Papers by Author: Jang Kyo Kim

Abstract: The microscopic mechanism of ultrasonic wire bonding is investigated by molecular dynamics simulation on the interfacial contact and adhesion. Considering that the real bonding area is in the state of plane strain, a two-dimensional atomic model is presented. Sutton-Chen potential is adopted for the interaction between gold atoms. Computational results indicate that a strong adhesion generates at the interface after intimate contact between the wire and the bond pad, and the adhesive force should be the mechanism of ultrasonic wire bonding. Combining the real contact area from finite element analysis with the adhesive force from molecular dynamics simulation, the bonding strength of ultrasonic wire bonding is estimated.

Abstract: The influence of nanoclay on the impact damage resistance of carbon fiber-epoxy (CFRP) composites has been investigated using the low-velocity impact and compression after impact tests. The load-energy vs time relations were analyzed to gain insight into the damage behaviors of the materials. Compression-after-impact (CAI) test was performed to measure the residual compressive strength. The CFRPs containing organoclay brought about a significant improvement in impact damage resistance and damage tolerance. The composites containing organoclay exhibited an enhanced energy absorption capability with less damage areas and higher CAI strengths compared to those made from neat epoxy. A 3wt% phr was shown to be an optimal content with the highest damage resistance.

Abstract: The carbon nanotube (CNT) surface is successfully modified using the UV/Ozone treatment and a triethylenetetramine (TETA) solution for use as the reinforcement for polymer matrix nanocomposites. These treatments along with ultrasonication are aimed to disperse the CNTs uniformly in the resin matrix, as well as to provide the CNT surface with chemical functionalities for adhesion with resin. Fourier transform infra-red (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) are performed to evaluate the changes in chemical structure and surface functional groups arising from the chemical treatment. The practical implications of the surface functional groups for improving the interfacial adhesion are discussed.

Abstract: This paper reports a study based on a novel concept of ‘self-healing’ coatings applied onto the brittle fibre surface to reduce the stress concentrations and thus to improve the reinforcing efficiency in a composite. The individual E-glass fibres as well as rovings were coated with a carbon nanotube (CNT) reinforced epoxy composite. The tensile strengths were measured for the individual and bundle fibres, which were treated statistically to determine the Weibull parameters and thus to evaluate the notch sensitivity of the fibres with and without coating. The results indicate that the tensile strength of the individual fibre increased by 10% after coating with neat epoxy. Coating with epoxy nanocomposite containing 0.3wt% MWNT further improved the tensile strength. However, increasing the nanotube content was not necessarily beneficial due to the formation of nanotube agglomerates within the matrix. The tensile tests on fibre roving also showed a clear trend of beneficial effect of nanocomposite impregnation on tensile strength. The rovings impregnated with nanocomposite exhibited a more uniform strength distribution and higher strengths than those impregnated with neat epoxy. Changes in prevailing failure mechanisms influenced by the epoxy and nanocomposite coatings are identified.

Abstract: This paper presents a method for chemical functionalization of CNTs through the combined process of UV/O3 treatment and silanization process. FT-IR and TEM were employed to characterize the changes in surface functionalities and morphology. The results indicate improved dispersion and attachment of silane molecules on the surface of CNTs. Epoxy matrix nanocomposites containing functionalized CNTs showed much better dispersion with associated higher mechanical properties than those without functionalization. These findings confirmed the improved interfacial interactions due to covalent bonding between the functionalized CNTs and epoxy resin.

Abstract: The wear resistance of epoxy-based nanocomposites reinforced with octadecylamine-modified clay was studied. Two testing methods, including the ball-on-disc abrasion test and the nanoscratch test, were used to measure the macro- and micro-wear behaviors. The ball-on-disc abrasion test suggests that the short- and long-term wear behaviors of neat epoxy and 5wt% nanoclay composites were similar, although the wear resistance as measured by the volume of material removed was greater for the clay nanocomposite than for the neat epoxy. The incorporation of nanoclay into the epoxy showed little effect on the coefficient of friction.

Abstract: The fracture resistance and mechanical properties of carbon fiber reinforced composites (CFRPs) containing organoclay-filled epoxy resin are studied. The XRD analysis and TEM examination revealed well-dispersed organoclay in the epoxy matrix displaying a mixture of exfoliation and intercalation. There was a significant improvement in flexural modulus and a marginal reduction in flexural strength of epoxy matrix due to the incorporation of organoclay. The quasi-static fracture toughness of epoxy increased nearly 60% with the addition of 3wt% clay, but there was a 45% drop in impact fracture toughness with 1wt% clay. When CFRPs were fabricated with the clay-modified epoxy resin, both the flexural modulus and strength of the hybrid composites showed negligible changes due to a few wt% of organoclay in the matrix. The interlaminar crack growth stability and the corresponding mode I interlaminar fracture toughness of the hybrid composites with organoclay improved substantially compared to those with carbon fibres only. The hybrid composites typically presented rough matrix surface associated with pinning and crack tip bifurcation, whereas the composite made from neat epoxy showed a smooth river line structure which is characteristic of brittle epoxy. The correlation between the composite interlaminar fracture properties and the toughness of modified matrix is discussed.