Moiré interferometry applied to fracture in titanium tubes

Despite there being a substantial body of evidence to the contrary, moiré interferometry is often regarded - even by some adherents - as a curiosity of the optics lab. The present work seeks to demonstrate still further that the method can be an effective tool for practical materials research and assessment, in this case, in a novel and challenging experimental application involving fracture testing of heat exchanger tube material, the work being conducted in a conventional materials test laboratory setting. The key to the utility of the present setup lies with the priority given to its optical efficiency. In standard fracture toughness tests, it is axiomatic that standard specimen geometries be used. A dilemma arises when a material's properties are transformed to a substantial degree by the final stages of its process of manufacture, and when the very nature of the finished form dictates that standard geometries cannot be produced. The focus of this investigation was to measure crack-tip opening displacements (CTODs) in thin-walled titanium tubes. Fringe patterns corresponding to in-plane displacement contours were obtained interferometrically and the method for extracting CTODs from these is described. Significant differences in yield, ultimate strength, elongation, and fracture behaviour were observed for different material orientations

Modified embedded-atom method interatomic potentials for the Mg-Al alloy system

We developed new modified embedded-atom method (MEAM) interatomic potentials for the Mg-Al alloy system using a first-principles method based on density functional theory (DFT). The materials parameters, such as the cohesive energy, equilibrium atomic volume, and bulk modulus, were used to determine the MEAM parameters. Face-centered cubic, hexagonal close packed, and cubic rock salt structures were used as the reference structures for Al, Mg, and MgAl, respectively. The applicability of the new MEAM potentials to atomistic simulations for investigating Mg-Al alloys was demonstrated by performing simulations on Mg and Al atoms in a variety of geometries. The new MEAM potentials were used to calculate the adsorption energies of Al and Mg atoms on Al (111) and Mg (0001) surfaces. The formation energies and geometries of various point defects, such as vacancies, interstitial defects and substitutional defects, were also calculated. We found that the new MEAM potentials give a better overall agreement with DFT calculations and experiments when compared against the previously published MEAM potentials.Comment: Fixed a referenc

Fatigue testing of a proximal femoral hip component

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Microstructural and strength study of MIG welded joints of AW7020 aluminium alloy, as a function of joint geometry

[EN] Medium strength AW7XXX aluminium alloys are widely used as welded structures and in transportation. The applications of these alloys are limited by the behaviour of the welded joints. There is no agreement on the joint geometry that must be used on 5 mm welds. The microhardness evolution is one of the most important strength indicators. For this reason, the aim of this work is to study the influence of welded joint geometry on microhardness profile and on the microstructure of a MIG welded AW7020 aluminium alloy, using AW5256 filler.Bloem, C.; Salvador Moya, MD.; Amigó, V.; Vicente-Escuder, Á. (2000). Microstructural and strength study of MIG welded joints of AW7020 aluminium alloy, as a function of joint geometry. Welding International. 14(12):970-974. doi:10.1080/09507110009549300S970974141

Strength-ductility behaviour of Al-Si-Cu-Mg casting alloys in T6 temper

A comparative study of the mechanical properties of 20 experimental alloys has been carried out. The effect of different contents of Si, Cu, Mg, Fe and Mn, as well as solidification rate, has been assessed using a strength-ductility chart and a quality index-strength chart developed for the alloys. The charts show that the strength generally increases and the ductility decreases with an increasing content of Cu and Mg. Increased Fe (at Fe/Mn ratio 0.5) dramatically lowers the ductility and strength of low Si alloys. Increased Si content generally increases the strength and the ductility. The increase in ductility with increased Si is particularly significant when the Fe content is high. The charts are used to show that the cracking of second phase particles imposes a limit to the maximum achievable strength by limiting the ductility of strong alloys. The (Cu + Mg) content (at.%), which determines the precipitation strengthening and the volume fraction of Cu-rich and Mg-rich intermetallics, can be used to select the alloys for given strength and ductility, provided the Fe content stays below the Si-dependent critical level for the formation of pre-eutectic alpha-phase particles or beta-phase plates

Focus on the management of thunderclap headache: from nosography to treatment

Thunderclap headache (TCH) is an excruciating headache characterized by a very sudden onset. Recognition and accurate diagnosis of TCH are important in order to rule out the various, serious underlying brain disorders that, in a high percentage of cases, are the real cause of the headache. Primary TCH, which may recur intermittently and generally has a spontaneous, benign evolution, can thus be diagnosed only when all other potential underlying causes have been excluded through accurate diagnostic work up. In this review, we focus on the management of TCH, paying particular attention to the diagnostic work up and treatment of the condition