IL112533A - Composite materials - Google Patents

Description

COMPOSITE MATERIALS Field of Invention: The invention relates to novel composite materials. More particularly, the invention relates to composite materials, which have a predetermined strength in desired directions. The composites can achieve a strength in various directions of space, including resistance to buckling.

The invention further provides a method for producing composites which enables 3-dimensional oriented strength, so as to adjust the products to various purposes. There can be produced bodies of various shapes, also complicated ones. It is easy to recycle most of the products of the invention. Means of production and the production process are simple and safe.

Background of Invention.

The present situation for metallic design may be numerically characterized as follows: 80 to 95 per cent of big and thin bodies' weight are intended for rigidity or buckling resistance criteria, i.e. most of the material is not efficiently utilized and its strength parameters are wasted. This refers not only to relatively simple bodies like boats, but to more complicated ones like planes (range of complicacy in this case determines specific numbers of support per cells skin square).

This has determined the necessity of development of skins of high moments of inertia, by increasing the thickness of "twin skins" and providing sandwich honeycomb structures. Composite fiberglass type products cannot change significantly this situation because, on one side, fiberglass includes a significant component (40-70%) of very low strength resin, and on the other hand, it is very complicated to achieve optimal distribution of strengthening threads, especially for local and global buckling.

Significant improvements may be achieved by sandwich honeycomb design. But this type of design is first of all applied in aeronautical industry and involves very high cost. Sandwich design products, as a rule, are not recyclable and involve complicated processes of production and treatment. Using foam material, such as corn in sandwich materials, as alternative, or side by side with honeycomb design, does not improve the situation.

Significant improvements are proposed in Israel Patent # 75426 of DU PONT DE NEMOURS AND CO and # 36522 of FOSTER GRANT CO INC, but these kinds of design are limited by a specific form of cells or profile as well as limitation in the choice of strength and matrix material pairs and that more significantly, they have no 3D-voIume oriented predetermined strength of material.

SUMMARY OF THE INVENTION, The invention relates to novel composite materials. More particularly, the invention relates to composite materials, which have a predetermined strength in desired directions. The composites have a predetermined strength in various directions, including those against buckling.

The invention further provides a method for producing composites which enable 3-dimensional strength optimal direction distribution, so as to adapt the products to various purposes. There can be produced various shapes, including complicated space forms. It is also be possible to recycle most of the products made by the invention process. Production means and the process are simple and safe.

The novel composites comprise any kind of foam matrix, including polymeric, strengthened in one or more directions, by means of filaments, fibers, threads, unwoven fabrics, fabrics and the like. Due to the combination of a foam matrix of predetermined cell sizes, and of filaments of predetermined cell and tread diameter, which fulfill the condition of a certain length to diameter ratio, which are given a predetermined spatial orientation, and which also fulfill certain parameters of strength there can be produced products with needed 3-dimensionaI strength parameter distribution.

The novel composites have a certain cell size of foam matrix, a certain controlled wall thickness and certain reinforcing threads (filaments) orientation.

The foamed polymer can be produced from different polymers, also of the same material that is used for strengthening-filaments material.

The range of pore size should be from about 0.2 mm to about 5 mm, with adequate density from 100 kg/m^, to about 500 kg/m3. (For polymer version) One of the objects of this invention is to achieve an optimum distribution of quantity and direction of threads. Achieving control of the product may be realized on the one hand via insertion methods and quantity and form of strengthening threads and on the other hand via foam matrix state, including foam-cell size distribution. Desired form of cell size distribution must be determined from size by Euler "critical length of bar" for microbuckling of thread, i.e. size of microcell vs diameter and modulus Young of the single filament. Some possible cases of pairs of thread and foam are: 1. Foam of low pressure Polyethylene and threads from high strength (molecular oriented) Polyethylene; 2. Foam of Low Pressure Polyethylene and threads made of the same material.

In the above first case 1 the Young Modulus achieved to 1 , 194,000 kg/cm2 and cell -threads diameter ratio is from 10 to 50.

In the second case young modulus is 10,000 kg/cm2 and cell - thread diameter ratio from 3 to 5 only.

But for the pair low pressure polyethylene-foam and molecular oriented polyethylene with modulus Young achieve to 1 , 194. 106 kg/cm2 need full cell/thread diameters relation achieve 38.2.

Advantageous parameters are: Thickness of the cell wall: about 10 μ, filaments matrix materials weight ratio are 30: 1 ; overall density is about 340kg/m3. Permissible stress (to elasticity limit) is 300 kg/cm2 - 3D compression. In this last case composite resistance to buckling (including total) is 80 times as large compared with that of the foam only.

