TOP STORY
Suresh Advani, Professor of Mechanical Engineering and Associate Director of CCM, has dedicated most of his research career to taking liquid molding processes from art to science. His LIMS (Liquid Injection Molding Simulation) software program, based on transport processes in materials processing and the physics of flow through fibrous porous media, is an important tool in the effort to improve and automate composite manufacturing processes such as Resin Transfer Molding (RTM), Vacuum Assisted Resin Transfer Molding (VARTM), and Compression RTM. |
Mold Filling simulation of keel beam with time history of resin flow |
These processes involve the injection of resin into a complex mold cavity filled with fibrous reinforcement. They enable the manufacture of net-shape parts, but the complexity in geometry and fiber preform placement can lead to processing inconsistencies. Simulation can eliminate costly trial-and-error mold design and processing strategies.
Advani explains that LIMS enables intelligent manufacturing systems to be constructed after various “what-if” scenarios are performed. For example, users can vary the geometry, the fiber preform arrangement and architecture, the injection parameters, the preform permeability, and the resin characteristics.
“LIMS started as a predictive tool,” he says. “It showed us where the resin was going but initially gave us no control over it. We found that in composites processing, there is a lot of stochastic variation from one part to another, and this was not reflected in the simulation. What we needed was a way to make it more like real life.”
The next phase of LIMS development enabled the program to be used for mold design and optimization, taking into account any variations or disturbances that occurred inside the mold.
“As VARTM grew in popularity,” Advani continues, “it became clear that there was a need to simulate 3-D flow with visualization capability. In VARTM you usually add a flow enhancement layer known as a distribution medium that delivers the resin quickly on top of one of the faces of the composite. Then the resin has to seep through the thickness to fill the regions between the fibers. We further advanced the technology so the program could combine 2D elements to describe the distribution medium and 3D elements to describe the fabric.”
The fabrics used in composites consist of fiber bundles or tows comprising thousands of individual strands of fibers that are woven or stitched together. During injection into such preforms, the region between the fiber tows fills more rapidly than that within the tows. This is crucial, according to Advani, because molders typically shut down the process when resin emerged from the mold vents, but post-processing inspection revealed that there were dry spots in the intra-tow areas.
“It was very important for us to capture the physics of this process in further developing the simulation,” he says. “We were able to introduce a numerical procedure that allows us to track how the fiber tows become saturated with the resin.”
Racetracking—the tendency for resin to race along the edges of the mold—is an important problem in mold-filling processes because it is not repeatable or predictable. “It may be weak or strong,” Advani explains, “depending on how the fabric was cut and placed. One way to ensure that the resin arrives at the vent after it has filled the rest of the mold is to introduce control into the process.”
Virtual sensors added to the simulation provide important information about the flow and enable auxiliary gates to be opened so that the resin moves into areas not being filled because of racetracking. The virtual control scenario has been experimentally validated, and it has been demonstrated that void-free mold filling can be accomplished.
Another way to control flow is by choosing the configuration of the distribution medium. This is especially important for a new area of materials research that Advani has initiated: multifunctional materials in which objects such as sensors and antennas have been embedded. “We've used the simulation to optimize the distribution medium shape so that the resin can easily flow around these objects without leaving any dry areas,” he says.
The simulation has a user-friendly interface that enables gates, vents, and boundary conditions to be changed via a pull-down menu. LIMS has even proved to be an effective and enjoyable learning tool for high school students. “We've developed a friendly competition in which we provide them with the mesh for a Humvee hood and ask them to select the gate that will enable it to fill the most rapidly.”
A number of companies and academic institutions are now using LIMS for research and education purposes. “The software continues to evolve,” says Advani, “and we're moving closer to our goal of making this complex process more science than art.”
Eugene T. Camponeschi, Jr., who earned a UD doctorate for research at the Center for Composite Materials, has been given a 2005 ASTM International Award of Merit and accompanying title of fellow. ASTM International Committee D30 on Composite Materials cited Camponeschi for outstanding leadership and technical contributions as member-at-large, vice-chairman, and chairman of Committee D30. The award is the highest Society recognition of individuals for distinguished service and outstanding participation in ASTM International committee activities.
Dr. Camponeschi wrote his dissertation "Compression Response of Thick-Section Composite Materials" under the advisement of Prof. Dick J. Wilkens, former director of CCM. His degree was granted by the Mechanical Engineering Department. Currently a Senior Program Manager in the Project Office of the Structures and Composites Department at the U.S. Naval Surface Warfare Center, Carderock Division, in West Bethesda, Md, Dr. Camponeschi has worked on numerous programs related to the implementation of composite materials and structures on U.S. Naval platforms. He managed the Advanced Enclosed Mast Sensor (AEM/S) system project for the LPD 17 class, the DD 21 Integrated Topside Design R&D Program, and is currently managing the composite deckhouse structures portion of the DD(X) program. As part of that program, he is involved in the Advanced Materials Intelligent Processing Center at CCM. In addition to ASTM, Dr. Camponeschi has been active in the Coordination Group for MIL-HDBK-17 and a member of Tau Beta Pi, SAMPE, ASC, ASNE, and NSPE .
EVENTS
Research Review: Processing Science June 15
Research Review: Mechanics and Design June 22
Research Review: Environmental Composites June 29
Composite Materials Research Program Review June 30
Pre-approval
is required for attendance. Please contact Lynn Julin (302-831-8149) if you
are interested in attending.
SAMPE-UD and CCM Space Beam Challenge July 13 & 14
Undergraduate Research Reviews August 13
NEW PUBLICATIONS
Conference Proceedings
Zhang, Y. H., S. K. Agrawal, H. R. Pota, and M. J. Piovoso, “Optimal Control using State Dependent Riccati Equation for a Flexible Transporter System with Arbitrarily Varying Cable Lengths,” 2005 IEEE Conference on Control Applications , Toronto, Canada, August 28-31, 2005
Reports
Gillespie, Jr., J. W., Chair, National Materials Advisory Board Committee on High-Performance Structural Fibers for Advanced Polymer Matrix Composites , National Research Council of the National Academies, 2005.
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