bluuebunny/crossref_metadata_2025 huggingface dataset:
Iatrogenic bile duct injury: The scourge of laparoscopic cholecystectomy
Authors: Slater K. , Strong R. W. , Wall D. R. , Lynch S. V.
Published: March 2003

Background: Laparoscopic cholecystectomy (LC) has become the first‐line surgical treatment of calculous gall‐bladder disease and the benefits over open cholecystectomy are well known. In the early years of LC, the higher rate of bile duct injuries compared with open cholecystectomy was believed to be due to the ‘learning curve’ and would dissipate with increased experience. The purpose of the present paper was to review a tertiary referral unit’s experience of bile duct injuries induced by LC.

Methods: A retrospective analysis was performed on all patients referred for management of an iatrogenic bile duct injury from 1981 to 2000. For injuries sustained at LC, details of time between LC and recognition of the injury, time from injury to definitive repair, type of injury, use of intraoperative cholangiography (IOC), definitive repair and postoperative outcome were recorded. The type of injury sustained at open cholecystectomy was similarly classified to allow the severity of injury to be compared.

Results: There were 131 patients referred for management of an iatrogenic bile duct injury that occurred at open cholecystectomy (n = 62), liver resection (n = 5) and at LC (n = 64). Only 39% of bile duct injuries were recognized at the time of LC. Following conversion to open operation, half the subsequent procedures were considered inappropriate. When the injury was not recognized during LC, 70% of patients developed bile leak/peritonitis, almost half of whom were referred, whereas the rest underwent a variety of operative procedures by the referring surgeon. The remainder developed jaundice or abnormal liver function tests and cholangitis. An IOC was performed in 43% of cases, but failed to identify an injury in two‐thirds of patients. The bile duct injuries that occurred at LC were of greater severity than with open cholecystectomy. Following definitive repair, there was one death (1.6%). Ninety‐two per cent of patients had an uncomplicated recovery and there was one late stricture requiring surgical revision.

Conclusions: The early prediction that the rate of injury during LC would decline substantially with increased experience has not been fulfilled. Bile duct injury that occurs at LC is of greater severity than with open cholecystectomy. Bile duct injury is recognized during LC in less than half the cases. Evidence is accruing that the use of cholangiography reduces the risk and severity of injury and, when correctly interpreted, increases the chance of recognition of bile duct injury during the procedure. Prevention is the key but, should an injury occur, referral to a specialist in biliary reconstructive surgery is indicated.
Australian audit for the endoluminal repair of abdominal aortic aneurysm: The first 12 months
Authors: Boult Maggi , Babidge Wendy , Anderson John , Denton Michael , Fitridge Robert , Harris John , Lawrence‐Brown Michael , May James , Myers Kenneth , Maddern Guy
Published: March 2003

Background: The Australian Safety and Efficacy Register for New Interventional Procedures – Surgical (ASERNIP‐S) was contracted by the Commonwealth Department of Health and Aged Care to audit the procedure of endoluminal repair of abdominal aortic aneurysm. The purpose of the audit was to examine the safety and efficacy of the endoluminal graft (ELG) and, where possible, compare it to the open procedure. The first 12 months of data collection has now been completed. An overview of these results and some of the problems associated with the establishment of this audit are given.

Methods: The administrative infrastructure to support the audit is based at the ASERNIP‐S office in Adelaide. To achieve high compliance rates, regular contact was maintained with surgeons. A reference group of senior vascular surgeons was established to provide expert support to the audit.

Results: By December 2000, ASERNIP‐S had collected data on approximately 85% of privately performed ELG procedures during the first year of the audit. The early mortality rate was 1.3% in the endoluminal group compared to 2.6% in the open group. The rate of procedural complications was 15% in both groups, but the percentage of systemic complications was higher following the open repair. Aneurysm size and the number of pre‐existing conditions had a statistically significant relationship to the variation in the number of complications for ELG patients.

Conclusions: Good compliance has been obtained from vascular surgeons for submission of the operative data sets. ASERNIP‐S aims to follow this group of patients closely to assess the medium to long‐term durability of this procedure.
Ultrasound‐guided, high‐energy extracorporeal ­ shock‐wave treatment of symptomatic calcareous tendinopathy of the shoulder
Authors: Jakobeit Christian , Winiarski Barbara , Jakobeit Susanne , Welp Lars , Spelsberg Gerhard
Published: March 2003

Background:  The objective of the present study was to test the effectiveness of ultrasound‐guided high‐energy extracorporeal shock‐wave treatment in symptomatic chronic calcareous tendinopathy of the shoulder rotator cuff, and to assess the morphology of the hydroxyapatite deposits before and after this treatment.

Methods:  The study involved 80 patients who suffered from calcification of the rotator cuff. These patients were treated with an instrument with electromagnetic induction of shock‐waves (Doli‐Lithotripter, Dornier, Munich, Germany) under continuous ultrasound location of the treatment focus. The treatments were carried out in one to five sessions at an interval of 4−6 weeks. Each patient received a total of 1800 shock waves in each therapy. The flow density of the energy in the therapy focus was 0.08−0.42 mJ/mm2.

