests itself via a considerable acceleration of crack growth.
ELEVATED TEMPERATURE FRACTURE OF PARTICULATE‐REINFORCED ALUMINUM PART I: FRACTURE TOUGHNESS
Authors: Somerday B. P. , Leng Yang , Gangloff R. P.
Published: April 2007

Abstract—The plane‐strain initiation and growth fracture toughnesses of powder‐metallurgy‐processed, SiC particulate‐reinforced 2009 plate were measured at temperatures from 25°C to 316°C. Initiation toughness from electrical potential monitoring (KJICi) is 18 MPa°m at 25°C, and is nearly constant to 220°C before decreasing sharply to 6 MPa°m at 316°C. Growth toughness, given by the tearing modulus (TR), is less than 3 from 25°C to 125°C, and increases dramatically above 200°C. The magnitude and temperature dependence of initiation toughness depend on detection of the critical fracture event. Standard measures of toughness KIC and KJIC exceed KJICi and increase to a plateau with increasing temperature. The fracture mode for the composite is microvoid nucleation, growth and coalescence at all temperatures. Void nucleation is associated with SiC; such particles both crack and create stress and plastic strain concentrations that rupture the interface or adjacent matrix, particularly at corners. Matrix plasticity and cavitation increase with increasing temperature. Void growth is regular at all temperatures, but limited by adjacent SiC particles. Both KJICi and TR are governed by the temperature‐dependent crack‐tip plastic stress and strain fields, and the intrinsic damage resistance of the composite microstructure.
AN APPROXIMATE METHOD FOR FATIGUE‐LIFE PREDICTION OF FRAMED STRUCTURES
Authors: Bolzon G.
Published: April 2007

The propagation of fatigue cracks in framed metal structures, usually described by Linear Elastic Fracture Mechanics, is analysed here and described by a numerical method based on classical beam theory. A procedure to be used in practice for the evaluation of stiffness degradation and energy release rate is presented. The procedure uses formulae which are explicitly given for statistically determinate beam structures that are being progressively damaged. If implemented into any beam‐oriented finite element code as shown here, the proposed approach allows one to deal also with redundant structures.
SOME ASPECTS OF FATIGUE CRACK GROWTH RETARDATION BEHAVIOUR FOLLOWING TENSILE OVERLOADS IN A STRUCTURAL STEEL
Authors: Shuter D. M. , Geary W.
Published: April 2007

Abstract— The effects of specimen thickness, stress intensity levels and R ratio following single tensile overloads, multiple overloads and overload/underload events have been investigated in a BS4360 Grade 50D steel. The amount of fatigue crack growth retardation increased with both decreasing applied baseline ΔK and increasing overload block size. Smaller increases in retardation were obtained for overload/underload block events compared with block overloads. The data suggests that crack flank plasticity resulting in crack closure adequately accounts for much of the observed behaviour. Near crack tip plasticity was thought to play a more important role in generating crack closure than that remote from the crack tip.
EFFECT OF A SINGLE PEAK OVERLOAD ON PHYSICALLY SHORT FATIGUE CRACK RETARDATION IN AN AXLE‐STEEL
Authors: Changqing Z. , Yucheng J. , Guangli Y.
Published: April 2007

Abstract— Experiments on the propagation behaviour of physically short fatigue cracks were conducted on an axle‐steel, using a direct current potential technique. Various overload ratios (OLR = 1.5, 1.7, 1.9 and 2.1) and different overload positions were employed. The experimental results show that physically short cracks are more sensitive to the overload retardation effect than long cracks. The overloads produce a beneficial effect when they are introduced early. Later overloads, although giving an increase in life, produce a smaller effect. The delay cycles ND due to the application of a single overload increase with increasing overload ratios. The experimental data, when plotted on a log‐log graph of ND/NCAL (where NCAL is the number of cycles under constant amplitude loading) versus overload ratio OLR, gives a straight line relationship, namely ND/NCAL= 2.81 × 10−3(OLR)10,12.
FATIGUE CRACK GROWTH UNDER THE CONJOINT ACTION OF MAJOR AND MINOR STRESS CYCLES
Authors: Hawkyard M. , Powell B. E. , Hussey I. , Grabowski L.
Published: April 2007

