WO2018112504A1

WO2018112504A1 - Composite material

Info

Publication number: WO2018112504A1
Application number: PCT/AU2017/000289
Authority: WO
Inventors: James Francis William Kingston; Gary Charles Strickland
Original assignee: Matrix Composites And Engineering Ltd
Priority date: 2016-12-23
Filing date: 2017-12-22
Publication date: 2018-06-28
Also published as: EP3559098A1; EP3559098A4; AU2017381391A1

Abstract

A material for filling a void, the material comprising multiple macrospheres, each macrosphere comprising a core encased in at least one shell, wherein each shell is formed of a coating reinforced by a plurality of randomly distributed fibre strands, and wherein the macrospheres are bonded together with an adhesive.

Description

TITLE

"COMPOSITE MATERIAL"

FIELD OF THE INVENTION

[0001] The present invention relates to a Composite Material.

[0002] More particularly, the present invention relates to a Composite Material for filling a void.

BACKGROUND

[0003] It is known to use foams or other relatively low density materials for filling voids.

[0004] This may be required for a number of reasons, for example where a relatively light weight structure is required, for buoyancy for example. Or for providing a filled void which provides an element of structural reinforcement without adding significant mass.

[0005] Syntactic foams are commonly used to provide a low density material to fill a void and provide structural reinforcement, whereby hollow spheres are added to a matrix to provide low density particles, while the surrounding matrix provides the structural integrity.

[0006] Such foams are subject to limitations in terms of cost and material properties.

[0007] Another use of low density foams is to assist with absorption of energy resulting from impact.

[0008] The range of possible applications of such material is significant and includes road side crash barriers, specifically designed crumple zones on vehicle bodies, or helmets to name a few. [0009] One type of material used in energy absorption applications is foam, such as expanded polystyrene ('EPS'), where gas bubbles are captured in a surrounding filler, and the collapse of the bubbles during impact absorbs energy, deforming the shape in the process.

[0010] A limitation of using materials such as EPS is that the material may not be suitable for significant impacts due to greater momentum, such as impacts at high velocity or by impactors of greater mass. This is because the structural integrity of the material is insufficient to withstand such forces, and would collapse before sufficient energy has been absorbed, resulting in significant residual momentum causing damage to the subject.

[001 1] Materials with greater structural integrity are generally less capable of absorbing energy effectively, where a material is brittle it may fracture at or around the point of impact, with the pieces moving away from the impact zone and failing to absorb the energy of the impactor.

[0012] For these applications it may be the case that using specifically formed expensive materials, such as aluminium honeycomb, can provide better results in high momentum impact situations, but the costs associated with producing such structures are prohibitive.

[0013] The present invention attempts to overcome at least in part the aforementioned disadvantages of previous composite materials by providing a low density material having improved structural properties over materials of similar cost.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention there is provided a material for filling a void, the material comprising multiple macrospheres, each macrosphere comprising a core encased in at least one shell, wherein each shell is formed of a coating reinforced by a plurality of randomly distributed fibre strands, and wherein the macrospheres are bonded together with an adhesive.

In accordance with another aspect of the present invention there is provided a method of producing a material for filling a void, the material comprising multiple macrospheres bonded together with an adhesive, wherein each macrosphere comprises a core encased in at least one shell, and wherein each shell is formed of a coating reinforced by a plurality of randomly distributed fibre strands, the method comprising the following steps: a. Multiple cores are agitated in a receptacle, b. During agitation, epoxy resin and hardener are added to the receptacle, coating the cores, the combination of the epoxy resin and hardener begins to cure the resin, c. The agitation continues to fully coat the cores before the resin hardens, d. Fibres strands are added to the receptacle before the resin has fully cured, e. The agitation continues to allow the fibres to stick to the resin coating, f. Steps b thru e are repeated until a sufficient number of shells have been applied. g. Once fully cured, the macrospheres are stored until required, at which time a quantity of macrospheres are agitated in a receptacle with an adhesive to create a mixture having bonds at contact points between macrospheres, h. The mixture is poured into the void to be filled before the adhesive has cured substantially, so that the material distribution is bounded by the limitations of the void, i. Once the void is sufficiently filled, the material is cured. [0016] Preferably, the coating is formed of epoxy resin. [0017] Preferably, the adhesive is a bonding epoxy resin. [0018] Preferably, the bonding epoxy resin contains a diluent.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a partial sectional view of a single macrosphere in accordance with an embodiment of the present invention.

Figure 2 is an isometric view showing multiple macrospheres of different diameters arranged in a composite material.

