bluuebunny/crossref_metadata_2025 huggingface dataset:
A SIMPLE RELIABILITY MODEL FOR THE FATIGUE FAILURE OF REPAIRABLE OFFSHORE STRUCTURES
Authors: Connolly Mark P. , Hudak Stephen J.
Published: April 2007

A simple reliability model for fatigue failure of tubular welded joints used in the construction of offshore oil and gas platforms is proposed. The stress‐life data obtained from large‐scale fatigue tests conducted on tubular joints is used as the starting point in the analysis and is combined with a fracture mechanics model to estimate the distribution of initial defect sizes. This initial defect distribution is hypothetical but it agrees well with other initial defect distributions quoted in the literature and when used with the fracture mechanics model results in failure probabilities identical to those obtained from the stress‐life data. This calculated distribution of initial defect sizes is modified as a result of crack growth under cyclic loading and the probability of failure as a function of fatigue cycles is calculated. The failure probability is modified by inspection, and repair and the results illustrate the trade‐off between inspection sensitivity and inspection interval for any desired reliability.
ASPECTS OF HIGH‐TEMPERATURE LOW‐CYCLE THERMOMECHANICAL FATIGUE OF A SINGLE CRYSTAL NICKEL‐BASE SUPERALLOY
Authors: Kraft S. , Zauter R. , Mughrabi H.
Published: April 2007

High‐temperature thermomechanical fatigue (TMF) tests were performed on monocrystalline specimens of the γ′‐precipitate‐strengthened nickel‐base superalloy CMSX‐6. The specimens had axial orientations near [001]. In‐phase, out‐of‐phase, clockwise‐diamond and counter‐clockwise‐diamond TMF tests were conducted in total strain control in symmetric push‐pull. The temperature interval extended from 873 to 1373 K, the total strain amplitude was 0.5% with a cycle time of 300 s. The stress response, the plastic strain amplitudes and the fatigue lives were measured. In addition, fatigue‐induced micro‐structural changes were investigated.

The shapes of the hysteresis loops and the mechanical TMF behaviour varied markedly with the shape of the strain‐temperature cycles. The TMF life of the alloy was found to correlate with the stress amplitude in the tensile half‐cycle. The evolution of the microstructure shows the formation of dislocation networks around the precipitates and in particular, severe changes in the size and the morphology of the γ'‐precipitate structure. These changes vary with the strain‐temperature cycle shape. Failure occurred exclusively by fatigue (and not creep) in the form of localized shear.
EFFECT OF YIELD STRENGTH ON THE BASIC FATIGUE STRENGTH OF WELDED JOINTS
Authors: Ohta A. , Maeda Y. , Suzuki N.
Published: April 2007

Abstract— The basic fatigue strength of welded joints in four steels having different yield strengths has been obtained by tests in which the maximum applied stress was held constant and equal to the yield strength, to simulate the tensile residual stress in real large‐scale structures. In the long‐life region superior properties occurred with a decrease in the yield strength. It is therefore suggested that both low yield strength steel, which can be produced by a thermo‐mechanical control process without affecting the tensile strength, and steels or welding consumables which show a low transformation temperature, may have a high fatigue strength.
THE INFLUENCE OF LOAD MISALIGNMENT DURING UNIAXIAL LOW‐CYCLE FATIGUE TESTING—I: MODELLING
Authors: Kandil F. A. , Dyson B. F.
Published: April 2007

Abstract— A quantitative model has been proposed which predicts the extent of lifetime scatter in low‐cycle fatigue due to the influence of bending caused by load misalignment. The main components of the model are the mechanism of bending, the type of extensometer used to control strain and the fatigue characteristics of the material being assessed. Three mechanisms of bending have been studied and it is argued that the most damaging one is a consequence of a lateral offset in the centre‐lines of the load‐train with respect to either a machine's frame or ram. Scatter in lifetime is a maximum when strain is controlled by a single extensometer (which is generally the case) and when fatigue behaviour is dictated by crack initiation at the largest surface defect. Two types of scatter have been examined, (i) repeatability scatter due to testing practice within a single laboratory, and (ii) reproducibility scatter between laboratories. An example of the magnitude of reproducibility scatter due to bending has been given by using an equation based on the universal slopes method due to Manson.
EFFECTIVE STRESSES AND MICROSTRUCTURE IN CYCLICALLY DEFORMED 316L AUSTENITIC STAINLESS STEEL: EFFECT OF TEMPERATURE AND NITROGEN CONTENT
Authors: Vogt Jean‐Bernard , Magnin Thierry , Foct Jacques
Published: April 2007

Abstract— This paper reports a study on the factors influencing dislocation slip during cyclic deformation of 316L austenitic stainless steel. TEM investigations show that low temperature and interstitial nitrogen content favour planar slip and lead to higher erective stress values. Measurements of effective and internal stresses with the Handfield‐Dickson technique indicate that the contribution of nitrogen in the effective component is more important than that of temperature. It is deduced that nitrogen acts through a pinning effect, while low temperature exerts an effect on friction stress. The results also suggest that cyclic plasticity could modify the short range order leading to a redistribution of nitrogen.
CORRELATION OF FATIGUE CRACK GROWTH RATE AT DIFFERENT STRESS RATIOS FOR QUENCHED AND TEMPERED STEELS AND OTHER ALLOYS
Authors: Robertson I. M.
Published: April 2007

