bluuebunny/crossref_metadata_2025 huggingface dataset:
A COMPARISON OF SMALL FATIGUE CRACK GROWTH, LOW CYCLE FATIGUE AND LONG FATIGUE CRACK GROWTH IN A1‐Li ALLOYS
Authors: Nicholls D. J. , Martin J. W.
Published: April 2007

The behaviour of small fatigue cracks in the A1‐Li‐Cu‐Mg‐Zr alloy 8090 has been studied. Growth rates of small fatigue cracks in these alloys were found to be proportional to ΔK2. This relationship is compared to that suggested by Murakami where crack growth rate was proportional to ε2pa. The difference between the equations is attributed to the relative importance of plastic strain for the two sets of data. It is suggested that the two equations are equivalent if crack growth rate is related to total strain. The common observation of a Paris law exponent of two in different alloys suggests that there is a single common mechanism for small fatigue crack growth. This contrasts with long fatigue crack growth, where a variety of Paris law exponents are observed. Other characteristics of this fatigue mechanism include crack propagation on {111} slip bands, insensitivity of crack propagation rate to precipitate distribution and a plastic zone comparable in size to the crack itself.
COMPLEX STRESS FUNCTIONS AND PLASTIC ZONE SIZES FOR NOTCH CRACKS SUBJECTED TO VARIOUS LOADING CONDITIONS
Authors: Youshi Hong , Miller K. J. , Brown M. W.
Published: April 2007

In this paper, the conformal mapping method is used to solve the plane problem of an infinite plate containing a central lip‐shaped notch subjected to biaxial loading at a remote boundary or a surface uniform pressure on the notch. The stress intensity factors KI and KII are obtained by the derived complex stress functions. The simple analytical expressions can be applied to the situation of cracks originating from a circular or an elliptical notch. The plastic zone sizes for such notch cracks are subsequently evaluated in light of the Dugdale strip yield concept. The results are consistent with available numerical data.
DYNAMIC MEASUREMENT OF CRACK CLOSURE BEHAVIOUR OF SMALL FATIGUE CRACKS BY AN INTERFEROMETRIC STRAIN/DISPLACEMENT GAUGE WITH A LASER DIODE
Authors: Akiniwa Yoshiaki , Harada Shoji , Fukushima Yoshihiro
Published: April 2007

An interferometric strain/displacement gauge (ISDG) system with a laser diode was developed to measure dynamically the crack closure behaviour of a small surface crack. Two Vickers indentations, about 100 μ apart, were illuminated with the laser pulse synchronized with the load signal. The interference fringe patterns moved as the indentation moved apart. The 95% confidence limit, obtained on the basis of the difference between the strain measured by the ISDG and that by the resistance strain gauge (RSG), was ±6.0 × 10−4μ for stepwise loading. The standard deviations of the relation between stress and displacement under elastic conditions were 1.7 for stepwise loading at 0.067 Hz and 2.6, 2.6, 2.3 for dynamic loading at 5, 10 and 20 Hz respectively. The crack mouth opening displacement was measured dynamically as well as statically with the system. The crack opening stress was determined using the unloading elastic compliance method. The measuring frequency hardly affected the crack opening stress. Smooth specimens of a type 304 austenitic stainless steel were fatigue tested. The crack propagation behavior was observed and crack closure measurements monitored for crack lengths ranging from 0.12 to 0.75 mm. The aspect ratio of the surface crack was determined on the basis of the relation between the surface crack length and the elastic compliance. The relation between the crack propagation rate and the J integral range was unique, and agreed well with that calculated by the effective stress intensity range for long cracks.
MEAN STRESS EFFECTS ON LOW CYCLE FATIGUE FOR A HIGH STRENGTH STEEL
Authors: Koh S. K. , Stephens R. I.
Published: April 2007

Abstract— ASTM A723 Q & T steel with a yield strength and ultimate strength of 1170 and 1262 MPa respectively was evaluated for mean stress‐strain effects under smooth specimen axial strain controlled low cycle fatigue conditions with strain ratios R of −2, −1, 0, 0.5 and 0.75. Cycles to failure ranged from 15 to 105. Cyclic stress‐strain response based upon half‐life hysteresis loop peaks were similar for all R ratios. Mean stress relaxation occurred for R≠−1 only when plastic strain amplitudes were present and this occurred above total strain amplitudes of 0.005. Thus, mean stress relaxation was completely dependent upon cyclic plasticity. Mean strains did not affect low cycle fatigue life unless accompanied by half‐life mean stress. Tensile mean stress was detrimental and compressive mean stress was beneficial and these effects only occurred at strain ampltidues below 0.005. Three different mean stress models were used to evaluate the low cycle fatigue data and the SWT log‐log linear model best represented the data. These results can be used with the local notch strain fatigue life prediction methodology.
CRACK CLOSURE AND PLASTIC ZONE SIZES IN FATIGUE
Authors: McClung R. C.
Published: April 2007