Results:  Sixty‐eight patients (85%) attained complete freedom from symptoms or only had minimal residual symptoms when stressing their shoulder joint. The calcification suffered by 57 (71.2%) patients was completely resorbed after treatment and partially resorbed in 16 patients (20%). Complete resorption of the calcareous deposits led to freedom from symptoms. In all patients with amorphous calcareous deposits, there was complete resorption of the calcification. Mixed calcareous foci were eliminated in 64.7−77% of the cases, depending on the extent of amorphous structures. Complete resorption was achieved in 44.4% of patients where homogeneous calcareous deposits were >1 cm in size.

Conclusion:  Shock‐wave treatment in periarthritis of the shoulder is a new and very effective method for symptomatic calcareous tendinopathy. Extracorporeal shock‐wave treatment has good prospects of success in any type of calcification. As a non‐invasive technique with a high success rate, shock‐wave treatment is an alternative to surgical operations in patients who remain symptomatic after exhaustive conservative treatment.
Dendritic cells
Authors: Yao Veronica , Platell Cameron , Hall John C.
Published: March 2003

Dendritic cells (DC) are the most effective or ‘professional’ of the antigen‐presenting cells (APC) that initiate primary immune responses. They are located at surveillance sites where they capture and process antigens. They then initiate and regulate T‐ and B‐cell responses by expressing lymphocyte costimulatory molecules, migrating to lymphoid organs and secreting biologically active molecules. Dendritic cells not only activate lymphocytes to induce the immune response, but they also minimize autoimmune reactions by tolerizing T cells to self‐antigens. Recent Phase I and II clinical studies have shown promise in the use of antigen‐pulsed autologous DC for vaccination of cancer patients. Dendritic cells also have applications in preventing rejection after transplantation, immunization against viral infections and immunosuppression in autoimmune diseases.
Elective resection and anastomosis for colorectal cancer: A prospective audit of mortality and morbidity 1976−1998
Authors: Killingback Mark , Barron Prudence , Dent Owen
Published: March 2003

Background:  The purpose of this paper is to audit the morbidity and mortality for colorectal cancer after open elective resection and anastomosis by a single colorectal surgeon (MK), with reference to any differences between intraperitoneal (IPA) and extra­peritonealanastomoses (EPA).

Methods:  The prospective documentation of postoperative complicationswas compiled by the surgeon, charge nurses and a research assistant (PB). The operations were performed in three hospitals between 1976 and 1998.

Results:  Some 1392 consecutive patients were treated electively by 1418 resections with anastomosis. There were 23 postoperative deaths (1.6%). Significant adverse events, which were potentially avoidable, occurred in 10 (43.5%) of the patients who died. Themorbidity rate was 41.6%. Clinical anastomotic leaks occurred more frequently in EPA (27/581, 4.7%) than in IPA (2/827, 0.2%; P < 0.0001).Anastomotic leak caused the death of two patients (0.14%).Routine prophylactic anticoagulation did not decrease the incidenceof pulmonary embolism. Significant thrombophlebitis at the intravenous cannula site occurred in 54 patients (3.8%), wound infection in 29 (2.1%), and postural peripheral nerve injury in the upper limbs occurred in 11 patients (0.8%). Thirty‐eightpatients (2.7%) were returned to the operating theatre for 42 unscheduled operations.

Conclusion:  Mortality associated with elective resection of colorectal cancer with anastomosis is principally related to age, cardio­vascular disease and avoidable adverse events. A wide range of complications may follow this type of surgery, especially after extra peritoneal operations. A classification of anastomotic leaks is suggested toassist in comparisons of this complication which remains a significant concern following extra peritoneal anastomoses.
Cholecystectomy for gall bladder dyskinesia: Symptom resolution and satisfaction in a rural surgical practice
Authors: Gall Carey Andrew , Chambers Kevin John
Published: March 2003

Background:  Gall bladder dyskinesia describes a clinical entity with symptoms of biliary colic but without objective evidence of gallstones. Recent work has suggested laparoscopic cholecystectomy as an effective treatment although this approach has not gained widespread acceptance in Australia.

Methods:  At the sole nuclear medicine facility in Mildura, Victoria, a retrospective search of patients with gallbladder ejection fractions ≤35% on CCK‐HIDA (cholecystokinin‐99mTc hepatoiminodiacetic acid) scanning over a 3‐year period from 1 January 1998 was undertaken. Twenty‐eight patients proceeded to cholecystectomy by the author and case notes were reviewed for symptoms, preoperative investigation, operation, pathology and complications. Telephone follow‐up was carried out assessing symptom response and overall satisfaction following operation.

Results:  Follow up was achieved in 100% of patients with a mean duration of 18 months. Twenty‐five of 28 underwent chole­cystectomy by laparoscopic approach and there were no complications in the series. All gall bladders demonstrated an abnormality at histology. Overall, 79% of patients had some symptom improvement at follow‐up with 29% completely symptom free. Six patients (21%) were not improved following cholecystectomy. Overall satisfaction was high with a median 8/10.

