Liste des documents
Experimental and Numerical Study of Polypropylene Composite Reinforced with Jute Fibers
This paper is devoted to the study of the mechanical response of polypropylene (PP) thermoplastic composite reinforced with jute fibers. In order to use these composites in structural applications it is necessary to understand the mechanisms governing their mechanical behavior and damage. For this purpose, we have fabricated two kinds of PP/jute laminates: [0°/90°]2S and [+45/-45°]2S with the fibers direction, using the molding technique under compression. The mechanical properties of the material are then characterized by tensile and compressive tests. The numerical part of this work concerns the incorporation of the Matzenmiller, Lubliner, and Taylor (MLT) damage model to take into account the post-elastic-peak and the post-peak strain softening responses observed in the PP/jute composite. This is possible by using formulation with two criterions. The 3D constitutive law has been implemented into the finite code Abaqus using an explicit scheme. In order to assess the capability of this model to describe the material behavior, comparisons are made between numerical and experimental results. Excellent agreements are found between numerical predictions and experimental observations. The model also captures correctly the zones where damage occurs in the two kinds of laminates. Voir les détails
Mots clés : PP/jute, mechanical behavior, damage, laminate, modeling
Inspection of laminated composite materials by two ultrasonic techniques
This paper presents some ultrasonic methods to detect and to characterize defects, possibly obtained after damage caused in composite materials. Firstly, artificial defects are located by two piezoelectric transducers. A two-dimensional ultrasonic cartography C-scan, performed section by section, at different positions which took part through the thickness of acarbon fiber-reinforced plastic composite beam, to be analyzed. Next, fundamental symmetric S0 mode of Lamb waves is used to measure the size of the delamination by scanning over the surface beneath which a delamination lies. A remarkable decrease in the arrival time due to the delamination is detected, and the delamination length can be calculated based on a simple model for Lamb-wave propagation. Furthermore, the delamination edge is located as a sudden decrease in the amplitude. The rate of decrease in amplitude of an individual pulse cycle was detected to vary with the depth of the delamination, being most sensitive to delaminations near the surface of the plate. This is particularly useful when sizing for defects close to the surface, where a normal-incidence pulse-echo ultrasonic method has problems, particularly when the depth of the defect or the back-wall echoes lie within the length of the transmitted ultrasonic pulse. The technique has potential for faster c-scanning of a complete plate than the usual normal-incidence pulse-echo method. Voir les détails
Mots clés : Ultrasonic C-scan, laminate plate, delamination, Lamb wave
Wavelet Transform for Bearing Faults Diagnosis
Fault diagnosis is useful for ensuring the safe running of machines. Vibration analysis is one of the most important techniques for fault diagnosis of rotating machinery; as the vibration signal carries the dynamic information of the system. Many signal analysis methods are able to extract useful information from vibration data. In the present work, we are interested to the vibration signal analysis by the wavelet transform. The monitoring results indicate that the wavelet transform can diagnose the abnormal change in the measured data. Voir les détails
Mots clés : fault diagnosis; vibration analysis; rotating machinery; monitoring; wavelet transform
Linear Fractional Order System Identification using Adjustable Fractional Order Differentiator
In previous decades, it has been observed that many physical systems are well characterised by fractional order models. Hence, their identification is attracting more and more interest of the scientific community. However, they pose a more difficult identification problem, which requires not only the estimation of model coefficients but also the determination of fractional orders with the tedious calculation of fractional order derivatives. This study focuses on an identification scheme, in the time domain, of dynamic systems described by linear fractional order differential equations. The proposed identification method is based on the recursive least squares algorithm applied to an ARX structure derived from the linear fractional order differential equation using adjustable fractional order differentiators. The basic ideas and the derived formulations of the identification scheme are presented. Illustrative examples are presented to validate the proposed linear fractional order system identification approach. Voir les détails
Mots clés : Adjustable fractional order differentiator, Least squares method, Linear fractional differential equation, Recursive identification.
Identification of Linear Fractional Systems of Commensurate Order
The identification of fractional order systems is a more difficult problem than the integer order systems because it requires not only the estimation of the model coefficients but also the determination of the fractional orders with the tedious calculation of fractional order derivatives. This paper addresses the identification of linear fractional systems of commensurate order. The proposed identification method is based on the recursive least squares algorithm applied to a linear regression equation derived from the linear fractional order differential equation using adjustable fractional order differentiator. The proposed technique does not require a prior knowledge of the commensurate order of the fractional linear differential equation. The derived formulations of the identification scheme are presented. Illustrative examples are also presented to validate the proposed linear fractional systems of commensurate identification approach. Voir les détails
Mots clés : Least squares method, Linear fractional differential equation, Recursive identification.
