STRUCTURAL MEMBER AND METHOD OF MANUFACTURE

Abstract: A structure is provided which may be formed from a sheet of paper, synthetic plastics or metal. The structure when assembled comprises a series of parallelograms arranged in a tessellating fashion. Uses of the structure include as a membrane for use in heat transfer equipment, or as a filter; as a structure arranged to absorb energy such as in crumpling or in sound absorption; as a mixing promotor so as to improve heat transfer or turbulence within reaction vessels or as a building slab, when suitably supported. The advantages of the structure depend on the particular use. For example when used as a slab for building it has a very high strength to weight ratio.

Description: STRUCTURAL MEMBER AND METHOD OF MANUFACTURE This invention concerns a structural member and method of manufacture thereof . In one embodiment the structural member is of light weight, but capable of withstanding substantial compressive, tensile, bending or torsional loads. Known such structural members include generally honeycomb formations sandwiched between outer covering sheets . One object of the present invention is to provide structural members having improved weight/strength characteristics . Further objects of the invention are to provide members structural and otherwise, having one, some or all of the improved characteristics; improved weight/strength; improved surface area; improved insulation; improved absorption; improved turbulence; improved heat transfer. According to a first aspect of the present invention there is provided a structural member comprising a corrugated sheet wherein the ridges on one face thereof are coplanar and of saw-tooth shape extending in axially spaced parallel relationship, the intermediate nadirs (which form the ridges on the opposite side of the sheet) being of identical saw-tooth shape, there being two panels of identical parallelogram shape joining any two transversely adjacent linear ridge sections. The inventor has realised that the structural member may be used in a myriad situations as a structure per se. This is because the structure has not only superior strength to weight characteristics, but also it has a very high surface area to volume ratio. According to a second aspect of the invention there is provided a structure comprising a plurality of cells arranged in an array, the cells comprising first, second, third and fourth sub-groups of planar regions, each region being in the form of a parallelogram, the sub-groups being arranged in groups such that in a transverse direction: a first group of regions comprises alternating members of a first and second sub-group; and a second group of regions comprises alternating members of the third and fourth sub-groups; and in a transverse direction: a third group of regions comprises alternating members of the second and third sub-groups; and a fourth group of regions comprises members of the first and fourth sub-groups, each member of each sub-group sharing a common interface with members of two different sub-groups along alternating edges. Preferably the members of each sub-group are parellograms comprising two equilateral triangles, joined along a common vertex. These are referred to as regular parallelograms. The triangles are advantageously congruous i.e. of identical size. However, the parallelograms may comprise isoceles or even scalene triangles and therefore do not have to be regular. Included angles in a parallelogram may lie in the range from 1° to 179°. Variation of the length of all sides of the parallelogram is also possible. The unassembled structure comprises a planar sheet or membrane onto which has been scored or impressed, lines of weakness. This is known as a preform. The impression or scoring of lines of weakness may be achieved mechanically, by scratching or rolling a cutter across the surface of the membrane so as to form a tesselating array of parellograms comprising adjacent equilateral triangles in a preferred embodiment. However, it is not necessary to form lines of weakness along each vertex of all the triangles. The preform is substantially planar. Alternatively forming the lines of weakness may be done by punching the pattern onto the membrane; by an etching method employing a photo-resist method or by any other suitable method known to the skilled man. For example in certain circumstances when it does not matter if small holes are formed in the surface of the sheet or membrane, it may be possible to cut slits or punch holes so as to preform the lines of weakness. Such a structure may be used as an energy absorber; as a support structure; as an absorbancy structure or as a turbulence promoter; or indeed in situations in which it exhibits combinations of the aforementioned uses. Some of these uses are described below. However, a structure preformed with lines of weakness defined by holes or slots clearly could not be used as a membrane or means to separate two fluids as mixing would occur. This aspect of the structure to act as an interface between two fluids will be described below. Of course holes could be formed within a region inside the vertices of the or each parallelogram in the structure. These holes may be circular, triangular, square, hexagonal or even smaller parallelograms and could be made during the preform stage. The resulting structure would be lighter and could be turned around "on itself" into a wheel or tyre. When the preform has been made, that is when the surface of a sheet has been weakened along predetermined lines, edges of the sheet are squeezed together at a predetermined rate using for example pneumatic and/or electric hydaulic pressers. Lateral pressure may be applied by the presses so as to form a corrugated structure. The height