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A new refined nonlocal beam theory accounting for effect of thickness stretching in nanoscale beams
Kheroubi, Boumediene,Benzair, Abdelnour,Tounsi, Abdelouahed,Semmah, Abdelwahed Techno-Press 2016 Advances in nano research Vol.4 No.4
In this paper, a simple and refined nonlocal hyperbolic higher-order beam theory is proposed for bending and vibration response of nanoscale beams. The present formulation incorporates the nonlocal scale parameter which can capture the small scale effect, and it considers both shear deformation and thickness stretching effects by a hyperbolic variation of all displacements across the thickness without employing shear correction factor. The highlight of this formulation is that, in addition to modeling the displacement field with only two unknowns, the thickness stretching effect (${\varepsilon}_z{\neq}0$) is also included in the present model. By utilizing the Hamilton's principle and the nonlocal differential constitutive relations of Eringen, the equations of motion of the nanoscale beam are reformulated. Verification studies demonstrate that the developed theory is not only more accurate than the refined nonlocal beam theory, but also comparable with the higher-order shear deformation theories which contain more number of unknowns. The theoretical formulation proposed herein may serve as a reference for nonlocal theories as applied to the static and dynamic responses of complex-nanobeam-system such as complex carbon nanotube system.
Abdlillah Benahmed,Bouazza Fahsi,Abdelnour Benzair,Mohamed Zidour,Fouad Bourada,Abdelouahed Tounsi 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.69 No.4
This paper presents an efficient higher-order nonlocal beam theory for the Critical buckling, of functionally graded (FG) nanobeams with porosities that may possibly occur inside the functionally graded materials (FG) during their fabrication, the nonlocal elastic behavior is described by the differential constitutive model of Eringen. The material properties of (FG) nanobeams with porosities are assumed to vary through the thickness according to a power law. The governing equations of the functionally graded nanobeams with porosities are derived by employing Hamilton’s principle. Analytical solutions are presented for a simply supported FG nanobeam with porosities. The validity of this theory is studied by comparing some of the present results with other higher-order theories reported in the literature, Illustrative examples are given also to show the effects of porosity volume fraction, and thickness to length ratios on the critical buckling of the FG beams.
Dynamic analysis of nanoscale beams including surface stress effects
Youcef, Djamel Ould,Kaci, Abdelhakim,Benzair, Abdelnour,Bousahla, Abdelmoumen Anis,Tounsi, Abdelouahed Techno-Press 2018 Smart Structures and Systems, An International Jou Vol.21 No.1
In this article, an analytic non-classical model for the free vibrations of nanobeams accounting for surface stress effects is developed. The classical continuum mechanics fails to capture the surface energy effects and hence is not directly applicable at nanoscale. A general beam model based on Gurtin-Murdoch continuum surface elasticity theory is developed for the analysis of thin and thick beams. Thus, surface energy has a significant effect on the response of nanoscale structures, and is associated with their size-dependent behavior. To check the validity of the present analytic solution, the numerical results are compared with those obtained in the scientific literature. The influences of beam thickness, surface density, surface residual stress and surface elastic constants on the natural frequencies of nanobeams are also investigated. It is indicated that the effect of surface stress on the vibrational response of a nanobeam is dependent on its aspect ratio and thickness.
Fethi Salah,Belhadj Boucham,Fouad Bourada,Abdelnour Benzair,Abdelmoumen Anis Bousahla,Abdeldjebbar Tounsi 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.33 No.6
In this work, a simple four-variable integral plate theory is employed for examining the thermal buckling properties of functionally graded material (FGM) sandwich plates. The proposed kinematics considers integral terms which include the effect of transverse shear deformations. Material characteristics and thermal expansion coefficient of the ceramic-metal FGM sandwich plate faces are supposed to be graded in the thickness direction according to a "simple power-law" variation in terms of the "volume fractions" of the constituents. The central layer is always homogeneous and consists of an isotropic material. The thermal loads are supposed as uniform, linear, and nonlinear temperature rises within the thickness direction. The influences of geometric ratios, gradient index, loading type, and type sandwich plate on the buckling properties are examined and discussed in detail.
Dynamic analysis of nanoscale beams including surface stress effects
Djamel Ould Youcef,Abdelhakim Kaci,Abdelnour Benzair,Abdelmoumen Anis Bousahla,Abdelouahed Tounsi 국제구조공학회 2018 Smart Structures and Systems, An International Jou Vol.21 No.1
In this article, an analytic non-classical model for the free vibrations of nanobeams accounting for surface stress effects is developed. The classical continuum mechanics fails to capture the surface energy effects and hence is not directly applicable at nanoscale. A general beam model based on Gurtin-Murdoch continuum surface elasticity theory is developed for the analysis of thin and thick beams. Thus, surface energy has a significant effect on the response of nanoscale structures, and is associated with their size-dependent behavior. To check the validity of the present analytic solution, the numerical results are compared with those obtained in the scientific literature. The influences of beam thickness, surface density, surface residual stress and surface elastic constants on the natural frequencies of nanobeams are also investigated. It is indicated that the effect of surface stress on the vibrational response of a nanobeam is dependent on its aspect ratio and thickness.
