WO2001039970A1 - Debonding resistant toughened composites prepared by small particle reinforcement of the fiber-matrix interface - Google Patents

Debonding resistant toughened composites prepared by small particle reinforcement of the fiber-matrix interface Download PDF

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Publication number
WO2001039970A1
WO2001039970A1 PCT/US2000/032555 US0032555W WO0139970A1 WO 2001039970 A1 WO2001039970 A1 WO 2001039970A1 US 0032555 W US0032555 W US 0032555W WO 0139970 A1 WO0139970 A1 WO 0139970A1
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WIPO (PCT)
Prior art keywords
fiber
mateπal
small particles
particles
composite
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PCT/US2000/032555
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French (fr)
Inventor
Yuris A. Dzenis
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University Of Nebraska-Lincoln
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Application filed by University Of Nebraska-Lincoln filed Critical University Of Nebraska-Lincoln
Priority to AU18080/01A priority Critical patent/AU1808001A/en
Publication of WO2001039970A1 publication Critical patent/WO2001039970A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C70/00—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts
    • B29C70/02—Shaping composites, i.e. plastics material comprising reinforcements, fillers or preformed parts, e.g. inserts comprising combinations of reinforcements, e.g. non-specified reinforcements, fibrous reinforcing inserts and fillers, e.g. particulate fillers, incorporated in matrix material, forming one or more layers and with or without non-reinforced or non-filled layers
    • B29C70/021—Combinations of fibrous reinforcement and non-fibrous material
    • B29C70/025—Combinations of fibrous reinforcement and non-fibrous material with particular filler
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
    • B29B15/00—Pretreatment of the material to be shaped, not covered by groups B29B7/00 - B29B13/00
    • B29B15/08—Pretreatment of the material to be shaped, not covered by groups B29B7/00 - B29B13/00 of reinforcements or fillers
    • B29B15/10—Coating or impregnating independently of the moulding or shaping step
    • B29B15/105—Coating or impregnating independently of the moulding or shaping step of reinforcement of definite length with a matrix in solid form, e.g. powder, fibre or sheet form
    • 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
    • C08J5/06—Reinforcing macromolecular compounds with loose or coherent fibrous material using pretreated fibrous materials
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M23/00—Treatment of fibres, threads, yarns, fabrics or fibrous goods made from such materials, characterised by the process
    • D06M23/08—Processes in which the treating agent is applied in powder or granular form

Definitions

  • the present invention relates generally to composite matenals and. more particularly, to the use of small particles to reinforce the interface between the matrix and fibers in fiber reinforced composites.
  • Fiber reinforced composite materials comprise fibrous or filamentary material embedded in a mat ⁇ x
  • the fiber is the load bearing component and the mat ⁇ x dissipates loads to the fibers, maintains fiber orientation, and protects the fiber from damaging environmental conditions
  • the externally applied load is transferred to the fibers by the matrix via the fiber-matrix interface. If the interface is weak and can easily be fractured, effective load transfer cannot be achieved, and the mechanical properties of the composite are impaired. Easy propagation of the mterfacial crack can lead to easy fiber pull-out. premature failure, and low overall fracture toughness of the composite On the other hand.
  • Elastomeric coating of fibers has been applied to reduce stress concentrations at the fiber-mat ⁇ x interface and to improve interfacial fracture toughness.
  • a coating impairs stress transfer between the matrix and fiber.
  • the thick coating layer leads to reduction of fiber volume fraction and an associated reduction of properties of the composite.
  • Elastomer coated fibers are taught, for example, in U.S. Patent Nos. 3,943,090, 4,737,527, and 5,080.968.
  • Typical reinforcing fibers have a smooth surface.
  • One way to improve interfacial fracture toughness in composites would be to roughen the fiber surface by an appropriate treatment such as mechanical roughening, chemical etching, and so forth. However, such a roughening would introduce defects on the fiber surface thus reducing fiber strength and other mechanical properties.
  • Such fiber surface treatment is taught, for example, in U.S. Patent No. 4,664,936.
  • Whiskered fibers are also known in the art for increasing fiber matrix bonding.
  • U.S. Patent No. 5,187,021 teaches growing whiskers on fibers for use in preparing composites.
  • the whiskers are taught to increase the strength of the fiber matrix interface, the whiskers are also taught to maintain fiber separation and provide uniform fiber distribution.
  • the size of the whiskers is generally on the order of the fiber diameter and larger, and the disclosed fiber separation causes a reduction in fiber volume fraction and an associated reduction of properties of the composite.
  • the present invention is directed to improved fiber-remforced composite products and methods for manufactu ⁇ ng composite mate ⁇ als B ⁇ efly, m accordance with the present invention, a method and product are disclosed for providing improved composite systems having increased interfacial fracture toughness
  • the present invention employs small particles to reinforce and/or toughen the interface between the mat ⁇ x and fibers
  • the small reinforcing particles used in accordance with the present invention are smaller than the diameter of core reinforcing fibers
  • the present invention provides a composite mate ⁇ al comp ⁇ sing a mat ⁇ x mate ⁇ al, a fibrous mate ⁇ al embedded withm the mat ⁇ x mate ⁇ al, and particles located at or near the fiber-mat ⁇ x interface, wherein the particles are not uniformly dist ⁇ ubbed throughout the mat ⁇ x, but rather are concentrated at or near the fiber-mat ⁇ x interface
  • the particles are small, 1 e , having a size smaller than the diameter of the fibrous mate ⁇ al
  • the small particles are attached to the fibrous mate ⁇ al
  • the particles are located at or near the fiber-mat ⁇ x interface, but are unattached to the fibrous mate ⁇ al
  • some particles are attached to the fibrous mate ⁇ al and some particles are unattached to the fibrous mate ⁇ al
  • the present invention provides a fiber for use in a composite mate ⁇ al comp ⁇ sing a core fiber and small particles attached to the core fiber, wherein the small particles have a size smaller than the diameter of the fibrous mate ⁇ al
  • the present invention provides a method of fab ⁇ catmg a composite mate ⁇ al comp ⁇ sing the steps of attaching small particles to a fibrous mate ⁇ al, wherein the small particles have a size smaller than the diameter of said fibrous mate ⁇ al, and consolidating the fibrous mate ⁇ al into a mat ⁇ x
  • the small particles are dist ⁇ ubbed uniformly over the entire fiber-mat ⁇ x interface
  • the small particles may be dist ⁇ ubbed over one or more individual parts of a fiber-mat ⁇ x interface, such as areas likely to undergo stress in a given application BRIEF DESCRIPTION OF THE DRAWINGS
  • the detailed description of the invention may be best understood when read in reference to the accompanying drawings wherein:
  • FIG. 1 illustrates the construction of a reinforcing fiber having small particles attached thereto in accordance with the present invention
  • FIG. 2 illustrates the path of interfacial crack propagation in fiber reinforced composites according to the present invention
  • FIGS. 3 and 4 illustrate possible damage mechanisms in fiber reinforced composites according to the present invention
  • FIG. 5 illustrates the construction of a fractal fiber-matrix interface in accordance with the present invention.
  • FIG. 1 there is shown a fibrous material 10 having small reinforcing particles 12 thereon.
  • the particles create multiple obstacles for the interfacial (debonding) crack propagation and will cause the crack to deflect. This will make the crack path more tortuous and the resulting fracture surfaces rougher. As a result, the energy required for the interfacial crack propagation (interfacial fracture toughness) will be increased.
  • the key in this fiber- matrix reinforcement concept is the small size of particles used for the modification. The reinforcement effect is achieved without reduction of the core fiber strength and other mechanical properties, as the reinforcing particles do not create stress concentrations in the core fiber. This effect is also achieved without substantial reduction of the core fiber volume fraction in the composite and the associated reduction of composite properties.
  • FIG.2 shows the path 14 of interfacial crack propagation between fiber 10 and matrix material 20 as it is deflected around reinforcing particles 12. In addition to the increase of interfacial fracture toughness, increased friction between the rougher fracture surfaces will cause increased
  • FIGS. 3 and 4 illustrate potential damage mechanisms of composite mate ⁇ als according to the present invention.
  • FIG 3 illustrates a potential damage mechamsm of a composite mate ⁇ al employing small particle reinforcement at the fiber mat ⁇ x interface in accordance with the present invention, wherein multiple discrete microcracks and/or nanocracks 16 develop before ma crack propagation, leading to increased energy required for interfacial crack propagation as the fractures develop, and thus, increased toughness of the interface
  • FIG.4 illustrates another potential damage mechanism of a composite mate ⁇ al employing small particle reinforcement at the fiber matrix interface m accordance with the present invention, wherein breakup of particles in the path of crack propagation increases the energy consumption by the mate ⁇ al as it fractures and thus, increases interfacial toughness.
  • the present invention is not limited to the use of any particular core reinforcing fiber.
  • any suitable fiber or filamentary mate ⁇ al there may be used any suitable fiber or filamentary mate ⁇ al.