of the corrugations are determined by the extent to which the edges of the sheet are pushed together. The maximum height of a corrugation is 3/2 L or approximately 0.58L. Where L is the length of a vertex of the equilateral triangle. Of course this would be different for non eqilateral triangles. A lubricant may be provided between sliding surfaces of presses and sheet so as ensure that no tearing of a material takes place. As the preform is squeezed in the longitudinal and transverse senses, at an optimum angle of 60 (when using regular parallelograms) there is a reduction to 0.58 of its projected area. In an alternative embodiment the shape of the structure may be suggested to a sheet and the sheet may be drawn through a suitably shaped die or dies at a predetermined speed, so as to ensure that the suggested shape is imposed upon the remainder of the sheet during formation of the structure. Such a process is analogous to the method in which newspapers are folded and stacked onto suitable mandrels. But is, by its very nature more complex and requires more control. According to a yet further aspect of the present invention there is provided a die for the manufacture of a tessellated parallelogram structure, the disc having walls dimensioned and arranged so as to urge a sheet passing through an orifice in the die, to adopt the shape and configuration of the tessellated parallelogram structure. Preferably the walls of the die are angled and there is a lead in section which gradually urges the sheet into the predetermined shape. Preforming may take place to some or all of an area of the sheet. However, this is not necessary as the suggested shape will in effect reflect off side walls of the die as the sheet moves towards it. Clearly height restrictors may be required on the lead in side so as to prevent suckling of the sheet prior to entry into the die. A preforming process may take place by way of a roller having suitable shaped raised portions. The planar sheet of material, after having passed under a roller (or between a pair of rollers) , will tend to bend more readily along the aforementioned lines of weakness. Lead in edges to the die will cause the sheet to begin to form and the suggested shape of the tessellated parallelogram structure will be formed. The appearance of the structure could be liked to the suggested shape forming in a wave-like manner as the sheet passes through the relatively stationary die. Rollers above and below the sheet may assist in drawing the sheet through the die. Similarly these or independent presses may be used to impress the lines of weakness onto the sheet. Of course suitable lubricants and/or coolants may be used during the fabrication process. These would reduce friction and therefore the risk of tearing. Sensing and control means may be provided for monitoring speed or throughput, height of the erected structure, cell size etc. Similarly the apparatus for the production of the tessellated parallelogram structure could be varied so as to accommodate sheet thickness from micrometres to metres in magnitude. Means may be positioned for cutting holes or portions of material prior to the sheet entering the die. Further details of the method of production appear below. Alternatively in certain embodiments or for certain uses, it may be desirable to cast the structure using a suitable support and/or by spraying the material forming the structure, onto the support. For example this may be achieved by spraying a plastics material onto a metal support; by vapour deposition of a material onto a suitable support; by spraying concrete onto a support; or by casting onto a suitably shaped support for example in a lost wax process. Clearly the exact method of production will depend upon the material forming the structure and its uses. The structure may be formed from a planar sheet such that each planar region of a sub-group is displaced so as to form alternating peaks and troughs defined by the parallelogram elements of the sub-group, wherein points defining the upper and lower regions conjoin so as to define zig-zag lines. In plan view the zig-zag lines defining the peak and trough regions may be, and are preferably, of identical length; the interspacing between adjacent zig-zag lines being defined by the characteristic length of an edge of the parallelogram. Preferably the parallelograms in an array are all of the same size and all have the same characteristic length "L" . That is they are congruous. Of course the cell sizes may be different. That is to say different size parallelograms may comprise smaller or larger size equilateral or any other shaped triangles. The purpose of having different size equilateral or any other shaped triangles and therefore different cell sizes in the structure is explained below with reference to the particular uses of this arrangement. Preferably first and second groups of parallelograms in the array are substantially parallel to one another so as to define a corrugated sheet in the form of an array which in longitudinal and transverse cross-sections define a saw-tooth like profile. The structure may be folded or wound about an axis substantially parallel to an axis defining a first sub-group so as to form a substantially cylindrical or part-cylindrical structure. This type of structure could form a tyre or tread for a wheel . If formed from rubber the tyre would require no air and the user would never suffer a puncture. Uses of this particular embodiment of the structure include protective windings around cylindrical bodies such as tubes, pipes or hoses. For example as a crush resistent protector for sensitive longitudinal objects such as hoses, cables, optical fibres or wires; or as a support for insulating materials. The term "insulating