bluuebunny/crossref_metadata_2025 huggingface dataset:
MAGNETOSTRICTION EFFECTS IN CRACK LENGTH MEASUREMENTS
Authors: Davis F. H. , Plumbridge W. J.
Published: April 2007

Abstract— Fatigue crack lengths were measured in a ferromagnetic material (a low alloy steel) using the d.c. potential drop technique. Significant cyclic fluctuations in potential were observed. Using discriminatory tests it has been established that the fluctuations may be attributed to inverse magnetostriction known as the Villari effect. The strain rate dependence of the fluctuations was investigated using sinusoidal, square and sawtooth waveforms, and the amplitude of the fluctuations was shown to be proportional to strain rate. In some cases the amplitude of the fluctuations was of similar magnitude to the crack length measurement potential.
A NUMERICAL STUDY ON GLOBAL AND LOCAL PARAMETERS CONTROLLING FRACTURE IN THE BRITTLE‐DUCTILE TRANSITION TEMPERATURE REGION
Authors: Dedovic S. , Bakker A. , Latzko D. G. H.
Published: April 2007

Abstract— In this report on fracture studies pertinent to the brittle‐ductile transition region the predictive capability of a local fracture parameter, i.e. maximum tensile stress normal to the crack plane (= maximum principal stress), and of a global fracture parameter, i.e. the J‐integral, are compared for SENB and CNT specimens fractured at −70°C. The influence of constraint is also investigated, both locally as defined by the ratios of mean (hydrostatic) stress and maximum principal stress to von Mises stress, and globally as defined by the factor m=J/(s̀γ.CTOD). Results obtained indicate that stress fields in a varying constraint environment (i.e. varying both spatially and with extent of plastic deformation) are not uniquely characterized by J and require additional information on the amount of constraint. Fracture predictions based on maximum principal stress ahead of the crack tip exhibit far less scatter than those based on J, but further investigations are required on the geometry (in)dependence of this local parameter.
A REVIEW OF FATIGUE CRACK GROWTH CHARACTERISATION BY LINEAR ELASTIC FRACTURE MECHANICS (LEFM). PART I—PRINCIPLES AND METHODS OF DATA GENERATION
Authors: Allen R. J. , Booth G. S. , Jutla T.
Published: April 2007

Abstract— The application of linear elastic fracture mechanics (LEFM) to the characterisation of fatigue crack growth has been reviewed. In Part I the present understanding of the factors influencing growth rate is summarised, and the current methods of fatigue crack growth rate data generation are considered in the light of this. In Part II, documents are reviewed which provide advice on the prediction of fatigue crack growth and also those national standards in which fatigue crack growth considerations are implicit.
WAVEFORMS IN FRETTING FATIGUE
Authors: Rooke D. P. , Edwards P. R.
Published: April 2007

Abstract— The magnitudes and directions of the frictional forces must be considered in any fracture mechanics analysis of crack growth under fretting fatigue conditions. A simple nonlinear friction model has been developed which relates the waveforms of the frictional forces to those of the applied forces when fretting occurs. It is shown that the waveforms are different in shape and that periods of dwell and phase shifts may occur in the frictional forces. These differences can significantly affect the rate of growth of cracks and hence life prediction.
THE EFFECT OF SPECIMEN SIZE ON THE CTOD R‐CURVE BEHAVIOUR OF A TITANIUM ALLOY
Authors: Gordon J. R. , Jones R. L.
Published: April 2007

Abstract— —This paper presents preliminary results from a large experimental programme to study geometry and size effects in CTOD R‐curves. The results presented were obtained from unloading compliance R‐curve tests performed at room temperature on different sized single‐edge‐notch bend specimens made from Ti–3Al–2V alloy. The crack growth resistance was measured in terms of both the conventional CTOD, δ0, (i.e. as defined in BS 5762) and CTOD corrected for crack growth, δR. It was found that the δ0 and δR R‐curves were independent of specimen size up to crack extensions corresponding to approximately 10–15% of the original uncracked ligament. Also, after crack extensions of 30–40% of the initial ligament the δ0 and δR R‐curves exhibited well defined upswings. The upswing in the CTOD R‐curves is thought to be a result of a reduction in crack tip constraint.
EFFECTS OF HYDROSTATIC PRESSURE ON THE RATE OF FATIGUE CRACK GROWTH
Authors: Davis F. H. , Ellison E. G. , Plumbridge W. J.
Published: April 2007

Abstract— Fatigue crack growth rate data have been obtained, for both positive and negative R stress ratios, in pressurised and unpressurised oil and in inert argon gas. Expected results show that for negative R the rate data should be correlated against the tensile stress intensity range. For tension‐compression loading constant hydrostatic pressure has a detrimental effect increasing the tensile stress intensity range. For tension‐tension loading constant hydrostatic pressure has a beneficial effect decreasing crack growth rates. A simple theoretical model has been proposed which describes these trends.
LOW‐CYCLE FATIGUE INVESTIGATIONS AND NUMERICAL SIMULATIONS ON DUAL PHASE STEEL WITH DIFFERENT MICROSTRUCTURES
Authors: Zhonghua Li , Jiangbuo Han , Yonglan Wang , Zhenbang Kuang
Published: April 2007

