bluuebunny/crossref_metadata_2025 huggingface dataset:
Primary hydatid cysts of psoas muscle
Authors: Melis Marcovalerio , Marongiu Luigi , Scintu Francesco , Pisano Michele , Capra Fabio , Zorcolo Luigi , Casula Giuseppe
Published: March 2003

Background:  Hydatid cysts may occur in any area of the body, but they usually localize to the liver and the lungs. Primary localization in muscle is not common, accounting for 2−3% of all sites; even rarer is the development of multiple cysts.

Methods: The patient presented with a painless abdominal mass which gradually increased in size to a diameter of approximately 16 cm. Organ imaging scan revealed multiple hydatid cysts within the right psoas muscle. Because of the proximity of the lesions to the iliac vessels, ureter and nerves to the lower limb, percutaneous drainage and alcoholization under local anaesthesia were ­performed with the aim of reducing the size of the cysts and sterilizing them prior to definitive surgery. This procedure was not effective. Two weeks after percutaneous treatment the patient underwent surgery.

Results:  At operation the cysts were localized and successfully removed under ultrasound guidance. Postoperative stay was ­uneventful. Two years after surgery the patient has no evidence of recurrent hydatid disease.

Conclusions:  Ultrasonography is the preferred method for detecting muscular hydatid cyst and for guiding the surgeon during resection.
Electrolytic ablation as an adjunct to liver resection: Safety and efficacy in patients
Authors: Wemyss‐Holden Simon A. , Berry David P. , Robertson Gavin S. M. , Dennison Ashley R. , De La M Hall Pauline , Maddern Guy J.
Published: March 2003

Background:  Electrolytic ablation is a relatively new method for the local destruction of colorectal liver metastases. Experimental work in animal models has shown this method to be safe and efficacious. However, before proceeding to clinical trials it was necessary to confirm these findings in a pilot study of five patients.

Methods:  Five patients with colorectal liver metastases were studied prospectively. Each patient underwent a potentially curative liver resection. One of the metastases to be removed was treated using electrolysis before resection. Each patient was monitored closely during and after electrolysis to determine any morbidity associated with the treatment. Once resected, the metastases were examined histologically for completeness of ablation.

Results:  All patients tolerated the electrolysis well; there were no deaths or complications related to the treatment. Histological examination of the resected metastases which had been treated electrolytically showed complete tissue destruction with no viable malignant cells remaining at the site of treatment.

Discussion:  This pilot study of electrolytic ablation of liver metastases in five patients showed the treatment to be well tolerated and safe. Additionally, it demonstrated total destruction of the malignant tissue at the site of electrolysis.

Based on these encouraging results, clinical trials can now begin.
Utilization of preoperative autologous blood donation in elective surgery
Authors: Savoia Helen F. , Metz Jack , Maxwell Ellen L. , Hauesler Michael N. , Mellor Jayne , Kiely Sarah
Published: March 2003

Background:   The aim of the present paper was to review the pattern of collection and transfusion of autologous red cells for elective surgical procedures

Methods:  Data on requests for preoperative autologous donation of blood were obtained from the Australian Red Cross Blood Service, Victoria and the Royal Melbourne Hospital for the calendar year 1998. The following information was collected: patient age, sex, surgery type, number of autologous units requested and collected and, if relevant, reasons for not achieving the requested collection. Transfusion of autologous units and any additional homologous units was confirmed from records at the blood banks of the Royal Melbourne Hospital and Melbourne Pathology (the pathology provider performing cross‐matching for the majority of autologous units collected by Australian Red Cross Blood Service, Victoria).

Results:  Over 12 months, 2803 units of autologous blood were requested and 2282 units collected from 1301 patients. The most common reason for failure to collect the number of units requested was insufficient time between referral and surgery. Of the autologous units collected, 73% were transfused giving a collection to transfusion ratio of 1.4. Sixty‐eight per cent of patients received their autologous units only, 10% received both autologous and homologous units, while 22% were not transfused. For the majority of procedures, patients using preoperative autologous donation of blood had higher transfusion rates than those who did not use this.

Conclusions:  Ninety per cent of patients undergoing preoperative autologous donation of blood successfully avoided homologous blood exposure. However, preoperative autologous donation of blood is both wasteful and increases the incidence of transfusion in surgical procedures.
Retrospective review of paediatric patients with acute scrotum
Authors: Mushtaq Imran , Fung Mary , Glasson Martin J.
Published: March 2003

Background:  The purpose of the present study was to evaluate the historical features and physical examination findings in boys presenting with acute scrotum and to determine the reliability of these modalities to make the correct clinical diagnosis.

Methods:  A retrospective review of all boys presenting with acute scrotal/testicular pathology between January 1994 and December 1998 was performed.