Abstract— Measurements of the effect of stress ratio on the constant amplitude fatigue crack growth rates in four quenched and tempered steels in the Paris regime are reported. This data and published data for other alloys (including lower strength steels and non‐ferrous alloys) are evaluated, and a correlation function suitable for practical fatigue life calculations is derived. In addition to stress intensity factor range and stress ratio, other significant parameters are the yield stress of the material and its thickness. For the four steels on which new measurements were made, the degree of dependence of the crack growth rate on stress ratio may be related to sensitivity to environmental conditions.
INTERLAMINAR FRACTURE ENERGY OF UHMPE/EPOXY COMPOSITES BY DOUBLE CANTILEVER BEAM AND PEEL TESTS
Authors: Gutowski W. S. , Pankevicius E. R.
Published: April 2007

Abstract— Interlaminar mechanical properties of composite materials such as shear strength and fracture toughness depend on the level of fibre‐matrix adhesion which has to be optimised according to the end‐use of the composite. Various surface treatments of fibres are used for this purpose. Double cantilever beam (DCB) tests are commonly used for estimating the interlaminar fracture toughness in Mode I. It is shown in this work that this parameter can be conveniently determined using a simpler technique involving a 90° flexible‐to‐rigid substrate peel test. The values of GIc determined by DCB and 90° peel tests are comparable within acceptable experimental error margins. These two alternative techniques are used for assessing the effectiveness of a novel surface engineering process for enhanced adhesion of ultra‐high modulus polyethylene (UHMPE) fibres to an epoxy matrix.
DISLOCATION SUBSTRUCTURES IN FERRITE OF PLAIN CARBON DUAL‐PHASE STEELS AFTER FATIGUE FRACTURE
Authors: Lei T. C. , Lin G. Y. , Cui Y. X.
Published: April 2007

Abstract— The dislocation substructures of ferrite in plain carbon, ferrite plus martensite, dual‐phase steels in different stages of fatigue crack propagation were examined by transmission electron microscopy. The experimental results show that the dislocations are in random arrays in the ferrite before cyclic loading. At stages of low ΔK (near threshold) values, parallel clusters of dislocations and prolonged dislocation lines can be observed. At stages of intermediate ΔK values, the dislocations are rearranged into networks and loops while at stages of high ΔK (prior to failure) values, they are changed into dislocation cells or patches. It was also found that the volume fraction and carbon content of martensite have significant effects on the dislocation substructures of ferrite after cyclic deformation.
RATCHETTING IN PRESSURISED PIPES
Authors: Rider R. J. , Harvey S. J. , Charles I. D.
Published: April 2007

Abstract— The plastic deformation of thin‐walled cylinders has been experimentally examined for the loading conditions of ±1% axial strain with hoop stresses of approximately 0, 1/4, 1/2 and 3/4 of the initial uniaxial yield stress.

Two materials similar to those used in the pipework of PWR nuclear plant in the U.K. have been tested, namely 304S11 stainless steel and En6 low‐carbon steel. The results of the tests were to be compared with the allowable stresses and deformations specified in the ASME Boiler and Pressure Vessel Code, Section III. The code specifies that a prescribed combination of primary stresses must not exceed 1.5Sm, where Sm is a stress value defined for each material.

The results indicate that the limit of 1.5Sm is excessively low for both materials and that in particular, the stainless steel could tolerate 5Sm. Although the En6 steel is more prone to ratchetting than the stainless steel, the results suggest that it too could tolerate a higher primary stress than the code allows. Both materials are shown to satisfy the proposed ASME ratchet strain limit of 5% hoop strain after 10 cycles of ±1% axial strain range, for any value of internal pressure.
THERMAL FATIGUE OF A 12% CHROMIUM MARTENSITIC STAINLESS STEEL
Authors: Alvarez‐Armas I. , Armas A. F. , Petersen C.
Published: April 2007

Abstract— The cyclic mechanical behaviour during thermal fatigue of a martensitic stainless steel (MANET I) is investigated and correlated with its microstructure. The tests were performed in air by allowing the sample to serve as its own heater and converting any longitudinal thermal deformation of the specimen into elastic or inelastic deformation. The effects of different thermal cycling ranges and the imposition of several hold‐time conditions on the mechanical behaviour and the accompanying microstructural changes in the specimen were evaluated. A continuous softening is the characteristic feature observed in all thermal fatigue tests. Higher mean temperatures, larger temperature changes and the application of temperature‐hold periods produce an accelerated softening process. All temperature hold‐time conditions influence the mechanical behaviour, reducing the number of cycles to failure. The initial tempered martensite lath structure evolves to a mixed structure of expanded laths and subgrains or a fully subgrain structure, depending on the mean temperature, the temperature change and the temperature at which the hold period has been applied. Tests with temperature holds at higher temperatures show more deleterious effects than tests with hold‐times at lower temperatures.
A FREQUENCY RESPONSE METHOD FOR CALCULATING STRESS INTENSITY FACTORS DUE TO THERMAL STRIPING LOADS
Authors: Jones I. S. , Lewis M. W. J.
Published: April 2007

Abstract— When incompletely mixed hot and cold fluid streams pass adjacent to the surface of a component or a structure, they can cause thermal fatigue damage. An analytical model, based on linear elastic fracture mechanics and the frequency response method, is presented for the assessment of thermal fatigue damage. Various shapes of surface temperature‐time histories, represented by their power spectral densities, are examined. The model is compared with an alternative method based on the impulse response method and good agreement is found. This kind of thermal fatigue is of particular concern in various types of nuclear reactors and rapid shut‐downs of hot plant. The model proposed is intended as an engineering design tool and has been developed as a computer code known as “TBL”.
ELECTRON BACKSCATTERING PATTERN IDENTIFICATION OF SURFACE MORPHOLOGY OF FATIGUE CRACKS IN TA6V
Authors: Sarrazin C. , Chiron R. , Lesterlin S. , Petit J.
Published: April 2007