Conclusion:  Laparoscopic cholecystectomy is recommended for gallbladder dyskinesia diagnosed on CCK‐HIDA scanning, after other causes have been excluded and informed discussion regarding incomplete symptom resolution has been undertaken. Improvement without operation occurs only in the minority and is rarely complete. Cholecystectomy affords at least partial symptom relief in the majority with high levels of patient satisfaction.
Pancreatic abscess: 10 years experience
Authors: Srikanth G. , Sikora Sadiq S. , Baijal Sanjay S. , Ayyagiri Archana , Kumar Ashok , Saxena Rajan , Kapoor Vinay K.
Published: March 2003

Background:  Secondary infections of pancreatic and peripancreatic necrosis account for most of the deaths following acute pancreatitis. These infections occur in the form of ‘infected pancreatic necrosis’ and ‘pancreatic abscess’. The latter is a rare complication of acute pancreatitis in comparison with the former.

Methods:  Twenty‐one patients with pancreatic abscess were managed over a 10‐year period at a tertiary care centre in Northern India. The present report details the clinical profile, investigations performed and management strategy (surgery and intervention radiology) of these patients. The role of surgery and percutaneous catheter drainage (PCD) in the management of pancreatic abscess is discussed, with emphasis on the successful outcome seen in a properly selected group of patients managed by PCD.

Results:  Of the 21 patients, 12 were managed by percutaneous intervention, nine were managed surgically (of these, two had a prior PCD) and two patients were managed conservatively. The overall mortality was 9.5% (2/21). Thus, percutaneous management was suitable for 57% patients, was successful in 83.3%, with a mortality of 8.3%. Surgical therapy alone was offered to 33% of patients, was successful in 85.7%, with a mortality of 14.2%. Complications were seen in four of the nine patients managed by percutaneous drainage alone and eight of the nine patients managed surgically.

Conclusions:  Pancreatic abscess is a potentially lethal complication in patients recovering from acute pancreatitis. Early diagnosis and prompt intervention with careful selection of patients based on computed tomography imaging for surgical or percutaneous radio­logical management, is met with a successful outcome in a majority of patients. The roles of surgery and PCD are complementary.
AN EXPERIMENTAL INVESTIGATION OF THE GROWTH OF SMALL CORNER FATIGUE CRACKS IN ALUMINIUM 6061‐T651
Authors: Carlson  , Steadman  , Dancila  , Kardomateas
Published: March 2003

Results of an experimental investigation of the fatigue growth of small corner cracks emanating from small flaws are presented. Growth‐arrest behaviour was observed, and increases in crack length during growth periods were of the order of the transverse grain size. For the test material, the corner crack front intersects, on average, only three–six grains in the small crack regime monitored, so only a small number of constrained, interior grains is encountered. It is suggested that the presence of partially constrained surface grains may contribute to the ‘anomalous’ growth behaviour which has been observed by a number of investigators.

The crack growth histories of the test data presented exhibit considerable scatter. It is shown that a Student’s t‐test can be used to estimate confidence intervals in order to provide a measure of the observed scatter. The variation in confidence intervals in the transition from small to long fatigue crack growth is discussed.
THE SIZE OF PLASTIC ZONES AND FATIGUE CRACK GROWTH BEHAVIOUR OF THREE FORMS OF A Ti–6Al–2.5Mo–1.5Cr ALLOY
Authors: Rosenberg G
Published: March 2003

The effect of microstructure on the fatigue properties of Ti–6Al–2.5Mo–1.5Cr alloy was investigated. The experimental results for both the fatigue crack initiation and propagation behaviour, as well as the dynamic fracture toughness (KId ) showed clearly that a lamellar microstructure is superior to two other structures. It was found that, as in the case of steels, the initiation and subsequent growth of cracks in the titanium specimens with a sharp notch may also occur on loading levels below the threshold values of the K factor (ΔKth ) determined for long fatigue cracks. In addition, measurements by interferential‐contrast of the plastic zone size on the surface of specimens revealed that the different rate of crack growth at identical values of ΔK in individual structural states can roughly be correlated with the size of the plastic zone. A general relationship between the fatigue crack growth rate and plastic zone size, the modulus of elasticity and the role of crack tip shielding is discussed.
A VIEW ON DUCTILE‐FRACTURE MODELLING
Authors: Thomason PF
Published: March 2003

Theoretical models of ductile fracture are reviewed in terms of experimental results from metallurgical studies of ductile fracture in metals and alloys. It is shown that the plastic limit‐load model, which is based on a criterion of void coalescence by internal microscopic necking of the intervoid matrix, is fully consistent with scanning electron microscope (SEM) observations of both the ductile‐fracture surface and the microstructure immediately adjacent to the fracture surface. On the other hand, the dilational‐plastic models of ductile fracture, which are based on the dilational‐growth of spherical voids to some arbitrary critical void‐volume fraction, are inconsistent with the microstructural observations of ductile fracture. This inconsistency between the dilational‐plastic models and experimental results is shown to be the combined effect of neglecting the controlling influence of extensional void‐growth and the failure to incorporate a physically realistic criterion of void coalescence.

