WO1993021011A1 - Composite material - Google Patents

Composite material Download PDF

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Publication number
WO1993021011A1
WO1993021011A1 PCT/GB1993/000775 GB9300775W WO9321011A1 WO 1993021011 A1 WO1993021011 A1 WO 1993021011A1 GB 9300775 W GB9300775 W GB 9300775W WO 9321011 A1 WO9321011 A1 WO 9321011A1
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WO
WIPO (PCT)
Prior art keywords
composite material
materials
composite
fibres
polymer
Prior art date
Application number
PCT/GB1993/000775
Other languages
French (fr)
Inventor
Paul John Martin
Original Assignee
Mclaren Cars N.V.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Mclaren Cars N.V. filed Critical Mclaren Cars N.V.
Publication of WO1993021011A1 publication Critical patent/WO1993021011A1/en

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
    • B32B5/22—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed
    • B32B5/24—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed one layer being a fibrous or filamentary layer
    • B32B5/26—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed one layer being a fibrous or filamentary layer another layer next to it also being fibrous or filamentary
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
    • B32B5/02—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by structural features of a fibrous or filamentary layer
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
    • B32B5/02—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by structural features of a fibrous or filamentary layer
    • B32B5/024—Woven fabric
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
    • B32B5/02—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by structural features of a fibrous or filamentary layer
    • B32B5/08—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by structural features of a fibrous or filamentary layer the fibres or filaments of a layer being of different substances, e.g. conjugate fibres, mixture of different fibres
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/04—Reinforcing macromolecular compounds with loose or coherent fibrous material
    • C08J5/047—Reinforcing macromolecular compounds with loose or coherent fibrous material with mixed fibrous material
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/04—Reinforcing macromolecular compounds with loose or coherent fibrous material
    • C08J5/047—Reinforcing macromolecular compounds with loose or coherent fibrous material with mixed fibrous material
    • C08J5/048—Macromolecular compound to be reinforced also in fibrous form
    • D—TEXTILES; PAPER
    • D03—WEAVING
    • D03D—WOVEN FABRICS; METHODS OF WEAVING; LOOMS
    • D03D1/00—Woven fabrics designed to make specified articles
    • D03D1/0035—Protective fabrics
    • D03D1/0052—Antiballistic fabrics
    • D—TEXTILES; PAPER
    • D03—WEAVING
    • D03D—WOVEN FABRICS; METHODS OF WEAVING; LOOMS
    • D03D15/00—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used
    • D—TEXTILES; PAPER
    • D03—WEAVING
    • D03D—WOVEN FABRICS; METHODS OF WEAVING; LOOMS
    • D03D15/00—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used
    • D03D15/20—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used characterised by the material of the fibres or filaments constituting the yarns or threads
    • D03D15/242—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used characterised by the material of the fibres or filaments constituting the yarns or threads inorganic, e.g. basalt
    • D03D15/267—Glass
    • D—TEXTILES; PAPER
    • D03—WEAVING
    • D03D—WOVEN FABRICS; METHODS OF WEAVING; LOOMS
    • D03D15/00—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used
    • D03D15/20—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used characterised by the material of the fibres or filaments constituting the yarns or threads
    • D03D15/283—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used characterised by the material of the fibres or filaments constituting the yarns or threads synthetic polymer-based, e.g. polyamide or polyester fibres
    • D—TEXTILES; PAPER
    • D03—WEAVING
    • D03D—WOVEN FABRICS; METHODS OF WEAVING; LOOMS
    • D03D15/00—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used
    • D03D15/50—Woven fabrics characterised by the material, structure or properties of the fibres, filaments, yarns, threads or other warp or weft elements used characterised by the properties of the yarns or threads
    • D03D15/573—Tensile strength
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2260/00—Layered product comprising an impregnated, embedded, or bonded layer wherein the layer comprises an impregnation, embedding, or binder material
    • B32B2260/02—Composition of the impregnated, bonded or embedded layer
    • B32B2260/021—Fibrous or filamentary layer
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2260/00—Layered product comprising an impregnated, embedded, or bonded layer wherein the layer comprises an impregnation, embedding, or binder material
    • B32B2260/04—Impregnation, embedding, or binder material
    • B32B2260/046—Synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/50—Properties of the layers or laminate having particular mechanical properties
    • B32B2307/51—Elastic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/50—Properties of the layers or laminate having particular mechanical properties
    • B32B2307/54—Yield strength; Tensile strength
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/50—Properties of the layers or laminate having particular mechanical properties
    • B32B2307/558—Impact strength, toughness
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/50—Properties of the layers or laminate having particular mechanical properties
    • B32B2307/56—Damping, energy absorption
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2605/00—Vehicles
    • D—TEXTILES; PAPER
    • D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
    • D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
    • D10B2101/00—Inorganic fibres
    • D10B2101/02—Inorganic fibres based on oxides or oxide ceramics, e.g. silicates
    • D10B2101/06—Glass
    • D—TEXTILES; PAPER
    • D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
    • D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
    • D10B2101/00—Inorganic fibres
    • D10B2101/10—Inorganic fibres based on non-oxides other than metals
    • D10B2101/12—Carbon; Pitch
    • D—TEXTILES; PAPER
    • D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
    • D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
    • D10B2321/00—Fibres made from polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • D10B2321/02—Fibres made from polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds polyolefins
    • D10B2321/021—Fibres made from polymers obtained by reactions only involving carbon-to-carbon unsaturated bonds polyolefins polyethylene
    • D—TEXTILES; PAPER
    • D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
    • D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
    • D10B2331/00—Fibres made from polymers obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds, e.g. polycondensation products
    • D10B2331/02—Fibres made from polymers obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds, e.g. polycondensation products polyamides
    • D10B2331/021—Fibres made from polymers obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds, e.g. polycondensation products polyamides aromatic polyamides, e.g. aramides
    • D—TEXTILES; PAPER
    • D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
    • D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
    • D10B2331/00—Fibres made from polymers obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds, e.g. polycondensation products
    • D10B2331/04—Fibres made from polymers obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds, e.g. polycondensation products polyesters, e.g. polyethylene terephthalate [PET]
    • D—TEXTILES; PAPER
    • D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
    • D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
    • D10B2401/00—Physical properties
    • D10B2401/06—Load-responsive characteristics
    • D10B2401/062—Load-responsive characteristics stiff, shape retention
    • D—TEXTILES; PAPER
    • D10—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
    • D10B—INDEXING SCHEME ASSOCIATED WITH SUBLASSES OF SECTION D, RELATING TO TEXTILES
    • D10B2401/00—Physical properties
    • D10B2401/06—Load-responsive characteristics
    • D10B2401/063—Load-responsive characteristics high strength