Abstract— Fatigue crack growth rates in corner notched specimens of forged Ti‐6A1‐4V, used in the manufacture of rotating aero‐engine components, have been measured for fatigue loadings that combine major and minor stress cycles. The loadings are simple representations of the flight cycle and the potential in‐flight vibrations, each loading block consisting of high‐frequency minor cycles superimposed on the major cycle dwell at maximum load. The crack growth rates are dependent on the number and stress ratio of the minor cycles, but only when they individually contribute to the growth of the crack. Estimates of the fatigue threshold values and near‐threshold growth rates associated with the minor cycles have been made, all potential load history effects having been ascribed to the minor cycle component of the loading. Using this data, satisfactory crack propagation life predictions have been demonstrated for a wide range of test conditions involving the conjoint action of major and minor stress cycles.
THE INFLUENCE OF ENVIRONMENT UPON THE ACCUMULATION OF DAMAGE UNDER CORROSION FATIGUE CONDITIONS
Authors: Akid R.
Published: April 2007

Abstract— There is an increasing demand for an understanding of the effects of complex load history on fatigue lifetime since it is realised that constant‐amplitude S‐N endurance data may not be appropriate for the prediction of the lifetime of components subject to variable amplitude loading. However the amount of damage accumulated within a component during its lifetime is a function, not only of its' load history, but of the synergistic effects of stress and operating environment. In this respect the ability of a material to resist the damaging effects of electrochemical corrosion can play a major role in determining the ultimate lifetime of a component; the effect of corrosion being dependent upon the specific combination of material/environment, the rate of application of load and the duration of metal/environment contact. For conditions where applied loads are below the fatigue or endurance limit the corrosion processes can lead to the development of defects which, under benign conditions, would not normally form or if developed would attain a non‐propagating condition.

The paper presented here includes the results of studies derived from two‐stage intermittent air/environment fatigue cycling and cumulative damage corrosion fatigue loading of a medium carbon steel in two microstructural conditions (i) normalised and (ii) quenched and tempered. From the results of these studies it is shown that a simple damage accumulation model is insufficient to satisfactorily predict ultimate lifetime and consideration should be given to processes such as multiple crack initiation, pitting, Stage I and Stage II environment‐assisted crack growth.
THE CONSECUTIVE WÖHLER CURVE APPROACH TO DAMAGE ACCUMULATION
Authors: Schott G. , Donat B. , Schaper M.
Published: April 2007

Abstract— From the engineering point of view no reliable lifetime prediction method exists, which would enable the life expectancy of structures to be calculated with sufficient accuracy. One of the primary drawbacks of current approaches is their obvious inability to adequately include into an engineering calculation scheme basic knowledge of the microstructural response to cyclic loads during each of the stages of the fatigue process. This article gives a brief introduction into the Consecutive Wöhler Curve Approach which, it is suggested, is capable of predicting with enhanced accuracy fatigue life under varying amplitude conditions. The load interaction behaviour, which is intimately connected with the material's microstructure, is included through “fatigue functions” which are derived from two‐step Wöhler tests.
FRACTURE TOUGHNESS CALIBRATION OF THE Si3N4/Fe JOINT SYSTEM: A PARAMETRIC STUDY
Authors: Stamos V. , Kostopoulos V. , Peteves S. D.
Published: April 2007