Results:  Two hundred and four boys were included in the study: 110 with torsion of the testicular appendage (TA), 40 with testicular torsion (TT), 29 with epididymo‐orchitis (EO) and 25 with other diagnoses. Seventeen boys were managed conservatively. With the exception of symptom duration, there was no statistically significant difference between boys with TA, TT and EO. Boys with TT sought medical attention significantly earlier (median: 9.5 h) than those with TA (median: 48 h). Boys requiring an orchidectomy (n = 8) presented later than those who did not (median 30 vs 9 h; P < 0.05): seven (88%) were under 7 years of age. The testicular salvage rate was 88% and 36% with a pain duration of <12 h and >12 h, respectively. The preoperative clinical diagnosis was correct in 80% of those boys who underwent surgical exploration. Testicular torsion was misdiagnosed clinically in five boys. Late testicular atrophy was not observed in the present study.

Conclusions:  Most boys presenting with acute scrotum have TA. The history and physical examination can reliably identify those boys who can be managed conservatively. Routine surgical exploration is no longer justified in all boys with acute scrotum.
Palpable parathyroid adenomas presenting as clinical solitary thyroid nodules and cytologically as follicular thyroid neoplasms
Authors: Weymouth Michael D. , Serpell Jonathan W. , Chambers David
Published: March 2003

Background:  A palpable parathyroid mass, in a patient with primary hyperparathyroidism, is presumed to be parathyroid carcinoma until proven otherwise, with other less common causes including parathyroid cysts and adenomas. These parathyroid pathologies can be more difficult to interpret with concomitant thyroid disease.

Methods:  A retrospective review was undertaken of a series of three patients with palpable parathyroid adenomas mimicking thyroid nodules.

Results:  Two of three patients had preoperative biochemical evidence of primary hyperparathyroidism. Sestamibi scanning confirmed the presence of parathyroid pathology in one case. Fine‐needle aspiration cytology revealed probable follicular neoplasms of the thyroid in all three cases. Only one of three parathyroid adenomas was diagnosed at neck exploration; the others were diagnosed at subsequent histopathology.

Conclusion:  Parathyroid and thyroid disease often occur simultaneously. Concomitant parathyroid pathology should be considered, even in the absence of biochemical and radiological evidence, at neck exploration for thyroid disease. Macroscopic identification of parathyroid disease at neck exploration can be difficult when within the thyroid gland capsule. Cytology and imaging of parathyroid adenomas may, on occasion, mimic follicular thyroid neoplasms.
FATIGUE CRACK PROPAGATION IN AUSTENITIC STAINLESS STEEL UNDER LOW FREQUENCY LOADING AND SALT WATER CONDITIONS
Authors: Jakubowski M
Published: March 2003

Fatigue crack growth rates (FCGR) for a steel similar to AISI 316LN have been evaluated in air and salt water. At free corrosion potential, a short crack effect appeared for crack lengths shorter than 4 mm. For longer cracks, a segment (called region I) of the corrosion FCGR curve can be described by an equation with the same coefficients as for steels of ordinary resistance to corrosion. Thus, the process controlling crack propagation is presumably the same for both steels. Corrosion FCGR in region II (range of longer crack lengths and higher ΔK values, where the curve cannot be described by the previously mentioned equation) are slower than for ordinary steels. The plateau in FCGR observed at a cathodic potential corresponds to the higher plateau at the free corrosion potential. An interpretation is presented for the shape of the corrosion FCGR curves at both potentials.
MICROMECHANICAL MODELLING OF DAMAGE AND FRACTURE OF DUCTILE MATERIALS
Authors: Steglich  , Brocks
Published: March 2003

A micromechanical model of ductile damage by void nucleation, growth and coalescence is widely and successfully applied to describe phenomena of ductile tearing. The model’s fundamental principles, and especially the constitutive equations of Gurson, Tvegaard and Needleman (GTN‐model), are briefly described. Some of the material parameters of the GTN‐model are calibrated by performing cell model calculations, which is a method of determining the structural behaviour of a single void in a plastic material. The approach is used to study the dependence of material strength and toughness on microstructural features of nodular cast iron. The numerical simulations were realized within the FE‐program ABAQUS by a user‐supplied material model.
NUMERICAL MODELLING OF A 3D RAIL RCF ‘SQUAT’‐TYPE CRACK UNDER OPERATING LOAD
Authors: Bogdański S , Olzak M , Stupnicki J
Published: March 2003

The analysis is based on the 3D FE model of the rail Rolling‐Contact‐Fatigue (RCF) ‘squat’‐type crack, which tends to be common in tracks with high‐speed passengers and mixed traffic. The model incorporates the section of rail and a wheel of real geometry, in which the wheel is rolling over the running band of rail containing the ‘squat’‐type crack. The state of stress in the vicinity of the crack front is determined, and consequently the values and ranges of the stress intensity factors (SIFs) KI , KII andKIII at the crack front are calculated for the cycle of rolling. To simulate loading conditions occurring in practice, residual, bending and thermal stresses acting in the presence of the tractive force were taken into account. The results indicate a significant role of face friction and tractive force in the loading mechanism at the ‘squat’. The longitudinal and lateral residual stresses may also influence the loading cycles, especially for the cases with reduced friction between the crack faces. Reduction of the face friction coefficient to values close to zero creates conditions for crack propagation driven by the shear mode mechanism. These results were obtained under a project sponsored by the ERRI D173 Committee, Utrecht, The Netherlands.
FRACTURE AND FATIGUE OF FERROELECTRICS UNDER ELECTRIC AND MECHANICAL LOADING
Authors: Yang  , Zhu
Published: March 2003