Definitions

  • the present invention relates to a composite material, for example, for forming a structure such as the whole or a part of the body monocoque or structure of a vehicle.
  • metals are relatively heavy, and accordingly, structures fabricated therefrom are correspondingly heavy.
  • composite materials such as glass fibre, carbon fibre, boron fibre or kevlar which results in an immediate, consequent major saving in the weight of the resultant structure.
  • these composite materials are generally more expensive to use than metal.
  • vehicle structures utilising a sandwich construction, in which, for example, a polymer or metal honeycomb core is sandwiched between two or more sheets of an appropriate composite material.
  • the composite materials are being used increasingly in automotive racing and in aerospace because of their intrinsically high specific strengths and moduli.
  • these light and stiff structures have the disadvantage that for good soundproofing, a high density, low stiffness material is required. Therefore, if it is also required to attenuate noise, it has generally been proposed to use a lead sheet clad on one or both sides with a foam in conjunction with the composite materials and structures formed therefrom.
  • a composite material comprising a combination of first and second materials, said first material having a high tensile strength and a low modulus of elasticity, and said second material having a high modulus of elasticity, the combination being arranged such that the composite material has both a high specific stiffness and a high load bearing or absorbing capability.
  • the composite material has a high specific stiffness, arising out of the high modulus of the second material, it is sufficiently stiff and rigid to be utilised to form the structure of a vehicle such as a motor vehicle or an aeroplane, for example.
  • the high load bearing or absorbing capability arises out of the low modulus of the first material and this also provides the composite material with the ability to attenuate noise.
  • the composite material can therefore be utilised to form the structure of a road vehicle, for example, without additional soundproofing being required.
  • both the first and second materials are low density.
  • the resultant composite material therefore has a low weight.
  • the first and second materials are intimately combined.
  • the first and second materials may be laminated, and/or embedded in a matrix, for example, of a plastics material, and/or hybridised.
  • the matrix may be of polyester, vinyl ester, epoxy, phenolic or polyethylene.
  • each of said first and second materials are fibrous.
  • the first and second materials may therefore be combined by physically combining their fibres.
  • the fibres may be entangled and/or embedded in a matrix.
  • the fibres of the first and second materials may also be interwoven.
  • one or more layers of said first material are arranged to form an external surface of said composite material.
  • the percentage of the first and second materials in said composite material may be chosen to provide the composite material with chosen physical characteristics. However, in a preferred embodiment, at least 50% of said composite material is said first material.
  • first and second materials may be chosen to provide the composite material with required physical characteristics.
  • said first material is an orientated polymer. The orientation provides the required high tensile strength.
  • the first material has good noise attenuation characteristics.
  • the first material is also, preferably, a material having a high crystallinity.
  • the first material is a high crystallinity, orientated, polymer.
  • the first material is a high crystallinity, orientated, polyethylene.
  • the second material provides the rigidity to the composite material and may be a metal, for example, aluminium. However, it is generally preferred that the second material is fibrous so that it may be intimately combined with said first material. It is thus preferred that said second material is a structural, fibrous material, such as glass fibre, carbon fibre, boron fibre, or kevlar.
  • the present invention also extends to a structure formed from a composite material as defined above.
  • Said structure which may be fabricated by any appropriate manufacturing technique, may comprise a body structure for a vehicle such as a motor vehicle or an aeroplane.
  • the manufacturing technique may comprise, for example, a wet lay-up technique, or pre-combined, pre- impregnation, resin transfer methods or the use of interleaved resin or polymer film.
  • an external surface of said structure is coated with one or more layers of said first material.
  • an energy absorbing structure formed of a composite material as defined above.
  • the invention also extends to a method of protecting a structure against wear by applying to the structure one or more layers of a material having a high tensile strength and a low modulus of elasticity.
  • Said material is preferably fibrous.
  • said material may be an orientated polymer.
  • the material has a high crystallinity.
  • the material is a high crystallinity, orientated, polyethylene.
  • the present invention is described below with reference to the production of a body structure for a vehicle.
  • the composite material forming this structure is described as a combination of a high crystallinity orientated polyethylene and carbon fibre.
  • the composite material may be used in any required application, and that the use of the composite material is not confined to the uses described herein.
