Sun K. Kim

Determination of three-dimensional permeability of fiber preforms by the inverse parameter estimation technique

A method is presented for measuring the permeability of three-dimensional orthotropic fiber preforms using the inverse parameter estimation technique. The method is based on an optimization procedure that minimizes differences between computed and measured times of arrival of the flow front at various locations in the mold during resin transfer molding. The arrival time is computed by numerical simulation using the control volume finite element method. The validity of this method was examined experimentally. It was shown that the proposed method can be implemented in a straightforward manner and yields reliable results.

Optimal control of accelerator concentration for resin transfer molding process

Resin cure following mold filling is an essential element in resin transfer molding. To fabricate a composite part with high dimensional stability and minimize residual stress, uniform resin cure should be achieved. This study considers a three-part resin system composed of epoxy, hardener and accelerator. The cure kinetics can be controlled by the accelerator concentration at the injection gate. A numerical method that can predict degree of cure distribution based on accelerator concentration at the gate was proposed. The degree of cure distribution is obtained by solving the resin flow, heat transfer, accelerator concentration and cure problems sequentially. Utilizing this numerical method, an optimal variation of accelerator concentration during mold filling was sought by solving a constrained optimization problem. The effect of accelerator control on degree of cure distribution was investigated and its validity was examined for two different geometries.

Solution To Inverse Heat Conduction Problem In Nanoscale Using Sequential Method

An inverse heat conduction problem for nanoscale structure is studied. The conduction phenomenon is modeled using the Boltzmann transport equation. Phonon-mediated heat conduction in one dimension is considered. One boundary is exposed to an unknown temperature and the other boundary, where temperature observation takes place, is subject to a known boundary condition. A sequential scheme with constant function specification is employed for inverse estimation of the unknown temperature. Sample results are presented and discussed.

Gas Flow Method for Detecting Local Preform Defects by Inverse Estimation of Space-Varying Permeability

A method using gas flow is proposed for testing the quality of fibrous preforms in the resin transfer molding process. The method is based on the idea that preform defects cause variation in permeability and deviation from Darcys law. This paper presents a gradient-based inverse method that estimate space-varying permeability by examining the consistency between computed and measured pressures at various locations in the mold during steady-state gas flow through the enclosed preform. Such consistency is achieved by the conjugate gradient method. The computed pressures are obtained by the control volume finite element method (CVFEM). The proposed method was demonstrated by using a specially designed mold with multiple ports for gas injection and pressure measurement, and testing for various cases with and without defects.

Pressure measurement technique in nano- and micro-channels using atomic force microscopy

This article presents a method for measuring pressure profiles in nano- or micro-channels from topographic imaging of thin channel surfaces using atomic force microscopy. The pressure distribution is calculated from the measured conduit deformation by solving an inverse problem. The related computational model and inverse formalism are proposed.