bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of the P−POSSUM mortality prediction algorithm in Australian surgical intensive care unit patients
Authors: Organ Nicole , Morgan Thomas , Venkatesh Balasubramanian , Purdie David
Published: March 2003

Background:  The Physiological and Operative Severity Score for enUmeration of Mortality and Morbidity (POSSUM) is an auditing tool designed to compare surgical outcomes independent of case mix. It uses patient physiological and operative data to predict morbidity and mortality for surgical patients. Thus far most evaluations of the POSSUM algorithm and its modifications have emanated from British hospitals. A single‐centre retrospective study was therefore performed to determine the applicability of this tool to the Australian surgical case mix.

Methods:  All surgical patients undergoing a surgical procedure admitted to the Royal Brisbane Hospital intensive care facility in 1999 were reviewed retrospectively. Mortality predictions using the Portsmouth modification of the POSSUM algorithm (P−­POSSUM) were compared to the actual outcomes using receiver‐operator characteristic curve analysis and the Hosmer and Lemeshow Goodness‐of‐Fit test.

Results:  The records of 229 admissions were reviewed. The area under the receiver‐operator characteristic curve was 0.68, significantly greater than 0.5 (P = 0.014). Predicted deaths were significantly greater than actual deaths (50 vs 28, P < 0.001), with over‐prediction of death rates in all mortality groupings except the two lowest risk deciles.

Conclusion:  The P−POSSUM algorithm tends to over‐estimate mortality in surgical intensive care patients. It may require further calibration before adoption as a surgical audit tool in Australia.
Colonic epithelial atrophy induced by a fibre‐free diet in rats is reversed by minimal amounts of luminal butyrate, but only in the short term
Authors: Sengupta Shomik , Tang Choong‐Leong , Wong Cynthia S. M. , Tjandra Joe J. , Gibson Peter R.
Published: March 2003

Background:  Luminal butyrate may be trophic to the colonic epithelium, but this effect is poorly characterized. The aim of the present study was to define the dose−response, time‐course, site‐specificity and the dependence on background diet of the effects of butyrate on epithelial proliferation in normal distal colon, using an in vivo rat model of colonic substrate delivery.

Methods:  Male Sprague‐Dawley rats, maintained on a fibre‐free diet, had butyrate infused twice daily into the colonic lumen via polyethylene tubes placed at laparotomy. Varying dose levels (0−80 µmol/d; 4 d), site (caecal vs distal colonic), duration of infusions (1−5 weeks; 80 µmol/d), or dietary fibre intake were investigated. Epithelial proliferative indices were assessed stathmokinetically.

Results:  Four‐day infusions of butyrate led to a progressive trophic effect (cells/crypt column increased from 37.9 ± 1.6 at 0 µmol/d to 44.7 ± 1.2 at 80 µmol/d) on fibre‐deprived colonic mucosa, related linearly to the daily butyrate dose (P < 0.001, linear regression). This effect was mediated by increases in the number and proportion of mitoses, related to the square of the butyrate dose (P < 0.001 in each case, polynomial regression). Butyrate (80 µmol/d) was associated with significantly higher cellularity (59.9 ± 1.4) and mitotic activity (4.9 ± 0.6) per crypt column compared to vehicle controls (50.3 ± 1.6 and 0.9 ± 0.2, respectively; P < 0.05, t‐tests), at 1 and 3 weeks, but not at 5 weeks. Butyrate had similar effects on distal colonic crypt cellularity (62.0 ± 1.5) when delivered caecally, but in rats fed a fibre‐containing diet, colonic crypt cellularity (55.3 ± 3.2) was similar to baseline (59.6 ± 1.9).

Conclusions:  Trophic effects of butyrate are concentration‐dependent and occur at low doses in the short term, but are not sustained over longer periods. They are seen only in a fibre‐deprived state and appear to be independent of the site of administration.
Results of resections for hepatocellular carcinoma in a new hepatobiliary unit
Authors: Sim Hong Gee , Ooi London Lucien P. J.
Published: March 2003

Background:  Hepatocellular carcinoma (HCC) is the fourth commonest cancer in Singapore. Surgical resection offers the only chance of ‘cure’. Resection tends to be difficult in HCC because of late presentation and concomitant liver cirrhosis. Specialized units with higher volume of operations are known to produce better results. The present review aims to evaluate early results with HCC resection and discuss the correlation between various tumour prognostic factors and the outcome.

Methods:  The records of 81 consecutive hepatic resections for HCC in the hepatobiliary unit of the Department of General Surgery at the Singapore General Hospital from 1 January 1996 to 31 December 1998 were retrospectively reviewed.