The problems of modelling the ductile crack‐growth process by both analytical and numerical (finite element) studies, where problems of uniqueness of the plastic velocity field may occur, are also considered. The limitations of the finite‐element method in modelling void‐coalescence problems, where the equations of plasticity are of second‐order hyperbolic form, are also discussed.
SMALL CRACK GROWTH AND FATIGUE LIFE PREDICTIONS FOR HIGH‐STRENGTH ALUMINIUM ALLOYS: PART I—EXPERIMENTAL AND FRACTURE MECHANICS ANALYSIS
Authors: Wu  , Newman  , Zhao  , Swain  , Ding  , Phillips
Published: March 2003

The small crack effect was investigated in two high‐strength aluminium alloys: 7075‐T6 bare and LC9cs clad alloy. Both experimental and analytical investigations were conducted to study crack initiation and growth of small cracks. In the experimental program, fatigue tests, small crack and large crack tests were conducted under constant amplitude and Mini‐TWIST spectrum loading conditions. A pronounced small crack effect was observed in both materials, especially for the negative stress ratios. For all loading conditions, most of the fatigue life of the SENT specimens was shown to be crack propagation from initial material defects or from the cladding layer. In the analysis program, three‐dimensional finite element and weight function methods were used to determine stress intensity factors and to develop SIF equations for surface and corner cracks at the notch in the SENT specimens. A plasticity‐induced crack‐closure model was used to correlate small and large crack data, and to make fatigue life predictions. Predicted crack‐growth rates and fatigue lives agreed well with experiments. A total fatigue life prediction method for the aluminium alloys was developed and demonstrated using the crack‐closure model.
EFFECT OF LASER BEAM RADIATION ON FATIGUE CRACK PROPAGATION IN AISI 4150 STEEL
Authors: Tsay  , Lin
Published: March 2003

The effect of laser beam radiation on fatigue crack growth in AISI 4150 steel was performed on compact‐tension (CT) specimens, in which a composite region (CR) comprised of the hardened zones (HZs) on the top and bottom surfaces and the base metal (BM) in the interior, was aligned either along or normal to the crack growth direction. The microstructure of the HZs consisted of martensite, while lower bainite was present in the 300 °C preheated laser‐hardened specimens. When the crack propagated along the laser tracks (LTs), the fatigue crack growth rates (FCGRs) of the laser‐hardened specimen were lower than those of the base plate, particularly at low ΔK ranges. On the other hand, for a crack propagating normally to the LTs, decelerated FCGRs in the regions preceding the CR and accelerated FCGRs within the CR itself were found. However, enhanced FCGRs in the CR were not found in preheated specimens with a bainite structure in the HZs as the crack grew normal to the LTs. The enhancement of FCGRs in the CR, which became more accentuated at high ΔK values, was closely related to an embrittled microstructure (martensite) in the HZs.
THE ENGINEERING FLAW ASSESSMENT METHOD (EFAM)
Authors: Schwalbe
Published: March 2003

This communication gives an introduction to the Engineering Flaw Assessment Method (EFAM) presently being developed at GKSS. The EFAM consists of various documents describing experimental procedures for determining fracture properties under various conditions, as well as analytical procedures for estimating the crack tip opening displacement in terms of δ5 , the rate of δ5 , (dδ5 /dt), and the J‐integral as driving force parameters.
MECHANICAL REASONS FOR PLASTICITY‐INDUCED CRACK CLOSURE UNDER PLANE STRAIN CONDITIONS
Authors: Riemelmoser  , Pippan
Published: March 2003

A mechanical explanation of plasticity‐induced crack closure under plain strain conditions is given first by means of dislocation mechanics and then by the methods of continuum mechanics. In plane strain, the event of crack closure is due to transport of material from the wake to the crack tip. It is an elastic effect caused by the response of the matrix surrounding the plastic wake. The transported material produces a wedge which follows the crack tip, and unlike the plane stress condition it does not leave a remaining layer on the crack flanks. The length of the produced wedge at the crack tip is of the same scale as the plastic zone. It is then shown that in spite of its smallness this wedge is able to cause the experimentally observed shielding effect. The results also suggest that the discrepancies concerning the interpretation of fatigue crack growth and closure experiments are likely to be due to differences in accuracy in the detection of such small but nevertheless effective wedges.
A FATIGUE LIFE PREDICTION METHOD BASED ON A MESOSCOPIC APPROACH IN CONSTANT AMPLITUDE MULTIAXIAL LOADING
Authors: Morel F
Published: March 2003

The aim of this paper is to present a high cycle multiaxial fatigue life prediction method for metallic materials based on Papadopoulos’ previous works and limited to constant amplitude loading. The initiation process of a crack is treated as a mesoscopic phenomenon taking place on a scale of the order of a grain or a few grains. The damage variable chosen is the accumulated plastic strain at this mesoscopic scale. Its estimation requires a macro‐meso passage and the location of the plane subjected to maximum damage. Initiation is achieved as soon as a critical value of the accumulated plastic mesostrain is reached in these grains, so‐orientated that their easy glide directions coincide with a particular direction of the critical plane. The detrimental effect of out‐of‐phase loading on damage accumulation is taken into account through a newly defined coefficient estimated from mechanical loading parameters; no adjustable parameter is required. A good agreement has been found between the predicted and experimental results for in‐phase and out‐of‐phase sinusoidal constant amplitude loadings by examining a large amount of experimental data.
Statistical analysis and reliability prediction with short fatigue crack data
Authors: Wilson S.P. , Taylor D.
Published: March 2003

This paper proposes a probability model to describe the growth of short fatigue cracks. The model defines the length of each crack in a specimen as a random quantity, which is a function of randomly varying local properties of the material microstructure. Once the model has been described, the paper addresses two questions: first, statistical inference, i.e. the fitting of the model parameters to data on crack lengths; and secondly, predicting the future behaviour of observed cracks or cracks in a new specimen. By defining failure of a specimen to be the time at which the largest crack exceeds a certain length, the solution to the prediction problem can be used to calculate a probability that the specimen has failed at any future time.

