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 Darcy's 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.