  • the two materials forming the composite material are given by way of example only. They may be utilised in combination with further materials, and/or alternative materials may be substituted.
  • a composite material of the invention includes at least 50% of a high crystallinity orientated polymer, such as polyethylene, which exhibits goods noise attenuation capabilities.
  • This material has a high specific tensile strength, low moduli of elasticity, and low density.
  • the second material is, for example, carbon fibre, and has a high modulus and a low density. This second material is sufficiently rigid to give any structure made therefrom the required panel stiffness properties.
  • the two materials are combined, for example by weaving together the fibres thereof, and then embedding the interwoven fibres in an epoxy matrix.
  • This composite material is then processed for example using wet lay-up, pre-combined, pre- impregnation, resin transfer methods, or interleaved resin or polymer films, to produce the body structure of a vehicle.
  • the resulting structure has a high specific stiffness.
  • the high crystallinity polymer exhibits hysteresis and subsequent energy loss as it is loaded and unloaded, and this provides good noise attenuation.
  • the composite material structures which have been used heretofore, for example, made of carbon fibre in an epoxy resin, are subject to brittle and catastrophic failure. This is avoided with a structure made of the composite material of the invention in that the polymer fibres exhibit a plastic deformation zone in their stress-strain relationship. This, coupled with the substantial difference moduli, results in the stiffer and more brittle carbon fibres failing first. The unfailed polymer fibres hold the structure together, preventing total failure or even absorbing further loads.
  • the carbon fibre initially takes the majority of the load due to its high modulus. However, once the strain limit of the carbon fibre is reached, it fails. However, so long as there is sufficient high crystallinity polymer in the structure, this material takes over and continues to carry the load. Its moduli are substantially lower and will deflect more per unit force. The effect is the plastic type deformation which is so apparent from the accompanying graph. Thus, the unfailed polymer fibres hold the structure together and prevent total failure.
  • the carbon fibre again takes the majority of the initial load because of its higher modulus. As the carbon fibre fails, the structure can start to collapse. However, the polymer fibres have a low sheer strength. Accordingly, although the polymer fibres come away from the resin and from the layers adjacent to it, the polymer fibres do not break, they just bend. The result is that under a direct compressive shock load, for example as occurs in a car crash, although the carbon fibre fails, the polymer fibres do not. As previously, the polymer fibres hold the structure together.
  • the particular composite material incorporating carbon fibre has a large advantage in a compressive force situation.
  • High strength carbon fibre can absorb more energy per unit mass than any other material. Under compressive shock loading, it absorbs energy because the fibres buckle over very short distances and then snap off. This buckling and breaking absorbs the energy, but the better the structure at absorbing energy, the smaller the span over which the structure buckles.
  • a structure made of a composite material of the invention has an improved transfer ballistic resistance as compared to known composite materials. This is because the high strain to failure ratio of the high crystallinity polymer allows the structure time to deflect and snag a projectile.
  • the carbon fibre is very strain dependent, and this low strain to failure does not give the material any chance to deflect substantially before it fails.
  • the polymer fibres again can carry the energy away after the carbon fibre has failed, and so reduce the possibility of through penetration. This is extremely useful as it enables the structure to resist stone chippings and other ballistic damage.
  • the polymer material also exhibits a work toughening characteristic which is extremely useful in resisting ballistic penetration.
  • the high crystallinity polymer is subject to further molecular orientation which provides the work toughening.
  • a first strike for example, by a stone chipping
  • more energy would be required on subsequent impacts to successfully penetrate.
  • the energy required to penetrate a previously impacted zone of the high crystallinity polymer which has not failed is actually higher than that of the virgin structure.
  • This work toughening effect coupled with the self lubricating properties of the high crystallinity polymer and the low modulus of the material improve its wear resistance considerably, for example, as compared with a conventional composite of pure carbon fibre with an epoxy matrix, for example.
  • the polymer material is of a neutral colour. This means that the thickness of any subsequent surface finish can be reduced as compared to a conventional composite material, and this also saves weight.
  • a composite material of the invention as described above, is light, has sufficient stiffness but yet attenuates noise. It is also resistant to penetration by stone chippings and the like. The material is therefore ideal for use to provide the structure of road vehicles and/or to form impact zones or wear resistant zones on such vehicles.