Abstract— Fully reversed low cycle fatigue tests were carried out on 7 mm diameter cylindrical specimens of a dual phase steel treated to give five different microstructures, namely F—ferrite (+ little carbide particles), CF—continuous ferrite + 8.2% martensite, FM—49.1% ferrite + 50.9% martensite mixed structure, CM—continuous martensite + 22.4% ferrite and M—100% martensite. A finite element program was developed based on Eisenberg's cyclic plasticity theory and the low cycle stress‐strain response of the steels with duplex phase microstructures was calculated from the low cyclic curves of the single ferrite (steel F) and martensite (steel M) phase. The experimental results show that fatigue performance of dual phase steel improves as martensite content is increased up to about 50%, thereafter it obviously deteriorates. During cyclic loading, the calculated plastic strain accumulated in ferrite is higher than that in martensite. Inhomogeneity of the plastic strain accumulation in steel CF is more pronounced than that in steel CM. In steel FM a relatively uniform strain distribution was found. Controlling the size of particle phase can result in an optimum strain distribution. Thus, the plastic deformation capability of the constituent phases can be enhanced leading to fatigue performance improvement. Crack initiation occurs easily at the ferrite/martensite interface with a coarse particle phase size, regardless of phase continuity. In steel CF, a crack initiates at the interface perpendicular to the stress axis and propagates in the ferrite matrix by deflecting around coarse martensite particles or by cutting fine martensite particles. In steel CM, a crack initiates at the interface along the stress axis and propagates in the martensite matrix through ferrite particles.
EFFECT OF ELECTRON BEAM WELDING ON FATIGUE CRACK GROWTH RATE IN AISI 4130 STEEL
Authors: Doong Ji‐Liang , Chi Jing‐Ming , Hwang Jiun‐Ren
Published: April 2007

Abstract— The purpose of this study is to investigate the effect of electron beam welding parameters on fatigue crack growth rate in AISI 4130 steel. The welding method was carried out by using nonoscillation and oscillation electron beam patterns. In nonoscillation welding, the welding speed, was varied; in oscillation welding just the oscillation pattern and the oscillation frequency were varied. After welding, X‐ray inspection, metallography, fatigue crack growth tests and scanning electron microscopy were employed to characterize these specimens. From the results, the weld centerline solidification structure transforms from a longitudinal raft structure to an interlocked structure with increasing welding speed, and the fatigue crack growth rate increases slightly. The transverse oscillation pattern provides a lower fatigue crack growth rate than the longitudinal oscillation pattern. The higher oscillation frequency gives a lower fatigue crack growth resistence for the longitudinal oscillation pattern, but the opposite is the case for the transverse oscillation pattern.
THE EMISSION OF RAYLEIGH WAVES FROM BRITTLE FRACTURE INITIATION, AND THE POSSIBLE EFFECT OF THE REFLECTED WAVES ON CRACK ARREST
Authors: Thaulow C. , Burget W.
Published: April 2007

Abstract— The pop‐in initiation and arrest behaviour in weldments of a structural steel, have been characterized with acoustic emission measurements. It was found that strong Rayleigh waves radiate from the crack tip in a preferred direction. Literature examinations and reanalysis of previous crack arrest test results, clearly indicate that the Rayleigh waves will be reflected back from edges on the crack surface and cause a crack closure effect upon arrival at the running crack tip. The phenomenon is tentatively called AUTOARREST (automatic arrest caused by release of stress waves from the crack itself).
FRACTOGRAPHIC ANALYSIS OF CRACK GROWTH AND SHEAR LIP DEVELOPMENT UNDER SIMPLE VARIABLE‐AMPLITUDE LOADING
Authors: Ling M. R. , Schijve J.
Published: April 2007

Fatigue crack growth experiments were carried out on 2024‐T3 sheet specimens, loaded under simple variable‐amplitude load sequences, including blocks of overload cycles or underload cycles and blocks of low amplitude cycles. The purpose was to study interaction effects by analysing striation measurements and shear lip developments. The striations clearly demonstrate delayed retardation. Shear lip measurements indicate significantly slower crack growth rates if the percentage shear lip increases from zero (no shear lips) to 100% (fully in the shear mode). The significance of incompatible shear lips during variable‐amplitude loading is discussed. The test results are evaluated with relation to interaction mechanisms and the meaning by cycle‐by‐cycle prediction models.
THERMAL FATIGUE UNDER MULTIAXIAL STRESSES
Authors: Junyi Feng , Mengxin Bian , Zijou Dang
Published: April 2007

Thermal fatigue under multiaxial stresses has been investigated. Circular cylindrical specimens were tested under thermal fatigue which was in‐phase with axial mechanical fatigue loading. The axial forces on the specimens were varied throughout the test programme, but all the temperature cycles were identical, so various biaxial stress and strain ratios were obtained. Straight thermal fatigue cracks occurred in different directions and also net‐like crazes in various patterns were observed on the surfaces of the specimens. The transient temperature, stress and strain fields have been calculated with a thermal elasto‐plastic Finite Element Method. Comparing test results with calculations, it appears that the patterns of thermal fatigue cracks are dependent on the stress state and the plastic strain state, not on the strain state. The direction of cracks is perpendicular to the maximum principal stress and the maximum plastic strain. Net‐like thermal fatigue crazes will occur when one principal stress is about the same as the other one and one plastic strain component is approximately equal to another.
THE BEHAVIOUR OF FATIGUE CRACK GROWTH IN THE FRETTING‐CORROSION‐FATIGUE OF HIGH TENSILE ROPING STEEL IN AIR AND SEAWATER
Authors: Takeuchi M. , Waterhouse R. B. , Mutoh Y. , Satoh T.
Published: April 2007

