MODELING AND SIMULATION OF DUAL SCALE FLOW IN WOVEN OR STITCHED PREFORMS IN LIQUID MOLDING PROCESSES

摘要

In Liquid Composite Molding (LCM) processes, most fabrics used contain fiber bundles called as fiber tows that are woven or stitched in a bi-directional weave. The resin impregnates the fiber tows at much slower rate than the regions in between the fiber tows due to the higher fiber volume fraction in the tows. This introduces a host of new issues that one must address in modeling and simulation to manufacture a void free part. The most important being that in addition to filling the regions in between the fiber tows, we also need to ensure the saturation of fiber tows with resin. In practice, this is achieved by letting the resin bleed through the vent after the resin reaches the vent in order to allow sufficient time for the fiber tows to saturate. Modeling this phenomenon will provide an estimate on the dwell time necessary for bleeding to saturate the tows and also make it possible to explore process innovations such as attaching additional resistance at the vent to reduce the dwell time. This paper will present the methodology of how we introduce the dual scale flow in our simulation and investigate the benefits of attaching additional resistance at the vent. Two composite panels are manufactured using the VARTM process with and without the use of vent resistance. Sections of the panel are examined for void content using an optical microscope and image analysis. The void content is found to be less when a vent resistance is used. Numerical simulation of the dual scale media is able to validate this trend qualitatively.