materials" is intended to include thermal as well as electrical insulators and embraces high voltage insulators. The structure when used on its side may be arranged so as to be a support for a tyre or rim. Thus replacing spokes and producing a very strong wheel. In an alternative embodiment the structure may be deformed about two non-parallel axes so as to form so-calledcomplex compound curves. Compound curves may be envisaged as surfaces defined in three dimensional space represented by at least three independent variables. The shape of compound curves includes such well known curves as saddle or double saddle curves. The structure could be formed into these complex shaped compound curves so as to enable the structure to be placed on or around car bumpers or grills or even within the bodywork of a car so as absorb energy on impact. Thus the structure has a further use as an energy absorber. The structure may be placed so as to compress it further, or it may be placed "flat" so as to cover the object to be protected. It could of course be that more than one structure is used and these are placed in different orientations. The structure as will be appreciated has a myriad uses. Some of these uses are defined in further aspects of the invention below. The structure as described above may therefore take different forms and could comprise different cell sizes. Accordingly what originated as a planar substrate with interlocking zig-zag peaks and troughs could be transformed into many different shapes and configurations. Such transformed structures, and indeed the original structure in its planar form, for the purposes of this specification shall be referred to hereinafter as a tessellated parallelogram structure. According to a third aspect of the present invention there is provided a tessellated parellelogram structure for use in processing vessels so as to promote mixing of substances within the vessel. Preferably the vessel is of the type found in chemical industries where mixing of liquids or gases is important so as to ensure complete reaction. In such vessels it is important to have large surface areas. Typically such vessels comprise mixing surfaces on which catalysts are disposed; or devices for promoting the mixing of the gas or liquid. It is important that active mixing takes place and this is achieved by introducing turbulence close to or at the surface across which movement of the fluid occurs. For example in some reaction vessels turbulence is achieved by roughening the surface or by providing turbulent promoters such as fins, channels or twisted regions. The structure, because of its interlocking shape promotes the flow of fluids whilst ensuring that a high degree of turbulence occurs. This turbulence increases the rate of change of portions of the fluid close to or within the boundary region and therefore ensures high velocity of fluid flow through channels created by the structure. Because of the turbulence is increased this leads to better mixing of the fluids. As a corollary of this mixing, heat transfer rates are improved and the structure finds myriad uses in refrigerators, radiators or any other fluid containing structure through which fluid passes in order to gain or lose energy. According to a further aspect of the present invention there is provided a honeycombed parallelogram structure for use as a membrane separating first and second fluids, the temperature of the first fluid being higher than that of the second fluid. It will be appreciated that the term fluid is intended to include, sludge, solid in liquid suspension, aqueous mixture or even a granulated solid or powder which may be pumped as a fluid or in a fluid suspension. Examples of this aspect of the invention include uses within for example in automobiles or any exhaust system for internal combustion engines. This includes within gas turbine, oil-fired or coal fired generators, drive systems, agricultural machinery, motor cycles, or any other equipment driven by an internal combustion engine. Heat exchangers in power plant or chemical processing or food processing industries require rapid and efficient mixing. The tessellated parallelogram structure promotes this. In metal processing industries, where metal is often required to be recovered, it is a advantageous to have large active surface areas, for example in electrolysis equipment. The structure may be used in this environment when suitably adapted. The structure suitably adapted may be used to promote almost all types of mixing where a simple mechanical mixing structure is required. It may be used within effluent treatment industries, such as in sewage treatment or disposal; in water purification o industries as both a support for a filter and as a turbulence inducing structure or in devices where bacterial filters are required; as it is important to remove filtrate from the surface of the structure and this may be achieved by the introduction of turbulence. According to a fifth aspect of the present invention the tessellated parallelogram structure is employed as an energy absorber. It is of particular importance in vehicles as a non linear terminal pressure structure which term is intended to include a shock or impact absorber and crumple zone if the structure is formed from a relatively thick material, such as mild steel, suitably coated or treated against corrosion. The structure provides superb controlled crumpling material which may be used in car bumpers, body panels, steering wheels or dashboards. For example, suitably formed structures may be placed around or on the surface or interior of vehicles in the form of compound curves. Because each parallelogram comprises in effect two equilateral triangles which enable folding or twisting of the structure