INTRODUCTION AND MOTIVATION

The reduction of void content is critical for high quality composites
• Voids reduce the mechanical properties
• Voids increase mechanical design risk
Voids can be trapped in between layers during lay-up or introduced during resin curing
A model experiment has been developed to explore void transport through fibrous porous media during composites processing
• Study the relative velocity of voids with respect to flowing resin
• Study void morphology and transport through fibrous porous media

EXPERIMENTAL METHODOLOGY

• The model experiment consists of a clear acrylic flow cell with porous media
-Simulated resin (i.e. glycerin) and voids (i.e. air) are injected to study relative void velocity during resin flow and changes in bubble morphology
-A 1D pore channel array is placed in the flow cell to simulate porous media
• A flow visualization setup records resin and void movement through the porous media

PROCESS MODELING

Key Parameters:
• Bubble mobility: U/V
-Ratio of average bubble velocity U and average resin velocity V
-Governed by viscous drag (F_D) and wall adhesion friction (F_a) force balance
• Capillary number: Ca=μV/γ
• Ratio of viscous stresses (μV/D_c) to interfacial stresses (γ/D_c)

VOIDS AT RESIN FLOW FRONT

• Observe bubble migration to the resin flow front during flow cell infusion

VOIDS INTO POROUS MEDIA

EXPERIMENTAL RESULTS

SUMMARY AND CONCLUSIONS

• A model experiment for partially impregnated thermoset prepreg processing was developed to characterize bubble mobility
• Results suggest that bubble mobility is a function of bubble size, Capillary number, and porous media properties
• Bubbles can travel through porous media without breakup under certain material and process conditions
• The model will prove useful to design pressure, temperature, and time profiles for void reduction during composites processing

ACKNOWLEDGEMENTS

Pavel Simacek (Research Associate II – University of Delaware)
Thomas Cender (PhDME Candidate – University of Delaware)
Volkan Eskizeybek (Visiting Professor – ÇOMÜ)
Phillip Mirabella (Research Intern – University of Delaware)
Micah Uzuh (S&E Scholar – University of Delaware)
Claire Daniel (Visiting Scholar – SUPMÉCA)

Research was sponsored by the Office of Naval Research (ONR) under Grant Number N00014-09-1-1011 and N00014-10-1-0971.

REFERENCES

Gangloff Jr. JJ, Daniel C, Advani SG. Modeling of in-plane void transport during composites processing. 19th Int Conf Compos Mater, Montreal, QC, CA: 2013.
Gangloff JJ, Hwang WR, Advani SG. Characterization of bubble mobility in channel flow with fibrous porous media walls. Int J Multiph Flow 2013;60:76–86.
Gangloff JJ, Simacek P, Sinha S, Advani SG. A Process Model for the Compaction and Saturation of Partially Impregnated Thermoset Prepreg Tapes. Compos Part A (Under Review).
Gangloff JJ, Daniel CD, Advani SG. A Model of Two-Phase Resin and Void Flow During Composites Processing. Int J Multiph Flow (Under Review).