bluuebunny/crossref_metadata_2025 huggingface dataset:
FRACTURE TOUGHNESS OF NODULAR GRAPHITE CAST IRONS UNDER STATIC, IMPACT AND CYCLIC LOADING
Authors: Krasowsky A. J. , Kramarenko I. V. , Kalaida V. V.
Published: April 2007

Abstract— The paper deals with the fracture toughness of nodular cast irons of differing microstructure and manganese content. Fracture toughness was determined for static and impact loading in the temperature range from 77 to 523 K. The dependences of fracture toughness on manganese content and microstructure were obtained.

Fatigue crack growth rate curves were obtained at room temperature and a correlation between the parameters characterizing fatigue crack growth rate was found.

Fractographic studies revealed an important role of graphite inclusions in the process of fracture. On the one hand, as stress raisers they favour the nucleation of microcracks while on the other hand, they cause local retardation of fatigue crack growth probably due to the residual compressive stress surrounding them. In the mid‐range of the fatigue crack growth rate curve a correlation was found between fatigue striation (or blocks of striations) spacings and the crack growth rate.
MODEL‐BASED STATISTICAL ANALYSIS OF SHORT FATIGUE CRACK GROWTH IN Ti 6Al‐2Sn‐4Zr‐6Mo
Authors: Cox B. N. , Morris W. L.
Published: April 2007

Abstract— The framework of a new probabilistic model of short fatigue crack growth was laid down in the preceding paper. In this paper, the model is used to analyze growth rate statistics for surface fatigue cracks in Ti 6Al‐2Sn‐4Zr‐6Mo. Specific models are proposed for the evolution of the stochastic growth control variable, which appears subsequently as an independent variable in a parametric law for the growth rate. Comparison with data shows that for cracks of length 10–250 μm in Ti 6–2‐4–6, fluctuations in the instantaneous rate of propagation of each surface crack tip depend only on the visible surface microstructure in the tip's immediate neighborhood. They are not influenced by the microstructural environment of the subsurface crack front. Furthermore, they probably depend only on the sizes of at most the three grains nearest the crack tip, i.e. those within about 30 μm of it.
Jc DETERMINATION FOR SHALLOW NOTCH WELDED BEND SPECIMENS
Authors: Sumpter J. D. G.
Published: April 2007

Abstract— Methods are presented for the determination of J from 3 point bend specimens having 0.1 ≤a/W≤ 0.5 using the load versus crack mouth opening displacement trace. It is intended that the procedure be used to determine Jc, J at unstable fracture in the brittle to ductile transition, from specimens and test procedures which conform to the CTOD test standard BS5762. Elastic‐plastic finite element computations are used to demonstrate the adequacy of the proposed estimation procedures for J and to show that it is still possible to apply them to specimens containing welded joints. The problems of defining a centre of rotation for plastic deformation in shallow notched bend specimens are discussed.
CEGB ASSESSMENT PROCEDURE FOR DEFECTS IN PLANT OPERATING IN THE CREEP RANGE
Authors: Ainsworth R. A. , Chell G. G. , Coleman M. C. , Goodall I. w. , Gooch D. J. , Haigh J. R. , Kimmins S. T. , Neate G. J.
Published: April 2007

In recent years considerable progress has been made in research work addressing the behaviour of defects at elevated temperature. Developments have been made both in structural assessment techniques and in methods for analysing representative materials data. On the basis of these developments a procedure has been produced within the CEGB for the assessment of defects in plant operating in the creep range under loadings for which creep rather than creep‐fatigue is the dominant failure mechanism. This paper describes the CEGB procedure. Calculations are required for three events: the time for overall structural failure by continuum damage mechanisms; the time for incubation prior to crack extension; and the time for subsequent growth to a maximum tolerable defect size. Methods are presented for calculating these times and for obtaining the materials data required to perform the calculations.
EXAMPLE OF AN APPLICATION OF AN ASSESSMENT PROCEDURE FOR DEFECTS IN PLANT OPERATING IN THE CREEP RANGE
Authors: Ainsworth R. A. , Coleman M. C.
Published: April 2007

A worked example is presented to illustrate the application of a CEGB procedure for the assessment of defects in plant that operates within the creep range. The example chosen is a large cylindrical pressure vessel with a fully circumferential crack for which experimental results are available. The example demonstrates that it is straightforward to perform the calculations required in the procedure for the time for structural failure by continuum damage mechanisms, the time for crack incubation and the time for crack growth. It is predicted that crack incubation in the pressure vessel occurs at about one‐third of life with the remaining life being taken up by crack growth. The predictions are in close agreement with the experimentally observed incubation, growth and final failure times.
A MODEL FOR SHORT FATIGUE CRACK PROPAGATION WITH AN INTERPRETATION OF THE SHORT‐LONG CRACK TRANSITION
Authors: Navarro A. , Rios E. R. deLOS
Published: April 2007