Results:  The mean age of the patients was 56.0 ± 15.4 years. There were more men (M:F: 72:9) and Chinese patients (75 Chinese patients (92.6%); four Malay patients (4.9%); two Indian patients (2.5%)) affected by the disease. Hepatitis B and C carrier status were present in 67.1% (n = 51) and 3.9% (n = 1) of the patients, respectively. Forty‐two patients (53.2%) had underlying liver cir­rhosis. Twenty‐eight patients (34.6%) underwent major hepatectomy and 53 (65.4%) underwent minor hepatectomies. Perioperative mortality was 4.9% (n = 4). The morbidity rate following hepatic resections was 28.4% (n = 23). The median follow up was 21 months (range: 1−52 months). The median survival was 43 months (95% confidence interval (CI): 34.6−51.4 months) after surgery and median time to recurrence was 9.6 months (range: 2−32 months). Overall survival was 79% and 59% at 1 and 3 years, respectively. Disease‐free survival was 59% and 30% at 1 and 3 years, respectively. Advance pathological tumour, nodes, metastases (TNM) stage (III and IV), and presence of adjacent organ involvement were risk factors for early recurrence. Advance pathological TNM stage (III and IV) and blood loss of more than 2 L were poor prognostic factors for overall survival.

Conclusion:  The results of hepatectomies for HCC in the newly established unit at Singapore General Hospital have been shown to be comparable to other established specialized hepatobiliary units with similar perioperative mortality and morbidity rates.
STRESS INTENSITY FACTORS FOR SURFACE CRACKS AT A HOLE BY A THREE‐DIMENSIONAL WEIGHT FUNCTION METHOD WITH STRESSES FROM THE FINITE ELEMENT METHOD
Authors: Zhao W , Newman Jr JC , Sutton MA , Shivakumar KN , Wu XR
Published: March 2003

Stress intensity factors for semielliptical surface cracks emanating from a circular hole are reported in this paper. The three‐dimensional weight function method with three‐dimensional finite element solutions for the uncracked stress distribution is used for the analysis. Two different loading conditions, i.e. remote tension and wedge loading, are considered for a wide range of geometrical parameters. Both single and double surface cracks are studied and compared with other solutions available in the literature. Typical crack opening displacements are also provided.
TOUGHNESS CHARACTERISTICS OF SYNTHETIC FIBRE‐REINFORCED CEMENTITIOUS COMPOSITES
Authors: Wang
Published: March 2003

The brittle nature of concrete is a reflection of its low toughness and the presence of defects. One effective way to enhance the toughness of concrete is by fibre reinforcement. Synthetic fibres, mostly polypropylene, have been widely used as a concrete additive at 1% or less volume fraction for toughness enhancement and shrinkage control. Pull‐out of fibres bridging a concrete matrix crack absorbs a significant amount of energy. This paper reviews some of the fracture mechanics approaches to the prediction of failure of fibre‐reinforced concrete structures, methods used to rank the toughness of fibre‐reinforced concrete, toughness optimization, and the properties of concrete reinforced with selected synthetic and recycled fibres.
NUMERICAL ANALYSIS OF CRACK PROPAGATION IN PIEZOELECTRIC CERAMICS
Authors: Fang  , Qi  , Yao
Published: March 2003

The formulation of an isoparametric displacement – electric potential finite element method that accounts for the electro‐mechanical coupling effect of piezoelectric materials is briefly presented in this paper. The crack propagation behaviour and the elasto‐electric fields near a crack tip in a PZT‐5 piezoelectric ceramic under mechanical, electrical and mechanical – electrical mixed loads are investigated using this electro‐mechanical finite element method. From the numerical results, it can be seen that crack propagation along the crack plane direction will be impeded and the crack will tend to propagate at an angle of about 84° to the crack plane under a negative electric field on the basis of the maximum stress criterion. The physical explanation of the phenomena is presented in this paper and it is shown that the mechanical strain energy release rate is not a good criterion for predicting crack propagation in the case where the ratio of the electric field to the mechanical load becomes large.
FATIGUE CRACKING POSSIBILITY ALONG GRAIN BOUNDARIES AND PERSISTENT SLIP BANDS IN COPPER BICRYSTALS
Authors: Zhang  , Wang  , Li
Published: March 2003

In this paper, the fatigue cracking possibility in different kinds of copper bicrystals with large‐angle grain boundaries (GBs) and copper multicrystals containing some low‐angle GBs are compared. The results showed that the fatigue cracks, in the copper bicrystals, always nucleated firstly along GBs no matter whether the GBs are perpendicular or parallel to the stress axis. Whereas, for the copper multicrystals containing low‐angle GBs, the persistent slip bands (PSBs) are always the preferential sites to initiate fatigue cracks no matter whether low‐angle GBs are perpendicular or parallel to the stress axis.

Additionally, the fatigue lives of the GBs, and the [1¯23] and [3¯35] grains in the [1¯23] ⊥ [3¯35] and [5¯913] ⊥ [5¯79] bicrystals were measured at different cyclic stresses and strain amplitudes. The results show that intergranular fracture always occurred prior to transgranular fracture in those bicrystals. The fatigue lives increased in the order of the GB, the [1¯23] and the [3¯35] grains in the [1¯23] ⊥ [3¯35] bicrystal under cyclic tension–tension loading. On the other hand, the fatigue life of the GB in the [5¯913] ⊥ [5¯79] bicrystal is about two to three times higher than that in the [1¯23] ⊥ [3¯35] bicrystal. Based on these experimental results from the copper bicrystals and multicrystals, it is indicated that the possibility of fatigue cracking increased in the order of low‐angle GBs, PSBs and large‐angle GBs. It is suggested that both the PSB–GB mechanism and the step mechanism required for GB fatigue cracking were questionable, and the interaction modes of PSBs with GBs may be more important for intergranular fatigue cracking.
EFFECTS OF STRESS–STRAIN CONDITIONS ON HYDROGEN‐INDUCED FRACTURE
Authors: Gao  , Cao
Published: March 2003