  • Such reinforcement fibers are generally known in the art and include, but are not limited to, alumina, alurmnosilicate, aramid (such as Kevlar® , Twaron ®, or other aramid fibers), black glass ceramic, boron and boron containing fibers (e.g., boron on titania, boron on tungsten, and so forth), boron carbide, boron nit ⁇ de, carbonaceous fibers, such as carbon or graphite fibers, ceramic fibers, glass fibers (such as A-glass, AR-glass, C-glass, D-glass, E-glass, R- glass, S-glass, S 1 -glass, S2-glass, and other suitable types of glass), high melting polyolefms
  • polyethylene e.g., Spectra ® fibers
  • high strength polyethylene liquid crystalline polymers
  • metal fibers metal coated filaments, such as nickel, silver, or copper coated graphite fiber or filament, and the like, nylon, paraphenylene terephthal amide, polyetheretherketone (PEEK), polyetherketone (PEK), polyacrylonit ⁇ le, polyamide, polyarylate fibers, polybenzimidazole (PBI), polybenzothiazole (PBT), polybenzoxazole (PBO), polybenzthiazole (PBT), polyester, polyethylene, polyethylene 2,6 naftalene dicarboxylate (PEN), polyethylene phthalate, polyethylene terephthalate, polyvinyl ha des, such as polyvinyl chlo ⁇ de, other specialty polymers, quartz, rayon, silica, silicon carbide, silicon nit ⁇ de.
  • silicon carbomt ⁇ de silicon oxycarbomt ⁇ de, titania, titanium bo ⁇ de, titanium carbide, zircoma toughened alumina. zirconium oxide, and so forth
  • the types of fiber most commonly used in advanced composites are carbon/graphite, aramid, and glass fibers
  • the core fiber may be discontinuous or continuous fiber, or combinations thereof, and may be present m any of the va ⁇ ous conventional forms
  • Discontinuous fiber includes, for example, milled fibers, chopped fibers, whiskers, acicular particles, etc
  • Continuous fibers include short discontinuous and long discontinuous fibers
  • the fiber may be present in va ⁇ ous forms, including but not limited to, monofilament fiber, multifilament yarn, woven fab ⁇ c, stitched fab ⁇ cs, braids, unidirectional tapes and fab ⁇ cs, non-woven fab ⁇ c, roving, chopped strand mat, tow, random mat, woven roving mat, and so forth
  • the fibers may be sized or unsized
  • the sizing may be any conventional sizing agent and may be applied according to any conventional sizing process The sizing may be applied to the fibers before or after the particles are attached to the fiber In one embodiment, the sizing is applied to improve the adhesion of the of the particles to the fiber, and
  • the present invention is not limited to any particular mat ⁇ x mate ⁇ al. Any suitable mat ⁇ x mate ⁇ al may be employed in one embodiment, the mat ⁇ x mate ⁇ al is a polymer, such as thermosets and thermoplastics
  • Polymer mat ⁇ x composite manufactu ⁇ ng processes generally involve the combining of a resm, a cu ⁇ ng agent, and some type of reinforcing fiber Typically, heat and pressure are used to shape and cure the mixture into a finished part
  • Thermosets require a cu ⁇ ng step to produce a cured or finished part Once cured, the part cannot be changed or reformed
  • Thermoplastics cu ⁇ ently represent a relatively small part of the PMC industry They are typically supplied as nonreactive solids (no chemical reaction occurs du ⁇ ng processing) and require only heat and pressure to form the finished part Unlike the thermosets, the thermoplastics can usually be reheated and reformed into another shape, if desired
  • the mat ⁇ x mate ⁇ al may be, for example, thermosetting mate ⁇ als based on epoxy resins, biscitraconicimide (BCD, bismaleimides (BMI), bismaleimide/tnazine/epoxy resms, cyanate esters, cyanate resins, furanic resins, phenolic resms, urea-formaldehyde resms, melamme-formaldehyde resms, phthalocyanine resins, polyacrylates, polybenzoxazole resms, polybutylene, polyester resms, polyimides, including high temperature polyimides such as PMR, PMR-15, and DMBZ polyimides), acetylene terminated polyimide resms, polyurethanes, sihcones.
  • BCD biscitraconicimide
  • BMI bismaleimides
  • cyanate esters cyanate resins
  • the mat ⁇ x mate ⁇ al may also be thermoplastic mate ⁇ als based on acrylomt ⁇ le butadiene styrene (ABS) copolymers, aromatic polycarbonates, aromatic polyesters, carboxymethylcellulose, ethyl cellulose, ethylene vinyl acetate copolymers, polyacetals, polyacetates, polyacrylomt ⁇ le and other mt ⁇ le resins, polyacrylomt ⁇ le-vinyl chlo ⁇ de copolymer, polyamides, aromatic polyamides (aramids), polyamide-imide, polyarylates, polyarylene oxides, polyarylene sulfides, polyarylsulfones, polybenzimidazole, polybutylene terephthalate, polycarbonates, polyester lmides, polyether sulfones, polyethe ⁇ mides, polyetherketones, polyetheretherketones, polyethylene terephthalate, polyimides, polymethacrylate, polyolef
  • elastome ⁇ c or rubber mate ⁇ als may be employed as the mat ⁇ x mate ⁇ al, including, but not limited to, butadiene-acrylomtnle copolymers.
  • butadiene-acrylomtnle copolymers ethylene butadiene block copolymer, ethylene-propylene base copolymer, natural rubber, polychloroprene rubber, polyisoprene-isobutylene coploymers, sihcone rubber, styrene-acrylomt ⁇ le copolymers, styrene-butadiene copolymers, styrene-maleic anhyd ⁇ de copolymers, and so forth
  • the mat ⁇ x mate ⁇ al may be a toughened resin mate ⁇ al
  • Methods of improving the toughness of resms, such as the thermoset resms listed above, wherein elastome ⁇ c or thermoplastic particles are incorporated into the resm mat ⁇ x system, are well known in the art and are attractive for use with the small particle fiber-mat ⁇ x reinforcement according to the present invention, such where it is desired to produce a composite mate ⁇ al with increased toughness, such as toughness against impact induced damage
  • the mat ⁇ x mate ⁇ al may be a thermosettmg resin toughened with elastome ⁇ c or thermoplastic particles
  • the mat ⁇ x mate ⁇ al may be an epoxy, cyanate, or bismaleimide resm toughened with elastome ⁇ c or thermoplastic particles
  • the mat ⁇ x mate ⁇ al may be an epoxy resm toughened with elastome ⁇ c or thermoplastic particles
  • the mat ⁇ x mate ⁇ al may also be a ceramic, such as oxides, bo ⁇ des. carbides, nit ⁇ des Likewise, glass mat ⁇ xes, carbon mat ⁇ xes, and the like, may also be employed
  • any other conventional additives may optionally be present m the mat ⁇ x system which include, but are not limited to, flame retardants, catalysts, promoters, dopants, or hardeners, such as cu ⁇ ng or cross-linking catalysts or catalysts to promote the growth of conductive matenals, fillers such as quartz powder to reduce thermal expansion or other relatively inert mate ⁇ als which may be added to reduce cost, or other fillers or extenders used to modify mechanical properties, serve as a base for color effects, or to improve surface texture, extenders, or to dilute or extend high cost resins without sigmficant lessening of properties, inhibitors, thixotropic agents, adhesion promoters, any other additive capable of exerting a positive effect on the substrate and dunng processing such as finishing agents to improve mat ⁇ x to fiber coupling or a noble metal or noble metal compound to make the matenal catalytic for electroless deposition of copper, and so forth
  • flame retardants such as flame retardants, catalysts, promoters, dopants, or
  • the fiber-mat ⁇ x reinforcement particles 12 may be of any shape or geometrical configration, including, but not limited to, round, angular, fibrous, flaky, etc , or any combinations thereof
  • the small particles may be of any mate ⁇ al, hard or soft, including, but not limited to, ceramic, carbon (including graphite and diamond), metal (including metals, metal alloys, and mtermetalhc compounds), mineral, glass, polymer (including thermoplastic and thermoset polymer mate ⁇ als), rubber, etc , and any combinations thereof
  • Small particles 12 to be used at the fiber-mat ⁇ x interface can be produced by any suitable method, including but not limited to: (1) Breakmg-down methods of size reduction and comminution, e.g., blending, crushing, g ⁇ ndmg, homogenizing, milling, disintegration under the action of radiation, thermal decomposition, combustion, disintegration due to elect ⁇ cal charging, physico-chemical and chemical reactions, etc.; and (2) Building-up methods of particle growth, e
  • Examples of building-up reaction techniques which have produced fine particles include: (1) gas phase techniques, e g., thermal decomposition, evaporation- condensation, gas evaporation, hydrogen reduction, nitrogen and hybrid plasma, electric arc, thermal hydrolysis, flame reaction methods; (2) solution techniques, e.g., precipitation, hydrolysis, solvent evaporation; and (3) solid-state reactions, e.g., thermal decomposition.
  • gas phase techniques e g., thermal decomposition, evaporation- condensation, gas evaporation, hydrogen reduction, nitrogen and hybrid plasma, electric arc, thermal hydrolysis, flame reaction methods
  • solution techniques e.g., precipitation, hydrolysis, solvent evaporation
  • solid-state reactions e.g., thermal decomposition.
