The main issue of interest is to understand the formation of micro voids during the filling process and to develop strategies for their removal. An example of such a strategy is pressure rise during the flushing phase of the process.
The group at AMS involved in RTM modeling consists of Wing Chui, James Glimm, Yu Song, and F. Tangerman.
Resin Transfer Molding (RTM) is a process for the manufacture of fiber-reinforced composites. The resulting light weight, high strength parts are attractive for many applications. Examples are consumer items such as chairs, automobile parts and aircraft components. RTM is of particular interest to the aerospace industry since it promises cost savings and performance improvements over traditional hand lay-up methods. In the RTM process, dry fiber reinforcement, or fiber preform, is packed into a mold cavity which has the shape of the desired part. The mold is then closed and resin is injected under pressure into the mold where it impregnates the preform. After the fill cycle, the cure cycle begins, during which the mold is heated and resin polymerizes to become rigid plastic.
A major issue in this new manufacturing process is the elimination of void spaces in the resin fill operation, so that products with high quality are manufactured. Process modeling is particularly useful in understanding, designing, and optimizing the process conditions to achieve this goal.
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Voids are formed by large disparities in permeabilities. For instance filling along the mat direction is much easier than filling transverse to the mat direction. In dimension three fluid tends to primarily flow outside of the fibers, and encounters changing weave orientations. A two dimensional geometrical model of a woven mat is a domain in which rectangles are placed, with varying transverse permeabilities. A particular examples of such a numerical experiment is shown below.
The numerical results were obtained using our front tracking code with a resin tranfer molding physics model
Resin (red) is injected into a fiber mat. The tows run parallel to the flow in the blue regions and transversely in the green regions. Both of these regions are hard to impregnate. The yellow region represents the channels through the mat and is easy to impregnate.
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| Initial Phase | Initially Resin Primarily Impregnates Fiber Complement. In the Green Domains Flow Parallel to Orientation |
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| Bubbles Form As Different Resin Branches Meet | Late Stage: Many Bubbles have formed, But Local Pressure Increase Makes Them Smaller and Thus More Mobile |
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