MONOTONICITY PROPERTIES FOR A SINGLE SERVER QUEUE WITH CLASSICAL RETRIAL POLICY AND SERVICE INTERRUPTIONS

MOHAMED BOUALEM,MOULOUD CHERFAOUI,DJAMIL AISSANI 장전수학회 2016 Proceedings of the Jangjeon mathematical society Vol.19 No.2

The purpose of this study is to introduce a new analytical approach namely, a qualitative analysis, which is another field of own right to establish insensitive stochastic bounds on some performance measures of a single server queue with classical retrial policy and service interruptions by using the monotonicity and comparability approach relative to the convex ordering. More precisely, we study the conditions of comparability of certain performance measures, namely the probability of number of external customers entering during a service period, the conditions of monotonicity of transition operator of embedded Markov chain and the conditions to compare the stationary distributions. Numerical studies are performed to support the theoretical obtained results.

Effect of modifying the thickness of the plate at the level of the overlap length in the presence of bonding defects on the strength of an adhesive joint

Attout Boualem,Sidi Mohamed Medjdoub,Madani Kouider,Kaddouri Nadia,Elajrami Mohamed,Belhouari Mohamed,Amin Houari,Salah Amroune,R.D.S.G. Campilho Techno-Press 2024 Advances in aircraft and spacecraft science Vol.11 No.1

Adhesive bonding is currently widely used in many industrial fields, particularly in the aeronautics sector. Despite its advantages over mechanical joints such as riveting and welding, adhesive bonding is mostly used for secondary structures due to its low peel strength; especially if it is simultaneously exposed to temperature and humidity; and often presence of bonding defects. In fact, during joint preparation, several types of defects can be introduced into the adhesive layer such as air bubbles, cavities, or cracks, which induce stress concentrations potentially leading to premature failure. Indeed, the presence of defects in the adhesive joint has a significant effect on adhesive stresses, which emphasizes the need for a good surface treatment. The research in this field is aimed at minimizing the stresses in the adhesive joint at its free edges by geometric modifications of the ovelapping part and/or by changing the nature of the substrates. In this study, the finite element method is used to describe the mechanical behavior of bonded joints. Thus, a three-dimensional model is made to analyze the effect of defects in the adhesive joint at areas of high stress concentrations. The analysis consists of estimating the different stresses in an adhesive joint between two 2024-T3 aluminum plates. Two types of single lap joints(SLJ) were analyzed: a standard SLJ and another modified by removing 0.2 mm of material from the thickness of one plate along the overlap length, taking into account several factors such as the applied load, shape, size and position of the defect. The obtained results clearly show that the presence of a bonding defect significantly affects stresses in the adhesive joint, which become important if the joint is subjected to a higher applied load. On the other hand, the geometric modification made to the plate considerably reduces the various stresses in the adhesive joint even in the presence of a bonding defect.

New optimization method of patch shape to improve the effectiveness of cracked plates repair

Mohamed S. Bouchiba,Boualem Serier 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.58 No.2

An optimization method of patch shape was developed in this study, in order to improve repair of cracked plates. It aimed to minimize three objectives: stress intensity factor, patch volume and shear stresses in the adhesive film. The choice of these objectives ensures improving crack repair, gaining mass and enhancing the adhesion durability between the fractured plate and the composite patch. This was a multi-objective optimization combined with Finite elements calculations to find out the best distribution of patch height with respect to its width. The implementation of the method identified families of optimal shapes with specific geometric features around the crack tip and at the horizontal end of the patch. Considerable mass gain was achieved while improving the repair efficiency and keeping the adhesive shear stress at low levels.

Numerical simulation of the femur fracture under static loading

Zagane Mohammed El Sallah,Benbarek Smail,Sahli Abderahmane,B. Bachir Bouiadjra,Serier Boualem 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.60 No.3

Bone is a living material with a complex hierarchical structure that gives it remarkable mechanical properties. Bone constantly undergoes mechanical. Its quality and resistance to fracture is constantly changing over time through the process of bone remodeling. Numerical modeling allows the study of the bone mechanical behavior and the prediction of different trauma caused by accidents without expose humans to real tests. The aim of this work is the modeling of the femur fracture under static solicitation to create a numerical model to simulate this element fracture. This modeling will contribute to improve the design of the indoor environment to be better safe for the passengers’ transportation means. Results show that vertical loading leads to the femur neck fracture and horizontal loading leads to the fracture of the femur diaphysis. The isotropic consideration of the bone leads to bone fracture by crack propagation but the orthotropic consideration leads to the fragmentation of the bone.

