Basalt rock is a black or gray fine-grained rock in the family of igneous rocks, formed by cooling of molten lava. It is commonly found in the Earth’s crust, is abundant throughout the world, and can be easily mined. Basalt rock possesses certain qualities similar to thermoplastics and metals, i.e., it melts when heated to specific temperatures (1100 to 1300 °C), and can be drawn into flexible fibers, a process similar to the manufacture of S-2 and E-glass fibers.
Along with the two obvious uses as toughening and insulation material, it is claimed that the fibers are naturally resistant to ultraviolet (UV) and high-energy electromagnetic radiation, maintain their properties in cold temperatures, and provide excellent acid resistance. The fibers are produced in a continuous process, similar to that for making glass fibers. The basalt material is initially fed into a heating furnace, followed by gravity feed through a bushing, and finally gathered into a single strand of continuous filament basalt fiber. The material is then quenched with a water-based sizing and packaged for sale.
There are certain things about basalt that make it attractive and economically comparable with production of glass fibers. Part of the process in the production of high-quality glass fibers involves addition of ingredients such as aluminum and other minerals needed to create the desired chemical and physical properties of the final product. Additional steps and ingredients will always increase production cost. Since natural basalt already contains these ingredients, these steps are eliminated from the manufacturing process.
Since basalt fabrics are fairly new for Army applications and currently in limited use, selection of different types and weights of fabric were considered for this study. The main goal is to obtain different products and perform the evaluation assuming that a lighter fabric or style may be better suited for smaller threats.
The raw material was purchased from Martintek U.S.A., Hexcel Corp., BGF Industries, and Sudaglass Fiber Technology. All of these vendors use basalt filaments manufactured and supplied by Kamenny Vek. These fabrics were infused with SC-15 epoxy resin at the Army Research Laboratory (ARL). Composite plates were fabricated at two areal densities, and the average fiber volume was 45%. There were three different weave styles: the 8-harness satin weave, a plain weave, and a 2/2 twill weave.
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
This Brief includes a Technical Support Package (TSP).
Investigation of Basalt Woven Fabrics for Military Applications
(reference ARL-0136) is currently available for download from the TSP library.
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