bluuebunny/crossref_metadata_2025 huggingface dataset:
Exploring the legacy of history
Authors: Mellick Sam
Published: March 2003

Herbert Michael Moran was born on 29 April 1885 in Sydney and died on 20 November 1945. I never had the good fortune to meet him but in 1946, when I was a fourth year medical student in Brisbane, I purchased a small brown‐coloured book called Beyond the Hill lies China. To this day I cannot recall what led me to that purchase but I have looked at it from time to time over the past years and found it increasingly evocative of my own student and early hospital days. I have drawn deeply from the previous Moran ­lectures, particularly Sir John Loewenthal’s lecture in 1974, which revealed for me the greatest detail about the man himself. I am indebted to Colin Smith, the College Archivist, for information held in his files; and Michael Moran who is here today for a number of personal reminiscences as well as family memorabilia. Moran was intensely interested in history. He was the founder of the first society dedicated to the study of the history of medicine in Australia, and through this activity he met the physician Leslie Cowlishaw whom he introduced to the College with the aim of securing Cowlishaw’s ‘vast knowledge of medical history and (his) wonderful library’. By a nice coincidence the third Cowlishaw Symposium was held at the College just 3 days ago, and Moran’s College legacy is thereby increasingly recognized.
Publication and patriotism
Authors: Weyden Martin B. Van Der
Published: March 2003

This commentary was previously published in The Medical Journal of Australia
2000; 175: 121. It is reproduced with permission. Copyright Australasian Medical Publishing Company.
Incidence of heterotopic bone formation after major hip surgery
Authors: Neal Bruce , Gray Harley , MacMahon Stephen , Dunn Louisa
Published: March 2003

Background:  Heterotopic bone formation is a well‐established complication of major hip surgery, but traditional reviews of the published literature may have underestimated its frequency.

Methods:  A systematic overview of all the relevant studies was performed to determine reliably the incidence of any heterotopic bone formation and the incidence of each Brooker equivalent grade. Separate estimates were made for patients with total hip replacement and patients with acetabular fracture repair.

Results:  A computer‐based search identified 218 studies with data on the incidence of heterotopic bone formation after either hip replacement or acetabular fracture repair. These studies included data from an estimated 59 121 operated hips among patients that received total hip replacement and an estimated 998 hips among patients that underwent acetabular fracture repair. In these studies, the incidence of any heterotopic bone formation was 43% after total hip replacement and 51% after acetabular fracture repair. The incidence of severe heterotopic bone formation was 9% and 19%, respectively.

Conclusions:  These results suggest that heterotopic bone formation occurs more frequently after total hip replacement than is generally believed. It is possible that heterotopic bone formation is a more important cause of postoperative disability than has previously been recognized and that effective prophylactic regimens might improve outcome in substantial numbers of patients.
Temporal trends and clinical correlates for the ret/PTC1 mutation in papillary thyroid carcinoma
Authors: Burgess John R. , Skabo Stuart , McArdle Kathryn , Tucker Paul
Published: March 2003

Background:  The incidence of papillary thyroid carcinoma (PTC) has increased in Australia at a rate exceeding 10% per annum over the past two decades. In Tasmania the increase has averaged 24% per year between 1982 and 1997. Exposure to ionizing radiation is the best characterized risk factor for PTC. Oncogenic mutations of the RET proto‐oncogene (ret/PTC rearrangements) have been associated with PTC arising following radiation exposure. In the present study it was sought to determine if PTC incidence trends were associated with an increased occurrence of the ret/PTC1 rearrangement.

Methods:  All cases of PTC diagnosed in Tasmania during the even numbered years 1978−1998 inclusive were sought for study (n = 98). Archival histopathology blocks for 62 cases were located. The RNA was successfully extracted from 41 tumours and ret/PTC1 status assessed by reverse transcription−polymerase chain reaction.

Results:  The ret/PTC1 mutation was found in 26 (63%) of PTC. The mean age at diagnosis for ret/PTC1‐positive and ret/PTC1‐negative tumours was 46.5 ± 15.46 and 41.9 ± 13.45 years, respectively. The ret/PTC1 positivity was significantly associated with larger tumour size. However, ret/PTC1 was not associated with an adverse prognosis. The prevalence of tumours positive for ret/PTC1 remained stable over the study period (1978−1998) and did not exhibit birth year or diagnosis year clustering.

Conclusion:  This is the first study to map temporal trends for the prevalence of ret/PTC1 relative to incidence trends for PTC. Although the ret/PTC1 mutation was frequently identified in Tasmanian PTC, there was no clear relationship between ret/PTC1 and recent PTC incidence trends.
Immunological findings in acute and chronic pancreatitis
Authors: Bhatnagar Archana , Wig Jai Dev , Majumdar Siddartha
Published: March 2003

Background:   In order to identify the role of mononuclear cells in pancreatitis, the immune picture at the cellular level has been studied. The cytokine production at the individual cell level in response to in vitro stimulation can help in identifying the percentage of specific cell types producing a particular cytokine.