Abstract— A fracture toughness calibration of the Si3N4/Fe joint system has been performed for various mixed‐mode loading conditions and for different thicknesses of the metal interlayer. The asymmetric four‐point‐bend loading geometry was used. The values for the calibration function (Y) as well as the mode mixity (ψ)of the system increase on increasing the thickness of the metal. As the loading conditions change from mode II to mode I the dependence of both parameters on metal thickness is more intensive.
HARDENING INTERACTION IN CYCLIC CREEP OF A TYPE 316 STAINLESS STEEL AT 20°C AND 500°C
Authors: Danks J. , Harvey S. J.
Published: April 2007

Abstract— The development of anisotropic material properties due to torsional cyclic plastic straining of tubes with sustained axial loads was examined for a type 316 stainless steel at room temperature and at 500°C. The effect of the cyclic strains and the cumulative ratchetting strains on the axial tensile properties was determined and the results show a significant increase in the tensile strength at both 20°C and 500°C, with more pronounced hardening at the higher temperature. The cyclic shear stress‐strain response of the material is shown to be extremely temperature dependent and the hardening ratio is much greater at 500°C, which is consistent with the dynamic strain ageing observed previously for this material. The ratchetting strains are controlled by the cyclic shear strain hardening, by the axial hardening resulting from the cyclic shear and the cumulative axial strains, and by the ratio of the secondary shear stress to the primary axial stress.
A SENSITIVITY ANALYSIS OF MATERIAL PARAMETERS FOR THE GURSON CONSTITUTIVE MODEL
Authors: Zhang Z. L.
Published: April 2007

Abstract—

Following a convincing demonstration of the prediction power of the Gurson model for ductile fracture, it is now required to select realistic material parameters for practical applications of the model. In this paper, using studies on a smooth tensile specimen, a notched tensile specimen, a centre‐cracked tensile panel and an analytical cell model, a sensitivity analysis of the material parameters is performed that includes the initial void volume fraction of the primary inclusions and the void volume fraction of the secondary inclusions when fitting the critical void volume fraction. Voids that nucleated from primary and secondary inclusions have been considered separately. It has been found that in either case the selection of material parameters for the finite element analyses is not unique, and the most significant parameter for the predictions is the nucleation burst strain. Some general conclusions concerning the selection of material parameters for the Gurson model have also been made.
J‐INTEGRAL SOLUTIONS FOR SHALLOW CRACK GEOMETRIES UNDER COMBINED TENSION AND BENDING
Authors: Lau C. L. , Lee M. M. K. , Luxmoore A. R.
Published: April 2007

Abstract—

This paper presentsJ‐integral solutions for geometries with shallow edge cracks (0.05 ≤a/W≤ 0.1) subjected to combined tension and bending. Tension and bending is applied simultaneously and sequentially. Curves ofJversus structural strain are obtained from two‐dimensional plane strain finite element analyses using medium to low work hardening power laws to represent material behaviour. Empirical equations are derived from the finite element results to estimate theJ‐integrals, using previously developedJ‐estimation schemes for SENT and SENB specimens with only minor modifications. The predictions presented are invariably safe, but due to the complexity of the problems studied and the variability of the loadings considered, the degree of conservatism is found to be high in some cases.
FURTHER OBSERVATIONS OF EARLY FATIGUE CRACK DEVELOPMENT
Authors: Wang Y.‐Z. , Akid R. , Clark A. , Atkinson J. D.
Published: April 2007

Abstract—

A scanning electron microscope (SEM) has been used to examine plastic replicas taken from the surface of fatigue specimens in order to understand the role of microstructure on the early stages of fatigue crack development under various environmental conditions. This involved shadowing and coating replicas and pre‐marking appropriate areas of interest prior to SEM examination.
LOW‐CYCLE FATIGUE UNDER NON‐PROPORTIONAL LOADING
Authors: Chen X. , Gao Q. , Sun X.‐F.
Published: April 2007

