WO2015145427A2 - Composite-based sandwich structures - Google Patents

Composite-based sandwich structures Download PDF

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Publication number
WO2015145427A2
WO2015145427A2 PCT/IL2015/050299 IL2015050299W WO2015145427A2 WO 2015145427 A2 WO2015145427 A2 WO 2015145427A2 IL 2015050299 W IL2015050299 W IL 2015050299W WO 2015145427 A2 WO2015145427 A2 WO 2015145427A2
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WO
WIPO (PCT)
Prior art keywords
resin
article
composite
fabric
strength
Prior art date
Application number
PCT/IL2015/050299
Other languages
French (fr)
Other versions
WO2015145427A3 (en
Inventor
Herman LEIBOVICH
Liran Katz
Ron INTRATER
Original Assignee
Israel Aerospace Industries Ltd.
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Filing date
Publication date
Application filed by Israel Aerospace Industries Ltd. filed Critical Israel Aerospace Industries Ltd.
Publication of WO2015145427A2 publication Critical patent/WO2015145427A2/en
Publication of WO2015145427A3 publication Critical patent/WO2015145427A3/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
    • B32B3/00—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar form; Layered products having particular features of form
    • B32B3/10—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar form; Layered products having particular features of form characterised by a discontinuous layer, i.e. formed of separate pieces of material
    • B32B3/12—Layered products comprising a layer with external or internal discontinuities or unevennesses, or a layer of non-planar form; Layered products having particular features of form characterised by a discontinuous layer, i.e. formed of separate pieces of material characterised by a layer of regularly- arranged cells, e.g. a honeycomb structure
    • 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
    • B32B15/00—Layered products comprising a layer of metal
    • B32B15/14—Layered products comprising a layer of metal next to 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
    • 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
    • B32B5/18—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 features of a layer of foamed material
    • 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
    • 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
    • B32B5/245—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 being a foam 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
    • B32B5/22—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
    • 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
    • B32B2260/02—Composition of the impregnated, bonded or embedded layer
    • B32B2260/021—Fibrous or filamentary layer
    • B32B2260/023—Two or more layers
    • 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
    • B32B2262/00—Composition or structural features of fibres which form a fibrous or filamentary layer or are present as additives
    • B32B2262/02—Synthetic macromolecular fibres
    • B32B2262/0261—Polyamide fibres
    • B32B2262/0269—Aromatic polyamide fibres
    • 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
    • B32B2262/00—Composition or structural features of fibres which form a fibrous or filamentary layer or are present as additives
    • B32B2262/10—Inorganic fibres
    • B32B2262/106—Carbon fibres, e.g. graphite fibres
    • 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
    • B32B2264/00—Composition or properties of particles which form a particulate layer or are present as additives
    • B32B2264/10—Inorganic particles
    • B32B2264/107—Ceramic
    • B32B2264/108—Carbon, e.g. graphite particles
    • 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
    • B32B2266/00—Composition of foam
    • B32B2266/02—Organic
    • 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
    • B32B2266/00—Composition of foam
    • B32B2266/02—Organic
    • B32B2266/0214—Materials belonging to B32B27/00
    • 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
    • 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
    • B32B2307/546—Flexural strength; Flexion stiffness
    • 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
    • B32B2307/70—Other properties
    • B32B2307/718—Weight, e.g. weight per square meter

