Joohyuk Park

Wear Behavior of Functionalized Multi-walled Carbon Nanotube Reinforced Epoxy Matrix Composites

This article studies the tribological behavior of functionalized multi-walled carbon nanotubes (MWNTs) reinforced epoxy matrix composites. MWNTs reinforced epoxy composites are fabricated by an injection molding process. The effects on the tribological properties of different loading concentrations and different functional groups of MWNTs are investigated by using a linear reciprocal wear tester. As increasing the concentration of MWNTs reduces wear loss, better tribological property was attained on functionalized MWNTs than as-produced MWNTs. The changes in worn surface morphology are observed in order to investigate the wear behavior. The MWNTs in the epoxy matrix near the surface are exposed and became a lubricating working film on the worn surface. The dispersion and interfacial bonding of MWNTs in the epoxy matrix are investigated from the fracture surface. The existence of MWNT at the wear surface is verified by a Raman spectrometer.

Alignment of multi-walled carbon nanotubes in a polyethylene matrix by extrusion shear flow: mechanical properties enhancement:

This article discusses the effect of shear rates on the alignment of Multi-walled Carbon Nanotubes (MWCNTs) in a polyethylene (PE) matrix. Shear forces were applied with a self-constructed controllable shear extrusion system, and the degree of orientation of the MWCNTs was analyzed through image analysis of the microtome sectioned surfaces. Partially aligned MWCNTs in a PE matrix are successful fabricated in this study. It was found that the degree of alignment was increased by increasing shear rates, and an optimal shear rate was discovered. Tensile test results indicate that the mechanical properties of composites increase with an increasing degree of CNTs alignment. A partially aligned MWCNTs PE composite exhibited greater mechanical properties than randomly oriented MWCNTs. Differential scanning calorimetry analysis revealed that MWCNTs alignment by shear flow extrusion played a major role in mechanical property enhancement as compared to the crystallization effect of the polymer.

A numerical simulation of the resin film infusion process

A numerical analysis was conducted for the resin film infusion (RFI) process using semi-cured thermosetting resin films. Mathematical models were developed for the compression of fiber and the viscosity of resin. The force balance between the fiber preform and the resin was considered to account for the deformation of fiber preform and the swell of fiber during the infusion. In an effort to locate the optimal process conditions such as the mold temperature, the fiber volume fraction, and the infusion pressure, a parametric study was carried out for the progression of resin and the infusion time for different process conditions. The numerical code developed in this study was found to be useful in determining the maximum height of vertical sections that can be infused by squeezing the liquefied resin film from the base panel.

Numerical study of the single fibre push-out test: Part III. Singularity of interface stresses

The singular behaviour at the free edges of the fibre-matrix interface is analysed for the fibre push-out test geometry based on the boundary element method. The fibre push-out test has been extensively used to measure the fibre-matrix interfacial properties in polymer, ceramic and metal matrix composites. There are two free edges in the fibre push-out specimen: one is at the loaded fibre end and the other at the supported fibre end. The singular stresses can be expressed as a function of singular exponent and singular stress intensity. It is shown that the singular exponents obtained at both fibre ends are characteristic of composite constituent properties, such as Youngs moduli of fibre and matrix, and does not vary with specimen dimensions. The singular exponents are real and identical for the shear and radial stress components at fibre ends where the wedge angles are the same. The singular stress intensities are also implicit in material properties, and vary with specimen dimensions, such as fibre to matrix radius ratio, fibre aspect ratio and support hole size. An interfacial failure criterion is proposed here based on the average stress concept to determine the critical singular stress intensities in mode I and mode II loads.