A cylindrical butt joint is widely utilised in bi-materials structures. Numerous examples can be found in micro-electronics, medicine and composite areas. Such bi-material structures normally have a very strong stress concentration at the interface, which often characterised by linear solutions of the theory of elasticity leading to the appearance of stress singularities. These singular solutions play a very important role in failure assessment of such joints by fracture mechanics approaches. In this paper we develop a compact solution for the generalized stress intensity factor at the interface of a cylindrical bi-material joint loaded by remote tensile loading parallel to the axis of symmetry. Based on a careful numerical modelling, a simple equation maintaining simplicity and accuracy over the wide range of problem's variables is suggested. Furthermore, the existence of scale effect on the interface corner stress intensity factor for a cylindrical butt joint structure is also discussed in detail.

The paper deals with the buckling instability of long interface cracks subjected to shear and tensile (compressive) loading parallel to the interface. A simplified mathematical model is developed within the Kirchhoff's plate bending theory; and a general semi-analytical solution is obtained based on the classical strategy for solving for the Euler buckling load. Asymptotic solutions are derived for extreme cases of the applied shear to tensile (compressive) load ratios. The obtained results correlate well with previous numerical studies and can be used to analyze many traditional problems in composite as well as many others, for example, the problem of triggering snow avalanches.

The concept of a stress singularity is a cornerstone of modern fracture mechanics. A new mode of stress singularity, the out-of-plane singular mode or K (O) mode, was recently identified for V-shaped notches subjected to in-plane loading. This new mode is coupled with the shear mode and related to Poisson's effect. The previous studies based on the first order plate theory focused on the derivation of a characteristic equation describing the strength of this singularity and provide no information regarding the intensity, extent and relevance of this mode to practical problems. This paper aims to fill this gap. The approach utilises the 3D finite element method and a standard regression technique for characterisation of the notch singular modes. A comprehensive study of the influence of Poisson's ratio, plate thickness and notch opening angle on the value of the notch stress intensity factor associated with this mode is conducted for infinite plates. Additionally, to demonstrate the relevance of this new singular mode to practical problems an investigation of the out-of-plane mode and associated three-dimensional effects are presented for the case of a welded lap joint. Main areas of further research are also identified.

When a crack or sharp notch is subjected to antisymmetric plane loading the Poisson's effect leads to the generation of a coupled out-of-plane singular mode. The latter was known to exist for problems with cracks for a long period of time; meanwhile this mode was largely ignored in theoretical studies of V-shaped notches subjected to in-plane loading as well as in practical fracture problems associated with such geometries. Only recently a characteristic equation describing the strength of the singularity of this mode was derived within the first order plate theory. Preliminary numerical investigations confirmed that a highly localized out-of-plane singular state linked to the transverse shear stress components does exist in the close vicinity of the notch tip with the singular behaviour as theoretically predicted. However, until now it is unclear how significant this mode is and whether it has to be taken into consideration in the stress analysis of engineering structures. This paper is aimed to discuss important features of this recently identified singular mode, out-of-plane singular mode, conduct a comprehensive three-dimensional numerical study of a typical problem of a welded lap joint to investigate the contribution of this mode into the overall stress state in the close vicinity of the notch tip and discuss the implementation of these new results to the failure and integrity assessment of plate structures with sharp notches.

This paper summarizes recent studies in the area and discusses some important features of the three-dimensional solutions for through-the-thickness cracks in elastic plates. In particular, the current work indicates that very thick plates must be treated with caution because within such plates a very strong presence of the out-of-plane singular mode may exist, which can significantly influence the fracture conditions.

Water-lubricated journal bearings are widely utilised in many engineering applications, especially in marine engineering. For example, the water-lubricated bearings are used as aft bearings to support the main drive shafts of ships and submarines. Water-lubricated friction conditions are also common for drilling, tooling operations and other engineering applications. The characteristics of water-lubricated systems are greatly affected by the bearing pressure, temperature, surface conditions and contamination. For example, severe contamination conditions in aft bearings of ships can lead to excessive wear, higher friction coefficients and excitation of self-induced low frequency oscillations, which negatively influence the performance and effectiveness of the ships and submarines leading to expensive maintenance and down time. This paper presents details of experimental rigs, designed and constructed to investigate the effect of the above parameters on the characteristics of a water-lubricated system. It also discusses the results of preliminary tests conducted to identify and quantify the main contributing factors to wear and friction. In addition, special attention is paid to the determination of the conditions, which could lead to the generation of self-induced low frequency oscillations.