Definitions

  • the present invention is in the field of light-weight structures and production thereof.
  • the invention relates to sandwich structures utilizing nano particles (i.e., carbon nanotubes) to improve overall properties.
  • the present invention utilizes carbon nano-tubes (CNT) and their associated high intrinsic properties to provide improved composite structures.
  • CNT carbon nano-tubes
  • the fabric or tape layers may include at least one layer of fibers of a composite material (e.g. carbon fibers, Aramid, or generally any fiber composite material) providing structure and stability.
  • a composite material e.g. carbon fibers, Aramid, or generally any fiber composite material
  • fabric refers to one or more layers of fibers aligned along at least two axes
  • tape refers to one or more layers of fibers aligned along a single axis.
  • fabric as used herein below refers to both fabric utilizing alignment along two or more axes and to tape structures utilizing fibers aligned along a single axis.
  • the present invention provides a composite structure having increased strength, while providing low weight relative to the standard available structures.
  • the composite sandwich structure comprises a core material (e.g. honeycomb structure or appropriate polymer foam) being sandwiched between at least two skins comprising of fabric or tape layers impregnated with resin.
  • the resin incorporates a predetermined concentration of CNT.
  • CNT/resin mixture provides the resin and fabric (or tape) layer with increased adhesive properties, thereby providing increased strength to resist peel and compression loads acting on the structure.
  • the present invention provides for a skin structure comprising at least one layer of fabric or tape combined with epoxy resin, wherein the epoxy resin comprises additional filling materials, such filling materials include carbon nanotubes (CNT) at a predetermined weight ratio with respect to the epoxy resin.
  • the present invention provides for a composite sandwich structure comprising a honeycomb or foam structure being sandwiched between top and bottom layers of such fabric or tape with epoxy resin incorporating CNT. It should be noted that the weight ratio of CNT within the epoxy resin is preferably at low concentrations, up to 3 wt. %.
  • the present invention provides for a method for producing a composite article, the method comprising mixing an epoxy resin with selected filling material to provide mixed resin, said filling material comprising carbon nanotube; and utilizing said mixed resin for impregnating of fabric or tape having one or more layers; constructing the article in a sandwich form having a top and bottom layer of said fabric or tape and mixed resin and a middle layer being a honeycomb or foam structure.
  • the impregnated fabric/tape and core are placed together and processed under vacuum bag and temperature, therefore forming the structure to the final article form.
  • an article comprising a composite structure
  • the structure comprises a core layer enclosed between at least two facesheets, at least one of said at least two facesheets comprise one or more layers of fabric or tape reinforcement and a resin matrix comprising a predetermined amount of CNT.
  • the resin mixture comprises a relatively low concentration of carbon nano-tubes.
  • the core layer may be a honeycomb structure or polymeric foam.
  • a method of producing an article comprising: mixing epoxy resin with predetermined amount of nanofiller materials comprising a predetermined amount of carbon nanotubes; impregnating one or more layers of fabric with said resin mixture to provide at least one facesheet layer; enclosing a core material between at least two facesheet layers to provide a sandwich structure; and vacuum bagging and heating of said structure to generate final article.
  • the resin mixture comprises up to 3% weight ration of carbon nano-tubes.
  • Fig. 1 illustrates a sandwich material structure including a core layer located in between two facesheets
  • Fig. 2 illustrates the advantages of sandwich composite structures with respect to solid laminates
  • Fig. 3 shows measurement results for the honeycomb-based sandwich structure of the invention as compared to a conventional reference structure
  • Fig. 4 shows compression load measurement results performed on a foam-based sandwich structure according to the present invention as compared to conventional reference structures.
  • the present invention provides stiffness and strength improvement for composite structures utilizing nano fillers in fabric or tape being impregnated by epoxy resin.
  • the technique and article of the present invention provides a composite structure with improved strength and weight reduction added value.
  • Generating an appropriate mixture of epoxy resin with predetermined amount of CNT is known to involve various difficulties causing poor dispersion of the CNT within the resin and stabilizing it for a prolonged use. It should be noted that such difficulties are known regardless of the matrix material.