Effects of stress–strain fields and stress–strain history on hydrogen‐induced fracture (HIF) have been studied. The investigation covers I/II and I/III mixed mode HIF, redistribution of hydrogen near a mixed‐mode crack tip, correlation between HIF initiation sites and critical stress intensity factors, and the influence of overloading on HIF life.
THE DEVELOPMENT OF AN INHOMOGENEOUS DAMAGE FIELD IN AN ELASTIC‐PLASTIC MODEL
Authors: Li  , Bai  , Xia
Published: March 2003

By making use of the evolution equation of the damage field as derived from the statistical mesoscopic damage theory, we have preliminarily examined the inhomogeneous damage field in an elastic–plastic model under constant‐velocity tension. Three types of deformation and damage field evolution are presented. The influence of the plastic matrix is examined. It seems that matrix plasticity may defer the failure due to damage evolution. A criterion for damage localization is consistent with the numerical results.
NUCLEATION, BLUNTING OR PROPAGATION OF A NANOCRACK IN DISLOCATION‐FREE ZONES OF THIN CRYSTALS
Authors: Chen  , Chu  , Gao  , Gu  , Zhang
Published: March 2003

Nucleation, blunting and propagation of nanocracks in dislocation‐free zones (DFZs) ahead of crack tips in ductile and brittle metals have been investigated by tensioning in situ with a TEM, and analysed using microfracture mechanics. The results show that in either ductile or brittle metals, many dislocations could be emitted from a loaded crack tip and a DFZ formed after equilibrium. The stress in the DFZ may be up to the cohesive strength of the material, and then a nanocrack is initiated in the DFZ or directly from the crack tip. In ductile metals, the nanocrack is blunted into a void or notch during constant displacement. In brittle metals, the nanocrack propagated as a cleavage microcrack rather than being blunted.
MODELLING FOR TRANSCRYSTALLINE AND INTERCRYSTALLINE FRACTURE BY VOID NUCLEATION AND GROWTH
Authors: Margolin BZ , Karzov GP , Shvetsova VA , Kostylev VI
Published: March 2003

A criterion has been formulated for transcrystalline and intercrystalline fracture caused by the evolution of voids located both in a grain and on grain boundaries. The criterion is based on the idea of plastic collapse for a unit cell that is a regular structural mezovolume of polycrystalline material. The criterion does not require the introduction of any empirical parameters, such as critical void size, critical size of ligament between voids and critical void volume fraction, which are used in most models.

Modelling has been performed for void nucleation and growth in a grain and on grain boundaries for elastic–plastic deformation and under creep conditions. A scheme is proposed to describe the transition from transcrystalline to intercrystalline cavitation fracture as a function of strain rate and temperature.

The effect of stress triaxiality on the critical strain and the lifetime for both transcrystalline and intercrystalline fracture has been investigated. A comparison of the results predicted by the suggested criterion with available empirical data has been performed.
Temperature dependence of stress–lifetime fatigue curves
Authors: Kohout J.
Published: March 2003

By analysing several finite‐life fatigue curves obtained at various temperatures, a relation describing the temperature dependence of fatigue strength is proposed, based on the Basquin equation. Accordingly, an approximate inverse law between fatigue strength and the square root of absolute temperature is demonstrated. Moreover, a boundary temperature above which creep begins to play a significant role is estimated. A simple extension of the relationship to the low‐cycle fatigue region, allows one to determine predictive curves describing fatigue behaviour at various temperatures, even in cases where only a single fatigue curve at a given temperature plus the temperature dependence of tensile strength are known.
Ductile fracture of commercial purity titanium at room temperature
Authors: Shatil G. , Smith D.J.
Published: March 2003

An experimental and numerical program was carried out to examine and assess the deformation and fracture behaviour of alloys of commercial purity (CP) titanium. The material rate‐dependent deformation under constant displacement rates and under sustained loads was directly simulated in finite element analyses using an implemented unified material model. The simulations predicted the fracture of compact tension specimens subjected to J–R tests and sustained load tests employing a dimensional analysis and strain‐hardening approach. Differences between two batches with different oxygen contents were examined and the limitation of the material model was investigated.
Fatigue life estimation after crack repair in 6005 A‐T6 aluminium alloy using the cold expansion hole technique
Authors: Ghfiri R. , Amrouche A. , Imad* A. , Mesmacque G.
Published: March 2003