A switch in the domain polarization direction near the tip of a flaw plays an important role in the fracture and fatigue of ferroelectrics under electric and mechanical loading. The present paper adopts a small‐scale switching model with the domain switch based on the combined electric and mechanical work increment. The model is capable of explaining electric fracture, fracture toughness anisotropy and electric fatigue.
FATIGUE CRACK GROWTH RATES IN Al–Li ALLOY, 2090. INFLUENCE OF ORIENTATION, SHEET THICKNESS AND SPECIMEN GEOMETRY
Authors: Mc FJ , Tabrett CP , Smith DJ
Published: March 2003

.The fatigue crack growth (FCG) behaviour of the aluminium–lithium (Al–Li) alloy 2090‐T84 has been investigated from a series of constant amplitude FCG tests. The influence of in‐plane orientation (L–T, T–L, L–T + 45°) and sheet thickness (1.6 and 6 mm) on the FCG rates for the rolled product has been examined. In general, the T–L orientation possesses superior FCG resistance for both thicknesses and the 6 mm thick sheet material showed marginally improved FCG resistance when compared to the 1.6 mm thick material, for all orientations. Closure‐corrected FCG data suggests that much of the difference between the L–T and T–L orientation for the 6 mm thick sheet arises from differences in crack closure levels. When comparing the crack closure levels for C(T) and M(T) specimens, a significant difference is shown as ΔK increases. Fatigue crack growth rates for ΔK less than 15 MPa m were significantly higher in the M(T) specimens compared to the C(T) specimens. Compared with other factors examined the influence of specimen geometry appears to be a dominant factor.
EXPERIMENTAL INVESTIGATION ON THE EFFECTS OF COLD EXPANSION OF FASTENER HOLES
Authors: Ball DL , Lowry DR
Published: March 2003

A series of experimental investigations concerning the residual stress fields at cold‐expanded fastener holes and of the behavior of fatigue cracks at such holes has been conducted. These studies have included measurement of the initial, cold‐work‐induced residual stress fields at both uncracked and cracked holes and the performance of both constant amplitude and spectrum fatigue crack growth tests.
Microstructural effects on the short crack behaviour of a stainless steel weld metal during low‐cycle fatigue
Authors: Zhao  , Gao  , Wang
Published: March 2003

An experimental study into microstructural effects on short fatigue crack behaviour of 19 stainless steel weld metal smooth specimens during low‐cycle fatigue is performed by a so‐called ‘effective short fatigue crack criterion’. This material has a mixed microstructure in which it is difficult to distinguish the grains and measure the grain diameter. The columnar grain structure is made up of matrix‐rich δ ferrite bands, and the distance between the neighbouring rich δ ferrite bands is an appropriate measurement for characterizing this structure. Particularly, the effective short fatigue cracks (ESFCs) always initiate from the bands of δ ferrite in the matrix in the weakest zone on one of the specimen surface zones which is orientated in accordance with the inner or outer surface of welded pipe from which the specimens were machined. These cracks exhibit characteristics of the microstructural short crack (MSC) and the physically small crack (PSC) stages. The average length of the ESFCs at the transition between MSC and PSC behaviour is ≈40 μm, while the corresponding fatigue life fraction is ≈0.3 at this transition. Different from previous test observations, the growth rate of the dominant effective short fatigue crack in the MSC stage still shows a decrease with fatigue cycling under the present low‐cycle fatigue loading levels. A statistical evolution analysis of the growth rates reveals that the short fatigue crack growth is a damage process that gradually evolves from a non‐ordered (chaotic) to a perfectly independent stochastic process, and then to an ordered (history‐dependent) stochastic state. Correspondingly, the microstructural effects gradually evolve from a weak effect to a strong one in the MSC stage, which maximizes at the transition point. In the PSC stage, the effects gradually evolve from a strong to weak state. This improves our understanding that the short crack behaviour in the PSC stage is mainly related to the loading levels rather than microstructural effects.
Assessment of stress corrosion cracking susceptibility by a small punch test
Authors: Yu Hyo‐Sun , Na Evi‐Gyun , Chung Se‐Hi
Published: March 2003

The object of this study is to establish a new test method for evaluating stress corrosion cracking (SCC) susceptibility of high‐strength steel using a small punch (SP) test and acoustic emission (AE). A miniaturized specimen (10 × 10 × 0.5 mm) is adopted for SCC evaluation. The experiments are conducted at various loading rates and at various orientations of the specimen. The cumulative average amplitude of the AE signal per unit equivalent fracture strain (εqf ) increases as the SCC susceptibility increases. Through the load–displacement behaviour, the fracture energy (ESP ), the SEM fractographs, and the correlation between the SCC susceptibility and the AE characteristics, it is proved that the small punch test method combined with AE measurements is a useful method to evaluate the SCC susceptibility of high‐strength steel.
A probabilistic approach to predict the very high‐cycle fatigue behaviour of spheroidal graphite cast iron structures
Authors: Chantier  , Bobet  , Billardon  , Hild
Published: March 2003

