Techno Press


sem
 
CONTENTS
Volume 44, Number 4, November25 2012
 

Abstract
Taking the superficial temperature increment as the major fatigue damage indicator, the infrared thermography was used to predict fatigue parameters (fatigue strength and S-N curve) of welded joints subjected to fatigue loading with a high mean stress, showing good predictions. The fatigue damage status, related to safety evaluation, was tightly correlated with the temperature field evolution of the hotspot zone on the specimen surface. An energetic damage model, based on the energy accumulation, was developed to evaluate the residual fatigue life of the welded specimens undergoing cyclic loading, and a good agreement was presented. It is concluded that the infrared thermography can not only well predict the fatigue behavior of welded joints, but also can play an important role in health detection of structures subjected to mechanical loading.

Key Words
fatigue performance; welded joint; infrared thermography; energetic damage model; residual fatigue life

Address
J.L. Fan: State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116024, China; School of Mechanical Engineering, Department of Mechanical Engineering, Purdue University,
West Lafayette, IN 47906, USA
X.L. Guo and C.W. Wu: State Key Laboratory of Structural Analysis for Industrial Equipment, Dalian University of Technology, Dalian 116024, China

Abstract
In this paper, the first-order shear deformation theory (FSDT) (Mindlin) for continuum incorporating surface energy is exploited to study the static behavior of ultra-thin functionally graded (FG) plates. The size-dependent mechanical response is very important while the plate thickness reduces to micro/nano scales. Bulk stresses on the surfaces are required to satisfy the surface balance conditions involving surface stresses. Unlike the classical continuum plate models, the bulk transverse normal stress is preserved here. By incorporating the surface energies into the principle of minimum potential energy, a series of continuum governing differential equations which include intrinsic length scales are derived. The modifications over the classical continuum stiffness are also obtained. To illustrate the application of the theory, simply supported micro/nano scaled rectangular films subjected to a transverse mechanical load are investigated. Numerical examples are presented to present the effects of surface energies on the behavior of functionally graded (FG) film, whose effective elastic moduli of its bulk material are represented by the simple power law. The proposed model is then used for a comparison between the continuum analysis of FG ultra-thin plates with and without incorporating surface effects. Also, the transverse shear strain effect is studied by a comparison between the FG plate behavior based on Kirchhoff and Mindlin assumptions. In our analysis the residual surface tension under unstrained conditions and the surface Lame constants are expected to be the same for the upper and lower surfaces of the FG plate. The proposed model is verified by previous work.

Key Words
functionally graded plates; surface energy effect; ultra-thin films; size-dependent analysis; finite element analysis

Address
M. Shaat, F.F. Mahmoud, A.E. Alshorbagy, S.S. Alieldin: Mechanical Engineering Department, Zagazig University, Zagazig 44511, Egypt
E.I. Meletis: Material Science and Engineering Department, University of Texas at Arlington, USA

Abstract
For buildings subjected to blast loading, structural failure can be categorized into local failure (direct blast effects) and progressive collapse (consequential effects). In direct blast effects, the intensive blast pressures create localized failure of structural elements such as exterior columns and walls. Columns, and their behaviour, play a key role in these situations. Therefore investigating the behaviour of columns under blast loading is very important to estimate the strength, safety and reliability of the whole structure. When a building is subjected to blast loading, it experiences huge loading pressures and undergoes great displacement and plastic behaviour. In order to study the behaviour of an element under blast loading, in addition to elastic properties of materials, plastic and elastic-plastic properties of materials and sections are needed. In this paper, using analytical studies and nonlinear time-history analysis by Ansys software, the effects of shape of column sections and boundary conditions, on behaviour and local failure of steel columns under blast load are studied. This study identifies the importance of elastic-plastic properties of sections and proposes criteria for choosing the best section and boundary conditions for columns to resist blast loading.

Key Words
steel column; blast load; local failure; nonlinear analysis; section shape

Address
Mohammad Ali Hadianfard, Ahmad Farahani: Department of Civil and Environmental Engineering, Shiraz University of Technology, Shiraz, Iran
Ali B-Jahromi: School of Computing and Technology, University of West London, UK

Abstract
Different mathematical models are proposed and their analytical solutions derived for the analysis of linear elastic Reissner\'s multilayer beams. The models take into account different combinations of contact plane conditions, different material properties of individual layers, different transverse shear deformations of each layer, and different boundary conditions of the layers. The analytical studies are carried out to evaluate the influence of different contact conditions on the static and kinematic quantities. A considerable difference of the results between the models is obtained.