This relation is optimal for the above mentioned 3D compression. For other cases one may use an increased cell size, resulting in material density decrease.

Cell size distribution control may be realized via control of the regime of matrix cooling from a topological and quantity point of view.

Methods of the invention may be used for strengthening of some part or part of the whole product. It may be done by 1. Different forms of the ST. M and/or different forms of compounding, 2. Preliminary insertion before foaming, 3. Simultaneous injection of S.M.. and foaming process. 1 . Strength enhancing materials may be inserted as part of the product, in the form of short filaments. Length must be proportional to its thickness and to the foam cell diameter and relations between permissible stress of reinforcing material and shear stress of the matrix material. This design type of the novel composites is close to optimal for any form of load, but especially for tension and compression under buckling conditions. 2. Strength enhancing materials may also be inserted in the form of very long random oriented filaments. This type of design of the novel material is close to optimal for volume-oriented low-intensity loads of any type. 3. Strength enhancing materials may be inserted in the form of a fabric. This is effective for shells subjected to internal pressure and plates subjected to different load forms.

BRIEF DESCRIPTION OF THE DRAWING.

Fig. la is a structure of foam material and size of cells without method strength inserting definition. Sectional view, as illustrated, shows that cells, placed near outer wall (was near to relative cold of matrix wall) have small size and internal cells that cool slowly - increase of his size, i.e. native structure of foam material has adequate microcells distribution from maximum moment inertia point of view.

Fig. lb illustrates plate shaped fabric layers, placed close to the outer surface of a thick plate and providing a high moment of inertia and determines its strength and rigidity. The resin part is in the form of layers with microdisposition and separate filaments microdisposition - support method.

Fig. 2 is a sectional view of interface between short threads and foam cells.

The Fig. 2 illustrates limiting (from thread buckling point of view). In this case, thread penetrates the cell approximately at the cell center. This is an extremely dangerous case.

As regard thread buckling a better case is a proper association of thread with cell wall. This case has more probability as a result of a coil of thread and foam wall material in foam processing. For different load direction may be optimal threads direction, i.e. for 3D tension or compression optimal distribution threads is ortogonal are proportional to direction components of load.

Fig. 3 illustrates a composition assembled from randomly oriented threads with a foamed resin.

Fig. 4 illustrates a combination assembled from outer, or outer and internal fabric layers.

Fig. 5 illustrates a method of strength increase by inserting a velour fabric before dividing it into to two layers. This method is especially attractive for complex load forces and for using existing plates.

DETAILED DESCRIPTION OF INVENTION.

Fig. la is a sectional view of a product, and explains the basic structural principles of foam design of the matrix of the composite. The main principle of this type of design of a composite matrix is by decreasing the component of the composite not providing strength and by increasing the moment of inertia for part sections by the use of matrix material in foam form with special microcell size distribution in part of the space of the elements. This distribution must be guaranteed to have the following properties: Adequate structure for required strength, structure with optimal strength imparting threads with desired orientation distribution providing internal support.

A pseudosolid shell part may be formed as a result of contact with a controlled cooled matrix wall and insertion of inserts into the internal hollow space. The outer part of the foam matrix may consist of small size niicrocells and the internal volume part may consist of big size niicrocells, the limit of microsize diameter being dictated by thread buckling.

Strength enhancement may be achieved using different forms of reinforcement that will be described in the following or via application of some or all of these methods in producing a certain unit.

Fig. la illustrates that the outer surface and close layer consist of small size foam microcells and internal volume of part consist of big size niicrocells.

Fig. l b illustrates one of the possible forms of reinforcing thread distribution in the form of a fabric layer. Layers of woven fabric are placed close to the outer surface of a thick plate for moment of inertia increase both from a strength and rigidity point of view. Fabric sheets are placed in press forms in needed order before foam injection. After injection, matrix and strength of material are internal components of monolitic material.

Fig. 2 is a sectional view of the interface between short threads and foam cells. The Fig. 2 illustrates a minimal needed microcell size from the point of view of thread buckling, where threads penetrate the cell approximately in the cell center. As regards thread buckling a better construction is an association of thread with the cell wall.

This case has a higher probability as a result of dampness of threads and foam wall material in the foam processing. For different directions of loads optimal thread directions, i.e. for 3D tension or compression, the optimal distribution of threads is ortogonal and proportional to the direction of components of load.

Cell size may be determined by "Euler critical length" of threads for microbuckling of threads i.e. size of microcell is versus thread diameter and Young modulus of thread material.

