Structural warp knit sheet and laminate thereof

Abstract

The structural warp knit sheet provided by this invention is a warp knit sheet for spars or stringers which comprises: a warp knit structure constituted of chain-stitch structures configured of ground knitting yarns; longitudinal insertion yarns that have been inserted in the longitudinal direction into the warp knit structure, the longitudinal insertion yarns being continuous carbon fiber yarns; and transverse insertion yarns that have been inserted in directions along which the transverse insertion yarns shuttle between the adjacent chain-stitch structures, the chain-stitch structures having been united by means of the transverse insertion yarns. The longitudinal insertion yarns are carbon fiber yarns which each is composed of 12,000-50,000 filaments and has a tensile strength of 4 GPa or higher, a tensile modulus of 220-450 GPa, and a drape value of 4-22.

Description

TECHNICAL FIELD[0001]The invention relates to a warp knit sheet and a laminate thereof advantageously used for beams for supporting structural bodies, particularly spars (wing beams) and stringers that support wing structures. The invention further relates to a warp knit sheet and a laminate thereof advantageously used for curved spars (wing beams and stringers, such as those forming part of main wings and tail units of aircraft, helicopter blades and windmill blades.BACKGROUND ART[0002]In recent years, structure-mounted wing structures (wings and blades) have been subject to strong demands for upsizing and weight reduction. For example, in the civilian aircraft application, a move towards main wings made of composite materials aimed at improving fuel efficiency has been underway, while wind power blades have been undergoing a shift towards high design outputs based on upsizing. In response to such demands, the use of carbon fibers has been expanding, particularly in spars and strin...

AI Technical Summary

Benefits of technology

The invention is a warp knit sheet for making spars and stringers. It consists of a warp knit structure with longitudinal insertion yarns and transverse insertion yarns. The longitudinal insertion yarns are made of carbon fiber yarns with high strength, tension, and drape value. The sheet can easily conform to curved shapes such as a hemisphere without creating unevenness or creases. By laminating multiple sheets together and attaching them with binders or stitching them, a composite with excellent mechanical properties can be obtained. This sheet is suitable for spars and stringers, particularly spar caps, and can be manufactured efficiently and quality for mass production.

Problems solved by technology

However, the use of carbon fiber prepregs or general-purpose carbon fiber fabrics (e.g., patent literature 3) for the purpose of obtaining curved spars has a problem in that it is difficult to arrange carbon fiber yarns along the shape of a curved plane without creating creases due to the inability of carbon fiber yarns to move in or perpendicular to the direction of their fiber axis independent of adjacent yarns.

Any attempt to forcibly apply a carbon fiber prepreg or general-purpose carbon fiber fabric to a curved plane ends in the formation of creases due to the slacking of the carbon fiber yarns present along the inside curvature caused by the difference between the arc lengths of the inside and outside curvatures, which is attributable to the low ability of carbon fiber yarns to expand and contract.

This gives rise to problems in terms of an inability to mold a composite into a desired shape and a dramatic reduction in mechanical properties due to internal creases as flaws.

In such cases, desired characteristics cannot be easily obtained, leading to a large increase in weight, so much so that the use of carbon fiber loses much of its significance.

Such problems apply equally to aircraft wing structures, and the manufacture of flawless molded products that conform to the complex shapes of spars and stringers have been very time consuming.

However, when conventional general-purpose fabrics are used as base material, it has been difficult to form such thick-wall structures using a molding method with excellent suitability for mass production (e.g., resin infusion molding).

Namely, the industrial-scale manufacturing of curved spars and stringers faces a major problem in that it has not been possible to apply a molding method conducive to high manufacturing efficiency and composite product quality with excellent suitability for mass production.

However, patent literatures 4 to 9 and other conventional techniques are designed to apply hand lay-up molding, and have not been verified in terms of, for example, the feasibility of fabricating preforms from multiple sheets laminated together, particularly 50 or more of them, and the applicability of laminates comprising large numbers of sheets to curved structures.

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