bluuebunny/crossref_metadata_2025 huggingface dataset:
SOME IMPLICATIONS OF THE USE OF THE PD6493 LEVEL 3 FAILURE ASSESSMENT PROCEDURE
Authors: Li Z. H. , Bilby B. A. , Howard I. C.
Published: April 2007

Abstract— Under a natural mapping between the standard R‐curve analysis diagram and the failure assessment diagrams of R6 and PD6493 Level 3 the R‐curve becomes the RCI (R‐curve image). It follows that whenever the assessment point moves along the failure assessment line during ductile crack growth, the implication is that the failure assessment line is the RCI. This result is used to test the conservatism of a specific PD6493 Level 3 analysis by two methods. The first calculates the variation during crack growth of the applied elastic‐plastic crack tip opening displacement (CTOD) parameter (or‘driving force') which is implied by the PD6493 analysis and then compares this variation with an independent estimate of it. The second uses an assumed driving force to deduce the CTOD resistance curve implied by the failure assessment line. It is shown by both methods and also by a direct R‐curve analysis that this particular PD6493 analysis is conservative relative to an R‐curve analysis which uses a crack driving force estimated by the EPRI (Electric Power Research Institute) procedures. However there is inconsistency between standard R‐curve analysis and PD6493 Level 3 analysis in that the latter implies a material resistance which, for a given material, depends on the geometry of the structure. A similar inconsistency arises in any failure assessment procedures like the Options 1 and 2 with Category 3 of R6, which require the assessment point to move on a geometry independent failure assessment line during crack growth; indeed, even when the failure assessment line is geometry dependent there is full agreement with R‐curve analysis only if the correct RCI is used as the failure assessment line. In a brief discussion it is noted that the new failure assessment diagram studies involving multi‐parameter fracture mechanics may help to ameliorate these problems.
MODE I AND MIXED‐MODE STABLE CRACK EXTENSIONS THROUGH STIFFENED THREE‐POINT BEND SPECIMENS
Authors: Mourad A.‐H. I. , Maiti S. K.
Published: April 2007

Abstract Both experimental and theoretical results on stable crack extensions are presented for symmetrically stiffened and unstiffened three point bend specimens subjected to mode I or mixed mode loading systems. Results concerning load‐displacement variation, growth of plastic zones, instantaneous crack edge profiles, tunnelling, etc., are presented. There is good agreement between the experimental and theoretical results. The whole of stable crack growth can be characterized by the crack opening angle criterion. The stiffening helps to increase substantially both the initiation load and the maximum fracture load.
EXPERIMENTAL J EVALUATION FROM A LOAD‐DISPLACEMENT CURVE FOR HOMOGENEOUS AND OVERMATCHED SENB OR CCT SPECIMENS
Authors: Hornet P. , Eripret C.
Published: April 2007

Abstract This paper addresses the problem of the determination of J‐intergral from experimentally measured quantities for homogeneous and overmatched single edge notched bending specimens (SENB) or through thickness centre cracked panels loaded in tension (CCT). Commonly, the experimental J‐integral is calculated from the area under the load versus load‐line displacement curve. Nevertheless, in the case of gross‐section yielding, which currently occurs for short cracked specimens or overmatching cases, this methodology mis‐estimates the real J‐integral. A new proposal, based on analytical considerations and finite element calculations, is made to estimate the J‐integral from the area under the load versus CMOD curves.
THE INFLUENCE OF PLASTIC PRESTRAINING ON BRITTLE FRACTURE RESISTANCE OF METALLIC MATERIALS WITH CRACKS
Authors: Pokrovsky V. V. , Troshchenko V. T. , Kopcmsky G. A. , Kaplunenko V. G. , Fiodorov V. G. , Dragunov Yu. G.
Published: April 2007

Abstract The purpose of the present work was to study the influence of different regimes of overloading of pressure vessel steels in different states which correspond to the steel properties at the beginning of a reactor operation and at different degrees of embrittlement (simulated by heat treatment). The experiments were performed on 25, 50 and 150 mm thick specimens with short and long cracks of various shape in the temperature range from 293 to 623 K corresponding to the service temperature range of those steels.

The following factors were investigated contribution of different effects (residual stresses, strain hardening, crack tip blunting) into the enhancement of the brittle fracture resistance of steels after warm prestressing, stability of the positive warm prestressing effect during subsequent exposure of the steels to different service loading conditions; size effect on optimal regimes of thermo‐mechanical prestressing and on the brittle fracture resistance characteristics of the steels studied after warm‐prestressing. An approach is proposed to predict the increase in the brittle fracture resistance of steels with cracks after warm prestressing.
NEAR‐THRESHOLD FATIGUE CRACK GROWTH IN A12O3 PARTICLE REINFORCED 6061 ALUMINIUM ALLOY
Authors: Papakyriacou M. , Mayer H. R. , Tschegg‐Stanzl S. E. , Gröschl M.
Published: April 2007