Abstract— An elastic‐plastic finite element simulation of growing fatigue cracks which accounts for plasticity‐induced crack closure is used to study the size of the forward and reversed plastic zones at the crack tip. Forward plastic zone widths for fatigue cracks and stationary, monotonically loaded cracks are compared and found to be similar. The width of the forward plastic zone at the tip of a fatigue crack is not significantly influenced by closure. The traditional Irwin‐Rice estimate for crack tip plastic zone size in plane stress is found to be generally consistent with the finite element results. The width of the reversed plastic zone at the tip of a growing fatigue crack in plane stress is found to be considerably less than one‐fourth the size of the forward plastic zone, the traditional Rice estimate. This decrease appears to be due to fatigue crack closure. A simple model is developed which permits estimation of the reversed plastic zone size for any stress ratio from information about maximum and minimum stresses and the closure stress. The predictions of this model agree closely with plastic zone sizes calculated by the finite element analysis. These observations appear to be consistent with experimental measurements of forward and reversed plastic zones sizes reported in the literature.
A REVIEW OF FRACTURE MECHANICS MODELS OF TUBULAR JOINTS
Authors: Haswell J. , Hopkins P.
Published: April 2007

Fracture mechanics methods are used to assess the significance of cracking in any structure, but a tubular joint is very complex to analyse. However the improvements in numerical methods, such as stress analysis using finite elements, and extensive full‐scale laboratory testing (UKOSRP, ECSC, etc.) have allowed various workers to propose fracture mechanics models of tubular joints.

This paper presents a critical review and comparison of these models. It concludes that simple plate models can provide upper and lower bound stress intensity factor solutions for cracked tubular joints. Stress intensity factors from three dimensional finite element analysis of a tubular joint are in reasonable agreement with semi‐empirical data. However, in the absence of a validated database the paper concludes that any analytical assessment of a crack in a joint should be viewed as tentative.
EFFECT OF PARTIAL‐COVERAGE UPON THE FATIGUE FRACTURE BEHAVIOUR OF PEENED COMPONENTS
Authors: Meguid S. A.
Published: April 2007

The achievement of full‐coverage during the application of shot‐peening to critical components represents a major concern in the aerospace and power generation industries. It has been accepted, for many years, that full‐coverage of such components is needed to attain the beneficial fatigue‐life effects of the treatment. It has also been proposed, by a number of industrialists, that partial‐coverage may apparently shorten the fatigue‐life of the component because of the presumed presence of tensile residual stresses in the uncovered areas. Three aspects of the investigation were accordingly examined. The first deals with the accurate measurement of peening coverage using a three‐dimensional surface profilometer arrangement. The second deals with the development of fatigue crack growth data for fully‐ and partially‐peened components using an instrumented rotating‐bend fatigue rig. The third deals with monitoring the residual stress field associated with different peening‐coverage using the dissection method. In order to highlight the effect of the treatment upon the fatigue behaviour of the tested components, both theoretical and experimental techniques were considered. In the theoretical work, three‐dimensional finite element analysis of circumferentially cracked notched and un‐notched cylindrical components was considered in the development of the corresponding stress‐intensity factor (KK1) under bending loads. The stress‐intensity factor vs crack length relationship was subsequently used in the experimental determination of fatigue crack growth rate data at the different stress levels examined. Accordingly, room temperature rotating‐bend fatigue tests were conducted on specimens made from medium carbon steel 080 M40 (En 8) and aluminium alloy (7075‐T6). Surprisingly, the results of both materials reveal that a life improvement of up to 50% can be attained at 35% coverage level.
BEHAVIOUR OF A 1Cr‐1Mo‐0.25V STEEL AFTER LONG‐TERM EXPOSURE–I. CHARPY IMPACT TOUGHNESS AND CREEP PROPERTIES
Authors: Moliniéa E. , Piques R. , Pineau A.
Published: April 2007

This paper deals with the effect of casting conditions and long‐term in‐service exposure on the Charpy‐V notch and creep properties of a 1Cr‐1Mo‐0.25V steel. The material is investigated under two conditions: (i) as‐cast in a thick part which produces a mixed ferrite‐bainite microstructure and (ii) as‐cast as a small ingot which produces a fully bainitic microstructure. The material from the thick part was taken from either the cold part (∽200°C) or the hot part (∽540°C) of a steam power casing which operated for about 150,000 h. A small shift in the ductile‐brittle transition temperature is shown after the long exposure time. This shift is related to segregation of phosphorus impurities along the grain boundaries as shown by Auger electron spectrometry. The bainitic microstructure exhibits a much better creep resistance compared to the thick part component material. Moreover, in the latter case, it is shown that long‐term in‐service exposure induces an increase in creep strain rate and a decrease in creep ductility at least for relatively short times to failure (≲1000 h). These variations in mechanical properties are briefly discussed in terms of microstructural changes. Scanning electron microscopy confirmed that grain boundary cavitation was responsible for decreasing the creep ductility at large times to failure (≳ 10,000 h).
ANALYSIS OF FATIGUE LIFE DATA USING THE BOX‐COX TRANSFORMATION
Authors: Hinkle A. J. , Emptage M. R.
Published: April 2007

Fatigue life data customarily analyzed using the logarithmic transformation may be better analyzed using the Box‐Cox transformation. This transformation has the advantages of stabilizing the variance, simplifying the model and transforming to approximate normality. In addition, simple schemes for imputing run‐outs can be constructed and the endurance limit can be easily calculated.