In this paper, the hole drilling (HD) and the cold expansion (CE) processes, which were used as a technique for crack repair, were investigated in order to estimate the beneficial effects on fatigue crack initiation (FCI). The FCI life is defined as the number of cycles to initiate a new crack of 0.2 mm on the surface of the specimen. Three hole radii and three degrees of cold expansion (DCE%) values were tested after a crack propagation period. Crack retardation after the CE process was observed. This phenomenon is due to two mechanisms: retardation owing to both geometric and mechanical effects, which is produced by the stress concentration at the drilled hole, and the large strain‐induced compressive residual stresses around the hole. In this report, the influence of the loading conditions was studied. For high values of the stress intensity factor range ΔKρ around the hole (based on the pseudo crack length a + ρ), the number of cycles corresponding to crack initiation Ni is low. At the edge of the hole, the maximum stress range can be approximated by the following formula: Δσmax = 2ΔKρ /√πρ , where ρ is the hole radius and ΔKρ is the related stress intensity factor range.The FCI life extension, defined by the number of cycles corresponding to crack re‐initiation Ni , is related to the relative maximum stress range ratio Rσ = [(Δσmax )/(Δσmax )th ] where (Δσmax )th is the value of the threshold maximum stress range obtained when Ni = 2 × 106 cycles. The relationship between Ni and Rσ may be written as a power function.
On numerical analysis of damage evolution in cyclic elastic‐plastic crack growth problems
Authors: Skallerud B. , Zhang Z. L.
Published: March 2003

Structures subjected to severe cyclic loading may fail due to low cycle fatigue. During the latter part of the fatigue life the crack growth rate may increase due to crack growth from static failure modes. This was investigated numerically by Skallerud and Zhang (Int. J. Solids Struct. 34, 3141–3161, 1997) for a butt‐welded plate with a circular crack growing from the centre of the weld. The weld material was slightly overmatching, and for simplicity, base material properties were employed in the finite element model. The predicted crack growth rate was significantly underpredicted in the early part of crack growth. In the present investigation, more detailed material modelling was used, and some metallurgical aspects were addressed. The fatigue part of the crack growth was determined by using the computed cyclic J‐integral, and the static mode crack growth from ductile tearing is determined from computations accounting for void nucleation/growth/coalescence by means of a modified Gurson–Tvergaard model.
Probability modelling and statistical analysis of damage in the lower wing skins of two retired B‐707 aircraft
Authors: Harlow D. G. , Wei R. P.
Published: March 2003

A plausible mechanistically based probability model for localized pitting corrosion and subsequent fatigue crack nucleation and growth is used to analyse tear‐down inspection data from two retired B‐707 aircraft that had been in commercial service for about 24 and 30 years. Sections of the left‐hand lower wing skins from these aircraft had been previously disassembled and inspected optically at 20× magnification. The inspections were augmented by metallographic examinations for the lower time aircraft. The evolution of damage in the fastener holes is estimated by using reasonable values for the localized corrosion and fatigue crack growth rates, statistically estimated from laboratory data. The primary loading, assumed to be the mean design load, is considered to be from ground–air–ground wing bending cycles, augmented by ‘average’ gust loading, only. The encouraging agreement between the estimated probability of occurrence and the observed distribution of multiple hole–wall cracks attests to the efficacy of the approach and its relevancy to airworthiness assessment and fleet life management.
Deformation analysis of notched components and assessment of approximate methods
Authors: Jiang Y. , Xu B.
Published: March 2003

Finite element modelling was conducted on notched members subjected to proportional and non‐proportional loading. A recently developed cyclic plasticity model capable of accurately describing cyclic material behaviour was implemented into a finite element code. A plate with a central hole and a shaft with a circumference groove were studied. Approximate methods for the notched problems were critically evaluated using the finite element results.
Study of composite patch repair by analytical and numerical methods
Authors: Tsamasphyros G. J. , Kanderakis G. N. , Karalekas D. , Rapti D. , Gdoutos E. E. , Zacharopoulos D. , Marioli‐Riga Z. P.
Published: March 2003

A combined analytical and numerical study of an isotropic cracked plate that was repaired by using a bonded composite patch was conducted. The analytical work was based on Rose's equations, whereas for the numerical investigation a three‐dimensional finite element analysis was implemented. A number of cracked plates with different crack lengths and overall dimensions of the composite repair were considered. The composite patch was made of unidirectional laminates with different stacking sequences. Both, one‐ and two‐sided patches were analysed. Results are presented for the stress intensity factor in the patched crack and the maximum stress reinforcement stress and adhesive strain. It was found that for the case of a two‐sided reinforcement the results obtained by both methods were in good agreement. However, for the case of a single reinforcement the accuracy of the analytical method decreased due to the tendency to out‐of‐plane bending as a result of bonding a reinforcing patch to only one face of a plate, which is ignored in the analysis.
Transient reliability of ceramic structures
Authors: Jadaan O. , Nemethm N.
Published: March 2003