Abstract— The influence of Al2O3 particle reinforcement on the fatigue crack growth properties of 6061‐T6 aluminium alloy in the near threshold regime has been investigated at a load ratio of R=– 1 using an alloy with 15 vol.% fine particles (6061/Al2O3/15p) and one with 21 vol.% coarser particles (6061/Al2O3/21p). The Al2O3 particles act as obstacles for fatigue crack growth and are especially effective at very low cyclic loads. For the reinforced alloy with fine particles the threshold of the stress intensity amplitude is higher than that for the alloy containing coarse particles, and the lowest threshold value of Kmax was obtained for pure 6061‐T6. Fracture of ceramic particles and interfaces between matrix and Al2O3 particles, both more frequent for coarser particles, may serve as an explanation for the more effective improvement of fatigue crack growth properties by fine particles. At maximum stress intensity factors above 6.5 MPa√m, fatigue crack growth in the particle reinforced alloys is faster than in the unreinforced alloy 6061‐T6, which is attributed to more frequent particle and interface fracturing.
A SIMULATION OF THE BEHAVIOUR OF MULTI‐SURFACE FATIGUE CRACKS IN TYPE 304 STAINLESS STEEL PLATE
Authors: Suh C. M. , Yoon K. B. , Hwang N. S.
Published: April 2007

Abstract— Fatigue tests were carried out to study the growth and coalescence behaviour of multi‐surface cracks which were initiated at semi‐circular surface notches, and an existing crack growth simulation program was developed to predict and compare with the experimental results. Additional comparisons with ASME and BSI conditions were also carried out to enhance the reliance and integrity of structures and machine elements. The results presented in this paper show that the simulation procedure has utility for fatigue life prediction.
LOW CYCLE FATIGUE BEHAVIOR OF TWO Al‐Li ALLOYS
Authors: Blankenship C. P. , Bray G. H. , Kaisand L. R. , Starke E. A.
Published: April 2007

Abstract—The low cycle fatigue (LCF) behavior of two aluminum‐lithium alloys was investigated. Efforts were aimed at understanding the effects of microstructure on the cyclic stress‐strain behavior and methods by which different microstructures accommodate plastic strain. These goals were achieved by analyzing the cyclic response and the deformed microstructure of each alloy. Direct‐chill cast and rolled X2095 exhibited immediate cyclic softening followed by a plateau region. Strain was distributed in a homogeneous manner throughout the microstructure. Mechanically alloyed and forged AA5091 (formerly referred to as 905XL) also deformed in a homogeneous manner, but the cyclic response was characterized by initial softening followed by gradual hardening. Over‐strain loops were applied during some of the LCF tests, the purpose of which was to simulate the strain history of the material ahead of a growing fatigue crack during a tensile overload. The over‐strain response suggested that the intrinsic material response does not contribute to crack retardation in X2095 or AA5091.
THE MECHANISM OF STAGE II FATIGUE CRACK GROWTH
Authors: TOMKINS B.
Published: April 2007

This paper describes the early work directed to understanding fatigue crack growth behaviour and the seminal role played by Regis Pelloux, at both the Boeing Aircraft Co and MIT, and other researchers in various parts of the world.

From this beginning, fatigue life assessment procedures for engineering components and structures developed and still continues.
FRACTOGRAPHY AND ITS ROLE IN FRACTURE INTERPRETATION
Authors: Thompson A. W.
Published: April 2007

Fundamental understanding of fracture requires accurate interpretation of fractography. Examples are drawn from recent work on titanium aluminide alloys based on both Ti3Al and TiAl. Although the fracture mode in these alloys is often characterized as “cleavage”, in reality the fracture surfaces are neither entirely cleavage‐like, nor do the “cleavage” regions generally correspond to the classical description of cleavage. Implications of such fractographic observations, and of model fracture calculations, are discussed. Needs for further work to clarify fracture processes are also identified.
DYNAMIC CRACK PROPAGATION AND CRACK ARREST INVESTIGATED WITH A NEW SPECIMEN GEOMETRY: PART II: EXPERIMENTAL STUDY ON A LOW‐ALLOY FERRITIC STEEL
Authors: Iung T. , Pineau A.
Published: April 2007

The novel experiment developed in our Institute to investigate crack initiation, rapid crack propagation and crack arrest with one specimen, the ring test, was applied to a ferritic HSLA pipeline steel. The maximum crack speed achieved in these experiments was between 230 m/s and 1165 m/s. The fracture toughness at crack arrest, KIa, was determined by a static analysis of this specific test. In all cases, it was found that KIa was much lower than KIc. The values of KIa decrease when the maximum crack speed increases, the results being largely scattered. The fracture toughness at crack arrest is therefore not an intrinsic parameter of the material for a given temperature. Cleavage fracture obtained under these conditions is characterized by the existence of numerous cleavage microcracks, mechanical twins and unbroken ligaments. The decrease in fracture toughness when crack speed increases is related, using the Beremin or the RKR model, to the high strain rates at the tip of a rapid propagating crack. A model which takes into account the effect of unbroken ligaments left in the wake of a propagating crack is developed to account for the large values of KIa which were occasionally measured.
UNIFIED CORRELATIONS IN TRANSITION TEMPERATURES OF LOW ALLOY STEELS AND WELD METALS OF VARIOUS TOUGHNESSES
Authors: Ma H. , Zhu L. , Wang Z.
Published: April 2007

Four types of toughness were measured over a range of temperatures using CVN, COD, 4PB and PCI specimens made of low alloy steels and weld metals. It was found that there were unified correlations in transition temperatures among the various toughness parameters which could be realized by the dependence of the yield strengths of the test materials on both temperature and strain rate.

