Abstract in English:Abstract In this paper three dimensional free vibration and transient response of a cylindrical panel made of two directional functionally graded materials (2D-FGMs) based on three dimensional equations of elasticity and subjected to internal impact loading is considered. Material properties vary through both radial and axial directions continuously. The 3D graded finite element method (GFEM) based on Rayleigh-Ritz energy formulation and Newmark direct integration method has been applied to solve the equations in space and time domains. The fundamental normalized natural frequency, time history of displacements and stresses in three directions and velocity of radial stress wave propagation for various values of span angel of cylindrical panel and different power law exponents have been investigated. The present results show that using 2D-FGMs leads to a more flexible design than conventional 1D-FGMs. The GFEM solution have been compared with the results of an FG thick hollow cylinder and an FG curved panel, where a good agreement between them is observed.
Abstract in English:Abstract Interfacial behavior between soil and shallow foundation has been found so influential to combined soil-footing performance and redistribution of forces in the superstructure. This study introduces a new thin-layer interface element formulated within the context of finite element method to idealize interfacial behavior of soil-framed structure interaction with new combination of degrees of freedom at top and bottom sides of the interface element, compatible with both isoparametric beam and quadrilateral element. This research also tends to conduct a parametric study on respective parameters of the new joint element. Presence of interface element showed considerable changes in the performance of the framed structure under quasi-static loading.
Abstract in English:Abstract This paper presents a nonlinear stability analysis of piles under bilateral contact constraints imposed by a geological medium (soil or rock). To solve this contact problem, the paper proposes a general numerical methodology, based on the finite element method (FEM). In this context, a geometrically nonlinear beam-column element is used to model the pile while the geological medium can be idealized as discrete (spring) or continuum (Winkler and Pasternak) foundation elements. Foundation elements are supposed to react under tension and compression, so during the deformation process the structural elements are subjected to bilateral contact constraints. The errors along the equilibrium paths are minimized and the convoluted nonlinear equilibrium paths are made traceable through the use of an updated Lagrangian formulation and a Newton-Raphson scheme working with the generalized displacement technique. The study offers stability analyses of three problems involving piles under bilateral contact constraints. The analyses show that in the evaluation of critical loads a great influence is wielded by the instability modes. Also, the structural system stiffness can be highly influenced by the representative model of the soil.
Abstract in English:Abstract This work presents a metamodel strategy to approximate the buckling load response of laminated composite plates. In order to obtain representative data for training the metamodel, some laminates with different stacking sequences are generated using the Latin hypercube sampling plan. These stacking sequences are converted into lamination parameters so that the number of inputs of the metamodel becomes constant. The buckling load for each laminate of the training set are computed using finite elements. In this way the inputs-outputs metamodel training pairs are the lamination parameters and the corresponding bucking load. Neural network and support vector regression metamodels are employed to approximate the buckling load. The performances of the metamodels are compared in a test case and the results are shown and discussed.
Abstract in English:Abstract In this work, new equations for first-order shear deformation plates are deduced taking into account the kinematic assumptions of the Bolle-Reissner theory but considering the equilibrium equations in the deformed configuration for the plate. The system of differential equations deduced is applicable to the calculation of the stresses in isotropic plates and is valid for thin and moderately thick plates. Analytical solutions are also presented in this work which are compared, when possible, with the ones obtained with other refined shear deformation plate theories.
Abstract in English:Abstract This research is dedicated to the inspection of a thin rectangular plate dynamic behavior traversed by an accelerated moving mass. BCOPs (boundary characteristic orthogonal polynomials) are utilized to treat the constitutive equation of plate vibration for different boundary conditions. Comprehensive parametric surveys are carried out to shed light on the effects of the plate fixities and aspect ratios as well as the moving mass weight, velocity and acceleration on the plate DAF (dynamic amplification factor). The convenience of adopting the presented solution dealing with various plate fixity cases makes it a superior approach comparing with eigenfunction expansion method.