A new probabilistic approach is developed to study structures made of spheroidal graphite cast iron and subjected to very high‐cycle fatigue. Until now, the probabilistic approach was based on S–N curves obtained from experiments carried out only until 107 cycles. To validate this approach, failure predictions relating to the safety of components are computed and compared to experimental results. In addition to this development, an extension is proposed in order to improve the very long life assessment of complex structures. An extrapolation of the previous fatigue results to 109–1011 cycles illustrates the error made on cumulative failure probabilities. Finally, the respective influence of the casting flaw distribution, volume and stress field heterogeneity within specimens and industrial components is studied.
SIF and threshold for small cracks at small notches under torsion
Authors: Beretta  , Murakami
Published: March 2003

The basic approach to the problem of torsional fatigue strength of pieces containing defects is based on the stress concentration factor concept. However, experiments have shown that the torsional fatigue limit of specimens containing small holes is controlled by the threshold condition for small cracks emanating from small notches. Therefore, the ratio of torsional to bending fatigue limit (τw /σw ) for specimens containing small defects must be studied from the viewpoint of fracture mechanics.

The scope of this paper is to address the calculation of the stress intensity factor for a small crack emanating from a three‐dimensional hole under a biaxial state of stress by using the weight function method and to apply it to the fatigue limit prediction. The results obtained are in good agreement with experimental results on specimens with defects.
The stress–life fatigue behaviour of aluminium alloy foams
Authors: McCullough  , Fleck
Published: March 2003

The tension–tension and compression–compression nominal stress versus fatigue life responses of Alulight closed cell aluminium alloy foams have been measured for the compositions Al–1Mg–0.6Si and Al–1Mg–10Si (wt %), and for relative densities in the range 0.1–0.4. The fatigue strength of each foam increases with the relative density and with the mean applied stress, and is greater for the transverse orientation than for the longitudinal orientation. Under both tension–tension and compression–compression loading the dominant cyclic deformation mode appears to be material ratchetting; consequently, the fatigue life is highly sensitive to the magnitude of the applied stress. A micromechanical model is given to predict the dependence of life upon stress level and relative density. Panels containing a central hole were found to be notch insensitive for both tension–tension and compression–compression fatigue loading: the net‐section strength equals the unnotched strength.
Multiaxial creep–fatigue under anisothermal conditions
Authors: Sermage  , Lemaitre  , Desmorat
Published: March 2003

Because creep–fatigue is mainly studied in uniaxial tension, it is shown here how to proceed to perform both experiments and calculations under multiaxial loading and when the temperature varies both in time and space. The constitutive equations used are those of elasto‐visco‐plasticity coupled or not, to damage, with isotropic and kinematic hardening. It is shown that the unified damage law first proposed for ductile failure and then for fatigue may also be applied to multiaxial creep–fatigue interactions with a new expression for the damage threshold. The procedure for the identification of material parameters is described in detail. Finally, it is shown that the uncoupled calculation procedure, where damage is calculated as a post‐processing of an elasto‐visco‐plastic computation, gives satisfactory results in comparison to the fully coupled analysis; the latter being more accurate but very expensive in computer time.
On the mechanism of fatigue failure in the superlong life regime (N>107 cycles). Part 1: influence of hydrogen trapped by inclusions
Authors: Murakami Y. , Nomoto T. , Ueda T. , Murakami Y.
Published: March 2003

The fracture surfaces of specimens of a heat‐treated hard steel, namely Cr–Mo steel SCM435, which failed in the regime of N = 105 to 5 × 108 cycles, were investigated by optical microscopy and scanning electron microscopy (SEM). Specimens having a longer fatigue life had a particular morphology beside the inclusion at the fracture origin. The particular morphology looked optically dark when observed by an optical microscope and it was named the optically dark area (ODA). The ODA looks a rough area when observed by SEM and atomic force microscope (AFM). The relative size of the ODA to the size of the inclusion at the fracture origin increases with increase in fatigue life. Thus, the ODA is considered to have a crucial role in the mechanism of superlong fatigue failure. It has been assumed that the ODA is made by the cyclic fatigue stress and the synergetic effect of the hydrogen which is trapped by the inclusion at the fracture origin. To verify this hypothesis, in addition to conventionally heat‐treated specimens (specimen QT, i.e. quenched and tempered), specimens annealed at 300 °C in a vacuum (specimen VA) and the specimens quenched in a vacuum (specimen VQ) were prepared to remove the hydrogen trapped by inclusions. The specimens VA and VQ, had a much smaller ODA than the specimen QT. Some other evidence of the influence of hydrogen on superlong fatigue failure are also presented. Thus, it is concluded that the hydrogen trapped by inclusions is a crucial factor which causes the superlong fatigue failure of high strength steels.
Characterizing the non‐proportional and out‐of‐phase extent of tensor paths
Authors: Bishop J. E.
Published: March 2003

