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Crack propagation and deviation in bi-materials under thermo-mechanical loading
Mourad Chama,Benali Boutabout,Abdelkader Lousdad,Wafa Bensmain,Bel Abbes Bachir Bouiadjra 국제구조공학회 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.50 No.4
This paper presents a finite element based numerical model to solve two dimensional bi-material problems. A bi-material beam consisting of two phase materials ceramic and metal is modelled by finite element method. The beam is subjected simultaneously to mechanical and thermal loadings. The mainobjective of this study is the analysis of crack deviation located in the brittle material near the interface. The effect of temperature gradient, the residual stresses and applied loads on crack initiation, propagation and deviation are examined and highlighted.
Probabilistic elastic-plastic analysis of repaired cracks with bonded composite patch
Mourad Chama,Belaïd Mechab,Khacem Kaddouri,Djelloul Slimani 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.20 No.6
The objective of this work was to evaluate the ductile cracked structures with bonded composite patch used in probabilistic elastic plastic fracture mechanics subjected to tensile load. The finite element method is used to analyze the stress intensity factors for elastic case, the effect of cracks and the thickness of the patch (<i>e<sub>r</sub></i>) are presented for calculating the stress intensity factors. For elastic-plastic the Monte Carlo method is used to predict the distribution function of the mechanical response. According to the obtained results, we note that the stress variations are important factors influencing on the distribution function of (J/Je).
Mourad Kchaou,Fernando Tadeo,Mohamed Chaabane,Ahmed Toumi 제어·로봇·시스템학회 2014 International Journal of Control, Automation, and Vol.12 No.1
The problem of observer-based robust control design is studied for discrete-time singular systems with norm-bounded uncertainties and a time-varying delay. More precisely, a delay-dependent criterion is established that guarantees the admissibility of the considered systems, without resorting to its decomposition. Based on the proposed criterion and without the assumption that the considered sys-tems are admissible, robust observer-based controllers are designed for discrete-time singular time-delay systems such that the closed-loop systems have the characteristics of regularity, causality and asymptotic stability. Seeking computational convenience, all the developed results are cast in the for-mat of strict linear matrix inequalities (LMIs). Finally, some numerical examples are presented to show the feasibility of the proposed approach.
Mechanical reliability analysis of tubes intended for hydrocarbons
Mourad Nahal,Rabia Khelif 대한기계학회 2013 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.27 No.2
Reliability analysis constitutes an essential phase in any study concerning reliability. Many industrialists evaluate and improve the reliability of their products during the development cycle—from design to startup (design, manufacture, and exploitation)—to develop their knowledge on cost/reliability ratio and to control sources of failure. In this study, we obtain results for hardness, tensile, and hydrostatic tests carried out on steel tubes for transporting hydrocarbons followed by statistical analysis. Results obtained allow us to conduct a reliability study based on resistance request. Thus, index of reliability is calculated and the importance of the variables related to the tube is presented. Reliability-based assessment of residual stress effects is applied to underground pipelines under a roadway, with and without active corrosion. Residual stress has been found to greatly increase probability of failure, especially in the early stages of pipe lifetime.
Automatic sleep-wake stages classifier based on ECG
Mourad Adnane,Zhongwei Jiang 제어로봇시스템학회 2009 제어로봇시스템학회 국제학술대회 논문집 Vol.2009 No.8
Sleep-wake stages discrimination is an important task in the study of cardiorespiratory diseases. Usually this is done by processing physiological signals such as electroencephalogram (EEG) that are, exclusively, recorded in hospitals using polysomnography (PSG) systems. In this paper, we report a simple automatic sleep-wake stages classifier using only RR series obtained from electrocardiogram (ECG). Seven features were extracted from the RR series by three methods, the heart rate variability (HRV), the detrended fluctuation analysis (DFA) and a proposed windowed detrended fluctuation analysis (WDFA). A subject-specific scheme was used where 20% of a subject’ data was used to train the classifier and 80% for the classification. The method was tested on the MIT/BIH Polysomnographic Database (MITBPD) using support vector machine (SVM). Finally, the sleep efficiency Seff was calculated for evaluation of sleep condition.
Three-dimensional modelling of functionally graded beams using Saint-Venant’s beam theory
Mourad Khebizi,Hamza Guenfoud,Mohamed Guenfoud,Rached El Fatmi 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.72 No.2
In this paper, the mechanical behaviour of functionally graded material beams is studied using the 3D Saint-Venant’s theory, in which the section is free to warp in and out of its plane (Poisson’s effects and out-of-plane warpings). The material properties of the FGM beam are distributed continuously through the thickness by several distributions, such as power-law distribution, exponential distribution, Mori-Tanaka schema and sigmoid distribution. The proposed method has been applied to study a simply supported FGM beam. The numerical results obtained are compared to other models in the literature, which show a high performance of the 3D exact theory used to describe the stress and strain fields in FGM beams.
Dynamic Hysteresis Model Based on Fuzzy Clustering Approach
Mourad, Mordjaoui,Bouzid, Boudjema The Korean Institute of Electrical Engineers 2012 Journal of Electrical Engineering & Technology Vol.7 No.6
Hysteretic behavior model of soft magnetic material usually used in electrical machines and electronic devices is necessary for numerical solution of Maxwell equation. In this study, a new dynamic hysteresis model is presented, based on the nonlinear dynamic system identification from measured data capabilities of fuzzy clustering algorithm. The developed model is based on a Gustafson-Kessel (GK) fuzzy approach used on a normalized gathered data from measured dynamic cycles on a C core transformer made of 0.33mm laminations of cold rolled SiFe. The number of fuzzy rules is optimized by some cluster validity measures like 'partition coefficient' and 'classification entropy'. The clustering results from the GK approach show that it is not only very accurate but also provides its effectiveness and potential for dynamic magnetic hysteresis modeling.
Finite element simulation of nanoindentation tests using a macroscopic computational model
Mourad Khelifa,Vanessa Fierro,Alain Celzard 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.8
The aim of this work was to develop a numerical procedure to simulate nanoindentation tests using a macroscopic computational model. Both theoretical and numerical aspects of the proposed methodology, based on the coupling of isotropic elasticity and anisotropicplasticity described with the quadratic criterion of Hill are presented to model this behaviour. The anisotropic plastic behaviour accountsfor the mixed nonlinear hardening (isotropic and kinematic) under large plastic deformation. Nanoindentation tests were simulated toanalyse the nonlinear mechanical behaviour of aluminium alloy. The predicted results of the finite element (FE) modelling are in goodagreement with the experimental data, thereby confirming the accuracy level of the suggested FE method of analysis. The effects of sometechnological and mechanical parameters known to have an influence during the nanoindentation tests were also investigated.