Figure 3 is a section view of two bonded macrospheres, indicating the bonded contact surface between.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0020] Referring to the Figures, there is shown a material for filling a void according to a preferred embodiment of the present invention, the material comprising multiple macrospheres, each macrosphere comprising a core encased in at least one shell, wherein each shell is formed of a coating reinforced by a plurality of randomly distributed fibre strands, and wherein the macrospheres are bonded together with an adhesive.

[0021] The core may be substantially spherical.

[0022] The coating may be formed of epoxy resin.

[0023] The fibre strands may be carbon fibre. The fibre strands may be mineral fibre.

The fibre strands may be a mixture of carbon fibre and mineral fibre. The adhesive may be epoxy resin.

The epoxy resin may be derived from either bisphenol A or bisphenol F.

The adhesive may be of sufficiently low viscosity to adequately cover the macrospheres, but of sufficiently high viscosity that it does not run off the surface of the macrospheres.

The adhesive may contain a diluent.

Interstitial gaps between the macrospheres may be maintained, so that the material remains substantially porous.

The material may have a packing factor of less than 74%.

According to another preferred embodiment of the present invention, there is shown a method of producing a material for filling a void, the material comprising multiple macrospheres bonded together with an adhesive, wherein each macrosphere comprises a core encased in at least one shell, and wherein each shell is formed of a coating reinforced by a plurality of randomly distributed fibre strands, the method comprising the following steps:

Multiple cores are agitated in a receptacle,

During agitation, epoxy resin and hardener are added to the receptacle, coating the cores, the combination of the epoxy resin and hardener begins to cure the resin,

The agitation continues to fully coat the cores before the resin cures substantially,

Fibres strands are added to the receptacle while the resin is still sticky, The agitation continues to allow the fibres to stick to the resin coating, f. Steps b thru f are repeated until a sufficient number of shells have been applied. g. Once fully cured, the macrospheres are stored until required, at which time a quantity of macrospheres are agitated in a receptacle with an adhesive to create a mixture having bonds at contact points between macrospheres, h. The mixture is poured into the void to be filled before the adhesive has cured substantially, so that the mixture assumes the form defined by limitations of the void, i. Once the void is sufficiently filled, the mixture is cured. [0033] The void to be filled may be a mould.

[0034] The hardener may be a multi-functional amine.

[0035] In use, the macrospheres 20 are formed using low density cores 22, preferably of expanded polystyrene (EPS), although it is recognised that other materials may be used.

[0036] The cores 22 are preferably spherical but may be of different forms to suit different applications.

[0037] The cores 22 may be of uniform diameter, but it is recognised that different sizes may be used.

[0038] Multiple low density cores 22 may then be coated in a shell 26 of fibre reinforced epoxy resin. The reinforcement may be provided by the addition of mineral fibre strands added to the mixture following coating.

[0039] Alternatively, the reinforcement may be provided by the use of carbon fibre strands added to the mixture following coating.

[0040] Alternatively, the reinforcement may be provided by a combination of carbon fibre strands and mineral fibre strands added to the mixture following coating. The proportion and quantity of fibre strands added to the resin may be altered to suit a particular application, resulting in macrospheres having shells with different material properties.

The coating operation begins with multiple low density cores 22 being agitated in a receptacle, with the epoxy resin being added with a suitable hardener.

The hardener may be a multi-functional amine.

The resin may be of too high a viscosity at room temperature to effectively coat the low density cores 22, and the temperature at which the coating operation is carried out may be raised to decrease the viscosity sufficiently.

A small amount of diluent may be added to the mixture to lower viscosity.

Once the epoxy resin and hardener have been added to the mixture, the reaction begins which results in the curing of the resin.

The mixture is agitated so that the low density cores 22 become fully coated before the resin cures.

The fibre strands are added to the mixture while the resin coating on the low density cores 22 is still tacky, and has not cured.

The fibre strands may be less than 5 millimetres in length, and less than 500 micrometres in diameter.

The fibre strands may be less than 1 millimetres in length, and less than 50 micrometres in diameter.

The fibre strands may be less than 300 micrometres in length, and less than 10 micrometres in diameter.

The fibres provide reinforcement to the coating and assist with drying the surface, thus preventing the low density cores 22 from sticking to one another. Once a low density core 22 has been coating with epoxy and fibre strands, the resultant coating is defined as a shell 26.

Due to the random application and distribution of the fibre strands, a single shell 26 may not provide a sufficient level of reinforcement, as the coverage of the fibre strands may leave areas of the shell 26 with little or no reinforcement.