This paper considers in detail the use of the transformation on fatigue life data from a thick plate Al‐Zn‐Cu‐Mg alloy. It presents a simplified method for determining the transformation, and then uses the transformation to determine distinctions in quality between different lots and confidence intervals on the lifetime.
THE VIRTUAL CRACK EXTENSION METHOD FOR CREEP FRACTURE
Authors: Hellen T. K.
Published: April 2007

Knowledge of the creep behaviour of materials used in structures which operate for many years is of fundamental importance when assessing the integrity of such structures. The additional consideration of cracks which may occur in metals is also important. For discrete cracks, characterising parameters associated with the creep conditions at the crack tip may be evaluated to determine whether the crack will grow slowly, rapidly, or remain stationary. For arbitrary structures containing such defects, the finite element method is particularly effective for calculating the time‐dependent stress analysis. The particular fracture parameters can then be evaluated using algorithms based on existing technology for contour integration, and a new virtual crack extension technique. These features are described and compared in application to a laboratory compact tension specimen.
THE EFFECTS OF MICROSTRUCTURE AND FRACTURE SURFACE ROUGHNESS ON NEAR THRESHOLD FATIGUE CRACK PROPAGATION CHARACTERISTICS OF A TWO‐PHASE CAST STAINLESS STEEL
Authors: Murakami Ri‐ichi , Kim Yun‐Hae , Ferguson W. G.
Published: April 2007

In this study, the effects of stress ratio, microstructure and fracture surface roughness on the fatigue properties of a two‐phase cast stainless steel were investigated. This behaviour was examined by means of the fracture mechanics approach and fractography. The fatigue crack growth rate decreased with decreasing stress ratio. The stress ratio markedly influenced the fatigue crack growth rate as ΔK approached the ΔKth value. The roughness of the fracture surface was greater in the as‐cast material than in the heat‐treated material. Analysis of the crack growth data using ΔKeff showed that the effect of R ratio could be explained but that the effect of microstructure on crack growth rate could not.
OXIDATION‐ASSISTED FATIGUE CRACK GROWTH BEHAVIOR IN ALLOY 718‐PART I. QUANTITATIVE MODELING
Authors: Ghonem H. , Zheng D.
Published: April 2007

This paper presents a new model to predict the high temperature, intergranular crack growth rate behavior in alloy 718 at 650°C. The model is based on the concept that the crack tip oxidation‐fatigue damage is a nonlinear process governed by the chemical‐mechanical interaction along the grain boundary fracture path at the crack tip. A concept of two‐stage oxidation mechanism was used here. This mechanism depends on the rate of formation of the chromia layer in relation to the build‐up of other oxide types at the crack tip. The saturation of the Cr2O3 build‐up signifies the occurrence of the oxide passivation effect. The determination of the amount of Cr2O3 depends on the amount of both oxygen diffused along the affected grain boundary and chromium transported via a mobile dislocation network. Here, both the grain boundary and effective dislocation pipe are treated as short‐circuit diffusion paths along which the diffusion process can be described using Whipple's solution. The model yields sufficient information to correlate the amount of Cr2O3 with the reduction in the grain boundary ductility within the affected oxide zone. The grain boundary ductility is balanced by the effective strain at the crack tip resulting from the external loading. This balance defines the fracture criterion of the model and permits the calculation of the crack advance per cycle which is the ultimate goal of this work.
ELEVATED TEMPERATURE FATIGUE CRACK PROPAGATION IN HOT WORK TOOL STEEL
Authors: Tang N.‐Y. , Plumtree A.
Published: April 2007

Cyclic tests have been carried out on a hot work tool steel (H13) over a range of temperatures using different waveforms. At a temperature of 125°C, a slow‐fast wave resulted in lower crack propagation rates than those with a balanced (or symmetrical) waveform. However, at 500°C normal fatigue crack propagation behaviour was observed in which the slow‐fast wave was more damaging than a balanced waveform at the same frequency. Dynamic strain aging is attributed to the reversed crack propagation effect at 125°C.
CORROSION FATIGUE FRACTURE‐MODE MAPS OF LOW ALLOY STEELS
Authors: Xing Zhiqiang , Song Yujiu , Tu Mingjing
Published: April 2007

The fatigue fracture features of low alloy steels in aqueous environments are investigated. It is revealed that microstructures, compositions and mechanical variables will affect the fracture mode. A series of fracture‐mode maps of structural steels are established and a corrosion‐fatigue‐mechanism map of 15 Mn dual‐phase steel is developed. The importance of fractography and fracture‐mode is emphasized.
RAINFLOW CYCLES IN GAUSSIAN LOADS†
Authors: Rychlik Igor
Published: April 2007

We present a new approximation of the expected damage for Gaussian loads. The approximation is based on an exact relationship between the rainflow cycle count and the range‐pair exceedances count. This relationship links the intensity of rainflow amplitudes to expectations of marked crossings of the random load. The method is best suited for the fatigue life prediction for locally stationary Gaussian loads with slowly varying means and covariance functions. These results are illustrated with numerical examples.
FATIGUE BEHAVIOUR OF Al2O3 SHORT FIBRE REINFORCED ALUMINIUM ALLOY
Authors: Liu Xi Cong , Bathias Claude
Published: April 2007

The room temperature fatigue strengths of A1‐7Si‐0.6Mg and A1‐SSi‐3Cu‐1Mg composites randomly reinforced with A12O3 short fibres were determined using a stress ratio of 0.1, a frequency of 50 Hz. The fatigue strength of the composites under these testing conditions can be expressed by a single curve‐fitting equation. The effect of surface roughness on fatigue strength was also studied and the results show that these composites are not sensitive to surface roughness. The orthogonal growth of cracks is an important fatigue fracture mechanism in these composites. The residual strength decreased as the fatigue load increased.
RESIDUAL STRESS FIELDS DURING FATIGUE CRACK GROWTH
Authors: Sun Wei , Sehitoglu Huseyin
Published: April 2007

