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CONTENTS
Volume 25, Number 6, December30 2017
 

Abstract
Fracture energy values KV have been measured on cast steel, used in the container manufacture, by instrumented Charpy impact testing. This material has a large ductility on the upper transition region at +20oC and a ductile tearing with an expended plasticity before a brittle fracture on the lower transition region at -20oC. To assess the fracture toughness of this material we use, the KIC-KV correlations to measure the critical stress intensity factor KIC on the lower transition region and the dynamic force - displacement curves to measure the critical fracture toughness JPC, the essential work of fracture Te on the upper transition region. It is found, using the KIC-KV correlations, that the critical stress intensity factor KIC remains significant, on the lower transition region, which indicating that our testing material preserves his ductility at low temperature and it is apt to be used as a container\'s material. It is, also, found that the Jp-p energetic criterion, used on the upper transition region, gives a good evaluation of the fracture toughness closest to those found in the literature. Finally, we show, by using the Te-KIC relation, on the lower transition region, that the essential work of fracture is not suitable for the toughness measurement because the strong scatter of the experimental data. To complete this study by a numerical approach we used the ANSYS code to determine the critical fracture toughness JANSYS on the upper transition region.

Key Words
Charpy impact test; fracture toughness; ductility; upper transition region; lower transition region

Address
Tassadit Bellahcene and Meziane Aberkane: Laboratoire d\'Elaboration, de Caracterisation des Materiaux et Modelisation (LEC2M), Universite Mouloud Mammeri de Tizi-Ouzou, BP 17 RP, Tizi-Ouzou, 15008, Algeria

Abstract
This paper is motivated by the lack of studies in the technical literature concerning to the influence of carbonnanotubes (CNTs) waviness and aspect ratio on the vibrational behavior of functionally graded nanocomposite annular sector plates resting on two-parameter elastic foundations. The carbon nanotube-reinforced (CNTR) plate has smooth variation of CNT fraction based on the power-law distribution in the thickness direction, and the material properties are also estimated by the extended rule of mixture. In this study, the classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes\' effective aspect ratio as the filler content increases. Parametric studies are carried out to highlight the influence of CNTs volume fraction, waviness and aspect ratio, boundary conditions and elastic foundation on vibrational behavior of FG-CNT thick sectorial plates. The study is carried out based on three-dimensional theory of elasticity and in contrary to two-dimensional theories, such as classical, the first- and the higher-order shear deformation plate theories, this approach does not neglect transverse normal deformations. The annular sector plate is assumed to be simply supported in the radial edges while any arbitrary boundary conditions are applied to the other two circular edges including simply supported, clamped and free. For an overall comprehension on 3-D vibration of annular sector plates, some mode shape contour plots are reported in this research work.

Key Words
CNTs waviness; CNTs aspect ratio; thick plates; vibration; mode shape analysis; two-parameter elastic foundations

Address
Vahid Tahouneh: Young Researchers and Elite Club, Islamshahr Branch, Islamic Azad University, Islamshahr, Iran

Abstract
The problem of layup optimization of the composite laminates involves a very complex multidimensional solution space which is usually non-exhaustively explored using different heuristic computational methods such as genetic algorithms (GA). To ensure the convergence to the global optimum of the applied heuristic during the optimization process it is necessary to evaluate a lot of layup configurations. As a consequence the analysis of an individual layup configuration should be fast enough to maintain the convergence time range to an acceptable level. On the other hand the mechanical behavior analysis of composite laminates for any geometry and boundary condition is very convoluted and is performed by computational expensive numerical tools such as finite element analysis (FEA). In this respect some studies propose very fast FEA models used in layup optimization. However, the lower bound of the execution time of FEA models is determined by the global linear system solving which in some complex applications can be unacceptable. Moreover, in some situation it may be highly preferred to decrease the optimization time with the cost of a small reduction in the analysis accuracy. In this paper we explore some machine learning techniques in order to estimate the failure of a layup configuration. The estimated response can be qualitative (the configuration fails or not) or quantitative (the value of the failure factor). The procedure consists of generating a population of random observations (configurations) spread across solution space and evaluating using a FEA model. The machine learning method is then trained using this population and the trained model is then used to estimate failure in the optimization process. The results obtained are very promising as illustrated with an example where the misclassification rate of the qualitative response is smaller than 2%.

