Showing papers by "Dai Gil Lee published in 2003"

Investigation of Optimal Surface Treatments for Carbon/Epoxy Composite Adhesive Joints

Abstract: Although an adhesive joint can distribute the load over a larger area than a mechanical joint, requires no holes, adds very little weight to the structure and has superior fatigue resistance, but it not only requires a careful surface preparation of the adherends but also is affected by service environments. In this paper, suitable conditions for surface treatments such as plasma surface treatment, mechanical abrasion, and sandblast treatment were investigated to enhance the mechanical load capabilities of carbon/epoxy composite adhesive joints. A capacitively coupled radiofrequency plasma system was used for the plasma surface treatment of carbon/epoxy composites and suitable surface treatment conditions were experimentally investigated with respect to gas flow rate, chamber pressure, power intensity, and surface treatment time by measuring the surface free energies of treated specimens. The optimal mechanical abrasion conditions with sandpapers were investigated with respect to the mesh number of sandpa...

Hybrid propeller shaft made of metal and composite material and method of manufacturing the same

Abstract: The propeller shaft comprises a transmission shaft 10 consisting of a hollow metal tube 11 with excellent torque transmissibility and a composite material prepregs 12 having higher specific stiffness than a metal material and stacked to the inner surface of the metal tube, and metal yokes 40 mounted on both ends of the transmission shaft and assembled with other devices. The composite material prepregs is co-cure bonded while applying an axial compressive preload to the transmission shaft and creating a vacuum in a space between a vacuum bag inserted in the transmission shaft and the composite material prepregs of the transmission shaft. Teeth 43 or embossments 44, and adhesive-retaining grooves 45 are formed on inner surfaces of the metal yokes, so the transmission shaft is desirably compression-fitted into the metal yokes. Accordingly, the propeller shaft has advantages of securing improved impact, abrasion, and water resistance.

Adhesion characteristics of carbon/epoxy composites treated with low- and atmospheric pressure plasmas

Abstract: Although an adhesive joint can distribute load over a larger area than a mechanical joint, requires no holes, adds very little weight to structures and has superior fatigue resistance, it requires careful surface preparation of adherends for reliable joining and low susceptibility to service environments. The load transmission capability of adhesive joints can be improved by increasing the surface free energy of the adherends with suitable surface treatments. In this study, two types of surface treatment, namely the low pressure and the atmospheric pressure plasma treatment, were performed to enhance the mechanical load transmission capabilities of carbon/epoxy composite adhesive joints. The suitable surface treatment conditions for carbon/epoxy composite adhesive joints for both low and atmospheric pressure plasma systems were experimentally investigated with respect to chamber pressure, power intensity and surface treatment time by measuring the surface free energies of the specimens. The change in surf...

Micro-drilling of alumina green bodies with diamond grit abrasive micro-drills

Abstract: Since ceramic plates containing many micro-holes are used for MCPs (Micro-channel plates) for electron amplification, catalytic converters, filters, electrical insulators and thermal conductors in integrated circuits, the efficient drilling of micro-holes in ceramic plates is important for productivity and cost. Since ceramics have poor machinability due to their low thermal conductivity, high hardness and high brittleness, in this work, alumina green bodies rather than sintered alumina were drilled to manufacture ceramic MCPs, followed by sintering the machined green bodies. Alumina green bodies were drilled with electro-deposited diamond grit WC micro-drills, and the cutting force with respect to drilling time was measured to determine a suitable micro-drilling condition. From the measurement of the micro-drill tip wear during micro-drilling of alumina green bodies, a model for the cutting force during micro-drilling was constructed.

Piezoelectric monitoring of the reliability of adhesive joints

Abstract: Since the reliability of adhesively bonded joints for composite structures is dependent on many parameters such as the shape and dimensions of joints, type of applied load, and environment, so an accurate estimation of the fatigue life of adhesively bonded joints is seldom possible, which necessitates an in-situ reliability monitoring of the joints during the operation of structures In this study, a self-sensor method for adhesively bonded joints was devised, in which the adhesive used works as a piezoelectric material to send changing signals depending on the integrity of the joint In order to validate the method, the piezoelectric properties of the adhesive were measured during the fatigue test Electrically conducting adherends were used as electrodes without embedded sensors, and the adhesively bonded joint was modeled as the equivalent parallel circuit composed of electric charge and capacitance From the investigation, it was found that the electric charge increased gradually as cracks initiated a

In situ cure monitoring of adhesively bonded joints by dielectrometry

Abstract: Since the reliability of adhesively bonded joints is much dependent on the curing status of thermosetting adhesives, the in situ cure monitoring during the cure of adhesive joints could improve the quality of adhesively bonded joints as it enables one to control the cure parameters. In this work, a dielectric method which measures the dissipation factor of the adhesive during the cure of joints and converts it into the degree of cure of the adhesive was devised. Steel adherends were used for the adhesively bonded joints because the steel adherends worked as the electrodes for the measurement of dissipation factor without additional electrodes. The relation between the dissipation factor and the degree of cure of adhesive was investigated, which could eliminate the temperature effect on the dissipation factor that is largely affected by the degree of cure and temperature of adhesive. Comparing the results obtained by the method developed with those by DSC (differential scanning calorimetry), it was found t...