Plane theory of elasticity lays a foundation for many important results in science and engineering. However, the understanding of the elastic solutions derived under plane stress or plane strain assumption, is far from complete. In particular, it is not clear how adequate the classical two-dimensional solutions of the plane theory of elasticity are when applied to the analysis of actual plate components having a finite thickness. So far there is no generally accepted criterion for identifying what thickness would qualify as plane stress or plane strain and, in general, what effect on the stress distribution the plate thickness has. In this work we review some recent analytical efforts, numerical and experimental studies in order to throw light onto how the plate thickness, which is largely ignored by the classical plane solutions of the theory of elasticity, influences the elastic deformation and quasi-brittle fracture of plate components.

Plane theories of elasticity are the theoretical foundation of many important developments in engineering. However, the understanding of the elastic solutions derived under plane stress or plane strain assumption, is rather far from complete. In particular, it is not clear how adequate the classical two-dimensional solutions of the plane theories of elasticity are when applied to the analysis of actual plate components made of sufficiently brittle material and having a finite thickness. So far there is no generally accepted criterion for identifying what thickness would qualify for plane-stress or plane-strain states and, in general, what effect on the stress distribution the plate thickness has. In this work we make an attempt to review some recent numerical studies and analytical efforts in order to throw light on this problem.

This paper summarizes recent theoretical studies on the three-dimensional singular stress state at sharp notches in infinite (or large) plates of finite thickness subjected to in-plane loading. In general, such loading produces a number of singular states: in-plane singularities (normally described as KI and KII fracture modes and known as Williams’ solution), singular states associated with corners and the out-of-plane singularity (KO mode), which is generated due to the Poisson’s effect. The latter mode has an interesting behavior and its intensity increases as a power function with the increase of the plate thickness when the notch is stresses in shear mode. From finite fracture mechanics considerations it is clear that at some certain thickness the out-of-plane singular mode will dominate over the fracture zone and with the further increase of the plate thickness will affect the strength of the notched plate, virtually reducing it to zero.

Sommario Il criterio della densità di energia di deformazione (SED) considera un preciso volume di controllo posizionato in corrispondenza del piede o della radice dei cordoni di saldatura, che rappresentano le zone di possibile innesco delle cricche di fatica. Modellati i cordoni come intagli a V non raccordati e con diverso angolo di apertura, il volume è riconducibile a un settore circolare nei casi di tensione o deformazione piana e il raggio vale circa 0.3 mm per i giunti saldati in acciaio strutturale. Il valore medio della densità di energia di deformazione dipende essenzialmente dalle distribuzioni singolari nei giunti di medio ed elevato spessore, mentre importante diventa il contributo della T-stress nei giunti di spessore ridotto. Entrambi gli effetti sono correttamente computati utilizzando modelli agli elementi finiti, anche utilizzando mesh con un numero ridotto di gradi di libertà. Agli effetti descritti, tipicamente riconducibili a una soluzione teorica di Williams, si possono accompagnare campi singolari non convenzionali, legati a effetti tridimensionali indotti dalla geometria. L'effetto out-of-plane, recentemente formalizzato da Koutosov, è qui discusso in relazione ai giunti a semplice sovrapposizione. Abstract In the application of the Strain Energy Density (SED) approach for fatigue strength assessments of welded joints a well-defined control volume is considered. This volume surrounds the weld root or weld toe, both modelled like sharp (zero radius) V-notches with different opening angles. The volume becomes a circular sector under plane strain conditions, with the radius being about 0.3 mm for welded joints made of structural steel. The mean value of the SED mainly depends on the singular stress fields when the main plate thickness is large enough, whereas the influence of the T-stress component cannot be neglected in the case of thin-walled welded joints. Both contributions are directly accounted for by using finite element models, also when the relevant meshes are quite coarse. This fact makes the application of the SED approach easier than any stress-based approach in the case of complex structures. Due to three-dimensional effects, a non conventional out-of-plane singular mode can be present, in addition to mode I and mode II stress singularities according to Williams' solution. This out-of-plane mode, which has recently been presented by Kotousov, is discussed here with reference to welded (seam) lap joints under tensile- shear loads. Parole chiave: Campi asintotici, Fattori di intensificazione delle tensioni, Out-of-plane mode, densità di energia di deformazione