Key Words
layered structures; delamination; analytical modelling; laminate mechanics; interlayer slip

Address
L. Skec: University of Rijeka, Faculty of Civil Engineering, Radmile Matejcic 3, 51000 Rijeka, Croatia
Schnabl, I. Planinc: University of Ljubljana, Faculty of Civil and Geodetic Engineering, Jamova 2, SI1115 Ljubljana, Slovenia
G. Jelenic:University of Rijeka, Faculty of Civil Engineering, Radmile Matejcic 3, 51000 Rijeka, Croatia

Abstract
Dynamic instability of beams subjected to periodic axial forces is studied using the discrete singular convolution (DSC) method with the regularized Shannon\'s delta kernel. The principal regions of dynamic instability under different boundary conditions are examined in detail, and the non-stationary vibrations near the stability-instability critical regions have been investigated. It is found that the results obtained by using the DSC method are consistent with the analytical solutions, which shows that the DSC algorithm is suitable for the problems considered in this study. It was found that there is a narrow region of beat vibration existed in the vicinity of one side (o/o > 1) of the boundaries of the instable region for each condition.

Key Words
dynamic stability; non-stationary vibration; discrete singular convolution (DSC)

Address
Zhiwei Song, Wei Li: School of Naval Architecture and Ocean Engineering, Huazhong University of Science and Technology,
Wuhan 430074, P.R. China
Guirong Liu: School of Aerospace Systems, University of Cincinnati, Cincinnati, Ohio 45221, USA

Abstract
Truss weight is one of the most important factors in the cost of construction that should be reduced. Different methods have been proposed to optimize the weight of trusses. The artificial bee colony algorithm has been proposed recently. This algorithm selects the lightest section from a list of available profiles that satisfy the existing provisions in the design codes and specifications. An important issue in optimization algorithms is how to impose constraints. In this paper, the artificial bee colony algorithm is used for the discrete optimization of trusses. The fly-back mechanism is chosen to impose constraints. Finally, with some basic examples that have been introduced in similar articles, the performance of this algorithm is tested using the fly-back mechanism. The results indicate that the rate of convergence and the accuracy are optimized in comparison with other methods.

Key Words
discrete optimum; optimization; truss; artificial bee colony; fly-back mechanism

Address
A.R. Fiouz, M. Obeydi: Civil Engineering Group, Faculty of Engineering, Persian Gulf University, Bushehr, Iran
H. Forouzani: Civil Engineering and Applied Mechanics Department, California State University, Northridge, CA 91330-8347, USA
A. Keshavarz: Civil Engineering Group, Faculty of Engineering, Persian Gulf University, Bushehr, Iran

Abstract
In this study, the transverse vibrations of an axially moving flexible beams resting on multiple supports are investigated. The time-dependent velocity is assumed to vary harmonically about a constant mean velocity. Simple-simple, fixed-fixed, simple-simple-simple and fixed-simple-fixed boundary conditions are considered. The equation of motion becomes independent from geometry and material properties and boundary conditions, since equation is expressed in terms of dimensionless quantities. Then the equation is obtained by assuming small flexural rigidity. For this case, the fourth order spatial derivative multiplies a small parameter; the mathematical model converts to a boundary layer type of problem. Perturbation techniques (The Method of Multiple Scales and The Method of Matched Asymptotic Expansions) are applied to the equation of motion to obtain approximate analytical solutions. Outer expansion solution is obtained by using MMS (The Method of Multiple Scales) and it is observed that this solution does not satisfy the boundary conditions for moment and incline. In order to eliminate this problem, inner solutions are obtained by employing a second expansion near the both ends of the flexible beam. Then the outer and the inner expansion solutions are combined to obtain composite solution which approximately satisfying all the boundary conditions. Effects of axial speed and flexural rigidity on first and second natural frequency of system are investigated. And obtained results are compared with older studies.

Key Words
beam vibrations; supported end; flexible beam; multiple supports; axially accelerating; small flexural stiffness; transverse vibrations

Address
S. Kural and E. Ozkaya: Department of Mechanical Engineering, Celal Bayar University, 45140 Muradiye, Manisa, Turkey

Abstract
The behaviour of beam-to-column connections plays an important role in the analysis and design of steel structures. A computer-based method is presented for nonlinear steel frames with semirigid connections accounting for shear deformations. The analytical procedure employs transcendental stability functions to model the effect of axial force on the stiffness of members. The member stiffness matrix, and the fixed end forces for various loads were found. The nonlinear analysis method is applied for three planar steel structures. The method is readily implemented on a computer using matrix structural analysis techniques and is applicable for the efficient nonlinear analysis of frameworks.

Key Words
nonlinear analysis; semi-rigid connection; shear deformation

Address
H. Gorgun and S. Yilmaz: Department of Civil Engineering, Dicle University, 21280, Diyarbakir, Turkey


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2014 Techno Press
P.O. Box 33, Yuseong, Daejeon 305-600 Korea, Tel: +82-42-828-7996, Fax : +82-42-828-7997, Email: technop@chol.com