  • the resulting resin mixture includes CNT at low concentrations, up to 3 wt. % is used for impregnating one or more layers of fabric or tape to provide hardened layers for the composite structure.
  • Sandwich structures are generally based on a core material located between at least two sheets (or facesheets) of shell skin material.
  • Fig. 1 illustrates a sandwich material structure including a core layer located in between two facesheets.
  • the facesheets are made of reinforced skin provided with one or more layers of fabric or tape impregnated with the above described mixed resin.
  • the facesheets and core are bonded together under vacuum and temperature to generate a composite sandwich article.
  • sandwich structures are suitable for use for aeronautical or transportation applications.
  • the Core material is usually comprised of two typical types: metallic or non-metallic honeycomb structure and/or polymer foams.
  • Fig. 2 illustrates the advantages of such sandwich composite structures with respect to solid laminates. As shown, the biggest advantage corresponds to high bending strength and stiffness. That means that as the core thickness increases, stiffness and strength of structure are increased up to an order of magnitude. Therefore, the use of sandwich structure in aeronautical and transportation applications is generally known in the art and relatively common.
  • An appropriately manufactured sandwich composite structure according to the present invention can provide higher stiffness, adhesion strength and skin compression strength.
  • Fig. 3 illustrates the principles of peel strength measurement
  • Fig. 4 shows measurement results for the structure of the invention as compared to a conventional sandwich composite structure.
  • the peel strength measurement is used for Honeycomb structures for testing adhesion strength between the skin (facesheet) and the honeycomb (or foam) core.
  • a conventional sandwich composite structure based on a resin areal density of 220 gr/m was measured to have peel strength of about 4.5 in*lb/in.
  • the structure of the present invention, with 1 wt. % CNT, was measured with three resin areal densities. At about 150 gr/m , the structure showed substantially similar strength (for lower density), while at similar areal density the structure showed an improvement of about 100% in peel strength.
  • the sandwich structure of the invention providing similar peel strength is 30% lighter with respect to the conventional structure. This is at least partially due to the lower resin areal density (150 gr/m for the structure with CNT relative to 220 gr/m for the conventional structure).
  • Fig. 4 shows skin compression load measurement results performed on a foam- based sandwich structure according to the present invention as compared to conventional reference structures with (Reference2) or without (reference 1) slurry composition for increased strength (e.g. adhesive strength).
  • the compression load test includes a 3 point loading test and measures skin compression strength of the structures.
  • the results shown in Fig. 4 are normalized to strength value of Reference2 sample, i.e. conventional structure utilizing slurry, in order to emphasize the added strength provided by the present technique (marked Nano in the figure).
  • Reference2 sample i.e. conventional structure utilizing slurry
  • Reference2 i.e. conventional structure utilizing slurry
  • the resin+CNT of the present invention provides improved strength results with respect to both reference samples. More specifically, the technique of the present invention may provide about 10% improvement in strength, while reducing weight, with respect to Reference2 sample that utilized slurry for improved strength. Additionally, the structure according to the present invention shows more than 20% improvement in skin strength with respect to the conventional structure without slurry (Referencel). Thus, when 1 wt. % CNT is added to the resin-impregnated skin without slurry layer (Nano specimen), skin strength values increases to the values achieved when the resin is impregnated with slurry. It should be noted that the use of slurry is to create smooth and uniform foam surfacing while at the same time increasing the total weight of the structure by about 400gr/m . Thus, the structure of the present invention provides
  • the technique of the present invention utilized small amount of nano particles as fillers in the resin provides improved strength while allowing reduced weight of the structure.
  • the present invention provides a "simple" resin upgrade allowing improved adhesive properties by utilizing CNT additions.
  • This approach is suitable for various practical applications providing improved joint edge strength where such effects dominate the performance of a bonded structure.
  • Good results for sandwich structures confirmed a smooth transition for CNT implementation to structural elements by improvement of resin and weight reduction of adhesive layer.