The probability model for crack lengths is called a population model, and the statistical inference uses the ideas of Bayesian statistics. Both these concepts are described. With a population model, the solution to statistical inference and prediction requires quite complicated Monte Carlo simulation techniques, which are also described.
Deformation behaviour at the tip of a physically short fatigue crack due to a single overload
Authors: Hammouda  , Ahmad  , Sherbini  , Sallam
Published: March 2003

A two‐dimensional elastic–plastic finite element analysis was utilized to investigate the transition behaviour of a physically short fatigue crack following the application of a single overload cycle. The deformation accommodated at the tip of a crack artificially advancing with a fully reversed load was considered. The development of the cyclic crack tip opening displacement was computed and then modelled to include the effects of the stress level of the base cycles, overload pattern and crack length at which the transient cycle was applied.

The cyclic crack tip opening displacement was initially of a relatively high value. It decreased and then increased to match the behaviour under the base load cycles. The extent and location of both the minimum and matching points were dependent on the overload crack length and the stress compared with the material’s yield stress. In the case of the yield stress being exceeded by the overload, the minimum and the‐return‐to‐normality points are identical.

A previously developed crack tip deformation parameter was invoked to predict relevant experimental fatigue growth rates of short cracks reported in the literature.
Modelling the effect of creep–fatigue interaction on crack growth
Authors: Grover  , Saxena
Published: March 2003

Time‐dependent creep–fatigue crack growth (CFCG) is a major consideration in estimating the remaining life of elevated temperature components. Fracture mechanics approaches have proven useful in providing a framework for characterizing crack growth under service conditions, and in defining safe operating conditions and selecting inspection criteria and intervals. Experimental and analytical approaches have been developed to characterize crack growth under combined creep and fatigue loading conditions using (Ct )avgas the crack tip parameter. The analytical approaches that have been proposed to characterize CFCG are limited in their application because they do not completely account for the effect of creep–fatigue interactions in modelling crack tip deformation, and thus, accurately estimating the (Ct )avgvalue. A new creep‐reversal parameter,CR , is defined in this study to quantify the extent of creep–fatigue interaction at the crack tip, and is used in an analytical scheme, suitable for components, for calculating (Ct )avg . This approach does not rely on any simplifying assumptions regarding the extent of reinstatement ofCt , which is dependent on the amount of creep reversal due to cyclic plasticity, during the unloading part of a trapezoidal loading waveform cycle. The (Ct )avgvalues calculated by this approach compare well with the experimentally obtained values for compact type (CT) specimens, thus providing an experimental verification of the approach.
Load interaction effects during fatigue crack growth under variable amplitude loading—a literature review. Part II: qualitative interpretation
Authors: Skorupa M.
Published: March 2003

The current understanding of the underlying reasons behind the load interaction effects in fatigue crack growth under variable amplitude loading is presented. Mechanistic arguments proposed to control the load interaction phenomena are reviewed and evaluated based on their capability to qualitatively explain empirical trends in variable amplitude fatigue crack growth summarized in Part I [Fatigue Fract. Engng Mater. Struct.1998,21(8), 987–1006] of the present paper. Mechanisms linked to plastic straining at the crack tip enable an interpretation of the majority of the experimental results. Some observations, however, which cannot be understood in terms of plasticity‐induced crack closure, or which are even in contradiction with the crack closure approach, indicate a possible role of other factors. A general conclusion is that conditions under which various phenomena can affect variable amplitude fatigue crack growth and interactions between them are insufficiently recognized.
Modelling of initial fatigue crack growth and crack branching under fretting conditions
Authors: Lamacq  , Dubourg
Published: March 2003

Crack propagation during Stage I, in terms of crack initiation sites and growth directions and crack branching mechanisms under fretting conditions, is investigated using both experimental and theoretical approaches. Fretting tests were conducted on an aeronautical aluminium alloy. Two crack types are observed during Stage I corresponding, respectively, to specific mode I and II conditions. Transition from Stage I to Stage II is characterized for both crack types by a crack branching towards a new propagation direction of ≈65° to the specimen surface. Specific parameters linked to mode I and II propagation driving forces are proposed. Crack location and initial growth directions during Stage I are predicted in accordance with these parameters, and are in very good agreement with experimental observations. The conditions governing the transition from Stage I to Stage II are then identified. It is shown that under fretting conditions, cracks branch along a new direction, thereby maximizing the crack‐opening amplitude.
The fatigue limit and its elimination
Authors: Miller  , O’donnell
Published: March 2003

The classical fatigue limit of ferrous metals is a consequence of testing materials at a constant range of cyclic stress and determining the cyclic stress range below which fatigue failures do not occur. This classical fatigue limit of a material is equated to the condition for which fatigue cracks can not propagate beyond microstructural barriers.