Methods:  A total of 30 patients with acute pancreatitis (AP; n = 15) and chronic pancreatitis (CP; n = 15) were entered into the study and peripheral blood samples were drawn at the time of admission. A control group of 12 healthy individuals (age and sex matched) were also included in the study. Mononuclear cells from the peripheral blood from all three groups were separated on Ficoll gradient and labelled for surface antigens (i.e. cluster of differentiation (CD)3, CD4, CD8, CD25, CD14 and human leucocyte antigen D receptor (HLA‐DR)) using monoclonal antibodies. The CD3+ and CD14+ cells were also stained for intracellular cytokines by specific monoclonal antibodies (i.e. for interferon (IFN)‐γ, interleukin (IL)‐2, IL‐4 & IL‐10 in CD3+ cells and IL‐6 and IL‐12 in CD14+ cells). These fluorochrome‐labelled cells were analysed on the flow cytometer.

Results:  The T‐cell population is affected in pancreatitis where the CD4+ and CD8+ T‐cell numbers are significantly altered. There is a marked reduction in CD4+ T cells in AP and CP. The CD8+ T cells were significantly reduced in AP. The IL‐2 receptor is expressed in large numbers in AP and CP patient groups. The T cells from the CP group had a typical IL‐2, IL‐4 secreting pattern, while AP patients had a high IL‐10, IFN‐γ and low IL‐2, IL‐4 population. The HLA‐DR expression on monocytes differed significantly between the two groups, being strikingly reduced in chronic cases and significantly reduced in acute cases. The percentage of IL‐6‐producing monocytes was significantly higher in patients with AP as well as CP while IL‐12 levels were higher in the CP than in the AP group.

Conclusions:  T cells in CP are polarized towards the T‐helper (Th)1 phenotype while the AP patients had a mixed population. This seems to be a part of immune deviation that is associated with development of CP and IL‐12 appears to be instrumental in this process. The monocytes synthesize proinflammatory cytokines, which play an important role in the local and systemic consequences of the disease. In the disease clinical assessment such a study can provide useful information about the involvement of the immuno­inflammatory system.
PRACTICE GREEN ENGINEERING, KEEP THE JUNKYARDS CLEAR
Authors: Rosenfield
Published: March 2003

This paper discusses the fracture prevention aspects of lifetime prediction. Initially, it is pointed out that lifetime can be determined by factors such as obsolescence and consumer rejection. Lifetime is then related to acceptable risk in order to make it compatible with advances in design philosophy for large welded structures.

Accident statistics are cited and the argument made that the major opportunities for lifetime improvement are revealed by failure analysis, and are shown to lie in design and production. However, there are some structures, e.g. boilers and pressure vessels, where the construction rules are so well established that failures occur mainly because of operational errors.

Based on the results of the Battelle/NBS Cost of Fracture Study, attention is focused on the effect of material–property reproducibility in driving failure probability. Little evidence could be found regarding reproducibility improvements of fatigue lifetime and brittle fracture toughness in production lots of alloys over time.
CRACK CLOSURE AND THE FATIGUE‐CRACK PROPAGATION THRESHOLD AS A FUNCTION OF LOAD RATIO
Authors: Mc  , Ritchie
Published: March 2003

The phenomenon of crack closure, which involves the premature closing of fatigue cracks during the unloading portion of a fatigue cycle resulting in the development of crack‐tip shielding due to crack wedging, has become widely accepted as a critical mechanism influencing many aspects of the behaviour of fatigue cracks in metallic materials; these include effects of load ratio, variable‐amplitude loading, crack size, microstructure, environment and the magnitude of the fatigue threshold. Recently, however, the significance of crack closure has been questioned and alternative suggestions made for many of these phenomena, e.g. the effect of the load ratio (i.e. the ratio R of the minimum to maximum loads) on threshold behaviour. In the light of this, the present paper provides evidence to rebut the assertion that crack closure is an insignificant process. Particular attention is given to the effect of crack closure on the threshold level as a function of load ratio.
CONTINUOUS SEM OBSERVATIONS OF CREEP‐FATIGUE DAMAGE PROCESSES
Authors: Ogata  , Arai
Published: March 2003

In order to examine the relation between damage evolution and changes in microstructure, e.g. from creep cavities, surface micro‐cracks and dislocation structures at high temperature, strain controlled creep‐fatigue tests were performed and interrupted at several damage levels on Types 304 and 316 stainless steels. The creep‐fatigue tests on Type 304 stainless steel at a low strain level were conducted in a high‐temperature fatigue testing machine combined with a scanning electron microscope, and the micro‐crack initiation and growth behaviour were continuously observed to clarify the damage extension mechanism. It was found that even though many cavities were initiated and grew on the internal grain boundaries of the specimens during the strain‐controlled tests, the failure life was governed by the propagation of surface cracks. On the other hand, micro‐cracks of about the order of one grain size were initiated mainly along grain boundaries normal to the loading axis under low stress creep‐fatigue, and the crack propagation rate of the micro‐cracks was slow and random due to the nature of the microstructures. The micro‐cracks gradually opened in the loading direction with increasing number of cycles and coalescence contributed to growth.
THREE‐DIMENSIONAL FINITE ELEMENT SIMULATION OF CRACK EXTENSION IN ALUMINIUM ALLOY 2024FC
Authors: Lin  , Cornec  , Schwalbe
Published: March 2003

