Composites Processes & Simulation

Liquid composite molding (LCM) is a processing method to manufacture high-performance composite parts like aircraft and automotive structural components, prosthetics, sports equipment, and the largest wind-turbine blades. It entails closing a mold on a dry fibrous reinforcement, and then pressure-pushing and/or vacuum-drawing a polymer resin such as epoxy through those fibers, and then curing the resin once the reinforcement is filled. LCM is a lower-cost processing alternative for these applications compared to the more traditional route of autoclave-cured prepreg. BYU’s composites lab is working on various ways to optimize the mechanical properties from LCM-made parts, to further reduce part cost, and any other strategy we can think of to help manufacturers learn the process, enabling the low-cost manufacture of light-weight super-strong components.

Faculty Supervisor

Dr. Andy George has been working on composites process optimization since starting a European PhD on the topic in 2007. He is heavily involved with a worldwide community of researchers on this topic, the Air Force Research Laboratory (AFRL), as well as with the Utah and national chapters of the Society for the Advancement of Material and Process Engineering (SAMPE).

Areas of Interest

Optimization of liquid composite molding, for minimal void content

The main drawback to LCM (compared to autoclave prepreg processing) is the tiny bubbles that are formed during the wet out of the reinforcement, owing from the different velocities of the flow within the yarns, and between the yarns. Once the resin cures, these bubbles become trapped in place and are known as voids which act as stress-concentrators and adversely affect the mechanical properties. This bubble/void formation, and what happens to the bubbles after they form, has been poorly understood because of the difficulties of characterizing tiny bubbles inside a mold during LCM processing. This is especially the case with carbon fiber reinforcements, as carbon fiber is black and opaque. A characterization method has been developed at BYU, however, which allows bubble imaging during LCM processing (“in situ”). The method involves macro-lens photography, thick transparent tooling, UV-sensitive dyes in the resin (for contrast) and black light illumination.

With these images of the bubbles, BYU researchers are now looking for the optimal flow velocities required to minimize void formation at the flow front, as well as determine what pressures are required to remove the bubbles after formation. This research is aimed at driving down the cost of high-performance composites by optimizing the resulting mechanical properties of parts made from these lower cost LCM processes. This will in turn allow automotive manufacturers to be able to improve fuel economy, by allowing greater use of composites, as well as increase the manufacturing rates of civilian and military aircraft.

Flow Simulation and Permeability Measurement

LCM flow simulation involves virtually simulating the flow of resin through the fibers, such as epoxy filling a carbon fiber reinforcement. Such simulation can be used to determine optimal processing conditions such as applied pressures and temperatures, and locations for the resin inlets and vents. This can all be done before the expensive tooling is made, and iterations of the process can be done with much less material and time costs compared to doing physical prototyping.

BYU researchers are investigating various facets of such LCM process simulation in order to make the simulation more accurate, and more useful to manufacturers. These include:

• Characterization of the compressibility of composite reinforcements, i.e. how thick will it be under a vacuum bag, and how much pressure will be required from a press to close a mold.
• Viscosity (kinetics and rheometry modeling), i.e. how fast does the viscosity build up as the epoxy is curing, and how long will the manufacturer have to mold the part before the epoxy cures.
• Reinforcement permeability, i.e. how easily does the resin flow through a given reinforcement, such as a carbon fiber weave.

BYU is involved in an international group of researchers tasked with development of an ISO standard for permeability measurement. This involves several parallel studies to determine possible variability in permeability measured caused by different test conditions, and will determine the future standard test method prescribed to everyone working with LCM process simulation.

Recent Publications

• A. Yong, A Aktas, D. May, A. Endruweit, S. Lomov, S. Advani, P. Hubert, S. Abaimov, D. Abliz, I. Akhatov, M. Ali, S. Allaoui, T. Allen, D. Berg, S. Bickerton, B. Caglar, P. Causse, A. Chiminelli, S. Comas-Cardona, M. Danzi, J. Dittmann, C. Dransfeld, P. Ermanni, E. Fauster, A. George, et al., “Experimental Characterization of textile compaction response: a benchmark exercise,” Composites Part A, Vol. 142, March 2021, p. 106243.
• Lystrup, C., A. George, B. Zobell, K. Boster, C. Childs, H. Girod, D. Fullwood, “Optical measurement of voids in situ during infusion of carbon reinforcements,” Journal of Composite Materials, Vol. 55(6), March 2021, pp. 775-786.
• Sisodia, S., D. Bull, A. George, E. Gamstedt, M. Mavrogordato, D. Fullwood, M. Spearing, “The effects of voids in quasi-static indentation of resin-infused reinforced polymers,” Journal of Composite Materials, Vol. 53(28-30), December 2019, pp. 4399-4410.
• May, D., A Aktas, S. Advani, D. Berg, A. Endruweit, E. Fauster, S. Lomov, A. Long, P. Mitschang, S. Abaimov, D. Abliz, I. Akhatov, M. Ali, T. Allen, S. Bickerton, M. Bodaghi, B. Caglar, H. Caglar, A. Chiminelli, N. Correia, B. Cosson, M. Danzi, J. Dittmann, P. Ermanni, G. Francucci, A. George, et al., “In-plane permeability characterization of engineering textiles based on radial flow experiments: A benchmark exercise,” Composites Part A, Vol. 121, June 2019, pp. 100-114.
• A. George, P. Hannibal, M. Morgan, D. Hoagland, S. Stapleton, “Compressibility Measurement of Composite Reinforcements for Flow Simulation of Vacuum Infusion,” Polymer Composites, Vol. 40(3), March 2019, pp. 961-973.
• Hoagland, D., A. George, “Continuous permeability measurement during unidirectional vacuum infusion processing,” Journal of Reinforced Plastics and Composites, Vol. 36(22), November 2017, pp.1618-1622.
• Sisodia, S., S. Garcea, A. George, D. Fullwood, M. Spearing, E.K. Gamstedt, “High-resolution computed tomography in resin infused woven carbon fibre composites with voids,” Composites Science and Technology, Vol. 131, August 2016, pp. 12-21.

Graduate Students

• Collin Childs – Permeability of Sheared Composite Reinforcements
• Garen Murray – Effect of Powdered Epoxy Resin Tackification on Room Temperature Composite Laminate Mechanical Properties

Opportunities

The Composite/Polymer Processes & Simulation Research Lab is hiring! If you are an undergraduate student interested in exploring composites or plastics, contact Andy George for information on how to apply. Thesis topics for Master's and Doctorate students are also available.