This paper discusses the causes leading to the elimination of this fatigue limit, including the introduction of transitory cyclic‐dependent mechanisms and time‐dependent processes that will permit a previously non‐propagating crack to grow across the different threshold states expressed in terms of linear‐elastic fracture mechanics (LEFM), elastic–plastic fracture mechanics (EPFM) and microstructural fracture mechanics (MFM).

These transitory mechanisms and processes include different loading and environmental conditions, which in a long‐life engineering plant (e.g. 30 years lifetime) can lead to apparently premature failures. Of greater concern is the creation of a new crack‐initiation zone, i.e. a transfer from a surface‐generated crack to an internal‐generated crack that eventually dominates the fatigue failure event.

The impact of these conditions on the elimination of the classical fatigue limit necessitates changes in Design Codes of Practice, and such changes are discussed in relation to the extremely long‐lifetime regime (107 < Nf < 1012 cycles‐to‐failure) which is increasingly applicable to the modern day engineering plant.
Effects of a single tensile overload on fatigue crack growth in a 316L steel
Authors: Wheatley  , Hu  , Estrin
Published: March 2003

The aim of this study was to investigate the effects of a single tensile overload on subsequent fatigue crack growth in a 316L stainless steel. Fatigue tests were conducted under the plane stress condition, and further supplemented with compliance measurements and field emission scanning electron microscopy (FESEM) observations. Effects of a tensile overload, e.g. initial acceleration and subsequent retardation of fatigue crack growth, were explained and quantified by FESEM and compliance measurements. The FESEM observations suggest that the initial crack growth acceleration stems from void and quasi‐cleavage fracture within the fatigue damage zone in the vicinity of the crack tip. Systematic compliance measurements taken during fatigue crack growth suggest that the overall crack growth retardation is related to strain hardening and residual compressive stress produced by the plastic deformation associated with the tensile overload.
Influence of pitting on the fatigue life of a turbine blade steel
Authors: Zhou  , Turnbull
Published: March 2003

The role of pits as stress raisers and their influence on fatigue life has been investigated for a 12Cr turbine blade material. A particular feature of this work was the establishment of an electrochemical procedure for generating pits with ‘controlled’ pit depth and low density.

Pits grown under laboratory conditions were partially spherical in shape and simulated, in general appearance, those observed in service. In terms of the threshold stress intensity factor, the results supported the concept of pits acting as effective cracks of the same depth, provided that a short crack model based on an effective crack length is used.
The influence of modified intermetallics and Si particles on fatigue crack paths in a cast A356 Al alloy
Authors: Gall  , Yang  , Horstemeyer  , McDowell  , Fan
Published: March 2003

Mechanical fatigue tests were conducted on uniaxial specimens machined from a cast A356‐T6 aluminium alloy plate at total strain amplitudes ranging from 0.1 to 0.8% (R = − 1). The cast alloy contains strontium‐modified silicon particles (vol. fract. ~6%) within an Al–Si eutectic, dispersed α intermetallic particles, Al15 (Fe,Mn)3 Si2(vol. fract. ~1%), and an extremely low overall volume fraction of porosity (0.01%). During the initial stages of the fatigue process, we observed that a small semicircular fatigue crack propagated almost exclusively through the Al–1% Si dendrite cells. The small crack avoided the modified silicon particles in the Al–Si eutectic and only propagated along the α intermetallics if they were directly in line with the crack plane. These growth characteristics were observed up to a maximum stress intensity factor of ~K trmax = 7.0 MPa m1/2(maximum plastic zone size of 96 μm). When the fatigue crack propagated with a maximum crack tip driving force above 7.0 MPa m1/2the larger fatigue crack tip process zone fractured an increased number of silicon particles and α intermetallics ahead of the crack tip, and the crack subsequently propagated preferentially through the damaged regions. As the crack tip driving force further increased, the area fraction of damaged α intermetallics and silicon particles on the fatigue fracture surfaces also increased. The final stage of failure (fast fracture) was observed to occur almost exclusively through the Al–Si eutectic regions and the α intermetallics.
Small‐crack growth and fatigue life predictions for high‐strength aluminium alloys. Part II: crack closure and fatigue analyses
Authors: Newman  , Wu  , Swain  , Zhao  , Phillips  , Ding
Published: March 2003

Small‐crack effects were investigated in two high‐strength aluminium alloys: 7075‐T6 bare and LC9cs clad aluminium alloys. Both experimental and analytical investigations were conducted to study crack initiation and growth of small cracks. In the experimental program, fatigue and small‐crack tests were conducted on single‐edge‐notch tension (SENT) specimens and large‐crack tests were conducted on middle‐crack tension specimens under constant‐amplitude and Mini‐TWIST spectrum loading. A pronounced small‐crack effect was observed in both materials, especially for the negative stress ratios. For all loading conditions, most of the fatigue life of the SENT specimens was shown to be crack propagation from initial material defects or from the cladding layer. In the analysis program, three‐dimensional finite‐element and weight‐function methods were used to determine stress intensity factors, and to develop equations for surface and corner cracks at the notch in the SENT specimen. (Part I was on the experimental and fracture mechanics analyses and was published inFatigue Fract. Engng Mater. Struct.21, 1289–1306, 1998.) This part focuses on a crack closure and fatigue analysis of the data presented in Part I. A plasticity‐induced crack‐closure model was used to correlate large‐crack growth rate data to develop the baseline effective stress intensity factor range (ΔKeff ) against rate relations for each material, ignoring the large‐crack threshold. The model was then used with the ΔKeffrate relation and the stress intensity factors for surface or corner cracks to make fatigue life predictions. The initial defect sizes chosen in the fatigue analyses were similar to those that initiated failure in the specimens. Predicted small‐crack growth rates and fatigue lives agreed well with experiments.
Bauschinger effect of alloys and plasticity‐induced crack closure: a finite element analysis
Authors: Pommier  , Bompard
Published: March 2003