The intrinsic reason for the correlations could be attributed to local cleavage conditions, which control the ductile‐to‐brittle transition during ductile fracture processes, whether the specimens were notched or precracked, under static or dynamic loading conditions. It is suggested that the ductile fracture process itself was independent of test temperature, but the local cleavage condition remains to be more fully understood in future work.
SHORT FATIGUE CRACK GROWTH BEHAVIOUR IN WASPALOY AT ROOM AND ELEVATED TEMPERATURES
Authors: Smith R. A. , Liu Y. , Grabowski L.
Published: April 2007

Short fatigue crack growth tests have been carried out at room and elevated temperatures using the nickel‐based superalloy known as Waspaloy. A fully automated computer controlled system has been developed and employed for controlling the testing and monitoring of the growth of freely initiated surface short cracks on smooth specimens. Surface cracks as small as 10 um in length have been detected and recorded at temperatures up to 700°C. Anomalous short crack propagation behaviour was observed when comparisons were made with the corresponding long crack behaviour. Some aspects of mechanical, microstructural and environmental effects on the short fatigue crack growth behaviour of the material are discussed.
A GENERALIZED FATIGUE LIMIT CRITERION AND A UNIFIED THEORY OF LOW‐CYCLE FATIGUE DAMAGE
Authors: Altenbach H. , Zolochevsky A.
Published: April 2007

Abstract— A generalized fatigue limit criterion for multiaxial stress state conditions of isotropic materials is presented. This criterion includes four material parameters and uses two invariants of stress amplitudes and furthermore two invariants of mean stresses. It is shown that the fatigue criteria of Sines and Crossland are particular cases of the formulated criterion. Practical recommendations for the use of different fatigue limit criteria are established. Theoretical predictions are compared with experimental data. Finally a continuum damage mechanics theory for low cycle fatigue of isotropic materials is proposed. This theory describes simultaneously the influence of the stress amplitude and the mean stress on the fatigue damage suffered by materials. The proposed theory is based on four material parameters. Special damage theories with a smaller number of material parameters are obtained. Practical recommendations for the use of these fatigue damage theories are presented.
BIAXIAL THERMAL FATIGUE TESTING WITH NON‐UNIFORM STRAIN DISTRIBUTIONS
Authors: Tretyachenko G. N. , Karpinos B. S. , Barilo V. G. , Solovyova N. G.
Published: April 2007

Abstract— Methods of producing a preset thermal stress state are presented. A specimen design for providing such a state under the action of heating or cooling, without external loading by mechanical forces, is suggested. The methods and some thermal fatigue test results are described. The influence of a non‐stationary biaxial state on the lifetime of a steel is shown.
SHORT CRACK GROWTH BEHAVIOUR UNDER VARIABLE AMPLITUDE LOADING OF SHOT PEENED SURFACES
Authors: De Los Rios E. R. , Mercier P. , El‐Sehily B. M.
Published: April 2007

Abstract— The effect of variable amplitude loading on the initiation and propagation of fatigue cracks from shot peened and unpeened surfaces was investigated. The results confirm the well‐known effect of shot peening, i.e. the increase of fatigue life in comparative tests under constant amplitude loading. Shot peening increases the time to crack initiation and also decreases crack propagation rate, particularly in the earlier stages of growth.

Variable amplitude tests were of various kinds: (i) half‐life at one stress level, followed by testing at the second stress level until failure, (ii) sequence loading at two stress levels, and (iii) a different number of overload cycles (1, 10, 100) following a given number of base amplitude cycles.

The results of the two amplitude tests showed different behaviour depending on whether the first half‐life cycles were of higher or lower stress levels. These results are explained in terms of crack density and crack coalescence. The extent of damage accumulation during block loading depends on the stress levels employed. The benefits of shot peening are compromised by high stress levels.

Results from the overload tests showed that the interpretation of results is not straight forward. A combination of the theories of crack retardation and microstructural‐fracture mechanics seems a necessary prerequisite in an explanation of the resultant behaviour.
FATIGUE DAMAGE CALCULATIONS ON BLOCK LOAD SEQUENCES
Authors: Svensson T.
Published: April 2007

Abstract— The problem of fatigue life predictions for variable amplitude loading is considered. A prediction model is proposed that is based on a level crossing count of the effective load, where the effective load is denned according to the crack closure concept. The proposed model is applied to block load sequences presented in the literature and compared to experimental data and other prediction methods. It can be concluded that, provided that the crack opening level can be determined, the model gives reasonable predictions.
ENERGY DAMAGE SUMMATION METHODS FOR CRACK INITIATION AND GROWTH DURING BLOCK LOADING IN HIGH‐TEMPERATURE LOW‐CYCLE FATIGUE
Authors: Skelton R. P. , Rees C. J. , Webster G. A.
Published: April 2007

Abstract— Strain‐controlled total endurance tests have been carried out on smooth specimens of 2¼Cr‐1Mo steel at 550°C in continuous cycling, and also using interspersed blocks of “major” and “minor” cycling. Similar low‐cycle fatigue crack growth tests were also carried out on cylindrical specimens of ½CrMoV steel containing a 0.2 mm deep starter defect using interspersed blocks of “major”, “intermediate” and “minor” cycling, their order being changed in separate tests.