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  • Engineering & Computer Science (AREA)
  • Textile Engineering (AREA)
  • Chemical & Material Sciences (AREA)
  • Polymers & Plastics (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Laminated Bodies (AREA)
  • Reinforced Plastic Materials (AREA)

Abstract

A composite material, for example to produce a vehicle body structure, includes at least 50 % of a high crystallinity orientated polymer, such as polyethylene, which exhibits good noise attenuation capabilities. This material has a high specific tensile strength, low moduli of elasticity, and low density. The second material in the composite is carbon fibre which has a high modulus and a low density. This second material is sufficiently rigid to give any structure made therefrom the required panel stiffness properties. The two materials are combined by weaving together the fibres thereof, and then embedding the interwoven fibres in an epoxy matrix. This composite material is then processed to produce the body structure which has a high specific stiffness.

Description

C0MP0SITE MATERIAL.
The present invention relates to a composite material, for example, for forming a structure such as the whole or a part of the body monocoque or structure of a vehicle.
At present, the bodywork of most vehicles, such as automobiles and aircraft, is made from metal. However, metals are relatively heavy, and accordingly, structures fabricated therefrom are correspondingly heavy. It is known to replace the metals with composite materials such as glass fibre, carbon fibre, boron fibre or kevlar which results in an immediate, consequent major saving in the weight of the resultant structure. However, these composite materials are generally more expensive to use than metal. It is also possible to construct vehicle structures utilising a sandwich construction, in which, for example, a polymer or metal honeycomb core is sandwiched between two or more sheets of an appropriate composite material.
The composite materials, either alone or in sandwich constructions, are being used increasingly in automotive racing and in aerospace because of their intrinsically high specific strengths and moduli. However, these light and stiff structures have the disadvantage that for good soundproofing, a high density, low stiffness material is required. Therefore, if it is also required to attenuate noise, it has generally been proposed to use a lead sheet clad on one or both sides with a foam in conjunction with the composite materials and structures formed therefrom.
Thus, the potential advantages arising out of the use of the known composite materials to form the body structure of a road vehicle are offset by an increase in noise levels or the need to provide soundproofing. It is an object of the present invention to provide a composite material which is suitable for use to form a vehicle body structure and yet which does not have the disadvantages of the presently available composite materials discussed above.
According to a first aspect of the present invention there is provided a composite material comprising a combination of first and second materials, said first material having a high tensile strength and a low modulus of elasticity, and said second material having a high modulus of elasticity, the combination being arranged such that the composite material has both a high specific stiffness and a high load bearing or absorbing capability.
Because the composite material has a high specific stiffness, arising out of the high modulus of the second material, it is sufficiently stiff and rigid to be utilised to form the structure of a vehicle such as a motor vehicle or an aeroplane, for example. The high load bearing or absorbing capability arises out of the low modulus of the first material and this also provides the composite material with the ability to attenuate noise. The composite material can therefore be utilised to form the structure of a road vehicle, for example, without additional soundproofing being required.
Preferably, both the first and second materials are low density. The resultant composite material therefore has a low weight.
Preferably, the first and second materials are intimately combined. For example, the first and second materials may be laminated, and/or embedded in a matrix, for example, of a plastics material, and/or hybridised. Where the first and second materials are provided in a matrix, the matrix may be of polyester, vinyl ester, epoxy, phenolic or polyethylene.
In a preferred embodiment, each of said first and second materials are fibrous. The first and second materials may therefore be combined by physically combining their fibres. For example, the fibres may be entangled and/or embedded in a matrix. In one embodiment, the fibres of the first and second materials may also be interwoven.
In an embodiment, one or more layers of said first material are arranged to form an external surface of said composite material.