In extreme case - if Eueler's critical force is equal to the limit of elasticity i.e. the thread material can withstand a possible maximum compression force and Young modulus equal to \ 06 kg/cm2, the relative size of cell must be 30 times thread diameters.

Thread material is regular low pressure polyethylene with Young modul 10 000 kg/cm2 only. In this case where the size of cell is equal to 3.5 of thread diameter thickness of cell wall is 10 microns, strength of matrix materials: weight ratio are 30: 1; overall density: 340 kg ni3; permissible stress (to elasticity limit) 300 kg/cm2 - 3D compression. In this case composite resistance to buckling (includes global) is 80 times greater because this form of thread reinforcement and the complete filling of irregular form of injection matrix.

This kind of reinforcement may be used as such or associated with fabric- layer reinforcement.

Fig. 4 illustrates a composite based on outer and internal fabric layers, fabric sheets and a mass of threads. This kind of design, on the one hand, guarantees a high moment of inertia, and on the other hand, this high-strength design. It permits optimal positioning of fabric layers during foam component injection, especially for vertical and ceiling matrix elements . As a result of the springy property of the threadmass it can press fabric layer or layers to the wall of the matrix before foam injection.

Fig. 5 illustrates possible method of strength enhancement by using poly- finish velour fabrics before dividing it to two layers. This method is especially attractive for complex loads and for the use of ready plates including special profile-plates.

Main difference between association fabric layers and mess thread is possibility for control of thread quantity length and placement in foam matrix.

Suitable filament (thread) materials are, for example, ceramic filaments, linear oriented polyethylene and dry thermosets and thermoplastic materials include such meltpoint low compared with foaming material.

Thread diameter may be from 10μ (for ceramic metal composit) mm to about 2-5 mm for big plastic parts, and the quantity of such reinforcing material per m3 is in the range of from about 30 to about 90% (plastic for 0.7 Kg/cm3 density). For a compression force of about 5000 kg/cm2, and for filaments of linear polyethylene, the cell size ought to be in the range of from 0.3 to 30 times filament diameter.

EXAMPLES USING AND REALISATION STRUCTURED FOAM GLUING MATERIALS EXAMPLE 1.

LOADING CASE - 3-D Compression with intensity 3000 kg/cm2 ADDITIONAL CONDITIONS - Permeability and surface quintile not significant.

STRENGTHENING MATERIAL - Molecular oriented polyethylene thread.

STRENGTHENING FORM ■ Thread diameter .2 mm chaotic oriented short thread pieces (30mm) or continuous mess thread.

STRENGTH PARAMETERS Young, Modulus psi • 17,000,000 Ultimative strength, psi • 375,000 Spec, weight 1780- 1920 kg/m3 STRENGTH QTY ■ 300 kg/m3 FOAM RESIN PARAMETERS FOAMED POLYETHYLENE INJECTED TO MATRIX FOAM CELLS DIAMETER 1 -2 mm STRENGTH TEMPERATURE -20 deg C COOLING INTENSIVITY 100,000 kcal/kg/m2/h PROCESS SPECIFICATION Cooled (-20 deg C) reinforcing material: insert in injection cooled press form in form of adequate disposition. Injection process, executed simultaneously with cooling matrix wall.

EXAMPLE 2 LOADING CASE Long bar round cross section global buckling.

ADDITIONAL CONDITIONS Permeability and surface quality not significant. STRENGTHENING MATERIAL Molecular oriented polyethylene thread vowen fabric, and mess continuous thread.

Density thread/cm Fabric warp 10 Fabric weft 2 Internal mass 1 Threads disposition Fabrics in form of tube placed in the periferal part of bar. Bar internal part filled with mess.

Warp disposition parallel to bar axis.

STRENGTHENING FORM - Thread diameter 2mm, chaotic oriented short thread pieces (30mm) or continuous mass of thread.

STRENGTH PARAMETERS Young, Modulus psi 375,000 Ultimate strength psi 17,000,000 spec weight 930-1050 kg/m3 STRENGTH QTY 300 kg/m3 FOAM RESIN PARAMETERS FOAM POLYTHEYLENE INJECTED TO MATRIX FOAM CELLS DIAMETER 1-2 mm STRENGTH TEMPERATURE -20 deg C COOLING INTENSIVITY - 100,000 kcal/kg/m2/h PROCESS SPECIFICATION - Cooled (-20 deg C) reinforcing material insert in injected cooled press form in form adequate his disposition in ready part.

Injection process executed simultaneously with cooling matrix wall.