Abstract— Fretting fatigue tests of high tensile roping steel, 1.5 mm in diameter, 1770 MPa grade, were carried out in air and seawater. S‐N curves were completed in both the environments and under cathodic protection at‐850 mV (SCE). The crack growth curves were determined at three different alternating stress levels. The coefficients of friction between the specimen and the fretting bridge, where the macro‐slip occurred, were found to be 0.63 in air and 0.38 in seawater. The prediction of the fretting fatigue lives were made according to the Tanaka—Mutoh model, where the frictional force was taken into consideration. The predicted fatigue life agreed well with the experimental results in air but in seawater the prediction defined a much higher fatigue limit compared with the experimental results which showed the absence of the fatigue limit. These results indicate that the method of removing the electrochemical component is very promising for the prevention of fretting fatigue failure in seawater.
FATIGUE CRACK INITIATION AND GROWTH BEHAVIOR OF Cu‐16 at.% A1 SINGLE CRYSTALS
Authors: Hong Sun Ig , Laird Campbell
Published: April 2007

In an attempt to understand the fatigue crack initiation and growth behavior of planar slip alloys, studies have been carried out in strain control on Cu‐16 at.% A1 single crystals oriented for easy glide. Alloy single crystals of Cu‐16 at.% A1 do not show saturation like copper crystals, but harden slowly and steadily throughout life, for the whole range of amplitudes applied. Cracks, the initiation and growth of which were studied by the sharp corner technique, were found to initiate when the peak stress reached 32 MPa irrespective of strain amplitude. The distribution of crack sizes in Cu‐16 at.% A1 single crystals was found to be more skewed to small cracks than that of copper. This behavior is attributed to the frequent migration of the bands of localized slip in this material. The fatigue lives of this alloy at low strain amplitudes (ypm < 6‐7 × 10−3) were found to be longer than those of copper single crystals because the strain is distributed more homogeneously than in copper. At high strain amplitudes, however, they become shorter because of the higher peak stress. The fatigue lives of Cu‐A1 crystals are predicted from those of copper on the basis of the different volume fractions of localized strain in the two materials; the prediction agrees well with the actual lives of Cu‐Al crystals. By geometrical consideration of secondary slip planes with respect to a primary crack, it was found that the critical system (A6) is most favored for secondary cracking adjacent to a primary crack.
POP‐IN AND CRACK ARREST IN AN HY80 WELD
Authors: Sumpter J. D. G.
Published: April 2007

It is generally thought that, when a material is in its brittle to ductile transition, it is more difficult to design for crack arrest than to prevent crack initiation (cleavage). This report shows that this is not always true for weldments. Comparison is made between compact crack arrest (CCA), Ka, and crack tip opening displacement (CTOD), KJc, toughness for the same HY80 weld. The value of Ka is shown to be much higher than the minimum KJc for pop‐in fracture initiation. It is considered that the results support the conclusion of Japanese research workers (Arimochi and Isaka) that small pop‐ins (in the CTOD test) propagate and arrest without load drop. It follows that prediction of structural failure for weldments need not be based on minimum pop‐in toughness from CTOD tests.
MODELLING RESIDUAL STRESSES AND FATIGUE CRACK GROWTH AT COLD‐EXPANDED FASTENER HOLES
Authors: Clark G.
Published: April 2007

This paper describes a model developed for predicting residual stresses and crack growth in residual stress fields, and the application of the model to crack growth from cold‐worked fastener holes in thick section aircraft components. Comparison with experimental results demonstrates that the model can provide useful predictions of critical crack length, and a capability for correctly predicting the maxima and minima in the crack growth rate for cracks from cold‐expanded holes. It also permits the observed asymmetry in cracking from cold‐worked fastener holes to be better understood.
SHORT FATIGUE CRACK GROWTH BEHAVIOUR OF A LOW CARBON STEEL UNDER CORROSION FATIGUE CONDITIONS
Authors: Akid R. , Miller K. J.
Published: April 2007

The effect of an aqueous chloride environment upon the development and growth of short fatigue cracks from smooth specimen surfaces has been studied under fully reversed torsional fatigue loading conditions. Crack initiation and growth has been monitored using a plastic replication technique enabling a full history of cracking characteristics to be recorded. Corrosion fatigue conditions were achieved by complete immersion in a 0.6 M NaCl solution, of nominal pH value 6.0, with specimens corroding at the free corrosion potential. Variations to these conditions were obtained by the addition of concentrated hydrochloric acid enabling test solution pH values to be altered, typically pH values of 3.5 and 2.0 were obtained. Further information regarding the effects of the environment on the early stages of crack development were obtained by conducting two stage alternate immersion type testing conditions. Evaluation of these effects through previously established Elastic‐Plastic Fracture Mechanics models shows that the environment plays a major role during the early stages of microstructure‐dominated crack growth particularly as cracks approach major barriers to propagation and at decreasing levels of applied shear stress.
CRACK‐FOLLOWING FOR ACCURATELY DETERMINING FRACTURE TOUGHNESS
Authors: Whitehead R. D.
Published: April 2007

