A Gas Assisted Method for Local Permeability Variation Detection in VARTM Process

In vacuum assisted resin transfer molding (VARTM) process, fiber preform defects result very often from inappropriate placement at edge regions when the fiber preform has three-dimensional shape. The unintentional permeability variation is difficult to detect by viewing through the transparent vacuum bag. In this paper, a method was proposed for detecting the local permeability variation of the orthotropic and isotropic fiber preform by measuring the pressure profile of the steady gas flow passing through the fiber reinforcement under low Reynolds number and comparing it with the ideal pressure profile of the steady gas flow under the condition of orthotropic, isotropic, and homogeneous permeability profile. The average principal permeability value of each subregion of a test preform was estimated based on the measured pressure profile, the values were then input into the simulation software to obtain the flow prediction. Low Reynolds number was maintained through the control of the pressure gradient profile of the steady gas flow. Water is used as the liquid that flows through the fiber preform and the flow pattern was compared with the prediction from the liquid flow simulation.