Tech Briefs

Investigation of Basalt Woven Fabrics for Military Applications

The resin infusion process was done with SC-15 epoxy resin, a two-phase cycloaliphatic amine resin. Typical vacuum- assisted resin transfer molding (VARTM) involves layering up plies of unimpregnated fabric cut to size or preformed, and vacuum bagging it with the appropriate number of resin feed and vent lines. The pressure differential, along with the evacuated plies, stimulates resin impregnation of the preform.

For the manufacturing of the plates for these evaluations, the dry fabric layers were layed up square on a flat glass table (acting as the mold) with the bottom ply of the fabric purposely oversized to assist with proper wet-out. A release agent was applied to the table prior to lay-up to prevent bonding to the glass mold. A release cloth was placed on the plies. A distribution media, a highly permeable material that allows the resin to rapidly proceed across the surface length and then slowly infuse through the thickness, was used. A vacuum bagging material is placed over the setup and held in place with tacky tape. Resin feed lines run down the center of the plates and the vacuum lines run parallel to the feed lines to pull the resin across the fabric.

Plates for mechanical testing were fabricated to be 25 × 25" with a 0.2" thickness, and had an average of 45% fiber and 55% SC-15 resin by volume. The number of plies required to achieve this thickness had to be varied from 8 to 19 plies due to different thicknesses of the fabrics. Plates were cut into individual coupon samples using a waterjet system to the appropriate sizes.

Five tests were run for each of the basalt materials. The samples were conditioned for a minimum of 48 hours at 23, ±2 °C and 50%, ±5% relative humidity. The elemental compositions of each fiber were also investigated to study the manufacturer’s material variance in surface treatments by energy dispersive spectroscopy (EDS).

To understand how basalt-epoxy composites perform for possible use as body protection and/or vehicle applications, two areal densities were chosen: 1-psf and 5-psf. To obtain V50 values (velocity at which the probability of penetration of an armor material is 50%), a 17-gn fragment simulating projectile (FSP) was used on the low-areal-density plates (1-psf). To represent some of the larger fragment threats, a 44-gn FSP (0.30 cal.) was used to obtain V50s against 5-psf plates.

There is potential for basalt fibers to be used as a reasonable replacement for structural and ballistic applications currently fielding S-2 glass/epoxy using the same SC-15 epoxy resin system. For most mechanical tests, there was at least one basalt candidate that performed within 10% of S-2 glass/epoxy. In some cases, the basalt showed higher properties. Ballistically, basalt fibers performed just as well as S-2 glass/epoxy for the 17-gn FSP tests.

This work was done by David M. Spagnuolo, Eugene Napadensky, Tomoko Sano, and James P. Wolbert of the Army Research Laboratory. ARL-0136

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