The percentage of the first and second materials in said composite material may be chosen to provide the composite material with chosen physical characteristics. However, in a preferred embodiment, at least 50% of said composite material is said first material.
The nature of said first and second materials may be chosen to provide the composite material with required physical characteristics. In a preferred embodiment, said first material is an orientated polymer. The orientation provides the required high tensile strength.
Preferably, the first material has good noise attenuation characteristics. The first material is also, preferably, a material having a high crystallinity.
In a preferred embodiment, the first material is a high crystallinity, orientated, polymer. Preferably, the first material is a high crystallinity, orientated, polyethylene. The second material provides the rigidity to the composite material and may be a metal, for example, aluminium. However, it is generally preferred that the second material is fibrous so that it may be intimately combined with said first material. It is thus preferred that said second material is a structural, fibrous material, such as glass fibre, carbon fibre, boron fibre, or kevlar.
The present invention also extends to a structure formed from a composite material as defined above.
Said structure, which may be fabricated by any appropriate manufacturing technique, may comprise a body structure for a vehicle such as a motor vehicle or an aeroplane. The manufacturing technique may comprise, for example, a wet lay-up technique, or pre-combined, pre- impregnation, resin transfer methods or the use of interleaved resin or polymer film.
In a preferred embodiment, an external surface of said structure is coated with one or more layers of said first material.
According to a further aspect of the present invention there is provided an energy absorbing structure formed of a composite material as defined above.
The invention also extends to a method of protecting a structure against wear by applying to the structure one or more layers of a material having a high tensile strength and a low modulus of elasticity.
Said material is preferably fibrous. For example, said material may be an orientated polymer. In a preferred embodiment the material has a high crystallinity. Preferably, the material is a high crystallinity, orientated, polyethylene.
Embodiments of the present invention will hereinafter be described, by way of example, with reference to the accompanying drawing which illustrates the stress characteristic of a composite material of the invention as compared to the stress characteristic of carbon fibre.
The present invention is described below with reference to the production of a body structure for a vehicle. Furthermore, the composite material forming this structure is described as a combination of a high crystallinity orientated polyethylene and carbon fibre. However, it should be understood that the composite material may be used in any required application, and that the use of the composite material is not confined to the uses described herein. Furthermore, the two materials forming the composite material are given by way of example only. They may be utilised in combination with further materials, and/or alternative materials may be substituted.
A composite material of the invention includes at least 50% of a high crystallinity orientated polymer, such as polyethylene, which exhibits goods noise attenuation capabilities. This material has a high specific tensile strength, low moduli of elasticity, and low density.
The second material is, for example, carbon fibre, and has a high modulus and a low density. This second material is sufficiently rigid to give any structure made therefrom the required panel stiffness properties.
In the composite material, the two materials are combined, for example by weaving together the fibres thereof, and then embedding the interwoven fibres in an epoxy matrix. This composite material is then processed for example using wet lay-up, pre-combined, pre- impregnation, resin transfer methods, or interleaved resin or polymer films, to produce the body structure of a vehicle. The resulting structure has a high specific stiffness. However, the high crystallinity polymer exhibits hysteresis and subsequent energy loss as it is loaded and unloaded, and this provides good noise attenuation.
The composite material structures which have been used heretofore, for example, made of carbon fibre in an epoxy resin, are subject to brittle and catastrophic failure. This is avoided with a structure made of the composite material of the invention in that the polymer fibres exhibit a plastic deformation zone in their stress-strain relationship. This, coupled with the substantial difference moduli, results in the stiffer and more brittle carbon fibres failing first. The unfailed polymer fibres hold the structure together, preventing total failure or even absorbing further loads.
The characteristics of the carbon fibre material and of the high crystallinity polymer are shown in the accompanying stress/strain graph. It will be seen that at a predetermined force there is brittle fracture of the carbon fibre, whereas with the combined composite material, there is a plastic type deformation.
