Search results

Friction stir welding (FSW) is simple, clean and cost effective joining technology which allows high‐quality joining of materials that have been traditionally troublesome to weld conventionally without distortion, cracks or voids such as high‐strength aluminium alloys. Since FSW has been identified as “key technology” for primary aerospace structures, the recent FAR regulations for damage tolerance and fatigue evaluations of aircraft structures require fatigue life predictions for this specific joint type also in the presence of corrosion. The purpose of this paper is to give an overview of the prediction of small coupon fatigue lives of thin section friction stir welded butt and T‐joints.

Particularly, as a special application, widespread fracture mechanics software will be used to predict the fatigue life of FSW joints and to obtain SN curves. The engineering approach will start from an easy definition of the damage affecting the fatigue life of any of the previously mentioned cases (inclusions, tool markings, corrosion pits) and will move through affordable fracture mechanics solutions. Particularly, a first step in predicting the fatigue life of complex friction stir welded structures will be taken by combining the FEM code with the fracture mechanics software in the prediction of the FSW T‐joints.

The calculations are in very good agreement with the experimental results once the following basic assumptions are done: the welded material is treated as base material; particle inclusions and welding imperfections are treated as initial flaws while predicting the life of polished and un‐polished (including the T‐joints) FSW material, respectively, and the entire fatigue life was comprised of crack propagation; pitting and inter‐granular corrosion are treated as a single corrosion damage source and the model surface crack comprehends this damage; and the several corrosion‐damaged areas of the specimen surface are simulated with a single semi elliptical surface crack having the dimensions of the deepest and the widest corrosion damage area.

A simple engineering approach which is based on a relatively solid background and which is checked against fatigue test data for various FSW test specimens was developed: it may provide a practical and reliable basis for the analysis of fatigue tests of integral structures in the presence of corrosion attack, by using widespread fracture mechanics principles.

The purpose of this paper is to consider an approximate model of accumulation of microdefects in a material under repeated loading which makes it possible to define theoretical parameters of the fatigue failure (durability, fatigue limit, etc.). The model is involving the relevant law of distribution of ultimate (yield) stresses in the material of these members in combination with the basic characteristics of main mechanical properties of a material (ultimate and yield stresses and associated standard deviations).

The model of fatigue failure of brittle and elastoplastic materials based on the use of the structural-probabilistic approach and up-to-date ideas on the mechanism of material fracture is proposed. The model combines statistical fracture criteria, which are expressed in terms of damage concentrations, with the approximate model of microcrack accumulation under repeating loading of the same level. According to these criteria, the fatigue failure begins with the accumulation of separation- or shear-type microdefects up to the level of critical values of their density.

The failure mechanism is associated with the accumulation of dispersed microdamages under repeated loading. The critical value of the density of the microdamages, which are identified with those formed either by separation or shear under static loading in consequence of simple tension, compression or shear, is accepted as the criterion of the onset of fatigue failure. The fatigue being low-cycle or high-cycle is attributed to accumulation of shear microdamages in the region of plastic deformation in the former case and microdamages produced by separation under elastic deformation in the latter one.

The originality of the paper consists in the following. The authors theoretically define parameters of the fatigue failure (durability, fatigue limit, etc.) using the model in combination with the statistical failure (yield) criteria appearing in the damage measures. The constructed fatigue diagram has discontinuities on the conditional boundary dividing domains with the shear-type and separation-type fractures of structural elements. Such results are supported by the experimental results.

This paper addresses important technical problems related with methodological limitations of welding project methods currently adopted, mostly regarding numerical modelling procedure of welding processes. The progress in high nano‐technologies give rise to the same approaches to be applied in traditional mechanics and material science, really concerning welding processes using various methods and techniques. Recent investigations of welded joints have shown the benefits related to the employment of neutron techniques, to obtain substantial information advancing quality and durability that cannot be found by using other means. Small Angle Neutron Scattering (SANS) and Neutron Diffraction (ND), in particular, consent materials characterization at atomic and nanoscale level, offering to the existing technologies the essential contribution of precise structural methods. The basic theoretical aspects are described, and some SANS investigations of weldments are reported. An experimental programme has been recently projected to develop welding processes, with quality assurance improvement, safety enhancement, life‐time management and cost effectiveness of the considered joints.

