Suong V. Hoa

Vibration of a rotating beam with tip mass

Abstract The vibration frequency of a rotating beam with tip mass is investigated. The finite element method is used, a third order polynomial being assumed for the variation of the lateral displacement. The effects of the root radius, the setting angle and the tip mass are incorporated into the finite element model. The results are compared with results from previous authors utilizing Myklestad and extended Galerkin methods. The results show that the setting angle has a significant effect on the first mode frequencies but not on the high frequencies. The tip mass tends to depress the frequencies at low speeds of rotation but it tends to increase the frequencies at high speeds of rotation. The results of this work have applications in wind turbine rotors, helicopter rotors, etc., and the method used here can be extended to investigate the vibration frequency of flexible blade auto cooling fans.

The study of tapered laminated composite structures: a review

Following laminated composite plates and beams, tapered laminated structures, which are formed by dropping off some of the plies at discrete positions over the laminate, have received much attention from researchers because of their structural tailoring capabilities, damage tolerance, and their potential for creating significant weight savings in engineering applications. A review of recent developments in the analysis of tapered laminated composite structures with an emphasis on interlaminar stress analysis, delamination analysis and parametric study is presented. A discussion of various approaches to modelling and analysis of interlaminar response of tapered composites using finite elements and non-finite elements is given. Displacement-based finite elements and hybrid finite elements that are commonly used are also reviewed. A review of various studies on delamination failure mechanisms as a result of drop-off plies in the tapered composites is given next, which mainly encompasses a stress-strength approach and a fracture-mechanics approach. Lastly, a variety of methods that are being used in the parametric studies regarding the structural integrity is presented. Overall remarks drawn from the reviewed works are given in the final section of the paper.

Toughening Mechanism of Epoxy Resins with Micro/Nano Particles

The toughening mechanism of epoxy resin mixed with micro/nano particles is investigated in this study. The effects of particle size on maximum stresses are studied. Analytical cell models of fracture are proposed to probe the toughening mechanism. These models are based on the assumption that increase of fracture surface area is a main factor to improve the toughness of the material. These models give the correlation of parameters (material properties, volume fraction, size, and amount of particles and epoxy resin) and the fracture toughness, and build the upper limit of toughness improvement. Some significant results are obtained for understanding the toughening mechanism of epoxy resin with micro/nano particles.

A vibration method for measuring mechanical properties of composite, theory and experiment

This paper presents a method for identifying elastic and damping properties of composite laminates by using vibration test data. The analysis model is established based on a finite element model which considers the effect of transverse shear deformation and hysteretic damping. The reduced elastic constants and material loss factors are selected as the updated parameters. Since the damping mainly causes a change of the imaginary part in eigenvalues and eigenvectors, the complex modal parameters are measured. The selected parameters are identified by minimizing an error function containing the deviations of eigenvalues and responses between experiment and analysis. The numerical study shows that satisfactory results including transverse shear moduli can be obtained by designing a suitable plate specimen. Experimental results demonstrate the efficiency of the proposed method. In principle, the present method allows all elastic constants and damping factors to be determined simultaneously.

The Effect of Geometry on Interlaminar Stresses of [0/90]s Composite Laminates with Circular Holes

The effect of the radius to thickness ratio R/t on the interlaminar stresses around the hole in a [0/90]s composite laminate containing a circular hole and loaded in uniaxial tension was investigated. Three dimensional finite elements with a technique that is similar to substructuring were used for the analysis. The results show that as the ratio R/t increases, the magnitude of the tangential interlaminar shear stress on the interface between the crossed plies and near the hole edge increases. Also, as the ratio R/t in creases, the maximum of the interlaminar normal stress on the midplane near the hole increases and its position on the hole edge shifts towards the transverse axis where other stresses are also maximum.

Carbon Nanotube Composites for Wideband Millimeter-Wave Antenna Applications

In this paper, we explore using carbon nanotube (CNT) composite material for wideband millimeter-wave antenna applications. An accurate electromagnetic model of the composite antenna is developed using Microwave Studio for numerical analysis. Good agreement between computed and measured results is shown for both copper and CNT antennas, and their performance is compared. The CNT antenna shows stable gain and radiation patterns over the 24 to 34 GHz frequency range. The dispersion characteristics of the CNT antenna show its suitability for wideband communication systems. Using a quarter-wave matched T-junction as feed network, a two-element CNT antenna array is realized and the performance is compared with a copper antenna. The housing effect on the performance of the CNT antenna is shown to be much lower than for the copper antenna.

Hybrid finite element method for stress analysis of laminated composites

Preface. 1. Introduction. 2. The Hybrid Finite Element Method. 3. Development of Hybrid Element Technique for Analysis of Composites. 4. Partial Hybrid Elements for Analysis of Composites. 5. Numerical Examples of Finite Element Analysis and Global/Local Approach. Index.

An analytical solution for anisotropic plates containing triangular holes

Abstract An analytical solution for the two-dimensional stress distribution around a triangular hole is investigated. The desired loading is a stress P in direction a from the x-axis of the plate. The solution presented here will account for anisotropic material and accept different length/height ratios of the triangular hole, different degrees of bluntness at the triangle vertex as well as different orientations of the load.

Curing simulation of thick thermosetting composites

Abstract A one-dimensional through-the-thickness simulation is developed in which heat conduction, kinetic, viscosity and flow (squeezed sponge model) equations are solved as a coupled system of equations. The control-volume method combined with the alternating direction explicit method is employed in the solution. Heat capacity, density, thermal conductivity and permeability of the composite are considered as functions of fibre volume fraction. It is shown that either temperature overshoot at the middle of the composite or incomplete through-the-thickness consolidation can put a restriction on the application of each cure cycle up to a certain thickness. Although the recommended cure cycles for a thick composite can satisfy the temperature conditions, complete through-the-thickness consolidation mostly cannot be achieved. Pressure effect, bleeding from the top and bottom and prebleeding are studied as possible solutions for incomplete consolidation. It seems that the prebleeding technique is the most promising method of fabrication for thick composites.

Full-Composite Fractal Antenna Using Carbon Nanotubes for Multiband Wireless Applications

In this letter, single-wall carbon nanotube (CNT) composite materials are explored for the design of multiband antennas. An accurate electromagnetic (EM) model of the modified Sierpinski fractal composite antenna is developed using Microwave Studio for numerical analysis. For antenna fabrication, we printed CNT on both sides of a substrate and then cut out the desired antenna pattern using a high-precision milling machine. The CNT material was hardened by resin infiltration in order to be processed on the milling machine. The CNT antenna shows satisfactory gain and radiation patterns for UHF-RFID (900 MHz), Bluetooth (2.4 GHz), and WLAN (5.5 GHz) applications. Good agreement between computed and measured results is observed.