Damage summation in the smooth specimen tests at failure was found to be less than unity (irrespective of the failure criterion) when Miner's rule was employed, and the results are compared with limited previous data. Damage was also summed on an energy‐expended basis and this was found to be (i) independent of strain range, and (ii) independent of cycle type (i.e. continuous loading or block loading). The nearer the chosen failure criterion to crack initiation, the closer was the agreement in accumulated energies.

Similarly, in the crack growth tests, the number of complete loops to “failure” (10% load drop) was independent of block order over a wide range of applied strain ranges, but was affected by the number of cycles in each block. However, the energy criterion was again able to rationalise all the data.
PREDICTION OF FATIGUE CRACK PROPAGATION UNDER IRREGULAR LOADING
Authors: Pokrovsky V. V. , Tkach Y. V. , Ivanchenko A. I.
Published: April 2007

Abstract— A method for predicting fatigue crack propagation, both through‐thickness and surface growth, is presented which takes into consideration kinetic effects of crack growth following tensile overloading. The fatigue crack propagation prediction is based on the consideration of the contribution of the following factors to the fatigue crack growth retardation after the overload: (a) generation of a residual compressive stress system ahead of the fatigue crack tip and fatigue crack closure due to residual plastic strains occurring in the wake of the growing crack tip; (b) plastic blunting of the fatigue crack tip. It is supposed that the total number of cycles of fatigue crack retardation Nd after overload will be composed by two components: (a) Nd(1), the number of cycles until the re‐establishment of the crack closure level equivalent to that just before overload; (b) Nd(2), the number of cycles until the initiation of the “continuation” fatigue crack from the blunted tip of the crack. Prediction of surface crack propagation is carried out taking into consideration the variable constraint effect along the fatigue crack front. The experimental verification of the proposed method for fatigue crack propagation was carried out on specimens which were fabricated from a 15Kh2MFA steel. Good agreement was obtained between experimental data and crack growth calculations.
PREDICTING THE EFFECTS OF CRACK TIP CONSTRAINT ON MATERIAL RESISTANCE CURVES USING DUCTILE DAMAGE THEORY
Authors: Burstow M. C. , Howard I. C.
Published: April 2007

Abstract— In recent years much interest has been focused on the geometry dependence of the resistance to stable ductile crack growth of engineering materials, and in particular, in explaining this in terms of “constraint” effects. This paper describes the results of work using the Rousselier ductile damage model in finite element studies to simulate the growth and coalescence of voids, and hence the mechanics of ductile crack growth, to predict the effect of constraint on resistance to fracture. Using the modified boundary layer solution, where constraint is controlled by the application of remote displacements, it was possible to simulate resistance curves for different constraint conditions. This has produced a “net” of resistance curves, within which the curve for any specimen geometry can be found from a knowledge of the crack tip constraint for that specimen. This has been tested by comparing the results with those obtained from two specimens for which the constraint conditions are known. Good agreement has been achieved.

The results show that, although constraint has very little effect on conditions at the crack tip at initiation of crack growth, beyond that constraint plays an important part in defining the resistance curve. For low constraint geometries there is a very large loss in crack tip constraint which results in a large increase in the slope of the resistance curve. On the other hand, high constraint geometries exhibit very little dependence on crack tip constraint.
A LOCAL GRID REFINEMENT METHOD FOR DETERMINING STRESS INTENSITY FACTORS FOR CRACKS AT NOTCHES
Authors: Cardew G. E. , Yates J. R.
Published: April 2007

Abstract— Stress intensity calibrations have been determined for cracks at the root of a semi‐circular edge notch loaded in tension using a localised grid refinement technique for finite element analysis. The technique is of particular value in situations where a fully connected mesh model is difficult to achieve or where enhanced accuracy is needed in a small sub‐region of a model. Solutions were as accurate as those from a conventional refined mesh but with an approximately two fold reduction in run time. The resulting stress intensity factors are in good agreement with those estimated using a notch correction function and the equivalent un‐notched crack solution.
A STUDY ON STRENGTH CHARACTERISTICS OF Si3N4 COIL SPRINGS
Authors: Sato S. , Taguchi K. , Adachi R. , Nakatani M.
Published: April 2007

Abstract—

Coil springs made of silicon nitride (Si3N4), which has higher strength and heat resistance than other ceramics, have recently been developed. By examining the range of strengths and the heat resistance of the coil springs, it is shown that the coil springs can be used at temperatures up to 1000°C. We derive an equation to calculate the effective volumes of coil springs and examine the influence of size on the strength of coil springs. In addition, using a process zone size failure criterion, proof tests were conducted and analysed. The results show that the mean strength of coil springs decreases with increasing effective volume. Therefore the strength of coil springs can be estimated from the value of the effective volume, and this relationship can be applied in design calculations. Furthermore, by conducting proof tests, coil springs that have relatively large defects can be eliminated and so only highly reliable coil springs can be placed in service.
A MODEL TO PREDICT THE FATIGUE LIFE OF FIBRE‐REINFORCED TITANIUM MATRIX COMPOSITES UNDER CONSTANT AMPLITUDE LOADING
Authors: De Los Rios E. R. , Rodopoulos C. A. , Yates J. R.
Published: April 2007

Abstract—

A model based on micro‐mechanical concepts has been developed for predicting fatigue crack growth in titanium alloy matrix composites. In terms of the model, the crack system is composed of three zones: the crack, the plastic zone and the fibre. Crack tip plasticity is constrained by the fibres and remains so until certain conditions are met. The condition for crack propagation is that fibre constraint is overcome when the stress at the location of the fibre ahead of the crack tip attains a critical level required for debonding. Crack tip plasticity then increases and the crack is able to propagate round the fibre. The debonding stress is calculated using the shear lag model from values of interfacial shear strength and embedded fibre length published in the literature.