A simulation of 3D crack extension using a cohesive zone model (CZM) has been carried out for a side‐grooved compact tension specimen and a surface‐crack tension specimen of aluminium 2024FC. Detailed finite element calculations were conducted by assuming crack extension only along the crack plane (mode I). For comparison, a 2D plane strain simulation is also presented. Load, displacement and crack extension histories are predicted and compared with the experiment. It is shown that the 2D approximation appears to agree reasonably well with experimental results, and that the 3D calculation gives very good agreement with test data. The determination of the CZM parameters is also discussed. Numerical results show that the CZM is a workable computational model which involves only a few microstructurally motivated phenomenological parameters for crack extension simulation.
THE ETM METHOD FOR ASSESSING THE SIGNIFICANCE OF CRACK‐LIKE DEFECTS IN ENGINEERING STRUCTURES
Authors: Schwalbe  , Zerbst  , Brocks  , Cornec  , Heerens  , Amstutz
Published: March 2003

The Engineering Flaw Assessment Method, EFAM, is presently being developed at GKSS. It consists of several individual documents for determining material properties and the crack driving force. The present paper briefly describes the document EFAM ETM 97 which provides guidance for estimating the crack tip opening displacement (CTOD) and theJ‐integral as driving force parameters for homogeneous structures. The CTOD andJcan be expressed as functions of applied force or applied strain.
FATIGUE CRACK GROWTH DUE TO TWO SUCCESSIVE SINGLE OVERLOADS
Authors: Hammouda  , Ahmad  , Seleem  , Sallam
Published: March 2003

The behaviour of fatigue growth and cyclic tip deformation of long cracks due to two successive single overloads was investigated both experimentally and numerically. The results show the effect of the ratio of the second and first overloads, and the crack increment between the two overloads. The contributions of both crack tip blunting and residual stress fields were separated and accommodated in a previously developed crack tip deformation parameter, which was utilized to predict the resulting fatigue crack growth behaviour.

The following trends were experimentally observed. Should the ratio of the second and first overloads not be less than one, fatigue crack growth rates followed the predictions based on the second overload. Otherwise, either of the following two situations resulted: (1) when the two overloads were closely applied, the second overload caused an initial acceleration in growth rates followed by a behaviour controlled by the first overload; (2) when the second overload was applied after the crack growth had reached its minimum rate due to the first overload, more retardation in growth rate was observed.

Based on the model developed in the paper, it is possible to enhance the retardation effect of an overload if this overload is preceded by another overload. This enhancement depends on the ratio of the two overloads and the crack increment between them.
STRESS INTENSITY FACTORS FOR A FUNCTIONALLY GRADED MATERIAL CYLINDER WITH AN EXTERNAL CIRCUMFERENTIAL CRACK
Authors: Li  , Zou
Published: March 2003

This paper presents mode I stress intensity factors for external circumferentially cracked hollow cylinders, which are assumed to be made of functionally graded materials and subjected to remote uniform tension. The conventional finite element method is improved by introducing isoparametric transformation for simulating the gradient variations of material properties in the finite elements. This improved finite element method is verified to be effective and efficient. Various types of functionally graded materials and different gradient compositions for each type are investigated. The results show that the material property distribution has a quite considerable influence on the stress intensity factors.
J‐ESTIMATION FOR SEMI‐ELLIPTICAL SURFACE CRACKS IN WIDE PLATES UNDER DIRECT TENSION
Authors: Boothman DP , Lee MMK , Luxmoore AR , Sumpter JDG
Published: March 2003

Large marine structures can be subjected to extensive localized damage, with strains reaching 10 times the yield strain. Small defects might propagate, and accurate defect assessment is required for safe operation. To simulate this problem, J‐integrals have been computed for semielliptical cracks in wide steel plates under tension. Three‐dimensional (3D) elastic–plastic finite element analysis was used to model shallow crack geometries with 0.2 ≤ a/c ≤ 0.57 and 0.05 ≤ a/t ≤ 0.15. The material responses were linear elastic followed either by power hardening, or perfect plasticity and power hardening. It was found that, in contrast to previous studies on single edge notch geometries, the material law does not have a major influence on the J–strain behaviour. Results obtained from the 3D analyses form the basis for the development of a J‐based estimation scheme.
PREDICTING THE EFFECTS OF LOAD RATIO ON THE FATIGUE CRACK GROWTH RATE AND FATIGUE THRESHOLD
Authors: Kardomateas  , Carlson
Published: March 2003