Abstract— Fatigue crack growth in an α+β titanium alloy (TA6V) with three microstructural conditions is studied in high vacuum at 300°C. The faster growth rates are observed in the material with a low content of primary α phase and a fine equiaxed microstructure. Near the threshold regime, a slow crystallographic Stage I‐like propagation is observed in the three microstructural types where slip occurs along a single‐plane system which develops within the α grains. These crystallographic facets are identified using an electron backscattering pattern (EBSP) technique and were found to lie on basal planes.
EFFECT OF GRINDING ON CRACKS AND THE STRENGTH OF CERAMICS
Authors: Kim B. A. , Ando K. , Sato S.
Published: April 2007

Abstract— Five kinds of silicon nitride samples with different microstructure were prepared in order to examine the effect of sintering condition on grain size and mechanical properties. The degradation in strength of ceramics caused by grinding is investigated in detail. It is shown that the critical process zone size is closely related to the grinding process. Futhermore, the crack size caused by grinding is estimated by the process zone size failure criterion and the Newman‐Raju formula. It can be concluded that the process zone size failure criterion is useful when evaluating the sensitivity of ceramics to grinding.
INVESTIGATIONS INTO THE MECHANICS OF CRACK ARREST IN LARGE PLATES OF 1.5%Ni TMCP STEEL
Authors: Wiesner C. S. , Hayes B. , Smith S. D. , Willoughby A. A.
Published: April 2007

Abstract— Large scale, structurally representative, double tension crack arrest tests have been undertaken at temperatures between −99°C and −87°C. Applied stresses and the length of the embrittled crack starter sections were varied to give different applied stress intensity factors in the tests. The results indicate that crack arrest in structures is not governed solely by a so‐called crack arrest temperature but that static linear elastic fracture mechanics can be used to describe it. The measured crack arrest toughness temperature curve of the 1.5%Ni TMCP steel investigated lies at the lower bound of published data.
BIMATERIAL INTERFACE CRACK TIP STRESS ANALYSIS: ANISOTROPIC THEORY
Authors: SÁNCHEZ M. I. , ATKINSON C. , BASTERO C.
Published: April 2007

Abstract— Near crack tip stress and displacement fields are obtained for anisotropic bimaterial interface cracks. A contact zone model is used in order to get rid of the unphysical oscillatory interpenetration between the edges of the crack. Semi‐infinite and the finite crack problems have been studied. Using the near crack tip results of this model crack branching angles can be predicted. These results are illustrated by numerical results for various materials.
NON‐PROPAGATION CONDITIONS (ΔKth) AND FATIGUE CRACK PROPAGATION THRESHOLD (δKT)
Authors: Marci G.
Published: April 2007

Abstract— Fatigue crack propagation threshold values have been determined with two experimental methods, it., the constant R method and the constant Kmax method. Three materials, namely A17075‐T7351 and Ti6A14V STA in the LT‐ and TL‐orientations, and a Ti‐turbine disk material (IMI 685) in the CR‐orientation, were investigated.

The paper is divided into 3 parts. In the first part the test conditions, the experimental results and the conclusions drawn from the experimental results are presented, namely that the three different functional dependencies of ΔKth on R cannot be reconciled with present continuum mechanics concepts. In the second part, some facts used in conjunction with the da/dN–ΔKeff methodology are applied to the non‐propagation condition ΔKth. Parameters such as KOp, the threshold ΔKT, and a parameter “KLL” are investigated by numerical modelling of their individual influence on the ΔKth versus R curves. This modelling work shows that the individual ΔKth versus R curves are primarily dependent on the Kop behavior of the respective material. Further, it is shown that the threshold ΔKT is a constant value, independent of any particular cyclic loading condition. In the third part of the paper, the ΔKeff concept is applied to the experimental results obtained in the first part. Using either experimentally or semi‐empirically determined Kop functions and the measured ΔKT values, the ΔKth versus R curves of the three materials investigated were accurately reconstructed. It follows that the ΔKth versus R curves of the individual materials are the natural consequence of the driving force for fatigue crack propagation, namely ΔKeff
THE IMPLICATIONS OF IMPOSING THE ANDERSON AND DODDS SIZE REQUIREMENT IN FRACTURE TOUGHNESS TESTING PROCEDURES
Authors: Neale B. K. , Sherry A. H. , Wardle G.
Published: April 2007

Abstract— Anderson and Dodds have recently introduced a test specimen size requirement in the transition regime which they suggest must be satisfied for the cleavage fracture resistance to be size independent. This paper assesses the implications of imposing the size requirement in fracture toughness testing standards. It is shown that imposing the size requirement can lead to a size dependence in fracture toughness data. This observation raises the general question of whether even existing size requirements for the lower shelf and upper shelf regimes are capable of giving size independent data.
INFLUENCE OF CONTACT LOADING ON FRETTING FATIGUE BEHAVIOUR
Authors: Faanes S. , Fernando U. S.
Published: April 2007

