Energy absorbent laminate

Abstract

This invention provides multi-layered composites, laminates and composite joints in which at least one resin-impregnated, fiber-containing layer is joined or laminated to a core layer having a lower flexural modulus or higher elongation at break, higher toughness, or a combination of all or some of these properties. The multi-layer composite produced by laminating or joining these materials together has improved shearout, impact and cutting resistance, since stresses caused by outside forces can be more widely distributed throughout the composite.

Description

FIELD OF THE INVENTION [0001] This invention relates to composite joints generally, and more specifically, to composite joints including at least one multi-layered composite having at least two layers of different toughness for helping to retard bearing stress and shearout stress. BACKGROUND OF THE INVENTION [0002] Fiber-reinforced composites are relatively brittle compared to conventional ductile metal alloys, such as stainless steel and aluminum. Yielding of ductile metals usually reduces the stress concentration around bolt holes so that there is only a loss of area, with no stress concentration at ultimate load on the remaining section at the joints. With composites, however, there is no relief at all from the elastic stress concentration, and catastrophic failure usually results without much warning. Even for small defects in composite structures, the stress-concentration relief is far from complete, although the local disbanding between the fibers and resin matrix and local in...

AI Technical Summary

Benefits of technology

This patent describes a new type of composite material that is stronger and more durable than traditional composites. The composite is made up of layers that are reinforced with fiber and resin. The composite has a core layer that is made up of lower modulus, higher elongation fibers, which helps to absorb and dissipate energy. This results in the composite being more resistant to damage from cutting, impact, and shear. The composite can also be made from recycled materials, which improves its environmental friendliness. The patent also describes a specific application of this composite in the form of a multi-layered laminate that is suitable for high-stress applications such as cockpit doors and bullet-proof vests.

Problems solved by technology

Fiber-reinforced composites are relatively brittle compared to conventional ductile metal alloys, such as stainless steel and aluminum.

With composites, however, there is no relief at all from the elastic stress concentration, and catastrophic failure usually results without much warning.

Since the stress resistant capability of bolted and riveted joints in composite materials is often unacceptably low, such laminates can never be loaded to levels suggested by the ultimate tensile strength of the laminated composite itself.

Indeed, after years of research and development, it appears that only the most carefully designed bolted composite joints will be even half as strong as the basic laminate.

However, because thick composite laminates are often impossible or impractical to adhesively bond or repair, there is a continued need for bolted composite structures.

Bolted joints of composite materials are known to experience many modes of failure, including tension failure, shearout failure, bolts pulling through laminate failure, cleavage tension failure, bearing failure, cutting, impact and bolt failure.

However, such an approach is not without drawbacks, since these modifications leave the structure outside the locally protected areas with little, if any, damage tolerance because the higher operating strain permitted by the softening strips and pad-ups severely limits the opportunity to perform repairs, which limits the number of situations in which such an approach is practical.

Images