Abstract in English:Abstract Low-velocity impact of a nanocomposite beam made of glass/epoxy reinforced with multi-wall carbon nanotubes and clay nanoparticles is investigated in this study. Exerting modified rule of mixture (MROM), the mechanical properties of nanocomposite including matrix, nanoparticles or multi-wall carbon nanotubes (MWCNT), and fiber are attained. In order to analyze the low-velocity impact, Euler-Bernoulli beam theory and Hertz's contact law are simultaneously employed to govern the equations of motion. Using Ritz's variational approximation method, a set of nonlinear equations in time domain are obtained, which are solved using a fourth order Runge-Kutta method. The effect of different parameters such as adding nanoparticles or MWCNT's on maximum contact force and energy absorption, stacking sequence, geometrical dimensions (i.e., length, width and height), and initial velocity of the impactor have been studied comprehensively on dynamic behavior of the nanocomposite beam. In addition, the result of analytical model is compared with Finite Element Modeling (FEM).The results reveal that the effect of nanoparticles on energy absorption is more considerable at higher impact energies.
Abstract in English:Abstract In this paper, the effect of ductile damage on the behavior of a dented Aluminum pipe subjected to internal pressure is investigated. The plastic behavior of pipes under indentation is studied using continuum damage mechanics theory and the elastic-plastic finite element analysis. Finite element calculations are carried out using the damage plasticity model proposed by Xue and Wierzbicki. The proposed damage plasticity model incorporates effects of both hydrostatic stress and the Lode angle to define the fracture envelope. Numerical calculations for different ranges of internal pressures and indenter diameters with and without damage effect are carried out and results are compared. It is shown that damage has a significant effect on the load bearing capacity of an indented pipe. Results of the present study confirm the credibility of the proposed model in predicting the ductile fracture under multi-axial state of stress loadings.
Abstract in English:Abstract An experimental investigation followed by fundamental characterization and discussion on the effect of nanoclay filler on the mechanical and fracture properties of polymer matrix was carried out. The study was carried out on clay/polymer nanocomposite made of High Density polyethylene (HDPE M40060) produced by Saudi Arabian company SABIC and montimorillonite MMT nanoclay (Nanomer I.34TCN) produced by Nanocore, USA. MMT nanomer I.34TCN is surface modified with organic surfactant to facilitate the bonding between nanoclay and HDPE. Current clay/polymer nanocomposite CPNC was produced by special technique of mixing, processing and molding. Samples of nanoclay, HDPE and nanocomposite were characterized by XRD, SEM and EDAX for investigating the chistillanity, distribution, desperion, intercalation, exfoliation, homogenity and defects. These aspects govern CPNC processing and bond between nanoclay and HDPE which controls the mechanical and fracture properties. Sheets of the produced CPNC were prepared for mechanical and fracture testing. Mechanical properties such as tensile strength, yield stress and elongation were tested and compared for both of pure HDPE and CPNC using non standard test specimens of flat sheets for comparison purposes. Fracture mechanics tests for checking and comparing the critical stress intensity factor due to stress concentration at the crack tips for mode I crack (KIc) were carried out using precracked non standard flat sheet specimens subjected to uniaxial uniform tensile stresses. Furthermore, standard experimental tests were conducted for both of HDPE and CPNC for investigating standard mechanical properties aspects based on ASTM D 638 using standard dumbbell-shaped specimen while for investigating standard fracture toughness standard single edge notch specimens SENB subjected bending moment due to effect of 3-point load based on ASTM D 5045 were carried out. The results showed that procedures of mixing, processing technique could produce nanocomposite with enhanced mechanical and fracture properties.
Abstract in English:Abstract The mechanical behavior of viscoelastic materials is influenced, among other factors, by parameters like time and temperature. The present paper proposes a methodology for a thermorheologically and piezorheologically simple characterization of viscoelastic materials in the time domain based on experimental data using Prony Series and a mixed optimization technique based on Genetic Algorithms and Nonlinear Programming. The text discusses the influence of pressure and temperature on the mechanical behavior of those materials. The results are compared to experimental data in order to validate the methodology. The final results are very promising and the methodology proves to be effective in the identification of viscoelastic materials.