Abstract— Fretting induced cracking is commonly observed in industrial components that are in contact and are subjected to small oscillatory movements between them. Fretting causes a considerable reduction in fatigue strength. In this paper recent knowledge on the short and long crack growth behaviour is applied to estimate crack propagation and fatigue life in fretting. The model is based on mode I stress intensity factors with a threshold modified for short cracks. The predicted results are compared with experiments and the influence of the contact pressure is examined. A good correlation between predictions and experimental results are obtained for crack growth rates as well as fatigue lives in terms of number of cycles to failure. It is seen that the increase of fatigue life observed for contact pressures above a certain level can be predicted by the crack growth model.
A BIAXIAL CYCLIC PLASTIC ANALYSIS FOR CYLINDRICAL SPECIMENS
Authors: YANG W. , BROWN M. W. , MILLER K. J.
Published: April 2007

The cylindrical specimen is a common configuration adopted for biaxial fatigue testing. A rigorous yet practical analysis is presented here under the framework of incremental plasticity. The cyclic stress‐strain curve is obtained from four different plasticity models, and correlated with twenty‐six in‐phase biaxial tests on En15R steel. Stabilized hysteresis loops can also be derived based on the cyclic stress‐strain curve under a J2‐kinematic hardening formulation with special consideration of the rounding transition at the instant of yielding. A correlation for the hysteretic strain hardening exponent N is required for materials that exhibit non‐Masing behaviour; i.e. do not allow a full description of hysteresis loops from knowledge of the cyclic stress‐strain curve. The solution is further generalized to out‐of‐phase loading, where the rotation of the active stress state around the yield surface is illustrated. This compares favourably with ten out‐of‐phase tests on En15R steel.
SHEAR LIPS ON FATIGUE FRACTURES OF ALUMINIUM ALLOY SHEETS SUBJECTED TO BIAXIAL CYCLIC LOADS AT VARIOUS R‐RATIOS
Authors: SHANYAVSKY A. A. , KORONOV M. Z.
Published: April 2007

An analysis is made of shear lip measurements as observed on fatigue crack surfaces of an aluminium alloy sheet material. It is shown that, for biaxial cyclic loads at stress ratios 1 and various R‐ratios, shear lips were controlled by an equivalent intensity factor Ke=K1F(λ,R).

For crack growth in air the shear lip width ts was approximately proportional to K2e at ts < t*s= 2.5 × 10−4 m and K4E, at ts > t*s where t*s is the critical value of the shear lip dimension. The initiation of shear lips and the orientation of crack growth for different parameters of the loading cycle are briefly considered in the discussion.
A VARIABLE Kf‐NEUBERS RULE FOR PREDICTING FATIGUE CRACK INITIATION LIFE
Authors: NIE H. , WU F. M. , LIU J. F.
Published: April 2007

As is well known, the fatigue strength reduction factor due to a notch (Kf) in the modified Neuber's rule should not be considered a constant since it varies with different stress levels. In this paper, the definition and the variation of Kf are discussed on the basis of theoretical and experimental analyses, leading to the presentation of a variable Kf‐Neuber's rule. Comparing the results of experimental stress analyses and the fatigue life tests of specimens, the variable Kf‐Neuber's rule gives good predictions and is applied to the life prediction of an aircraft component.
A MICRO AND MACRO APPROACH TO THE ENERGY DISSIPATION RATE MODEL OF STABLE DUCTILE CRACK GROWTH
Authors: TURNER C. E. , KOLEDNIE O.
Published: April 2007

Abstract—

The equations for the energy dissipation rate, D per unit area of crack growth, for plasticity and fracture combined, are presented for equilibrium crack extension in a real elastic‐plastic material. These relationships are a necessary condition for stable growth. The term D is identical to G for lefm and to the rate at which work is done for the rigid‐plastic limit. Crack growth is seen at both micro‐ and macro‐levels as a two stage process of damage accumulation in a process zone followed by actual separation as a micro‐instability at the crack tip. Some examples of the behaviour of ductile metals are cited in support at both micro‐ and macro‐level. For the fully plastic case, D reduces strongly with growth. Relationships with conventional rising R‐curves are stated for contained and uncontained yield.
CLASSIFICATION OF THE FATIGUE DOMAIN AND PREDICTION OF DAMAGE WITH CRACK EXTENSION PARAMETERS
Authors: Weiss M. P.
Published: April 2007

The whole fatigue domain has been divided into six Werent zones, each governed by a separate fatigue regime. Some of these regimes coincide with a known classification of fatigue, and others are new regimes, where new prediction methods have been introduced. The proposed predictions are to be considered as practical curve fitting relations for special cases, but those cases can also be fairly general and useful for design purposes. The proposed fatigue diagram can be used as a basis for a quantified explanation of several known fatigue phenomena.
THE INFLUENCE OF MACHINING DEFECTS AND INCLUSIONS ON THE FATIGUE PROPERTIES OF A HARDENED SPRING STEEL
Authors: Bergengren Y. , And M. Larson , Melander A.
Published: April 2007

Abstract In hardened steel with high tensile strengths the fatigue strength is often limited by defects, either surface defects or interior defects. In this work the influence of different surface conditions on the fatigue strength of a hardened spring steel has been studied. The fatigue limit of hour‐glass shaped specimens with turned, ground or polished surface was found using load‐controlled testing combined with the stair‐case method.