The effect of overloads, underloads and stress ratio on plasticity‐induced crack opening level is examined for different ‘model’ materials. This study is focused on the consequences of the Bauschinger effect on the crack opening level. Various finite element analyses were conducted using ABAQUS to test these effects, involving the Chaboche constitutive equations that take into account both the Bauschinger effect of the material and its cyclic hardening or softening. The cyclic plastic behaviour of the material is found to strongly affect the crack behaviour after an overload or an underload. The experimental data obtained on a 0.4% carbon mild steel confirm the numerical results.
Fatigue strength of Inconel 718 at elevated temperatures
Authors: Kawagoishi  , Chen  , Nisitani
Published: March 2003

The strength of Inconel 718 under rotary bending fatigue is investigated at room temperature, 300, 500 and 600 °C in air. It is found that in the long‐life region, the fatigue strength of a plain specimen is much higher at elevated temperatures than at room temperature, though the static strength decreases with the increase in temperature. The effect of temperature on the fatigue strength is examined in terms of the initiation and early growth behaviour of a small crack. The results are discussed in relation to the competition between the softening of the nickel matrix (γ phase) and the surface oxidation at elevated temperatures.
Finite element modelling of cracked inelastic shells with large deflections: two‐dimensional and three‐dimensional approaches
Authors: Skallerud  , Zhang
Published: March 2003

Higher utilization of structural materials leads to a need for accurate numerical tools for reliable predictions of structural response. In some instances, both material and geometrical non‐linearities are allowed for, typically in assessments of structural collapse or residual strength in damaged conditions. The present study addresses the performance of surface‐cracked inelastic shells with out‐of‐plane displacements not negligible compared to shell thickness. This situation leads to non‐linear membrane force effects in the shell. Hence, a cracked part of the shell will be subjected to a non‐proportional history of bending moment and membrane force. An important point in the discretization of the problem is whether a two‐dimensional model describes the structural performance sufficiently, or a three‐dimensional model is required. Herein, the two‐dimensional modelling is performed by means of a Mindlin shell finite element. The cracked parts are accounted for by means of inelastic line spring elements. The three‐dimensional models employ eight‐noded solid elements. These models also account for ductile crack growth due to void coalescence by means of a modified Gurson–Tvergaard constitutive model, hence providing detailed solutions that the two‐dimensional simulations can be tested against. Using this, the accuracy of the two‐dimensional approach is checked thoroughly. The analyses show that the two‐dimensional modelling is sufficient as long as the cracks do not grow. Hence, using fracture initiation as a capacity criterion, shell elements and line springs provide acceptable predictions. If significant ductile tearing occurs before final failure, the line spring ligaments have to be updated due to crack growth.
Effects of cyclic frequency and contact pressure on fretting fatigue under two‐level block loading
Authors: Iyer  , Mall
Published: March 2003

Fretting fatigue tests involving the contact of flat and cylindrical titanium alloy Ti–6Al–4V surfaces, and constant‐ and two‐level block remote bulk stresses are described. The constant‐amplitude tests have been performed at cyclic frequencies of 1 and 200 Hz. The two‐level block spectra involve the superposition of a 1‐Hz, low‐cycle fatigue (LCF) constant‐amplitude component and a 200‐Hz, high‐cycle fatigue (HCF) component. Two values of contact pressure are considered. The cyclic frequency of 200 Hz is found to curtail the constant‐amplitude fretting fatigue life regardless of the contact pressure applied. Increasing the contact pressure reduces life at 1 Hz but does not have any effect at 200 Hz. Under two‐level block loading, the fretting fatigue life is determined primarily by the stress amplitude and high‐cyclic frequency of the HCF component of the load spectrum. The LCF component is found to play a secondary role in the determination of the two‐level block fretting fatigue life. Fracture topographies for the different test conditions are documented.
The analysis of thermoelastic isopachic data from crack tip stress fields
Authors: Dulieu‐Barton  , Fulton  , Stanley
Published: March 2003

A computer program—FACTUS (fracture analysis of crack tips using SPATE)—has been developed for the efficient analysis of thermoelastic data obtained from around a crack tip. The program is based on earlier work for the determination of stress intensity factors (SIFs), and also includes a novel solution procedure for the derivation of the non‐singular stress termσ0x . The program has been used in the analysis of a series of large plate specimens with central or edge slots/cracks. The derived SIFs are compared with independent values. Issues, e.g. crack closure and the extent and effect of the plastic zone, are discussed.
Surface and cyclic microplasticity
Authors: Sauzay  , Gilormini
Published: March 2003

