Tech Science Press
Not a member yet
3972 research outputs found
Sort by
Dynamic Instability of Rectangular Composite Plates under Parametric Excitation
Get PDFThe dynamic instability of rectangular graphite/epoxy composite plates under parametric excitation was investigated analytically and experimentally. In analysis, the dynamic system of the composite plate, obtained based on the assumedmodes method, is a general form of Mathieu’s equation, including parametrically excited terms. The instability regions of the system, each separated by two transition curves, were found to be functions of the modal parameters of the composite plate and the position and the excited amplitude of the electromagnetic device on the composite plates. The fiber orientation, the aspect ratio and the layer numbers of the composite plates were varied to assess their effects on the dynamic instability behavior of the composite plates. In experiment, an electromagnetic device, acting like a spring with alternating stiffness, was used to parametrically excite the composite plates. The frequency and the amplitude of the excitation force were accurately controlled by the AC current flowing through the coil of the electromagnetic device. Since the excitation force was a transversely non-contact electromagnetic force, the disturbances induced by the eccentricity of the usual planar excitation force and by the geometric imperfection of the composite plate were effectively avoided. The experimental results, for the cases of twice the fundamental frequency, were found to agree well with the analytical ones. The excitation frequencies at tip of instability regions decrease as the fiber orientation increases for composite plates with [±θ2]s lamination at bending mode; while the excitation frequencies increase to a maximum at 45° fiber orientation for composite plates with [±θ2]sslamination at torsional mode. The excitation frequency at tip of instability regions decreases for higher aspect ratios and thinner composite plates
A Multiscale Progressive Failure Modeling Methodology for Composites That Includes Fiber Strength Stochastics
Get PDFA multiscale modeling methodology was developed for continuous fiber composites that incorporates a statistical distribution of fiber strengths into coupled multiscale micromechanics/ finite element (FE) analyses. A modified twoparameter Weibull cumulative distribution function, which accounts for the effect of fiber length on the probability of failure, was used to characterize the statistical distribution of fiber strengths. A parametric study using the NASA Micromechanics Analysis Code with the Generalized Method of Cells (MAC/GMC) was performed to assess the effect of variable fiber strengths on local composite failure within a repeating unit cell (RUC) and subsequent global failure. The NASA code FEAMAC and the ABAQUS finite element solver were used to analyze the progressive failure of a unidirectional SCS-6/ TIMETAL 21S metal matrix composite tensile dogbone specimen at 650°C. Multiscale progressive failure analyses were performed to quantify the effect of spatially varying fiber strengths on the RUCaveraged and global stress-strain responses and failure. The ultimate composite strengths and distribution of failure locations (predominately within the gage section) reasonably matched the experimentally observed failure behavior. The predicted composite failure behavior suggests that use of macroscale models that exploit global geometric symmetries are inappropriate for cases where the actual distribution of local fiber strengths displays no such symmetries. This issue has not received much attention in the literature. Moreover, the model discretization at a specific length scale can have a profound effect on the computational costs associated with multiscale simulations
Surface/interface Energy Effect on Electromechanical Responses Around a Nanosized Elliptical Inclusion under Far-field Loading at an Arbitrary Angle
Get PDFElectro-elastic surface/interface around nano-sized piezoelectric inclusions shows great effect on the response of piezoelectric nano-structures. In this paper, a theoretical model is proposed to examine the surface/interface effect on the electromechanical responses around a nano-sized elliptical piezoelectric inclusion embedded in an infinite piezoelectric matrix under far-field loading with an arbitrary angle, and the effect of loading angle is considered Combining the conformal mapping technique and electro-elastic surface/interface theory, a closed form solution of this problem is obtained and the interactive effect between the surface/interface and the aspect ratio of the elliptical inclusion is examined
Mechanical Analysis of 3D Composite Materials by Hybrid Boundary Node Method
Get PDFIn this paper, an improved multi-domain model based on the hybrid boundary node method (Hybrid BNM) is proposed for mechanical analysis of 3D composites. The Hybrid BNM is a boundary type meshless method which based on the modified variational principle and the Moving Least Squares (MLS) approximation. The improved multi-domain model can reduce the total degrees of freedom (DOFs) compared with the conventional multi-domain solver. It is very suitable for the inclusion-based composites, especially for the composites when the inclusions are solid and totally embedded in the matrix domain. Numerical examples are presented to verify the improved multi-domain model and the results have shown the accuracy and efficiency of the improved model
Analytical Treatment of the Isotropic and Tetragonal Lattice Green Functions for the Face-centered Cubic, Body-centered Cubic and Simple Cubic Lattices