Present capabilities of the NASA Ceramic Analysis and Reliability Evaluation of Structures/Life (CARES/Life) code include probabilistic life prediction of ceramic components subjected to fast fracture, slow crack growth (SCG) (stress corrosion), and cyclic fatigue failure modes. Currently, this code has the capability to compute the time‐dependent reliability of ceramic structures subjected to simple time‐dependent loading. For example, in SCG type failure conditions CARES/Life can handle the cases of sustained and linearly increasing time‐dependent loads, whereas for cyclic fatigue applications, it can account for various types of repetitive constant amplitude loads. In real applications applied loads are rarely that simple, but rather vary with time in more complex ways such as engine start up and shut down and dynamic and vibrational loads. In addition, when a given component is subjected to transient environmental and/or thermal conditions, the material properties also vary with time. The objective of this paper is to demonstrate a methodology capable of predicting the time‐dependent reliability of components subjected to transient thermomechanical loads that take into account the change in material response with time. In this article, the dominant delayed failure mechanism is assumed to be SCG. This capability has been added to the NASA CARES/Life code, which has also been modified to have the ability of interfacing with commercially available finite element analysis codes executed for transient load histories. An example involving a ceramic exhaust valve subjected to combustion cycle loads is presented to demonstrate the viability of this methodology and the CARES/Life program.
Creep failure mechanisms of a Ti‐6Al‐4V thick plate
Authors: Seco F. J. , Irisarri A. M.
Published: March 2003

The creep failure operating mechanisms of a 17‐mm thick plate of a Ti–6Al–4V alloy in various heat treating conditions have been investigated. Specimens in the as‐received, mill‐annealed, condition (50 min maintenance at 720 °C and air cooled as the final step of the thermomechanical process) showed the lowest creep resistance and their metallographic analysis revealed that the temperature‐activated dislocation climb was the mechanism responsible for the failure and that observed holes were generated by plastic deformation, rather than by creep cavitation. Conversely, maximum times to failure were recorded in beta‐annealed specimens (1030 °C for 30 min, air cooled and aged for 2 h at 730 °C). The fracture surfaces of these broken specimens exhibited an intergranular morphology that was attributed to grain boundary sliding along the former beta grains. Finally, alpha–beta field‐annealed samples (940 °C 4 h, and furnace cooled to 700 °C) possessed intermediate lives between those of mill‐annealed and beta‐annealed specimens and the failure operating mechanism was diffusional creep by the nucleation and coalescence of the creep cavities generated at the alpha–beta interfaces and the triple points.
Effect of microcracking on the micromechanics of fatigue crack growth in austempered ductile iron
Authors: Ortiz J. , Cisilino A. P. , Otegui J. L.
Published: March 2003

The effect of microcracking on the mechanics of fatigue crack growth in austempered ductile iron is studied in this paper. The mechanism of fatigue crack growth is modelled using the boundary element method, customized for the accurate evaluation of the interaction effects between cracks and microcracks emanating from graphite nodules. The effects of nodule size and distribution and crack closure are considered, with deviation bounds of computed results estimated through weight‐function analyses. A continuum approach is employed as a means of quantifying the shielding effect of microcracking on the dominant propagating crack, due to the reduction of stiffness of the material in the neighbourhood of the crack tip. Although the results obtained may not yield actual numbers for real cases, they are in accordance with experimental observations and demonstrate how the main factors affect the crack growth of the macrocrack.
Interfacial fatigue crack propagation in Ni‐base superalloy protective coatings
Authors: Okazaki M. , Okamoto M. , Harada Y.
Published: March 2003

It is important to control the interface strength of coatings and composite materials; a feature that has been noted for many years. However, how can interface strength be evaluated and controlled? In order to explore this aspect, subcritical fatigue crack growth behaviour was investigated along the interface of a CoNiCrAlY coated Ni‐Base superalloy. According to the traditional fatigue test methodology, fatigue crack propagation tests were carried out, using double cantilever beam specimens. The resistance to the fatigue crack propagation was successfully evaluated by a fracture mechanics approach. Particular attention was given to the effects of surface finish of the substrate as a coating parameter, the test temperature, and long‐term thermal ageing after the coating.
Non‐destructive evaluation of fatigue and creep‐fatigue damage by means of the induced‐current focused potential drop technique
Authors: Sato Y. , Takeda Y. , Shoji T.
Published: March 2003

Quantitative evaluation of damage accumulation including crack initiation and propagation is one of the major concerns of industrial plant management and plant licence renewal. In order to develop a novel non‐destructive testing (NDT) and non‐destructive evaluation (NDE) technique for damage evaluation, the induced‐current focused potential drop (ICFPD), originally proposed for a defect inspection, was employed. In this study, ICFPD was successfully applied to a non‐destructive damage evaluation based on crack measurements. The measurements were taken on fatigued specimens with various degrees of fatigue damage. The ICFPD can clearly detect and differentiate the damage accumulation processes including crack initiation, small crack growth and subsequent macroscopic crack growth. In order to demonstrate the applicability of damage evaluation assessments based on small crack measurements, ICFPD has also been applied to creep–fatigue loading where damage evaluation of a fusion reactor material is based on small crack measurements by the ICFPD technique and a novel methodology is proposed.
Experimental and computational investigation of three‐dimensional mixed‐mode fatigue
Authors: Forth S. C. , Keat W. D. , Favrow L. H.
Published: March 2003

