Sang-Eui Lee

Mechanical Properties of MWNT-Loaded Plain-Weave Glass/Epoxy Composites

Carbon nanotubes (CNTs) have shown great potential for the reinforcement of polymers or fiber-reinforced composites. In this study, mechanical properties of multi-walled carbon nanotube (MWNT)-filled plain-weave glass/epoxy composites intended for use in radar absorbing structures were evaluated with regard to filler loading, microstructure, and fiber volume fraction. The plain-weave composites containing MWNTs exhibited improved matrix-dominant and interlaminar fracture-related properties, that is, compressive and interlaminar shear strength. This is attributed to strengthening of the matrix rich region and the interface between glass yarns by the MWNTs. However, tensile properties were only slightly affected by the addition of MWNTs, as they are fiber-dominant properties.

Prediction of mechanical behavior of spatially reinforced composites for kick motor nozzle

Abstract This paper predicts the material properties of spatially reinforced composites (SRCs) and analyzes the mechanical behavior of a kick motor nozzle manufactured from that material. To find the appropriate SRC structure for the nozzle throat that satisfies given design conditions, the equivalent material properties of the SRC are predicted using the superposition of rod and matrix stiffnesses. The kick motor nozzle considered in this study consists of graphite or SRC as the throat part, carbon/phenol as the outer surface of the entrance part and inner surface of the expansion part, and steel as the outer surface of the expansion part. The material properties in arbitrary spatial directions are predicted and compared for 3-D and 4-D SRCs suitable to an axisymmetric kick motor nozzle structure. The 4-D SRC shows the smallest and uniform deformation in the nozzle throat, which has a favorable effect on the rocket thrust. The equivalent material properties of SRC are input to analyze the mechanical behavior of the kick motor nozzle using finite element method.

A Study on Electromagnetic Wave Absorbing Sandwich Structures

The object of this study is to design the Radar Absorbing Structures (RAS) having sandwich structures in the X-band () frequencies. Glass fabric/epoxy composites containing conductive carbon blacks and carbon fabric/epoxy composites were used for the face sheets. Polyurethane(PU) foams containing multi-walled carbon nanotube (MWNT) were used for the core. Their permittivities in the X-band were measured using the transmission line technique. The reflection loss characteristics for multi-layered sandwich structures were calculated using the theory of transmission and reflection in a multi-layered medium. Three kinds of specimens were fabricated and their reflection losses in the X-band were measured using the free space technique. Experimental results were in good agreements with simulated ones in 10dB absorbing bandwidth.㨊吀Ѐ㘹〻Ⰰ䉵楬摩湧Ⱐ捯湳瑲畣瑩潮⁡湤⁣楶楬⁥湧楮敥物湧

A Study on Mechanical Properties of MWNT/PMMA Nanocomposites

ABSTRACT Multi-walled carbon nanotube (MWNT)/poly (methyl methacrylate) composites were fabricated with the variation of the nanotube-concentration through film casting. It was confirmed that the nanotubes were well dispersed in PMMA according to SEM images. To investigate the mechanical properties of the MWNT/PMMA nanocomposites, tensile tests were performed varying the MWNT-concentrations. As the MWNT concentration increased from 0 to 0.15 wt%, MWNT/PMMA nanocomposites were improved by about 20% in the tensile strength and by about 32% in the tensile modulus. Because MWNTs in MWNT/PMMA nanocomposites were assumed to be randomly oriented, the tensile modulus of the nanocomposite was evaluated through the Tsai-Pagano equation which has been applied to short fiber composites for estimating their modulus. However, the estimated results were not in agreement with the experimental results from tensile tests. It is attributed to two reasons. First, MWNTs in this research were not stretched straightly but entangled ones. That is, MWNT could not be assumed to be a short fiber. Second, the concentration of MWNT is too small to be compared with that of the short fiber composites.