Microstructural evolution and texture analysis of magnesium phosphate cement

Three-dimensional quantitative image analysis from synchrotron X-ray microcomputed tomography indicated a coarsening of the microstructure of magnesium potassium phosphate cements driven by crystallization of K-struvite from the first amorphous product. Porosity and pore surface area increased because of the progressive build-up of a network of elongated/tabular crystal domains, with density higher than the amorphous. The known increase in strength with time is thought to occur thanks to the overwhelming contribution of a developing interlocked lath-shaped microstructure. Combined X-ray and neutron diffraction texture analysis indicated that at least a fraction of K-struvite nucleates at the surface of MgO grains, suggesting the intervention of more than one crystallization mechanism. The detected weak texture, compatible with a nearly random orientation of crystallites, and the isotropic pore fabric, are beneficial with respect to crack propagation.     

Impact of interfacial stresses distribution of structures reinforced by composites FRP: new model of the laminate layers

This work allows us to determine the interfacial stresses concentrations which are the cause of the debonding phenomenon in the structures strengthened by composites fiber-reinforced plastic (FRP). This method permits to replace the classic techniques based on welding and bolting the elements of the structure that give stresses concentrations to the level of the assembly zone. The technique of reinforcement by patches in composites gives more resistance and rigidity, but it can give stresses concentrations to the edges of the reinforcement zone which can exceed the ultimate loads of the structure and cause failures. In this work, an original interfacial stress theory is developed between the structure and the composite (FRP) and has finalized, taking into account, the mechanical and thermal loads coupled with the shear lag effects. This original method carried out the terms neglected by the previous studies, such as shear lag effect of structure and composites, and thermal load coupled with the model of mechanical and fiber orientation effect. The geometrical and physical parameters taken into account play an important role in the stresses values concentration and thus the phenomenon of delamination     

Effect of thermomechanical loads on the propagation of crack near the interface brittle/ductile

The purpose of this paper is to understand the combined effect of thermal and mechanical loading on the initiation and behaviour of sub-interface crack in the ceramic. In this study a 2D finite element model has been used to simulated mixed mode crack propagation near the bimaterial interface. The assembly ceramometalic is subjected simultaneously to thermomechanical stress field. The extent of a plastic zone deformation in the vicinity of the crack-tip has a significant influence on the rate of its propagation. The crack growth at the joint specimen under four-point bending (4PB) loading and the influence of residual stresses was also evaluated by the maximum tensile stress criterion. The J-integral at the crack tip is generally expressed by the thermomechanical local stresses. The results obtained show the effect of the temperature gradient ΔT, the size of the crack and the applied stresses on the J-integral.     

Effect of humidity absorption by the adhesive on the performances of bonded composite repairs in aircraft structures

In this study, an experimental work was done to analyse the effect of the humidity absorption on the mechanical properties of the adhesive Adekit A140 epoxy. The measured properties were introduced in a finite element model in order to analyse the effects of the humidity absorption on the performances of bonded composites repair in aircraft structures by computing the J integral around the crack tip and the distribution of the adhesive shear stresses. The obtained results show that the adhesive losses its rigidity by the humidity absorption which reduce the repair efficiency but increases the repair durability.     

Evolutionary computation approaches to the Curriculum Sequencing problem

Within the field of e-Learning, a learning path represents a match between a learner profile and his preferences from one side, and the learning content presentation and the pedagogical requirements from the other side. The Curriculum Sequencing problem (CS) concerns the dynamic generation of a personal optimal learning path for a learner. This problem has gained an increased research interest in the last decade, as it is not possible to have a single learning path that suits every learner in the widely heterogeneous e-Learning environment. Since this problem is NP-hard, heuristics and meta-heuristics are usually used to approximate its solutions, in particular Evolutionary Computation approaches (EC). In this paper, a review of recent developments in the application of EC approaches to the CS problem is presented. A classification of these approaches is provided with emphasis on the tools necessary for facilitating learning content reusability and automated sequencing.     

