Fiberglass reinforced plastic is a relatively new engineering material. World War II initiated a demand for fiberglass reinforced plastic as a construction material in radomes, aircraft parts, and marine craft. Since then, the material has found wide use in many other applications, including automobile parts, skis, and a greater variety of military and commercial aircraft and marine parts.
The most common type of fiberglass reinforced plastic is comprised of varying ratios of glass fiber reinforcement and thermosetting polyester resins. Ordinarily, a catalyst is introduced into the resin to initiate hardening, thereby forming a solid matrix fully incapsulating the glass fibers. The resin provides chemical and corrosion resistance, durability, light weight, texture, electrical and thermal insullation, and molded-in color. The glass reinforcement contributes mechanical strength, rigidity, dimensional stability, and temperature resistance.
Fiberglass reinforcing material has been available in continuous strand, chopped strand, woven roving, and matt form. The continuous strand is a single continuous strand used in wrapping situations to provide, for example, for radial burst strength in a pressure bottle. Continuous strand may also come in fabric form wherein a plurality of parallel, uniaxial structural yarns are held together by a sewing stitch or knitting stitch which runs perpendicular to the axis of the structural yarns. A continuous or uniaxial material results in high compressive and tensile strength in one direction.
Chopped strands are short fibers oriented in all directions. A resulting laminate has equal strength in all directions. Since the fibers are less than two inches in length, however, the strength is not as great as it would be with continuous strand or woven roving.
Woven roving is used for high strength laminates having a minimal thickness requirement. Woven roving is comprised of a plurality of continuous strands running in two directions perpendicular to each other and held together by weaving the one set of strands with the other. Individual strands are not uniaxial in woven roving fabric.
Previously known reinforcing materials have been limited to fabrics having structural yarns running parallel with the centerline of the material or perpendicular to it. With the increased use and demand for fiberglass reinforced plastic, it has been found that many more applications could utilize the material if the structural yarn in the reinforcing fabric could be oriented in directions different from the Zero degree and 90 degree directions relative to the fabrics longitudinal centerline. Additionally, some applications have demanded high strength in more than one direction, yet not all directions. Hence, a need has developed for a reinforcing material which can provide variable or multiple directional strength characteristics. The present invention addresses these problems.