  • small particles of va ⁇ ous shapes can be prepared by methods based on the coalescence of even smaller particles, including: coagulation in aerosols, e.g., Brownian, laminar, turbulent, acoustic, electrostatic, coagulation due to velocity difference under gravity or centrifugal force, etc. ; coagulation in solutions, e.g., coagulation with electrolytes, coagulation with polymers and surfactants, etc ; agglomeration; aggregation; flocculation; smte ⁇ ng; fusion; solid and liquid bndgmg; interlocking; and so forth
  • Small particles can also be prepared from droplets obtained by any method of atomization of a liquid (mechanical, elect ⁇ c, magnetic, ultrasonic, etc) with the consequent conversion of droplets into particles by any suitable method, e g , solvent evaporation, solidification by cooling, crystallization, hydrolysis, etc Examples of droplet-based techniques which have produced fine particles include' atomization into flame, spray drying, condensation with subsequent solidification, atomized hydrolysis, etc. Small particles can be separated and/or collected by any suitable method, e.g., sieving, filtermg, sedimentation, electrostatic, magnetic, magnetohydrostatic, or dielect ⁇ c separation, electrophoresis, wet scrubbing, segregation, stratification, etc
  • Particles can be placed on fiber surface p ⁇ or to embedding the fiber into the mat ⁇ x mate ⁇ al
  • Previously prepared particles can be placed on fiber surface by any suitable method, e g , adsorption from a suspension, deposition from gas or liquid fluidized bed or slurry, electrodeposition from suspension (particles can be elect ⁇ fied by contact electnfication, elect ⁇ fication by impaction, elect ⁇ fication through breakage), etc
  • Particles can also be grown directly on the fiber surface by any method of particle growth on a substrate (see the methods of particle preparation by growth desc ⁇ bed above), e.g., chemical or physical vapor deposition, surface polyme ⁇ zation, surface precipitation from solutions, etc
  • Particles can also be formed from droplets deposited directly on the fiber surface by any method of liquid atomization with subsequent solidification (see the methods of particle preparation from droplets desc ⁇ bed above), e.g , spray congealing, vacuum evaporation, electrostatic engulfing, spray drying
  • small particles can be placed at the fiber-mat ⁇ x interface from a suspension in mat ⁇ x or grown from a solution in mat ⁇ x by methods of interfacial precipitation, interfacial deposition, interfacial polyme ⁇ zation, etc These methods are based on the fact that in many suspensions and solutions, the concentration of a component is higher in a thin interfacial layer near the surface
  • Small particles can be attached to the fiber surface by any suitable force or combination of forces, including but not limited to forces of
  • the solid b ⁇ dges between the fiber and particles can form du ⁇ ng any process of particle growth on fiber surface, e.g , solidification and crystallization from melts, crystallization of dissolved substances, precipitation from solutions, chemical and physical vapor deposition, etc
  • the b ⁇ dges can also form as a result of va ⁇ ous treatments of the fiber with small particles, e.g , resolidification or recrystallization as a result of thermal treatment, sinte ⁇ ng, brazing, welding (cold, ultrasonic, explosion, diffusion welding and bonding), fusion, etc
  • the third phase b ⁇ dges can be formed by hardening binders and particle and/or fiber coatings, solde ⁇ ng, etc
  • the b ⁇ dges can also form as a result of surface diffusion, volume diffusion, etc (4) Mechanical interlocking small fibers,
  • small particles may produce positive effect on interfacial fracture toughness without being intimately attached to the fiber surface. This will happen, for instance, when interfacial cracking takes place not at the interface (for example, due to a very strong adhesion between the fiber and mat ⁇ x), but m a thm layer of mat ⁇ x near the interface
  • the mechanisms and strength of attachment of small particles to the fiber can be controlled by particle and/or fiber surface treatment, coating, microencapsulation, any combination thereof
  • the fiber surface can be modified by chemical treatment, mechanical treatment, thermal treatment thermochemical treatment, coating, etc before or after small particle modification
  • chemical sizing to improve fiber-mat ⁇ x adhesion can be performed on a virgin fiber or after small particle were deposited/ grown on fiber surface
  • the small particles at the interface in accordance with the present invention can be o ⁇ ented or diso ⁇ ented, arranged randomly or m patterns, chains, etc
  • the small particles can be coated, sized, or otherwise treated both separately, before the deposition, or on the fiber
  • the small particle reinforcement according to this teaching does not substantially decrease the volume fraction of the core fiber, the small particles may advantageously be placed at the entire fiber-mat ⁇ x interface
  • it is not necessary that all of the fiber be coated with the small particle reinforcement of the present invention For example, in some embodiments, only a portion of the fibers in the composite are coated with the small particles according to the present invention Likewise, in some embodiments, the small particles may be dist ⁇ ubbed over one or more individual parts of a fiber-mat ⁇ x interface
  • the reinforcement fiber 10 content by volume in the mat ⁇ x will usually be from about 5 percent to about 90 percent, typically from about 40 percent to about 70 percent, and may be va ⁇ ed approp ⁇ ately depending on the particular purpose for which the composite is to be used It will be recognized that given the small particle size of the reinforcing particles, no substantial decrease in fiber volume fraction will result due to the presence of the small reinforcing particles in accordance with this teaching
  • small size reinforcement particles are needed to implement the present invention
  • the term "small” refers to the size of the particle relative to the transverse or diameter dimension of the reinforcement fibers
  • the size of the reinforcing particles depends on the diameter of the reinforcement fibers
  • the term "size” m reference to the reinforcing particles generally refers to a diameter or traverse dimension of the particle, or, where the particle has a geomet ⁇ cal configuration wherein a longitudinal dimension thereof exceeds a transverse or diameter dimension thereof, to the longitudinal dimension thereof
  • the small particles should be sufficiently small so as to provide fiber-mat ⁇ x interface reinforcement without substantial reduction of core fiber volume fraction and associated reduction in properties
  • the small particles according to the present invention generally have a size of up to about one-half of the diameter or transverse dimension of the core fiber
  • the small particles according to the present invention generally have a size of up to about one-third, or less, of the diameter or transverse dimension of the core fiber.
  • the small particles according to the present invention generally have a size of up to approximately one-fourth, or less, of the diameter or transverse dimension of the core fiber In an embodiment, the small particles according to the present invention generally have a size of up to approximately one-fifth, or less, of the diameter or transverse dimension of the core fiber In an embodiment, the small particles according to the present invention generally have a size of up to approximately one-sixth, or less, of the diameter or transverse dimension of the core fiber In an embodiment, there is a difference of about one order of magnitude or greater between the size of the reinforcing particle and the core fiber diameter or transverse dimension As an example, typical reinforcing fibers in composites are about 5-10 micrometers in diameter In such cases, submicron (nanoscopic) particles may be especially effective It will be recognized that the small particles need not be uniform in size and small particles having different sizes or a range of sized may be used Refer ⁇ ng now to FIG.
  • FIG. 5 there is shown an embodiment wherein reinforcement particles of at least two different sizes are employed to provide a fractal fiber-mat ⁇ x interface.
  • core fiber 10 treated with small particles 22, 24, and 26, of decreasing size.
  • three different size particles are shown m FIG. 5 for illustrative purposes, the number of different sizes of particles may be 2 or more.
  • it is not necessary to use generally discretely sized particles, and particles having a generally continuous size dist ⁇ bution range may be used as well
  • the differently sized particles 22. 24, and 26 may be contacted with the core fiber sequentially in the order of decreasing particle size, beginning with the largest particle size, or.
  • the plurality of particle sizes creates a fractal fiber-mat ⁇ x interface
  • the propagation of an interfacial crack will be deflected along a path 14 that is likewise fractal in nature and thus more tortuous Also, after debonding, the resulting fracture surfaces will be rougher As a result, the energy required for the interfacial crack propagation is increased, as is energy consumption du ⁇ ng fiber pull-out subsequent to debonding
  • all of the differently sized panicles are smaller than the diameter of the core fiber
  • some of the reinforcing particles may be larger than the diameter of the core fiber, so long as at least one of the differently sized particles is smaller than the diameter of the reinforcing fiber.
  • the fiber modified by small particles in accordance with the present invention may be employed to produce composite materials at the fiber-matrix interface by any conventional composite fabrication process wherein a fibrous material is embedded or consolidated in a matrix material.
  • Such process include, but are not limited to, composite fabrication using prepregs, filament winding processes, including wet filament winding processes, processes involving the use of preforms, resin transfer molding processes, including reaction resin transfer molding processes, or other techniques as may be employed in preparing polymer matrix, metal matrix, ceramic matrix, glass matrix, and carbon matrix composites.

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Abstract

Fiber reinforced composite materials comprising a matrix and reinforcement fibers (10) and further comprising small particles (12) at the fiber-matrix interface provide reinforcement and/or toughening of the fiber-matrix interface without substantial reduction of the core fiber volume fraction in the composite. In another aspect, the present invention provides a method of fabricating a composite material comprising the steps of attaching small particles to a fibrous material, and consolidating the fibrous material into a matrix.