The behaviour of short cracks approaching growth barriers (e.g. grain boundaries) is considered. The crack model of Bilby, Cottrell and Swinden is applied to simulate the blocking of the plastic zone at the grain boundary and to obtain the stress concentration ahead of the crack as it approaches the barrier. The idea of the Hall‐Petch type relationship that the transmission of slip across grain boundaries needs the previous achievement of a critical stress has been used. By making the crack growth rate proportional to the plastic displacement at the root of the crack the deceleration behaviour of short cracks and the existence of non‐propagating cracks may be explained. The fatigue limit is related to the stress below which a crack growing in a single grain is unable to promote slip in the neighbouring grain. The different behaviour in the so‐called long crack period has been rationalized in terms of the plastic zone exceeding the grain size. For this case, and in the grain completely included within the plastic zone, the Hall‐Petch analysis must be applied. Hence the maximum back‐stress sustained by this grain cannot exceed the yield stress. After this point the Bilby et al. model is used with uy as a friction stress (i.e. the Dugdale model). Finally use is made of Fracture Mechanics to correlate the results in the long crack phase.
SURFACE CRACKS AND THE FATIGUE LIMIT OF METALS
Authors: Troshchenko V. T. , Prokopenko A. V. , Torgov V. N.
Published: April 2007

Abstract— A technique based on indenting a sphere into a material has been developed for measuring the yield strength of metals at various depths from the surface. Proceeding from the experimentally established reduction in the yield strength of the metal surface layer and cyclic crack growth resistance characteristics, the authors suggest a model simulating fatigue fracture based on the continuum mechanics assumptions which allows the fatigue limit to be estimated on the basis of a critical non‐propagating fatigue crack size for components of various thickness in tension‐compression or in bending; considering stress concentrations under both alternating and oscillating loads in the presence of near‐surface stresses. Theoretical predictions using the model for three martensitic stainless steels and a titanium alloy showed a fair agreement with experimental data.
A CRITICAL PLANE APPROACH TO MULTIAXIAL FATIGUE DAMAGE INCLUDING OUT‐OF‐PHASE LOADING
Authors: Fatemi Ali , Socie Darrell F.
Published: April 2007

Abstract— A modification to Brown and Miller's critical plane approach is proposed to predict multiaxial fatigue life under both in‐phase and out‐of‐phase loading conditions. The components of this modified parameter consist of the maximum shear strain amplitude and the maximum normal stress on the maximum shear strain amplitude plane. Additional cyclic hardening developed during out‐of‐phase loading is included in the normal stress term. Also, the mathematical formulation of this new parameter is such that variable amplitude loading can be accommodated. Experimental results from tubular specimens made of 1045 HR steel under in‐phase and 90° out‐of‐phase axial‐torsional straining using both sinusoidal and trapezoidal wave forms were correlated within a factor of about two employing this approach. Available Inconel 718 axial‐torsional data including mean strain histories were also satisfactorily correlated using the aforementioned parameter.
EXPERIMENTAL FATIGUE EVALUATION OF EXTERNALLY WELDED BOX GIRDERS
Authors: Abo‐Hamd M. , Haddad M. El , Raouf H. Abdel
Published: April 2007

Abstract— An experimental study has been carried out to evaluate the fatigue strength and life of externally welded box girders used in gantry cranes and bridge structures. In this study, a reduced scale model was fabricated and tested under conditions similar to those of the prototype. Model analysis was used to select the model dimensions and loads. The test model was subjected to bending, shear and torsional stresses under load control conditions. After test completion, the critical sections were visually and microscopically inspected. No fatigue crack initiation was found. The results of this investigation is expected to help in establishing a fatigue design criteria for externally welded box girders.
INFLUENCE OF THE PORE MORPHOLOGY AND SECONDARY CAVITIES ON THE PLASTIC BEHAVIOUR OF POROUS MATERIALS
Authors: Guennouni T. , François D.
Published: April 2007

Abstract— Using an homogenization technique the plastic behaviour of a porous material containing two populations of cavities is constructed. The corresponding load function is given. It is shown that the interaction between the main and the secondary cavities increases greatly the relative growth rate of the porosity. This effect is the more important the higher the stress triaxiality ratio or the smaller the ratio between the main and the secondary porosities. The influence of the pore morphology on the yield criterion of porous material is also studied. It is shown that the pore morphology modifies the yield criterion only for high triaxiality ratio. For small or medium ones, the main effect comes from the porosity.
THERMAL FATIGUE OF MAR‐M509 SUPERALLOY—II. EVALUATION OF LIFE PREDICTION MODELS
Authors: Rezai‐Aria F. , Dambrine B. , Remy L.
Published: April 2007

Abstract— Thermal fatigue data on MAR‐M509 reported in a companion paper were used to evaluate four life prediction models. The temperature‐stress‐strain history of the critical element at the thin edge of wedge specimens was computed for this purpose. The analysis method uses a finite element computation of the temperature field and a uniaxial calculation of the stress‐strain cycle using a cyclic viscoplastic constitutive equation. The influence of specimen geometry and of maximum temperature on the thermal fatigue life to initiate a macroscopic crack was accounted for by variations in stress and mechanical strain ranges at the thin edge. The accumulated and cyclic creep damage models were found to overestimate thermal fatigue life in all the cases. Models which describe oxidation fatigue crack growth interactions, and which are borne out by metallographic observations on wedge specimens, were found to give reliable predictions of thermal fatigue life.
ON FATIGUE CRACK GROWTH AND STABLE TEARING
Authors: Neale B. K. , Priddle E. K.
Published: April 2007

Abstract— An experimental and analytical investigation has been performed to examine the effect of concurrent fatigue cycling and stable tearing on the crack growth fracture resistance of EN3A steel at 360°C. The steel was tested in the as‐received and hardened conditions, hardening being achieved by pre‐cracking at a load comparable to the elastic limit of the test specimens. For each condition of the steel, resistance curves are obtained both with and without concurrent fatigue cycling.

