Characterization of local preform defects in resin transfer molding by the gas flow method and statistical analysis

An in situ gas flow method has been developed to determine the quality of fibrous preforms in resin transfer molding (RTM) prior to injection. Defects resulting from preform misplacement, accidental inclusions, etc., are quantified. Unintentional permeability variations can result in defective part production and excessive part scrapping. Pressure profiles generated during steady-state gas flow are affected by such variations. To determine defect location and severity, a multivariate statistical approach is applied to compare measured quantities from a test preform with quantities obtained from known groups. The tested preform is then classified into a defect free group or any one of several groups associated with specific types of defects. A specially designed mold, with multiple ports for gas injection and pressure measurement, was used to test various cases with and without defects. Application of this process has been accomplished on an unmodified industrial mold used to fabricate composite curved I-Beam stiffeners.