Key Words
failure estimation; layup optimization; machine learning; finite element analysis; numerical analysis

Address
Alexandru Şerban: Faculty of Mechanical Engineering, University of Gh. Asachi, Iasi, 700050, Romania

Abstract
Elastic-plastic shear buckling behaviors of the web-post in a Castellated Steel Beam (CSB) with hexagonal web openings under vertical shear force were investigated further using Finite Element Model (FEM) based on a sub-model, which took the upper part of the web-post under horizontal shear force to represent the whole web-post under vertical shear force. A simplified design method for the web-post elastic-plastic shear buckling strength was proposed based on simulation results of the sub-model. Proper boundary conditions were applied to the sub-model to assure that its behaviors were identical to those of the whole web-post. The equation to calculate the thin plate elastic shear buckling strength was adopted as the basic form to build the design equation for elastic-plastic buckling strength of the sub-model. Parameters that might affect the elastic-plastic shear buckling strength of the whole web-post were studied. After obtaining the vertical shear buckling strength of a sub-model through FEM, the shear buckling coefficient k can be obtained through the back analysis. A practical calculation method for k was proposed through curving fitting the parameter study results. The elastic-plastic shear buckling strength of the web-post calculated using the proposed shear buckling coefficient k agreed well with that obtained from the FEM and test results. And it was more precise than those obtained from EC3 based on the strut model.

Key Words
castellated steel beam; web-post; elastic-plastic shear buckling; plate shear buckling coefficient; design method

Address
Mei Liu; Kangrui Guo; Peijun Wang; Chao Lou : School of Civil Engineering, Shandong University, Jinan, Shandong Province, 250061, China
Kangrui Guo : Shandong Urban and Rural Planning Design Institute, Jinan, Shandong Province, 250061, China
Yue Zhang : Shanghai Construction No. 1 (Group) Co. LTD, Shanghai, 200120, China

Abstract
In this study, the effect of various adhesively bonded composite patches on mechanical properties of notched Al-Mg alloy plates was analyzed. For this purpose firstly, the un-notched and notched specimens were fabricated from 5086 Al-Mg alloys which have been used in armor-plated military vehicles. The surface notches as a flaw were machined with circular cutting tool to form notch aspect ratio a/c=0.15 and notch-to-thickness ratios a/t=0.5 in the radial direction on the test specimens. Then, various composite patches which reinforced by glass, carbon and Kevlar fibers were bonded adhesively at elliptically surface notches. Finally, experimental measurements conducted by applying tensile static loading. The experimental results showed that repairing with composite patches with order of carbon, glass and Kevlar fibers have remarkable effect on tensile strength of the notched plate. Also the finite element models were developed using Abaqus/Explicit code to predict the tensile strength and elongation of unrepaired notched specimen and specimen repaired by carbon fiber composite patch. The comparison between numerical and experimental results showed good agreement between them and proved the accuracy of numerical modeling.

Key Words
composite patch repair; finite element method; adhesively bonded; tensile strength; notch

Address
Ahmad P. Meran : Department of Mechatronics Engineering, Faculty of Engineering and Architecture, Necmettin Erbakan University, Konya, Turkey
Ahmet Samanci : Department of Aeronautical Engineering, Faculty of Aeronautics and Astronautics, Necmettin Erbakan University, Konya, Turkey

Abstract
In this research, a simple hyperbolic shear deformation theory is developed and applied for the bending, vibration and buckling of powerly graded material (PGM) sandwich plate with various boundary conditions. The displacement field of the present model is selected based on a hyperbolic variation in the in-plane displacements across the plate\'s thickness. By splitting the deflection into the bending and shear parts, the number of unknowns and equations of motion of the present formulation is reduced and hence makes them simple to use. Equations of motion are obtained from Hamilton\'s principle. Numerical results for the natural frequencies, deflections and critical buckling loads of several types of powerly graded sandwich plates under various boundary conditions are presented. The accuracy of the present formulation is demonstrated by comparing the computed results with those available in the literature. As conclusion, this theory is as accurate as other theories available in the literature and so it becomes more attractive due to smaller number of unknowns.

Key Words
functionally graded materials; sandwich plates; hyperbolic plate theory; various boundary conditions; free vibration; buckling loads; bending

Address
Hadj Henni Abdelaziz, Mohamed Ait Amar Meziane, Abdelmoumen Anis Bousahla, Abdelouahed Tounsi : Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of SidiBel Abbes, Algeria
Hadj Henni Abdelaziz, Mohamed Ait Amar Meziane : Universite Ibn Khaldoun, BP 78 Zaaroura, 14000 Tiaret, Algeria
Abdelmoumen Anis Bousahla, Abdelouahed Tounsi : Laboratoire de Modelisation et Simulation Multi-echelle, Universite de Sidi Bel Abbes, Algeria
Abdelmoumen Anis Bousahla : Centre Universitaire de Relizane, Algerie
S.R. Mahmoud : Department of Mathematics, Faculty of Science, King Abdulaziz University, Saudi Arabia
Afaf S. Alwabli : Biology Department, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia


Abstract
The objective of this study is to investigate the actual behavior of studs in structures under earthquake load through laboratory tests and numerical simulation. A test program including eighteen specimens was devised with consideration of different concrete strengths and stud diameters. Six of specimens were subjected to monotonically increasing loading while the others were subjected to cyclic loading. Mechanical behavior including the failure mechanism, load-slip relationship, stiffness degradation, energy dissipation and the damage accumulation was obtained from the test results. An accurate numerical model based on the ABAQUS software was developed and validated against the test results. The results obtained from the finite element (FE) model matched well with the experimental results. Furthermore, based on the experimental and numerical data, the design formulas for expressing the skeleton curve were proposed and the simplified hysteretic model of load versus displacement was then established. It is demonstrated that the proposed formulas and simplified hysteretic model have a good match with the test results.

