Composite material

Abstract

A composite material includes a layer of fibres conjoined to a matrix, wherein one of the matrix and fibres has a first component which exhibits auxetic behaviour for loading along a first direction, and the other of the matrix and fibres has a second component which exhibits non-auxetic behaviour for loading along the first direction.

1 . A composite material comprising a layer of fibres conjoined to a matrix, wherein one of the matrix and fibres comprises a first component which exhibits auxetic behaviour for loading along a first direction, and the other of the matrix and fibres comprises a second component which exhibits non-auxetic behaviour for loading along the first direction. 
     
     
         2 . A composite material according to  claim 1 , wherein the layer of fibres comprises the first component and the matrix comprises the second component. 
     
     
         3 . A composite material according to  claim 1 , wherein the layer of fibres comprises the second component, and the matrix comprises the first component. 
     
     
         4 . A composite material according to  claim 1 , wherein the layer of fibres is embedded in the matrix, partially embedded in the matrix, or forms a separate layer in contact with the matrix. 
     
     
         5 . A composite material according to  claim 1 , wherein the layer of fibres comprises unidirectional fibres or a woven, knitted or non-woven mesh. 
     
     
         6 . A composite material according to  claim 5 , wherein the layer of fibres comprises unidirectional fibres, and wherein the first direction, along which loading is applied for the assessment of auxetic behaviour, is parallel to the direction of the fibres. 
     
     
         7 . A composite material according to  claim 1 , wherein the coefficients of thermal expansion of the composite material, measured parallel and perpendicular to the first direction, are substantially equal. 
     
     
         8 . A composite material according to  claim 1 , wherein the volume fraction of the second component is between 60 and 70%. 
     
     
         9 . A composite material according to  claim 1 , wherein the volume fraction of the first component is less than 40%. 
     
     
         10 . A composite material according to  claim 1 , wherein the composite material additionally comprises a matrix material which exhibits non-auxetic behaviour for loading along the first direction. 
     
     
         11 . A composite material according to  claim 10 , wherein the volume fraction of the non-auxetic matrix material is less than 40%. 
     
     
         12 . A composite material according to  claim 1 , wherein the auxetic material is selected from auxetic thermoplastic (polyester urethane), thermosetting (silicone rubber) and metal (copper) foams, auxetic thermoplastic microporous polymeric cylinders (ultra high molecular weight polyethylene (UHMWPE), polypropylene (PP), and nylon), monofilaments (PP, nylon and polyester) and films (PP), naturally-occurring polymers (crystalline cellulose), composite laminates (carbon fibre-reinforced epoxy, glass fibre-reinforced epoxy and aramid-reinforced epoxy), certain bismuth cuprate superconducting polycrystalline compounds, 69% of the cubic elemental metals, and naturally-occurring polymorphs of crystalline silica (α-cristobalite and α-quartz). 
     
     
         13 . A composite material according to  claim 1 , wherein the matrix material comprises one or more polymeric materials, selected from thermosetting polymers, thermoplastic polymers, or both thermosetting and thermoplastic polymers. 
     
     
         14 . A composite material according to  claim 1 , wherein the matrix material further comprises one or more additional components including any of the following either alone or in combination: curing agent, accelerator, pigment, softener, flame retardant and toughening agent. 
     
     
         15 . A composite material comprising a layer of fibres and an uncured matrix, whereby curing of the matrix will produce a composite having a layer of fibres conjoined to a matrix, wherein one of the matrix and fibres comprises a first component which exhibits auxetic behaviour for loading along a first direction, and the other of the matrix and fibres comprises a second component which exhibits non-auxetic behaviour for loading along the first direction. 
     
     
         16 . A composite material according to  claim 16 , wherein the matrix impregnates the layer of fibres during curing. 
     
     
         17 . A method of making the composite material of  claim 1 , comprising the steps of conjoining the layer of fibres to the matrix.