A model based on a statistical treatment of the machining defects (surface) and the inclusions (interior) combined with fracture mechanics has been used to predict the fatigue limit. It was intended to consider the total effect of surface defects and interior defects. The model also makes it possible to predict the failure mode, i.e. surface‐defect initiated failures or inclusion‐initiated failures.
PREDICTION OF FATIGUE LIFE BASED ON LEVEL CROSSINGS AND A STATE VARIABLE
Authors: Holm S. , Josefson B. L. , DeMaré J. , Svensson T.
Published: April 2007

Abstract The differences between the cycle count approach and the level crossing approach are discussed from the general fatigue life estimation assumptions as formulated by Holm and de Maré. It is concluded that the differences are related to the interpretation of the assumption of order independence, i.e. the neglecting of sequential effects.

A revised level crossing model is proposed where damage accumulation depends on the level crossing and the stress history condensed in a state variable. In order to formulate a mean fatigue life the stationarity and ergodicity conditions on the involved processes are outlined.

In this revised model sequential effects can be taken into account and in an example the state variable is chosen as the opening stress of a fatigue loaded crack. The dynamics of the opening stress is described by a simple two parameter auto‐regressive model. The entering parameters are estimated from published experimental results and the model is applied to different variable amplitude results from the literature. Calculated results for fatigue life are promising compared to experimental results.
TENSILE IMPACT DELAMINATION OF A CROSS‐PLY INTERFACE STUDIED BY MOIRÉ PHOTOGRAPHY
Authors: Melin L. G. , Thesken J. C. , Nilson S. , Benckert L. R.
Published: April 2007

Abstract Impact induced delamination along a cross‐ply interface in carbon fiber/epoxy laminates is studied by high resolution moiré photography. The specimens were loaded in a tensile split‐Hopkinson bar giving mode I dominated fracture, and a high speed camera captures images during loading and delamination. The resulting moiré fringes are analysed to produce full field displacement maps of the area around the loaded and propagating crack tips. The displacement map prior to failure shows good agreement with numerical solutions, calculated using a 3D self‐adaptive p‐version of the finite element method. The calibrated finite element solutions are then used to give further information about the matrix cracking zone size around the crack tip and the energy release rate. In comparison to quasi‐static loading, tensile impact loading was found to increase the failure load and the resulting energy release rates; some physical explanations for this behaviour are discussed. It was concluded that the procedures presented have good potential for further determination of rate dependent material properties in carbon/fiber epoxy composites.
FRACTURE MECHANICS ASSESSMENT OF PLANAR BRANCHED CRACKS IN AN EQUIBIAXIAL STRESS FIELD
Authors: Kullig E. , Brüuckner‐Foit A.
Published: April 2007

AbstractA simplified fracture mechanics assessment is presented of branched planar cracks in an equibiaxial stress state. In linear‐elastic fracture mechanics the stress intensity factors which characterize the load at the crack tips depend, for a given external load, only on the crack geometry. The stress intensity factors of a large number of branched cracks were evaluated using the Boundary Element method, and correlations between the stress intensity factors and the crack geometry were investigated. Formulae are presented which assign an individual effective crack length to each crack tip of a branched crack and hence allow approximate stress intensity factors to be determined for very complicated crack geometries. An algorithm is used for the stochastic simulation of an irregular crack pattern formation in thermal fatigue.
EXPERIMENTAL AND COMPUTATIONAL EVALUATION OF CRACK GROWTH THROUGH A SPATIALLY NON‐UNIFORM MICROSTRUCTURE
Authors: DeGiorgi V. G. , Harvey D. P. , Kirby G. C. , Matic P.
Published: April 2007

Abstract— Crack growth through a spatially non‐uniform microstructure of 1045 steel edge‐notched and pre‐cracked panel specimens was investigated experimentally and computationally. The microstructural gradient was produced by heat treatment and differential quenching. A fractographic examination was performed on the crack growth specimens to correlate fracture mode and local toughness. Tensile specimens, corresponding to different sites in the edge‐notched panel, were used to characterize the constitutive response and fracture resistance of the as‐treated material. The Rockwell B hardness was used to identify and map material constitutive responses to corresponding locations in a finite element model of the panel. A debonding algorithm was used in the finite element simulations to model stable crack growth using a local fracture criterion.
SOME COMMENTS ON A CURRENT MODEL FOR SCATTER OF FRACTURE TOUGHNESS IN CARBON STEELS
Authors: Mimura H.
Published: April 2007

Abstract The present paper proposes possible mechanisms to explain the following experimental facts reported in the literature.

Fracture toughness has little dependence on plate thickness in the low temperature range.

In some steels, crack initiation sites are much closer to the crack tip than predicted in the transition temperature range by current theory.

The former was attributed to little difference between fracture toughness at crack initiation and that of crack arrest in the low temperature range, and the latter was explained by accounting for the plastic strain effect on crack initiation.
CRACK PROPAGATION AND FRACTURE IN CONTACTING BODIES
Authors: Orringer O.
Published: April 2007

When a body subject to contact loads develops a crack, the origin, orientation, and tendency to propagate or not depend on fabrication details and maintenance history as well as the service environment. Research over the past twenty years has led to better characterization of crack behavior in some contacting bodies (railroad rail and wheels). Computational methods in solid mechanics provide the basis for quantitative results, but true understanding also requires application of materials science principles. The two disciplines are being brought to bear in combination; quantitative assessments of potential manufacturing improvements and prediction of effects on performance in service are now within reach.
EFFECTS OF ENVIRONMENT AND HEAT TREATMENT ON THE TENSILE AND FATIGUE PROPERTIES OF Ti‐24 at%A1‐11 at%Nb
Authors: Fox T. R. , Knorr D. B. , Stoloff N. S.
Published: April 2007

