bluuebunny/crossref_metadata_2025 huggingface dataset:
HIGH TEMPERATURE FATIGUE DAMAGE IN THREE AUSTENITIC ALLOYS
Authors: Plumtree A. , Nilson J.‐O.
Published: April 2007

Abstract— A series of cyclic strain controlled tests have been carried out at 600°C on three high temperature austenitic iron‐based alloys. These alloys were AISI type 316 stainless steel, Alloy 800 H and Sandvik 253 MA. The tests were carried out under constant total strain control using a constant strain rate of 0.005 s−′. Damage mechanics was applied to the results in order to follow the accumulation of damage. By consideiing the changes in modulus throughout the life of each specimen it was found that damage evolution could be successfully predicted as a function of plastic strain range despite the fact that each alloy had been chosen because of a different stress response at 600°C, namely cyclic saturation, hardening, and softening followed by hardening for the AISI 316, 253 MA and Alloy 800 H respectively. Although each alloy accumulated fatigue damage in a similar manner the longer lives of Sandvik 253 MA and Alloy 800 H at a given total strain range were due to a smaller plastic strain component and a reduced stage I crack propagation rate. In the 253 MA alloy. slip was predominantly planar with some cells occasionally forming at high strain ranges. Slip was localized in Alloy 800 H due to the shearing of small γ precipitates. In the AISI 316 stainless steel, dislocation cells formed at all strain ranges. It is concluded that all these alloys accumulate damage similarly, independent of their deformation behaviour.
GROWTH OF SEMI‐ELLIPTICAL SURFACE CRACKS IN FERRITIC STEEL PLATES UNDER CYCLIC THERMAL SHOCK LOADING
Authors: Bethge K. , Munz D. , Stamm H.
Published: April 2007

Abstract—Investigations of crack growth under thermal fatigue loading are presented. The experiments were performed with a ferritic reactor pressure vessel steel. A plate, containing a semi‐elliptical surface crack is heated up to a homogeneous temperature and cyclically cooled down by a jet of cold water. On the basis of linear elastic fracture mechanics, stress‐intensity factors are calculated with the weight function method. The prediction of crack growth under thermal fatigue loading using data from standard specimens is compared with the experimental result.
FRACTURE ENERGY OF WEAKLY REINFORCED CONCRETE BEAMS
Authors: Azad A. K. , Mirza M. S. , Chan P.
Published: April 2007

Abstract— An experimental investigation was conducted on a series of simply supported concrete beams with an aim to determine the fracture energy of the composite beam and apply the concept of fracture mechanics to predict flexural strength. In order that a single crack from the tip of the premolded central notch would propagate, the beams were lightly reinforced with a large cover so that the moment capacity of the beam as unreinforced section would be greater than that of the reinforced section. Based on test data, compliance calibration and energy release rate (G1) curves are presented for progressive cracking and a correlation between the critical energy release rate and ultimate moment capacity is suggested.
IRRADIATION EMBRITTLEMENT OF A LOW ALLOY STEEL INTERPRETED IN TERMS OF A LOCAL APPROACH OF CLEAVAGE FRACTURE
Authors: Mundheri M. Al , Soulat P. , Pineau A.
Published: April 2007

Abstract— One heat of A 508 steel is investigated in both the unirradiated and the irradiated condition to determine the variation of the fracture toughness with temperature and specimen thickness. CT type specimens with three thicknesses B (12.5, 25 and 50 mm) are used. Two fluence levels (3·1019 and 8·19 n/cm2)(E < 1 MeV) are investigated. It is shown that the fracture toughness is a decreasing function of both specimen thickness and temperature. A model developed previously by Beremin is used to interpret the results. Axisymmetric notched specimens are tested to determine the factors used in the statistical approach of cleavage fracture. It is confirmed that the Beremin model is able to account for the large scatter in fracture toughness observed at a given temperature on the unirradiated material. The specimen thickness effect is also reasonably well interpreted by the model. The irradiation embrittlement can be explained by assuming that the cleavage fracture resistance is not modified by irradiation and by taking into account only the variations of yield strength with irradiation and test temperature.
A CODE OF PRACTICE FOR CONSTANT‐AMPLITUDE LOW CYCLE FATIGUE TESTING AT ELEVATED TEMPERATURES
Authors: Thomas G. B. , Hales R. , Ramsdale J. , Suhr R. W. , Sumner G.
Published: April 2007

Abstract— This paper comprises the text of a code of testing practice prepared under the auspices of a British High Temperature Mechanical Testing Committee. The code makes recommendations concerning equipment, test specimens and procedures; it includes several explanatory and cautionary notes and references to related standards and publications. It was considered that the American National Standard ASTM E606–80 [1] contained much of the required material and in order to avoid unnecessary divergence of practice the recommendations therein have been used as far as possible but with specific modifications and additions to account for current UK needs and practice. It is anticipated that this document may form the basis of a future BSI publication and consequently, the general format is similar to that recommended by BSI in BS O 1981 [2]. Currently a programme of intercomparative Low Cycle Fatigue testing is being carried out under the auspices of and with support from the Community Bureau of Reference (BCR) of the Commission of European Communities. This programme will shortly be widened to include non‐European countries as part of a broader initiative in the field of Materials and Standards (VAMAS). In consequence it is intended to consider and, if necessary, revise the Code of Practice in the light of results from this programme and of other on‐going work in the field.
CRACK GROWTH RATES DURING CREEP, FATIGUE AND CREEP‐FATIGUE IN AN AUSTENITIC FEATURE WELD SPECIMEN
Authors: Gladwin D. N. , Miller D. A. , Priest R. H.
Published: April 2007