A significant increase in the crack growth rates occurred as a result of concurrent fatigue cycling. The rates are in reasonably close agreement with the values predicted from the sum of the fatigue crack growth and stable tearing components. The J‐estimation formula of Ainsworth is used to demonstrate that there is no interaction between stable tearing and fatigue in the tests for the steel in the as‐received condition.
ENERGY DISTRIBUTION AND ASSOCIATED FRACTURE PHENOMENA WHEN EXPLOSIVELY LOADING PARABOLOIDAL‐ENDED PERSPEX RODS EMBEDDED IN LEAD AND AIR
Authors: Mamalis A. G. , Gioftsidis G. N. , Johnson W.
Published: April 2007

Abstract— Fracture damage development in paraboloidal‐ended cylindrical rods of Perspex due to stress waves initiated by explosive point loading at the flat end of a rod with a detonator, embedded in surrounding media of solid lead or atmospheric air is discussed. An attempt has been made to explain the form and the location of the terminal internal fractures and the spalls in terms of stress optics considering first and second reflections of the incident waves at the interfacial boundary and the energy distribution of the incident waves when reflected from a boundary or refracted into the surrounding medium.
CYCLIC MECHANICAL BEHAVIOR AND MICROSTRUCTURE OF A 12Cr‐Mo‐V MARTENSITIC STAINLESS STEEL
Authors: Vogt J‐B. , DeCallaix G. , Foct J.
Published: April 2007

Abstract— The low cycle fatigue properties of a 12Cr‐IMo‐V martensitic stainless steel are investigated at room temperature and correlated with its microstructure. The mechanical test results show that the behavior of this steel depends on the applied strain level. The SEM and TEM studies bring out the role of ferrite islands embedded in a tempered martensite lath matrix. Plastic deformation is essentially accommodated by ferrite; this results in extrusion formation on the surface specimen and a cellular dislocation structure. When the strain level is high, it requires a greater contribution of the tempered martensite, ferrite alone being unable to accomplish all the plastic deformation.
THE PROGRESSION OF BENDING FATIGUE IN INCONEL 625
Authors: Price C. E. , Houghton N. R.
Published: April 2007

Abstract— Inconel 625 (N06625) was fatigued in reversed bending and the sequence of surface damage observed. A comparison was made with nickel and Monel K500 studied previously. It was found that, as with nickel, slip markings were present at one cycle even in high life samples. In the Inconel 625, the slip was always planar, multiple slip was common and a plethora of secondary slip was associated with most crack fronts. A noticeable distinction, from nickel and Monel, was the absence of any intergranular cracking. Microhardness measurements revealed that, as with Monel and in contrast to nickel, strain amplitudes high enough to give surface zone hardening led to short lives. from which the inference was made that the inherent fatigue properties of Inconel 625 are inferior to nickel, for advantage cannot be taken of its high strain hardening exponent. Nevertheless, the fatigue limit, as in nickel remains above the yield stress because cracks only initiate when the grains are replete with slip and a rumpled topography has developed.
THE EFFECT OF BIAXIAL STRESS STATE AND CHANGES OF STATE ON FATIGUE CRACK GROWTH BEHAVIOUR
Authors: Yuuki R. , Akita K. , Kishi N.
Published: April 2007

Abstract— The effect of biaxial loading on the fatigue crack growth properties for a stainless steel has been examined. From comprehensive experiments, a significant biaxial stress effect on crack growth was found when the stress level was high and the crack was short. In this paper, the critical region where the effect of biaxial stress appears was clarified quantitatively. Moreover, the effect of changing the biaxial stress condition on fatigue crack growth behaviour was investigated. Significant acceleration of crack growth was observed just after the uniaxial or equibiaxial stress condition was changed to the shear stress condition. This acceleration seems to be due to the change of plastic zone shape at the crack tip.
MIXED MODE (I + III) FATIGUE THRESHOLDS IN A FORGING STEEL
Authors: Yates J. R. , Miller K. J.
Published: April 2007

Abstract— The results of mixed mode (I + III) fatigue tests on a low pressure steam turbine rotor steel are presented. Tests were performed on a uniaxial servohydraulic fatigue machine fitted with a torsion‐bending loading frame. The onset of failure was marked by fatigue facets which grew perpendicular to the maximum principal stress direction. A criterion for mixed mode (I + III) fatigue thresholds based on the orientation and the crack opening displacement of fatigue cracks is proposed.
CLOSURE DEVELOPMENT AND CRACK OPENING DISPLACEMENT IN THE SHORT CRACK REGIME FOR FINE AND COARSE GRAINED A533B STEEL
Authors: James M. N. , Sharpe W. N.
Published: April 2007

Abstract— —This paper reports the results of an investigation of the closure, growth rate and COD behaviour of small cracks in A533B steel. A laser‐based interferometric strain/displacement measurement system was used in the work to quantify closure and COD values in both fine and coarse grained microstructures at stress ratios of ‐ 1 and 0.1. The data obtained clarify the relative dominance of closure or microstructure in the two conditions of the steel and appear to shed some light on the size of crack tip plastic zones for small cracks in the two microstructures.
EFFECT OF HOLD‐TIME DAMAGE ON HIGH TEMPERATURE FATIGUE BEHAVIOUR
Authors: Plumtree A. , Tang Nai‐yong
Published: April 2007

