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Volume 1, Number 1, June 2019

In this work, a novel higher-order shear deformation theory (HSDT) is presented for buckling analysis of functionally graded plates. The present theory accounts for both shear deformation and thickness stretching effects by a parabolic variation of all displacements across the thickness, and satisfies the stress-free boundary conditions on the upper and lower surfaces of the plate without requiring any shear correction factor. The number of independent unknowns of this theory is four, as against five in other shear deformation theories. Unlike the conventional HSDT, the present one has a new displacement field which introduces undetermined integral variables. The material properties of the faces of sandwich plate are assumed to vary according to a power law distribution in terms of the volume fractions of the constituents. The core layer is made of an isotropic ceramic material. The governing equations are obtained by the principle of virtual work. Analytical solutions for the buckling analyses are solved for simply supported sandwich plate. Numerical examples are given to show the effects of varying gradients, thickness stretching, and thickness to length ratios on the critical buckling loads of functionally graded sandwich plate.

Key Words
functionally graded plates; refined plate theory; buckling analysis; stretching effects

Abdelouahed Tounsi: Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia
Hassen Ait Atmane, Mokhtar Khiloun, Abdelouahed Tounsi, Mohamed Sekkal: Material and Hydrology Laboratory, University of Sidi Bel Abbes, Faculty of Technology,
Civil Engineering Department, Algeria
Hassen Ait Atmane: Departement de genie civil, Faculte de genie civil et d'architecture,
Univesite Hassiba Benbouali de Chlef, Algerie
Mokhtar Khiloun: Departement de Genie Civil, Faculte des Sciences Appliquees, Universite Ibn Khaldoun, Tiaret, Algerie.
Ouahiba Taleb: University Mustapha Stambouli of Mascara, Department of Civil Engineering, Mascara, Algeria
Ouahiba Taleb: Laboratoire des Sciences et Techniques de l'Eau,
University Mustapha Stambouli of Mascara, Mascara, Algeria
Abdelmoumen Anis Bousahla: Laboratoire de Modelisation et Simulation Multi-echelle, Departement de Physique, Faculte des Sciences Exactes, Departement de Physique, Universite de Sidi Bel Abbes, Algeria.
Abdelmoumen Anis Bousahla: Centre Universitaire Ahmed Zabana de Relizane, Algerie

In this letter, nonlocal Timoshenko beam theory has been implemented to investigate the free vibration response of chiral single-walled carbon nanotubes (SWCNTs). According to nonlocal Timoshenko vibration equation for (SWCNTs), The analytical solution is derived and two solutions for vibration are obtained. Influence of nonlocal small-scale coefficient, the vibrational mode number, the chirality of carbon nanotube and aspect ratio of the (SWCNTs) on frequency of the (SWCNTs) are studied and discussed. The results indicate significant dependence of natural frequencies on the chirality of single-walled carbon nanotube with increase the nonlocal small-scale coefficient, the vibrational mode number and the nanotube aspect ratio of length to diameter.

Key Words
single-walled carbon nanotubes; vibration; nonlocal elasticity; chirality; small-scale

Tayeb Bensattalah, Mohamed Zidour, Tahar Hassaine Daouadji: Departement de genie civil, Universite Ibn Khaldoun Tiaret; BP 78 Zaaroura, Tiaret, Algerie.
Laboratoire de Geomatique et Developpement Durable, Universite de Tiaret, Algerie

Damage detection in structural elements using curvature mode shape technique has become a research focus of increasing interest during the last few years. A noticeable deficiency of curvature mode shape, however, is its susceptibility to measurement noise, easily impairing its advantage of sensitivity to damage. To overcome this drawback, a nonlinear operator called Teager Energy Operator (TEO) is incorporated. The efficacy of TEO is analytically verified through modal curvatures in a steel reinforced concrete cantilever beam with an induced damage (stiffness loss) along its length. The applicability of the proposed curvature mode shape technique is experimentally validated for detecting simulated damage (mass attached) in an aluminum plate from mode shapes acquired by a non-contact Scanning Laser Doppler Vibrometer (SLDV). Normal responses (out of plane flexure response) are measured with SLDV. The excitation is given with the help of a data-physics exciter based on the frequencies obtained from the free vibration tests using a roving hammer attached with a forced transducer. The proposed algorithm is to compute a robust nonlinear operator - TEO using the attained curvature, dynamic rotation and displacement mode shapes. This algorithm has been successfully implemented and tested for detecting damages on beam and plate elements, using finite element simulations as well as laboratory experiments. It is anticipated that the suggested approach facilitates damage localization in a comparatively fast and accurate manner.

Key Words
damage detection; health monitoring; curvature mode shape; energy operator; scanning laser vibrometer; beam/plate elements

T. Jothi Saravanan: Institute of Advanced Sciences, Yokohama National University, Kanagawa- 2408501, Japan
N. Gopalakrishnan: CSIR-Central Building Research Institute, Roorkee- 247667, India
B. Karthick Hari: Department of Civil Engineering, Birla Institute of Technology & Science, Pilani-333031, India

Several methods for evaluation of uniformity of distribution of fibers in steel-fiber-reinforced concrete (SFRC) exist today. All of them are either ineffective, biased or their execution requires special expensive equipment. A promising new approach based on computer aided SFRC digital image analysis was developed and tested with excellent results. The process of taking and adjusting the pictures of SFRC samples is described in the paper. ASEF (Automatic Specimen Evaluation of Fibers) program was prepared in MATLAB environment for quick and accurate detection of fibers in the photographs. Basically, the detection algorithm exploits different reflectance of steel fibers and concrete matrix. No unusual devices are needed for employment of the method. The whole procedure is very simple and can be used successfully in both laboratory and construction site. Examples of application of the method are presented in the paper. Several mixtures of high-performance concrete containing 120 kg of steel fibers per cubic meter of concrete were compared with respect to the uniformity of dispersion of fibers, optimal mix composition was selected. Large scale specimens made of normal strength SFRC for tunnel linings were examined, the analysis led to a conclusion that sufficient uniformity of dispersion of the fibers in the mix was reached.

Key Words
fiber-reinforced concrete; distribution of fibers; homogeneity; computer aided design; digital image analysis; MATLAB

Department of Concrete and Masonry Structures, Faculty of Civil Engineering, Czech Technical University in Prague, Thákurova 7, 16629 Prague, Czech Republic

In this manuscript, a comprehensive numerical analysis is conducted to assess the accuracy of the Tan's model of obtaining the stress concentration factor, for a plate with finite dimensions containing an open hole. The influence of plate length on the stress distribution around the hole is studied. It is demonstrated that the plate length has a significant impact on the degree of accuracy of the method. Therefore, a critical length is proposed for this approach. Critical length is defined as the minimum length the plate requires, to ensure that the SCF which is obtained from the Tan's model will have sufficient accuracy. Finally, the approach of finite-width correction factor is adapted to develop a new model which is applicable for plates under biaxial loading conditions. In this method, biaxial loading is considered as a dominant axial force along the x-direction and lambda times the load (-1<= lambda <=1), along the y-direction. A comparison between the SCFs obtained from the proposed analytical method and the SCFs obtained from the extensive FE studies, revealed an excellent agreement when the plate-width to hole-diameter ratio is more than 3 and the lambda is between -0.5 and 1.

Key Words
stress concentration factor (SCF); composite plate; circular hole; correction factors; finite element analysis

School of Mechanical Engineering, Iran University of Science and Technology,
Narmak, Tehran, 16846-13114, Iran

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