Scalar measures are developed for characterizing the non‐proportional and out‐of‐phase extent of any symmetric second‐order tensor path. These scalar measures are constructed by introducing the concept of the principal axes of the tensor path. These measures are independent of the parameterization of the tensor path. As required these measures are invariant under coordinate transformations. For an example, these measures are used to characterize the stress history in the combustion dome of an internal‐combustion automotive engine.
Fatigue behaviour and lifing of two single crystal superalloys
Authors: MacLachlan D. W. , Knowles D. M.
Published: March 2003

A model has been developed to predict the high temperature cyclic life of single crystal superalloys RR2000 and CMSX‐4 under conditions of creep and fatigue. A combined creep–fatigue model is used, although it is found that failure always occurs by creep or fatigue separately, and that creep–fatigue interaction has a minor influence. Microstructural investigation of a series of interrupted high‐ and low‐frequency tests are presented, these are combined with the results of a series of interrupted creep tests to identify the separate and interactive mechanisms of creep and fatigue. When creep damage is present the material behaves homogeneously. Under these conditions crack growth is initiation controlled, the mechanism of failure is surface or casting pore‐initiated planar crack growth followed by shear on crystallographic planes. As the temperature is lowered or the cyclic frequency increased, the material behaves less homogeneously and shear bands are formed during cycling. Crack growth under these conditions is again initiation controlled and failure is by rapid crystallographic crack growth along shear bands. Such a failure is a distinct fatigue failure and occurs when little creep damage is present. Under certain cyclic conditions, mainly those where the crystallographic failure mechanism is dominant, the material shows an anomalous increase in fatigue resistance with temperature up to approximately 950 °C. This behaviour has been quantified by relating it to the effect of strain rate and temperature on the yield strength of the material.
Multiaxial fatigue of welded joints under constant and variable amplitude loadings
Authors: Sonsino C. M. , Kueppers M.
Published: March 2003

Flange‐tube joints from fine grained steel StE 460 with unmachined welds were investigated under biaxial constant and variable amplitude loading (bending and torsion) in the range of 103 to 5 × 106 cycles to crack initiation and break‐through, respectively. In order not to interfere with residual stresses they were relieved by a heat treatment. In‐phase loading can be treated fairly well using the conventional hypotheses (von Mises or Tresca) on the basis of nominal, structural or local strains or stresses. But the influence of out‐of‐phase loading on fatigue life is severely overestimated if conventional hypotheses are used. However, the hypothesis of the effective equivalent stress that is introduced leads to fairly good predictions for constant as well as for random variable amplitude loads. Therefore, the knowledge of local strains or stresses is necessary. They are determined by boundary element analyses that are dependent on weld geometry. This hypothesis considers the fatigue‐life‐reducing influence of out‐of‐phase loading by taking into account the interaction of local shear stresses acting in different surface planes of the material. Further, size effects resulting from weld geometry and loading mode were included. Damage accumulation under a Gaussian spectrum can be assessed for in‐ and out‐of‐phase combined bending and torsion using an allowable damage sum of 0.35.
A shear stress‐based parameter for fretting fatigue crack initiation
Authors: Lykins C. D. , Mall S. , Jain V.
Published: March 2003

The purpose of this study was to investigate the fretting fatigue crack initiation behaviour of titanium alloy, Ti–6Al–4V. Fretting contact conditions were varied by using different geometries of the fretting pad. Applied forces were also varied to obtain fretting fatigue crack initiation lives in both the low‐ and high‐cycle fatigue regimes. Fretting fatigue specimens were examined to determine the crack location and the crack angle orientation along the contact surface. Salient features of fretting fatigue experiments were modelled and analysed with finite element analysis. Computed results of the finite element analyses were used to formulate a shear stress‐based parameter to predict the fretting fatigue crack initiation life, location and orientation. Comparison of the analytical and experimental results showed that fretting fatigue crack initiation was governed by the maximum shear stress, and therefore a parameter involving the maximum shear stress range on the critical plane with the correction factor for the local mean stress or stress ratio effect was found to be effective in characterizing the fretting fatigue crack initiation behaviour in titanium alloy, Ti–6Al–4V.
Effect of high‐temperature protective coatings on fatigue lives of nickel‐based superalloys
Authors: Itoh Y. , Saitoh M. , Takaki K. , Fujiyama K.
Published: March 2003