Deep sternal wound infections: Evidence for prevention, treatment, and reconstructive surgery
Luigi Schiraldi,Gaby Jabbou,Paolo Centofanti,Salvatore Giordano,Etienne Abdelnour,Michel Gonzalez,Wassim Raffoul,Pietro Giovanni di Summa 대한성형외과학회 2019 Archives of Plastic Surgery Vol.46 No.4
Median sternotomy is the most popular approach in cardiac surgery. Post-sternotomy wound complications are rare, but the occurrence of a deep sternal wound infection (DSWI) is a catastrophic event associated with higher morbidity and mortality, longer hospital stays, and increased costs. A literature review was performed by searching PubMed from January 1996 to August 2017 according to the guidelines in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. The following keywords were used in various combinations: DSWI, post-sternotomy complication, and sternal reconstruction. Thirty-nine papers were included in our qualitative analysis, in which each aspect of the DSWI-related care process was analyzed and compared to the actual standard of care. Plastic surgeons are often involved too late in such clinical scenarios, when previous empirical treatments have failed and a definitive reconstruction is needed. The aim of this comprehensive review was to create an up-to-date operative flowchart to prevent and properly treat sternal wound infection complications after median sternotomy.
Besseghier, Abderrahmane,Heireche, Houari,Bousahla, Abdelmoumen Anis,Tounsi, Abdelouahed,Benzair, Abdelnour Techno-Press 2015 Advances in nano research Vol.3 No.1
In the current study, the nonlinear vibration properties of an embedded zigzag single-walled carbon nanotube (SWCNT) are investigated. Winkler-type model is used to simulate the interaction of the zigzag SWCNTs with a surrounding elastic medium. The relation between deflection amplitudes and resonant frequencies of the SWCNT is derived through harmonic balance method. The equivalent Young's modulus and shear modulus for zigzag SWCNT are derived using an energy-equivalent model. The amplitude - frequency curves for large-amplitude vibrations are graphically illustrated. The simulation results show that the chirality of zigzag carbon nanolube as well as surrounding elastic medium play more important roles in the nonlinear vibration of the single-walled carbon nanotubes.
On the bending and stability of nanowire using various HSDTs
Youcef, Djamel Ould,Kaci, Abdelhakim,Houari, Mohammed Sid Ahmed,Tounsi, Abdelouahed,Benzair, Abdelnour,Heireche, Houari Techno-Press 2015 Advances in nano research Vol.3 No.4
In this article, various higher-order shear deformation theories (HSDTs) are developed for bending and buckling behaviors of nanowires including surface stress effects. The most important assumption used in different proposed beam theories is that the deflection consists of bending and shear components and thus the theories have the potential to be utilized for modeling of the surface stress influences on nanowires problems. Numerical results are illustrated to prove the difference between the response of the nanowires predicted by the classical and non-classical solutions which depends on the magnitudes of the surface elastic constants.
Khadra Bouafia,Abdelhakim Kaci,Mohammed Sid Ahmed Houari,Abdelnour Benzair,Abdelouahed Tounsi 국제구조공학회 2017 Smart Structures and Systems, An International Jou Vol.19 No.2
In this paper, size dependent bending and free flexural vibration behaviors of functionally graded (FG) nanobeams are investigated using a nonlocal quasi-3D theory in which both shear deformation and thickness stretching effects are introduced. The nonlocal elastic behavior is described by the differential constitutive model of Eringen, which enables the present model to become effective in the analysis and design of nanostructures. The present theory incorporates the length scale parameter (nonlocal parameter) which can capture the small scale effect, and furthermore accounts for both shear deformation and thickness stretching effects by virtue of a hyperbolic variation of all displacements through the thickness without using shear correction factor. The material properties of FG nanobeams are assumed to vary through the thickness according to a power law. The neutral surface position for such FG nanobeams is determined and the present theory based on exact neutral surface position is employed here. The governing equations are derived using the principal of minimum total potential energy. The effects of nonlocal parameter, aspect ratio and various material compositions on the static and dynamic responses of the FG nanobeam are discussed in detail. A detailed numerical study is carried out to examine the effect of material gradient index, the nonlocal parameter, the beam aspect ratio on the global response of the FG nanobeam. These findings are important in mechanical design considerations of devices that use carbon nanotubes.
Deep sternal wound infections: Evidence for prevention, treatment, and reconstructive surgery
Schiraldi, Luigi,Jabbour, Gaby,Centofanti, Paolo,Giordano, Salvatore,Abdelnour, Etienne,Gonzalez, Michel,Raffoul, Wassim,di Summa, Pietro Giovanni Korean Society of Plastic and Reconstructive Surge 2019 Archives of Plastic Surgery Vol.46 No.4
Median sternotomy is the most popular approach in cardiac surgery. Post-sternotomy wound complications are rare, but the occurrence of a deep sternal wound infection (DSWI) is a catastrophic event associated with higher morbidity and mortality, longer hospital stays, and increased costs. A literature review was performed by searching PubMed from January 1996 to August 2017 according to the guidelines in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. The following keywords were used in various combinations: DSWI, post-sternotomy complication, and sternal reconstruction. Thirty-nine papers were included in our qualitative analysis, in which each aspect of the DSWI-related care process was analyzed and compared to the actual standard of care. Plastic surgeons are often involved too late in such clinical scenarios, when previous empirical treatments have failed and a definitive reconstruction is needed. The aim of this comprehensive review was to create an up-to-date operative flowchart to prevent and properly treat sternal wound infection complications after median sternotomy.