Current standard fracture‐mechanics methods encourage sudden, explosive and total testpiece fracturing in which one catastrophic event produces one set of measurements. By demanding conformance to the overall elasticity requirement while relaxing thickness and crack‐length specifications and following a slow crack‐growth sequence, series of simultaneous measurements were made on single testpieces. From these measurements independent values of the Mode‐I critical stress‐intensity factor and strain‐energy release rate were determined. Polyethersulphone injection‐moulded discs were prepared as round‐compact testpieces. The crack grown from a chevron‐notch was propagated under control, slowly. A large number of measurements were made as the crack extended. The fractures were smooth, square to the body of each disc and had a stable crack path across the diameter. The independent fracture‐toughness values were small but their derived modulus agreed well with directly measured values of Young's modulus, thus confirming the elastic integrity of the test.
FATIGUE CRACK PROPAGATION CHARACTERISTICS OF GLASS FIBRE REINFORCED POLYCARBONATE IN HOT DISTILLED WATER
Authors: Murakami Ri‐ichi , Noguchi Shinji
Published: April 2007

The fatigue crack propagation behaviour of polycarbonate and glass fibre reinforced polycarbonate was studied in hot distilled water. The effects of temperature, distilled water and glass fibre content on fatigue crack growth rate were determined. In distilled water at 333 K, the fatigue crack growth rate decreased with increasing glass fibre content. A melting was observed of the adhesive bond between the glass fibres and the matrix. It was evident that the fracture morphology closely relates to the fatigue crack growth rate which depends on the ΔK parameter rather than the Kmax parameter when the materials are tested in hot distilled water.
A STUDY OF SPECIMEN SIZE ON J‐R CURVE BEHAVIOUR
Authors: Jones R. L. , Gordon J. R. , Challenger N. V.
Published: April 2007

This paper presents results from an experimental programme to study size effects in J‐R curves. Results are presented from unloading compliance R curve tests on different sized single edge notch bend specimens of nickel aluminium bronze and compared with previously published R curve data on a Ti3A1‐2.5V titanium and an HY 100 steel alloy. The crack growth resistance was measured in terms of the standard fracture resistance J, J corrected for crack growth and the J modified parameter proposed by Ernst. It was observed that following a region of size independence small specimen J‐R curves could fall either above or below the large specimen curve. It was found that although the limit to J controlled crack growth could be extended the limit is not unique but dependent on material type.
PREDICTION OF FATIGUE CRACK GROWTH UNDER SINGLE OVERLOAD APPLICATION IN Ti‐6Al‐4V
Authors: Ghonem H. , Zeng M.
Published: April 2007

Abstract— This paper is concerned with the use of a Markovian stochastic crack growth model to predict crack growth behavior in zones affected by a single overload application. The model introduces an effective stress intensity factor in the definition of the transition intensity of the stochastic process. This in turn, generates a unified probability growth law that was used to predict scatter in single overload history. An experimental program was carried out on compact tension specimens of Ti‐6Al‐4V material to generate sample crack growth curves, each of which contains three single overload zones. The sample curves were then manipulated into experimental constant probability growth curves. These curves were compared with those theoretically generated using the proposed model. A good agreement was established between these two data sets.
THE DETERMINATION OF R‐CURVES FOR SHORT, WIDE CENTRE CRACKED PANELS OF ALUMINIUM ALLOY SHEET
Authors: Sutton G. R. , Wheeler C. , Thomas C. E. , Wilson R. N.
Published: April 2007

Abstract— The feasibility of conducting an R–curve test on centre crack test pieces with a length/width ratio of between 1.3 and 0.25 has been investigated. To allow for the undefined mixed mode loading present with short, wide test pieces, two experimental methods of determining the geometric correction for the stress intensity factor have been proposed and compared. Also an experimental determination of the compliance calibration used to calculate the effective crack length has been made for these geometries. These methods have been evaluated by conducting R‐curve tests on clad 2024‐T3 aluminium alloy centre crack sheet test pieces. 2 m and 760 mm wide panels with length/width ratios of > 1.3, 0.5 and 0.25 were tested. The derived R‐curves agreed well for both widths and for length/width ratios as low as 0.5.
INTERACTION OF OVERLOADS ON FATIGUE CRACK GROWTH FOR 40CrNi STEEL
Authors: Yang Shuilong , Li Hua
Published: April 2007

This work was designed to improve the general understanding of loading sequence effects on fatigue crack growth and lead to the development of improved methods for predicting crack propagation behaviour. Two loading histories were selected (1) a baseline amplitude with periodic overloads or underloads, and (2) several overloads without interactive effects. The specimen used was of a Wedge Opening Loading type and the material was a low alloy high strength steel, i.e. 4OCrNi. It was found that the Linear Summation of Damage (LSD) assumption could be applied in predicting fatigue crack growth rate (FCGR) under periodic overloads or underloads within the scatterband of the constant amplitude data obtained using an Alternating Current Potential Drop technique for measuring crack length for multiple specimens with several load amplitudes. A discrepancy existed between the FCGR predicted from LSD and the one actually measured during several hundreds of loading cycles immediately following every non‐interactive overload of the latter loading history although the overload ratio was the same as that of periodic overloading. The causes of this phenomenon are discussed.
PARABOLIC CURVED CRACK FRONTS IN FRACTURE TOUGHNESS SPECIMENS OF PARTICULATE REINFORCED ALUMINIUM ALLOY METAL MATRIX COMPOSITES
Authors: Roebuck B.
Published: April 2007

Crack front shapes in relatively thick fracture toughness specimens of Sic particulate reinforced metal matrix composites have been analysed. They were found to have a common shape, that of a parabola. This shape is thought to arise as a result of a distribution of residual stress across the test‐piece. A simple analysis is used to derive an expression for an effective crack length which can be used to calculate KIC values in specimens in which the crack fronts are excessively curved and do not meet relevant criteria for curvature in current standards for toughness testing of metallic materials.
SOME MECHANICAL CHARACTERISTICS OF NITROGEN STRUCTURAL STEELS
Authors: Minchev Kiril
Published: April 2007