This study concerns MCrAlY coatings (M is Ni, Co or both) sprayed by a vacuum plasma spraying process for protection against high‐temperature corrosion and oxidation of gas turbine components, such as turbine blades and duct segments. The effect of high‐temperature protective coatings on fatigue lives of nickel‐based superalloys were investigated at high temperature under push–pull loading and rotary bending and then compared with uncoated superalloys, such as equiaxed IN738LC, unidirectional solidified CM247LC and single‐crystal CMSX‐2. The high‐cycle fatigue lives of MCrAlY‐coated superalloys at high temperature under push–pull loading showed an inferior performance when compared with the uncoated superalloys. This was because the crack initiation site was different. The high‐cycle fatigue cracks of nickel‐based superalloys initiated at casting cavities which were exposed on the specimen surface, whereas the high‐cycle fatigue cracks of MCrAlY‐coated specimens initiated at interface defects, such as small pores and grid residue, between the MCrAlY coating and the substrate and grew into the MCrAlY coating, and then into the substrate. Similarly, the rotary bending fatigue properties of MCrAlY‐coated superalloys at high temperature showed an inferior performance when compared with the uncoated superalloys. This is because of a high stress due to the higher Young’s modulus of the MCrAlY coating (in comparison with the substrate) being induced at the MCrAlY coating surface. The crack initiation site was on the specimen surface in both cases of the nickel‐based superalloys and the MCrAlY‐coated superalloys, respectively. As a result, it was considered that, for rotary bending tests, the fatigue life reduction was due to the high stress that originated from the difference of elastic constants between the MCrAlY coating and the superalloy. Consequently, in fatigue life design it is necessary to take account of the stress levels in a coating layer.
Microstructural influences on the growth of small cracks in Ti‐6Al‐4 V
Authors: Jin Ohchang , Hamm Richard W. , Johnson W. Steven
Published: March 2003

ABSTRACT The effects of microstructure on the growth of small cracks in Ti‐6Al‐4 V under fatigue loading are presented. The small crack growth is compared with large crack growth. Two large crack tests were performed at a stress ratio of 0.4 and a frequency of 15 Hz. For small crack growth tests, double edge notch specimens were loaded under constant amplitude at four maximum stresses with a stress ratio of 0.4 and a frequency of 15 Hz. A plastic replication technique was used to monitor the small fatigue crack growth rate. The microstructure consists of bands of α and β phases. The present study indicates that the crack growth direction and shape are dependent upon the grain size and grain orientations, and that the crack growth rate seems to be affected by the spacing of α‐rich and β‐rich bands. Small cracks are propagated at stress intensity factors well below the large crack threshold stress intensity factor.
Stress distribution ahead of an interface crack tip in a ductile adhesive layer
Authors: KANG K.‐J. , KIM D.‐H.
Published: March 2003

ABSTRACT In an adhesive layer sandwiched by stiff substrates, if the plastic zone size rp reaches several layer thicknesses ahead of the crack tip, the maximum stress develops around the region of x1=rp, and the stress level is even higher than the one predicted by the remote K‐field. The unusual high stress is due to the restraint of the plastic flow by adhesion with the substrates, which is similar to the ‘friction hill’ occurring in plane strain compression or tension. As a theoretical approach, a slip line field model is proposed, which provides a fairly good approximation of the stress distribution σ22
−
x1 within the plastic zone. Using the slip line field approach, a new model is proposed to estimate the plastic zone size.
High cycle fatigue mechanisms in a cast AM60B magnesium alloy
Authors: HORSTEMEYER M. F. , YANG N. , GALL K. , McDOWELL D. , FAN J. , GULLETT P.
Published: March 2003

ABSTRACT We examine micromechanisms of fatigue crack initiation and growth in a cast AM60B magnesium alloy by relating dendrite cell size and porosity under different strain amplitudes in high cycle fatigue conditions. Fatigue cracks formed at casting pores within the specimen and near the surface, depending on the relative pore sizes. When the pore that initiated the fatigue crack decreased from approximately 110 µm to 80 µm, the fatigue life increased two times. After initiation, the fatigue cracks grew through two distinct stages before final overload specimen failure. At low maximum crack tip driving forces (Kmax < 2.3 MPa√m), the fatigue crack propagated preferentially through the α‐Mg dendrite cells. At high maximum crack tip driving forces (Kmax > 2.3 MPa√m), the fatigue crack propagated primarily through the β‐Al12Mg17 particle laden interdendritic regions. Based on these observations, any proposed mechanism‐based fatigue model for cast Mg alloys must incorporate the change in growth mechanisms for different applied maximum stress intensity factors, in addition to the effect of pore size on the propensity to form a fatigue crack.
Fretting fatigue crack nucleation in Ti–6Al–4V
Authors: WALLACE J. M. , NEU R. W.
Published: March 2003

Fretting fatigue crack nucleation in Ti−6Al−4V when fretted against itself is investigated to determine the influence of contact pressure, stress amplitude, stress ratio, and contact geometry on the degradation process. For the test parameters considered in this investigation, a partial slip condition generally prevails. The resulting fatigue modifying factors are 0.53 or less. Cycles to crack nucleation, frictional force evolution, crack orientations and their relationship to the microstructure are reported. The crack nucleation process volume is of the same order as the microstructural length scales with several non‐dominant cracks penetrating 50 μm or less. The effective coefficient of friction increases during early part of fretting. Observations suggest that cyclic plastic deformation is extensive in the surface layers and that cyclic ratchetting of plastic strain may play a key role in nucleation of the fretting cracks. A Kitagawa–Takahashi diagram is used to relate the depth of fretting damage to the modifying factor on fatigue life.
Two‐stage fatigue loading of woven carbon fibre reinforced laminates
Authors: FOUND M. S. , QUARESIMIN M.
Published: March 2003