The effect of the load ratio, R, on fatigue crack growth behaviour is analysed on the basis of the recently proposed inelastic discrete asperities model. A wide range of load ratios, both positive and negative, are examined. Particular emphasis is placed on compressive excursions, i.e. negative R loadings. The inelastic discrete asperities model is a micro‐mechanical analysis based on the plastic crushing of a single asperity (or multiple asperities) located on the crack face close to the crack tip and under dominantly plane strain conditions. Experimental data have indicated that the primary crack face contacts which obstruct closure are immediately adjacent to the crack tip, although segments of the crack face more distant from the crack tip are not neglected. However, the more distant asperities are a part of the past crack advance history which does not influence current behaviour. By use of this model, it is shown that the effect of the load ratio can be adequately predicted once some baseline information on mechanical material properties and surface roughness is provided. The model also provides useful trend information and explains many of the observed phenomena, e.g. the ‘saturation’ of the compressive underload effects. For a constant applied nominal stress intensity factor range, ΔKnom , it is shown that the effective stress intensity factor range, ΔKeff , initially decreases as the positive R decreases (corresponding to the increasing influence of closure), reaches a minimum around R = 0, and then starts increasing with negative R (corresponding to the plastic crushing of the asperities which reduces closure), eventually reaching a saturation level below ΔKnom . Conversely, for an assumption of a constant ΔKeff , the applied ΔKnomincreases as the positive load ratio decreases, reaching a maximum around R = 0, and then decreases with more negative R values, eventually reaching again a saturation level (above ΔKeff ). It is also shown that the effect of material hardness can be directly analysed based on this model.
CRACK TIP PARAMETERS FOR CREEP‐BRITTLE CRACK GROWTH
Authors: Hall  , McDowell  , Saxena
Published: March 2003

Crack growth histories for creep‐brittle aluminium alloy 2519‐T87 are simulated by controlling the rate of release of finite element nodes along the crack growth path using a variable time‐step, nodal release algorithm. While earlier experimental studies established little or no correlation between time‐dependent fracture parameters and the crack growth rate,a˙, during creep‐brittle fracture, the numerical results presented here indicate excellent correlation of theCtparameter witha˙during the quasi‐steady state crack growth regime. Differences in the experimental and numerical determination of time‐dependent fracture parameters are likely to be due to difficulties in experimental determination of the creep component of the load line deflection rate,V˙c , during creep‐brittle crack growth. A new quantity, K/rqc, is derived from time‐dependent fracture parameters to predict crack growth for transient, quasi‐steady state and steady state crack growth. However,Ctand K/rqc should only be employed as parameters for predicting creep‐brittle crack growth with an understanding of the couplings which exist between these parameters and the crack growth rate.
A phenomenological model of fatigue macrocrack initiation near stress concentrators
Authors: Ostash  , Panasyuk  , Kostyk
Published: March 2003

Fatigue macrocrack initiation is considered to be a two‐parameter process. It is governed by the local or strain amplitude, and a certain linear parameter of the material. Corresponding parameters have been proposed, i.e. the local stress range Δσ*y and a characteristic distance d *, the prefracture zone size. The formation of this zone is conditioned by a decrease in yield strength within the material’s surface layers, microstructure, loading amplitude, cyclic strain hardening and environment. The value of d * is estimated experimentally by several methods and is assumed to be a certain material constant, independent of both notch and specimen geometry. At the prefracture zone boundary, a major barrier exists that retards the growth of a physically small fatigue crack. The moment when the physically small crack overcomes the prefracture zone boundary is assumed to be a quantitative criterion, ai = d *, for the micro‐ to macrocrack transition. The proposed relationships, Δσ*y versus Ni , and d * versus Ni , can be used as a basis for the establishment of the materials resistance to macrocrack initiation.
A two‐dimensional elastic–plastic finite element analysis of friction effects on sliding crack surfaces in full or partial contact
Authors: Hammouda  , El‐Sehily
Published: March 2003

Sliding crack surfaces are analysed, that are completely or partially in contact, using a two‐dimensional plane‐stress elastic–plastic finite element technique. Our in‐house program was modified to account for the friction which acts between two rough mating surfaces. The analysis is applied to a cantilever beam cracked along its span through its centroidal plane. Twelve cracks with length‐to‐span ratios ranging from zero to 0.5 were analysed. The effect of friction was investigated by considering 0, 0.4, 0.8, 1.2 and 1.6 as values for the coefficient of friction with each crack length. The results show the influence of friction on the beam stiffness, strain energy release rate, modes of crack tip and surface displacements, and the development of plastic deformation. The present finite element outputs assist in the explanation of experimental events associated with mode II crack tip displacement data found in the literature.
Interfacial fatigue crack growth in foam core sandwich structures
Authors: Shipsha  , Burman  , Zenkert
Published: March 2003

This paper deals with the experimental measurement of face/core interfacial fatigue crack growth rates in foam core sandwich beams. The so‐called ‘cracked sandwich beam’ specimen is used, slightly modified, which is a sandwich beam that has a simulated face/core interface crack. The specimen is precracked so that a more realistic crack front is created prior to fatigue growth measurements. The crack is then propagated along the interface, in the core material, during fatigue loading, as is assumed to occur in a real sandwich structure. The crack growth is stable even under constant amplitude testing. Stress intensity factors are obtained from the FEM which, combined with the experimental data, result in standard da/dN versus ΔK curves for which classical Paris’ law constants can be extracted. The experiments to determine stress intensity factor threshold values are performed using a manual load‐shedding technique.
The preferred fatigue crack propagation mode in a M250 maraging steel loaded in shear
Authors: Pinna  , Doquet
Published: March 2003