Abstract

An article comprising a composite structure and a method for producing the same is presented. The structure comprises a core layer enclosed between at least two facesheets, at least one of said at least two facesheets comprises one or more layers of a fabric and resin mixture comprising a predetermined amount of carbon nano-tubes.

Description

COMPOSITE-BASED SANDWICH STRUCTURES
TECHNOLOGICAL FIELD AND BACKGROUND
The present invention is in the field of light-weight structures and production thereof. The invention relates to sandwich structures utilizing nano particles (i.e., carbon nanotubes) to improve overall properties.
The quest for lighter stronger materials is a long one. Various achievements utilizing composite material fabrics provided structures having tailored properties, being stiff and strong while maintaining very light weight, and have been commercially introduced. Various techniques are known in the art to provide strong and light sandwich structures.
GENERAL DESCRIPTION
There is a need in the art for providing composite structure with increased stiffness and improved strength-to-weight ratio (SWR). Additionally, there is a need to provide such a composite structure comprising a resin impregnated fabric or tape and a core. The present invention utilizes carbon nano-tubes (CNT) and their associated high intrinsic properties to provide improved composite structures. The structure and technique of the present invention relies on the inventor's understanding about connection of CNT from the building block level to a full macroscopic scale structure
The inventors have found that the use of small amount of CNT within resin used for composite structures can upgrade the standard resin epoxy system and eliminate the need for adhesive in sandwiched structures. It should be noted that the fabric or tape layers may include at least one layer of fibers of a composite material (e.g. carbon fibers, Aramid, or generally any fiber composite material) providing structure and stability. Generally the term fabric refers to one or more layers of fibers aligned along at least two axes while the term tape refers to one or more layers of fibers aligned along a single axis. It should also be noted that the term fabric as used herein below refers to both fabric utilizing alignment along two or more axes and to tape structures utilizing fibers aligned along a single axis. Thus, the present invention provides a composite structure having increased strength, while providing low weight relative to the standard available structures. The composite sandwich structure comprises a core material (e.g. honeycomb structure or appropriate polymer foam) being sandwiched between at least two skins comprising of fabric or tape layers impregnated with resin. According to the present invention, the resin incorporates a predetermined concentration of CNT. The use of CNT/resin mixture provides the resin and fabric (or tape) layer with increased adhesive properties, thereby providing increased strength to resist peel and compression loads acting on the structure.
Thus, according to one broad aspect, the present invention provides for a skin structure comprising at least one layer of fabric or tape combined with epoxy resin, wherein the epoxy resin comprises additional filling materials, such filling materials include carbon nanotubes (CNT) at a predetermined weight ratio with respect to the epoxy resin. Additionally, the present invention provides for a composite sandwich structure comprising a honeycomb or foam structure being sandwiched between top and bottom layers of such fabric or tape with epoxy resin incorporating CNT. It should be noted that the weight ratio of CNT within the epoxy resin is preferably at low concentrations, up to 3 wt. %.
According to one other broad aspect, the present invention provides for a method for producing a composite article, the method comprising mixing an epoxy resin with selected filling material to provide mixed resin, said filling material comprising carbon nanotube; and utilizing said mixed resin for impregnating of fabric or tape having one or more layers; constructing the article in a sandwich form having a top and bottom layer of said fabric or tape and mixed resin and a middle layer being a honeycomb or foam structure. The impregnated fabric/tape and core are placed together and processed under vacuum bag and temperature, therefore forming the structure to the final article form.
Thus, according to one broad aspect of the invention, there is provided an article comprising a composite structure, the structure comprises a core layer enclosed between at least two facesheets, at least one of said at least two facesheets comprise one or more layers of fabric or tape reinforcement and a resin matrix comprising a predetermined amount of CNT. According to some embodiments, the resin mixture comprises a relatively low concentration of carbon nano-tubes. Additionally or alternatively the core layer may be a honeycomb structure or polymeric foam.
According to one other broad aspect there is provided a method of producing an article, the method comprising: mixing epoxy resin with predetermined amount of nanofiller materials comprising a predetermined amount of carbon nanotubes; impregnating one or more layers of fabric with said resin mixture to provide at least one facesheet layer; enclosing a core material between at least two facesheet layers to provide a sandwich structure; and vacuum bagging and heating of said structure to generate final article. According to some embodiments, the resin mixture comprises up to 3% weight ration of carbon nano-tubes.
BRIEF DESCRIPTION OF THE DRAWINGS
In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:
Fig. 1 illustrates a sandwich material structure including a core layer located in between two facesheets;
Fig. 2 illustrates the advantages of sandwich composite structures with respect to solid laminates;
Fig. 3 shows measurement results for the honeycomb-based sandwich structure of the invention as compared to a conventional reference structure; and
Fig. 4 shows compression load measurement results performed on a foam-based sandwich structure according to the present invention as compared to conventional reference structures.
DETAILED DESCRIPTION OF EMBODIMENTS
As indicated above, the present invention provides stiffness and strength improvement for composite structures utilizing nano fillers in fabric or tape being impregnated by epoxy resin. The technique and article of the present invention provides a composite structure with improved strength and weight reduction added value. Generating an appropriate mixture of epoxy resin with predetermined amount of CNT is known to involve various difficulties causing poor dispersion of the CNT within the resin and stabilizing it for a prolonged use. It should be noted that such difficulties are known regardless of the matrix material.