A brief review of the models used to predict the cumulative fatigue damage in FRP composites is presented. Two‐stage fatigue loading of a [0/90,± 452,0/90]s quasi‐ isotropic woven carbon fibre/epoxy resin laminate was evaluated at stress ratio R = 0.05 and the failure mechanisms investigated using x‐radiography after each loading stage. The results are presented in terms of fatigue strength and damage growth and are compared with those in the literature. A low‐to‐high loading sequence is more damaging than a high‐to‐low one and the Palmgren‐Miner linear damage rule may no longer be valid for this kind of material, as previously reported.
Effect of single and multiple overloading on the residual fatigue life of a structural steel
Authors: RAMOS M. S. , PEREIRA M. V. , DARWISH F. A. , MOTTA S. H. , CARNEIRO M. A.
Published: March 2003

This work was carried out to determine the effect of overload cycles on the fatigue life of a structural steel used for offshore applications. Single and multiple overloads were adopted and the corresponding fatigue crack growth retardation was evaluated. Residual stress fields were measured in the vicinity of the crack tip using an X‐ray diffraction technique and their size compared with that of the overload cyclic plastic zone. In regard to crack growth retardation, the results indicated that the extension in fatigue life increases with an increase in overload, as a consequence of the generation of higher compressive residual stress levels over a larger distance ahead of the crack tip. The effect of two equal and consecutive overloads, with the second one applied at different intervals of crack propagation from the first, was also considered. Larger intervals were shown to lead to a longer residual fatigue life.
Large‐scale patterns of host use by parasites of freshwater fishes
Authors: Poulin
Published: March 2003

Organisms that are abundant locally in a habitat patch are commonly observed to be frequent regionally, or among patches. In parasites, species present in high numbers in host individuals are also present in many individuals in the host population. On a larger scale, however, when host species are considered as patches, we may expect the opposite pattern because of the cost of producing mechanisms to evade the immune responses of several host species. Thus parasite species exploiting many host species may achieve lower average abundance in their hosts than parasite species exploiting fewer host species. This prediction was tested with data from 188 species of metazoan parasites of freshwater fish, using a comparative approach that controlled for study effort and phylogenetic influences. A negative correlation was found between the number of host species used by parasites and their average abundance in hosts, measured as either prevalence or intensity of infection. There was no evidence that parasite species fall into distinct categories based on abundance patterns, but rather that they fall along a continuum ranging from a generally low abundance in many host species, to a generally high abundance in few host species. These results applied to both ecto‐ and endoparasites. The pattern observed suggests the existence of a trade‐off between how many host species a parasite can exploit and how well it does on average in those hosts.
The role of stolon internodes for ramet survival after clone fragmentation in Potentilla anserina
Authors: Stuefer  , Huber
Published: March 2003

Stoloniferous herbs are common in disturbed habitats, where interconnected ramets frequently become separated by water, grazing animals or human activity. Stolon internodes serve as spacers and transport channels for resources, but they may also fulfil a storage function. We simulated physical disturbance and breakage of stolon connections in the stoloniferous herb Potentilla anserina, to test the hypothesis that juvenile ramets can survive clone fragmentation better if they remain attached to an internode after being severed from the rest of the clone. Juvenile, unrooted ramets were cut off from stolons with and without the preceding (basal) internode and placed on wet soil in a greenhouse. All ramets with an attached internode survived, while survival rates dropped to 37% for ramets from which internodes had been removed. The dry weight per unit volume of internodes decreased by about 20% during the experiment. We conclude that stolons are likely to fulfil a storage function that may be of ecological importance in disturbed habitats.
Linear analysis solves two puzzles in population dynamics: the route to extinction and extinction in coloured environments
Authors: Ripa  , Heino
Published: March 2003

In this paper, we give simple explanations to two unsolved puzzles that have emerged in recent theoretical studies in population dynamics. First, the tendency of some model populations to go extinct from high population densities, and second, the positive effect of autocorrelated environments on extinction risks for some model populations. Both phenomena are given general explanations by simple, linear, sto‐chastic models. We emphasize the predictive and explanatory power of such models.
The differing effects of interference on individuals of different rank
Authors: Ruxton G.D.
Published: March 2003

A widely studied ecological model considers the distribution of individuals of different competitive abilities between a number of resources, such that each opti‐mizes its reward rate. Recently this model has been criticised for making the predic‐tion that the reward rate of an individual can increase under some circumstances with increasing competitor number. The originators of the model have challenged the suggestion that this prediction is biologically implausible and challenged empiricists to test this prediction. Here it is shown that a previous study on hares is consistent with the controversial prediction of the original model, but not with that of an alternative formulation.
Apparent competition between parasitoids mediated by a shared hyperparasitoid
Authors: Van Nouhuys Saskya , Hanski Ilkka
Published: March 2003