Abstract—

A series of strain‐controlled, low‐cycle fatigue experiments have been conducted on 42CrMo steel under various loading paths including circular, square, cruciform, and rectangular paths. Present experiments have shown that there is additional hardening under non‐proportional cyclic loading. Non‐proportional cyclic additional hardening also results in a shorter life for multiaxial low cycle fatigue. A non‐proportionality measure of strain path based on both a physical basis and macromechanical phenomena is proposed. The loading path effect on additional hardening is also described well. Low‐cycle fatigue damage accumulation and the evolution process under non‐proportional loading is analysed via the Continuum Damage Mechanics Model of Chaboche. A non‐proportinality measure is introduced in the damage evolution equation and a modified Coffin‐Manson type formula is derived. A novel fatigue life prediction approach based on the critical‐plane concept of Brown and Miller is proposed.
THE EFFECT OF CATHODIC PROTECTION POTENTIAL ON CORROSION FATIGUE CRACK GROWTH RATE OF AN OFFSHORE STRUCTURAL STEEL
Authors: Yu J. , Brook R. , Cole I. , Morabito D. , Demofonti G.
Published: April 2007

Abstract— Duplicate tests have been performed to determine the effect of cathodic protection potential on corrosion fatigue crack growth rate of a modern offshore structural steel, produced by thermo‐mechanically controlled processes. The experiments were carried out using compact tension specimens exposed to artificial seawater at 10°C and subjected to constant amplitude loading at 0.35 Hz. Reproducible results showed that the merits of cathodic protection potentials are strongly dependent on stress intensity ratio R and stress intensity range ΔK. It appears that a specific value of cathodic potential may not give comprehensive protection against corrosion fatigue within the spectrum of variable amplitude loading experienced in service. Fractography showed the initiation of secondary cracks on the fracture surface to be associated with the dissolution of calcium sulphide inclusions, regardless of imposed cathodic potential.
LONG LIFE SPECTRUM FATIGUE OF CARBON AND STAINLESS STEEL WELDS
Authors: Marquis G.
Published: April 2007

Abstract— Fatigue tests of non‐load carrying carbon and stainless steel fillet welds have been performed using spectrum loading typical for rail vehicles. The proportion of spectrum cycles exceeding the constant amplitude fatigue limit ranged between 0.86% and 100% and cycles to failure ranged from 4.2 ± 105 to 2.1 ± 107. For the longest tests, the majority of fatigue damage was contributed by cycles with stress ranges less than the constant amplitude fatigue limit. For the carbon steel welds a significant portion of fatigue damage was produced by cycles with stress ranges less than 50% of the fatigue limit but only a small fraction of damage was produced by cycles of this size for the stainless steel welds. The carbon steel welds had slightly better fatigue strength at lives less than 107 cycles but results suggest that stainless steels may have superior long‐life variable amplitude fatigue strength when a greater portion of life is spent in the early stages of crack nucleation and growth.
ON DETERMINING STRESS INTENSITY FACTORS FOR MIXED MODE CRACKS FROM THERMOELASTIC DATA
Authors: Tomlinson R. A. , Nurse A. D. , Patterson E. A.
Published: April 2007

Abstract— An alternative methodology is presented for determining stress intensity factors for cracks subject to mixed‐mode displacements. The methodology involves thermoelastic data generated from a SPATE (Stress Pattern Analysis by Thermal Emission) system and has been adapted from one used successfully in photoelasticity. The thermoelastic data is collected throughout the elastic stress field dominated by the crack tip singularity. The stress field is described using a Fourier series within Muskhelishvili's approach. This method allows different applied stress fields to be described which may include transient or non‐uniform stress fields. The results obtained using the new methodology are at least as good as those obtained previously for pure mode I cases, and generally better for mixed mode displacement conditions.
CRACK INITIATION AND SMALL FATIGUE CRACK GROWTH BEHAVIOUR OF SQUEEZE‐CAST Al‐Si ALUMINIUM ALLOYS
Authors: Shiozawa K. , Tohda Y. , Sun S‐M.
Published: April 2007