Experimental and computational methods were developed to model three‐dimensional (3‐D) mixed‐mode crack growth under fatigue loading with the objective of evaluating proposed 3‐D fracture criteria. The experiments utilized 7075‐T73 aluminium forgings cut into modified ASTM E740 surface crack specimens with pre‐cracks orientated at angles of 30, 45 and 60° in separate tests. The progress of the evolving fatigue crack was monitored in real time using an automated visualization system. In addition, the amplitude of the loading was increased at prescribed intervals to mark the location of the 3‐D crack front for post‐test inspection. In order to evaluate proposed crack growth equations, computer simulations of the experiments were conducted using a 3‐D fracture model based on the surface integral method. An automatic mesher advanced the crack front by adding a ring of elements consistent with local application of fracture criteria governing rate and direction of growth. Comparisons of the computational and experimental results showed that the best correlation was obtained when KII and KIII were incorporated in the growth rate equations.
Constraint effects on the elastic–plastic fracture behaviour in strain gradient solids
Authors: WEI Y.
Published: March 2003

ABSTRACT Crack‐tip constraint effects (or T‐stress effects) on the elastic–plastic fracture behaviour in strain gradient materials are analysed in the present study. The T‐stress effects on the stress distributions along the plane ahead of the stationary and growing crack tip, respectively, are analysed by using the Fleck and Hutchinson strain gradient plasticity formation. For a steadily growing crack, the T‐stress effects on the steady‐state fracture toughness are analysed by adopting the embedded fracture process zone model. In addition, the analysis for the growing crack is applied to an interfacial cracking experiment for a metal/ceramic system, and the material length‐scale parameter appearing in the strain gradient plasticity theory is predicted. In the present analyses, a new finite element method specially designed for strain gradient problems by Wei and Hutchinson is adopted.
A probabilistic simulation of fluid leakage in multiple cracks situation
Authors: XIE L. , YU Z.
Published: March 2003

ABSTRACT In pressure vessels and piping the leak‐before‐break (LBB) assessment method is employed to avoid any catastrophic failure prior to a detectable leakage. One of the most important parameter, the leak rate, is investigated in the present paper by means of the Monte Carlo method.

A brief review is carried out with emphasis on aspects such as crack growth, crack size with detectable leakage, crack opening area and leak rate. Issues concerning the property and behaviour of multiple cracks are also covered along with a review of the characteristics of leak rate through distributed multiple cracks using a statistical simulation method.

The simulation results show that the effect of multiple cracks is quite significant to the LBB concept. Both the relationship between leak rate and crack length (or time) and the statistical characteristics of the leak rate are considerably different for different initial crack conditions.
A mode II weight function for subsurface cracks in a two‐dimensional half‐space
Authors: MAZZÙ A.
Published: March 2003

The general properties of a mode II Weight Function for a subsurface crack in a two‐dimensional half‐space are discussed. A general form for the WF is proposed, and its analytical expression is deduced from the asymptotic properties of the displacements field near the crack tips and from some reference cases obtained by finite elements models. Although the WF has general validity, the main interest is on its application to the study of rolling contact fatigue: its properties are explored for a crack depth range within which the most common failure phenomena in rolling contact are experimentally observed, and for a crack length range within the field of short cracks. The accuracy is estimated by comparison with several results obtained by FEM models, and its validity in the crack depth range explored is shown.
On the development of crack closure at high R levels after an overload
Authors: McEVILY A. J. , ISHIHARA S.
Published: March 2003

ABSTRACT In a 1999 paper it was asserted that crack closure cannot be of major importance in the mechanism of crack retardation following an overload, particularly since the authors found no evidence for crack closure at high R‐values, although crack retardation was observed. In the present work, overload experiments were carried out at R
= 0.5 and crack closure was observed. In addition, the rate of fatigue crack growth in both constant amplitude and overload tests was found to be a function of ΔKeff. It is concluded that crack closure is an important part of the retardation mechanism.
Fatigue life prediction of offshore tubular joints using fracture mechanics
Authors: LEE M. M. K. , BOWNESS D.
Published: March 2003

ABSTRACT Fatigue crack growth calculations were performed on offshore tubular joints using the Paris crack growth law. The stress intensity factors required for such calculations were obtained from T‐butt solutions previously proposed by the authors. The applicability of the solutions to tubular joints was first demonstrated by comparing the fatigue life of a base case with that obtained from a mean S–N curve, and the influence on fatigue life of various factors including load shedding, the size of initial defects, weld geometry, etc. was investigated. The solutions were then used to predict the lives of tubular T‐joints from an experimental database. The results show that the solutions underestimate the fatigue life; this underestimation was shown to be primarily due to ignoring the combined effects of load shedding and the intersection stress distribution. In general, however, the trends in the predicted fatigue lives with joint geometry and other details were seen to be superior to predictions from the S–N approach, with the solutions significantly reducing the dependency on loading mode exhibited by the test data.
Cumulative fatigue damage taking the threshold into account
Authors: SVENSSON T.
Published: March 2003

ABSTRACT Prediction of fatigue life at variable amplitude often demands considerations about the contribution of loads below the nominal fatigue limit. Different engineering approaches include acceptance of the limit, neglecting of the limit, or making ad hoc corrections for damage contributions originating from loads below the limit. Theories that consider the fatigue limit as controlled by crack thresholds suggest that the limit decreases as the damage accumulates, i.e. as the dominating crack grows. This idea is used here to find an extension of the Palmgren–Miner rule to the case with a fatigue limit decreasing with increasing damage.
Corrosion fatigue behaviour and fracture mechanisms in nitrided low alloy steel
Authors: TOKAJI K. , TAKAHASHI S.
Published: March 2003