If a composite material of the invention is subjected to high forces, the carbon fibre initially takes the majority of the load due to its high modulus. However, once the strain limit of the carbon fibre is reached, it fails. However, so long as there is sufficient high crystallinity polymer in the structure, this material takes over and continues to carry the load. Its moduli are substantially lower and will deflect more per unit force. The effect is the plastic type deformation which is so apparent from the accompanying graph. Thus, the unfailed polymer fibres hold the structure together and prevent total failure.
Under impact conditions, that is a compressive failure, the carbon fibre again takes the majority of the initial load because of its higher modulus. As the carbon fibre fails, the structure can start to collapse. However, the polymer fibres have a low sheer strength. Accordingly, although the polymer fibres come away from the resin and from the layers adjacent to it, the polymer fibres do not break, they just bend. The result is that under a direct compressive shock load, for example as occurs in a car crash, although the carbon fibre fails, the polymer fibres do not. As previously, the polymer fibres hold the structure together.
The particular composite material incorporating carbon fibre has a large advantage in a compressive force situation. High strength carbon fibre can absorb more energy per unit mass than any other material. Under compressive shock loading, it absorbs energy because the fibres buckle over very short distances and then snap off. This buckling and breaking absorbs the energy, but the better the structure at absorbing energy, the smaller the span over which the structure buckles.
After an impact occurs on a material including carbon fibre alone, little is left except dust, and so any additional shock compressive loads cannot be absorbed. However, by hybridising carbon fibre with the polymer fibres, the advantage of the high energy absorbence of the carbon fibre is utilised, and the polymer fibres hold the structure together. Thus, even when the carbon fibre has failed, there still remains a collapsed structure capable of absorbing further energy.
A structure made of a composite material of the invention has an improved transfer ballistic resistance as compared to known composite materials. This is because the high strain to failure ratio of the high crystallinity polymer allows the structure time to deflect and snag a projectile. The carbon fibre is very strain dependent, and this low strain to failure does not give the material any chance to deflect substantially before it fails. The polymer fibres again can carry the energy away after the carbon fibre has failed, and so reduce the possibility of through penetration. This is extremely useful as it enables the structure to resist stone chippings and other ballistic damage.
To take full advantage from the ballistic resistance of high crystallinity polymer, it is useful to coat the external surface of a vehicle structure, whether or not made of the composite material of the invention, with one or more layers of the high crystallinity polymer.
The polymer material also exhibits a work toughening characteristic which is extremely useful in resisting ballistic penetration. Thus, after it has been initially stretched, the high crystallinity polymer is subject to further molecular orientation which provides the work toughening. After a first strike, for example, by a stone chipping, if penetration has not occurred, more energy would be required on subsequent impacts to successfully penetrate. Thus, the energy required to penetrate a previously impacted zone of the high crystallinity polymer which has not failed is actually higher than that of the virgin structure. This work toughening effect, coupled with the self lubricating properties of the high crystallinity polymer and the low modulus of the material improve its wear resistance considerably, for example, as compared with a conventional composite of pure carbon fibre with an epoxy matrix, for example.
The polymer material is of a neutral colour. This means that the thickness of any subsequent surface finish can be reduced as compared to a conventional composite material, and this also saves weight.
Accordingly, a composite material of the invention, as described above, is light, has sufficient stiffness but yet attenuates noise. It is also resistant to penetration by stone chippings and the like. The material is therefore ideal for use to provide the structure of road vehicles and/or to form impact zones or wear resistant zones on such vehicles.
However, it will be appreciated that the composite material now described may be utilised for any other appropriate application.
It will be appreciated that further modifications to, and improvements in, the present invention as described above, may be made within the scope of the present application.