Macroscopic torsional fatigue cracks are shown to propagate in shear, in plain tubular specimens, in the M250 maraging steel, for stress ranges from 90% down to 40% of the yield stress. This cannot be explained in terms of microcrack coalescence for the smallest stress range, for which microcracks are scarce. The kinetics and mechanisms of mode II fatigue crack growth are thus investigated, using precracked CTS or tubular specimens. For a high ΔKII , slowly decelerating mode II propagation takes place for a distance that increases with ΔKIIbefore branching occurs. Friction stresses along the crack flanks shield the applied load and explain this deceleration. An inverse analytical procedure is used to derive the effective stress intensity factor, allowance being made for friction effects, from displacement profiles measured from microgrids using a scanning electron microscope. The measured crack growth rates correlate much better with the effective stress intensity factor than with the nominal ΔKIIvalue. The crack paths observed in torsion are discussed in terms of maximum crack velocity.
Fatigue life assessment of nodular cast iron containing casting defects
Authors: Nadot  , Mendez  , Ranganathan  , Beranger
Published: March 2003

The fatigue behaviour of a nodular cast iron containing casting defects has been investigated in the high‐cycle fatigue regime. In this paper, we propose a fatigue life assessment model for flawed materials based on a fracture mechanics approach which takes into account the position and size of the defect, short crack behaviour and the notch effect introduced by the defect. The fatigue behaviour of smooth samples, and long and short crack behaviour have been experimentally determined in order to identify the relevant mechanical parameters; these being introduced into the model. An experimental study has been made both in air and in vacuum in order to account for the position of the defect, noting that internal defects are supposed to be under vacuum conditions. Experimental results, which are based on a two‐crack front‐marking technique specially developed for this study, show that the propagation of natural cracks is controlled by the effective stress intensity factor in air as well as in vacuum. The K calculation for a short crack in the stress field of a notch is analysed using numerical elastic–plastic results. Comparison between experimental results and the computation of fatigue life for fatigue lives less than 106 cycles shows that the fatigue behaviour of nodular cast iron is controlled by a propagation process. The model proposed is thus relevant for fatigue lives less than 106 cycles so that the defect can be considered as a crack and the initiation stage neglected. Closer to the fatigue limit, this study shows that the initiation stage should be considered in the assessment of fatigue life of nodular cast iron, because a single macroscopic propagation assessment is not enough to describe the whole fatigue life. The defect cannot be considered as a pre‐existent crack in the high‐cycle fatigue range (>106 cycles), and the initiation stage that contains microcrack propagation around the defect should be evaluated when assessing the high‐cycle fatigue life of nodular cast iron.
Effect of tempering treatment on hydrogen‐induced cracking in high‐strength steel
Authors: Nakatani Y. , Higashi T. , Yamada K.
Published: March 2003

The fracture characteristics of high‐strength steel ASTM A‐490 under a hydrogen environment were investigated, with special emphasis placed on changes in fracture characteristics due to a tempering treatment at temperatures from 200 to 400 °C. A mechanical test was performed on cathodically charged specimens subjected to a constant load. Experimental analyses show that tempering treatment in the range from 200 to 400 °C does not alter the essential nature of delayed fracture due to crack growth. However, the role of intergranular (IG) cracking becomes prominent in the subcritical crack growth period with an increase in the tempering temperature to 400 °C. This development of IG cracks in the subcritical crack growth period is uniquely dependent on the tempering treatment performed in the tempering range from 250 to 400 °C. Furthermore, an increase in the fraction of the IG facet in the subcritical crack growth area is dependent on the increase in the stress intensity at the crack tip in those specimens tempered at 300 and 400 °C.
The characterization of fatigue crack growth behaviour by constant ΔKcontrol testing
Authors: Zheng Z. , Powell B. E. , Byrne J. , Hussey I. W.
Published: March 2003

Essential to the assessment of the fatigue integrity of critical components is the prediction of their crack propagation lives. This requires the effective and efficient characterization of the fatigue crack growth behaviour of the material when using a small number of specimens. A test facility, able to control the range of applied load (ΔP ) and range of stress intensity factor (ΔK ), has been used to determine the fatigue crack growth rates in corner notched specimens of Udimet 720 for stress ratios of 0.5, 0.1 and −1.0. Initially, the results were analysed in terms of the three‐point secant data reduction method. Subsequently, the benefits to be gained by the use of alternative methods involving regression analysis have been examined. The effectiveness of the procedures has been assessed in terms of the extent to which they reduce the width of the scatter band representing the fatigue crack growth behaviour and the accuracy with which the experimental observed fatigue lives are predicted. On this basis, the results from the ΔKcontrolled tests were superior to those obtained under ΔPcontrol, when analysed by similar data reduction methods. In addition, the results from ΔKtests were improved when the secant method was replaced by a linear regression method, which allowed the sample interval to be reduced and more levels of constant ΔKto be examined in a single specimen.
The influence of cross‐sectional thickness on fatigue crack growth
Authors: Guo W. , Wang C. H. , Rose L. R. F.
Published: March 2003