Abstract— Static creep crack growth tests and displacement controlled fatigue and creep‐fatigue crack growth tests have been performed on austenitic feature weld specimens at 650°C. The creep‐fatigue tests incorporated hold times of up to 96 h. During these tests, crack growth appeared to comprise cyclic and dwell components. Cyclic crack growth components were characterised by the fracture mechanics parameter K whilst creep crack growth contributions were correlated with C*. In order to determine K and C* for the non‐standard feature weld specimen, elastic and elastic‐plastic creep finite element analyses were conducted. Good correspondence is shown between the feature weld data and comparable data from compact tension specimen tests on similar materials. Equations obtained from the compact tension specimen results, which describe total crack growth rates as the sum of the cyclic and dwell contributions, are shown to adequately describe the features test results also. Furthermore, it is demonstrated that a reference stress approach can be used to estimate C* for the features specimens.
APPLICATION OF LOCAL DAMAGE MODELS TO THE NUMERICAL ANALYSIS OF DUCTILE RUPTURE
Authors: Sun D.‐Z. , Siegele D. , Voss B. , Schmitt W.
Published: April 2007

Abstract— Two damage models were implemented into the finite element program ADINA to study the correlation between microscopical damage and macroscopical material failure. In the first model, based on the Gurson yield function the nucleation, growth and the coalescence of voids were incorporated into the constitutive relations. In the second model the void growth was determined according to the Rice and Tracey model using the von Mises yield function, and material failure was simulated by eliminating the elements where the critical void growth ratio was exceeded. The numerical results for the local and global behaviour of the specimens were compared with experiments. The generality of the damage parameters was checked by investigating several specimen geometries. Both damage models deliver qualitatively consistent results with regard to the influence of the stress triaxiality on the void growth and on the beginning of the material failure. However, the Gurson model gives a more accurate numerical simulation because the damage development and the stress drop continue after the onset of void coalescence while the critical void growth model causes less convergence problems in the simulation of large crack extension. The Jn‐curve was estimated on the basis of both models.
LOW CYCLE FATIGUE LIVES OF NOTCHED COMPONENTS
Authors: James M. N. , Dimitriou C. , Chandler H. D.
Published: April 2007

Abstract— In low cycle fatigue situations, the plastic behaviour of the material at the root of stress concentrators is of prime importance in determining the cyclic life. However, simple procedures such as Neuber's rule do not adequately describe the development of plastic behaviour at a notch root, while the expense of a finite element analysis is not justified in many instances. This paper describes a simple, approximate numerical method of calculating plastic notch stresses and strains that would be of use in such situations. The usefulness of the technique is demonstrated by comparing low cycle fatigue lives predicted from notch plastic strains with those determined by fatigue testing of smooth specimens subjected to similar plastic strain ranges.
A CRACK CLOSURE STUDY TO PREDICT THE THRESHOLD BEHAVIOUR OF SMALL CRACKS
Authors: Journet B. G. , Lefrancois A. , Pineau A.
Published: April 2007

Abstract— The small crack problem is addressed within the applicability of Linear Elastic Fracture Mechanics as the result of crack closure phenomenon. The variation of crack closure stress intensity factory Kop as a function of crack length, a, was determined in two materials, namely a A508 steel and a 2024A1 alloy. These results were obtained on two‐dimensional small cracks (a≫ 0.1 mm) which were machined from long fatigue cracks. These measurements of Kop in addition to data published in the literature on a nodular cast iron and a 9Cr–1Mo steel yield to a unique characteristic function: Kop/Ko= 1 –exp(–ka) in which k is the only parameter to characterize the small crack effect. A prediction of the threshold behaviour of small and long cracks on A508 steel is made using the results of crack closure measurements.
STUDY ON FATIGUE THRESHOLD BEHAVIOUR AND FATIGUE CRACK PROPAGATION IN A CAST Co‐Cr‐Mo ALLOY USED FOR SURGICAL IMPLANTS
Authors: Zhuang L. Z. , Langer E. W.
Published: April 2007

Abstract— —Fatigue crack propagation rates (da/dN) and fatigue crack thresholds (ΔKth) have been studied in a cast Co‐Cr‐Mo alloy used for surgical implants with various grain sizes. Results for materials with average grain sizes of about 400 and 60μm respectively are presented. Threshold values close to 10–15 MPam have been measured with decreasing values observed on increasing the grain size. Similar effects of grain size are found on the crack propagation behaviour at higher growth rates, where a coarse grain size material show a higher crack growth rate than a fine grain size material at the same ΔK levels. The effects of microstructure on fatigue properties of the cast Co‐Cr‐Mo alloy are caused not only by grain size variation but are also attributed to the microstructural differences: a coarse‐grained material with a directionally grown dendritic structure vs a fine‐grained material with an equiaxed grain structure.
THRESHOLD STRESS INTENSITY BEHAVIOUR OF CRACKED STEEL STRUCTURAL COMPONENTS
Authors: Ibrahim Faisal K.
Published: April 2007