This study outlines the distinction between (1) residual stresses at an ideal crack tip, undergoing reversed deformation in the absence of crack closure, and (2) additional residual stresses generated due to plasticity induced closure upon fatigue crack growth. Residual stresses resulting from reversed deformation in plane strain were higher compared to the plane stress case, while residual stresses generated behind the crack tip were more significant in plane stress compared to plane strain. The origin of these residual stresses was studied for two specimen geometries over a wide range of loading conditions. We define a new crack tip parameter, Stt as the applied stress level that corresponds to the development of tensile stresses immediately ahead of crack tips. The Stt levels were significantly higher for a fatigue crack than for an ideal crack. We attribute the difference in Stt levels between these two cases to plasticity induced closure. The results demonstrate the importance of the Stt parameter, since the stresses ahead of crack tips could remain compressive even when the crack surfaces are open. Moreover, the study emphasizes the need, when describing fatigue crack growth, to incorporate both the closure concept and residual stress field ahead of a crack tip.
LEAK‐BEFORE‐BREAK CONDITIONS OF PLATES AND PIPES UNDER HIGH FATIGUE STRESSES
Authors: Nam Ki Woo , Ando Kotoji , Yuzuru Sakai , Ogura Nobukazu
Published: April 2007

The leak‐before‐break(LBB) behaviour of a structural component under high fatigue stress, low‐cycle fatigue conditions is an important problem in nuclear power plants, liquid nitrogen gas tankers and chemical plants. This paper is an experimental study to clarify the crack shape at penetration, crack opening behaviour after penetration and the LBB condition for plate specimens and pipe specimens. The fatigue load which realizes the LBB condition, PFLBB' is based on a net‐stress criterion. It is found that PFLBB is dependent only on the initial crack length a0. Furthermore, it is shown that the crack opening displacement V at the centre of a penetrated crack can be derived using the gross stress, σG' and the front surface crack length, as' together with the back surface crack length, ab.
SINGLE‐CRYSTALS AS AN INDICATOR OF FATIGUE DAMAGE
Authors: Zasimchuk E. E. , Radchenco A. I. , Karuskevich M. V.
Published: April 2007

Abstract— The possibility of using specially prepared single crystals as indicators of fatigue damage is outlined. Results are described of an analysis of deformation patterns developed in the single‐crystal indicator surface, under fatigue and static loading. It is shown that the density and direction of deformation bands correlate with the number of loading cycles.
SAFETY ASSESSMENT OF A CAST STEEL VALVE CASING USING NDE AND FRACTURE MECHANICS
Authors: Hodulak L. , Blauel J. G. , Berger Ch. , Saß J.
Published: April 2007

Abstract— The possibilities and limitations of failure predictions, based on the determination of defect size and shape by NDE, on material characterization using standard testing methods and on calculations using a failure assessment program for personal computers have been investigated for a control valve casing by comparing analytical calculations with component tests.
A METHOD FOR THE CONSTRUCTION OF SAFE S‐N CURVES
Authors: Sweeting T. J.
Published: April 2007

Abstract— The fatigue life behaviour of airframe components under spectrum loading differs markedly in the moderately high and low loading severity regimes. Statistical analysis of fatigue test and strength data leads to suitable safe S‐N curves for each of these regions and the problem is how to construct a single S‐N curve which blends these two curves together. A method of constructing such a curve is described here. This method has been incorporated into recent guidelines for compliance with design and airworthiness requirements.
EFFECTS OF BRUSH ELECTROPLATING AND SHOT PEENING ON THE FATIGUE STRENGTH OF A MEDIUM STRENGTH STEEL
Authors: Li Yang Guang , Qiao Ji Song
Published: April 2007

Abstract— Brush electroplating causes a marked reduction in the fatigue strength of the base steel. For the medium carbon steel reported in this paper, the fatigue limit is reduced 28.6% by nickel brush electroplating. A large number of short cracks are found in the nickel coating, and the coating usually suffers a high value of internal tensile stress. These are two reasons that cause the loss of fatigue strength. Shot peening has been used to minimize the loss of fatigue strength caused by brush electroplating.
CONSTANT AMPLITUDE AND POST‐OVERLOAD FATIGUE CRACK GROWTH BEHAVIOR IN PM ALUMINUM ALLOY AA 8009
Authors: Reynolds A. P.
Published: April 2007

Abstract— The fatigue crack growth behavior of a recently developed, rapidly solidified, powder metallurgy, dispersion strengthened aluminum alloy, AA 8009, was studied at room temperature in laboratory air. Constant amplitude/constant ΔK and single spike overload conditions were examined. Alloy 8009 exhibited high fatigue crack growth rates and low closure levels in comparison to typical ingot processed aluminum alloys. It was proposed that minimal crack roughness and crack path deflection, along with limited slip reversibility, resulting from the ultra‐fine microstructure were responsible for the relatively poor (versus ingot processed aluminum alloys) da/dN versus ΔK performance of AA 8009.
THE DEVELOPMENT OF CREEP SINGULAR FIELDS FOR DEFECTS IN THERMALLY LOADED STRUCTURES
Authors: Joch J. , Ainsworth R. A.
Published: April 2007

Abstract— This paper provides an initial examination of the development of singular fields for defects in creeping structures for combined mechanical and thermal loading. Finite‐element analyses are reported for cylindrical and plate geometries with different ratios of mechanical and thermal loading. It is shown that approximations for estimating the time‐development of the amplitude of the singular fields are given by formulae developed previously for mechanical loading, provided a normalised timescale is defined appropriately.
CRACK GROWTH ANALYSIS FOR VARIABLE LOADING CONDITIONS
Authors: Baumshtein M. V. , Vainshtok V. A.
Published: April 2007