For thin structures, fatigue crack growth rates may vary with the structure's thickness for a given stress intensity factor range. This effect is mainly due to the change in the nature of the plastic deformation when the plastic zone size becomes comparable with, or greater than, the cross‐sectional thickness. Variations in the constraint affect both the crack tip plastic blunting behaviour as well as the fatigue crack closure level. Approximate expressions are constructed for the constraint factor based on asymptotic values and numerical results, which are shown to correlate well with finite element results. It is demonstrated that the present results not only permit predictions of the specimen thickness effects on fatigue crack propagation under spectrum loading, but also eliminate the need to determine the constraint factor by curve‐fitting crack growth data.
On the life‐controlling microstructural fatigue mechanisms in ductile metals and alloys in the gigacycle regime
Authors: Mughrabi
Published: March 2003

The high‐cycle fatigue (HCF) behaviour of ductile metals and alloys, and the life‐controlling microstructural fatigue mechanisms known from HCF are reviewed critically with respect to their possible role in the gigacycle or ultra‐high‐cycle fatigue (UHCF) regime. Arguments are presented to support the hypothesis that, at the very low amplitudes of the UHCF regime, fatigue crack initiation, resulting from cyclic strain localization, and slow early Stage I fatigue crack propagation are the life‐controlling mechanisms and that these processes can essentially be described in terms of the microstructurally irreversible portion of the cumulative cyclic plastic strain. Emphasis is placed on the important role of the so‐called slip irreversibility which decreases as the amplitude becomes lower and lower. Finally, the Manson–Coffin law is reformulated for very low amplitudes in terms of microstructurally relevant parameters, and a fatigue life diagram is developed, based on these preceding microstructural considerations. Important features of this diagram are: (i) the plastic strain fatigue limit in the HCF regime which is related to the threshold for cyclic strain localization in persistent slip bands; and (ii) the transition from this plastic strain fatigue limit to a threshold of negligible slip irreversibility at still lower amplitudes in the UHCF regime.
A dilatancy model of tensile macrocracks in compressed rock
Authors: Nikitin  , Odintsev
Published: March 2003

A model is developed for tensile fracture under compression for a brittle material with microcracks. The final stage of failure with the formation of macroscopic‐splitting cracks is considered. Pre‐existing microcracks act as a converter of compression into tension in one direction. This results in the nucleation of other tensile microcracks. Rupture of spacings between the microcracks generates a mode I macrocrack parallel to the direction of maximum compression. Crack propagation is due to sliding along planes that are inclined to the compression microcrack surfaces and is stimulated by the forces distributed along the interacting macrocrack surfaces. Equilibrium, stability and growth of cracks are studied on the basis of the theory of fracture mechanics under the assumption of the plane strain state. The behaviour of both short and long macrocracks are analysed. Parameters of the model are evaluated with the help of data from fracture experiments on some rocks.
Mixed‐mode crack surface interference under cyclic shear loads
Authors: Yu  , Abel
Published: March 2003

A previous modelling analysis predicted that crack surface interference under cyclic shear loads is a combination of cyclic shear attenuation and cyclic wedge‐opening. In the present study, experimental evidence is provided on notched thin‐walled tubular specimens to evaluate the modelling predictions. Tests were carried out with varied static tensions superimposed on fully reversed (Rτ = −1) or pulsating (Rτ = 0) cyclic shear loads. The crack surface interference was measured by near‐tip strain gauge methods. Based on the single and dual strain gauge readings, the strains induced by the mode I and II interference are separately identified so that the cyclic wedge‐opening behaviour was noted as a companion of the cyclic shear attenuation. The crack surface interference under cyclic shear loads is compared with the influence from varied static tensions and shear stress ratios. A comparison of the mode I crack surface interference is also made between the conditions with cyclic shear loads and cyclic tensile loads. Finally, the characteristics of crack surface displacements are discussed, and the experimental results of effective mode I and II stress intensity ranges are compared with the modelling predictions.
Fatigue strength of mash seam welded joints
Authors: Tokaji  , Shiota  , Minagi  , Miyata
Published: March 2003

Reversed bending fatigue tests have been conducted using four series of mash seam welded joints obtained from the coupling of two different steels and plate thicknesses. Fatigue strength was evaluated and the effects of material property changes resulting from welding were studied. Fatigue strength of all series of the welded joints decreased slightly compared with that of the base steel. Type of steel and plate thickness in the welded samples exerted very little influence on fatigue strength. In the welded joints between steels with the same plate thickness, fatigue failure took place at a location away from the weld zone in the plate with the lower strength, while in the welded joints between plates of different thickness, failure occurred at the shoulder between the thin and thick plate, i.e. at the weld zone. Regardless of the type of steel and the plate thicknesses joined, fatigue strengths of the mash seam welded joints were slightly higher than those of the laser welded butt joints.
Failure due to semielliptical surface cracks under arbitrary stress distributions
Authors: Fett
Published: March 2003

