|M.Sc Student||Steckelman Yoav|
|Subject||On the Effective Permeability of Dry Fabrics during Liquid|
Composite Molding Processes
|Department||Department of Chemical Engineering||Supervisors||Professor Emeritus Avinoam Nir|
|Dr. Anthony Green|
|Full Thesis text - in Hebrew|
An increasingly popular method to manufacture composite materials is the direct injection of an epoxy matrix into dry carbon fabric, following by heating the material to cure the resin. One method of this type is LRI -Liquid Resin Infusion. The resin system (the matrix) is injected into a predetermined fabric layup- called a Preform. The driving force for the LRI technique is the pressure gradient between the inlet and the outlet. The inlet pressure is usually atmospheric pressure, and the outlet pressure is vacuum pressure. The process itself is accomplished using a vacuum bag and additional auxiliary materials which accelerate the resin flow. The important parameters of this technology are the fluid viscosity, the fiber volume fraction, the pressure gradient and the permeability of the fabric which is a measurement to fabric's resistance to resin flow.
The Research objectives were:
· Study of the main parameters which influence the resin flow into the fabric (such as pressure, viscosity and fiber volume fraction)
· Developing simple experimental methods to calculate the permeability tensor in 3D, which allows modeling accurately the resin flow inside the fabric.
· Implementation of the flow equations on the porosity media in the defined experiments using the parameters mentioned above.
In this research the following were achieved:
1. We formulated the governing equation which controls the flow of resin inside the fabric, incorporating the flow equations, the reaction equation, the viscosity changes, and changes of fabric parameters due to external pressure variation.
2. We explained the swelling phenomenon of the vacuum bag near the injection point and we explained the flow rate changes.
3. We measured each parameter separately:
a. The viscosity by altering the resin system without incorporating its hardener.
b. Fiber volume fraction by using theoretical calculation and backup with actual measurements (like digestion experiments).
c. The thickness of the fabric and the influence of pressure using Instron tests.
4. We developed a simple technique for measuring the permeability of dry fabrics using edge injection with several carbon fabrics common in the aviation industry.
5. We calculated the permeability using 3 different methods:
a. The differential method using Darcy's equation.
b. The integral method using an analytical solution.
c. Numeric/Simulation method using parametric fitting.
6. Support to the design and development of some aircraft parts.