Bhaskar Ramakrishnan

Research Project

Studies on Resin Flow and Cure During Liquid Composite Molding Processes

Liquid composite molding, including techniques such as resin transfer molding and its variants, offers potential for viable commercial fabrication of composite products of complex shapes and sizes. The physical phenomena involved in the process are the fluid mechanics of the resin permeating the preform, and the heat transfer associated with curing of the composite. The study addresses issues related to both these phenomena. Preform permeability plays a critical role in the analysis of mold filling during the process. Due to the complex nature of the preform pore structures, a quantitative description towards their characterization, and consequently, the evaluation of their permeabilities presents a major challenge. Toward addressing this challenge, a fundamental description of the disordered preform pore structures using fractal techniques is developed, and an analytical permeability model is constructed using the fractal description. The model development, experimental studies, and model validation are presented and discussed. The second part of the thesis pertains to the curing the composite, which is often the critical productivity controlling stop in the fabrication process. The overall processing times can be reduced significantly through shortening the cure cycle time, while ensuring a complete and uniform cure in the product. Toward this objective, this thesis presents the use of conductive carbon mats embedded inside the composite as a means of providing additional heat generation in the form of resistance heating form within the composite during the cure process. In the context of application to liquid composite molding, systematic experimental studies on the effects of the power supplied to, and relative placement of, the resistive heating elements within the preform are presented with respect to the cure time and the microstructural quality of the product.

Publications

1. B. T. Ramakrishnan and R. Pitchumani, "Fractal Permeation Characteristics of Preforms Used in Liquid Composite Molding," Proceedings of the NSF Design & Manuf. Grantees Conference, pp. 341-342, 1997.
2. B. Ramakrishnan and R. Pitchumani, "A Fractal Geometry Approach to Evaluating the Permeabilities of Preforms Used in Liquid Composite Molding," in Proceedings, 12th Tech. Conf. of the Amer. Soc. for Composites, R. Gibson and G. Newaz, eds., pp. 846-855, 1997.
3. B. Ramakrishnan and R. Pitchumani, "Fractal Permeation Model for Preform Infiltration During Liquid Composite Molding," MRS Annual Meeting, 1997.
4. B. Ramakrishnan, L. Zhu, and R. Pitchumani, "Accelerated Curing of Composites Using Supplemental Internal Resistive Heating," in Proceedings, Int. SAMPE Symposium & Exhibition, 43(1), pp. 243-253, 1998.
5. R. Pitchumani and B. Ramakrishnan, "A Fractal Geometry Model for Evaluating Permeabilities of Porous Preforms Used in Liquid Composite Molding," Int. J. Heat and Mass Transfer, 42(12), 2219-2232, 1999.
6. B. Ramakrishnan, L. Zhu and R. Pitchumani, "Curing of Composites Using Internal Resistive Heating," ASME Journal of Manufacturing Science and Engineering, 122(1), 124-131, 2000.
7. B. Ramakrishnan and R. Pitchumani, "Fractal Permeation Characteristics of Preforms Used in Liquid Composite Molding," Polymer Composites, 21(2), 281-296, 2000.

Sponsors