Description

IN THE UNITED STATES PATENT AND TRADEMARK OFFICE
APPLICATION FOR PATENT
TITLE:
DEBONDING RESISTANT TOUGHENED COMPOSITES
PREPARED BY SMALL PARTICLE REINFORCEMENT
OF THE FIBER-MA TRIX INTERFA CE
S P E C I F I C A T I O N
FIELD OF THE INVENTION The present invention relates generally to composite matenals and. more particularly, to the use of small particles to reinforce the interface between the matrix and fibers in fiber reinforced composites.
BACKGROUND OF THE INVENTION Fiber reinforced composite materials comprise fibrous or filamentary material embedded in a matπx The fiber is the load bearing component and the matπx dissipates loads to the fibers, maintains fiber orientation, and protects the fiber from damaging environmental conditions The externally applied load is transferred to the fibers by the matrix via the fiber-matrix interface. If the interface is weak and can easily be fractured, effective load transfer cannot be achieved, and the mechanical properties of the composite are impaired. Easy propagation of the mterfacial crack can lead to easy fiber pull-out. premature failure, and low overall fracture toughness of the composite On the other hand. a strong, fracture resistant interface can assure that the composite is able to bear load even when some fibers are broken The load will be transferred through the intact portions of the interface to the damaged as well as undamaged fibers Chemical fiber sizing has been applied to improve the strength of fiber-matrix interface in composites. The size creates a strong chemical bond between the fiber and matrix. However, the high strength often leads to embrittlement of the interface. In such composites, the propagation of the interfacial cracks is still easy, and the overall fracture toughness of the composite is low. The use of fiber sizing to improve the bonding between fiber and matrix is discussed, for example, in U.S. Patent Nos. 4,364,993 and 4,990,549.
Elastomeric coating of fibers has been applied to reduce stress concentrations at the fiber-matπx interface and to improve interfacial fracture toughness. However, such a coating impairs stress transfer between the matrix and fiber. The thick coating layer leads to reduction of fiber volume fraction and an associated reduction of properties of the composite.
Elastomer coated fibers are taught, for example, in U.S. Patent Nos. 3,943,090, 4,737,527, and 5,080.968.
Typical reinforcing fibers have a smooth surface. One way to improve interfacial fracture toughness in composites would be to roughen the fiber surface by an appropriate treatment such as mechanical roughening, chemical etching, and so forth. However, such a roughening would introduce defects on the fiber surface thus reducing fiber strength and other mechanical properties. Such fiber surface treatment is taught, for example, in U.S. Patent No. 4,664,936.
Whiskered fibers are also known in the art for increasing fiber matrix bonding. For example, U.S. Patent No. 5,187,021 teaches growing whiskers on fibers for use in preparing composites. The whiskers are taught to increase the strength of the fiber matrix interface, the whiskers are also taught to maintain fiber separation and provide uniform fiber distribution. However, the size of the whiskers is generally on the order of the fiber diameter and larger, and the disclosed fiber separation causes a reduction in fiber volume fraction and an associated reduction of properties of the composite.
It would, therefore, be desirable to provide improved composites with better debondmg resistance and interfacial fracture toughness without impairing the load transfer between the matrix and fiber, without reducing the fiber strength and other properties, and without reducing the fiber volume fraction and associated composite properties. SUMMARY OF THE INVENTION The present invention is directed to improved fiber-remforced composite products and methods for manufactuπng composite mateπals Bπefly, m accordance with the present invention, a method and product are disclosed for providing improved composite systems having increased interfacial fracture toughness The present invention employs small particles to reinforce and/or toughen the interface between the matπx and fibers The small reinforcing particles used in accordance with the present invention are smaller than the diameter of core reinforcing fibers
In one aspect, the present invention provides a composite mateπal compπsing a matπx mateπal, a fibrous mateπal embedded withm the matπx mateπal, and particles located at or near the fiber-matπx interface, wherein the particles are not uniformly distπbuted throughout the matπx, but rather are concentrated at or near the fiber-matπx interface Preferably, the particles are small, 1 e , having a size smaller than the diameter of the fibrous mateπal In some embodiments, the small particles are attached to the fibrous mateπal In some embodiments, the particles are located at or near the fiber-matπx interface, but are unattached to the fibrous mateπal In still other embodiments, some particles are attached to the fibrous mateπal and some particles are unattached to the fibrous mateπal
In another aspect, the present invention provides a fiber for use in a composite mateπal compπsing a core fiber and small particles attached to the core fiber, wherein the small particles have a size smaller than the diameter of the fibrous mateπal
In still another aspect, the present invention provides a method of fabπcatmg a composite mateπal compπsing the steps of attaching small particles to a fibrous mateπal, wherein the small particles have a size smaller than the diameter of said fibrous mateπal, and consolidating the fibrous mateπal into a matπx In some embodiments, the small particles are distπbuted uniformly over the entire fiber-matπx interface In other embodiments, the small particles may be distπbuted over one or more individual parts of a fiber-matπx interface, such as areas likely to undergo stress in a given application BRIEF DESCRIPTION OF THE DRAWINGS The detailed description of the invention may be best understood when read in reference to the accompanying drawings wherein:
FIG. 1 illustrates the construction of a reinforcing fiber having small particles attached thereto in accordance with the present invention;
FIG. 2 illustrates the path of interfacial crack propagation in fiber reinforced composites according to the present invention;
FIGS. 3 and 4 illustrate possible damage mechanisms in fiber reinforced composites according to the present invention; and FIG. 5 illustrates the construction of a fractal fiber-matrix interface in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION Here follows a description of various embodiments of the invention. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
In FIG. 1, there is shown a fibrous material 10 having small reinforcing particles 12 thereon. The particles create multiple obstacles for the interfacial (debonding) crack propagation and will cause the crack to deflect. This will make the crack path more tortuous and the resulting fracture surfaces rougher. As a result, the energy required for the interfacial crack propagation (interfacial fracture toughness) will be increased. The key in this fiber- matrix reinforcement concept is the small size of particles used for the modification. The reinforcement effect is achieved without reduction of the core fiber strength and other mechanical properties, as the reinforcing particles do not create stress concentrations in the core fiber. This effect is also achieved without substantial reduction of the core fiber volume fraction in the composite and the associated reduction of composite properties. FIG.2 shows the path 14 of interfacial crack propagation between fiber 10 and matrix material 20 as it is deflected around reinforcing particles 12. In addition to the increase of interfacial fracture toughness, increased friction between the rougher fracture surfaces will cause increased
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energy consumption duπng fiber pull-out, subsequent to debonding, thus further increasing the overall fracture toughness of the composite.
FIGS. 3 and 4 illustrate potential damage mechanisms of composite mateπals according to the present invention. FIG 3 illustrates a potential damage mechamsm of a composite mateπal employing small particle reinforcement at the fiber matπx interface in accordance with the present invention, wherein multiple discrete microcracks and/or nanocracks 16 develop before ma crack propagation, leading to increased energy required for interfacial crack propagation as the fractures develop, and thus, increased toughness of the interface FIG.4 illustrates another potential damage mechanism of a composite mateπal employing small particle reinforcement at the fiber matrix interface m accordance with the present invention, wherein breakup of particles in the path of crack propagation increases the energy consumption by the mateπal as it fractures and thus, increases interfacial toughness.
The present invention is not limited to the use of any particular core reinforcing fiber.
As the core fiber 10, there may be used any suitable fiber or filamentary mateπal. Such reinforcement fibers are generally known in the art and include, but are not limited to, alumina, alurmnosilicate, aramid (such as Kevlar® , Twaron ®, or other aramid fibers), black glass ceramic, boron and boron containing fibers (e.g., boron on titania, boron on tungsten, and so forth), boron carbide, boron nitπde, carbonaceous fibers, such as carbon or graphite fibers, ceramic fibers, glass fibers (such as A-glass, AR-glass, C-glass, D-glass, E-glass, R- glass, S-glass, S 1 -glass, S2-glass, and other suitable types of glass), high melting polyolefms
(e.g., Spectra ® fibers), high strength polyethylene, liquid crystalline polymers, metal fibers, metal coated filaments, such as nickel, silver, or copper coated graphite fiber or filament, and the like, nylon, paraphenylene terephthal amide, polyetheretherketone (PEEK), polyetherketone (PEK), polyacrylonitπle, polyamide, polyarylate fibers, polybenzimidazole (PBI), polybenzothiazole (PBT), polybenzoxazole (PBO), polybenzthiazole (PBT), polyester, polyethylene, polyethylene 2,6 naftalene dicarboxylate (PEN), polyethylene phthalate, polyethylene terephthalate, polyvinyl ha des, such as polyvinyl chloπde, other specialty polymers, quartz, rayon, silica, silicon carbide, silicon nitπde. silicon carbomtπde. silicon oxycarbomtπde, titania, titanium boπde, titanium carbide, zircoma toughened alumina. zirconium oxide, and so forth Mixtures of any such suitable fibers may also be employed The types of fiber most commonly used in advanced composites are carbon/graphite, aramid, and glass fibers
The core fiber may be discontinuous or continuous fiber, or combinations thereof, and may be present m any of the vaπous conventional forms Discontinuous fiber includes, for example, milled fibers, chopped fibers, whiskers, acicular particles, etc Continuous fibers include short discontinuous and long discontinuous fibers The fiber may be present in vaπous forms, including but not limited to, monofilament fiber, multifilament yarn, woven fabπc, stitched fabπcs, braids, unidirectional tapes and fabπcs, non-woven fabπc, roving, chopped strand mat, tow, random mat, woven roving mat, and so forth The fibers may be sized or unsized When the fibers are sized, the sizing may be any conventional sizing agent and may be applied according to any conventional sizing process The sizing may be applied to the fibers before or after the particles are attached to the fiber In one embodiment, the sizing is applied to improve the adhesion of the of the particles to the fiber, and in such case, is preferably applied before the particles are attached In one embodiment, the particles are coated/sized pπor to application to the fiber, with the fiber itself bemg either sized or unsized. In still other embodiments, the particles are uncoated pπor to application to the fiber, with the fiber itself being either sized or unsized.