Recent studies show that Italian women’s education and skills are high and that they have access to the job market, but, at the same time, there are many difficulties in maintaining a job in certain periods of their lives. Exactly, the critic period is connected to the choice of having children or a “traditional family” and, in general, with family duties. To explain the different percentage of women participation to job market in different countries, recent studies have looked to peculiar institutional structure of “municipal” job market and to social support services. The public offer of childcare and family support explains lots of the differences among different countries, but it is a complex datum, really hard to detect, collect, and interpret. Other relevant data are statute provisions on parental leave (mother or father oriented). A systematic analysis has shown that we have, both at a national and at a European level, legal rules and models which should promote equal opportunities, but that we miss cultural promises going in the direction of supporting families and encouraging the preservation of female job place. This study also investigates two different kinds of answers, analyzing and comparing microchoices (technical and juridical instruments) and macrochoices (legal policies) that different legal systems, have adopted in the European context to promote an effective integration between lifetime and job time, to support families in terms of public services, and suggest possible new instruments connected with partnership of public and private programs.¹

This study aims to introduce a novel approach in form of a comprehensive software suite to help understanding and optimizing the build orientation toward maximizing the fatigue lifetime of complex geometries. The objective is to find an optimized build orientation under a given in-service loading state, which brings on smoother surfaces in stressed regions, mitigated roughness-induced stress concentration and deferred crack initiation stage. The solution addresses scenarios that no post-build surface treatment can be applied.

To account for the surface topography, the staircase induced surface roughness is registered as a function of build angle using the white light interferometry characterization, based on which the stress concentration factor (k_t) is calculated. Thereafter, the developed module in “Fatlab toolbox” is used to find the optimum build angle, considering the integrated surface orientations and stress analysis under a given loading condition.

Surface topography creates local stress concentrations upon loading, directly influencing the fatigue lifetime. It is a well-established fact that the conditions of the staircase geometry and surface roughness affect the magnitude of the stress concentration upon loading, which is influenced by the build orientation of the component. The proposed solution suggests the best build orientation that mitigates staircase-related surface roughness.

The suggested numerical approach assists the designers with positioning of the part on the build plate to minimize the build orientation-induced surface roughness and improve the as-built fatigue lifetime of the component.

A theoretical study is performed to investigate turbulent flow and heat transfer characteristics in a concentric annulus with a heated inner cylinder moving in the direction of flow (Couette flow). The two‐equation k‐ε model is employed to determine turbulent viscosity and kinetic energy. The Reynolds stress and turbulent heat flux are expressed by Boussinesq’s approximation. The governing boundary‐layer equations are discretized by means of a control volume finite‐difference technique and numerically solved using a marching procedure. Results are obtained for the time‐averaged streamwise velocity profile, turbulent kinetic energy profile, friction factor, and Nusselt number. These results agree well with experimental data in the existing literature. It is concluded from the study that the streamwise movement of the inner wall induces an attenuation in the turbulent kinetic energy, resulting in a reduction in the heat transfer performance and an increase in the velocity ratio of the moving inner cylinder to the fluid flow causes a substantial decrease in both the friction factor and the Nusselt number as well as a drastic reduction in the turbulent kinetic energy in the inner wall region.

Looks at the first 100 years of Italian cinema examining its role in Italy’s recent history. Provides a bibliography of major film directors, Italian cinema sources, reference works, histories, themes, theory and criticism and articles in journals.

AIEST Les préparatifs du 30e Congrès AIEST du 14 au 20 septembre 1980 à l'Hôtel Son Vida, Palma de Mallorca, sont de façon que le programme définitif a pu être envoyé aux membres début juin, après un rappel de faire parvenir des contributions écrites touchant le sujet principal «Limites du développement touristique» pour être publié dans la publication du Congrès. Celle‐ci sera envoyée aux membres avant le Congrès.

A numerical study is performed to investigate turbulent Couette flow and heat transfer characteristics in concentric annuli with a slightly heated inner cylinder moving in the flow direction. A two‐equation k‐ε turbulence model is employed to determine the turbulent viscosity and the turbulent kinetic energy. The turbulent heat flux is expressed by Boussinesq approximation in which the eddy diffusivity for heat is given as functions of the temperature variance t^2‐ and the dissipation rate of temperature fluctuations ε_t, together with k and ε. The governing boundary‐layer equations are discretized by means of control volume finite‐difference technique and numerically solved using a marching procedure. It is disclosed from the study that the streamwise movement of the inner core causes substantial reductions in the turbulent kinetic energy and the temperature variance, particularly near the inner wall region, resulting in the deterioration of the Nusselt number, and that an attenuation in heat transfer performance is induced by the velocity ratio of the moving inner cylinder to the fluid flow.