High‐cycle fatigue of metals involves microplasticity: under low remote stresses, plastic slip occurs in a few grains at the surface of a specimen, and cracks eventually nucleate. For a given applied stress and crystallographic orientation, plasticity is well known to be larger in well‐orientated grains at the free surface rather than in the bulk, and an evaluation of this surface effect is now proposed. Using finite element computations, the cyclic plasticity in surface grains is evaluated, and it is shown that a semianalytical approach allows a good estimation. In practical applications, the surface plasticity is obtained by first computing analytically the result for a grain in an infinite matrix, and then multiplying by a corresponding factor given in the paper, depending on the facet direction and on the type of remote loading.
Notch sensitivity of Ti‐based unidirectional metal matrix composites under tensile and fatigue loading
Authors: De Los Rios E. R. , Rodopoulos C. A. , Yates J. R.
Published: March 2003

Neuber’s rule and the notch equivalent crack length concept were utilized to predict the effect of notches on the fracture strength and fatigue limit of unidirectional metal matrix composites. For the examination of the fracture strength, the strain of the notch is compared to that required for debonding or fracture of the fibres. The notch effect under fatigue loading is determined by examining the ability of the notch to achieve premature debonding.
Two measurement techniques for determining effective stress intensity factors
Authors: Wong S. L. , Bold P. E. , Brown M. W. , Allen R. J.
Published: March 2003

Two methods were studied for determining crack closure and locking effects under combinations of mixed mode I and II loading, namely the strain gauge and the surface replica methods. They demonstrated that strain gauges are able to detect the mode I crack closure but not mode II crack locking. As an alternative, the surface replica method is suggested as a practical technique for measuring mode II crack locking effects. The effective mode II stress intensity factor range can be estimated by comparison of the actual measured sliding range between a pair of crack faces and the theoretical sliding range.
Using torsional bar testing to determine fracture toughness
Authors: Wang J. A. , Liu K. C. , McCabe D. E. , David S. A.
Published: March 2003

A new method to determine fracture toughness KIC of materials is introduced. A round‐rod specimen having a V‐grooved spiral line with a 45° pitch is tested under pure torsion. An equibiaxial tensile/compressive stress state is effectively created to simulate conventional test methods using a compact‐type specimen with a thickness equivalent to the full length of the spiral line. KIC values are estimated from the fracture load and crack length with the aid of a three‐dimensional finite element analysis. KIC of 7475‐T7351 aluminium is estimated to be 51.3 MPa √m, which is higher than the vendor’s value in the TL orientation by ∼0.8% and higher than 0.5T compact tension (CT) value by 6%; A302B steel yields 54.9 MPa √m being higher than CT test value by ∼2%. Good agreement between the KIC values obtained by different methods indicates the proposed method is sound and reliable.
Acceptable prior fatigue damage and failure threshold for impact loading of an aluminium alloy
Authors: Auzanneau T. , Froustey C. , Lataillade J.‐L.
Published: March 2003

In a competitive economic context that aims at gains in safety, some problems of combined fatigue‐impact loadings are crucial, particularly in the case of light alloys used in the transport and aeronautical industries. One important challenge is to quantify the fatigue preloading effect on the residual dynamic plasticity of a 2017‐A T3 aluminium alloy. From an experimental modal analysis, the change in mechanical properties of prefatigued material under impact loading allows us to define the best mechanical parameter for a limiting threshold between a no‐damage state and weakened states due to fatigue predamage. For this situation a hybrid technique has been developed. A numerical model including voids (which represent surface micro‐cracks produced by the fatigue preloading) is fitted to the results obtained by the modal analysis of the damaged sample. Hence, an acceptable damage threshold (i.e. a damage critical volume below which the impact toughness is not affected by fatigue preloading) and a failure threshold are established. On the basis of this methodology, it is possible to predict the energy required for the impact failure of prefatigued specimens and therefore to predict a safe or a dangerous mechanical state.
Modelling of load interaction and overload effect on fatigue damage of steel bridges
Authors: Li Z. X. , Ko J. M. , Chan T. H. T.
Published: March 2003

This paper studies the effects of load sequence and interaction, and overloading effect on the fatigue damage of bridges on the basis of a non‐linear fatigue damage model. The model is derived from the theory of continuum damage mechanics for high‐cycle fatigue. Fatigue behaviour at two levels of constant stress range is first discussed in detail. The formulation for the effective fatigue strength of the predamaged members is then derived, and the results predicted by the model are compared with the experimental data for two stress level tests and other results obtained from linear and double linear fatigue damage models. The variation of cycle ratio and fatigue life due to overloading is secondly investigated; the equations for evaluating the effect of overloading on fatigue damage accumulation on bridges at normal traffic loading are then derived. It has been demonstrated that the developed model can well describe the effect of load sequence and interaction and has also been verified by comparing the predicted results obtained by the model with the experimental data based on two levels of stress tests. The effect of accidental overloading on the fatigue damage of existing bridges can also be evaluated using the model. The model is applied to evaluate the fatigue damage and service life of the Tsing Ma Bridge, an essential portion of the transport network for the Hong Kong airport, under normal traffic loading and possible accidental overloading.