Rotary bending fatigue tests have been performed in 3%NaCl aqueous solution using specimens of a low alloy steel (Cr–Mo steel) with different nitride case depths. The effect of case depth on corrosion fatigue strength, the fracture process and mechanisms were studied. The corrosion fatigue strengths of the nitrided materials increased compared with the untreated material and increased with increasing thickness of the compound layer, but tended to saturate above a certain thickness. All the materials showed lower fatigue strength in 3%NaCl aqueous solution than in laboratory air and the reduction of fatigue strength decreased with increasing thickness of the compound layer, but remained nearly constant above a certain thickness. Corrosion pits were seen underneath the compound layer, from which cracks initiated. The corrosion fatigue strengths of the specimens whose compound layer was completely removed by electropolishing were almost the same as that of the untreated material, indicating a very significant role of the compound layer in improving corrosion fatigue strength. Because of the porous nature of the compound layer, particularly in the surface‐adjacent part, the solution penetrated the compound layer and reached the base steel, thus the corrosion fatigue strength of the nitrided materials was controlled by the penetration of corrosive media.
Increased abundance of the red admiral butterfly Vanessa atalanta in Britain: the roles of immigration, overwintering and breeding within the country
Authors: Pollard  , Greatorex‐Davies
Published: March 2003

The migratory butterflyVanessa atalantaincreased in abundance at monitored sites in Britain from 1976 to 1996. Three possible causes of the increase are improved winter survival within Britain, greater breeding success within Britain, and increased immigration.

  Trends during most of the season were similar to those of immigrant or overwintered individuals in spring; thus the evidence does not support greater breeding success in Britain. As abundance in spring was not correlated with abundance in the previous autumn, when trend was taken into account, it seemed unlikely that overwintering in Britain was important. Thus the increase in abundance was probably due to increased immigration. Incidental to the main study, the mean index per site per year was closely correlated with the collated index, the usual measure of annual fluctuations. This agreement suggests that the mean index may be a useful check for trends in monitoring data for other wide‐ranging organisms.
Condition‐dependent reproductive success in bighorn ewes
Authors: Festa‐Bianchet
Published: March 2003

Individual bighorn ewes (Ovis canadensis) at 4–14 years of age were 1.5% heavier preceding years when they weaned a lamb than preceding years when their lamb died before weaning. Intra‐individual differences in mass between years of successful and unsuccessful reproduction appeared independent of a ewe’s multiyear average mass. Relative mass loss both in the winter before and in the winter after a given repro‐ductive episode increased with reproductive success. Long‐term monitoring of individual mass and reproductive success is a promising technique to study life histories in capital breeders, because it allows to partially account for differences in reproductive potential.
Travelling wave dynamics and self‐organization in a spatio‐temporally structured population
Authors: Kaitala  , Ranta
Published: March 2003

We analyse spatial population dynamics showing that periodic or period‐like chaotic dynamics produce self‐organization structures, such as travelling waves. We suggest that self‐organized patterns are associated with spatial synchrony patterns that often depend on geographical distance between subpopulations. The population dynamics also show statistical spatial autocorrelation patterns. We contrast our theoretical simulations with empirical data on annual damages in young sapling stands caused by voles. We conclude, on the basis of the periodicity, synchrony, and spatial autocorrelation patterns, and our simulation results, that vole dynamics represent travelling waves in population dynamics. We suggest that because such synchrony patterns are frequently observed in natural populations, spatial self‐organization may be more common in population dynamics than reported in the literature.
Defining the abundance body‐size constraint space: data from a real food web
Authors: Leaper  , Raffaelli
Published: March 2003

Using density and body‐size data for a well‐documented food web, the Ythan estuary, Aberdeenshire, we show that the shape of the constraint space is broadly similar to that proposed by Brown, and the slope (regression coefficient) of the plot of the central tendency is not significantly different from global or community data sets. However, the steepness of the plot is very sensitive to the degree of taxonomic resolution of species entities, particularly those of small body‐size, although the overall shape of the constraint space does not change. When more fully resolved, the regression slope differs markedly from those of most freshwater and terrestrial studies. In addition, the upper bound of the constraint space is, contrary to theoretical expectations, insensitive to gross changes in the system’s productivity. The dramatic increase in productivity that has led to an increase in abundance of invertebrates in the Ythan does not visibly affect the upper bound of the constraint space. Our results show that the traditional approach to comparing systems by the regression slopes of central trends is probably meaningless unless data sets are resolved to a similar degree of taxonomic resolution, and that detecting productivity effects on the location of the upper bound will be difficult.
A failed attempt to demonstrate pheromone communication in archaic moths of the genus Sabatinca Walker (Lepidoptera, Micropterigidae)
Authors: Kozlov  , Zvereva
Published: March 2003

