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A treatment which protects thermally stabilized polybenzimidazole (PBI) from the effects of repeated laundering was developed, providing retention of stability through 15 wash-dry cycles in alkaline detergent.

This study compares the properties of shuttle and shuttleless webbings for three fiber types: nylon 6,6, nylon 6, and polyester. Tensile strength, elongation and energy absorption were measured on the original webbings and after hex bar abrasion, weathering, high speed impact, and edge abrasion. For all webbing types there were no statistically significant differences in tensile properties between webbings produced on shuttle or shuttleless looms. Among the fiber types, the polyester webbings showed several significant differences. However, the polyester constructions were not optimized for performance, and many of the differences observed could have been significantly affected by the construction. Keywords: Parachutes; Tensile strength; Napping.

Kevlar has acquired a reputation for poor abrasion resistance. Replacement of nylon parachute materials with Kevlar has been hampered by Kevlar's reputation. However, abrasion testing of these materials under conditions designed to simulate parachute deployment had never been performed. A test procedure was designed to simulate the high speed rubbing of Kevlar and nylon webbings, braids and ribbons against themselves and a common abrasive surface under various conditions of loading at speeds ranging from 20 to 240 fps. Evaluation of abrasive damage was based upon strength loss for each material at each test condition. Extensive testing of both Kevlar and nylon materials showed conclusively that Kevlar's resistance to abrasive damage sustained due to high speed rubbing was superior to that of nylon. Investigation of the effects of many test parameters on strength loss due to abrasive damage showed that Kevlar relative to nylon was much less affected by test speed and normal force due to its superior thermal stability.

A new lightweight one-way stretch parachute canopy fabric was developed for use in personnel parachutes, whose mechanical properties are equal to the conventional 1.1 oz/sq yd canopy fabric, but which shows a greatly increased air permeability under the loading conditions experienced during deployment. The variation of permeability with pressure differential for a range of biaxial loading conditions was investigated for the new fabric and for other canopy fabrics, and it was shown that for maximum effectiveness the easy stretch direction of the new fabric should be oriented parallel to the direction of maximum stress in the parachute canopy.

Estimates of burn injury potential of Navy work clothing materials have been made by measuring retention of tensile properties during exposure to radiant heat; resistance to ignition; heat transfer during exposure to either radiant heat or flame impingement. Seventeen outerwear fabrics were tested, including polyester, cotton (normal and FR), wool, polyester/cotton, polyester/wool, polyester/rayon, nylon/cotton and Nomex/Kevlar blends of weights ranging from 3.5 to 10.3 oz/sq yd. Four underwear fabrics, both woven and knit, made from 100% cotton and 65/35 polyester/cotton were also included, as well as various outerwear/underwear combinations. The analytical work of Alice M. Stoll and her associates was extended to obtain an estimate of burn injury potential from heat transfer data. (Author)

Testing procedures which are used for nylon parachute materials have not been satisfactory for testing their Kevlar counterparts. Kevlar's high strength and low elongation can result in premature breaks and, thus, inordinately low values of breaking strength. In an effort to understand the causes of these spuriously induced failures, a study was designed to investigate the reasons for premature breaks. Extensive tensile testing with a wide variety of Kevlar parachute component materials has led to the adoption of new jaws and testing techniques designed to give breaks in the free length with nearly simultaneous failure of all warp yarns, high values of breaking strength and low variability. The new jaws are described and their use illustrated for a range of typical parachute component materials. A set of design drawings for the optimized jaws is included, and a proposed text which describes the procedure to be used in tensile testing Kevlar narrow fabrics has been drafted for inclusion in Military Specifications. (Author)

Designs for decelerator systems materials made from Kevlar 29 have been developed consisting of 4 braided cords, 1 sewing thread, 12 ribbons, 10 tapes and webbings, and 2 canopy fabrics. Draft Military Specifications have been written for all of these materials, and sample quantities of each produced. (Author)

Nonflammable finishes were developed to improve the functional properties of fabric for flight clothing made from Nomex, Kynol, Kynol/Nomex blends and HT-4. Improvements in abrasion resistance, water repellency, electrostatic resistance, pilling and fuzzing resistance were obtained without adversely affecting flame and thermal resistance, breaking strength, tearing strength or moisture regain. (Author)

The objective of the work was to improve the durability of the aluminized fabric currently used for the outer layer of fireffighters' proximity coats. Two possible improvements were developed: (a) Substituting a Viton/bronze coating for the aluminum, and adding a topcoat of pigmented urethane to improve wear resistance; (b) Adding a topcoat of pigmented urethane to the aluminized fabric to improve wear resistance. Sample lengths of both types of coated fabric were produced., Rept. no. GIDEP-574.01.01.00-G7-01.

The results of the first year's work under this contract are reported in full in AFML-TR-74-65, Parts I and II, and are only summarized herein. Results of the second year's work are described in full. The tensile properties of wet Kevlar yarns were measured at 70 and 190 F, as well as the response of Kevlar 29 yarn to low speed tensile strain cycling at 70 and 400 F. Torsional stress-strain behavior of Kevlar fibers and yarns was studied extensively, including the effect of elevated temperature exposure on this behavior. The bending recovery of Kevlar filaments was measured for different imposed curvatures and different times under strain. The effect of exposure to elevated temperature or bending recovery was investigated, and some deductions made concerning the behavior of these fibers in compression, particularly in respect to the existence of compressive yield. Preliminary measurements of the tensile properties of Durette and HT-4 fabrics under radiant heat flux were made, and the value of such measurements discussed. Finally, the morphology of Kevlar 49 fibers subjected to various types of mechanical working was examined using a scanning electron microscope., See also report dated May 1974, ADB002047.

Designs for Kevlar parachute component materials have been developed, including ribbons, tapes, webbings, tubular webbings, canopy and pack fabrics, braided cords, and sewing threads. Kevlar materials weigh approximately 1/3 as much as corresponding nylon materials of the same strength. This permits a saving of about 50% as the weight and bulk of parachutes made from Kevlar instead of nylon. (Author)

An aluminum-colored, coated outer fabric for use in fire proximity suits has been developed. The basic fabric used was a filament Kevlar fabric weighing 6.7 oz/sq yd. This was primed with Viton L-31, followed by three coats of Viton A containing bronze pigment, a polyurethane topcoat containing aluminum pigment, and a finish coat of clear polyurethane. The fabric does not burn, and exhibits good resistance to heat transfer. It is expected to be more comfortable and durable than the presently used aluminized Novatex fabric. Three hundred yards of the fabric were delivered to the Air Force for manufacture of experimental fire proximity suits of conventional design, and 30 yards of manufacture of six experimental suits of unconventional design. (Author)

A tubular fabric has been woven to make two 23 x 17 foot pillow tanks. A nitrile coating which could be applied as an aqueous latex was developed. The fabric will be coated and the tanks fabricated in Phase II of this report.

The degradation of nylon parachute materials and similar materials made from dacron, glass, an organic fiber, and stainless steel was studied at temperatures up to 1000 F, pressures up to 250 psi and times up to 72 hr. The amount of degradation for most of the materials was found to be consistent with that reported by other authors who did not study the influence of pressure. Pressure decreased degradation somewhat because of the reduction in the amount of oxgen contained within the structure. The increased resistance to degradation of Type 700 nylon was apparet in the results. The improved resistance to degradation of dacron as compared to nylon is well known. Glass fabrics retained most of their strength up to 500 F, and the organic fiber up to 600 F (although at 650 F it was badly degraded). Stainless steel showed little change after being exposed to 1000 F for 72 hr. (Author)