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CONTENTS
Volume 6, Number 1, January 2019
 

Abstract
This present article represents the study of the forced vibration of nanobeam of a single-walled carbon nanotube (SWCNTs) surrounded by a polymer matrix. The modeling was done according to the Euler-Bernoulli beam model and with the application of the non-local continuum or elasticity theory. Particulars cases of the local elasticity theory have also been studied for comparison. This model takes into account the different effects of the interaction of the Winkler\'s type elastic medium with the nanobeam of carbon nanotubes. Then, a study of the influence of the amplitude distribution and the frequency was made by variation of some parameters such as (scale effect (e0a), the dimensional ratio or aspect ratio (L/d), also, bound to the mode number (N) and the effect of the stiffness of elastic medium (Kw). The results obtained indicate the dependence of the variation of the amplitude and the frequency with the different parameters of the model, besides they prove the local effect of the stresses.

Key Words
carbon nanotube; nanocomposite; nanobeam; vibration; Euler-Bernoulli; Winkler

Address
Samir Belmahi, Mohammed Zidour: Department of Civil Engineering ,University of Ibn Khaldoun, PB 78 Zaaroura, 14000 Tiaret, Algeria.
Samir Belmahi. Mustapha Meradjah: Laboratory of Materials and Hydrology, University of Djillali Liabes,Sidi Bel Abbés, Algeria
Mohammed Zidour: Laboratory of Geomatics and Sustainable Development, University of Ibn Khaldoun Tiaret, Algeria

Abstract
Two- and three-dimensional turbulent airflows in a 9-degrees-bent channel are studied numerically. The inner surfaces of upper and lower walls are parallel to each other upstream and downstream of the bend section. The free stream is supersonic, whereas the flow at the channel exit is either supersonic or subsonic depending on the given backpressure. Solutions of the Reynolds-averaged Navier-Stokes equations are obtained with a finite-volume solver ANSYS CFX. The solutions reveal instability of formed shock waves and a flow hysteresis in considerable bands of the free-stream Mach number at zero and negative angles of attack. The instability is caused by an interaction of shocks with the expansion flow formed over the convex bend of lower wall.

Key Words
shock waves; curved channel; instability; hysteresis; turbulent boundary layer

Address
Department of Fluid Dynamics, St. Petersburg State University, 28 University Avenue, 198504, Russia

Abstract
Flutter is a dangerous phenomenon encountered in flexible structures subjected to aerodynamic forces. This includes aircraft, helicopter blades, engine rotors, buildings and bridges. Flutter occurs as a result of interactions between aerodynamic, stiffness and inertia forces on a structure. The conventional method for designing a rotor blade to be free from flutter instability throughout the helicopter\'s flight regime is to design the blade so that the aerodynamic center (AC), elastic axis (EA) and center of gravity (CG) are coincident and located at the quarter-chord. While this assures freedom from flutter, it adds constraints on rotor blade design which are not usually followed in fixed wing design. Periodic Structures have been in the focus of research for their useful characteristics and ability to attenuate vibration in frequency bands called \"stop-bands\". A periodic structure consists of cells which differ in material or geometry. As vibration waves travel along the structure and face the cell boundaries, some waves pass and some are reflected back, which may cause destructive interference with the succeeding waves. In this work, we analyze the flutter characteristics of a helicopter blades with a periodic change in their sandwich material using a finite element structural model. Results shows great improvements in the flutter forward speed of the rotating blade obtained by using periodic design and increasing the number of periodic cells.

Key Words
finite element; vibration; periodic structure; rotor; helicopter; aeroelastic; flutter

Address
Hossam T. Badran and Hani M. Negm: Aerospace Engineering Department, Cairo University, Giza 12511, Egypt
Mohammad Tawfik: Academy of Knowledge, Cairo 11765, Egypt

Abstract
AMOSC (Automatic Margin Of Safety Calculation) is a SW tool which has been developed to calculate the failure index of layered composite structures by referring to the cutting edge state-of-the-art LaRC05 criterion. The stress field is calculated by a finite element code. AMOSC allows the user to calculate the failure index also by referring to the classical Hoffman criterion (which is commonly applied in the aerospace industry). When developing the code, particular care was devoted to the computational efficiency of the code and to the automatic reporting capability. The tool implemented is an API which has been embedded into Femap Siemens SW custom tools. Then, a user friendly graphical interface has been associated to the API. A number of study-cases have been solved to validate the code and they are illustrated through this work. Moreover, for the same structure, the differences in results produced by passing from Hoffman to LaRC05 criterion have been identified and discussed. A number of additional comparisons have thus been produced between the results obtained by applying the above two criteria. Possible future developments could explore the sensitivity of the failure indexes to a more accurate stress field inputs (e.g. by employing finite elements formulated on the basis of higher order/hierarchical kinematic theories).

Key Words
API; visual basic programming; FEMAP; material science; classical/advanced failure criteria

Address
Amedeo Grasso and Maria Cinefra: Mechanical and Aerospace Engineering Department, Politecnico di Torino, Italy
Pietro Nali: Thales Alenia Space, Strada Antica di Collegno, 253, 10146, Turin, Italy

Abstract
This paper discusses the use of the Digital Image Correlation (DIC) technique for the displacement and strain measurements of a wet lay-up composite wing. As opposed to classical strain gages, DIC allows to conduct full field strain analysis of simple to complex structural parts. In this work, wing-up bending tests and measurements of the composite wing of the Dardo Aspect by CFM Air are carried out through an ad-hoc test rig and the Q-400 DIC system by Dantec Dynamics. Also, the results are used to validate a finite element model of the structure under investigation.

Key Words
digital image correlation; composite wings; full field strain analysis

Address
A. Pagani, E. Zappino, A.G. de Miguel and E. Carrera: MUL2 group, Department of Mechanical and Aerospace Engineering, Politecnico di Torino, Turin, Italy
V. Martilla: C.F.M. Air s.r.l., Cirié, Turin, Italy


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