The present invention is not limited to any particular matπx mateπal. Any suitable matπx mateπal may be employed In one embodiment, the matπx mateπal is a polymer, such as thermosets and thermoplastics Polymer matπx composite manufactuπng processes generally involve the combining of a resm, a cuπng agent, and some type of reinforcing fiber Typically, heat and pressure are used to shape and cure the mixture into a finished part Thermosets require a cuπng step to produce a cured or finished part Once cured, the part cannot be changed or reformed Thermoplastics cuπently represent a relatively small part of the PMC industry They are typically supplied as nonreactive solids (no chemical reaction occurs duπng processing) and require only heat and pressure to form the finished part Unlike the thermosets, the thermoplastics can usually be reheated and reformed into another shape, if desired
The matπx mateπal may be, for example, thermosetting mateπals based on epoxy resins, biscitraconicimide (BCD, bismaleimides (BMI), bismaleimide/tnazine/epoxy resms, cyanate esters, cyanate resins, furanic resins, phenolic resms, urea-formaldehyde resms, melamme-formaldehyde resms, phthalocyanine resins, polyacrylates, polybenzoxazole resms, polybutylene, polyester resms, polyimides, including high temperature polyimides such as PMR, PMR-15, and DMBZ polyimides), acetylene terminated polyimide resms, polyurethanes, sihcones. tetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymers, tπazmes. alkyds, unsaturated polyester (UP) resins, vinyl ester resins, vinyl esters, xylene resms, specialty polymers, and so forth
The matπx mateπal may also be thermoplastic mateπals based on acrylomtπle butadiene styrene (ABS) copolymers, aromatic polycarbonates, aromatic polyesters, carboxymethylcellulose, ethyl cellulose, ethylene vinyl acetate copolymers, polyacetals, polyacetates, polyacrylomtπle and other mtπle resins, polyacrylomtπle-vinyl chloπde copolymer, polyamides, aromatic polyamides (aramids), polyamide-imide, polyarylates, polyarylene oxides, polyarylene sulfides, polyarylsulfones, polybenzimidazole, polybutylene terephthalate, polycarbonates, polyester lmides, polyether sulfones, polyetheπmides, polyetherketones, polyetheretherketones, polyethylene terephthalate, polyimides, polymethacrylate, polyolefins (polyethylene, polypropylene), polyallomers, polyoxadiazole, polyparaxylene, polyphenylene oxides (PPO), modified PPOs, polystyrene, polysulfone, polytetrafluoroethylene, polyvinyl acetate, polyvinyl alcohol, polyvinyl halides such as polyvinyl chloπde, polyvinyl chlonde-vmyl acetate copolymer, polyvinyl pyrrolidone, polyvmyhdene chloπde, specialty polymers, and so forth
Also, other elastomeπc or rubber mateπals may be employed as the matπx mateπal, including, but not limited to, butadiene-acrylomtnle copolymers. ethylene butadiene block copolymer, ethylene-propylene base copolymer, natural rubber, polychloroprene rubber, polyisoprene-isobutylene coploymers, sihcone rubber, styrene-acrylomtπle copolymers, styrene-butadiene copolymers, styrene-maleic anhydπde copolymers, and so forth
In one embodiment, the matπx mateπal may be a toughened resin mateπal Methods of improving the toughness of resms, such as the thermoset resms listed above, wherein elastomeπc or thermoplastic particles are incorporated into the resm matπx system, are well known in the art and are attractive for use with the small particle fiber-matπx reinforcement according to the present invention, such where it is desired to produce a composite mateπal with increased toughness, such as toughness against impact induced damage In one embodiment, the matπx mateπal may be a thermosettmg resin toughened with elastomeπc or thermoplastic particles In another embodiment, the matπx mateπal may be an epoxy, cyanate, or bismaleimide resm toughened with elastomeπc or thermoplastic particles In yet another embodiment, the matπx mateπal may be an epoxy resm toughened with elastomeπc or thermoplastic particles
Other suitable matπx mateπals operable to embody the present invention include any metal containing mateπal, including metals, metal alloys, mtermetalhc compounds, with exemplary metals including aluminum and titanium The matπx mateπal may also be a ceramic, such as oxides, boπdes. carbides, nitπdes Likewise, glass matπxes, carbon matπxes, and the like, may also be employed
Any other conventional additives may optionally be present m the matπx system which include, but are not limited to, flame retardants, catalysts, promoters, dopants, or hardeners, such as cuπng or cross-linking catalysts or catalysts to promote the growth of conductive matenals, fillers such as quartz powder to reduce thermal expansion or other relatively inert mateπals which may be added to reduce cost, or other fillers or extenders used to modify mechanical properties, serve as a base for color effects, or to improve surface texture, extenders, or to dilute or extend high cost resins without sigmficant lessening of properties, inhibitors, thixotropic agents, adhesion promoters, any other additive capable of exerting a positive effect on the substrate and dunng processing such as finishing agents to improve matπx to fiber coupling or a noble metal or noble metal compound to make the matenal catalytic for electroless deposition of copper, and so forth Such additives and their use are generally known to those skilled m the art
The fiber-matπx reinforcement particles 12 may be of any shape or geometrical configration, including, but not limited to, round, angular, fibrous, flaky, etc , or any combinations thereof The small particles may be of any mateπal, hard or soft, including, but not limited to, ceramic, carbon (including graphite and diamond), metal (including metals, metal alloys, and mtermetalhc compounds), mineral, glass, polymer (including thermoplastic and thermoset polymer mateπals), rubber, etc , and any combinations thereof Small particles 12 to be used at the fiber-matπx interface can be produced by any suitable method, including but not limited to: (1) Breakmg-down methods of size reduction and comminution, e.g., blending, crushing, gπndmg, homogenizing, milling, disintegration under the action of radiation, thermal decomposition, combustion, disintegration due to electπcal charging, physico-chemical and chemical reactions, etc.; and (2) Building-up methods of particle growth, e g , any physical or chemical method of particle growth from gaseous, liquid, or solid phase or plasma, chemical vapor deposition, chemical spray deposition, photo-assisted chemical vapor deposition, plasma-assisted chemical vapor deposition, laser chemical vapor deposition, physical vapor deposition, sputteπng, ion planting, physical and chemical condensation from vapor, particle growth by assisted crystallization, nucleation solidification, pyrolysis, precipitation, hydrolysis, laser synthesis, polymeπzation, etc. Examples of building-up reaction techniques which have produced fine particles include: (1) gas phase techniques, e g., thermal decomposition, evaporation- condensation, gas evaporation, hydrogen reduction, nitrogen and hybrid plasma, electric arc, thermal hydrolysis, flame reaction methods; (2) solution techniques, e.g., precipitation, hydrolysis, solvent evaporation; and (3) solid-state reactions, e.g., thermal decomposition.