Abstract— —A series of tests has been carried out to investigate the effect of sequential high frequency fatigue cycles interspersed with hold times on elevated temperature crack growth rates in AISI type 304 stainless steel. Each test sequence included different combinations of fatigue cycles and hold‐times. Those sequences which included the smallest number of fatigue cycles resulted in the fastest crack propagation rates. The sequence with a block of 1000 cycles and a 120min hold time had the slowest crack propagation rate, similar to that for a reference 5 Hz fatigue test. Examination of the fracture surfaces revealed alternating regions of transgranular and intergranular fracture corresponding to the respective fatigue block and hold‐time period. Intergranular fracture was observed to be characteristic of maximum time‐dependent and time‐independent damage interaction, which was associated with those specimens subjected to sequences including a block of 50 fatigue cycles, possessing the fastest crack propagation rates. The results may be explained using a model based on fatigue‐creep‐environment interaction. During the hold‐time a damaged zone due to oxidation induced cavitation formed at the crack tip. Depending on the stress intensity factor range, the subsequent fatigue cycles continued to extend the crack through part or whole of the remaining portion of this region. For the remainder of the fatigue block the crack propagated in its normal transgranular mode. Oxide induced closure at low ΔK levels brought about the lowest crack propagation rate for the sequence consisting of a block of 1000 cycles and a 120 min hold period.
INITIATION AND GROWTH OF FRETTING FATIGUE CRACKS IN THE PARTIAL SLIP REGIME
Authors: Kuno M. , Waterhouse R. B. , Nowell D. , Hills D. A.
Published: April 2007

Abstract— —Recent work addressing the problems of fretting fatigue crack initiation and propagation under a carefully controlled axi‐symmetric Hertzian contact is described. Both experimental work, enabling the fretting damage, sites of initiation, and crack trajectory to be viewed, and theoretical work, permitting a prediction of those processes are presented. Good correlation between the two strands of work is found. In particular, the initiation criterion proposed by Ruiz, Boddington and Chen for a very different geometry is found to work well, and would seem to indicate its potential as a design tool.
THE INTRODUCTION OF FATIGUE LOADING INTO THE ROUTINE TESTING OF POLYETHYLENE GAS PIPE SYSTEMS
Authors: Lawrence C. , Sumner C.
Published: April 2007

Abstract— —This paper discusses a programme of work instigated to establish the feasibility of introducing dynamic loading into the routine quality control testing of plastic gas pipe and fittings. The initial data proved to be exceptionally consistent and showed that fatigue loading reduced the time to failure with comparable static loading by an order of magnitude at least and provided a real opportunity to get short term data that would relate to long term (50 to 60 years) service life. The work showed also that many parameters markedly affect failure times and that these would have to be closely controlled or optimised in any subsequent test procedure. As an example the effects of frequency are illustrated and a method of selecting the optimum test frequency is given.
CLOSURE AND GROWTH OF MODE I CRACKS IN BIAXIAL FATIGUE
Authors: McClung R. C.
Published: April 2007

Abstract— —The closure behavior of mode I fatigue cracks under biaxial loading is studied with an elastic‐plastic plane stress finite element model. Biaxial stresses are shown to have a significant impact on crack closure behavior at higher maximum stresses. In general, normalized crack opening stresses are highest for equibiaxial loading and lowest for pure shear loading. The differences are apparently negligible for maximum applied stresses less than about 0.4 σ0. Experimental crack growth data are quantitatively consistent with these trends. Correlations of the experimental data with a simple ΔKeff were successful as first‐order engineering estimates. Changes in forward and reversed plastic zone sizes with biaxiality are not entirely consistent with trends in crack growth rates.
LIFE PREDICTION FOR CREEP‐FATIGUE BASED ON THE GROWTH OF SHORT CRACKS
Authors: Renner E. , Vehoff H. , Neumann P.
Published: April 2007

Abstract— For two types of steels (comparable to the 304‐type and 347‐type of steels) the nucleation and growth of short surface cracks was examined as a function of hold‐time, strain rate, and temperature. In addition, for the same range of parameters, damage parameter vs cycles to failure curves were calculated from measured lifetimes. The measured rates, dα/dN, were compared with a model for the growth of creep‐fatigue cracks. At large strains, life was found to be dominated by the growth of short cracks. The life data were compared with the life calculated from the crack growth data. The results showed that except for cases in which crack growth is controlled by the coalescence of cavities, the specimen life can be predicted correctly by integrating the growth rate of microcracks.
ON CRACK INITIATION LIFE DURING LOW CYCLE FATIGUE
Authors: Jun Din , Jianchen Qing
Published: April 2007

Abstract— A new method of investigating life to crack initiation during low cycle fatigue, which combines hour‐glass shape specimen testing with scanning electron‐microscopy observations, was introduced in the paper. The effect of grain size on low cycle fatigue crack initiation life of 37CrNi3MoV steel and the propagation of cracks in this multi‐phase steel was studied. Results show that refining the grain size can increase fatigue initiation lifetime.
FATIGUE CRACK GROWTH AND CLOSURE BEHAVIOUR THROUGH A COMPRESSIVE RESIDUAL STRESS FIELD
Authors: Kang Ki J. , Song Ji H. , Earmme Youn Y.
Published: April 2007