In this paper, test conditions and microstructural factors have been investigated for newly developed nitrogen steels at load rates and test temperatures suitable for future operating conditions. Static tests have been carried out at ε∼ 10−4 s‐1 and dynamic tests at ε∼ 102 s−1. Different test temperatures enable fracture mechanisms and fracture toughness variations to be studied. Anisotropy of some characteristics in the initial (non‐heat‐treated) state, together with heat treatment effects and structural changes under two load rates have been analysed. Fracture appearance transition temperature (FATT) values have been obtained from absorbed energy and fracture surface crystallinity values. Using yield strength and fracture toughness data, an estimate has been made of critical crack lengths for unstable fracture.
EFFECTS OF CONSTITUENT SCALE ON STRESS TRANSFER AND MATRIX CRACKING
Authors: Karbhari V. M.
Published: April 2007

The fundamental aspect of composites is that of stress transfer from the matrix to the fibers, and a number of mechanisms derive from this basic consideration. A previous analysis, although relatively simple and elegant, has a basic flaw, in that it assumes that there is no adhesion between the fiber and the matrix at the fiber ends, leading to the sometimes erronous condition of no stress transfer through those points. In this paper a modified end condition that better describes stress transfer is investigated and applied in determining the development of fiber, matrix and interfacial shear stress distribution in the uncracked, singly cracked and multiple cracked matrix configurations, with emphasis on the effects due to constituent dimensions.
EFFECT OF CYCLE MEAN STRAIN ON SMALL CRACK GROWTH IN ALLOY 718 AT ELEVATED TEMPERATURES
Authors: Rosenberger A. H. , Ghonem H.
Published: April 2007

The influence of the cyclic compressive excursion on the fatigue crack growth behavior of small surface cracks in Alloy 718 at 650°C is experimentally studied. Test conditions were chosen to simulate the cyclic plasticity found at notch locations in high temperature structural components. During cycling, the crack lengths were continuously monitored using the direct current potential drop method while the near field crack mouth opening displacement and global cyclic stressstrain behavior were measured using a laser interferometry technique and mechanical extensometry, respectively. Two aspects related to cyclic compressive excursion have been studied; crack closure and crack tip plasticity. Attempts have been made to use several modified ΔK expressions as well as ΔJeff to account for the effects of closure and decrease crack tip plasticity. It was concluded that the compressive excursion is most prominent in this alloy in its effect on the global plasticity and the subsequent loss of constraint. Closure was not found to be significant in the consolidation of test data.
FATIGUE CRACK PROPAGATION BEHAVIOUR UNDER VARIABLE AMPLITUDE LOADING IN THE NEAR‐THRESHOLD REGION OF A HIGH‐STRENGTH LOW‐ALLOY STEEL
Authors: Hénaff G. , Petit J. , Journet B.
Published: April 2007

The near‐threshold behaviour of a high‐strength low‐alloy steel used in helicopter rotors under variable amplitude loading is investigated in ambient air and in vacuum. Strong sequence effects occur, in particular a high decrease in crack growth rates after overloads of 40% on maximum load while keeping the amplitude constant. A detailed study of the retardation phenomenon due to the overloads provides an explanation for the different behaviour observed in air and in vacuum and has laid the basis for a method of predicting crack propagation under helicopter loading spectra.
FRACTURE ASSESSMENT FOR SECONDARY LOADS
Authors: Hallbäck Nils , Nilsson Fred
Published: April 2007

The fracture assessment of structures subjected to secondary loading systems was studied by FEM‐analysis of a few illustrative two‐dimensional examples. The first example is an edge‐cracked plate with a thermal gradient. The FEM‐calculations revealed that a purely elastic analysis yielded J‐values that are in most cases considerably more conservative than the ones calculated from an elastic‐plastic analysis. The results were further compared with different engineering type non‐linear estimates. As a second example a crack emanating from a semi‐circular notch in a rectangular plate was chosen. The plate was subjected to uniaxial tension along its boundaries. It turned out that for the cases considered the J‐values were fairly close to those elastically predicted.
A MODEL FOR THE COMBINED EFFECTS OF STRESS RATIO AND GRAIN SIZE ON THE LEFM FATIGUE THRESHOLD CONDITION
Authors: Lal D. N.
Published: April 2007

A long‐crack, fatigue‐threshold model which explains and predicts the commonly observed effects of stress ratio, R, and grain size, d, on δK0, is proposed. The inclusion of a grain‐size‐effect is an extension of a recently proposed model that examined the effect of the R ratio. The extended model is based on the hypothesis that near‐threshold, crack growth involves two micro‐mechanical processes of fracture; Kmax‐controlled submicroscopic cleavage, which predominates when the defect concentration is small, and δK‐controlled reversed shear which predominates when the defect concentration is large, both processes occurring in a critically stressed volume, Vc, ahead of the crack tip. Defect concentration in Vc is reduced by a low value of R and a coarse grain size and is increased by a high value of R and a fine grain size. Good agreement is shown to exist between predicted and experimental curves of δK0 versus R and δK0 versus grain size for several steels and aluminium alloys. In particular, δK0 is shown to have an upper and a lower bound value for a material. The model may be used as an alternative procedure for obtaining quick, approximate but conservative estimates of δK0 for practical design applications.
A MODEL FOR THE EFFECT OF A GASEOUS ENVIRONMENT ON THE LEFM FATIGUE THRESHOLD CONDITION OF STEELS
Authors: Lal D. N.
Published: April 2007