Abstract— The effects of stress variables on the fatigue design of steel structural components (SAE 1010 steel) in the threshold region are investigated. The threshold and the closure threshold stress intensity ranges both decreased linearly as the stress ratio is increased. The threshold and opening threshold stress intensities also decreased linearly as the magnitude of compressive peak stress is increased. Crack opening stress measurements using a mechanical extensometer showed that the crack is not fully closed throughout the stress cycle at the threshold level. The crack opening stress is found to be independent of the crack length up to a certain crack length depending on the loading conditions. It is also found that the threshold stress intensity consists of two components: opening or closure stress intensity required to overcome crack closure, and intrinsic stress intensity range required to grow the crack. Linear relationships are obtained for the intrinsic stress intensity range as a function of stress ratio or compressive peak stress.
AN INTELLIGENT CAD‐METHOD BASED ON BIOLOGICAL GROWTH
Authors: Mattheck C. , Moldenhauer H.
Published: April 2007

Local stress peaks are the main reason for fatigue failure of structures. It is therefore of interest to understand the stress distribution in a component under service conditions. A systematic method is proposed to show how engineering components may be designed by simulation of biological growth. The method is based on “misuse” of the swelling option in the FE‐code Abaqus in order to simulate “growth” of structures into a shape more appropriate for the actual loading case considered. The method promises to be an extremely powerful “intelligent” CAD approach.
A FATIGUE CRACK GROWTH MODEL FOR FIBER‐REINFORCED METAL–MATRIX COMPOSITES
Authors: Chan K. S.
Published: April 2007

A fracture‐mechanics based model is proposed for fatigue crack growth in fiber‐reinforced metal‐matrix composites (MMCs). The model incorporates most of the fracture micromechanisms commonly observed in fiber‐reinforced MMCs, including (1) formation of microcracks ahead of the crack tip by either fiber fracture or interface decohesion, (2) interactions of the main crack tip with fibers and microcracks, (3) linkage of the main crack with microcracks, and (4) crack deflection by fibers. Statistical variations of fiber or interface strength are also considered. The essential feature of the model is to compute the changes in the local stress intensity due to various fracture mechanisms; the local stress intensity is then utilized to predict crack growth rate in MMCs via an elastic modulus normalization procedure. Application of the model to predicting crack growth in an alumina fiber Mg‐alloy composite is presented.
UNSTABLE AND STABLE CRACK GROWTH: IMPLICATIONS FOR THE BEHAVIOUR OF SMALL AND LONG FATIGUE CRACKS
Authors: Jingjun Yang , Hongxun Pei , Wei Ke
Published: April 2007

Abstract— The effects of the changes of crack shapes on the behaviour of small cracks were investigated on single edge crack specimens and small surface crack specimens with different initial crack shapes. Experimental results obtained from beach mark measurements on the fracture surfaces indicated that the behaviour of small cracks was strongly dependent on the crack shape itself. While the initial shape of a small crack was unstable with respect to the state of specimen‐geometry‐stress system, the crack gradually adjusted its shape to a specific preferred shape by means of non‐uniform growth. In addition, the deceleration and subsequent acceleration of crack growth corresponds to the transition from unstable to stable crack growth.
CRACK TIP FIELDS UNDER NON‐STEADY CREEP CONDITIONS—II. ESTIMATES OF ASSOCIATED CRACK GROWTH
Authors: Ainsworth R. A. , Budden P. J.
Published: April 2007

Abstract— In a companion paper, estimation formulae have been presented for describing the amplitude of the crack‐tip fields under load and displacement controlled boundary conditions. In this paper the associated amounts of creep crack growth are derived. For constant loading, it is shown that the transition period before the attainment of steady creep conditions can be neglected provided the accumulated creep strain at a reference stress exceeds the elastic strain at the same stress. Under constant displacement conditions, it is shown that the amount of creep crack growth is limited and can be predicted from the extent of load relaxation due to creep. This result is confirmed by comparison with experimental data.
EFFECT OF SPECIMEN GEOMETRY ON FATIGUE CRACK GROWTH IN PLANE STRAIN—II. OVERLOAD RESPONSE
Authors: Shercliff H. R. , Fleck N. A.
Published: April 2007

Abstract— Overload tests were performed on compact tension (CT) and centre cracked panel (CCP) specimens made from 6082‐T6 aluminium alloy and BS4360 50B structural steel. The specimens were sufficiently thick for plane strain conditions to apply. Consistently greater retardation was observed in the CCP geometry than in the CT geometry. The effect of geometry is understood in terms of the T‐stress and its effect on the overload plastic zone size. This was confirmed by biaxial tests in which the T‐stress was varied independently of K. The action of machining off the side faces of an overloaded specimen did not eliminate the retardation; thus overload retardation is not due to a propping open by the surface regions of the specimen. Discontinuous closure was observed after overloads in the aluminium alloy and steel, as predicted by finite element calculations.
THE EFFECTS OF STRESS RATIO ON THE GROWTH BEHAVIOUR OF SMALL FATIGUE CRACKS IN AN ALUMINUM ALLOY 7075‐T6 (WITH SPECIAL INTEREST IN STAGE I CRACK GROWTH)
Authors: Tokaji Keiro , Ogawa Takeshi , Kameyama Yoshikatsu
Published: April 2007