Abstract— Structural element service conditions often involve a number of thermo‐mechanical loading factors. Increasing the number of these variable factors, the evaluation of crack growth resistance becomes rather complicated. So, it is of practical importance to predict the material crack growth resistance over a wide range of service conditions from the results of a limited number of standard specimen tests under specified loading conditions. The present note is based on a mathematical theory and tests on a limited number of standard specimens. A functional dependence has been obtained between the crack growth rate and kinetic equation parameters and the values of thermo‐mechanical loading factors.
OVERLOAD RETARDATION OF FATIGUE CRACK GROWTH IN A 9%Cr 1%Mo STEEL AT ELEVATED TEMPERATURES
Authors: Cotterill P. J. , Knott J. F.
Published: April 2007

This paper describes an investigation into the effects of a single‐peak tensile overload on fatigue crack propagation in a 9%Cr 1 %Mo steel. Overloads were applied during cycling at a constant stress intensity range (ΔK), and any consequent transients in growth rate were recorded. The severity of retardation rises as the magnitude of the applied overload is increased. The effect of temperature is complex, but a 525˚C retardation is significantly less marked than at 25 or 225˚C. Signs of crack face contact are seen on post‐overload fracture surfaces, but there is little crack branching. The dominant cause of overload retardation in this steel appears to be plasticity‐induced closure. At 525˚C, post‐overload dwell periods significantly reduce the severity of retardations. This is not observed at lower temperatures, indicating that the residual clamping stresses that lead to closure are gradually relieved at 525˚C.
CRACK FACE INTERACTIONS AND NEAR‐THRESHOLD FATIGUE CRACK GROWTH
Authors: Tschegg E. K. , Stanzl S. E. , Mayer H. R. , Czegley M.
Published: April 2007

Rough fracture surfaces usually influence substantially the fatigue growth properties of materials in the regime of low growth rates. Friction, abrasion, interlocking of fracture surface asperites and fretting debris reduce the applied load amplitude to a smaller effective value at the crack tip (“sliding crack closure”, or “crack surface interaction” or “crack surface interference”). The influence of these phenomena on the fatigue crack growth properties of structural steel is discussed and compared for the two kinds of mixed mode loading employed in this work. Mixed mode loading was performed by (A): cyclic mode III + superimposed static mode I and (B): cyclic mode I + superimposed static mode III loading. Such loading cases frequently occur in rotating load‐transmission devices.

Several differences are typical for these two mixed‐mode loading cases. A superimposed static mode I load increases the crack propagation rate under cyclic mode III loading whereas cyclic mode I fatigue crack propagation is retarded when a static mode III load is superimposed. Increase of the R ‐ratio (of the cyclic mode III load) leads to an insignificant increase of fracture surface interaction and subsequently to a small decrease of the crack growth rate for cyclic mode III loading, whereas higher R ‐values during cyclic mode I+ superimposed static mode III loading lead to a significant reduction of the crack growth rates.
A CRACK CLOSURE MODEL FOR PREDICTING THE THRESHOLD STRESSES OF NOTCHES
Authors: Ting Jason C. , Jr Frederick V. Lawrence,
Published: April 2007

A model is proposed to estimate the threshold stress range of a notched component. The model considers the variation of crack closure with crack length in the presence of a notch. The threshold stress range was found from the condition that the minimum value of effective threshold stress intensity range of a crack emanating from a notch equals the effective threshold stress intensity range of a “long” crack. The effects of notch depth, of notch acuity, of notch and specimen type, of load ratio, and of material properties on the threshold stresses were considered. Experimental data reported in the literature were used to assess the validity of the model. It was found that the model correctly predicts the behavior of cracks in notched components.
FATIGUE BEHAVIOUR OF FIBRE ALUMINIUM LAMINATES WITH DIFFERENT RESIDUAL STRESSES
Authors: Danmei Liu , Wei Qu , Weifeng Yang , Mei Yao , Reiping Zhang , Yuebo Xia
Published: April 2007

In this study two kinds of fibre aluminium laminates (aramid aluminium laminates, ARALL and glass aluminium laminates, GLARE) with different residual stresses in the aluminium layers were prepared. Fatigue crack propagation tests were performed. It is found that the residual stress condition plays an important role in the fatigue behaviour of fibre aluminium laminates. With a decrease of the tensile residual stress in the aluminium layers, the fatigue crack growth rate of the laminates is greatly reduced, and the shape of the curves of fatigue crack propagation rate as a function of the stress intensity factor changed. Compared to GLARE, the ARALL is more sensitive to the residual stress condition. The fatigue properties of non‐prestressed GLARE are better than those of ARALL. The influence of the residual stress is discussed in detail.
THE EFFECTS OF CRACK DEPTH ON THE J‐INTEGRAL AND CTOD FRACTURE TOUGHNESS FOR WELDED BEND SPECIMENS
Authors: Shi Y. W. , Han Z. X.
Published: April 2007