Adaptive support vector machine-based surface qualityevaluation and temperature monitoring. Applicationto billet continuous casting process
A method for surface quality evaluation and tem-perature monitoring of the billet in continuous casting isconsidered in this paper. This method uses the differencebetween the measured and the filtered temperature comput-ed using an adaptive support vector machine method. Thetemperature field, measured by an infrared camera, is affect-ed by an important noise called calamine (a metal oxidegenerated during the cooling process). The quality of thebillet ’ s surface temperature is connected to the secondarycooling behavior, and therefore an evaluation of the cala-mine effect is needed. Methods such as soft sensing andadaptive support vector machine are used for a global eval-uation of calamine intensity on the monitored area of thebillet in continuous casting. This kind of approaches isapplied in continuous casting process for constructing acomplementary condition monitoring system, which allowsan online calamine evaluation. Simulation results, based onthe measured surface temperature and the adaptive supportvector machine analysis, showed that this new combinedapproach is easily implementable and gives good resultswhen applied online. Voir les détails
Mots clés : Continuous casting . Surface billet casting . Infrared temperature measurement . Adaptive support vector machine (ASVM) . Process and quality evaluation
Inferential sensor – Based adaptive principal componentsanalysis for mechanical properties prediction and evaluation
This paper is concerned with a method for on-line quality prediction and evaluation ofmechanical properties in metal testing. This method uses an Adaptive Principal ComponentAnalysis (APCA) as a multi predictor of different sub-models defining the mechanical prop-erties such as constraints limits and elongation. The PCA technique, characterized by itsmultivariate component, is strongly recommended to model a multi-input-multi-outputsystem. The complex system is generally known as a non-linear and unsteady state pro-cess. The PCA method is a linear projection. To adapt it and to improve the prediction accu-racy, a variant of this method is considered based on iteratively using a specific algorithm.This kind of approaches is applied for constructing an inferential model, which allows areliable and accurate predictor. Simulation results, based on the measured and computeddata using the above-cited method, show that the proposed approach is easily implement-able and give an accurate prediction. Voir les détails
Mots clés : Soft sensor, Mechanical testing, Adaptive principal component analysis, Uncertainties evaluation
Synthesis, characterization of cesium and cobalt substitutedwells–Dawson heteropolyoxotungstates salts and their photocatalytic applications
Heteropoly compounds in the solid state are ionic crystals (sometimes amorphous) consisting of large polyanions, cations, water of crystallization, and other molecules. Heteropolyacids (HPAs) have several advantages as catalysts. On the one hand, they have a very strong Brønsted acidity, especially the cobalt and cesium salts; on the other hand they are exhibiting fast reversible multielectron redox transformations under mild conditions. The cobalt and cesium salts of wells–Dawson HPAs were synthesized and characterized using elemental analysis and spectroscopic techniques (31P-NMR, FT-IR).The wells–Dawson anions possess the ability to accept or release electrons through an xternal potential or upon exposure to UV radiation (photochemical reactions). The catalytic tests of these salts were investigated on phenol degradation where the UV photodegradation of acidified aqueous solutions (pH = 2) were studied in a batch photoreactor under ambient temperature and continuous circulation of phenol solution. The results reveal high catalytic activity for two HPAs, the best catalyst is the salt of cesium; where the presence of cesium improves significantly both the photcatalytic activity and the selectivity to oxalic acid. Voir les détails
Mots clés : Characterisation Heteropolyacids Dawson- Type, Cesium, Cobalt Photo Catalysis
Influence of heat treatment condition on passivity of titaniumaluminum-vanadium alloy in sodium chloride solution
Corrosion of Ti6Al4V was study with different heat treatments in3,5% NaCl solution by electrochemical measurements, includedpotenthiodynamic polarization curves, linear polarization resistance(LPR) measurements and electrochemical impedance spectroscopy(EIS), in order to focus on exploring the effect of annealing on theelectrochemical response in a quantitative manner. The samples wereprepared in the state of the art; heat treatments were applied at fourdifferent temperatures of 550, 750, 950 and 1100°C. Themicrostructure of samples has been studied using the opticalmicroscopy and the mechanical properties have been evaluated suchas microhardness HV. The electrochemical test show that the corrosionrates of treated samples at temperature equal or more then 750 ° C;are much better for the untreated sample. Although, the corrosionproduct on the surface is identified as titanium dioxide by XRD in allsamples. Voir les détails
Mots clés : Ti6Al4V, corrosion, heat treatment, Corrosion product, XRD
Short-term HDPE pipe degradation upon exposure to aggressiveenvironments
Natural gas and drinkable water are regularly transported by underground polyethylene pipenetworks in urban and rural areas. The interaction between materials such as high density polyethylene(HDPE) and contact environments is a critical factor which strongly influences pipe behaviour for short andlong terms. The aim of this study is to establish separate effects of H2SO4, a mixture of toluene–methanoland distilled water on the mechanical properties of HDPE pipes. Two testing geometries representing thepipe wall are considered: (1) orthogonally machined filaments and (2) ASTM standard specimens. Tensiletests are carried out on both specimen types using a computer controlled Zwick machine. It is observedthat chemical environments degrade mechanical properties causing a structural weakening especially thosespecimens exposed to organic solvent and acid. For instance, filaments show a reduction in elastic modulusof 64% after 7 days of exposure to toluene and methanol. Compared to standard specimens, the obtainedproperties are much higher indicating that geometry has an effect on the measured values. Fluctuationsin mechanical properties are most probably caused by cristallinity gradients all the way through the pipewall. This type of results allowed establishing the linear relationship between the elastic modulus and theyield stress and is intended to contribute to a better understanding of properties heterogeneity effects whenexposed to unfavourable environments. Voir les détails
Mots clés : polyethylene pipe, environmental stress effect, short-term degradation, yield stress-Young’s modulus correlations, failure strain, OIT