If the fibres in the crack wake remain unbroken, friction stresses on the crack flanks are generated, as a result of the matrix sliding along the fibres. The friction stresses (known as the bridging effect) shield the crack tip from the remote stress, reducing the crack growth relative to that of the matrix alone. The bridging stress is calculated by adding together the friction stresses, at each fibre row bridging the crack, which are assumed to be a function of crack opening displacement and sliding distance at each row. The friction stresses at each fibre row will increase as the crack propagates further until a critical level for fibre failure is reached. Fibre failure is modelled through Weibull statistics and published experimental results. Fibre failure will reduce the bridging effect and increase the crack propagation rate.

Calculated fatigue lives and crack propagation rates are compared with experimental results for three different materials (32% SCS6/Ti‐15‐3, 32% and 38% SCS6/Ti‐6‐4) subjected to mode I fatigue loading. The good agreement shown by these comparisons demonstrates the applicability of the model to predict the fatigue damage in Ti‐based MMCs.
A FRACTURE MODEL TO STUDY THE EFFECT OF SPECIMEN SIZE ON DYNAMIC ENERGY RELEASE RATES
Authors: Dear J. P.
Published: April 2007

Abstract—

The aim of this research was to simulate the ability of a material to transfer energy to the tip of a rapidly propagating crack when varying the specimen geometry and other factors. For this study, a distributed mass spring model was used which could be hosted on a Personal Computer (PC) of the type now available in most fracture laboratories to capture and process experimental data. The distributed mass spring model was chosen because it was easy to reconfigure for different studies. Also, it could produce the required data in the same format as more powerful FE models and at a quality not dramatically less than FE models. A most useful feature of the model was the good visibility of the fracture processes it was able to represent.
J‐Q MODEL FOR PREDICTING FRACTURE IN THE DUCTILE‐BRITTLE TRANSITION
Authors: Landes J. D.
Published: April 2007

Abstract—

A model is proposed to predict cleavage failure of precracked bodies in the transition region for steels. It is based on the concept that the failure of a weak link triggers the failure of the entire body. The model is similar to that originally proposed by Heerens et al. which assumes that the weak link has a given level of stress labeled the cleavage stress needed to cause failure. This weak link is located at some characteristic but variable distance from the crack tip. The variation in distance from the crack tip to the weak link causes variation in the transition fracture toughness. The crack tip stress is given by the J‐Q model of O'Dowd and Shih where Q characterizes the constraint level in the body.

Given a set of input data, that is fracture toughness from a given specimen geometry at a known temperature, toughness values can be predicted from these inputs at a different temperature where the yield stress is known or for a different size or geometry where Q is known. The model is applied here for two steels; a DIN 20MnMoNi55 steel and a CrMoV steel. For the first steel fracture toughness values measured on compact specimens are used to predict cleavage fracture throughout the transition for the same geometry. For the second steel the transition trend is predicted for the same compact geometry. The results show that the model is good for predicting the sudden end of the transition that is often observed but does not predict the lower shelf or early transition very well. This is a region where a weak link mechanism may not be operating.

A model is proposed to predict the cleavage fracture toughness in the transition for steels. It is based on a weak link failure concept and a crack tip stress distribution that is influenced by the constraint level. The model uses measured fracture toughness data to predict a distance from the crack tip to the weak link. This distance is a variable that is used to account for all of the variability in the fracture toughness. For a new temperature or geometry the toughness can be predicted by assuming that the cleavage stress is fixed and the material has the same range of weak link distances. The magnitude of the crack tip stresses can change due to a change in yield stress or constraint.

The model was used to predict the toughness trend in the transition and the end of the transition. It was applied to two steels, a 20MnMoNi55 steel and a CrMoV steel. For the 20MnMoNi55 steel the transition trend and the end of the transition that were predicted by the model compared well with experimental results. For the CrMoV steel the interesting part was that the lower shelf region of the transition was not predicted well. The prediction from the model overestimated the measured fracture toughness values. This suggests, as was previously believed, that a weak link mechanism may not operate near the lower shelf part of the transition. The model could also be used to predict the toughness for a new geometry such as a component model geometry. That will be reported in a later work.
QUANTITATIVE FRACTOGRAPHIC ANALYSES OF FATIGUE CRACK GROWTH IN LONGERONS OF IN‐SERVICE HELICOPTER ROTOR‐BLADES
Authors: Shaniavski A. A.
Published: April 2007

Abstract— An analysis is made of striation spacing measurements as observed on fatigue crack surfaces of specimens and longerons of helicopter rotor‐blades made from the aluminium alloy AVT. It is shown that, for the combined cyclic tensile stresses at various R‐ratios and static rotation angles, α, striation spacings were controlled by an equivalent intensity factor Ke=K1F(α, R). Values of the F(α) for Ri= const were computed.