Multiple shells 26 may be applied, with a greater number of laminae providing greater structural integrity. Each shell 26a must be cured before the subsequent coating can be applied to form the subsequent shell 26b.

Once the required number of shell 26 layers have been applied, and the resin cured, the resultant particle is defined as a macrosphere 20.

Loose macrospheres 20 may be stored until they are required.

It can be noted that the low density core 22 of the macrosphere 20 may be destroyed during the curing process, resulting in a macrosphere 20 being a hollow shell.

The purpose of the low density core 22 is to provide a surface for formation of the shell, whereby the shell provides the desired structural properties of the macrosphere 20, and the core contributes nothing once the shell is cured.

Consequently, the term macrosphere 20 may refer to a hollow particle, or a particle having a low density core, where the two are interchangeable.

Consequently, the term low density, as referred to throughout the specification, may refer to the resulting hollow space, where a low density core has been destroyed.

Although the term macrosphere 20 implies a spherical particle, and spherical particles are the predominant shape used, it is understood that macrospheres may be of alternate shapes, as required by a particular application.

The macrospheres 20 may be within the range of 0.5mm to 100mm across. Alternatively, macrospheres 20 may be within the range of 1mm to 25mm across.

Alternatively, the macrospheres 20 may be within the range of 1mm to 10mm across.

Alternatively, the macrospheres 20 may be within the range of 1mm to 5 mm across.

A quantity of macrospheres 20 may be bonded together to create the crushable composite material 10.

The material 10 may alternatively be described as a Single Phase Syntactic Foam.

To create the crushable composite material 10 a quantity of macrospheres 20 are blended with an adhesive 30 to create a bond 32 at the contact points.

The adhesive 30 may be epoxy resin, and is described as such henceforth, although it is recognised that other types of adhesive may be suitable.

It is important to recognise that the epoxy resin 30 used for bonding the macrospheres may be different to the fibre reinforced epoxy resin used to form the shells 26 of the macrospheres 20.

The blending operation may be carried out using an agitated receptacle, for example a concrete mixer or similar apparatus.

The epoxy resin 30 used must be of sufficiently low viscosity to adequately cover the macrospheres 20, but sufficiently viscous that it does not run off the surface of the macrospheres 20.

The surface tension of the epoxy resin 30 assists the operation by gathering the resin 30 at and around the contact points between the macrospheres 20. The low viscosity of the resin further enables the resin to collect around the contact points. [0075J The greater the surface tension of the epoxy resin 30, the greater the bond area 32 between the macrospheres 20, and the greater the bond strength.

[0076] The greater the quantity of epoxy resin 30 added, the greater the bond 32 area between macrospheres 20, and the greater the bond 32 strength.

[0077] The bond 32 area between the macrospheres 20 may be of a size selected to provide adequate bond strength, while not being so large that the interstitial gaps between the macrospheres 20 are filled.

[0078] Where sufficient interstitial gaps are maintained, the material 10 may be substantially porous, allowing drainage of collected liquid.

[0079] Consequently, the viscosity and surface tension of the epoxy resin 30 used to bond the macrospheres 20 directly affect the bond 32 area between macrospheres 20, and therefore the material properties of the crushable composite material 10.

[0080] Commonly used epoxy resins 30 suitable for bonding include, but are not limited to, epoxy resins derived from bisphenol A or bisphenol F.

[0081] Typically, epoxy resin derived from bisphenol A is low cost but has a high viscosity, and as such is unsuitable for bonding as it is unable to effectively cover the surface of the macrospheres 20 and create a suitable bond 32.

[0082] Bisphenol F epoxy resin on the other hand, has lower viscosity and sufficiently high mechanical properties, but is expensive.

[0083] The viscosity of bisphenol A epoxy resin can be reduced by the addition of a small amount of epoxy diluent, to the point where it becomes sufficiently fluid to become suitable for bonding, however this reduces the mechanical properties, particularly the stiffness.

[0084] A further effect of the addition of diluent to epoxy resin is that, while the stiffness is reduced, the elasticity is increased. The increased elasticity could be considered beneficial to the crushable composite material 10. While elasticity is not particularly desirable in isolation, when combined with the relatively rigid but collapsible macrospheres 20 it provides a suitable composite structure.

The quantity and thickness of shells 26 provided on the macrospheres 20, together with the variable properties of the bonding epoxy 30, can be tailored so that the bonds 32 between the macrospheres 20 can withstand a greater impact force than the shells of the macrospheres 20.