Abstract— The growth behaviour of small fatigue cracks has been investigated on aluminum alloy 7075‐T6 at stress ratios R of 0, −1 and −2. The effects of stress ratio are discussed with special interest in the stage I region of small crack growth. Cracks which initiated at R=−1 and −2, grew by a stage I mechanism up to a certain depth followed by stage II crack growth. The stage I to stage II transition occurred under a constant maximum stress intensity factor which was approximately consistent with the threshold effective stress intensity range, λKeff,th, for large cracks. At R= 0, on the other hand, stage I crack growth was not observed because of crack initiation at inclusions. Small cracks grew more rapidly than large cracks subjected to the same nominal stress intensity ranges at all the stress ratios, and they grew below the threshold stress intensity range, λKth, for large cracks. Stage I cracks, in particular, showed much higher growth rates than large cracks and grew even below λKeff,th. It is suggested that stage II crack growth rates should be characterized in terms of an effective stress intensity range, while a micromechanics approach will be necessary to evaluate stage I crack growth rates.
A COMPARISON OF NEAR‐THRESHOLD FATIGUE CRACK PROPAGATION IN TWO HIGH STRENGTH STEELS
Authors: Oni O. , Bathias C.
Published: April 2007

Abstract— Fatigue crack growth rate data for long and short cracks were obtained from two high strength steels used in the aerospace industry. Differences in the behaviour of the two cracks were noted and explained in terms of the three‐dimensional nature of short cracks compared to two‐dimensional long cracks, the interaction between cracks, the applicability of Linear Elastic Fracture Mechanics (LEFM) and their effect of crack closure.
EFFECTS OF CRACK CLOSURE AND MEAN STRESS ON THE THRESHOLD STRESS INTENSITY FACTOR FOR FATIGUE OF AN ALUMINIUM CASTING ALLOY,
Authors: Couper M. J. , Griffiths J. R.
Published: April 2007

Abstract— Observations have been made of the threshold fatigue properties of an Al‐Mg‐Si casting alloy. First, it has been shown that there exists a critical value of the stress ratio, R, below which the threshold stress intensity factor decreases with increasing R but above which it is constant. Second, measurements of the cyclic crack opening displacement have been used to examine crack closure effects and to deduce the effective cyclic stress intensity factor. The two sets of data are compared with existing models for threshold phenomena.
QUANTIFYING POP‐IN SEVERITY IN FRACTURE TOUGHNESS TESTS
Authors: Dawes M. G.
Published: April 2007

This paper describes the rationale and details of a conservative pop‐in assessment procedure that has been included in some new ASTM and BSI fracture toughness test methods. The procedure may be used for either graphical or numerical assessments of pop‐in.
EXPERIMENTAL VERIFICATION OF RANDOM LOAD FATIGUE ENDURANCE
Authors: Bílý M.
Published: April 2007

Abstract— This paper is concerned with various problems related to laboratory experimental verification of fatigue endurance under random loading. Based on statistical characteristics of stationary and non‐stationary operating random processes (probability density function and/or power spectral density, transition probability densities) it is shown how to design real time simulation algorithms that are further used to create inputs of computer controlled electrohydraulic loading systems. The corresponding fatigue tests (strain or stress constrolled) produce endurance curves that can be plotted in various coordinates (peak or RMS values vs fictitious number of cycles or time to failure) offering non‐identical conclusions and qualitative interpretations. Some examples of the influence of simulated random process probability density function and/or power spectral density on the resulting fatigue endurance are presented and also certain suggestions concerning prospects for random load fatigue tests are summarized.
COMPRESSION FATIGUE IN β‐ALUMINA
Authors: James M. N. , Tait R. B. , Mech D. G.
Published: April 2007

In the presence of a notch, fully compressive loading has been shown to develop fatigue cracks, typically less than 1 mm in length, from the notch root in metals, cemented carbides and ceramics. The crack length is dependent on factors like load range, stress ratio, frequency and environmental influences. This paper examines the influence of these factors on crack growth in β‐alumina under compression fatigue. Results obtained support the constitutive microcracking model advanced by Brockenborough and Suresh, but are influenced by crack tip shielding and, at low frequencies, a small stress corrosion component of growth.
A STATISTICAL ANALYSIS OF SHORT FATIGUE CRACK GROWTH
Authors: Wang S. Z. , Miller K. J. , Brown M. W. , De Los Rios E. R.
Published: April 2007

This paper explores short fatigue crack growth behaviour in torsion and tension at the same equivalent stress level of 880 MPa. Quantum steps (i.e. crack growth following crack arrests at grain boundaries) occurred randomly along the curve of crack length vs number of cycles applied. A statistical model for the short crack growth process is presented in the form of a non‐stationary Markov chain which can be described with a probabilistic transformation matrix. The endurance mean value is described with a prescribed confidence level. Fatigue life, with a high degree of survivability, is determined with respect to a specified crack length. This should assist engineers concerned with the damage‐tolerant design of critical components.
MICROSCOPIC FAILURE MECHANISMS OF AN UNIDIRECTIONAL GLASS FIBER COMPOSITE
Authors: Wang S. J. , Baptiste D. , Bompard Ph. , Franclois D.
Published: April 2007

Abstract— The tensile failure mechanisms and the effects of manufacture flaws on the tensile behavior of an unidirectional composite (E‐glass fiber/epoxy matrix) were investigated. Macroscopic failure processes were determined by an enhanced X‐ray radiography technique and microstructural changes analysed by both optical and scanning electron microscopy. An axisymmetric finite element model was developed for analysing the microstress distributions in the composite containing broken fibers in order to determine the effect of local fiber volume fraction on the local failure process. Finally, the measurement of the volume fraction distribution of fiber misalignment was carried out and a simple analytical model was proposed to interpret the fiber misalignment effect. A correlation between the fiber misalignment distribution in the specimens and their tensile strengths was obtained statistically.
A GENERAL CRITERION FOR HIGH CYCLE MULTIAXIAL FATIGUE FAILURE
Authors: McDiarmid D. L.
Published: April 2007