Thermal barrier coatings were introduced to reduce operating temperatures and thermal stresses in structures and machine components across a wide range of industries and applications. The focus of the present study is to develop a new, relatively simple and low cost technique of manufacturing thermal barrier coatings based upon the slurry spray method. The challenge of this work is to make this technique comparable, in terms of the quality of the coating, to existing manufacturing methods, which are often expensive and inapplicable to coat large or curved surfaces. This paper describes the developed technique and selected results of thermo-mechanical testing of fabricated coatings including functionally graded coatings.

: A feasibility study of a relatively simple and economical method for producing functionally graded thermal barrier coatings using the Wet Powder (Slurry) and Sintering method showed promising results. This method is relatively undeveloped and under utilised compared to more expensive techniques such as chemical vapour deposition, physical vapour deposition, plasma spraying and powder metallurgy. It utilizes a pressurized spray gun to spray a slurry mixture of the powdered coating material suspended in a liquid solution directly onto a substrate surface followed by sintering using an oxyacetylene torch. The effects of slurry composition, type of ceramic powder, compatibility with substrates, spraying and sintering conditions were studied. Several TBC specimens have been fabricated under various conditions to develop a procedure which produce good quality coatings (of up to 3 layers) with little or no spallation. The optimum time, heat flux and applied pressure level for sintering were deduced. TBCs produced from a 40-45% ceramic, 4% binder and 0.4% dispersant composition and sintered for 30 minutes with an applied pressure of 30 MPa produced good quality coatings with a uniform and very smooth surface. Scanning electron micrographs of the fabricated TBC coatings showed good contact between the grain boundaries of the ceramic powder. In phase 2 of this project, the Wet Powder and Sintering method will be further developed. Improvements to this method include automating the sintering procedure and optimizing the fabrication conditions. A much more extensive micromechanical testing program will be conducted to obtain a more qualitative measure of the quality of the FGM thermal barrier coatings and to develop high temperature constitutive models for input into the FE modeling.

The paper investigates the buckling mode of failure of long interfacial cracks subjected to shear loading. A criterion which describes the transition from fracture to buckling instability failure modes is derived.

Placenta accreta is a rare complication of human placentation with fertility and life‐threatening sequelae. Traditional management has centred upon hysterectomy and its prompt undertaking has been well documented in saving lives. While in many situations hysterectomy will remain appropriate, there are other management options available involving conservative approaches. This article reviews the diagnosis and demographics of this potentially frightening pathology and highlights the important aspects of conservative management if hysterectomy is to be avoided.

BACKGROUND:Concomitant with the increase in Caesarean birth over the past three decades there has been an apparent rise in the incidence of placenta accreta and its variants. The sequelae of an increase in the occurrence of abnormal placentation is the enhanced potential for severe maternal morbidity.AIM:To determine the contempory demographics of placenta accreta over a 5-year period in a tertiary level teaching hospital.METHODS:A retrospective review of all cases of placenta accreta and variants during the period of 1998-2002. Individual charts review followed case ascertainment via the hospital obstetric database.RESULTS:Thirty-two women with placenta accreta (or variant) were identified. Median maternal age was 34 years, with a median parity of 2.5. Seventy-eight percent of cases had had at least one prior Caesarean birth, and 88% of cases were associated with placenta praevia. Pre-delivery ultrasonography was performed in all cases, providing diagnostic sensitivity of 63% and specificity of 43% with a predictive value of 76%. Hysterectomy was performed in 91% of cases with median intraoperative blood loss of 3000 mL. There were no maternal deaths in the current series.CONCLUSION:A strong association between placenta accreta, placenta praevia and prior Caesarean birth has been demonstrated. As there is the potential for significant maternal morbidity the risk of placenta accreta needs to be recognised and women at risk should be considered for delivery at an institution with appropriate expertise and resources in managing this condition.