This work deals with the influence of crack depth on the fracture toughness at initiation of crack growth and the constraint factor in relationship between the J‐integral and the crack tip opening displacement (CTOD). A series of tests were performed on high strength low alloyed HT80 steel welds, and the critical J‐integral and CTOD were determined using the load versus load point displacement record from three‐point bend specimens with 0.05 < a/W < 0.5. It was found that the fracture toughness for shallow cracks at the onset of crack growth was larger than that for deep cracks for the steel welds tested, but it is felt that there is no fixed relationship between these values in the welds tested. The constraint factor is also a function of crack depth, and values of the factor increase from 0.5 to 1.5 when a/W increases from about 0.05 to 0.5. The factors are not very sensitive to the crack tip materials (HAZ or weld metal) in the welds tested.
EFFECT OF AN ELASTIC‐PLASTIC SHOCK WAVE PART A: ON THE FATIGUE STRENGTH OF WELDED JOINTS
Authors: Liangshan Chen , Huaining Chen , Zhongyao Si , Shenyu Tan , Guangyuan Chui
Published: April 2007

Fatigue data for welded joints subjected to an explosion treatment (ET) were obtained using rotary bending fatigue specimens. The fatigue fracture surfaces were observed by SEM and the dislocation morphologies by TEM. Mechanical properties have been quantitively studied by considering elastic and plastic shock wave characteristics. The test results indicate that the fatigue strength of welded joints subjected to ET is apparently improved due to the action of elastic or plastic stress waves while the ductility of the welded joints, i.e., reduction in area, is greatly increased.
THE PROBLEM OF SCATTER OF FRACTURE TOUGHNESS DATA
Authors: Troshchenko V. T. , Yasniy P. V. , Pokrovsky V. V. , Podkolzin V. Yu.
Published: April 2007

The authors studied the influence of the conditions for growing an initial fatigue crack on the scatter of fracture toughness data determined under static loading. It was found that the values of static fracture toughness for cyclically softening steels at temperatures below the brittle‐to‐ductile transition are essentially dependent on the degree of the material fatigue damage in the vicinity of the crack tip during the final stage of crack initiation. A method is proposed for evaluating the fracture toughness under static loading which makes it possible to take into account the material damage in the vicinity of the crack tip.
A STUDY OF RETARDING FATIGUE CRACK GROWTH USING AN ARTIFICIAL WEDGE
Authors: Yanyan Wang , Mingxu Zho , Daqing Feng
Published: April 2007

Based on the analysis of an artificial wedge, a model for an equivalent crack opening load for three point bend specimens is presented. It has been verified by experiments that the crack growth force calculated from the above model, and the relationship between the calculated ΔKeff and da/dN are almost the same as those of cracked specimens without a wedge. Therefore this model can be applied to estimate retardation or crack arrest behaviour.
A NEW APPROACH TO THE DETERMINATION OF THE MACROCRACK NUCLEATION PERIOD NEAR A STRESS CONCENTRATOR
Authors: Panasyuk V. V. , Ivanitska G. S. , Ostash O. P.
Published: April 2007

The stress‐strain state of a rectangular plate with a central circular hole and a disc with an edge notch is analyzed both for elastic and elastic‐plastic behaviour when cracks emanate from the contours of these concentrators. Stress intensity factors are determined as well as the value of the inelastic deformation at stress concentration zones. The parameters describing the process of crack nucleation are established. The computational results are compared with experimental data when evaluating the period of macrocrack nucleation.
A SUMMARY REPORT OF AN ESIS WORKING PARTY ON FRACTURE CONTROL GUIDELINES FOR ENVIRONMENTALLY ASSISTED CRACKING OF LOW ALLOY STEELS
Authors: Gabetta Giovanna , Cole Ivan
Published: April 2007

This paper provides guidelines for obtaining and using Environmentally Assisted Cracking (EAC) test data for low alloy steels, which are used in a wide range of industrial applications. Both fracture mechanics and non‐fracture mechanics tests are considered, but the emphasis is on using fracture mechanics as part of an overall strategy—a fracture control plan—to prevent or control EAC in service. Prevention is the usual strategy, but the control of crack growth is possible for thick‐walled components. Fracture control planning can, for low and medium strength steel structures, be directed to both preventing and controlling EAC in service.
MODELING THE LONG‐LIFE FATIGUE BEHAVIOR OF A CAST ALUMINUM ALLOY
Authors: Ting Jason C. , Lawrence Frederick V.
Published: April 2007

As‐cast specimens and smooth specimens of a AA 319 cast aluminum alloy containing casting porosity were fatigue tested with special attention given to the long‐life region (N 1.25 × 108 cycles). Fatigue cracks were observed to initiate from the near‐surface casting pores or from discontinuities resulting from the as‐cast surface texture. The observed fatigue lives were strongly dependent on the size (√area) of these casting defects.

The effect of casting defects on the fatigue life was modeled assuming the fatigue life to be the sum of the crack nucleation and the crack propagation life (including both the growth of short and long cracks). The crack growth behavior of (mechanically) short cracks was considered in detail by a developed crack‐closure‐at‐a‐notch (CCN) model. The CCN model predicted the fatigue lives for both as‐cast and machine‐notched specimens. Extension of the CCN model to reliability‐based design was attempted using the measured size distribution of the fatigue‐initiating casting pores.
COHESIVE ZONE MODELLING OF DAMAGE AT THE TIP OF CRACKS IN SLENDER BEAM STRUCTURES
Authors: ÖStlund Sören , Nilsson Fred
Published: April 2007