Abstract— A new simple general criterion of failure for high cycle multiaxial fatigue, τa/tA.B+σn. max/2σT= 1 presented. The failure criterion is based on a critical plane approach where fatigue strength is a function of the shear stress amplitude and the maximum normal stress on the critical plane of maximum shear stress amplitude. The criterion takes account of whether case A cracks, growing along the surface, or case B cracks, growing into the surface, occur. It requires knowledge of the material properties, tensile strength, σT, and reversed shear fatigue strength for case A, tA, or case B, tB, cracking, whichever is relevant. tA is the reversed torsion fatigue strength and tB is found from a case B cracking test case. The criterion is applicable in the region, 0.5t≤ta≤t, and 0 ≤σn.max≤σT.
BEHAVIOUR OF A 1Cr‐1Mo‐0.25V STEEL AFTER LONG‐TERM EXPOSURE‐II. CREEP CRACK INITIATION AND CREEP CRACK GROWTH
Authors: Moliniéa E. , Piques R. , Pineau A.
Published: April 2007

Both the initiation and the propagation of creep cracks have been studied in a 1Cr‐1Mo‐0.25V steel at 550°C using CT type specimens. The material taken from a large turbine casing was investigated in two conditions: (i) unaged and (ii) after a long exposure in‐service time of about 150,000 h at 540°C. In both cases the material was found to be creep ductile, which is justified in terms of fracture mechanics applied to creeping solids. It is shown that fracture mechanics is unable to provide unique correlations with global load‐geometry parameters, either K or C* for all the stages of both crack initiation and crack growth. However there exists a unique correlation between C* and the time to initiation, ti. This correlation does not depend on the initial conditions of the material. During crack growth two stages are defined. Stage I is a transient regime in which C* is almost constant, but the correspondence between the crack growth rate and C* is not unique since largely dependent on the initial loading applied to the specimens. It is shown that the apparent correlation between the crack propagation rate in stage II which corresponds to large crack growth rate is doubtful. A simplified method based on reference length and reference stress is used to calculate C* parameter and to simulate the load‐line displacement rate. The results obtained from this method are compared to those derived from finite element calculations published in the literature.
STUDY OF THE PHYSICAL PROPERTIES OF POLYETHYLENE POLYMERS THAT AFFECT CRACK INITIATION AND PROPAGATION
Authors: Dear J. P.
Published: April 2007

High‐speed photography has been used to study the behaviour of polymer specimens subjected to high velocity impacts that excite the specimen into strong, complex vibrations. These photographic data are correlated to the outputs of sensors located on the specimen, striker and supports. Optical and scanning electron‐microscope studies of the crack initiation zone and the size and texture of other features on the fracture surfaces are also correlated to other fracture data. To obtain better information about the threshold of crack initiation of these materials and other data difficult to obtain by impact testing, a new experimental method has been developed. To assist in predicting and analysing experimental data a desk‐top computer model has been devised with good visibility of the computing steps and how these relate to crack propagation in polymeric materials.
TRANSIENT RETARDATIONS IN FATIGUE CRACK GROWTH FOLLOWING A SINGLE PEAK OVERLOAD
Authors: Damri D. , Knott J. F.
Published: April 2007

Retardation in the fatigue crack growth rate following the application of a single peak overload in a fatigue loading sequence has been studied for a low carbon structural steel. Tests have been performed at load ratios of R= 0.2 and R= 0.6 at a baseline stress intensity range, ΔKb, corresponding to fatigue crack growth rates in the Paris regime. Single peak overloads were applied at a crack‐length to specimen‐width ratio of a/W= 0.5. At the load ratio of R= 0.6 monotonic or “static” fracture modes were observed upon application of the overload, and these produced an immediate increase in growth rate. A subsequent retardation is attributed to the presence of a residual compressive stress field ahead of the crack tip. A similar retardation was observed at a load ratio of 0.2. The importance of residual stress was established by performing stress relieving experiments. In addition, removal of the surface deformation after an overload by machining “T” sidegrooves resulted in an extended transient, which could not be explained by residual machining stresses.
CYCLIC DAMAGE AND FRACTURE IN A CAST NICKEL BASED ALLOY AT HIGH TEMPERATURE
Authors: Ellison E. G. , Plumbridge W. J.
Published: April 2007

Cyclic tests, with and without dwell periods, were carried out at temperatures of 750, 850 and 1000°C on a cast nickel base super alloy MAR M002. The cracking mechanism was mainly transgranular in the continuous cycle tests. The incorporation of a tensile dwell had little effect on life compared with the continuous cycle data though there was a significant amount of additional internal intergranular cracking. However, an unbalanced compressive dwell at 750 and 850°C caused a shorter life with transgranular cracking: only at 1000°C was the life not reduced. Prediction of life was attempted by means of what were thought to be three of the more promising methods, i.e. ductility exhaustion, crack propagation and hysteresis energy. However, these did not appear to be accurate, and it is clear that more appropriate base line data are required.
STATISTICAL INVESTIGATION OF THE BEHAVIOUR OF MICROCRACKS IN CARBON STEELS
Authors: Goto M.
Published: April 2007