Using a different approach to those methods involving hydrogen‐embrittlement and crack‐closure mechanisms a previously developed model is extended to predict the commonly observed effects of yield strength and a gaseous environment on the long‐crack fatigue crack growth threshold. The model assumes the existence of two intrinsic thresholds namely an upper bound value and a lower bound value related to, respectively, Kmax‐controlled cleavage and δK‐controlled reversed shear mechanisms of crack growth in a critically stressed volume at the crack tip. This new development assumes that nascent hydrogen atoms, liberated from moisture in the environment, assist in reducing dislocation mobility thereby rationalizing experimental observations on low strength materials in moist laboratory air when compared to a dry inert environment. Quantitative predictions of fatigue thresholds in laboratory air and inert environments show good agreement with experimental data for several low and high strength steels. This alternative procedure may be found to be useful in practical design applications when reasonably fast and accurate estimates are required.
BEHAVIOUR OF FIBRE‐REINFORCED CONCRETES WITH REFERENCE TO FRACTURE RESISTANCE
Authors: Lai Sergio
Published: April 2007

This paper examines the effect of beam size, fibre volume fraction and various fibres on the flexural behaviour of concretes, and their fracture resistance. The ratio of flexural strength to tensile strength is used as a measure of brittleness; a low value indicating a more brittle material.

Two flexural toughness indices are used which provide a basis for analysing load–deflection curves. The relation between these structural indices and the material fracture resistance is assessed by adopting parameters which involve flexural and tensile strengths alone and fibre length to reflect fracture resistance.
PREDICTING FATIGUE CRACK INITIATION LIFE OF AN ALUMINIUM ALLOY AT LOW TEMPERATURES
Authors: Baotong Lü , Xiulin Zheng
Published: April 2007

Abstract— A simple approach to predict the fatigue crack initiation (FCI) life of notches at low temperatures is developed. The stress cycle to initiate a 0.25 mm crack at a notch tip is presented as a function of an equivalent stress amplitude. The results of the study indicate that the FCI life of an aluminium alloy increases with decrease in temperature and the effect of temperature on the FCI resistance can be predict in the form of an FCI coefficient C and the FCI threshold. The coefficient C is the parameter controlling FCI resistance in the low cycle fatigue region and it can be calculated from the elasticity modulus and the strain hardening exponent. The threshold is the parameter governing FCI resistance in the high cycle fatigue region and its value depends mainly upon the endurance limit. The temperature‐ dependence of the endurance limit can be predicted by a thermal activation model. By means of this approach, the fatigue crack initiation life at low temperatures can be predicted from the material tensile properties without any additional low temperature fatigue tests and without any empirical modification so long as the endurance limit of the metal at room temperature is predetermined. The results suggest that this approach is applicable to other aluminium alloys.
THE EFFECTS OF MEAN AND ALTERNATING SHEAR STRESSES ON SHORT FATIGUE CRACK GROWTH RATES
Authors: Wang C. H. , Miller K. J.
Published: April 2007

Abstract— Torsion fatigue tests were conducted at room temperature on plain specimens of a 1.99% NiCrMo steel subjected to various combinations of mean and alternating shear stress. The growth behaviour of both microstructurally short cracks (MSC) and physically short cracks (PSC) has been studied. Mean shear stress was found to play a fundamental role in promoting both MSC and PSC cracks. The empirical Brown‐Hobson model, relating the alternating shear stress (or strain) to the short crack growth rate, is modified to incorporate the influence of mean shear stress in both the MSC and PSC growth regimes. The investigtion of the two crack growth equations leads to a satisfactory prediction of the fatigue endurance curves determined for a variety of mean and alternating shear stress levels.
AN EVALUATION OF FATIGUE AND FRACTURE MECHANICS PROPERTIES OF ULTRA‐HIGH STRENGTH 7XXX SERIES Al‐ALLOYS
Authors: de Sanctis M. , Lazzeri L.
Published: April 2007

Abstract— The fatigue and fracture mechanics properties of rapidly solidified ultra‐high strength 7XXX series Al‐alloys have been studied. With respect to conventional high‐strength Al‐alloys, these materials exhibited a better fatigue‐endurance on both plain and notched specimens at low stress amplitude in constant amplitude fatigue tests, whereas the opposite occurred at high stress amplitudes. Fatigue crack growth tests indicated lower crack growth rates at low ΔK‐levels, but at intermediate and high ΔK‐values these materials were particularly prone to additional components of “static” crack propagation, which led to steeply inclined da/dN vs ΔK curves. Moreover, the increase in tensile strength was linked with some loss of ductility and fracture toughness. Overload regions were characterized by a large amount of intergranular decohesion, possibly facilitated by the presence of incoherent particles at grain boundary regions and by the large strength differential between the matrix and precipitate free zone. The best results in terms of elongation to rupture and toughness were obtained by reducing the amount of Cr/Mn incoherent dispersoid‐forming elements, in order to lessen the tendency towards matrix‐dispersoid interface decohesion at grain boundaries.
FATIGUE CRACK GROWTH OF Al 2024‐T3 UNDER LOW AMPLITUDE TWO‐STEP LOADING
Authors: Mayer H. R. , Stanzl S. E. , Tschegg E. K. , Schijve J.
Published: April 2007