The use of simple beam theory for cohesive zone modelling of the damage response at the crack tip in linear elastic isotropic double cantilever beam (DCB) specimens has been investigated. Damage resistance curves (DR‐curves) relating the applied stress intensity factor to the growth of the cohesive zones for beam theory modelling has been compared with two‐dimensional elasticity calculations for different material parameters and specimen dimensions. A substantial difference is observed between DR‐curves for the two types of models. As expected this difference vanishes for decreasing beam heights. For large beam heights the DR‐curves calculated by two‐dimensional elasticity are approaching small‐scale yielding DR‐curves, i.e. DR‐curves for an edge crack in an infinite plate. The beam height for which beam theory is applicable could be up to 10‐3 times the height for which small scale bridging DR‐curves are applicable.
NOTCH ROOT CRACK CLOSURE UNDER CYCLIC INELASTICITY
Authors: Sunder R.
Published: April 2007

Aluminium alloy sheet coupons with a central hole were tested in fatigue under specially designed programmed load sequences. Electron microscopy of the fatigue fracture surfaces showed striation mode fatigue crack extension up to more than a millimeter before onset of rapid failure. Crack opening stress was determined from striation patterns. Under variable amplitude loading and conditions of notch root cyclic inelasticity, crack opening stress exhibits noticeable hysteresis. The hysteresis is attributed to a difference between crack closure and opening stresses. A linear model of this phenomenon appears to describe observed behaviour.
REPAIR EFFICIENCY IN FATIGUE‐CRACKED ALUMINIUM COMPONENTS REINFORCED WITH BORON/EPOXY PATCHES
Authors: Baker A. A.
Published: April 2007

This paper describes studies on fatigue crack propagation in cracked aluminium alloy (2024 T3) panels repaired with boron/epoxy patches, adhesively bonded with either an epoxy‐nitrile film adhesive or an acrylic adhesive. Studies were undertaken to assess the effect on patching efficiency of (a) disbonding of the patch system and (b) test temperature. A simple model is proposed for estimating the reduction of patching efficiency due to cyclic disbonding of the reinforcement. In the elevated‐temperature tests it was found, unexpectedly, that patching efficiency in panels patched using the film adhesive was unaffected by temperatures up to 100°C.
SCATTER IN SMALL CRACK PROPAGATION AND FATIGUE BEHAVIOUR IN CARBON STEELS
Authors: Goto M.
Published: April 2007

In order to investigate the physical basis of scatter in fatigue behaviour, rotatory bending of smooth fatigue specimens was carried out using two steels with different microstructures (ferrite/pearlite and tempered martensite). Fifteen or sixteen specimens were fatigued at each stress, and the initiation and propagation behaviour of a crack which led to the final fracture were examined for all the specimens. The emphasis was to investigate the scatter characteristics of fatigue behaviour based on the scatter of small crack propagation data. The data were analysed by assuming the Weibull distribution, and a statistical investigation of the physical basis of scatter was performed, i.e. the distributions for fatigue life, crack propagation life and growth rate of small cracks were established and the relation between the scatter in those distributions was studied.
FATIGUE CRACK GROWTH BEHAVIOUR AND FRACTURE RESISTANCE IN CERAMICS
Authors: Ogawa T. , Ochi T. , Tokaji K.
Published: April 2007

Fatigue crack growth and the fracture resistance curve (R‐curve) were investigated in a polycrystalline alumina (AD90) and a silicon carbide whisker‐reinforced alumina composite (Al2O3‐SiCw) at room temperature in air using a combined loading technique for stabilizing crack growth, and a surface film technique for monitoring crack length. Fatigue crack growth was evaluated successfully with those experimental techniques. Load shedding tests were performed until the crack became dormant, in order to determine the threshold stress intensity factor Kth. Subsequently, the specimens were used for quasi‐static crack growth tests under a monotonic loading condition. The R‐curves were determined in this experiment; however, fracture resistance did not increase markedly with crack growth. Detailed observations of the crack growth behaviour revealed that the flat R‐curve was attributed to the shielding effect of the fatigue crack tip wake. Thus, the fatigue precrack introduced by the load shedding test was not regarded as an ideal crack for determining the R‐curve. Fractographic observations were performed to investigate the mechanistic difference between fatigue and quasi‐static crack growth. It was found that the cyclic loading produced fretting damage in the wake region and it reduced the shielding effect of the fatigue cracks. Based on the experimental results, the relationship between the fatigue crack growth and the R‐curve is discussed as is the significance of Kth as a material parameter.
FATIGUE CRACK GROWTH IN SEVERAL CERAMIC MATERIALS
Authors: Mutoh Y. , Takahashi M. , Takeuchi M.
Published: April 2007

Fatigue crack growth tests of five ceramic materials were carried out in order to investigate the general characteristics of cyclic and static fatigue crack growth in ceramics. A cyclic effect was found in Si3N4, Al2O3and TiB2, where the main fracture mechanism was intergranular separation, and stress shielding due to grain bridging occurred near the crack tip. On the other hand, no cyclic effect was observed in Sic and ZrO2, where the main fracture mechanism was transgranular fracture. The fatigue crack growth curves reduced to a unique curve by using the parameterKup/E, regardless of the kind of ceramics studied.
PREDICTION OF THE LIFETIME DISTRIBUTION OF HIGH‐STRENGTH COMPONENTS SUBJECTED TO FATIGUE LOADING
Authors: Brückner‐Foit A. , Jäckels H. , Quadfasel U.
Published: April 2007