Abstract— In order to clarify the statistical behaviour of microcracks, rotating bending fatigue tests of plain specimens were carried out using two kinds of carbon steel with different microstructures, normalized 0.21% C steel and heat‐treated 0.45% C steel. The emphasis is to investigate separately the statistical properties of the initiation and propagation of microcracks through successive observations of the specimen surface. Results show that the microcrack initiation life distributions of normalized and heat‐treated steels are expressed by a two‐parameter Weibull distribution and a Weibull distribution of the mixed type, respectively. On the other hand, the microcrack propagation life distributions of these steels are represented by three‐and two‐parameter Weibull distributions, respectively. The three‐parameter Weibull distribution is well fitted to the crack length distribution for both the steels.
CRACK BRIDGING IN THE FATIGUE OF FIBROUS COMPOSITES
Authors: Cox B. N. , Marshall D. B.
Published: April 2007

Abstract— Recent observations of fatigue cracks bridged by continuous fibers in titanium alloy and titanium aluminide composites are compared to analogous observations in fiber‐reinforced ceramics under monotonic loading. Three failure modes have been identified under axial loading in each case: longitudinal failure (failure parallel to the fibers) and noncatastrophic and catastrophic mode I failure (failure normal to the fibers). The criteria for transition from one failure mode to another are reviewed. Models developed previously to describe the failure of fiber‐reinforced ceramics are extended to describe the mechanics of mode I fatigue crack growth. The extension is straightforward as long as the fibers do not fail in the crack wake, i.e. the failure mode is noncatastrophic mode I failure.
FATIGUE CRACK PROPAGATION OF SINTERED SILICON NITRIDE IN VACUUM AND AIR
Authors: Horibe S. , Hirahara R.
Published: April 2007

Abstract— Static and cyclic fatigue in vacuum and air have been investigated for pressureless sintered silicon nitride. Cyclic crack propagation occurred even in vacuum where environmental effects are negligible. Hence such damage is attributed to pure mechanical fatigue unaffected by environment. Crack growth occurs in air even below KISCC and the growth rate is higher than in vacuum. Therefore, it is believed that cyclic crack growth in air is accelerated by stress corrosion cracking for a wide range of Kmax values.
MICROMECHANICAL STRESSES DURING LOW CYCLE FATIGUE OF AN OVERAGED Al‐Mg‐Si ALLOY
Authors: Jain Mukesh
Published: April 2007

The evolution of micromechanical stresses; flow stress, kinematic back stress and isotropic drag stress during room temperature, uniaxial, low cycle fatigue of overaged Al‐Mg‐Si alloy is studied. Continuous real‐time measurements of yield stresses are made in cyclic tension and compression, within the hysteresis loop, at different strain amplitudes, strain rates and number of cycles. An asymmetry is observed in flow stress and kinematic back stress in tension and compression half cycles during cyclic hardening and saturation. The phenomenological results have been analyzed in terms of kinematic and isotropic type microstructural mechanisms.
ON THE RELATIONSHIP BETWEEN LOW CYCLE FATIGUE AND CRACK GROWTH RATE PROPERTIES IN WELDED STEEL COMPONENTS
Authors: Skallerudn Bjørn
Published: April 2007

Previous investigations have shown that for plain materials, the crack growth rate constants applied in an elastic‐plastic crack growth model may be obtained indirectly from the constants describing the low cycle fatigue capacity of the material. In the present study a simple EPFM crack growth model, based on bulk strain amplitude as the governing parameter, is assumed. The crack growth constants derived from the linear regression constants describing the LCF capacity of manually butwelded components are determined, and the validity of the resulting EPFM crack growth model is checked against measured LCF crack growth data.
ELASTIC‐PLASTIC FRACTURE MECHANICS FOR PRESSURE VESSEL DESIGN
Authors: Nilsson Fred , Faleskog Jonas , Zaremba Krzysztof , ÖBerg Hans
Published: April 2007

The project has been concerned with the verification of the J‐philosophy for initiation and growth of cracks on laboratory type specimens as well as on larger surface cracked plates. The analysis of the experiments involved extensive fully three‐dimensional finite element calculations. It was found that the initiation events for the six surface cracked plates occurred at approximately the same J‐value. A corresponding relation to the laboratory type specimen was less successful, mainly because of the short‐comings of current methods for JIC‐evaluations. A somewhat puzzling feature of the surface crack experiments was that unstable crack growth occurred immediately after crack growth initiation in four out of six tests, while some amount of stable crack growth was evident in the remaining two and in all of the laboratory type specimens. An evaluation of the surface experiments by a type of R6‐analysis was also performed. Using as Kcr the mean value from the surface crack experiments, it was found that the R6‐method yielded conservative predictions.
AN EXPERIMENTAL STUDY OF FRETTING BY MEANS OF X‐RAY DIFFRACTION
Authors: Farrahi G.H. , Maeder G.
Published: April 2007

This paper introduces a new method of investigation in the field of fretting. This method employs X‐ray diffraction for the characterization of surface layer damage through residual stresses and work‐hardening by tribologjcal action. The effect of hardness and material residual stresses upon the state of the surface have been studied. The results showed that fretting, being a surface phenomenon, created work‐hardening of soft material or work‐softening of hard material in the near‐surface layers. When the initial residual stresses were high, fretting could not modify them because they had already reached the saturation limit. A Pole figure shows that fretting modified the texture of the specimen surface.
A REVIEW OF FATIGUE CRACK GROWTH IN STEELS UNDER MIXED MODE I AND II LOADING
Authors: Bold P. E. , Brown M. W. , Allen R. J.
Published: April 2007