The resulting resin mixture includes CNT at low concentrations, up to 3 wt. % is used for impregnating one or more layers of fabric or tape to provide hardened layers for the composite structure. Sandwich structures are generally based on a core material located between at least two sheets (or facesheets) of shell skin material. Fig. 1 illustrates a sandwich material structure including a core layer located in between two facesheets. According to the present invention the facesheets are made of reinforced skin provided with one or more layers of fabric or tape impregnated with the above described mixed resin. The facesheets and core are bonded together under vacuum and temperature to generate a composite sandwich article. Such sandwich structures are suitable for use for aeronautical or transportation applications. The Core material is usually comprised of two typical types: metallic or non-metallic honeycomb structure and/or polymer foams.
Fig. 2 illustrates the advantages of such sandwich composite structures with respect to solid laminates. As shown, the biggest advantage corresponds to high bending strength and stiffness. That means that as the core thickness increases, stiffness and strength of structure are increased up to an order of magnitude. Therefore, the use of sandwich structure in aeronautical and transportation applications is generally known in the art and relatively common.
An appropriately manufactured sandwich composite structure according to the present invention can provide higher stiffness, adhesion strength and skin compression strength.
CNT resin strength effect is tested in sandwich structure. To this purpose peel strength was measured on the sandwich composite structure of the present invention. Fig. 3 illustrates the principles of peel strength measurement and Fig. 4 shows measurement results for the structure of the invention as compared to a conventional sandwich composite structure.
Generally, the peel strength measurement is used for Honeycomb structures for testing adhesion strength between the skin (facesheet) and the honeycomb (or foam) core. As shown in Fig. 3, a conventional sandwich composite structure based on a resin areal density of 220 gr/m was measured to have peel strength of about 4.5 in*lb/in. The structure of the present invention, with 1 wt. % CNT, was measured with three resin areal densities. At about 150 gr/m , the structure showed substantially similar strength (for lower density), while at similar areal density the structure showed an improvement of about 100% in peel strength.
It should be noted, that the sandwich structure of the invention providing similar peel strength is 30% lighter with respect to the conventional structure. This is at least partially due to the lower resin areal density (150 gr/m for the structure with CNT relative to 220 gr/m for the conventional structure).
Fig. 4 shows skin compression load measurement results performed on a foam- based sandwich structure according to the present invention as compared to conventional reference structures with (Reference2) or without (reference 1) slurry composition for increased strength (e.g. adhesive strength). The compression load test includes a 3 point loading test and measures skin compression strength of the structures. The results shown in Fig. 4 are normalized to strength value of Reference2 sample, i.e. conventional structure utilizing slurry, in order to emphasize the added strength provided by the present technique (marked Nano in the figure). As shown in the middle column the conventional structure utilizing resin-impregnated skin with slurry formulation, marked as Reference2, provides improved results with respect to the conventional structure without the use of slurry (i.e. Referencel). This is while the resin+CNT of the present invention (marked - Nano) provides improved strength results with respect to both reference samples. More specifically, the technique of the present invention may provide about 10% improvement in strength, while reducing weight, with respect to Reference2 sample that utilized slurry for improved strength. Additionally, the structure according to the present invention shows more than 20% improvement in skin strength with respect to the conventional structure without slurry (Referencel). Thus, when 1 wt. % CNT is added to the resin-impregnated skin without slurry layer (Nano specimen), skin strength values increases to the values achieved when the resin is impregnated with slurry. It should be noted that the use of slurry is to create smooth and uniform foam surfacing while at the same time increasing the total weight of the structure by about 400gr/m . Thus, the structure of the present invention provides
2 similar skin compression strength while reducing the total weight by 400gr/m . Thus, the technique of the present invention utilized small amount of nano particles as fillers in the resin provides improved strength while allowing reduced weight of the structure.
Thus, the present invention provides a "simple" resin upgrade allowing improved adhesive properties by utilizing CNT additions. This approach is suitable for various practical applications providing improved joint edge strength where such effects dominate the performance of a bonded structure. Good results for sandwich structures confirmed a smooth transition for CNT implementation to structural elements by improvement of resin and weight reduction of adhesive layer.

Claims

CLAIMS:
1. An article comprising a composite structure, the structure comprises a core layer enclosed between at least two facesheets, at least one of said at least two facesheets comprises one or more layers of a fabric and resin mixture comprising a predetermined amount of carbon nano-tubes.
2. The article of Claim 1 , wherein the resin mixture comprises up to 3% weight ratio of carbon nano-tubes.
3. The article of claim 1 or 2, wherein the core layer is a honeycomb structure or polymeric foam.
4. A method of producing an article, the method comprising: mixing epoxy resin with a predetermined amount of nanofiller materials comprising a predetermined amount of carbon nanotubes; impregnating one or more layers of fabric with said resin mixture to provide at least one facesheet layer; enclosing a core material between at least two facesheet layers to provide a sandwich structure; and vacuum bagging and heating of said structure to generate final article.
5. The method of claim 4, wherein the resin mixture comprises up to 3% weight ratio of carbon nano-tubes.
PCT/IL2015/050299 2014-03-24 2015-03-23 Composite-based sandwich structures WO2015145427A2 (en)

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