The α2+β alloy Ti‐24 at%A1‐11 at%Nb was evaluated for mechanical properties in the as‐received, mill annealed condition (nearly equiaxed) and in the β annealed condition (basketweave). The as‐received condition had a moderately strong basal transverse α2 texture which gave a higher yield strength, higher elastic modulus, and higher fatigue crack growth rate (FCGR) for loading in the transverse direction at room temperature. The β annealed material was stronger and more isotropic in both texture and properties. The fatigue crack growth rate is higher at 732°C in argon than at room temperature. A hydrogen environment results in a FCGR at 732°C comparable to or less than the FCGR in argon at 732°C for the as‐received and β annealed conditions respectively. Although the hydrogen in solution at levels as high as several thousand ppm does not embrittle at elevated temperature, embrittlement is found after cooling to room temperature.
DYNAMIC CRACK PROPAGATION AND CRACK ARREST INVESTIGATED WITH A NEW SPECIMEN GEOMETRY: PART I: EXPERIMENTAL AND NUMERICAL CALCULATIONS
Authors: Iung T. , Pineau A.
Published: April 2007

A new test specimen geometry was advised to investigate unstable crack propagation and crack arrest. This geometry is a cracked ring which is subjected to a compressive load applied to its poles while the crack is located on the equatorial plane at the outer surface of the specimen. The main interest of this geometry lies in the variation of the stress intensity factor, K, with crack length which follows a bell‐shaped curve numerically determined. The increasing part of the curve enables us to study unstable propagation and the decreasing one ensures crack arrest. This experiment has two major advantages in comparison with other specimen geometries; the boundary conditions are well controlled during the propagation, and the loading conditions of the crack are therefore precisely known. The round shape of the ring reduces wave reflection effects from free boundary surfaces. It is therefore shown that a static analysis can then be used to investigate crack arrest behaviour.
CYCLIC FATIGUE OF ZIRCONIA
Authors: Schmitt R. , Fett T. , Munz D.
Published: April 2007

Two partially‐stabilized zirconia materials, Mg‐PSZ and Y‐PSZ, were investigated in static and cyclic fatigue tests. The crack growth rates were determined as a function of the stress intensity factor (static tests) and the stress intensity factor range (cyclic tests). For all R‐ratios investigated the crack‐growth relations are sufficiently described by power laws. An influence of frequency is obvious. Finally, the crack growth behaviour of natural flaws is compared with that of macroscopic cracks
THE INFLUENCE OF HYDROGEN ON THE FATIGUE BEHAVIOUR OF THE BETA‐TITANIUM ALLOY Ti‐3Al‐8V‐6Cr‐4Mo‐4Zr
Authors: Christ H.‐J. , Alvarez A.‐M. , Birnbaum H. K. , Robertson I. M.
Published: April 2007

In order to characterize the influence of hydrogen on the mechanical properties of β‐titanium alloys, monotonic tensile and strain‐controlled fatigue tests were performed on samples of the metastable alloy Ti‐3Al‐8V‐6Cr‐4Mo‐4Zr in uncharged (0.5 at.% hydrogen) and hydrogen‐charged (3‐4 at.% hydrogen) conditions. The hydrogen was introduced into the material during the last 8 h of an ageing treatment (28 h at 482°C) from the gas phase, whereas the reference (uncharged) specimens were annealed completely in vacuum. The results of the mechanical tests indicate that hydrogen slightly increases the strength of the alloy in monotonic as well as in cyclic loading. Under tensile loading the fracture strain decreases as a result of hydrogen. Under cyclic loading both charged and uncharged conditions show initial softening followed by a saturation state. The cyclic lifetime at a constant total strain amplitude, however, is not reduced by the hydrogen charging. The effect of hydrogen on the mechanical behaviour can be interpreted and understood on the basis of microstructural observations that reveal a hydrogen‐induced change in the precipitation state. This indirect influence of hydrogen on the microstructure, which leads to a reduction of the mean size of the α‐precipitates, in combination with a slight decrease on the volume fraction of the α‐phase, seems to dominate over any direct intrinsic hydrogen effect
DEVELOPMENT OF SEMI‐ELLIPTIC FATIGUE CRACKS IN AK6 ALUMINIUM ALLOY UNDER BIAXIAL LOADING
Authors: Shanyavskii A. A.
Published: April 2007

Fatigue mechanisms are investigated in AK6 aluminum alloy under biaxial loading. The development of a semi‐elliptic crack under conditions of biaxial compression‐tension is connected with the emergence of spherical particles. A mechanism of rotational instability is suggested, connecting the processes of particle formation with a specific mechanism of material failure. A similarity is revealed in the formation of fatigue striations within the studied ratio λ of biaxial loads from –0.9 to +0.9. As λ increases, the crack‐growth rate also increases. It is suggested that this be allowed for when introducing a correction to the mode I stress‐intensity factor.
DETERMINATION OF KI AND KII FOR CURVILINEAR CRACKS UNDER A NON‐UNIFORM BIAXIAL STRESS FIELD
Authors: Molski K. L. , Truszkowski W.
Published: April 2007

Abstract— Any structural element subjected to a static or alternating biaxial load with variable or random amplitudes may suffer from damage that can be described by fracture mechanics parameters. Brittle fracture conditions, fatigue crack growth rate and direction, as well as corresponding safety margins, are the most important unknowns which have to be predicted.