The crack growth life in terms of the number of flights and stress equivalents were computed for various longeron sections of the helicopter rotor‐blades which had failed in service.

SUMMARY AND CONCLUSIONS

(1) A fatigue striation spacing analysis was made from measurements on AVT Al‐alloy specimens tested in air under combined cyclic tension and static‐rotation loads at various a‐angles of rotation, and stress ratios, R. Fractographic analyses have shown similarities in terms of striation spacing formation in the investigated range of α‐angles and R ratios.

(2) The similarity in the fatigue fracture mechanisms attested to the possibility of characterizing the striation spacing formation by a unified kinetic diagram via a Ke= K1F(α, R) approach for different α‐angles and R ratios. The function F(α, R) was determined and it can be used to calculate the tensile stress equivalent according to values of σi measurements taken from components broken in tests or in service.

(3) It was a longeron of the rotor‐blade of helicopters manufactured from AVT Al‐alloy broken in service and tested cyclically that were investigated fractographically. An analysis of the formation of striations and their spacing has shown similarities with the investigated longerons fatigued in tests and in service. The crack growth life versus number of flights and stress equivalent was calculated according to values of the σi measurements.

(4) It was shown that a fatigue crack will not nucleate in longerons in service if the depth of defects on the external surface have a size less than 0.3 mm. The stress for tested longerons is near to the calculated equivalent for longerons that failed in service.
A MODEL FOR FATIGUE DEFECT NUCLEATION IN THERMITE RAIL WELDS
Authors: Fry G. T. , Lawrence F. V. , Robinson A. R.
Published: April 2007

Abstract— A fatigue model for thermite rail welds is presented in this paper. The aim of the model is to provide a means for predicting the types of rail‐head fatigue defects that might form under a given set of railway operating conditions and to provide an estimate of the life consumed during stage I growth of incipient fatigue cracks. Eshelby's equivalent inclusion method is incorporated in the model so that an assessment of the effects of metallurgical discontinuities can be made. Findley's critical‐plane fatigue parameter is used as the criterion for computing fatigue damage. Results from using this model indicate that pores are the more damaging of the discontinuities typically present in thermite rail welds which also contain alumina inclusions. The shape and orientation of pores is predicted to have a strong influence on rail‐head fatigue defect formation in thkwermite rail welds.
EARLY DEVELOPMENT OF FATIGUE CRACKING AT MANUAL FILLET WELDS
Authors: Verreman Y. , Nie B.
Published: April 2007

Abstract— An experimental study within the Canadian Offshore Corrosion Fatigue Research Programme was performed on the early development of fatigue cracking along the wavy toe of manual fillet welds between structural steel plates. Stress relieved and as‐welded cruciform joints were tested under R =−1 and R= 0 loading at different stress amplitudes. The depth and the opening level of cracks as small as 10–20 μm were monitored using miniature strain gauges installed along the toe apex, in combination with beach marking. Most of the “initiation life” (25% to 50% of total life), conventionally defined by a crack depth of 0.5 mm, is consumed in short crack propagation. Three types of short crack development for different combinations of local mean stress and stress range are identified and analyzed. Growth rates in as‐welded specimens are faster than in stress relieved specimens, which results in shorter “initiation lives”. This is associated with a higher effective stress range, particularly under R = ‐ 1 loading where cracks are open over nearly the full stress range. The V‐notch stress intensity factor is a promising parameter to rationalize the crack “initiation life”. It takes into account the thickness effect experimentally observed. Under R = ‐ 1 loading of as‐welded joints, using R = 0 data and taking the whole stress range gives a reasonably conservative approximation of the crack “initiation life”.
CYCLIC CRACK RESISTANCE OF WELDED JOINTS WITH NON‐UNIFORM FIELDS OF RESIDUAL WELDING STRESSES
Authors: Trufiakov V. I. , Mikheev P. P. , Knysh V. V. , Kovalenko I. S.
Published: April 2007

Abstract— The use of linear elastic fracture mechanics to describe the kinetics of fatigue fracture of welded joints with high welding residual stresses (WRS) is experimentally evaluated in this paper. A correction analysis is used to show that the crack propagation rate of cracks in joints, as a function of the applied stress intensity factor, is linear on a log‐log scale in the Paris regime when non‐uniform fields of WRS are superimposed on the applied cyclic loading. It is shown that crack growth rates in joints with high WRS do not depend on the characteristics of the loading cycle. The parameters of the Paris exponential equation are determined by the initial WRS distribution, by the range of cyclic stresses and by the load ratio. A method for calculating the cyclic crack resistance of joints is proposed which explicitly allows for a non‐uniform field of WRS that influences the fatigue crack growth rate.
INFLUENCE OF STRESS RELIEVING BY VIBRATION ON THE FATIGUE BEHAVIOUR OF WELDED JOINTS IN COMPARISON TO POST‐WELD HEAT TREATMENT
Authors: Sonsino C. M. , Müller F. , Back J. de , Gresnigt A. M.
Published: April 2007