Consequently, the macrospheres 20 are able to collapse sacrificially, while the bonds 32 between them are maintained due to the bonding epoxy 30 being sufficiently elastic which prevents the material 10 from cracking.

The diluent provides sufficient elasticity to the epoxy 30 to retain the macrospheres 20 in position, but the collapse of the macrospheres 20 prevents the material 10 springing back to its original form, which would result in the impactor 'bouncing.'

The amount of diluent used in the bonding epoxy 30 can be altered to suit the application. This, in combination with the variable reinforcement options used in the shells 26 of the macrospheres 20, allows the crushable composite material 10 to be tailored to a particular application.

Following the blending operation, the coated macrospheres 20 may be poured into a mould or may be used to fill a void, to enable the crushable composite material 10 to assume the desired form.

The percentage of a volume which may be filled by macrospheres 20 is dependent on the shape and size of the macrospheres 20 used, and is known as the packing factor.

Where spherical macrospheres 20 of uniform diameter are used, and packed in an orderly arrangement, the packing factor can be up to 74%. Where spherical macrospheres 20 of uniform diameter are used, but are packed randomly, the packing factor is typically around 60%.

Where different shape and size macrospheres 20 are used, the packing factor may be different, and may be tailored to suit the application.

An increased packing factor may be achieved by using different sized, or particularly shaped, macrospheres 20.

Where the material 10 is to be formed into a particular shape, for example for a panel for a vehicle, the material 10 would be formed in a mould, allowing the process to be carried out in a factory and thus providing greater repeatability and control over the process.

Where the process is to be carried out on site, for example for the local repair of a damaged structure, the material 10 may mixed locally, with the macrospheres 20 being added to a drum or other receptacle suitable for mixing.

Once in the receptacle the bonding epoxy 30 having diluent may be added and the contents mixed before being poured into the void to be filled.

Once the void is filled the material 10 may be left to cure.

Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

Claims

CLAIMS What is claimed is:

1. A material for filling a void, the material comprising multiple macrospheres, each macrosphere comprising a core encased in at least one shell, wherein each shell is formed of a coating reinforced by a plurality of randomly distributed fibre strands, and wherein the macrospheres are bonded together with an adhesive.

2. The material of claim 1, wherein each core is substantially spherical.

3. The material of claim 1 or 2, wherein each coating is formed of epoxy resin.

4. The material of any one of claims 1 to 3, wherein the fibre strands are carbon fibre.

5. The material of any one of claims 1 to 3, wherein the fibre strands are mineral fibre.

6. The material of any previous claim, wherein the fibre strands are a mixture of carbon fibre and mineral fibre.

7. The material of any previous claim, wherein the adhesive is epoxy resin.

8. The material of claim 7, wherein the epoxy resin is derived from either bisphenol A or bisphenol F.

9. The material of claim 7 or 8, wherein the adhesive is of sufficiently low viscosity to adequately cover the macrospheres, but is of sufficiently high viscosity that it does not run off the surface of the macrospheres.

10. The material of any one of claims 7 to 9, wherein the adhesive contains a diluent.

11. The material of any one of claims 7 to 10, wherein interstitial gaps between the macrospheres are maintained, so that the material remains substantially porous.

12. The material of any one of claims 7 to 11 , wherein the material has a packing factor of less than 74%.

13. A method of producing a material for filling a void, the material comprising multiple macrospheres bonded together with an adhesive, wherein each macrosphere comprises a core encased in at least one shell, and wherein each shell is formed of a coating reinforced by a plurality of randomly distributed fibre strands, the method comprising the following steps: a. Multiple cores are agitated in a receptacle, b. During agitation, epoxy resin and hardener are added to the receptacle, coating the cores, the combination of the epoxy resin and hardener begins to cure the resin, c. The agitation continues to substantially coat the cores before the resin cures substantially, d. Fibres strands are added to the receptacle while the resin is still sticky, e. The agitation continues to allow the fibres to stick to the resin coating, f. Steps b thru e are repeated until a sufficient number of shells have been applied. g. Once fully cured, the macrospheres are stored until required, at which time a quantity of macrospheres are agitated in a receptacle with an adhesive to create a mixture having bonds at contact points between macrospheres, h. The mixture is poured into the void to be filled before the adhesive has cured substantially, so that the mixture assumes the form defined by limitations of the void, i. Once the void is sufficiently filled, the mixture is cured.

14. The method of claim 13, wherein the void to be filled is a mould.

15. The method of claim 13 or 14, wherein the hardener is a multi-functional amine.