A method is presented for estimating stress intensity factors KI and KII for a curvilinear crack subjected to a non‐uniform biaxial stress field. The method is based on the assumption of an equivalent arc crack, determined separately for each of the real crack tips. The KI and KII values are estimated by means of a modified weight function, called a unitary weight function, evaluated here for the arc crack by using the boundary element method (BEM). According to the principle of superposition any form of non‐uniform stress field may be considered. Accuracy of the method and associated problems of curvilinear crack analysis are also discussed.
CRACK CLOSURE AND EFFECT OF LOAD VARIATION ON SMALL FATIGUE CRACK GROWTH BEHAVIOUR
Authors: Jono M. , Sugeta A.
Published: April 2007

Abstract— Constant amplitude, plus high and low and repeated two‐step loading fatigue tests were conducted on a structural steel and a titanium alloy. Detection and measurement of very small crack sizes were possible by using a specially designed small‐sized test specimen. By improving the unloading elastic compliance technique, the crack closure behaviour was continuously monitored without interruption of the test. It was found that the growth process of a small crack is a transition process from the incipient, ideal crack to the conventional long fatigue crack. Fatigue cracks longer than 0.2 mm were shown to have a residual tensile deformed region in the wake of the crack tip and exhibited retardation after load reductions due to differences in closure levels. However, for cracks smaller than 0.1 mm, closure is insufficient to control the crack growth behaviour, and the high level loading may give rise to an acceleration of crack growth.
PREDICTION OF FCG BEHAVIOUR UNDER VARIABLE AMPLITUDE LOADING IN MMC's
Authors: De Los Rios E. R. , Rodopoulos C. A. , Yates J. R.
Published: April 2007

Abstract— A model which describes fatigue crack propagation in fibre‐reinforced, metal‐matrix composites is further developed in this paper in order to characterise crack propagation under variable amplitude loading. The crack system is divided into three zones: the crack, the plastic zone and the fibre zone. Crack tip plasticity is constrained by the fibres and remains so until certain conditions are met.

The solution of the equilibrium equation of all the forces (internal and external) acting on the crack system, determines two important relationships, first, the stress distribution throughout the system and second, the crack opening displacement. The conditions for crack propagation are such that when the stresses at the fibre zone attain the level required to debond the fibre from the matrix, the fibre constraint is overcome. Crack tip plasticity increases and the crack is then able to propagate round the fibre. If the fibres remained unbroken they would introduce a friction or clamping stress on the crack flanks which would be a function of the local COD. Crack propagation rate is assumed to be proportional to crack tip plastic displacement, which in turn depends on the level of fibre bridging, the degree of matrix cyclic hardening, fibre spacing, the debonding strength, the fibre strength and the applied load.

The effect of overloads of various intensities, and applied at different stages of fatigue life, are assessed in terms of the magnitude of the damage generated. The damage is mainly in the form of fibre‐matrix debonding and fibre failure.
MIXED MODE FATIGUE CRACK THRESHOLDS FROM BENDING AND CYCLIC TORSION OF A PLATE
Authors: Egami N. , Kitaoka S.
Published: April 2007

Abstract—

The effects of plate thickness and crack shape on the threshold condition for crack propagation under cyclic bending or torsion, was studied using a through or a surface pre‐crack in a carbon steel plate of various thicknesses. It was concluded that the magnitude of the frictional stress acting on the crack surface at the propagation threshold under cyclic torsion was significantly affected by the plate thickness. An estimation method for the threshold condition for crack propagation under mixed‐mode loading for a particular plate thickness was proposed on the basis of the strain energy density criterion.
MEASUREMENT OF STRETCH ZONE HEIGHT AND ITS RELATIONSHIP TO CRACK TIP OPENING DISPLACEMENT AND INITIATION J‐VALUE IN AN AISI 316 STAINLESS STEEL
Authors: Sreenivasan P. R. , Ray S. K. , Vaidyanathan S. , Rodriguez P.
Published: April 2007

Abstract—

An accurate method using SEM for the measurement of stretch zone height (SZH) on fracture surfaces has been established. This method does not make any assumption regarding crack blunting angle θ, and for 316 stainless steel in the present investigation θ was in the range of 50 to 67°, contrary to the common assumption of 45°. The semi‐empirical equations, SZH(T) = 2.5 SZW (stretch zone width) and SZW = 89(J/E), reported in the literature were found to give very conservative predictions of initiation toughness Ji for an AISI 316 stainless steel. Lowerbound values of the coefficient m in the equation, J = mσyδ, relating J to CTOD, δ, is found to be 1.5–1.7 for the 316 SS used in this investigation; the upperbound value for m is found to be 2.6. The plastic CTOD values (δmax) corresponding to the maximum load‐point on the instrumented impact test traces are not sensitive to the aging conditions and as they incorporate significant crack growth effects they cannot be used for predicting Ji, by a procedure similar to that discussed above. The ratio t1/tT, where ti is the time to crack initiation and ti is the time to total fracture, in precracked Charpy tests of unaged and aged 316 SS used in this investigation (a/W=0.55 to 0.8) corresponds to 0.15 to 0.17.
TRANSIENT FATIGUE CRACK GROWTH BEHAVIOUR FOLLOWING SINGLE OVERLOADS AT HIGH STRESS RATIOS
Authors: Tsukuda H. , Ogiyama H. , Shiraishi T.
Published: April 2007