Experimental and numerical prediction of the weakened zone of a ceramic bonded to a metal

Zaoui, Bouchra,Baghdadi, Mohammed,Mechab, Belaid,Serier, Boualem,Belhouari, Mohammed Techno-Press 2019 Advances in materials research Vol.8 No.4

In this study, a three-dimensional Finite Element Model has been developed to estimate the size of the weakened zone in a bi-material a ceramic bonded to metal. The calculations results were compared to those obtained using Scanning Electron Microscope (SEM). In the case of elastic-plastic behaviour of the structure, it has been shown that the simulation results are coherent with the experimental findings. This indicates that Finite Element modeling allows an accurate prediction and estimation of the weakening effect of residual stresses on the bonding interface of Alumina. The obtained results show us that the three-dimensional numerical simulation used by the Finite Element Method, allows a good prediction of the weakened zone extent of a ceramic, which is bonded with a metal.

Highly Ammonia Sensing Using Direct In Situ Electro-Deposited Polypyrrole-Dodecylbenzene Sulfonic Acid Film on ITO Coated Flexible Substrates

Fateh Merdj,Ahmed Mekki,Djamil Guettiche,Boualem Mettai,Zakaria Bekkar Djeloul Sayah,Zitouni Safidine,Abderrazak Abdi,Rachid Mahmoud,Mohamed M. Chehimi 한국고분자학회 2018 Macromolecular Research Vol.26 No.6

Air quality monitoring is of major concern as it is directly linked to public health. It requires the development of high sensitive devices with fast response towards hazardous gas and volatile compounds. Such performances depend on the nature and quality of deposition of the sensing layer. Herein, adherent polypyrroledodecylbenzene sulfonic acid (PPy–DBSA) films were deposited on a N-(3-trimethoxysilylpropyl) pyrrole modified ITO coated polyethylene teraphtalate (PET) flexible substrate by facile direct electrochemical oxidation of pyrrole in an aqueous solution of sulfonic acid. The obtained PPy-DBSA films were subjected to various characterization techniques such as, FTIR, Raman, SEM and conductivity measurements. Chemiresistive gas sensing tests have demonstrated selectivity and sensitivity of films toward ammonia vapors over the other vapors (nitrogen dioxide, carbon dioxide, hydrogen sulfide, acetone, methanol and ethanol) with higher response at 20 ppm, reasonably fast response time of 3 min and reaching detection limit of 3ppm. The response of the sensor can reasonably be related to the strong electrostatic interactions between vapor molecules and the dopant agents within PPy films. In comparison PPy- DBSA films prepared on pristine ITO/PET has exhibited lower response at 20 ppm of ammonia exposure, which highlights the role of surface modification and the contribution from the dopant agent nature for ammonia sensing. Moreover, chemiresistive response performances have been tested in the presence of humidity, under varied temperatures, and finally their behaviors were featured by an impedance spectroscopy in both presence and absence of gas. This work conclusively shows that the sensing performances are not only driven by the molecular interactions between the sensor and the analyte but also by the quality of deposition and adhesion of the former to the transducer. The latter feature can be controlled by appropriate chemical surface modification.

Highly Ammonia Sensing Using Direct In Situ Electro-Deposited Polypyrrole-Dodecylbenzene Sulfonic Acid Film on ITO Coated Flexible Substrates

Fateh Merdj,Ahmed Mekki,Djamil Guettiche,Boualem Mettai,Zakaria Bekkar Djeloul Sayah,Zitouni Safidine,Abderrazak Abdi,Rachid Mahmoud,Mohamed M. Chehimi 한국고분자학회 2018 Macromolecular Research Vol.25 No.6

Air quality monitoring is of major concern as it is directly linked to public health. It requires the development of high sensitive devices with fast response towards hazardous gas and volatile compounds. Such performances depend on the nature and quality of deposition of the sensing layer. Herein, adherent polypyrroledodecylbenzene sulfonic acid (PPy–DBSA) films were deposited on a N-(3-trimethoxysilylpropyl) pyrrole modified ITO coated polyethylene teraphtalate (PET) flexible substrate by facile direct electrochemical oxidation of pyrrole in an aqueous solution of sulfonic acid. The obtained PPy-DBSA films were subjected to various characterization techniques such as, FTIR, Raman, SEM and conductivity measurements. Chemiresistive gas sensing tests have demonstrated selectivity and sensitivity of films toward ammonia vapors over the other vapors (nitrogen dioxide, carbon dioxide, hydrogen sulfide, acetone, methanol and ethanol) with higher response at 20 ppm, reasonably fast response time of 3 min and reaching detection limit of 3ppm. The response of the sensor can reasonably be related to the strong electrostatic interactions between vapor molecules and the dopant agents within PPy films. In comparison PPy- DBSA films prepared on pristine ITO/PET has exhibited lower response at 20 ppm of ammonia exposure, which highlights the role of surface modification and the contribution from the dopant agent nature for ammonia sensing. Moreover, chemiresistive response performances have been tested in the presence of humidity, under varied temperatures, and finally their behaviors were featured by an impedance spectroscopy in both presence and absence of gas. This work conclusively shows that the sensing performances are not only driven by the molecular interactions between the sensor and the analyte but also by the quality of deposition and adhesion of the former to the transducer. The latter feature can be controlled by appropriate chemical surface modification.