Cocoons of the specialist parasitoidCotesia melitaearum, which attacks the Glanville fritillary butterfly in the Åland islands of SW Finland, are parasitized by the generalist hyperparasitoidGelis agilis. We added experimentally to the system a second host species forG. agilis,C. glomerata, with whichC. melitaearumdoes not compete for resources. After the one‐time addition of the second parasitoid the natural populations ofC. melitaearumdeclined in the treatment, as predicted by the apparent competition theory.
Smaller amphipod mothers show stronger trade‐offs between offspring size and number
Authors: Glazier Douglas S.
Published: March 2003

Trade‐offs between embryo mass and number were studied in 10 populations of the freshwater amphipod Gammarus minus. Trade‐offs were stronger in populations with small brooding females than in those with larger brooding females. Relationships between embryo mass and maternal body mass were also stronger in populations dominated by small versus large brooding females. These patterns are likely the result of morphological constraints, at least in part. Embryo size is more affected by brood size and maternal size in small mothers, probably because of offspring‐packaging constraints associated with small brood pouches. Energy constraints appear to be less important. These results suggest that body size may not only affect the magnitude of individual life‐history traits, as is well known, but also the covariance between traits.
The ecological and evolutionary significance of frost in the context of climate change
Authors: Inouye D.W.
Published: March 2003

The effects that below‐freezing temperature (frost) can have at times of year when it is unusual are an interesting ecological phenomenon that has received little attention. The physiological consequence of formation of ice crystals in plant tissue is often death of the plants, or at least of sensitive parts that can include flower buds, ovaries, and leaves. The loss of potential for sexual reproduction can have long‐lasting effects on the demography of annuals and long‐lived perennials, because the short‐term negative effects of frosts can result in longer‐term benefits through lowered populations of seed predators. The loss of host plants can have dramatic consequences for herbivores, even causing local extinctions, and the loss of just flowers can also affect populations of seed predators and their parasitoids. Frosts can cause local extinctions and influence the geographical distribution of some species. The potential for global climate change to influence the frequency and distribution of frost events is uncertain, but it seems likely that they may become more frequent in some areas and less frequent in others.
Causes of species diversity differences: a comparative analysis of Markov models
Authors: Wootton J.T.
Published: March 2003

While many dynamic processes have been proposed to produce diversity differences among communities, most empirical investigations focus on static system attributes. An ideal analysis would consider multiple dynamic processes and their impact on many community members, but such analyses can be logistically daunting. I compared Markov chain models of ecological communities to explore general processes leading to diversity differences of sessile species between coral reefs and rocky intertidal mussel beds. As predicted by diversity theory, high diversity coral reefs had lower species replacement probabilities and higher disturbance rates than did lower diversity mussel beds. Intransitivities in species replacements, recruitment limitation and responses to perturbing species from equilibrium (Jacobian elements) did not differ significantly between systems. Tradeoffs between the displacement risk or displacement ability of a species and either disturbance risk or colonising ability were not apparent. Manipulating the coral reef model to eliminate disturbance or intransitivities caused declines in species diversity, whereas removing recruitment limitation or increasing the probability of interspecific replacement did not. Higher overall disturbance levels can explain part of the diversity difference between systems, but much remained unexplained, indicating that details of the pattern and strengths of species interactions were probably extremely important.
Higher species diversity explained by stronger spatial aggregation across six neotropical Drosophila communities
Authors: Krijger  , Sevenster
Published: March 2003

Spatial aggregation of competitors over resource patches is generally accepted as an important mechanism maintaining coexistence of species in insect communities exploiting fragmented resources. However, its quantitative effects on local diversity, i.e. the relationship between the degree of aggregation in a community and community diversity, remain unexplored. In this paper, we tested whether stronger spatial aggregation does lead to the predicted higher local diversity. We compared six species‐rich Drosophila communities exploiting decaying fruits in central Panama, monitored over one full year (> 25 generations). We found a clear positive relationship between the overall degree of aggregation and community diversity. In addition, aggregation over fruit trees was found to contribute greatly to the overall degree of aggregation and was largely responsible for the observed relationship between aggregation and diversity across communities. In addition, both diversity and aggregation strength were lower in communities in disturbed habitats, which was explained by altered spatial distribution of fruiting trees. This study shows that the aggregation model cannot only explain coexistence, but also differences in local diversity.
The exploitation of mutualisms
Authors: Bronstein Judith L.
Published: March 2003

Mutualisms (interspecific cooperative interactions) are ubiquitously exploited by organisms that obtain the benefits mutualists offer, while delivering no benefits in return. The natural history of these exploiters is well‐described, but relatively little effort has yet been devoted to analysing their ecological or evolutionary significance for mutualism. Exploitation is not a unitary phenomenon, but a set of loosely related phenomena: exploiters may follow mixed strategies or pure strategies at either the species or individual level, may or may not be derived from mutualists, and may or may not inflict significant costs on mutualisms. The evolutionary implications of these different forms of exploitation, especially the threats they pose to the stability of mutualism, have as yet been minimally explored. Studies of this issue are usually framed in terms of a “temptation to defect” that generates a destabilizing conflict of interest between partners. I argue that this idea is in fact rather inappropriate for interpreting most observed forms of exploitation in mutualisms. I suggest several alternative and testable ideas for how mutualism can persist in the face of exploitation.