Effects of void size and fiber alignment on void mobilization
Trapped pockets of air or voids are formed during the production of composites and are detrimental to the physical properties of the resulting part. The two main types of voids formed are spherical macro-voids formed outside the fiber tows and cylindrical micro-voids formed within the fiber tows. Under certain flow conditions, these micro-voids can be forced out of the fiber bundle by the incoming resin. The focus in much of the previous work on this subject has been control of the overall void fraction in molded parts. The object of the present paper is to arrive at an understanding of how the size and shape of inclusions in conjunction with preform characteristics affects the mobilization process. This question has been explored here with neutrally buoyant immiscible drops in square packed and hexagonal packed model arrays of cylinders having a porosity of 60 percent. For both arrays, it was found that the critical capillary number, Ca* (the ratio of the hydrodynamic forces to the surface tension forces) at which the drops became mobilized was lower for longer drops. Ca* for the hexagonal array was significantly less than for the square array; this is consistent with the higher strain rates obtained in the hexagonal packed arrays. The drop velocity increased with increasing fluid flow but remained much lower than the fluid velocity. The drops were more unstable in the hexagonal array and would break apart at much lower Ca than in the square array. If the drop breaks into smaller pieces, these pieces often will become immobilized because Ca* is higher for smaller drops.
- OSTI ID:
- 577604
- Report Number(s):
- CONF-970431-; TRN: 98:000974-0026
- Resource Relation:
- Conference: United new generation vehicle conference and exposition, Detroit, MI (United States), 7-10 Apr 1997; Other Information: PBD: 1997; Related Information: Is Part Of Advanced composites - proceedings; PB: 639 p.
- Country of Publication:
- United States
- Language:
- English
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