The majority of methods for predicting the direction of propagation of mixed mode cracks have assumed that they branch to grow as mode I cracks. However, under some circumstances mode II crack growth occurs. Rolling contact fatigue cracks are one example of an industrial problem where cracks appear to grow under predominantly mode II loading without branching. This paper reviews the available models and the experimental studies in the literature on mixed mode I and II loading, and discusses the parameters that affect the mode of crack growth.
STATISTICAL CHARACTERIZATION OF RANDOM CRACK PATTERNS CAUSED BY THERMAL FATIGUE
Authors: Winkler T. , Brückner‐Foit A. , Riesch‐Oppermann H.
Published: April 2007

Thermal fatigue experiments performed with an austenitic steel give rise to an irregular pattern of cracks on the specimen surface. The investigations are aimed at characterizing the patterns in quantitative terms and at discerning trends with increasing numbers of cycles. Statistical methods based on different models of stochastic geometry are applied to take into account the random influence in pattern formation. Descriptive statistics as well as stochastic models are used to characterize the damage level. The stochastic models, such as fibre processes and random mosaics, will finally correlate the physical damage process with the random crack pattern observed. It is shown in this paper how the statistical characteristics of the random crack patterns can be related to the statistical characteristics of the stochastic models and the way the physical nature of the damage process influences these quantities.
A SIMPLE PATH‐INDEPENDENT INTEGRAL FOR CALCULATING MIXED‐MODE STRESS INTENSITY FACTORS
Authors: Zhang Z. L. , Mikkola T. P. J.
Published: April 2007

A path‐independent integral is introduced for calculating stress intensity factors. The derivation of the integral is based on the application of the known Bueckner's fundamental field solution for a crack in an infinite body and on the reciprocal theorem. The method was applied to two‐dimensional linear elastic mixed‐mode crack problems. The key advantage of the present path‐independent integral is that the stress intensity factor components for any irregular cracked geometry under any kind of loading can be easily obtained by a contour integral around the crack tip. The method is simple to implement and only the far field displacements and tractions along the contour must be known. The required stress analysis can be made by using any analytical or numerical method, e.g. the finite element method, without special consideration of the modelling of crack tip singularity. The application of this integral is also independent of the crack type, that is, there is no difference between an edge crack and an embedded crack, provided that the crack tip asymptotic behaviour exists.
THREE‐DIMENSIONAL CONSTRAINT EFFECTS ON STRESS INTENSITY DISTRIBUTIONS IN PLATE GEOMETRIES WITH THROUGH‐THICKNESS CRACKS
Authors: Bakker A.
Published: April 2007

Three‐dimensional finite element analyses of through‐thickness cracks in plate geometries are presented. It is shown that the local constraint variation towards the crack tip causes an increase in stress intensity which is neglected in analyses which assume a constant stress state throughout the geometry. This means that stress intensity factors for these types of crack geometries are a factor (1 — v2)‐0.5 higher than generally reported in stress intensity handbooks.

Analyses on crack tunnelling situations show that if plane stress dominates the global behaviour, an almost constant stress intensity across the thickness is reached for a relative tunnelling depth of a 2.5% of the plate thickness. For geometries which are not predominantly in plane stress this value will be somewhat larger. Crack front tunnelling does not influence the mean stress intensity across the thickness.

Shear lips are shown to reduce the mean equivalent stress intensity (the mode I stress intensity which has the same energy release rate as the actual combined mode I, II and III loading) by a factor equal to the square root of the ratio between plate thickness and projected length of the crack front. This may explain the reduction in crack growth rate caused by shear lips during fatigue crack growth experiments. The reduction of the mode I stress intensity factor is considerably larger, which may cause a further reduction of fatigue crack growth rate for crack growth mechanisms that depend primarily on the mode I crack tip loading.

Analyses on CNT and SENB specimens show that the conclusions reached on infinite plate models also hold for real structures. However for an SENB specimen with an uncracked ligament equal to the plate thickness, the overall constraint is larger than that of a pure plane stress situation, and the effect of stress intensity increases due to the constraint transition is less pronounced.
SIMPLE Jc, ESTIMATION FORMULAE FOR THREE‐POINT BEND SPECIMENS
Authors: Sumpter J. D. G.
Published: April 2007

This report reviews some simple methods for determining Jc at the onset of cleavage fracture in a three‐point bend crack tip opening displacement test. It is concluded that acceptable estimates of J, can be made from specimen mouth opening displacement without precise measurement of crack length.
ELLIPTICAL‐ARC SURFACE CRACKS IN ROUND BARS
Authors: Carpinteri Andrea
Published: April 2007

The crack aspect ratio influence on the stress‐intensity factor of elliptical‐arc edge flaws in solid round bars under tension or bending loading is discussed. The relative crack depth ξ=a/D between the depth a of the crack's deepest point and the bar diameter D ranges from 0.1 to 0.6, while the aspect ratio a/b of the flaw is made to vary from 0.0 (straight crack front) to 1.0 (circular‐arc crack front). For each value of ξ being considered, the maximum stress‐intensity factor is attained in correspondence to the deepest point on the crack front in the case of a/b= 0.0, while it is attained near the external surface in the case of a/b= 1.0. For intermediate aspect ratios, the stress‐intensity factor presents the maximum value at the crack's deepest point for ξ≤ξCR and near the free surface for ξ≥ξCR, with the critical relative crack depth ξCR getting lower and lower as the parameter a/b is increased.
PROCESS ZONE SIZE FAILURE CRITERION AND PROBABILISTIC FRACTURE ASSESSMENT CURVES FOR CERAMICS
Authors: Ando K. , Kim B. A. , Iwasa M. , Ogura N.
Published: April 2007