EXAMPLE 3 LOADING CASE Symmetrical Plate loaded in the form created bending perpendicular to plate surface, ADDITIONAL CONDITIONS permeability and surface quality are required. STRENGTHENIMR MATERIAL Molecular oriented polyethylene tread vowen fabric in velvet form.

Density tread/cm Fabric warp 10 Fabric weft 10 Connections treads 5 Treads disposition 2 Fabric layers placed in the periphery of plate surfaces, Space between outer layers filled by connecting threads and foam cells.

STRENGTHENING MATERIAL Thread diameter .2mm chaotic oriented short thread pieces (30 mm) or continuous mass of thread.

STRENGTH PARAMETERS Young Modulus, psi 17,000,000 Ultimative strength psi 375,000 Spec weight 930 - 1050 kg/m3 STRENGTH QTY 300 kg/m3 FOAM RESIN PARAMETERS FOAMED POLYETHYLENE INJECTED TO MATRIX FOAM CELLS DIAMETER Outer surface mm .01 -.05 Internal space mm 1 -2 mm STRENGTH TEMPERATURE -20 deg C COOLING INSTENSIVITY 150,000 kcal/kg/m2/h PROCESS SPECI FICATION Cooled (-30 deg C) strength enhancing material insert in injected cooled press form in form adequate his disposition in ready part.

Injection process executed simultaneously with cooling matrix wall. Foaming material injected between outer fabric layers and envelope of these to press form walls.

EXAMPLE 4 LOADING CASE 3-D Compression with intensivity 2000 kg/cm2 ADDITIONAL CONDITIONS Permeability and surface quality are significant.

STRENGTHENING MATERIAL HT Graphite or HM Graphite or Boron ceramic treads.

STRENGTHENING FORM Thread diameter .2 mm chaotic oriented short thread pieces (30 mm) or continuous mess thread.

STRENGTH PARAMETERS Young, Modulus psi 10, 150,000 Ultimative strength psi 175,0000 Spec weight 1800 kg/m3 STRENGTH QTY 500 kg/m3 FOAM MATRIX PARAMETERS Foamed Alluminium or magnesium Die casting.

FOAM CELLS DIAMETER outer layers -.005 - .01 Internal space - 1-2 mm STRENGTH TEMPERATURE - 800 deg C COOLING 1NTENS1VITY - 500,000 kcal/kg m2/h PROCESS SPECIFICATION - Reinforcing material inserted in matrix before or simultaneously with casting process.

Claims (16)

CLAIMS:

1. A structural material, with strength against forces of compression and which is resistant to internal buckling, which comprises a foam of a suitable substance of pore size in the range of from below 1 mm and up to about 10 mm, where the foam matrix is strengthened by libers, filaments, threads, non-woven fabric, woven fabric oriented so as to provide the required mechanical strength.

2. A material according to Claim 1, where the foam is made from a suitable polymer or metal (aluminum, magnesium, etc.), and which material has a density in the range of from about 100 kg/m3 to about 500 kg/m3.

3. A material according to Claim 1 or 2, where the ratio between pore size and diameter of reinforcing filament, fiber or thread is from about 3 to 1 to about 50 to 1.

4. A material according to any of Claims 1 to 3 where the foam is a plastic foam, and where the reinforcing material is made from molecularly oriented polyethylene.

5. A material according to Claim 1 , where the reinforcing material is a ceramic fiber, filament or thread.

6. A material according to Claim 1, where the reinforcing material is a woven or non-woven cloth.

7. A material according to any of Claims 1 to 6, where the reinforcing fibers or filaments have a diameter of from a few microns to 1 to 2 mm for In rue cells.

8. A material according to any of Claims 1 to 7, where the walls of the pores have a thickness of from about 5 to about 20 microns.

9. A material according to Claim 1, where the reinforcing material is in the form of a mono-filament.

10. A material according to Claim 1, where the reinforcing material is of the pre-velour type fabric.

11. 1 1. A material according to any of Claims 1 to 10, where the outer boundaries of the foamed structure are of smaller pore size than those of the interior.

12. A material according to any of Claims 1 to 1 1, where through each pore there passes at least one reinforcing fiber, filament or thread.

13. A method of producing a material according to any of Claims 1 to 7, which comprises introducing into a mold a suitable arranged reinforcing material, a foaming material and foaming such material until the desired foam reinforced by said reinforcing material is formed.

14. A method according to Claim 13, where the material is a high polymer or metal.

15. A method according to Claim 13, where the reinforcing fibers are made of oriented polyethylene.

16. A method according to Claim 14, where the foaming is made under such conditions that the wall thickness of the millimeter size foam cells is of the order of 5 to 20 microns.