Abstract— The significance of interaction effects has been studied in tests with a continuous repetition of blocks with low and high amplitude cycles under conditions characteristic for ultrasound fatigue. Significant retardation effects were observed. However, low‐intensity cycles, which according to a previous investigation might be harmless, did contribute to crack growth. Delayed retardation explains this observation. A fractographic analysis indicated the significance of surface roughness. Low‐amplitude cycles may induce a smoother fracture surface, and thus increase the crack growth rate at higher amplitudes. Accurate predictions are therefore problematic. For similar reasons, omitting numerous low‐amplitude cycles in random load experiments should be done with great care.
AN EVALUATION OF THE FRACTURE RESISTANCE OF ENGINEERING MATERIALS FROM THE FRACTURE SURFACE MORPHOLOGY
Authors: Alcala J. , Ledezma M.
Published: April 2007

Abstract— The following work examines the fracture morphology in relation to the COD R‐curves of three stainless steels. Additional considerations are noted concerning crack growth behaviour based on simple, optical microscopic observations. Procedures for the determination of R‐curves and initiation values are outlined when a multi‐specimen technique is used and the crack growth is measured by a light microscope. The COD R‐curves are obtained for different conditions which reduce fracture ductility in two 310S and one 304H stainless steels. These conditions include a sigma‐phase in one 310S, and sensitization of the large grain size microstructure in the other 310S stainless steel.
INTERACTION OF HIGH‐STRAIN AND HIGH‐CYCLE FATIGUE IN TURBINE MATERIALS
Authors: Suhr R. W.
Published: April 2007

Abstract—An investigation has been conducted to examine the interaction between high‐strain and high‐cycle fatigue under combined cycling conditions on 2% NiCrMoV and a 12% CrNiMo alloy. The results reveal that the application of high‐strain fatigue cycles prior to low‐strain high‐cycle fatigue is significantly less damaging than the equivalent number of single high‐strain cycles applied between periods of high‐cycle fatigue, indicating a much greater damaging interactive effect under the combined cycling condition. A damage summation, based on high‐strain and high‐cycle fatigue initiation curves and calculated at various endurances, was found to approach zero under combined cycling conditions indicating that a prediction of damage using the Palmgren‐Miner linear damage rule is inapplicable. Cumulative damage curves, based on an assessment of hypothetical crack growth behaviour under high‐strain and high‐cycle fatigue conditions, can be constructed to explain the large departure from the Palmgren‐Miner prediction of unity. Such curves, however, fail to predict the more damaging interactive effect observed under combined cycling conditions. The apparent contradiction between experimental results and theoretical assessment is discussed and a mechanism proposed to account for the observed interactive effect.
FATIGUE CRACK SIZE PROBABILITY DISTRIBUTION VIA A FILTER TECHNIQUE
Authors: Casciati F. , Colombi P. , Faravelli L.
Published: April 2007

Abstract— A Markovian method of crack propagation analysis is studied. Non‐physical negative and/or unbounded crack growth rates are avoided. The cumulative distribution function of the crack length is evaluated at a fixed time by using a technique based on Hermite moments which are calculated by means of classical Itô calculus. A numerical example illustrates the main features of the method. The agreement between theoretical results and experimental data is very satisfactory.
ON THE EFFECT OF PERSISTENT SLIP BAND (PSB) PARAMETERS ON FATIGUE LIFE
Authors: Cao Wei‐di , Conrad Hans
Published: April 2007

Abstract— An examination of PSB data pertaining to the effects of an air‐excluding environment and electric current on the fatigue life of polycrystalline Cu and 316 stainless steel in rotating bending reveals that the spacing and width of the PSBs are smaller throughout the fatigue test for those conditions which lead to increased fatigue life. Moreover, the life correlates directly with the square of the product of the surface area fraction of PSB patches and the density of the PSBs contained therein. These results suggest that in these cases slip‐homogenization is responsible for the increased fatigue life and not a consequence of it. A model is proposed for the observed relationship between slip band parameters and fatigue life, which is based on the strain concentration that exists at or near the PSB‐matrix interface. The mechanisms by which an air‐excluding environment or an electric current can increase slip homogenization are considered.
FRACTURE MECHANICS APPROACH FOR PREDICTION OF FATIGUE LIFE OF HIGH STRENGTH STEEL COMPONENTS
Authors: Barui K. L. , Bhattacharya B.
Published: April 2007

Abstract— A fatigue life estimation procedure based on a fracture mechanics approach is analytically developed for components made of a 4140 grade high strength steel. The maximum allowable flaw sizes for both static and cyclic loads are computed. For different stress levels and shapes of the defects, initially‐existing, allowable defect size versus number of operating cycles, as well as the thickness versus tolerable defect sizes curves, are presented. The maximum allowable operating cycles of components for non‐destructively detectable minimum defects are also estimated. From these estimations, a more realistic prediction of the safe service life of components is possible.
A RANDOMIZED ENDURANCE LIMIT IN FATIGUE DAMAGE ACCUMULATION MODELS
Authors: Kopnov V. A.
Published: April 2007

The use of random parameters for describing S‐N curves requires special caution. A Peculiar Fatigue Curves (PFC) method based on a linear damage accumulation rule is proposed for modelling the fatigue damage accumulation process. The fatigue properties of a component are presented in the PFC form by randomizing its endurance limit which facilitates a simple technique to predict fatigue life and residual life distributions. Possible usages of the models and their restrictions are illustrated for some common load histories of a component. Particular attention is paid to the stochastic relations between random variables having in some cases improper distributions. The problem of experimental testing of the models is also discussed.
THE USE OF A FAILURE ASSESSMENT DIAGRAM FOR INITIATION AND PROPAGATION OF DEFECTS AT HIGH TEMPERATURES
Authors: Ainsworth R. A.
Published: April 2007

The use of a failure assessment diagram, of the type in the R 6 defect assessment procedure, is investigated for creep crack growth under steady loading. While a detailed approach based on C* remains attractive for appreciable creep crack growth, it is shown that a simplified approach can be formulated for limited crack extension. A failure assessment diagram is derived based on the option 2 curve of R 6 using isochronous stress‐strain data. The inclusion of elastic strains in the isochronous data covers stress redistribution effects.