Behaviour of fatigue crack growth and closure through a compressive residual stress field is investigated by performing fatigue crack growth tests on welded SEN specimens of a structural steel (JIS SM50A). Depending on the type of the initial residual stress in the region of crack growth, the growth and closure of the crack show different behaviour. In particular, in the transition region from a compressive residual stress field to a tensile residual stress field, the fatigue crack growth rates cannot be described by the effective stress intensity factor range ΔKeff, based on the measured crack opening stress intensity factor Kop. Also it is found that the R'‐method using the data of da/dN vs ΔK for residual stress‐free specimens, with the effective stress ratio R'[=(Kmax+Kr)/(Kmin+Kr)], gives non‐conservative predictions of the growth rates in the transition region. Observations of crack closure behaviour in this study indicates that partial opening of the crack occurs and this plays an important role in crack growth through a compressive residual stress field. Based on the concept of a partial opening point (defined and measured in this work), fatigue crack growth behaviour can be better explained.
GEOMETRY INDEPENDENT R‐CURVES IN A TITANIUM ALLOY USING A NORMALISED AXIS FOR CRACK GROWTH
Authors: John S. J. , Turner C. E.
Published: April 2007

Data from a study of the effect of geometric variation on J‐R curves for a titanium alloy in three‐point bending are presented up to large amounts of growth. Four series are reported, various widths, various a/W ratios, various thicknesses and various absolute sizes, all failing in the limit load regime by stable tearing. Analysis is made in terms of Jm‐R curves, adjusted to a common initiation toughness, J1, to clarify the effects of geometry. Strong trends are then found with absolute size over a four fold range and with width over a two fold range; a weaker trend with a/W over a four fold range but practically none with thickness over a nine fold range. Many of these trends are different from those reported for other more ductile materials but consistent in some cases with those reported for another high strength material, HY130. All the deep notch cases (14 tests) reduce to a single group when plotted as Jm against a normalised abscissa, Δa/bo, with a very slight trend to a higher curve for the thinner pieces.
NUCLEATION AND SHORT CRACK GROWTH IN FATIGUED POLYCRYSTALLINE COPPER
Authors: Polák J. , Liškutían P.
Published: April 2007

Surface evolution in polycrystalline copper specimens with a shallow notch has been studied in interrupted constant strain amplitude cyclic loading. The inhomogeneous strain distribution close to stress amplitude saturation leads to the formation of extrusions and intrusions along persistent slip bands within the grain and also in suitably oriented grain boundaries. Numerous primary cracks within a grain or at a grain boundary are nucleated. Some cracks can grow further either by linking with existing cracks or by nucleation of new elementary cracks ahead of the crack tip. Crack growth rates of individual cracks fluctuate considerably but for each strain amplitude, which results in a saturated plastic strain amplitude, a crack growth rate of an equivalent crack can be established. This crack growth rate was found to depend strongly on the plastic strain amplitude in agreement with the Manson‐Coffin law.
STRESS INTENSITY FACTOR EXPRESSIONS FOR REGULAR CRACK ARRAYS IN PRESSURISED CYLINDERS
Authors: Pook L. P.
Published: April 2007

Arrays of radial cracks are sometimes observed at the bore of pressurised cylinders. The stress intensity factors of closely spaced regular arrays of edge cracks depends primarily on the crack spacing and are approximately proportional to the square root of crack spacing for crack length to spacing ratios down to 0.16. A stress intensity factor expression for this range of spacing ratios and of engineering accuracy has been developed for a large regular array of radial cracks at the bore of a pressurised cylinde. For smaller spacing ratios the stress intensity factor depends on crack length than crack spacing and a complementary expression has been developed.
STATIC AND CYCLIC LOADING OF NOTCHED 304 STAINLESS STEEL BARS AT 650°C
Authors: Wu Kuang‐Hsi , Leckie Frederick A.
Published: April 2007

Circular‐notched and sharp‐notched specimens made from 304 stainless steel have been tested at 650°C. The notched specimens are subjected to both constant and cyclic loading. The cyclic loading consists of a ramp increase in load followed by constant load and ramp unloading. The cycle times are 1 min and 10 min. It is found for the circular‐notched specimen that failure is dictated by the time on load and is independent of the number of cycles. Metallographic observations support the test results with fatigue damage being apparent only in the sharp‐notched specimens subjected to short‐time cyclic loading. Otherwise damage has the character of intergranular creep rupture.
CASTING DEFECTS AND THE FATIGUE BEHAVIOUR OF AN ALUMINIUM CASTING ALLOY
Authors: Couper M. J. , Neeson A. E. , Griffiths J. R.
Published: April 2007

Abstract— The fatigue properties of un‐notched polished specimens of an aluminium casting alloy have been measured for various heat‐treatment conditions and at various mean stresses. The relation between fatigue life and alternating stress is insensitive to heat‐treatment and, apparently, to mean stress. It was observed that failure initiated at interdendritic shrinkage defects: evidence of classical crack initiation from persistent slip bands was also seen but such cracks, being less severe than the casting defects, never caused failure. A fracture mechanics analysis for the growth of fatigue cracks from the pores is described. It shows that the fatigue life can be quantitatively predicted from a knowledge of the size of casting defects: in particular it explains the lack of effect of heat‐treatment and the apparent absence of a mean stress effect is shown to be caused by the variation in size of maximum defect present among the specimens tested. It is shown that reducing the size of shrinkage defects will increase the life, but only up to the stage at which initiation from persistent slip bands becomes operative.
A THEORETICAL SOLUTION FOR THE ESTIMATION OF “RAINFLOW” RANGES FROM POWER SPECTRAL DENSITY DATA
Authors: Bishop N. W. M. , Sherratt Frank
Published: April 2007