A procedure is described that is based on the two‐dimensional weight function equation of Rice. This enables one to determine the equilibrium semiellipses characterized by a constant stress intensity factor along the crack‐tip line for any stress distribution. The applicability is explained for the special case of thermal stresses caused by a thermal shock. Local stress intensity factors are estimated for the same stresses by using solutions for exponential stress distributions. A comparison of the two methods showed good agreement.
Numerical investigation of creep crack growth in cross‐weld CT specimens. Part II: influence of specimen size
Authors: Andersson P. , Segle P. , Samuelson L. Å.
Published: March 2003

A numerical investigation of the influence of specimen size on creep crack growth in cross‐weld CT specimens with material properties of 2.25Cr1Mo at 550 °C is performed. A three‐dimensional large strain and large displacement finite element study is carried out, where the material properties and specimen size are varied under constant load for a total of eight different configurations. The load level is chosen such that the stress intensity factor becomes 20 MPa √m regardless of specimen size. The creep crack growth rate is calculated using a creep ductility‐based damage model, in which the creep strain rate ahead of the crack tip perpendicular to the crack plane is integrated taking the degree of constraint into account. Although the constraint ahead of the crack tip is higher for the larger specimens, the results show that the creep crack growth (CCG) rate is higher for the smaller specimens than for the larger ones. This is due to much higher creep strain rates ahead of the crack tip for the smaller specimens. If, on the other hand, the CCG rate is evaluated under a constant C * condition, the creep crack growth rate is found to be higher for the larger specimens, except when the crack is located in a HAZ embedded in a material with a lower minimum creep strain rate; then, the creep crack growth rate is predicted to be higher for the smaller specimen. In view of these results, it is obvious that the size effect needs to be considered in assessments of defected welded components using results from CCG testing of cross‐weld CT specimens.
Reduction of hydrogen embrittlement in an ultra‐high‐strength steel by laser surface annealing
Authors: Tsay  , Yang
Published: March 2003

This paper shows that laser beam irradiation improves the resistance to hydrogen embrittlement (HE) in an ultra‐high‐strength maraging steel. Localized laser irradiation of a peak‐aged steel plate resulted in the formation of a soft surface layer called the laser‐annealed zone (LAZ). A composite region (CR) was formed when both the top and bottom surfaces of a peak‐aged specimen were laser‐annealed (LA) to leave an interior layer of untransformed base metal (BM) sandwiched between the two LAZs. Slow strain rate tensile tests showed that LA specimens had lower strength and ductility than the peak‐aged specimens when tested in air, but in a H2 S solution, the soft LAZs showed less susceptibility to HE than the BM. The fatigue crack growth rates (FCGRs) in the CR were lower than those in the BM regardless of testing environment and stress ratio (R ). The retarded crack growth in the CR was attributed to the combination of residual compressive stresses and the soft microstructures in the LAZs. The tensile fracture appearance of LA specimens tested in a H2 S solution exhibited intergranular fracture in the BM. Fractographs of the fatigue specimens tested in gaseous hydrogen revealed transgranular fracture in the LAZs and mainly quasi‐cleavage fracture in the BM.
A model for fatigue crack growth, part I: phenomenology*
Authors: Lang
Published: March 2003

A fatigue crack growth model for metals is presented in this two part paper. The model is based on experimental evidence obtained on the aluminium alloy Al 7475‐T7351. In Part I of this paper, the physical basis of the model is discussed. The model accounts for residual compressive stresses ahead of the crack front and crack closure, which constitute an intrinsic and extrinsic effect, respectively. The centre of this model is the crack propagation stress intensity factor,KPR . There are two basic sequences involving a load step following constant amplitude loading which cause two different types of transitional processes that are fundamental to fatigue crack growth. An increase in the maximum load causes instant and ‘dynamic’ changes inK PR . This transition inKPRiscycle dependent.An example is a multiple overload sequence. A decrease in the maximum load causes acrack growth dependenttransition. Crack growth retardation after a tensile overload is an example of this type of a transition. The general description of these two transitional processes constitutes the complete solution for the fatigue crack growth problem in metals for Mode 1 loading. Part I of this paper provides the general description of the two transitional processes in terms ofKPR . In Part II, the results of Part I are generalised, which leads to a new fatigue crack growth prediction model for variable amplitude loading.
Fatigue fracture in plates in tension and out‐of‐plane shear
Authors: Zehnder  , Viz  , Potdar
Published: March 2003