Key Words
headed stud shear connector; push-off test; cyclic loading; energy dissipation; finite element model

Address
Fa-xing Ding, Guo-an Yin, Hai-bo Wang, Liping Wang, Qiang Guo : School of Civil Engineering, Central South University, Changsha, Hunan Province, 410075, P.R. China
Qiang Guo : CRRC CONSTRUCTION ENGRG. CO., LTD., P.R. China


Abstract
In this paper, a new simple shear deformation theory for bending analysis of functionally graded plates is developed. The present theory involves only three unknown and three governing equation as in the classical plate theory, but it is capable of accurately capturing shear deformation effects, instead of five as in the well-known first shear deformation theory and higher-order shear deformation theory. A shear correction factor is, therefore, not required. The material properties of the functionally graded plates are assumed to vary continuously through the thickness, according to a simple power law distribution of the volume fraction of the constituents. Equations of motion are obtained by utilizing the principle of virtual displacements and solved via Navier\'s procedure. The elastic foundation is modeled as two parameter elastic foundation. The results are verified with the known results in the literature. The influences played by transversal shear deformation, plate aspect ratio, sideto-thickness ratio, elastic foundation, and volume fraction distributions are studied. Verification studies show that the proposed theory is not only accurate and simple in solving the bending behaviour of functionally graded plates, but also comparable with the other higher-order shear deformation theories which contain more number of unknowns.

Key Words
a simple 3-unknown theory; bending; functionally graded plates, elastic foundation

Address
Houari Hachemi, Abdelhakim Kaci, Mohamed Bourada, Abdelouahed Tounsi : Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria
Houari Hachemi, Abdelhakim Kaci : Department of Civil Engineering and Hydraulics, University Dr. Taher Moulay of Saida, Algeria
Mohammed Sid Ahmed Houari : Department of Civil Engineering, Universite Mustapha Stambouli de Mascara, Mascara, Algeria
Mohammed Sid Ahmed Houari, Mohamed Bourada, Abdelouahed Tounsi : Laboratoire des Structures et Materiaux Avances dans le Genie Civil et Travaux Publics, Faculte de Technologie
Abdelouahed Tounsi : Laboratoire de Modelisation et Simulation Multi-echelle, Faculte des Sciences, Departement de Physique, Universite de Sidi Bel Abbes, Algeria
S.R. Mahmoud : Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia

Abstract
This paper describes a quasi-static finite element analysis, which uses the explicit integration method, of the apex joint of a cold-formed steel portal frame. Such cold-formed steel joints are semi-rigid as a result of bolt-hole elongation. Furthermore, the channel-sections that are being connected have a reduced moment capacity as a result of a bimoment. In the finite element model described, the bolt-holes and bolt shanks are all physically modelled, with contact defined between them. The force-displacement curves obtained from the quasi-static analysis are shown to be similar to those of the experimental test results, both in terms of stiffness as well as failure load. It is demonstrated that quasi-static finite element analysis can be used to predict the behavior of cold-formed steel portal frame joints and overcome convergence issues experienced in static finite element analysis.

Key Words
cold-formed steel; bolted moment-connections; finite element analysis; quasi-static

Address
Chia Mohammadjani, Amir M. Yousefi, Shu Qing Cai, G. Charles Clifton and James B.P. Lim : Department of Civil Engineering and Environmental Engineering, The University of Auckland, New Zealand


Abstract
This work presents a free vibration analysis of functionally graded plates by employing an original high order shear deformation theory (HSDT). This theory use only four unknowns, which is even less than the classical HSDT. The equations of motion for the dynamic analysis are determined via the Hamilton\'s principle. The original kinematic allows obtaining interesting equations of motion. These equations are solved analytically via Navier procedure. The accuracy of the proposed solution is checked by comparing it with other closed form solutions available in the literature.

Key Words
vibration; functionally graded plate; plate theory

Address
Imene Ait Sidhoum, Djilali Boutchicha : Laboratoire de Mecanique Applique, Departement de Genie Mecanique, Universite des Sciences et Technologie
d\'ORAN Mouhamed Boudiaf, BP 1505 Elmnouar 31000, ORAN, Algeria
Samir Benyoucef, Abdelouahed Tounsi : Material and Hydrology Laboratory, Civil Engineering Department, University of SidiBel Abbes, Faculty of Technology, Algeria
Abdelouahed Tounsi : Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals,31261 Dhahran, Eastern Province, Saudi Arabia


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