Abstract— Fatigue strength, crack initiation and small crack growth behaviour in two kinds of squeeze‐cast aluminium alloys, AC8A‐T6 and AC4C‐T6 were investigated using smooth specimens subjected to rotatary‐bending fatigue at room temperature. Fatigue resistance of these alloys was almost the same as that of the wrought aluminium alloys because of their fine microstructure and of the decrease in defect size due to squeeze‐casting. Fatigue crack initiation sites were at the eutectic silicon particles on the surface of specimens or at internal microporosity in the specimens. Crack initiation life, defined as a crack length of 50 μm on the specimen surface, was successfully estimated from an evaluation of initiation sites using fracture mechanics and the statistics of extrema. Small fatigue crack growth in the two kinds of alloys obeys the relation proposed by Nisitani et al., namely that d(2c)/dN = C(σa/σB)n· (2c), where C is a constant and σB is the ultimate tensile strength. It is pointed out that an improvement in fatigue strength of cast aluminium alloys can be expected by refining the eutectic silicon rather than by an increase in static strength.
ESIS TC 6 ROUND ROBIN ON FRACTURE TOUGHNESS
Authors: Prmas R. J. , Gstrein R.
Published: April 2007

Abstract— The Technical Committee “Ceramics” (TC 6) of the European Structural Integrity Society (ESIS) organized a round robin relating to the fracture toughness of ceramic materials at room temperature. Five materials were tested with five testing methods by eighteen laboratories. The five testing methods were: chevron notched beam in four point bending, direct measurement of the cracks emanating from a Vickers indentation, indentation strength by four‐point bending, single edge precracked beam in four‐point bending, and single edge notched beam in four‐point bending. The results of the round robin performed in the period 1993 to 1994 are presented and discussed.
DETERMINATION OF THE MOST APPROPRIATE MESH SIZE FOR A 2‐D FINITE ELEMENT ANALYSIS OF FATIGUE CRACK CLOSURE BEHAVIOUR
Authors: Park S.‐J. , Earmme Y.‐Y. , Song J.‐H.
Published: April 2007

Abstract— A two‐dimensional elastic‐plastic finite element analysis is performed for plane stress conditions with 4‐node isoparametric elements to examine closure behaviour of fatigue cracks, giving special attention to the determination of the most appropriate mesh sizes. It is found that a smaller mesh size does not always give more accurate simulation results in the fatigue crack closure analysis, unlike a conventional structural analysis. A unique, most‐appropriate mesh size exists for a given loading condition that will provide numerical results which agree well with experimental data. The most appropriate mesh size can be determined approximately in terms of the theoretical reversed plastic zone size. In particular, the ratio of the most appropriate mesh size to the theoretical reversed plastic zone size is nearly constant for a given stress ratio in the so‐called crack‐length‐fixed method proposed in this study. By using the concept of the most appropriate mesh size, the finite element analysis can predict fatigue crack closure behaviour very well.
ANALYSIS AND MODELISATION OF SHORT CRACK GROWTH BY DUCTILE FRACTURE MICROMECHANISMS
Authors: Betegon C. , Rodriguez C. , Belzunce F. J.
Published: April 2007

Abstract— A ductile medium strength steel has been modelled by means of the Gurson model, and been used to investigate the effect of crack tip constraint in several fracture mechanics specimens. Both numerical and experimental results have been obtained, in the course of the crack extension process, for single edge notch bending specimens with different crack length‐to‐width ratios. The geometries with the shorter cracks always exhibited higher J values at initiation and steeper J crack growth resistance curves, and these results have been explained in terms of the stress and strain fields and damage development in the region ahead of the crack tip.
FRACTURE BEHAVIOUR OF UNTREATED AND SILANE‐TREATED TALC‐FILLED POLYPROPYLENE COMPOSITES
Authors: Velasco J. I. , De Saja J. A. , Martínez A. B.
Published: April 2007