Abstract— Constant amplitude fatigue tests with welded specimens under fully reversed four‐point bending as well as under axial loading have shown that vibration stress relieving does not lead to a fatigue life improvement of welded parts when compared to the as‐welded state. Thus, a substitution of thermal stress relieving by a vibration treatment is not successful. This was also proved by residual stress measurements in the welded parts studied in this paper.
STRESS INTENSITY FACTOR SOLUTIONS FOR SEMI‐ELLIPTICAL WELD‐TOE CRACKS IN T‐BUTT GEOMETRIES
Authors: Bowness D. , Lee M. M. K.
Published: April 2007

Abstract— Weld toe magnification factors are widely used in the evaluation of stress intensity factors for cracks in welded structures. Traditionally, the weld magnification factor has been determined from 2‐D plane strain models containing edge cracks. However, it has long been recognised that a semi‐elliptical weld toe crack cannot be accurately represented by a 2‐D approximation due to the 3‐D nature of the geometry. As a consequence, some recent research has been carried out using 3‐D numerical modelling, which highlights the limitations of the 2‐D approach. Nevertheless, 3‐D solutions are still scarce and are of limited validity due to the difficulties associated with creating the numerical models. This paper reports the most extensive 3‐D numerical investigation of semi‐elliptical cracks in T‐butt geometries to date. Based on the numerical results, new and accurate equations for weld magnification factors were derived, which quantify the 3‐D effects present and emphasise the importance of the attachment. The results obtained from these equations are then used in an assessment of existing solutions.
COMPRESSION FATIGUE CRACK GROWTH BEHAVIOUR OF AN ALUMINIUM ALLOY: EFFECT OF OVERLOADING
Authors: Lenets Y. N.
Published: April 2007

Abstract— The behaviour of fatigue cracks in an Al‐alloy under cyclic compression, either with or without overloads, was studied. For constant‐amplitude compressive cycling, a non‐catastrophic (saturation) character of the fatigue crack behaviour was confirmed, with the final depth of a crack depending on the applied load level. Single (tensile or compressive) intermittent overloads were shown to re‐activate a previously arrested crack while reversed (tensile—compressive or compressive—tensile) ones were also shown to maintain continual fatigue crack extension under otherwise fully compressive cycling.
HIGH TEMPERATURE FATIGUE IN SINGLE CRYSTAL SUPERALLOYS
Authors: Martínez‐Esnaola J. M. , Martín‐Meizoso A. , Affeldt E. E. , Bennett A. , Fuentes M.
Published: April 2007

Abstract— The growth rate of fatigue cracks in two single crystal nickel base superalloys, CMSX‐6 and SRR99, along the <001> planes are presented and rationalised in terms of two interacting crack propagation mechanisms: one attributed to crack tip plastic blunting and the other attributed to the brittle failure of the oxide scales. The role of the oxide scale is twofold as it also wedges the crack and modifies the blunting term through a crack closure effect. On the other hand, a positive effective stress intensity range is required to fracture the oxide scale. Fatigue tests were carried out at different temperatures (500 to 1050°C), frequencies (0.001 to 20 Hz), cycle waveforms and load ratios (0 to 0.9), with starter crack lengths of abut 100 μm. The model predictions match the crack growth rates obtained for both materials. Even though both materials are nickel base superalloys, they have very different oxidation behaviours. CMSX‐6 has an improved oxidation resistance over SRR99, however, because of the twofold nature of the oxidation process, which material provides the better life expectancy depends on the applied test temperature and loading cycle.
LIFE PREDICTION FOR ADVANCED FERRITIC STEELS SUBJECT TO THERMAL FATIGUE
Authors: Bicego V. , Taylor N. , Bontempi P.
Published: April 2007

Abstract— Thermal fatigue is a well recognised source of damage in headers and steam piping of thermoelectric power plant. This topic has been extensively examined in the past for low alloy ferritic steels typically used in such applications. Experimental evidence obtained in low cycle fatigue testing with tensile hold times on Modified 9Cr1Mo and E911 steels suggests that the Linear Damage Summation rule conventionally used in engineering codes for high temperature damage analysis may not be particulary appropriate for the advanced 9Cr steel family. For this reason two alternatives have been examined: (a) a strain based creep damage evaluation using the R5 ductility exhaustion approach and (b) a creep‐fatigue continuum damage mechanics method. The potential advantages and disadvantages of both are discussed. In addition, results from low cycle fatigue and thermomechanical fatigue tests on crossweld specimens machined from welded joints in the Mod.9Cr1Mo alloy are evaluated. Even if the usual cyclic life reduction factor of 2 with respect to base material behaviour appears adequate to account for the mean trend of cross‐weld results, the large variability observed risks making the use of such a factor non‐conservative for accurate life prediction.
A THERMAL ACTIVATION APPROACH TO THE CRACK RESISTANCE OF STEELS
Authors: Saidov G. I.
Published: April 2007

Abstract— In this study, the relation between fracture toughness and mechanical properties, grain structure, temperature and strain rate is analysed on the basis of a thermo‐activation analysis of the plastic deformation of metals.

As a result of the study, the relationships obtained are of sufficient accuracy in relation to standard cracked samples of many steels.

These relations can be used as a tool when designing new alloys which have a strong resistance to crack growth.