Abstract— This report outlines a theoretical solution for the estimation of rainflow range density functions using statistics computed directly from power spectral density data. The rainflow range mechanism is broken down into a set of events which can be analyzed using Markov process theory. The dependence between extremes in this instance is modelled using an approximation of the joint distribution of peaks and troughs first proposed by Kowalewski.
LIFETIME PREDICTION ON Cr‐Mo‐V AND 316L STEELS UNDER THERMAL AND MECHANICAL CYCLING
Authors: Degallaix Gearard , Korn Christophe , Pluvinage Guy
Published: April 2007

The thermal‐mechanical fatigue resistance of a Cr‐Mo‐V steel and a 316L steel under combined complex mechanical strain and temperature cycling has been evaluated. The applicability to thermal‐mechanical lifetime prediction of several isothermal fatigue damage concepts is investigated. From a designer viewpoint, some predictions are well acceptable, in particular with the Degallaix thermal activation model for which a recent development is reported.
ESTIMATIONS OF STRESS INTENSITY FACTORS FOR SMALL CRACKS AT NOTCHES
Authors: Kujawski D.
Published: April 2007

This paper presents a simple method for determining the stress intensity factors for small notch‐emanating cracks. The proposed method is based on similarities between elastic notch‐tip stress fields described by two parameters; the stress concentration factor K1, and the notch‐tip radius ρ. The method developed here is rather general, and can be used for a variety of central and edge notches with through‐thickness of semi‐elliptical cracks. The predicted values are in good agreement with the available numerical data.
FINITE ELEMENT ELASTIC‐PLASTIC‐CREEP AND CYCLIC LIFE ANALYSIS OF A COWL LIP
Authors: Arya V. K. , Melis M. E. , Halford G. R.
Published: April 2007

Results are presented of elastic, elastic‐plastic and elastic‐plastic‐creep analyses of an actively cooled cowl lip. A cowl lip is part of the leading edge of an engine inlet of proposed hypersonic aircraft and is subject to severe thermal loadings and gradients during flight. Values of stresses calculated by elastic analysis are well above the yield strength of the cowl lip material. Such values are highly unrealistic, and thus elastic stress analyses are inappropriate. The inelastic (elastic‐plastic and elastic‐plastic‐creep) analyses produce more reasonable and acceptable stress and strain distributions in the component. Finally, using the results from these analyses, predictions are made for the cyclic crack initiation life of a cowl lip. A comparison of predicted cyclic lives shows the cyclic life prediction from the elastic‐plastic‐creep analysis to be the lowest and, hence, most realistic.
THE EFFECT OF STRAIN RATE ON THE TENSILE AND FRACTURE PROPERTIES OF BS 4360 ‘A’ GRADE SHIP STEEL
Authors: Jones R. L. , Davies P. C.
Published: April 2007

Abstract— The results of high rate tensile and compact tension fracture toughness tests conducted on BS 4360 ‘A’ grade ship steel are presented. Tensile results are reported for strain rates within the range 10–2–103/s and fracture toughness values at rates of increase of J integral within the range 103–106 N/mm/s. The tensile properties of upper yield, lower yield and UTS are shown to be linearly dependent on the logarithm of strain rate whilst fracture toughness is shown to decrease with increasing loading rate prior to approaching a minimum value. The decrease in fracture toughness with increasing test rate is shown to be related to a change in the micro‐mechanism of fracture.
LOW CYCLE FATIGUE DAMAGE ACCUMULATION IN ARMCO‐IRON
Authors: Vašek A. , Polak J.
Published: April 2007

A study has been performed relating to fatigue damage accumulation in Armco‐iron with a mean ferrite grain size of 40 μ. Two constant strain amplitudes, εa= 1 × 10−3 (Nf= 250,000 cycles) and εa= 6 × 10−3 (Nf= 3050 cycles) were employed to derive base data for cumulative fatigue loading where unit blocks of low (1000 cycles) and high (10 cycles) strains were mixed until failure occurred. Observations in a scanning electron microscope permitted a periodic evaluation of surface damage to be recorded. Two regimes of damage were noted. During the early crack initiation phase, crack density increased and crack growth rate was constant. During the later phase, or crack propagation stage, new cracks did not nucleate, the smallest cracks arrested, crack density decreased, and the largest cracks grew in an exponential manner, which included linkage with smaller cracks. A damage accumulation model is presented which permits a prediction of fatigue lifetime under variable amplitude loading.
THE EFFECT OF MEAN SHEAR STRESS ON TORSIONAL FATIGUE BEHAVIOUR
Authors: Wang C. H. , Miller K. J.
Published: April 2007

Torsional tests under different mean shear stresses were conducted at room temperature using a 1.99% NiCrMo steel. A technique was developed to control both the mean and the alternating shear stresses. It is shown that the mean shear stress plays a fundamental role in promoting stage I, mode II short crack growth. The effect of mean shear stress on the plastic deformation at stage II crack tips is discussed, which illustrates the mean shear effect on the transition between stage I and stage II crack growth. The polarity of mean shear stress is found to have no effect on the fatigue crack growth rate and the fatigue lifetime of an isotropic material. A model is proposed to account for the effect of mean shear stress on the fatigue lifetime under torsional loading.
THE FATIGUE PERFORMANCE OF MACHINED SURFACES
Authors: Taylor D. , Clancy O. M.
Published: April 2007