Data on pheromones of phylogenetically archaic moths are very scant, despite being needed to understand the life history evolution and phylogeny of the basal lineages of Lepidoptera. Two New Zealand micropterigid moths, Sabatinca (Palaeomicra) chalcophanes Meyr. and Sabatinca (s.str.) demissa Philp., were investigated for pheromone communication. Consistent negative results were demonstrated by (i) behavioural observations, (ii) exposure of blends containing active components of pheromones identified in caddis‐flies and archaic moths, (iii) exposure of caged males and females in sticky traps, and (iv) detection of male and female antennal responses to both male and female extracts. Since no data indicated the presence of long‐distance sex pheromones in Sabatinca, we concluded that these moths use visual clues to meet sexual partners. The secondary lack of pheromone communication in Micropterigidae suggests a high degree of ecological specialization in this plylogenetically most archaic moth family.
Direct and indirect estimates of the selfing rate in small and large individuals of the bumblebee pollinated Cynoglossum officinale L (Boraginaceae)
Authors: Vrieling K. , Saumitou‐ Laprade P. , Cuguen J. , Van Dijk H. , De Jong T.J. , Klinkhamer P.G.L.
Published: March 2003

We measured the relationship between selfing rates and flower number in an experimental population of bumblebee pollinated Cynoglossum officinale, with plants differing in flower number. Results were compared with the prediction of a model based on pollen dynamics and pollinator behaviour. The selfing rate, as measured by multilocus oligonucleotide DNA fingerprinting, increased with flower number and ranged from 0% to 70%. Flowers on large plants received an equal number of visits from bumblebees as flowers on small plants. On large plants more flowers in a row were visited, inducing geitonogamy. The overall relationship between selfing rate and number of flowers can be explained by pollen dynamics and pollinator behaviour without invoking postpollination processes such as differential pollen tube growth and abortion.
Timing of foetal growth spurts can explain sex ratio variation in polygynous mammals
Authors: Forchhammer M.C.
Published: March 2003

The prediction from sex ratio theory that natural selection on sexually dimorphic mammals should favour an excess of male offspring only when mothers are in good condition, has been tested extensively but with little consistency in results. Although recent studies have shown that environmental variations may cause some of the discrepancy, there have also been reports of contrasting sex ratios under similar environmental settings. Here it is suggested that variation in timing of environmental stress and sex‐specific differences in foetal growth pattern in relation to maternal condition, may explain such seeming contradictions in sex ratio variation of polygynous mammals.
Diversity, function and stability in parasitoid communities
Authors: Rodríguez M.Á. , Hawkins B.A.
Published: March 2003

The parasitoid assemblages associated with grass‐feeding chalcid wasps in Great Britain were used to examine the relationships between diversity (species richness), community function (total parasitism rate) and stability (variability in parasitism rate over time). Species‐rich communities did not generate higher parasitism rates than species‐poor communities, nor was temporal variation of parasitism rates related to parasitoid community richness. The mechanisms underlying hypotheses linking species richness and community function and stability are discussed in the light of these results. Because all parasitoid species represent a single functional group, a lack of complementarity in the ways they use their resources may explain why diversity is not linked to function or community stability. A second likely reason is that these parasitoid communities are under bottom‐up control, thus exerting little or no influence on total system function and variability. This is likely to be common in parasitoid communities.
Pollution suppresses delayed inducible resistance in boreal willow Salix borealis
Authors: Zvereva Elena L. , Kozlov Mikhail V.
Published: March 2003

We studied the effects of aerial pollution on the expression of Delayed Inducible Resistance (DIR) against herbivores in the boreal willow Salix borealis, growing naturally around the nickel‐copper smelter at Monchegorsk (NW Russia). In slightly polluted and clean sites, the manual defoliation (simulated insect herbivory) of willows resulted in the development of DIR, which was expressed in the post‐treatment year as (i) a decrease in leaf damage, (ii) the dispersion of grazing damage within a plant, and (iii) a decrease in foliar quality, detected by the adverse effects on the larval relative growth rate of the autumnal moth, Epirrita autumnata. At the same time, in heavily and moderately polluted sites these effects were not observed, suggesting that DIR in plants growing under pollution impact was not expressed. Since DIR may be one of the important feedbacks regulating the population dynamics of herbivores, the disturbance of this feedback by pollution‐induced environmental deterioration may contribute to the high densities of many herbivorous insects in polluted areas.
Testing for local species saturation with nonindependent regional species pools
Authors: Fox  , McGrady‐Steed  , Petchey
Published: March 2003

Identifying the factors controlling local community structure is a central problem in ecology. Ecologists frequently use regression to test for a nonlinear saturating relationship between local community richness and regional species pool richness, suggesting that species interactions limit the number of locally coexisting species. However, communities in different regions are not independent if regions share species. We present a Monte Carlo test for whether an observed local‐regional richness relationship is significantly different from that expected when regions are nonindependent and species interactions do not limit community membership. We illustrate this test with data from experimental microcosm communities. A conventional F‐test suggests a significant saturating relationship between realized community richness and species pool richness. However, the Monte Carlo test fails to reject the null hypothesis that species interactions do not affect community richness. Strong species interactions do not necessarily set an absolute upper limit to the number of locally coexisting species.