Claims

1 A composite material comprising a combination of first and second materials, said first material having a high tensile strength and a low modulus of elasticity, and said second material having a high modulus of elasticity, the combination being arranged such that the composite material has both a high specific stiffness and a high load bearing or absorbing capability.
2 A composite material as claimed in Claim 1, wherein both first and second materials are low density.
3 A composite material as claimed in Claim 1 or Claim 2, wherein the first and second materials are intimately combined.
4 A composite material as claimed in Claim 3, wherein the first and second materials are laminated.
5 A composite material as claimed in Claim 3 or 4, wherein the first and second materials are embedded in a matrix of a plastics material.
6 A composite material as claimed in any of Claims 3 to
5, wherein the first and second materials are hybridised.
7 A composite material as claimed in any of Claims 3 to
6, wherein the first and second materials are provided in a matrix, and the matrix is of polyester, vinyl ester, epoxy, phenolic or polyethylene.
8 A composite material as claimed in any preceding claim, wherein each of said first and second materials is fibrous. 9 A composite material as claimed in Claim 8, wherein the first and second materials are combined by physically combining their fibres.
10 A composite material as claimed in Claim 9, wherein the fibres are entangled and/or embedded in a matrix.
11 A composite material as claimed in Claim 9 or Claim 10, wherein the fibres of the first and second materials are interwoven.
12 A composite material as claimed in any preceding claim, wherein one or more layers of said first material are arranged to form an external surface of said composite material.
13 A composite material as claimed in any preceding claim, wherein at least 50% of said composite material is said first material.
14 A composite material as claimed in any preceding claim, wherein said first material is an orientated polymer.
15 A composite material as claimed in Claim 14, wherein the first material is a high crystallinity, orientated polyethylene.
16 A composite material as claimed in any preceding claim, wherein said second material is a structural, fibrous material.
17 A composite material as claimed in Claim 16, wherein said second material is chosen from glass fibre, carbon fibre, boron fibre, or kevlar. 18 A structure formed from a composite material as claimed in any preceding claim.
19 A structure as claimed in Claim 18, wherein an external surface of the structure is coated with one or more layers of said first material.
20 An energy absorbing structure formed of a composite material as claimed in any of Claims 1 to 17.
21 A method of protecting a structure against wear by applying to the structure one or more layers of a material having a high tensile strength and a low modulus of elasticity.
22 A method as claimed in Claim 21, wherein said material is fibrous.
23 A method as claimed in Claim 21 or Claim 22, wherein said material is an orientated polymer.
24 A method as claimed in any of Claims 21 to 23, wherein the material is a high crystallinity, orientated, polyethylene.
25 A composite material substantially as hereinbefore described with reference to the accompanying drawing.
26 A structure formed from a composite material substantially as hereinbefore described with reference to the accompanying drawing.
27 A method of protecting a structure against wear substantially as hereinbefore described with reference to the accompanying drawing.
PCT/GB1993/000775 1992-04-14 1993-04-14 Composite material WO1993021011A1 (en)

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GB929208221A GB9208221D0 (en) 1992-04-14 1992-04-14 Improvements in or relating to vehicles

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AU3902693A (en) 1993-11-18
GB9307654D0 (en) 1993-06-02
GB9208221D0 (en) 1992-05-27

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