Le glissement de terrain d’Ain El Hammam (Algerie): causes et evolution

Some natural slopes are or may become unstable. Instabilities are one of the most difficult problems of engineering geology. The difficulty arises because the estimate of the stability of a site depends on several factors that often interact simultaneously. To better analyze the landslide of Ain El Hammam, these factors were set into two broad categories (passive and active factors). The factors include the liabilities related to geological causes, to the geomorphology and to the hydrology of the site. The structure of the slope is conducive to landslides; the encountered formations are often altered and cracked. They are characterized by a dip and schistosity endorsements favoring the displacement of the layers and also by an alternation of shallow soils and other resistant layers as we go deeper. Tests results show that the geological formations encountered in this area have favorable characteristics to landslides. The mineralogical study shows that the shale rock has reached an advanced weathering and very low content of quartz makes little resistance. The morphological nature of this slope also affects considerably the instability, the steep slope of the site, the nature of the geological formations encountered and the high density of cracks make it vulnerable with regard to this phenomenon. The hydrology has an important role in the erosion and weathering of unstable slopes and on the initiation and activity of the movement. The active factors include climate measures, anthropogenic factors and the effect of seismicity in this region. An important link between the activity of movement and changes in climatic conditions has been observed for this instability. Two basic types of actions have been identified: the action of heavy rainfall and the action of snow cover. Human activity has also contributed to the emergence and evolution of this instability. We have noticed essentially the following effects: the effect of the significant overhead of the head of the unstable slope, the effect of the removal of drainage systems and the role of sewerage not connected flowing directly into the unstable slope. The seismicity of this region also plays an important role and its effects must be evaluated and taken care of in the study of this landslide. The landslide affects a formation of Shale (shale satin) frequently altered and cracked. The structure of this movement and deformation mechanisms induced are very complex. It is a multitude of overlapping and nested ruptures forming a global instability of the slope. Six sliding surfaces were determined on a longitudinal slope (profile EE); some are superficial and others are deep. The observed maximum depth of rupture is greater than 75?m. However, the presence of other sliding surfaces and more complex mechanisms which could not be determined at this stage of the study is not excluded. This shift is characterized by a very active movement extending over a large area and phases of calm and activation (accelerations of movement). The movement is changing both laterally and in depth. Four stages of evolution have been observed for this ground movement (period 1969–2005, the period of 2005–2008, the period from 2008 to April 2009 and the period from May 2009 to March 2011). However, its movement often gives rise to new shallow sliding surfaces (superficial to less deeper) in the basin. Predicting the future behavior of the slope is difficult, the mechanisms are generally poorly known and difficult to understand and model. Knowledge of factors leading to instability is essential in predicting disorders.     

Semi-analytical calculation of the impedance of a differential sensor for eddy current non-destructive testing

In this contribution, we aim at the modelling of the impedance of a differential sensor in eddy-current non-destructive testing. This mode of control is very common in the detection of abrupt geometrical and electromagnetic variations, disturbances generated by slow variations of dimensions and temperature being in particular not observed. We develop a direct semi-analytical model of a voltage-excited system. The formulation is based upon the use of coupled electric circuits. It provides a particular form of the differential impedance, which clarifies the role of the electromagnetic and geometric characteristics. This form of impedance will allow the investigation of non-destructive testing by means of differential sensors and will facilitate the development of real-time inversion procedures. The model is validated by results published in the literature. We exploit it in order to study various electric and geometrical parameters of the control system.     

A Combined Analysis of Laser Optogalvanic and Fourier Transform Emission Spectra of NH2 near its Barrier to Linearity

The ?2A1-&Xtilde;2B1 electronic transition of NH2 is reinvestigated in the region of its barrier to linearity. A detailed rotational analysis is performed on its laser optogalvanic spectrum recorded in the region 11 300-14 300 cm-1 and on its near infrared Fourier transform emission spectrum. Many new excited levels are identified resulting from more than 2900 assigned lines. A number of them are high levels of &Xtilde;2B1. A set of molecular parameters has been obtained. Numerous perturbations are detected and discussed. This analysis confirms the predictions obtained from previous calculations and allows the estimation of their accuracy. Copyright 1999 Academic Press.     

Study of the inhibition of the corrosion of iron steel in neutral solution by electrochemical techniques and theoritical calculations

The effect of triazole organic molecules (triazole thiol and amino triazole) containing heteroatoms such as nitrogen or sulfur on the corrosion behavior of iron was investigated. Electrochemical studies of the iron samples were performed in an aerated solution of NaCl (3%) by means of electrochemical impedance spectroscopy (EIS) as well as polarisation curves. These results are completed with theoretical calculations, which allow determining the possible anchoring site suitable for bonding.     

A New Coupled Solution for Interfacial Stresses Analysis in a Repaired Beam with an Adhesively Bonded Prestressed FRP Plate

This paper focuses on a new coupling solution for determining the elastic interfacial shear and normal stresses in an adhesive joint between a strengthening plate and a simply supported beam. The mismatch of the curvatures in the beam and plate is considered by including both the effect of the adherend shear deformations and the prestressed laminates model. This new method leads to the coupling of governing differential equations for the interfacial shear and normal stresses. Most of the other solutions in the literature assume that the beam and plate have an equal curvature to uncouple this effect. In this paper, however, a solution is presented to calculate the interfacial stresses of beams strengthened with a prestressed composite plate having a new rigidity model coupled with the shear lag effect, which are neglected by the previous studies. It is found that the present method can predict accurately stresses in the interior and near the ends of the adhesive layer, where the stress fields can be significantly influenced by the edge effects. A parametric study was carried out to show how the stress concentration and distribution are influenced by the dimensions of the adherends and the material properties of the strengthened beam.