Data of fracture toughness and fracture stress of ceramics, generally show considerable size effects and scatter. This presents problems for the integrity of structural ceramics. Fracture mechanics test results on Si3N4 and A12O3 reveal a sensitivity to crack size and the necessity to invoke probabilistic concepts to evaluate their integrity. A new failure criterion is proposed here, based on the existence of a crack‐tip process zone. A probabilistic failure assessment curve is also proposed to quantitatively evaluate reliability.
A δJ‐BASED APPROACH TO BIAXIAL FATIGUE
Authors: McDowell David L. , Berard Jean‐Yves
Published: April 2007

An energy‐like approach is introduced for correlation of biaxial fatigue. The approach is motivated by the elastic‐plastic δJ‐integral which has previously been successfully applied to correlate uniaxial fatigue microcrack propagation. In addition, the most salient aspects of critical plane theories are included to reflect the driving force for microcracks in Stage I shear‐dominated fatigue growth. Comparisons are made with some recent critical plane theories on the basis of generic completely reversed fatigue life behavior and for specific Case A and Case B biaxial loadings of Inconel 718 and 1045 steel.
ELASTIC‐PLASTIC FINITE ELEMENT ANALYSES OF CRACKED NOTCHES IN PLATES UNDER MIXED‐MODE LOADING
Authors: Kfouri A. P. , Wong H. D. , Miller K. J.
Published: April 2007

Plates containing inclined elliptical notches with and without cracks are analysed for five different major axis inclinations, namely, θ equal to 0, 11.25, 22.5, 33.75 and 45˚. Short cracks emanating from the roots of such inclined circular and elliptical notches are analysed. Under various mixed‐mode loading conditions, when cracks are present, a simple method is described for the evaluation of the Mode I and Mode II stress intensity factors, for the elastic state. Values of the J integral along three different contours are also evaluated in the elastic and elastic‐plastic states, as well as the Mode I and Mode II components of the crack tip opening displacenient (CTOD), the maximum principal stresses, the maximum average equivalent plastic strains and the location of the elements in which they occur. Comparisons of the different loading conditions are presented and the implications of the effects of mixed‐mode loading on fracture and fatigue crack propagation are discussed.
PROBABILISTIC ASPECTS OF CLEAVAGE CRACK INITIATION SITES AND FRACTURE TOUGHNESS
Authors: Ando K. , Mogami K. , Tuji K.
Published: April 2007

Abstract— Fracture toughness tests were performed in the ductile‐brittle transition temperature range using 110 specimens of the three‐point bend and CT types. Probabilistic characteristics of fracture toughness and cleavage crack initiation sites were analysed in detail, together with the fibrous crack shape, from which the plane strain region in the specimen was deduced. The criterion for obtaining plane strain at the mid plane of the specimen was established as: B≤ 0.004{Kc(J)/σy}2+ 0.01. The thickness effect of cleavage fracture toughness for the specimen satisfying this equation is mainly caused by the statistical distribution of the weakest points ahead of the crack front (the Weibull volume effect).
FATIGUE CRACK GROWTH FROM A CIRCULAR NOTCH UNDER HIGH LEVELS OF BIAXIAL STRESS
Authors: Youshi Hong , Brown M. W. , Miller K. J.
Published: April 2007

Abstract— A series of experiments have been conducted on cruciform specimens to investigate fatigue crack growth from circular notches under high levels of biaxial stress. Two stress levels (Δσ1= 380 and 560 MPa) and five stress biaxialities (λ=+1.0, +0.5, 0, −0.5 and −1.0; where λ=σ2/σ1 were adopted in the fatigue tests in type 316 stainless steel having a monotonic yield strength of 243 MPa. The results reveal that fatigue crack growth rates are markedly influenced by both the stress amplitude and the stress biaxiality. A modified model has been developed to describe fatigue crack growth under high levels of biaxial stress.
FATIGUE CRACK INITIATION AND PROPAGATION IN LASER‐HARDENED, MEDIUM‐CARBON STEEL
Authors: Kocanda S. , Natkaniec D.
Published: April 2007

Abstract— The results of investigations into fatigue crack behaviour of laser‐hardened, medium‐carbon steel specimens under reversed bending (R= ‐1) are presented. Characteristic features of crack behaviour, such as crack source location, temporary crack arrest at the border between laser tracks and the matrix material, and discontinuous crack growth in the laser tracks are discussed. In order to explain the sites of primary crack sources, results of residual stress measurements are included as well as analytical descriptions of these stress distributions as a function of sample depth. A mechanism of cracking has been established on the basis of fractographic analyses of fracture surfaces.
CRACK OPENING STRESS MEASUREMENTS OF SURFACE CRACKS IN 7075‐T6 ALUMINIUM ALLOY PLATE SPECIMEN THROUGH ELECTRON FRACTOGRAPHY
Authors: Putra I. S. , Schijve J.
Published: April 2007

Abstract— Crack opening stress measurements were carried out on 9.6 mm thick specimens of 7075‐T6 aluminium alloy with semi‐elliptical surface cracks. Measurements were made through a fractographic technique based on a load sequence which can produce distinct striation characteristics on the fracture surface. The crack opening stress Sop is deduced from the striation pattern. The variation of Sop along the crack periphery and during crack extension was measured. Close to the front surface Sop is higher due to plane stress condition. At a large crack depth a strong influence of plasticity in the ligament on Sop was found, i.e. Sop decreases as the crack extends to breakthrough. The agreement of da/dN=ΔKeff curves between surface cracks and through cracks data was only found for a limited range of crack depth of the elliptical cracks.