Void Formation During Manufacturing of Composites with Liquid Composite Molding Processes

University Of Delaware, Newark DE

Investigators

Abstract

A manufacturing process, termed Liquid Composite Molding and used to fabricate polymer composites, places a fibrous textile-based reinforcement into a mold and injects a polymer resin into it. A common manufacturing defect in the polymer composite are voids which form and grow during the process. Voids during composite processing may form at all length scales: at the macro (cm to mm scale- part scale); meso (mm to sub mm scale- the fiber tow scale); and micro scale (micron to submicron scale filament diameter scale). The presence of voids results in a significant reduction in properties and even rejection of the part. Due to lack of understanding about void formation and growth, expensive inspection techniques need to be incorporated to ensure fidelity of the produced part to design specifications. This work will conduct fundamental research to incorporate the required knowledge in a manufacturing simulation to provide guidelines to reliably manufacture void-free parts. This will reduce costs due to less rejections and inspections from the use of computer simulations instead of time-consuming and expensive trial and error methodology. In turn, composites will be more cost competitive with steel and aluminum and reduce the need for import of these materials. The research will re-invigorate US manufacturing sector by fabricating cost effective, light weight and corrosion free composite parts in aerospace, automotive, biomedical, energy and sports industries benefiting the U.S. economy and society. The research will be incorporated in a computer simulation which will also provide the much-needed training to practitioners and professionals to reduce the manufacturing cycle time from design to prototype to product and encourage high school students to pursue STEM fields to advance US competitiveness in the global economy. This research describes the void dynamics to model the mold filling stage of the Liquid Composite Molding processes. The general framework developed will couple the macro, meso and micro scale physics to predict void formation, growth and movement as a function of material, process and geometric parameters. To accomplish this, (i) a multi-scale flow modeling approach will be developed with governing equations that include the void transport and dynamics to (ii) be included into an existing simulation to improve its predictive capabilities for porosity at macro, meso and micro scale. This will help determine material and processing parameter window that will ensure successful resin filling within tolerated target porosity. Such guidelines will allow manufacturing engineers to develop strategies such as improving vacuum effectiveness, introducing local consolidation to increase resin pressure and manipulate resin flow front to avoid entrapment of voids. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.