Alternatively, small particles of vaπous shapes can be prepared by methods based on the coalescence of even smaller particles, including: coagulation in aerosols, e.g., Brownian, laminar, turbulent, acoustic, electrostatic, coagulation due to velocity difference under gravity or centrifugal force, etc. ; coagulation in solutions, e.g., coagulation with electrolytes, coagulation with polymers and surfactants, etc ; agglomeration; aggregation; flocculation; smteπng; fusion; solid and liquid bndgmg; interlocking; and so forth
Small particles can also be prepared from droplets obtained by any method of atomization of a liquid (mechanical, electπc, magnetic, ultrasonic, etc) with the consequent conversion of droplets into particles by any suitable method, e g , solvent evaporation, solidification by cooling, crystallization, hydrolysis, etc Examples of droplet-based techniques which have produced fine particles include' atomization into flame, spray drying, condensation with subsequent solidification, atomized hydrolysis, etc. Small particles can be separated and/or collected by any suitable method, e.g., sieving, filtermg, sedimentation, electrostatic, magnetic, magnetohydrostatic, or dielectπc separation, electrophoresis, wet scrubbing, segregation, stratification, etc
Particles can be placed on fiber surface pπor to embedding the fiber into the matπx mateπal Previously prepared particles can be placed on fiber surface by any suitable method, e g , adsorption from a suspension, deposition from gas or liquid fluidized bed or slurry, electrodeposition from suspension (particles can be electπfied by contact electnfication, electπfication by impaction, electπfication through breakage), etc Particles can also be grown directly on the fiber surface by any method of particle growth on a substrate (see the methods of particle preparation by growth descπbed above), e.g., chemical or physical vapor deposition, surface polymeπzation, surface precipitation from solutions, etc Particles can also be formed from droplets deposited directly on the fiber surface by any method of liquid atomization with subsequent solidification (see the methods of particle preparation from droplets descπbed above), e.g , spray congealing, vacuum evaporation, electrostatic engulfing, spray drying, mechanochemical deposition (high-speed-impact deposition), etc
Alternatively, small particles can be placed at the fiber-matπx interface from a suspension in matπx or grown from a solution in matπx by methods of interfacial precipitation, interfacial deposition, interfacial polymeπzation, etc These methods are based on the fact that in many suspensions and solutions, the concentration of a component is higher in a thin interfacial layer near the surface
Small particles can be attached to the fiber surface by any suitable force or combination of forces, including but not limited to forces of
(1) Physical adsorption Van der Waals, electrostatic, magnetic, liquid bπdge, capillary forces, forces of dispersion or London attraction, polaπzabihty attraction, dipole-dipole interactions, magnetic dipole interactions, hydrogen bonding (sometimes called chemisorption), etc The physical adsorption can be assisted by mechanochemical activation of particles duπng size reduction, charge pick-up duπng high-temperature growth in flame or plasma or duπng electrostatic precipitation, etc The forces of physical attraction dramatically increase with the decrease of particle size [Handbook of Powder Science and Technology, M.E Fayed, L Otten, Eds , Van Nostrand, 1984, p 232]
(2) Chemical adsorption forces of ionic bonding, metallic bonding, covalent bonding, interfacial polymeπzation, etc (3) Cohesive and adhesive forces in solid bπdges The solid bπdges between the fiber and particles can form duπng any process of particle growth on fiber surface, e.g , solidification and crystallization from melts, crystallization of dissolved substances, precipitation from solutions, chemical and physical vapor deposition, etc The bπdges can also form as a result of vaπous treatments of the fiber with small particles, e.g , resolidification or recrystallization as a result of thermal treatment, sinteπng, brazing, welding (cold, ultrasonic, explosion, diffusion welding and bonding), fusion, etc The third phase bπdges can be formed by hardening binders and particle and/or fiber coatings, soldeπng, etc The bπdges can also form as a result of surface diffusion, volume diffusion, etc (4) Mechanical interlocking small fibers, platelets, or bulky particles can interlock or fold around the fiber and/or each other.
(5) Alternatively, small particles may produce positive effect on interfacial fracture toughness without being intimately attached to the fiber surface. This will happen, for instance, when interfacial cracking takes place not at the interface (for example, due to a very strong adhesion between the fiber and matπx), but m a thm layer of matπx near the interface
(this type of fracture will still be classified as an interfacial fracture) Small particles dispersed in this thm layer will deflect the crack and produce benefits similar to the benefits descπbed above for the interfacial crack
The mechanisms and strength of attachment of small particles to the fiber can be controlled by particle and/or fiber surface treatment, coating, microencapsulation, any
\aπous surface modifications
The fiber surface can be modified by chemical treatment, mechanical treatment, thermal treatment thermochemical treatment, coating, etc before or after small particle modification For example, chemical sizing to improve fiber-matπx adhesion can be performed on a virgin fiber or after small particle were deposited/ grown on fiber surface The small particles at the interface in accordance with the present invention can be oπented or disoπented, arranged randomly or m patterns, chains, etc The small particles can be coated, sized, or otherwise treated both separately, before the deposition, or on the fiber Because the small particle reinforcement according to this teaching does not substantially decrease the volume fraction of the core fiber, the small particles may advantageously be placed at the entire fiber-matπx interface However, it is not necessary that all of the fiber be coated with the small particle reinforcement of the present invention For example, in some embodiments, only a portion of the fibers in the composite are coated with the small particles according to the present invention Likewise, in some embodiments, the small particles may be distπbuted over one or more individual parts of a fiber-matπx interface, such as areas likely to be stress-prone m given application
The reinforcement fiber 10 content by volume in the matπx will usually be from about 5 percent to about 90 percent, typically from about 40 percent to about 70 percent, and may be vaπed appropπately depending on the particular purpose for which the composite is to be used It will be recognized that given the small particle size of the reinforcing particles, no substantial decrease in fiber volume fraction will result due to the presence of the small reinforcing particles in accordance with this teaching
As stated above, small size reinforcement particles are needed to implement the present invention As used herein, the term "small" refers to the size of the particle relative to the transverse or diameter dimension of the reinforcement fibers Thus, the size of the reinforcing particles depends on the diameter of the reinforcement fibers As used herein, the term "size" m reference to the reinforcing particles, unless it is otherwise clear from the context, generally refers to a diameter or traverse dimension of the particle, or, where the particle has a geometπcal configuration wherein a longitudinal dimension thereof exceeds a transverse or diameter dimension thereof, to the longitudinal dimension thereof The small particles should be sufficiently small so as to provide fiber-matπx interface reinforcement without substantial reduction of core fiber volume fraction and associated reduction in properties In an embodiment, the small particles according to the present invention generally have a size of up to about one-half of the diameter or transverse dimension of the core fiber In an embodiment, the small particles according to the present invention generally have a size of up to about one-third, or less, of the diameter or transverse dimension of the core fiber. In an embodiment, the small particles according to the present invention generally have a size of up to approximately one-fourth, or less, of the diameter or transverse dimension of the core fiber In an embodiment, the small particles according to the present invention generally have a size of up to approximately one-fifth, or less, of the diameter or transverse dimension of the core fiber In an embodiment, the small particles according to the present invention generally have a size of up to approximately one-sixth, or less, of the diameter or transverse dimension of the core fiber In an embodiment, there is a difference of about one order of magnitude or greater between the size of the reinforcing particle and the core fiber diameter or transverse dimension As an example, typical reinforcing fibers in composites are about 5-10 micrometers in diameter In such cases, submicron (nanoscopic) particles may be especially effective It will be recognized that the small particles need not be uniform in size and small particles having different sizes or a range of sized may be used Referπng now to FIG. 5, there is shown an embodiment wherein reinforcement particles of at least two different sizes are employed to provide a fractal fiber-matπx interface. In the illustration of FIG. 5, there appears core fiber 10 treated with small particles 22, 24, and 26, of decreasing size. Although three different size particles are shown m FIG. 5 for illustrative purposes, the number of different sizes of particles may be 2 or more. In an alternative embodiment, not shown, it is not necessary to use generally discretely sized particles, and particles having a generally continuous size distπbution range may be used as well The differently sized particles 22. 24, and 26 may be contacted with the core fiber sequentially in the order of decreasing particle size, beginning with the largest particle size, or. alternatively, may be applied simultaneously The plurality of particle sizes creates a fractal fiber-matπx interface The propagation of an interfacial crack will be deflected along a path 14 that is likewise fractal in nature and thus more tortuous Also, after debonding, the resulting fracture surfaces will be rougher As a result, the energy required for the interfacial crack propagation is increased, as is energy consumption duπng fiber pull-out subsequent to debonding In an embodiment, all of the differently sized panicles are smaller than the diameter of the core fiber In another embodiment, some of the reinforcing particles may be larger than the diameter of the core fiber, so long as at least one of the differently sized particles is smaller than the diameter of the reinforcing fiber.
The fiber modified by small particles in accordance with the present invention may be employed to produce composite materials at the fiber-matrix interface by any conventional composite fabrication process wherein a fibrous material is embedded or consolidated in a matrix material. Such process include, but are not limited to, composite fabrication using prepregs, filament winding processes, including wet filament winding processes, processes involving the use of preforms, resin transfer molding processes, including reaction resin transfer molding processes, or other techniques as may be employed in preparing polymer matrix, metal matrix, ceramic matrix, glass matrix, and carbon matrix composites.
Having described the invention of fiber-matrix reinforcement using small particles by way of reference to particular materials and techniques, many additional variations and modifications will now become apparent to those skilled in the art without departing from the spirit and scope of the present invention as defined by the appended claims. For example, it will be recognized that the specific matrix materials, core fiber materials, and small particle materials disclosed herein are provided for exemplary, illustrative, and explanatory purposes only. Any such listings of specific materials are not intended to be exhaustive and are not in any way limiting of the present invention as defined in the appended claims. Also, it will be noted that specific methods and techniques of forming composite materials and parts have been discussed as being readily adaptable to employ the novel concept of small particle reinforcement of the fiber-matrix interface. It will be recognized that any specific fabrication methods and techniques mentioned are exemplary only provided to illustrate and explain the principles of the invention. Such methods and techniques specifically mentioned are not intended in any way to provide a comprehensive or exhaustive listing and are not in any way limiting of the invention as claimed. It is the intention of the appended claims to encompass and include such changes. Accordingly, the scope of the invention should be determined solely by the appended claims and their legal equivalents.