Abstract— Fracture behaviour of injection‐moulded polypropylene filled with silane‐treated talc was studied as a function of filler volume fraction (0–20%) and compared to that of polypropylene filled with untreated talc. High‐rate tests (0.57 m/s) on SENB specimens were carried out using an instrumented Charpy impact pendulum, and linear elastic fracture mechanics (LEFM) was applied to calculate the fracture parameters, KC and GC. It was found that moderate fractions of talc which were added to the polypropylene matrix increased the fracture toughness of the composite independent of the talc surface treatment. This general improvement seems to be due to the peculiar orientation of the talc platelets in the injection‐moulded specimens. The fracture behaviour of the composites was also studied at low strain rate (1 mm/min) by tests on J‐integral type specimens with the same SENB geometry. In this case, the composites with silane‐treated talc presented poor J‐integral values compared to those of the samples with untreated talc. This was attributed to a reduction of the plastic zone at the crack tip, since the improved coupling between the talc platelets and matrix increased the yield strength of the composite. All the results are explained on a basis of morphological and microstructural details.
A PROCEDURE FOR FATIGUE LIFE PREDICTION OF SPOT WELDED JOINTS
Authors: Salvini P. , Scardecchhia E. , Demofonti G.
Published: April 2007

Abstract— The problem of predicting the fatigue life of spot welded joints has not yet been satisfactorily resolved. Several approaches exist, but many of them are difficult to apply to general structures, which are widely different from simple laboratory specimens. A general criterion is proposed in this paper, based on a theoretical extrapolation of the radial stress. The criterion must be used together with a Finite Element model of the joint and so this paper presents the steps required to get the necessary FE data; steps that are also applicable to the case of complex joints. The advantage of the proposed method is its independence of notch effects near the spot‐weld edge. The suggested procedure is applied to several specimens of different materials and the results obtained are successfully compared with experimental data.
SIZE EFFECTS IN THE FRACTURE OF A PIPE‐GRADE HIGH DENSITY POLYETHYLENE
Authors: Frassine R. , Rink M. , Pavan A.
Published: April 2007

Abstract— The effect of specimen size on fracture toughness of a pipe‐grade high density polyethylene has been examined using the J integral approach. It was found that the size requirements set up by common standards appear inadequate for this material. Measurements at low temperatures, at which a plane strain fracture toughness value could be obtained, turned out to be very effective in establishing a more appropriate size requirement for this material.
CTODi MEASURED BY MEANS OF A MODIFIED CHARPY‐V‐SPECIMEN
Authors: Reiff K. , Ernst P.
Published: April 2007

Abstract— Measurements of CTODi on Charpy‐V‐specitnens of mild steel St 37 and pressure‐vessel steel 22NiMoCr37 have been carried out. Slotted and precracked specimens have been used besides the original V‐notched ones. A definition of CTOD = 2(R – Ro) has been proposed which corresponds to δ45, defining the CTOD of fatigue cracks. The symbols Ro and R represent the original and the actual crack tip radii respectively. Additionally, this definition presents the opportunity to measure CTOD and CTODi by a direct metallographic method. It is demonstrated that COD testing, based on the hinge model, can also be applied to slotted bars, delivering CTOD and CTODi values which are equal to those evaluated by direct metallographic measurements.

The results obtained on four different tip radii, Ro, show a linear increase of CTODi as a function of Ro, which is steeper for the softer material St 37. The extrapolation to the tip radius Ro=0 gives a CTODi, which is equal to those determined from precracked specimens.
The Relative Relationship Between Systematic Risk and Value Added Variables
Authors: Karpik Philip , Belkaoui Ahmed
Published: April 2007

The objective of this study is to determine whether value added variables possess incremental information beyond both accrual earnings and cash flows in the context of explaining market risk. The evidence points to the superior explanatory power of value added variables in explaining the variability in market betas. A case can be made for the disclosure of value added reports.