Abstract—

Fatigue crack growth tests with constant amplitude loading and single overload have been performed on a long mode I crack in 2017‐T3 aluminium alloy at various stress ratios from 0 to 0.7. Two crack tip parameters of σop and σtt were evaluated using a finite element analysis for a growing crack under these loading conditions. The former is the crack opening stress and the latter is the applied stress level at which the stress at the crack tip becomes tensile. It was found that transient crack growth behaviour following single overloads at high stress ratios was significantly different from that at a low stress ratio: at higher stress ratios, following the application of the overload, there was a rapid retardation which was followed by an acceleration in growth rate and then a faster return to the steady state level at baseline loading. The experimentally observed transient post‐overload behaviour is discussed in terms of the two effective stress range ratios of Uop and Utt, which are determined from σop and σtt, respectively. For the stress ratios and overload ratios studied, the results indicate that the changes in Utt with crack extension after the overload are reasonably consistent with the crack growth rate trends. The stress distribution at minimum applied stress would account for the transient changes in Utt.
THE ASSESSMENT OF SURFACE FATIGUE EFFECTS IN TOUGHENED ZIRCONIA USING A NEW POINT CONTACT METHOD
Authors: Henshall J. L. , Guillou M.‐O. , Hooper R. M.
Published: April 2007

Abstract—

The effects of repeated point contact loading of a toughened ceria‐stabilised zirconia ceramic, CeTZP, by softer metallic cones, have been investigated. All tests were conducted on a purpose‐designed and built computer‐controlled apparatus. The results clearly indicate that zirconia is susceptible to cyclic loading. The evolution of the cyclic deformation and cracking processes have been analysed in terms of contact pressures, applied loading conditions and number of cycles. The ground tips of both quenched, and quenched and tempered, silver steel cones are plastically deformed during the initial loading cycle to produce a conforming planar surface approximately 50‐100 μm in diameter. In all cases, plastic deformation in the CeTZP was observed within, and adjacent to, the contact zones. The degree of plastic deformation increased as the number of cycles increased. The expansion associated with the tetragonal‐to‐martensitic phase transformation in the zirconia caused granular lifting from the surface, at the edge of the contact zone. This resulted in localised spalling at the peripheries of the contact zones, where the tensile stresses are the highest, followed by a radial expansion at higher cycle numbers. This investigation has identified that the rate of evolution of the fatigue damage, in decreasing order of significance, was controlled by: (a) cone hardness, (b) cyclic load amplitude and (c) mean load.
HIGH TEMPERATURE CYCLIC DEFORMATION OF A DIRECTIONALLY SOLIDIFIED Ni‐BASE SUPERALLOY
Authors: Marchionni M. , Osinkolu G. A. , Maldini M.
Published: April 2007

Abstract— The high temperature low cycle fatigue behaviour of a directionally solidified Ni‐base superalloy hardened by about 65% volume fraction of γ'‐precipitates was investigated in order to determine the fatigue life parameters for longitudinal (L) and longitudinal transverse (LT) grain orientations. The fatigue resistance was compared with that of two oxide dispersion strengthened (ODS) Ni‐base superalloys with a similar elongated grain structure.

The fatigue life of the alloy can be adequately predicted by Basquin and Coffin‐Manson empirical relationships and the fatigue ductility parameters in these relationships show a similar trend with the tensile ductility properties.

The studied alloy exhibits a fairly stable cyclic stress response, with only a slight stress softening. Fatigue crack initiation occurs mainly at shrinkage pores on the surface or sub‐surface of the specimens. The crack growth direction is predominantly perpendicular to the applied load. The fracture mode in the LT‐direction is transgranular and fatigue life is shorter by a factor of about six compared to the L‐direction. The fatigue life of the alloy is longer than that of the ODS Ni‐base superalloys with which it is compared.
EFFECT OF LASER SURFACE TREATMENT ON HIGH CYCLE FATIGUE OF AISI 316L STAINLESS STEEL
Authors: Stamm H. , Holzwarth U. , Boerman D. J. , Marques F. Dos Santos , Olchini A. , Zausch R.
Published: April 2007

Abstract— The effect of a laser surface treatment on the high‐cycle fatigue behaviour of the austenitic stainless steel AISI 316L was investigated. The specimens were subjected to a surface melting using a CO2‐laser. Although this treatment introduced tensile residual stresses in the melted and resolidified surface layer and intensified the surface roughness, the fatigue limit could be increased by 20% with respect to the as‐received specimens. It is suggested that grain refinement in the rapidly resolidified surface layer is mainly responsible for this improvement.
EQUIVALENT CONSTANT AMPLITUDE CONCEPTS EXAMINED UNDER FATIGUE CRACK PROPAGATION BY BLOCK LOADING
Authors: Ranganathan N. , Desforges J. R.
Published: April 2007

Abstract— Fatigue crack growth behaviour under block loading sequences has been studied on the aluminium alloy 2024 T351, using four different equivalent constant amplitude concepts. The root mean squared method gives acceptable results only for relatively long blocks. The equivalent method based on the Paris law (modified to take into account crack closure) gives good predictions for the observed growth rates as does Elbers' method. Finally, a new method based on energy considerations gives excellent results for the studied test conditions.
A COMPARATIVE ANALYSIS OF EXISTING TEST DATA ON WELDED ALUMINIUM TUBULAR JOINTS
Authors: Kosteas D. , Gietl B.
Published: April 2007

Abstract— The paper summarises existing fatigue data for welded aluminium tubular joints and attempts a first classification and formulation of design values on the basis of statistical‐regressional analysis to be utilised in new design code drafts. A comparison with results in steel is performed and the need for further investigations outlined.