Claims

CLAIMS What is claimed is
1 A composite mateπal compπsing a matπx mateπal, a fibrous mateπal embedded within said matπx mateπal. said matπx mateπal and said fibrous mateπal forming an interface, and particles located at said interface
2 A composite mateπal according to claim 1. wherein the small panicles compπse one or more mateπals selected from the group consisting of ceramic, metal, carbon, mineral, glass, polymer, thermoplastic, thermoset. and rubber mateπals
3 A composite mateπal according to claim 1, wherein the small particles compπse a configuration selected from the group consisting of smooth, round, angular, flaky, and fibrous
4 A composite matenal according to claim 1, wherein the small particles are applied to said fiber by fiber coating
5 A composite mateπal according to claim 1 , wherein the small particles are applied to said fiber by depositing said particles from a gas suspension
6. A composite mateπal according to claim 1, wherein the small particles are applied to said fiber by depositing said particles from a liquid suspension 7 A composite mateπal according to claim 1 , wherein the small particles are applied to said fiber by spraying a gas suspension of said particles
8 A composite mateπal according to claim 1 , wherein the small particles are applied to said fiber by spraying a liquid suspension of said particles
9 A composite mateπal according to claim 1, wherein application of the small particles onto said fiber is assisted by placing an electπcal charge on said particles, on said fiber, or both
10 A composite mateπal according to claim 1. wherein the small particles are applied to said fiber bv growth of the particles on the fiber
11 A composite mateπal according to claim 1 , wherein the small particles are applied to said fiber bv chemical vapor deposition of the particles on the fiber
12. A composite mateπal according to claim 1. wherein the small particles are applied to said fiber by deposition from the matπx.
13 A composite mateπal according to claim 1, wherein the small particles are applied to said fiber by growth of said particles from the matπx 14 A composite mateπal according to claim 1, wherein the matπx mateπal compπses a mateπal selected from the group consisting of a polymer, ceramic, metal, glass, and carbon mateπal
15 A composite mateπal according to claim 1, wherein the matπx mateπal compnses a mateπal selected from the group consisting of a thermosetting resin and a thermoplastic resm
16 A composite mateπal according to claim 1 , wherein said fiber compπses one or more mateπals selected from the group consisting of metal fibers, carbon fibers, ceramic fibers, and polymer fibers
17 A composite mateπal according to claim 1 , wherein the small particles have a size of up to about one-half of the diameter of the core fiber.
18 A composite mateπal according to claim 1 , wherein the small particles have a size of up to about one-third of the diameter of the core fiber.
19 A composite mateπal according to claim 1 , wherein the small particles have a size of up to about one-fourth of the diameter of the core fiber 20 A composite mateπal according to claim 1 , wherein the small particles have a size of up to about one-fifth of the diameter of the core fiber
21 A composite mateπal according to claim 1 , wherein the small particles have a size of up to about one-sixth of the diameter of the core fiber
22 A composite mateπal according to claim 1 , wherein the small particles have a size of up to about one-tenth of the diameter of the core fiber
23 A. composite mateπal according to claim 1. wherein the small particles have a size of up to about one-one hundredth of the diameter of the core fiber
24 A composite mateπal according to claim 1 wherein at least some of said panicles are attached to said fibrous mateπal
25. A composite mateπal according to claim 1 , wherein said particles have a size smaller than the diameter of said fibrous material.
26. A composite mateπal according to claim 1, wherein said fibrous material is coated and said particle is uncoated. 27. A composite mateπal according to claim 1. wherein said fibrous material is coated and said particle is coated.
28. A composite mateπal according to claim 1, wherein said fibrous mateπal is uncoated and said particle is uncoated.
29. A composite mateπal according to claim 1, wherein said fibrous material is uncoated and said particle is coated.
30. A composite material according to claim 1 , wherein a portion of said fibrous mateπal is coated and a portion of said fibrous material is uncoated.
31. A composite mateπal comprising: a matrix material; a fibrous material embedded within said matrix material, said matrix material and said fibrous material forming an interface; and small particles attached to said fibrous material, said small particles having a size smaller than the diameter of said fibrous material.
32. A composite material according to claim 31, wherein the small particles comprise one or more materials selected from the group consisting of ceramic, metal, carbon, mineral, glass, polymer, thermoplastic, thermoset, and rubber materials.
33. A composite mateπal according to claim 31, wherein the small particles compπse a configuration selected from the group consisting of smooth, round, angular, flaky, and fibrous. 34. A composite mateπal according to claim 31 , wherein the small particles are applied to said fiber by fiber coating
35 A composite mateπal according to claim 31 , wherein the small particles are applied to said fiber by depositing said particles from a gas suspension.
36 A composite mateπal according to claim 31, wherein the small particles are applied to said fiber by depositing said panicles from a liquid suspension. 37 A composite mateπal according to claim 31 , wherein the small particles are applied to said fiber by spraying a gas suspension of said particles
38 A composite mateπal according to claim 31 , wherein the small particles are applied to said fiber by spraying a liquid suspension of said particles 39 A composite mateπal according to claim 31 wherein application of the small panicles onto said fiber is assisted by placing an electπcal charge on said particles, on said fiber, or both
40 A composite mateπal according to claim 31 , wherein the small particles are applied to said fiber by growth of the particles on the fiber 41 A composite mateπal according to claim 31 , wherein the small particles are applied to said fiber by chemical vapor deposition of the particles on the fiber
42 A composite mateπal according to claim 31 , wherein the small particles are applied to said fiber by deposition from the matπx
43 A composite mateπal according to claim 31 , wherein the small particles are applied to said fiber by growth of said particles from the matπx
44 A composite mateπal according to claim 31 , wherein the matπx mateπal compπses a mateπal selected from the group consisting of a polymer, ceramic, metal, glass, and carbon mateπal
45 A composite mateπal according to claim 31 , wherein the matπx mateπal compπses a mateπal selected from the group consisting of a thermosetting resin and a thermoplastic resin
46 A composite mateπal according to claim 31 , wherein said fiber compπses one or more mateπals selected from the group consisting of metal fibers, carbon fibers, ceramic fibers, and polymer fibers 4" A composite mateπal according to claim 31 , wherein the small particles have a size of up to about one-half of the diameter of the core fiber
48 A. composite mateπal according to claim 31 , wherein the small particles have a size of up to about one-third of the diameter of the core fiber
49 A. composite mateπal according to claim 31 , wherein the small particles have a size of up to about one-fourth of the diameter of the core fiber 50 A composite mateπal according to claim 31 , wherein the small particles have a size of up to about one-fifth of the diameter of the core fiber
51 A composite mateπal according to claim 31. wherein the small particles have a size of up to about one-sixth of the diameter of the core fiber 52 A composite mateπal according to claim 31 , \\ herein the small particles have a size of up to about one-tenth of the diameter of the core fiber
53 A composite mateπal according to claim 31 , w herein the small panicles have a size of up to about one-one hundredth of the diameter of the core fiber
54 A composite mateπal according to claim 31. wherein the small particles are distπbuted randomly on the fibrous mateπal
55 A composite mateπal according to claim 31. wherein the small particles are aπanged m an ordered pattern on the fibrous mateπal
56 A composite mateπal according to claim 31 , further compπsing particles unattached to said fibrous mateπal, said unattached particles located at said interface. 57 A composite mateπal according to claim 31 , wherein said fibrous mateπal is coated and said particle is uncoated
58. A composite mateπal accordmg to claim 31 , wherein said fibrous mateπal is coated and said particle is coated.
59 A composite mateπal according to claim 31 , wherein said fibrous mateπal is uncoated and said particle is uncoated
60 A composite mateπal according to claim 31. wherein said fibrous mateπal is uncoated and said particle is coated
61 A composite mateπal according to claim 31 , herein a portion of said fibrous mateπal is coated and a portion of said fibrous mateπal is uncoated 62 A fiber for use in a composite mateπal. compπsing a core fiber and small panicles attached to said core fiber, said small panicles having a size smaller than the cross- sectional size of saiα fibrous mateπal
63 A fiber according to claim 62, wherein the small panicles compπse one or more mateπals selected from the grouD consisting of ceramic, metal, carbon, mineral, glass, polvmer, thermoplastic thermoset. and rubber mateπals 64 A fiber according to claim 62, wherein the small particles compπse a configuration selected from the group consisting of smooth, round, angular, flaky, and fibrous.
65 A fiber according to claim 62. wherein the small particles are applied to said fiber by fiber coating
66 A fiber according to claim 62. wherein the small particles are applied to said fiber by depositing said particles from a gas suspension
67. A fiber according to claim 62, wherein the small particles are applied to said fiber by depositing said particles from a liquid suspension. 68. A fiber according to claim 62, wherein the small particles are applied to said fiber by spraying a gas suspension of said particles.
69. A fiber according to claim 62, wherein the small particles are applied to said fiber by spraying a liquid suspension of said particles.