It is well known that surface condition has a strong effect on fatigue life, and that most surfaces produced by conventional manufacturing operations such as machining and forging have poorer fatigue behaviour than polished surfaces commonly used for laboratory specimens. As yet, there are no reliable quantitative models to predict the behaviour of such surfaces; the problem is a multi‐parameter one, involving surface roughness, surface microstructure and residual stress. High‐cycle fatigue data was obtained for En19 steel, using four types of machined surface, produced by: polishing, grinding, milling and shaping. Residual stress was eliminated by heat treatment. Fatigue limit data were plotted as a function of roughness parameters using Kitagawa‐type diagrams, and compared to simple notch‐based and crack‐based models. It was found that, whilst both theories tended to be overly conservative, fracture mechanics approaches are useful for relatively low roughness, when the surfaces can be modelled as a series of short cracks. For higher roughness a notch‐based approach is appropriate.
STRESS RESPONSE BEHAVIOUR OF A CAST NICKEL BASE SUPERALLOY SUBJECT TO COMBINED CREEP‐FATIGUE
Authors: Plumbridge W. J. , Ellison E. G.
Published: April 2007

Abstract— An advanced nickel base alloy, MAR MOO2, was subject to creep‐fatigue, strain controlled, cycling at temperatures of 750, 850 and 1000°C. Under continuous cycling the alloy exhibited cyclic stability at 750 and 850°C but not at 1000°C. The presence of a tensile or compressive dwell caused softening at 750 and 850°C compared with the pure fatigue case. At 1000°C a tensile dwell caused slight hardening and a compression dwell caused cyclic softening. The stress response for a balanced, tensile plus compressive, dwell was similar to that for continuous cycling. Unbalanced tensile dwells produced significant compressive mean stresses and compressive dwells resulted in large tensile mean stresses at 750 and 850°C. However, at 1000°C no significant mean stresses were produced whatever cycle was used. Stress relaxation behaviour was similar for both tensile‐only and compressive‐only dwells. In the balanced case the amount of stress relaxation was double that in each dwell of an unbalanced cycle. Reliable predictions of stress relaxation were possible using stress exponents from available creep data and the Gittus equation. Severe ageing (104 h at 1000°C) does not destroy the cyclic stability of the alloy although some softening occurred in the compression‐only dwell at 850°C. Tentative explanations for the observed stress response in terms of dislocation‐precipitate interactions have been suggested.
A DUCTILE FRACTURE MODEL IN MIXED MODES 1 AND 2
Authors: Budden P. J. , Jones M. R.
Published: April 2007

Abstract— Fracture due to crack growth under mixed Modes 1 and 2 loading is considered. The cracking mechanism addressed is that of microvoid growth and linkage under small‐scale‐yielding conditions. Stress analyses are described which take into account the blunting of the crack tip as the load increases. A damage function is defined, and is evaluated in the intensely‐straining region near the blunted notch tip. As the load increases, the size of this damaged region increases until a critical level of damage has been reached over a material‐dependent length scale and fracture ensues. The local fracture criterion is then related to the applied loads. The predictions of the model are tested against experiments under Mode 1 loading and also against some mixed Modes 1 and 2 data on a range of materials. The results of the model are conservative and reproduce the experimentally observed Mode 1 failures, in terms of AT, at fracture, to within 25%. In the case of mixed mode loading the model conservatively predicts the fracture load for most of the data.
SIMPLE MODELS FOR PREDICTING STRESS INTENSITY FACTORS FOR TUBULAR JOINTS
Authors: Haswell J.
Published: April 2007

Offshore structures are subjected to onerous environmental conditions. These conditions can cause cracking at tubular joints in these jacket structures and increasingly fracture mechanics is being applied to assess the cracks.

There are a variety of fracture mechanics approaches to assessing cracks in tubular joints, all of which predict similar trends but give a wide variation of stress intensity factors. This variation is caused by the different models and inconsistent input parameters used.

This paper presents a finite element study of a cracked tubular joint using several different structural models and consistent input parameters. The analysis includes both simple representations of a tubular joint, e.g. a plate model, and a full‐scale analysis on the joint. A comparison of the full‐scale analysis and the simple representations allow conclusions to be drawn on the applicability of simplifications to the problem and also allows errors to be quantified.
RECENT STUDIES INITIATED BY THE NAFEMS FRACTURE MECHANICS WORKING GROUP
Authors: Remzi E. M.
Published: April 2007

The U.K. National Agency for Finite Element Methods and Standards (NAFEMS) is a government agency funded by the Department of Trade and Industry. The task of the Agency is to evaluate the standards used in developing FE programs in order to improve the general level of user competence in industry. The Agency has established Working Groups to consider various aspects of FE techniques. The responsibility of the Working Groups is to identify the analytical work required to investigate specific techniques and applications, and to ensure the execution of the work. One Working Group is concerned with finite element fracture mechanics and its activities are described in detail in this paper. Various categories of benchmark specifications were identified by the Working Group along with the need to provide educational input, guidance documents and a general interest in current developments and user requirements.
OXIDATION‐ASSISTED FATIGUE CRACK GROWTH BEHAVIOR IN ALLOY 718‐PART II. APPLICATIONS
Authors: Zheng D. , Ghonem H.
Published: April 2007

In previous work by the authors, a quantitative model based on a two‐stage oxidation mechanism was developed to describe the oxidation‐assisted crack growth behavior in alloy 718. This model is used here to predict the crack growth rate in this alloy at 650°C for two different loading conditions: one is a continuous cycle with a hold time duration of 300 s imposed at minimum load, the other is a continuous cycle without a hold time duration. The results obtained from applying the model to these loading profiles were then compared with those obtained experimentally. Good agreement was observed between the two data sets. Details of the model calculations are discussed, and suggestions to further extend the model capabilities are made in this paper.
THE EFFECT OF HARDNESS ON THE FRETTING FATIGUE OF ALLOY STEELS
Authors: Husheng Gao , Haicheng Gu , Huijiu Zhou
Published: April 2007