This study is limited to temperatures in the range 0 ≤ T ≤ 0.2Tm and BCC metals.
FACTORS CONTROLLING THE FATIGUE STRENGTH OF NITRIDED TITANIUM
Authors: Morita T. , Takahashi H. , Shimizu M. , Kawasaki K.
Published: April 2007

Abstract— The factors affecting the fatigue strength of nitrided titanium were clarified. The fatigue strength depended strongly on the fracture strength of the compound layer formed on the surface by nitriding. We found a Hall‐Petch relationship between the fatigue strength of nitrided titanium and the grain size. The findings indicated that the reduction in the fatigue strength by nitriding results from both the formation of the compound layer possessing low fracture strength and grain growth occurring from ordinary nitriding. Furthermore, low‐temperature nitriding (620°C, 24 h) was proposed to suppress grain growth. This treatment method improved not only the wear resistance and the corrosion resistance but also the fatigue strength of titanium.
Economic Effects of Multinational Accounting Diversity
Authors: Choi Frederick D. S.
Published: April 2007

The purpose of this paper is to whet the appetite of accounting researchers by providing a menu of research issues in accounting and auditing that merit scholarly attention and which appear suitable for publication in JIFMA. Especially needed are inquiries that examine the economic impacts of accounting differences in a world economy characterized by unconstrained capital flows, far‐flung multinational operations and financial decisions which are made within the context of organizational complexity with diverse practices and traditions of economic behavior. The research questions that need to be addressed are substantive and will soon dwarf national inquiries in importance as the trend toward a world economy continues.
Voluntary Corporate Disclosure by Swedish Companies
Authors: Cooke T. E.
Published: April 2007

Sweden is of interest because of the rapid growth in the Stockholm Stock Exchange and because of the country's disproportionate number of multi‐national enterprises. This paper reports on the extent of voluntary disclosure in the corporate annual reports of unlisted and listed Swedish companies. A wide‐ranging definition of voluntary disclosure is adopted because of the flexibility of approach accepted in Sweden. This should not be construed that Swedish accounting is largely unregulated, rather it reflects a problem of interpretation of what constitutes generally accepted accounting principles in Sweden. In addition, the paper assesses whether there is a significant association between a number of independent variables and the extent of disclosure.
Accounting Information and Investment Risk Perception in Japan*
Authors: Ferris K. , Hiramatsu K. , Kimoto K.
Published: April 2007

This paper investigates the issue of whether financial reports appear to convey information on risk on a consistent basis across international capital markets. Data collected from a sample of Japanese financial analysts are compared to previously reported data from U.S. analysts. The results indicate that traditional accounting measures of risk explain substantial variation in the average risk perceptions of financial analysts in both the U.S. and Japan; however, while accounting risk measures were found to explain significant variation in ex post beta for the U.S. sample, this was not found to be the case for the Japanese sample. The implications of these cross‐national differences and similarities are discussed.
Managerial Perceptions of the Net Benefits of Foreign Listing: Canadian Evidence
Authors: Mittoo Usha R.
Published: April 2007

This study provides some insights into managerial perceptions of the costs, benefits, and net benefits of foreign listing through a survey of Canadian firms that have listed their securities on the foreign exchanges in the U.S. and U.K. Access to foreign capital markets and increased stock marketability are perceived to be the major benefits. The SEC reporting and compliance requirements are cited as the major costs of foreign listings. Overall, benefits are perceived to outweigh costs although not significandy. Managerial perceptions of positive net benefits are strongly linked to the levels of trading volume in their firm's stock on foreign exchanges. This study is useful for managers contemplating foreign listings. Our findings indicate that the listing decision requires careful scrutiny in terms of potential costs and benefits which may depend on many firm specific factors. Firms conducting most of their business abroad and issuing a greater percentage of equity abroad are likely to have a greater appeal for foreign investors irrespective of their size and industry. While multiple listings on foreign exchanges may not imply higher foreign trading volumes, fewer domestic exchange listings are associated with higher foreign trading volumes.
The Economic Determinants of the Home Country Bias in Investors' Portfolios: A Survey
Authors: Uppal Raman
Published: April 2007

In this article, we survey the international portfolio choice literature to investigate why investors choose to bias their portfolios towards domestic equity, even though there are significant gains to diversifying internationally. We focus on three potential explanations. First, we consider if the high proportion of domestic assets in investors' portfolios can be explained by their desire to hedge home inflation. While the models of Krugman (1981), Sercu (1980), Adler and Dumas (1983), and Stulz (1981a, 1983) suggest that this is the case, the model in Uppal (1993) shows that this is true only when relative risk aversion is less than one. Second, we consider the prevailing institutional barriers to foreign investment to see if they are sufficiently large to explain the bias observed in investors' portfolios. Halliday (1989) reports that there are few constraints on investing in foreign stock markets. This is especially true when investing in the markets of developed countries. Even when restrictions exist, they are usually not binding. Third, we consider the models of Black (1974) and Stulz (1981b) to see if transactions costs for investing abroad and taxes on income from foreign assets can explain the home equity bias. Cooper and Kaplanis (1986, 1991) and French and Porterba (1991) estimate that the taxes required to explain the observed bias are much larger than those investors actually face. We conclude that it is unlikely that these three factors are significant enough to explain the degree of the bias in portfolios that is observed empirically.