Straight cracks near a stiffening element, or curved cracks, in a pressurized shell can be subjected to out‐of‐plane tearing stresses in addition to normal tensile stresses due to the membrane stresses in the shell. To predict the rate of fatigue crack growth in such situations a theory and a crack growth rate correlation are needed. Such loadings are modelled as a superposition of plane stress tensile fracture (mode I) and Kirchhoff plate theory shearing fracture (mode 2). Finite element analyses using shell elements are used to compute the energy release rate and stress intensity factors associated with the loading. Three fatigue crack growth rate experiments were carried out on sheets of 2024‐T3 aluminium alloy loaded in tension and torsion. The first set of experiments is constant amplitude fatigue crack growth tests. The second consists of experiments where crack closure is artificially eliminated to determine the rate of crack growth in the absence of crack face contact. The third is a set of constant stress intensity factor amplitude tests. The results all show that as the crack grows extensive crack face contact occurs, retarding crack growth. In the absence of crack face contact, however, the addition of out‐of‐plane shear loading increases the crack growth rate substantially.
Probabilistic modelling of safe crack growth and estimation of the durability of structures
Authors: Lepikhin  , Makhutov  , Moskvichev  , Doronin
Published: March 2003

Probabilistic models of crack growth are considered at the macro‐level of material deformation. These probabilistic models have parameters that can be determined from a fracture mechanics approach. Results from statistical analyses of defects in welded joints show that it is possible to use a two‐parameter Weibull distribution as a basic model for the distribution of defect size. On the basis of a Monte Carlo numerical simulation of crack growth, one can construct complete probabilistic diagrams for structural integrity. These diagrams are the basis for designing structures containing defects.
Constraint effects on probabilistic analysis of cracks in ductile solids
Authors: Rahman S. , Chen G.
Published: March 2003

This paper presents a method for evaluating constraint effects on probabilistic elastic–plastic analysis of cracks in ductile solids. It is based on fracture parameters J and Q, correlation between Q and J–resistance curve of the material, and J‐tearing theory for predicting fracture initiation and instability in cracked structures. Based on experimental data from small‐scale fracture specimens, correlation equations were developed for fracture toughness at crack initiation and the slope of the J–resistance curve as a function of constraint condition. The random parameters may involve crack geometry, tensile and fracture toughness properties of the material, and applied loads. Standard reliability methods were applied to predict probabilistic fracture response and reliability of cracked structures. The results suggest that crack‐tip constraints have little effect on the probability of crack initiation. However, the probability of fracture instability can be significantly reduced when constraint effects are taken into account. Hence, for a structure where some amount of stable crack‐growth can be tolerated, crack‐tip constraints should be considered for probabilistic fracture‐mechanics analysis.
Bithermal low‐cycle fatigue evaluation of automotive exhaust system alloy SS409
Authors: Lu G.‐Y. , Behling M. B. , Halford G. R.
Published: March 2003

This investigation provides thermomechanical fatigue data for the ferritic stainless steel alloy SS409, used extensively in automotive exhaust system components. The data were generated to assess the total strain version of the strain range partitioning (TS‐SRP) method for the design and durability assessment of automotive exhaust systems. The cyclic lifetime and the cyclic stress–strain–temperature–time behaviour for alloy SS409 were measured using bithermal tests with extreme temperatures of 400 and 800 °C. Fatigue lives ranged up to 10 000 cycles with hold‐times of 0.33–2.0 min. The bithermal fatigue behaviour was compared to isothermal, strain‐controlled fatigue behaviour at both 400 and 800 °C. Thermomechanical cycling was found to have a profound detrimental influence on the fatigue resistance of SS409 compared to isothermal cycling. Supplementary bithermal tests with hold‐times ranging from 40 s to 1.5 h were conducted to calibrate the TS‐SRP equation for extrapolation to longer lifetimes. The observed thermomechanical (bithermal) fatigue lives correlated well with estimated lives using the TS‐SRP equations: 70% of the bithermal fatigue data fall within a factor of 1.2 of calculated life; 85% within a factor of 1.4; and 100% within a factor of 1.8.
Damage mechanics models of ductile crack growth in welded specimens
Authors: Burstow M. C. , Howard I. C.
Published: March 2003

Two‐dimensional, plane strain, finite element analyses of strength‐mismatched welded joints have been performed using the modified boundary layer formulation. The welds were idealized as two‐material joints with the material interface running parallel to the crack, which was embedded in the weld material. The Rousselier ductile damage model was employed within the weld material to simulate crack extension due to the growth and coalescence of microvoids. By analysing models with different levels of material mismatching, weld dimensions and applied T‐stress levels, it was possible to analyse the effects of crack tip constraint due to both material mismatching and specimen geometry on the fracture resistance of the weld material.

The results show that material strength overmatching (where the weld material is stronger than the base material) reduces the level of constraint ahead of the crack, which can increase the resistance to fracture of the weld material. Conversely, material strength undermatching increases crack tip constraint, reducing the fracture resistance of the joint. By employing estimates for the crack tip constraint levels, QM , based on the applied load, level of material mismatching and weld region thickness, it has been possible to ‘order’ the J–resistance curves of overmatched joints by generating a family of J–QM loci which describe the effects of constraint on the fracture resistance of the weld material. However, it is shown that the QM‐stress parameter is not capable of describing the effect of material strength undermatching on the fracture resistance of a joint, which can be much lower than that obtained from a high‐constraint homogeneous specimen of weld material.