70. A fiber according to claim 62, wherein application of the small particles onto said fiber is assisted by placing an electrical charge on said particles, on said fiber, or both.
71. A fiber according to claim 62, wherein the small particles are applied to said fiber by growth of the particles on the fiber.
72. A fiber according to claim 62, wherein the small particles are applied to said fiber by chemical vapor deposition of the particles on the fiber. 73. A fiber according to claim 62, wherein the small particles are applied to said fiber by deposition from a matπx.
74. A fiber according to claim 62, wherein the small particles are applied to said fiber by growth of said particles from a matπx
75. A fiber according to claim 62, wherein said fiber compπses one or more mateπals selected from the group consisting of metal fibers, carbon fibers, ceramic fibers, and polymer fibers
76 A fiber accordmg to claim 62, wherein the small particles hav e a size of up to about one-half of the diameter of the core fiber
77 A fiber according to claim 62. wherein the small panicles ha\ e a size of up to about one-third of the diameter of the core fiber 78 A fiber according to claim 62, wherein the small particles have a size of up to about one-fourth of the diameter of the core fiber
79 A fiber according to claim 62, wherein the small particles have a size of up to about one-fifth of the diameter of the core fiber 80 A fiber according to claim 62. wherein the small particles have a size of up to about one-sixth of the diameter ot the core fiber
81 A. fiber according to claim 62, wherein the small particles have a size of up to about one-tenth of the diameter of the core fiber
82 A fiber according to claim 62, wherein the small particles have a size of up to about one-one hundredth of the diameter of the core fiber
83 A fiber according to claim 62, wherein said fibrous mateπal is coated and said particle is uncoated
84 A fiber according to claim 62, wherein said fibrous mateπal is coated and said particle is coated 85 A fiber according to claim 62, wherein said fibrous mateπal is uncoated and said particle is uncoated
86 A fiber according to claim 62, wherein said fibrous mateπal is uncoated and said particle is coated.
87 A method for making the fiber of claim 62, said fiber for use in a composite mateπal, said method compπsing attaching small particles to a fibrous mateπal, said small particles having a size smaller than the cross-sectional size of said fibrous mateπal
88 A method of fabπcatmg a composite mateπal, compπsing attaching small particles to a fibrous mateπal, said small particles having a size smaller than the cross-sectional size of said fibrous mateπal, and consolidating said fibrous mateπal into a matπx
89 A. method according to claim 88 wherein the small particles compπse one or more mateπals selected from the grouϋ consisting of ceramic, metal, carbon, mineral, glass polvmer thermoplastic thermoset and rubber mateπals 90 A method according to claim 88, wherein the small particles compπse a configuration selected from the group consisting of smooth, round, angular, flaky, and fibrous
91 A method according to claim 88. wherein the small particles are applied to said fiber bv fiber coating
92 A method according to claim 88. wherein the small particles are applied to said fiber bv depositing said particles from a gas suspension
93 A method according to claim 88, wherein the small particles are applied to said fiber by depositing said panicles from a liquid suspension 94 A method according to claim 88, wherein the small particles are applied to said fiber bv spraying a gas suspension of said particles
95 A method according to claim 88, wherein the small particles are applied to said fiber by spraying a liquid suspension of said particles
96 A method according to claim 88, wherein application of the small particles onto said fiber is assisted by placing an electπcal charge on said particles, on said fiber, or both.
97 A method according to claim 88, wherein the small particles are applied to said fiber by growth of the particles on the fiber.
98. A method according to claim 88, wherein the small particles are applied to said fiber by chemical vapor deposition of the particles on the fiber
99 A method according to claim 88, wherein the small particles are applied to said fiber bv deposition from the matπx
100 A method according to claim 88, wherein the small particles are applied to said fiber by growth of said particles from the matπx 101 A method according to claim 88, wherein the matπx mateπal compπses a mateπal selected from the group consisting of a polymer, ceramic, metal, glass, and carbon mateπal
102 A method according to claim 88. wherein said fiber compπses one or more mateπals selected from the group consisting of metal fibers, carbon fibers, ceramic fibers, and polvmer fibers 103 A method according to claim 88, wherein the small particles have a size of up to about one-half of the diameter of the core fiber
104 A method according to claim 88, wherein the small particles have a size of up to about one-third of the diameter of the core fiber 105 A method according to claim 88, wherein the small particles have a size of up to about one-fourth of the diameter of the core fiber
106 A method according to claim 88, wherein the small particles have a size of up to about one-fifth of the diameter of the core fiber
107 A method accordmg to claim 88, wherein the small particles have a size of up to about one-sixth of the diameter of the core fiber
108 A method according to claim 88, wherein the small particles have a size of up to about one-tenth of the diameter of the core fiber
109 A method according to claim 88, wherein the small particles have a size of up to about one-one hundredth of the diameter of the core fiber 110 A method according to claim 88, wherein said fibrous mateπal is coated and said particle is uncoated
111 A method according to claim 88, wherein said fibrous mateπal is coated and said particle is coated
112 A method according to claim 88, wherein said fibrous mateπal is uncoated and said particle is uncoated
113 A method according to claim 88, wherein said fibrous mateπal is uncoated and said particle is coated
114 A method according to claim 88, wherein a portion of said fibrous mateπal is coated and a portion of said fibrous mateπal is uncoated 115 A method of fabπcatmg a composite mateπal, compπsing the steps of providing a fibrous mateπal. particles, and a matπx mateπal, and consolidating said fibrous mateπal and said particles into said matπx mateπal, wherein said small particles are located at an interface formed between said fibrous mateπal and said matπx mateπal
116 A. method according to claim 1 15. wherein said particles have a size smaller than the cross-sectional size of said fibrous mateπal
117. A method according to claim 116, wherein the small particles comprise one or more mateπals selected from the group consisting of ceramic, metal, carbon, mineral, glass, polymer, thermoplastic, thermoset, and rubber mateπals.
118. A method according to claim 116, wherein the small particles compπse a configuration selected from the group consisting of smooth, round, angular, flaky, and fibrous
1 19 A method according to claim 116, wherein the small particles are applied to said fiber by fiber coating
120. A method according to claim 116, wherein the small particles are applied to said fiber by depositing said particles from a gas suspension.
121. A method accordmg to claim 116, wherein the small particles are applied to said fiber by depositing said particles from a liquid suspension.
122. A method according to claim 116, wherein the small particles are applied to said fiber by spraying a gas suspension of said particles. 123. A method according to claim 116, wherein the small particles are applied to said fiber by spraying a liquid suspension of said particles.
124. A method according to claim 116, wherein application of the small particles onto said fiber is assisted by placing an electrical charge on said particles, on said fiber, or both. 125. A method according to claim 116, wherein the small particles are applied to said fiber by growth of the particles on the fiber.
126 A method according to claim 116, wherein the small particles are applied to said fiber by chemical vapor deposition of the particles on the fiber
127 A method according to claim 1 16, wherein the small particles are applied to said fiber by deposition from the matπx.
128 A method according to claim 1 16, wherein the small particles are applied to said fiber by growth of said particles from the matπx
129 A method according to claim 116. wherein the matnx mateπal compπses a mateπal selected from the group consisting of a polymer, ceramic, metal, glass, and carbon mateπal
130. A method according to claim 116, wherein the matπx mateπal compπses a mateπal selected from the group consisting of a thermosetting resm and a thermoplastic resm.
131. A method according to claim 116, wherein said fiber compπses one or more mateπals selected from the group consisting of metal fibers, carbon fibers, ceramic fibers, and polymer fibers
132 A method according to claim 116, wherein the small particles have a size of up to about one-half of the diameter of the core fiber
133. A method according to claim 116, wherein the small particles have a size of up to about one-third of the diameter of the core fiber
134 A method according to claim 116, wherein the small particles have a size of up to about one-fourth of the diameter of the core fiber
135. A method according to claim 116, wherein the small particles have a size of up to about one-fifth of the diameter of the core fiber. 136. A method according to claim 116, wherein the small particles have a size of up to about one-sixth of the diameter of the core fiber.
137. A method according to claim 116, wherein the small particles have a size of up to about one-tenth of the diameter of the core fiber.
138. A method according to claim 116, wherein the small particles have a size of up to about one-one hundredth of the diameter of the core fiber.
139. A method according to claim 116, wherein at least some of said particles are attached to said fibrous mateπal
140 A method according to claim 116, wherein said particles have a size smaller than the diameter of said fibrous mateπal 141 A method according to claim 1 16, wherein said fibrous mateπal is coated and said particle is uncoated
142 A method according to claim 116. wherein said fibrous mateπal is coated and said particle is coated
143 A method according to claim 1 16. wherein said fibrous mateπal is uncoated and said particle is uncoated
144. A method according to claim 116, wherein said fibrous material is uncoated and said particle is coated.
145. A method according to claim 116, wherein a portion of said fibrous material is coated and a portion of said fibrous material is uncoated.
PCT/US2000/032555 1999-11-30 2000-11-30 Debonding resistant toughened composites prepared by small particle reinforcement of the fiber-matrix interface WO2001039970A1 (en)

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