A probabilistic model is developed for predicting the lifetime distribution of a high‐strength component subjected to low cycle fatigue loading. The damage process considered consists of two consecutive stages. First, cracks are initiated from microstructural inhomogeneities such as non‐metallic inclusions. These cracks will then extend stably until final failure occurs or the component is removed from service. The probabilistic model is used to determine the maximum tolerable inclusion size for a model turbine disc. This quantity is defined as the size of the initial defect for which the number of load cycles to failure at a given reliability level exceeds the design life of the component. This maximum tolerable inclusion size is compared with the results of a deterministic lifetime analysis.
FORMULATION OF A STOCHASTIC MODEL OF FATIGUE CRACK GROWTH
Authors: Doliński K.
Published: April 2007

Based on a global/local energy balance a deterministic model of fatigue crack growth under constant amplitude loading is derived. The energy terms resulting from the continuous plasticity and localized fracture around the crack tip are determined for small scale yielding leading to the fatigue crack growth equation involving the stress intensity factor and its amplitude. Four material parameters which should be identified from experimental data have a physical interpretation; these are eventually assumed to be random variables and model the statistical scatter of the crack growth versus N curves observed in experiments. A Gaussian white noise random field is additionally assumed to describe the stochastic material non‐homogeneity within a specimen. Its effect on the crack growth is derived and results in a positive non‐stationary random function depending on the crack length. Statistical parameters of the random fields are identified. Verification of the model by comparison with experimental results is undertaken in a subsequent paper.
STRATEGY FOR CHARACTERIZING FRACTURE TOUGHNESS IN THE DUCTILE TO BRITTLE TRANSITION REGIME
Authors: Heerens J. , Zerbst U. , Schwalbe K.‐H.
Published: April 2007

Abstract— A tentative method is proposed for treating the scatter and size effects of fracture toughness of ferratic steels in the ductile‐to‐brittle transition regime. The method is aimed at the determination of the probability function for initiation of fast growing cleavage cracks under the plane strain condition. The practical relevance of this method has been checked with toughness data sets obtained from various CT‐specimen sizes and CCT‐specimens of a pressure vessel steel tested at two different temperatures in the transition regime.
MODELING THE INFLUENCE OF INITIAL MATERIAL INHOMOGENEITIES ON THE FATIGUE LIFE OF NOTCHED COMPONENTS
Authors: Grandt A. F. , Scheumann T. D. , Todd R. E. , Hinkle A. J.
Published: April 2007

This paper summarizes a fracture mechanics analysis developed to study the effect of initial size and spatial distribution of inherent material inhomogeneities on fatigue life. Calculations were performed for a set of experiments conducted previously to determine the influence of microporosity size and frequency on the fatigue life of notched 7050‐T7451 aluminum specimens. The favorable comparison between the numerical and experimental results indicates the analysis method could be used to predict the benefits to fatigue life obtained by reducing the size and distribution of initial inhomogeneities such as those due to microporosity.
THE EFFECTS OF A MARINE ENVIRONMENT ON THE CORROSION FATIGUE CRACK PROPAGATION RATE OF PURE TITANIUM AND ITS WELD METAL
Authors: Murakami Ri‐ichi , Ferguson W. G.
Published: April 2007

The effects of stress ratio and microstructure on fatigue crack growth rate in air and natural seawater were investigated for pure titanium and its weld metal. The corrosion fatigue characterization of pure titanium was also studied under a cathodic potential in natural seawater. In air, the fatigue crack growth rates of pure titanium and its weld metal increased with increasing stress ratio. In natural seawater, the effect of stress ratio was similar to that in air. However, the crack growth rates were greater for pure titanium than for the weld metal. These results indicate that the corrosion action is sensitive to the microstructure in front of the crack tip. When the crack growth rate for the weld metal was plotted using the effective stress intensity factor range, the crack growth rate in natural seawater was coincident with that in air, regardless of stress ratio. For the base metal, there is a significant difference in the crack growth rate between natural seawater and air.
ELEVATED TEMPERATURE FATIGUE CRACK GROWTH IN ALLOY 718—PART I: EFFECTS OF MECHANICAL VARIABLES
Authors: Ghonem H. , Nicholas T. , Pineau A.
Published: April 2007

Abstract— In this paper observations concerning the effects of mechanical variables on the crack growth process in alloy 718 are reviewed and analyzed on the basis of the related deformation characteristics in the crack tip region. The variables included temperature, frequency, wave shape, hold time, load ratio and load interaction. These analyses have suggested that the role of each parameter in the acceleration of crack tip damage is governed mainly by their relative influence on the nature of the corresponding plastic deformation and associated slip line density. On the basis of this view (which assumes crack growth damage covers the range from cyclic‐ to fully time‐dependent processes), the interactive effects of loading parameters are discussed when considering the corresponding fracture mode. Conflicting experimental observations under different operating conditions are examined.
AN ASSESSMENT OF A MICRO‐MECHANIC MODEL OF HYDROGEN‐INDUCED STRESS CORROSION CRACKING, BASED ON A STUDY OF AN X65 LINE PIPE STEEL
Authors: Cole I. S. , Andenna C.
Published: April 2007

Abstract— The susceptibility of an X65 line pipe steel to hydrogen‐induced stress corrosion cracking (SCC) is investigated. SCC tests on the steel are carried out in three environments of different aggressivity based on a NACE TM‐01‐77 solution with dissolved gaseous H2S. The threshold stress intensity factor is calculated for each environment using the multiple specimen technique. The steel is tested in the as‐received condition and after homogenisation. Permeation tests are carried out on specimens of the same steel in the same environment. The relationship between threshold stress intensity factor and hydrogen concentration is obtained. The results from these studies are used to generate the parameters in the micro‐mechanic model of Akhurst and Baker. The validity and physical significance of the model is assessed.