Get PDFIn this paper, we propose an efficient method to calculate the isotropic and tetragonal lattice Green functions for the face-centered cubic (FCC), bodycentered cubic (BCC) and simple cubic (SC) lattices. The method is based on binomial expansion theorems, which provide us with analytical formulae through basic integrals. The resulting series present better convergence rates. Several acceleration techniques are combined to further improve the efficiency of the established formulas. The obtained results for the lattice Green functions are in good agreement with the known numerical calculation results
Active Metamaterials for Modulation and Detection
Get PDFThis paper illustrates some new concepts in the area of hybrid metamaterials, which are metamaterials that are embedded with active circuit elements such as transistors. Such transistor/metamaterial hybrids can exhibit some exotic electromagnetic properties which can be exploited for unusual and exciting functions. Two specific examples are provided. In one application, terahertz (THz) modulator based on embedding of psuedomorphic high electron mobility transistor (pHEMT) within the metamaterial resonator, all implemented monolithically in a commercial gallium arsenide (GaAs) technology is presented. In another application, a detector array based on metamaterial perfect absorber for room-temperature detection of gigahertz (GHz) radiation within each sub wavelength metamaterial unit cell is presented. The latter application utilizes a hybridization of metamaterial on printed circuit board (PCB) with discrete microwave electronic components. Both applications indicate the promise of the approach of integrating electronics or semiconductor devices with metamaterials for new and innovative functions
Mass Transger in an Eccentric Annular Region Through Diffusion
No full textThe mass transfer in an eccentric annular region through diffusion by taking blood as a Newtonian fluid with the investigation of oxygen transfer and drug transport to the tissue cells in an eccentric catheterized artery is studied. The region bounded by eccentric circles in x-y plane is mapped conformally to concentric circles in plane using a conformal mapping . The resulting governing equations are analytically solved by using transformation for the concentration. Numerical computations are carried out to understand the simultaneous~effects of absorption parameter and eccentricity on the flow. ~The observation through the numerical computation reveals that, as absorption parameter and eccentricity enhances, the solute concentration diminishes. This mathematical model provides an insight for physiologists to understand the drug transport to the tissues in various clinical treatments of cardiovascular diseases
Optimal Mass Distribution Prediction for Human Proximal Femur with Bi-modulus Property
Get PDFSimulation of the mass distribution in a human proximal femur is important to provide a reasonable therapy scheme for a patient with osteoporosis. An algorithm is developed for prediction of optimal mass distribution in a human proximal femur under a given loading environment. In this algorithm, the bone material is assumed to be bi-modulus, i.e., the tension modulus is not identical to the compression modulus in the same direction. With this bi-modulus bone material, a topology optimization method, i.e., modified SIMP approach, is employed to determine the optimal mass distribution in a proximal femur. The effects of the difference between two moduli on the final material distribution are numerically investigated. Numerical results obtained show that the mass distribution in bi-modular bone materials is different from that in traditional isotropic material. As the tension modulus is less than the compression modulus for bone tissues, the amount of mass required to support tension loads is greater than that required by isotropic material for the same daily activities including one-leg stance, abduction and adduction
Nonlinear Bending and Thermal Post-Buckling Analysis of FGM Beams Resting on Nonlinear Elastic Foundations
Get PDFA model of FGM beams resting on nonlinear elastic foundations is put forward by physical neutral surface and high-order shear deformation theory. Material properties are assumed to be temperature dependent and von Kármán strain-displacement relationships are adopted. Nonlinear bending and thermal postbuckling are given by multi-term Ritz method, and influences played by different supported boundaries, thermal environmental conditions, different elastic foundations, and volume fraction index are discussed in detail. It is worth noting that the effect of nonlinear elastic foundation increases with increasing deflection
Parallel Control-volume Method Based on Compact Local Integrated RBFs for the Solution of Fluid Flow Problems
Get PDFIn this paper, a high performance computing method based on the Integrated Radial Basis Function (IRBF), Control Volume (CV) and Domain Decomposition technique for solving Partial Differential Equations is presented. The goal is to develop an efficient parallel algorithm based on the Compact Local IRBF method using the CV approach, especially for problems with non-rectangular domain. The results showed that the goal is achieved as the computational efficiency is quite significant. For the case of square lid driven cavity problem with Renoylds number 100, super-linear speed-up is also achieved. The parallel algorithm is implemented in the Matlab environment using Parallel Computing Toolbox based on Distributed Computing Engine