Adhesion characteristics of plasma surface treated carbon/epoxy composite

Abstract: The load transmission capability of adhesive joints can be improved by increasing the surface free energy of the adherends with surface treatments. In this paper, suitable plasma surface treatment conditions for carbon/epoxy composite adherend were investigated to enhance the strength of carbon/epoxy composite adhesive joints using a capacitively coupled radio-frequency plasma system. Effects of plasma surface treatment parameters on the surface free energy and adhesion strength of carbon/epoxy composite were experimentally investigated with respect to gas flow rate, chamber pressure, power intensity, and surface treatment time. Quantitative chemical bonding analysis determined with XPS (X-ray photoelectron spectroscopy) was also performed to understand the load transmission capabilities of composite adhesive joints with respect to surface treatment time.

Ultraviolet surface treatment for adhesion strength improvement of carbon/epoxy composite

Abstract: —As the applications of composite structures have increased, various techniques to join composite parts to the structures have been developed in order to meet the required adhesion strength In this work, surface modification of carbon/epoxy composites was investigated using ultraviolet (UV) surface treatment to increase the adhesion strength between the carbon/epoxy composite and the epoxy adhesive After UV surface treatment, X-ray photoelectron spectroscopy (XPS) analysis and contact angle measurements were performed to analyze the surface characteristics of the carbon/epoxy composites From the results of XPS analyses and adhesion strength tests, it was found that the increase of C O bond density on the surface of carbon/epoxy composite caused the enhancement of adhesion strength Also it was found that the UV-B (wavelength 280–315 nm) surface treatment resulted in a superior adhesion strength compared to the UV-A (wavelength 315–400 nm) surface treatment

Trenchless Repairing of Underground Pipes Using RTM Based on the Axiomatic Design Method

Abstract: To overcome the problems of excavation technology for repairing damaged underground pipes, such as sewer pipes, various trenchless (excavation free or no-dig) technologies has been proposed and tried, but they have some drawbacks such as high cost and inconvenience of operation.In this study, the rehabilitation process of underground pipes with glass fiber fabric polymer composites using Resin Transfer Molding (RTM), which overcomes the problems of present trenchless technologies has been developed through the axiomatic design approach. For the reliable and faultless operation, all the problems and situations that may occur during the real construction has been taken into account at every stage of the design process.The developed process requires shorter operation time and lower cost with smaller and simpler operating equipments than conventional trenchless technologies. From the investigation, it has been found that the developed repair technology with appropriate process parameters determined by design ...

Reliability Monitoring of Adhesive Joints by Piezoelectricity

Abstract: Since the reliability of adhesively bonded joints for composite structures is dependent on many parameters such as the shape and dimensions of joints, type of applied load, and environment, so an accurate estimation of the fatigue life of adhesively bonded joints is seldom possible, which necessitates an in-situ reliability monitoring of the joints during the operation of structures. In this study, a self-sensor method for adhesively bonded joints was devised, in which the adhesive used works as a piezoelectric material to send changing signals depending on the integrity of the joint. From the investigation, it was found that the electric charge increased gradually as cracks initiated and propagated in the adhesive layer, and had its maximum value when the adhesively bonded joint failed. So it is feasible to monitor the integrity of the joint during its lifetime. Finally, a relationship between the piezoelectric property of the adhesive and crack propagation was obtained from the experimental results.

Dielectric Cure Monitoring of Thermosetting Matrix Composites

Abstract: Cure monitoring can be used to improve the quality and productivity of thermosetting resin matrix composite products during their manufacturing process. In this work, the sensitivity of dielectrometry was improved by adequate separation the efforts of sensor and externals on the measured signal. A new algorithm to obtain the degree of cure during dielectric cure monitoring of glass/polyester and glass/epoxy composites was developed by employing a function of both temperature and dissipation factor, in which five cure monitoring parameters were used to calculate the degree of cure. The decreasing pattern of dissipation factor was compared with the relationships between the degree of cure and the resin viscosity. The developed algorithm might be employed for the in situ cure monitoring of thermosetting resin composites.

Peel strength improvement of foam core sandwich beams by epoxy resin impregnation on the foam surface

Abstract: The interfacial adhesion characteristics between foam cores and faces affect much the structural integrity of foam core sandwich structures. The peel strength between the face plate and the foam core is one of the appropriate parameters for the interfacial characteristics of sandwich structures and its peel energy is also measured for the interfacial characterization. The peel strength is the first peak force per unit width of bondline required to produce progressive separation, and the peel energy is the amount of energy per unit bonding area associated with a crack opening. In this study, to improve the peel strength between the foam core and the face plate of foam core sandwich beams, the surfaces of foam core sandwich beams were resin-impregnated. Then the peel strength as well as peel energy of resin impregnated polyurethane foam core sandwich beams were measured by the cleavage peel test and compared with those of the same sandwich beams without surface resin impregnation on the foam surface.