Papers by Author: Shiuh Chuan Her

Abstract: In this investigation, the methodology for predicting the dynamic response of a composite laminate shell subjected to low velocity impact is presented. A non-linear integro-differential equation is derived and solved by the numerical scheme of Runge-Kutta method to obtain the time history of the contact force at the impact point of the shell. The contact force is then taken as external force acting on the apex of the shell and solved by the finite element method. The results are validated with the numerical calculation published in the literature.

Abstract: In this investigation, the weight function method was employed to calculate the stress intensity factors for semi-elliptical surface crack in a hollow cylinder. An uniform stress and a linear stress distributions were used as the two references to determine the weight function. The weight function was then applied to a wide range of semi-elliptical surface cracks subjected to non-linear loadings. The stress intensity factors obtained by the weight function were compared with literature results. Good agreement demonstrates the accuracy of the present approach.

Abstract: Multi-walled carbon nanotubes (MWCNT) were dispersed in a mixture of sulfuric and nitric acid with volume ratio of 3:1. Carboxylic acid-functionalized MWCNTS (MWCNT-COOH) were obtained by oxidation pristine MWCNTs via sonication in sulfuric-nitric acid. Epoxy-based nanocomposites reinforced with MWCNTs with and without functionalization were prepared. Chemical functionalization of MWCNTs by oxidation (MWCNT-COOH) was confirmed by FTIR. The properties of nanocomposites were characterized using scanning emission microscopy (SEM). Experimental results showed that functionalization of MWCNTs improved the dispersion of MWCNTs in epoxy matrix compared to those containing MWCNTs without functionalization.

Abstract: Zinc oxide (ZnO) thin films were deposited on glass substrate by Radio frequency (RF) magnetron sputtering. The effect of substrate temperature on the microstructure of the ZnO films has been investigated. Crystal structure and surface morphology of the films were examined by X-ray diffraction (XRD) and atomic force microscopy (AFM). XRD patterns and AFM images show that the crystallinity and grain size are increasing with the increase of substrate temperature.

Abstract: Stress transfer in the carbon nanotube reinforced nanocomposites is investigated in this work. The model consists of two concentric cylinders, namely, a single-walled carbon nanotube cylinder (SWCNT) and a matrix cylinder, as the representative volume element (RVE). The stress analysis is performed using the shear lag model for the axisymmetric RVE. Analytical solutions for the axial normal stresses in the SWCNT and matrix, and the interfacial shear stress across the SWCNT/matrix interface are obtained. Numerical results show that using a large volume fraction improves the efficiency of the stress transfer from the matrix to the carbon nanotubes.

Abstract: The effect of functionalization of multi-walled carbon nanotubes (MWCNT) on the thermal stbility of MWCNT/epoxy nanocomposites was investigated. Epoxy-based nanocomposites reinforced with MWCNTs with and without functionalization were prepared. The thermal stability of nanocomposites was characterized using thermal gravimetric analysis (TGA). Experimental results showed that functionalization of MWCNTs enhanced the decomposition temperature of MWCNTs reinforced nanocomposite compared to those containing pristine MWCNTs.

Abstract: Surface cracks are the most common defects in structures. Ultrasonic has been widely used as a non-destructive evaluation technology in the case of crack characterization. In this investigation, surface waves are applied to a steel block with artificial slots to characterize the crack depth. A series of test specimen with different depths of surface crack ranging from 4mm to 10mm was fabricated. The depth of the surface crack was evaluated using the pitch-catch ultrasonic technology. In this work, 2.25 MHz, 5 MHz and 10 MHz of incident waves were employed to investigate the effect of frequency on the crack depth detection. Experimental test results show that the accuracy of crack depth detection is increasing with the increase of frequency.

Abstract: A tri-layered cracked beam under opening loading is developed for the interfacial fracture toughness measurement. Determination of the mode I strain energy release rate along the second and third layers of the tri-layered beam is carried out analytically. The analytical prediction of the strain energy release rate is validated with the finite element results. The influences of the layer thickness and Young’s modulus on the strain energy release rate are examined through a parametric study.

Abstract: Titanium Nitride (TiN) coatings with high surface hardness, good wear and corrosion resistance, low friction coefficient have been widely used in many applications such as a hard coating of cutting tool, a diffusion barrier layer. In this work, TiN thin films were deposited by D.C. magnetron sputtering process on SUS 304 steel substrate. Magnetron sputtering provides a wide variation of the deposition parameters which affect the morphology of the films and, consequently, their properties. The effects of substrate temperature on the microstructure and corrosion resistance of TiN films were studied in details using atomic force microscopy and potentiostat test. Considerable improvements in the surface roughness and corrosion resistance were observed when the substrate temperature was increased from C to C.

Abstract: Optical fiber sensors with light weight, small size and immunity to electromagnetic interference have been found to be a promising device for use in the development of smart structures. It is well known that the strain transfer from the host structure to the optical fiber sensor is dependent on the bonding characteristics such as adhesive layer and bonded length. In this investigation, the optical fiber sensor is surface bonded on the host structure. A theoretical model consisting of the optical fiber, adhesive layer and host material, is proposed to determine the strain in the optical fiber sensor induced by the host structure. The theoretical predictions were validated with the numerical analysis using the finite element method.