The fretting fatigue behaviour of several alloy steels is reported in this paper. Fretting fatigue experiments were conducted on flat fretting junctions in axial tension at a stress ratio of 0.1. In all cases the same materials were fretted against each other. The fretting fatigue strength at a slip amplitude of 45 μ is rather insensitive to the hardness of the materials. The fretting fatigue strength at the slip amplitude of 10 μ increases with increase in hardness. As the slip amplitude increases the fretting fatigue life of 3SCrMo steel decreases, the depth of wear scars increases and the wear damage becomes more severe. The reason for similarity of fretting fatigue to the fatigue of notched specimens is that the effect of wear scars is similar to that of notches.
ESTIMATION OF SERVICE LOADING FROM THE WIDTH AND HEIGHT OF FATIGUE STRIATIONS OF 2017‐T4 A1 ALLOY
Authors: Murakami Yukitaka , Shiraishi Nobuhiko , Furukawa Katsuaki
Published: April 2007

A case‐study method is proposed to determine service loading from fracture surface striations. Although it is well known that striation spacing relates to the crack growth rate, it is considered impossible to determine maximum and minimum loads under service loading conditions, and which define the stress ratioR, from an analysis of the striation spacing. This paper presents a new method of determining the maximum and minimum loads which is based on the experimental fact that the relative height of a striationHto striation spacingsis strongly influenced by the stress ratio. The results of fatigue tests on 2017‐T4 A1 alloy showed a definite correlation between these parameters. The difficulty of measuring striation height was overcome by taking the measurements in a scanning electron microscope after sectioning the specimens at a large inclined angle. Striations under a stress ratioR=−1 are compressed and flat, and the ratioH/sis small. With increasingR, the value ofH/sbecomes large. Therefore a standard laboratory test that determines the relationship betweensand ΔK, and also betweenH/sandRenables one to estimate service loadings from fatigue fracture surfaces.
SCATTER CHARACTERISTICS OF FATIGUE LIFE AND THE BEHAVIOUR OF SMALL CRACKS
Authors: Goto M.
Published: April 2007

Usually, there is large scatter in fatigue data and this should be evaluated quantitatively when fatigue data are applied to the design of machines and structures. Consequently it is important to clarify the physical basis of scatter in fatigue life. In this present study, rotary bending fatigue tests were performed on an annealed 0.21% carbon steel. At least sixteen smooth specimens were fatigued at each of three stress ranges and successive observations of the surface were studied for all the specimens using the plastic replica method. By examining the initiation and propagation behaviour of cracks the physical basis of scatter in fatigue life is analysed and discussed. To estimate the scatter characteristics quantitatively, the distributions of crack initiation life, propagation life, fatigue life and crack length were individually studied by assuming a Weibull distribution for each set of data.
CRACK NUCLEATION AND PROPAGATION IN BLADE STEEL MATERIAL
Authors: Gabetta G. , Torri L.
Published: April 2007

Stress corrosion cracking and corrosion fatigue of 12 Cr steel in sodium chloride solution has been investigated. Tests have been performed in air at room temperature and in aqueous solution with 22% NaCl at 80°C. The influence of corrosion pits on crack nucleation has been investigated. On fracture surfaces tested in environment (22% NaCl solution), crack initiation was observed in correspondence with corrosion pits; in this case fatigue life can be described using a fracture mechanics approach. The ΔK value for crack nucleation from a pit in rotating bending fatigue tests is very low in air (about 3 MPa√m). The results of slow strain rate tests on smooth specimens show that there is a threshold stress intensity, KISCC, of about 15 MPa√m and a plateau in stress corrosion crack growth rate of about 10‐5mm/s.
INFLUENCE OF MICROSTRUCTURE ON THE FRACTURE TOUGHNESS AND FRACTURE TOPOGRAPHY OF A DUPLEX STAINLESS STEEL
Authors: Erauzkin E. , Irisarri A. M.
Published: April 2007

The effect of heat treatment on the fracture toughness and fracture topography of a duplex stainless steel has been studied. Samples treated above 1050˚C exhibit just a slight decrease in toughness in good agreement with the metallographic and fractographic analyses. However, in those coupons annealed between 675 and 900˚C a marked loss of toughness was detected. This embrittlement is maximum in samples treated at 825˚C and has been associated with sigma phase precipitation clearly seen in the metallographic examination. Elongated splits of brittle walls are present in their fracture surfaces. Specimens treated at lower temperatures for short times show a certain decrease in toughness. The almost featureless surfaces of the fissures present in these samples suggest a delamination along the austeniteferrite interfaces. Longer exposure times produce a greater loss of toughness and fracture morphologies similar to those in 825˚C treated specimens. Treatment at 475˚C produces an embrittlement attributed to alpha‐prime phase.
DELTA‐K‐EFFECTIVE: WHICH FORMULA?
Authors: Finney J. M. , Deirmendjian G.
Published: April 2007

Several equations are examined which were developed to eliminate the R‐effect in fatigue crack growth rate by using the concept of a δKeff. Their performance was objectively rated by using a limited set of growth rate data with the result that an early equation by Schijve proved the best. However, relatively small variations in growth rates markedly affected the order of rating the equations, and none of them appear to include the variables necessary to cope with a wide range of R‐values and growth rates. The usefulness of an effective δK in predicting fatigue crack growth is thus brought into question.