Equations are given which enable a toughness, Kmat, for assessments at temperatures in the creep range to be evaluated from creep crack incubation and growth data presented in terms of C*. The toughness, Kmat, replaces the fracture toughness used in low temperature R 6 assessments. Thermal stresses can be included in assessments by evaluating the stress intensity factor for the combined thermal and mechanical loading. A formula is given which enables the effect of thermal stresses to be reduced when creep strains are sufficient to relax out part or all of the thermal stress.
THE STATISTICAL TREATMENT OF SMALL SPECIMEN FRACTURE TOUGHNESS DATA IN THE TRANSITION REGION
Authors: Brožová Anna , Ruščák Martin
Published: April 2007

Abstract— The paper deals with the fracture toughness data gained from small Charpy‐COD specimens of CrNiMoV steel in both unirradiated and irradiated states. The new single transition temperature is defined as the quantile of the Pui distribution. The Weibull (2‐ and 3‐parameter) and Neville models are used for the statistical treatment of the data. The lower part of the failure probability distribution can well be described by the models, the upper part, less steep, needs a new approach. The change between these two conditions is considered to be caused by failure of the small scale yielding condition. The effect is more significant for irradiated materials. A new definition of the limit for Jmax values reflecting the effect of both flow stress and work hardening exponent is suggested.
THE EFFECT OF HYDROGEN ON SHORT FATIGUE CRACK GROWTH IN AN Al‐Li ALLOY
Authors: de Los Rios E. R. , Sun Z. Y. , Miller K. J.
Published: April 2007

Abstract— Experimental results are presented to illustrate the degree of susceptibility to hydrogen embrittlement in an Al‐Li 8090 alloy. The ductility of the alloy (as recorded in slow strain rate tests) is reduced by hydrogen charging which induces microcrack formation on the surface of the hydrogen treated specimens. Results of fatigue tests show that small fatigue cracks propagate 1.5 to 10 times faster in specimens charged with hydrogen and fractographic evidence shows that short crack growth in hydrogen precharged specimens is transgranular, along persistent slip bands. The effect of hydrogen is reversible, the embrittlement effect being eliminated by holding the specimens for 24 hr at 470°C.
FINITE ELEMENT ANALYSIS OF STABLE CRACK GROWTH IN THREE SIZES OF COMPACT SPECIMENS OF A508 STEEL
Authors: Xin X. J. , Goldthorpe M. R.
Published: April 2007

Abstract— Plane strain, elastic‐plastic, finite element analyses have been undertaken to simulate stable crack growth in an A508 forging steel for three different sizes of compact tension specimen and for small scale yielding by enforcing the same experimentally‐measured deformation theory J resistance curve. The results show that path‐dependence of the numerically calculated J‐integral occurs from the very beginning of crack growth, and the degree of path‐dependence is not strongly related to the amount of crack growth expressed as a proportion of the uncracked ligament. Crack tip stresses and strains are only mildly sensitive to changes in specimen size for the range of crack extension investigated. Small specimens appear to produce more intense deformation than small scale yielding and therefore cause more damage. For a tough steel such as A508 the parameter bσf/Jd, appears to be the most important in limiting the validity of J‐characterized fields of deformation ahead of the growing crack.
COMPARISONS OF THEORETICAL AND FINITE ELEMENT STRESS ANALYSIS SOLUTIONS FOR A BIMATERIAL STRIP AND PLATE SUBJECTED TO THERMAL LOADING
Authors: Kfouri A. P. , Wong H. D.
Published: April 2007

Abstract— A study is made on a bimaterial beam of length 2L and height 2h, composed of a lower half‐beam made from material A and an upper half‐beam made from material B, under thermal loading. The geometrically identical half‐beams are bonded together at the interface. Materials A and B have similar elastic properties, i.e., Young's modulus E(=207 GPa) and Poisson's ratio v(=0.3) are the same for both materials but the coefficients of linear thermal expansion are αA for material A and αB for material B, where αA > αB.

A theoretical solution based on simple beam theory is derived for the stress‐strain‐displacement fields at a temperature T1 > T0 where T0 corresponds to an initial stress‐free state, when the beam is held at the centre only to prevent rigid‐body motion. The main purpose of the investigation is to compare the results of the theoretical solution with those obtained from elastic, plane‐stress, finite element analyses, using two different meshes. The case when the ends of the beam are held down is also examined.

Finally the analogous axisymmetric problem of a bimaterial circular plate comprising a lower and an upper half‐plate bonded together, is investigated and a theoretical solution of the biharmonic equation, using Legendre polynomials, is derived. The results from the theoretical solutions are compared with the results from an axisymmetric finite element analysis and also from a simulation plane‐stress analysis using E1 as the effective modulus of elasticity, where E1=E/(1 –v). Some interesting features and oddities arising from these investigations are discussed.