about more than one axis; it is possible to use the structure within areas of vehicles wherein high forces could be generated on impact resistance to different forces so that a varying crumple strength structure may be achieved by varying the cell sizes within the material and/or the type of material and/or the material thickness. Further examples of uses of impact absorbing structures could be in the packaging industry; in mats for example for camping or for playgrounds such as crash mats; in any form of material wherein pressure is to be absorbed such as shoe soles; sports equipment, tennis rackets, cricket bat handles, skis; in crash barriers, on motorways, in car bumpers, in seat padding, in crash helmets and protective clothing; around sheathing and pipes for protection of insulated cables or for transport of fluids. According to a sixth aspect of the present invention a tessellated parallelogram structure is incorporated in sound absorption apparatus. The structure is beneficial to environments where there is a high amount of vibration and/or noise which needs to be absorbed. The structure is particularly effective at absorbing all types of energy, including sound. Sound absorption is achieved by spreading the sound or vibration waves incident on each cell into the material itself. The material may be loosely held in a "sandwich" between two planar sheets. As the material shape tends not to reflect or transmit energy, it is found to be particularly effective at reducing the amount of sound or vibration penetration. Uses of the structure as a sound absorption medium include use in vehicle body panels, vehicle exhausts, motor or engine housings. Also when modified into panels it coule be used in door fillings, wall fillings, building materials, plaster-boards, acoustic speaker housings, recording studio linings, bricks and building blocks, ceiling and partitioning walls or almost any other type of building material, including floor tiles and wall panels. According to a seventh aspect of the present invention there is provided a tessellated parallelogram structure for use when sandwiched between first and second planar structures as a building material. This aspect of the structure enables the construction of immensely strong components, using less materials, or alternatively stronger components, using the same amount of materials, having superior strength to weight characteristics Some of the uses of the structure as a building component include covering or insertion within bricks and building blocks, laminating furniture and panels, use as flooring, use as roof tiles; use in aeronautic fusilages, wings, and aircraft structures. Also the tessellated parallelogram structure, when suitably modified may be used in R.S.J, use on platform flooring used in aircraft or vehicle wheels, used in packaging material, for example in the form of cardboard, paper, polystyrene or metal reinforced packaging; used in building and cladding of other materials, so as to provide protection and/or additional strength. It may be used in ceilings struts, structures and partitioning materials, in portable buildings, in shipping containers or in commercial vehicle body panels . Suitably modified tessellated parallelogram structures may also be used on boats; in gears; in luggage and packaging cases, in paving blocks, in foundations for buildings, wherein a waterproof or moisture proof layer may be included, in temporary roads or car parks, on pontoons, or as buoyancy materials wherein laminated layers may be stuck together. The tessellated parrallelogram structure could be used in steps for escalators, walkways, gangways, playground equipment or in virtually any other environment where high strength to weight ratio is required. According to a further aspect of the present invention a tessellated parallelogram structure, with a large surface area to volume ratio. The uses of this embodiment are multifarious. For example the large surface area to volume ratio could be employed in chemical processing industries where it is desired to have a chemical in contact with a catalyst for as long a duration as possible so as to promote reaction or increase reaction rates. The tessellated parallelogram structure could also be used in lead-acid batteries, in catalytic converters for automobiles or even in artificial lungs, so as to provide a large surface for gaseous diffusion of oxygen into haemoglobin in a patient's blood. The structure also has many other uses in the field of medicine. According to a yet further aspect of the present invention there is provided a tessellated parallelogram structure for use as a filter. Because the surface area to volume ratio is so high the tessellated parallelogram structure may act as an absorber when formed from a suitable material or when a suitable absorbent material is layered on a substrate. Uses of such a filter include medical swabs and absorbancy pads; or tampons, when the structure is rolled into a suitable cylindrical form. Similarly the structure when impregnated with requisite substances or when supporting a suitable filter, may be used in kidney dialysis machines. Of course the filter may find other applications in non-medical environments, such as in a water purifier, oil filter in an engine or air filter for an inlet manifold to a carburettor. The structure is also beneficial in areas where a large amount of heat is required to be transferred in a relatively small volume, or alternatively, when suitably modified so as to comprise or encapsulate an insulator where a high degree of insulation is required. The features of this aspect of utilisation of the product depend on the specific application. For example, the structure may be used in heat exchangers, fridges, freezers, air-conditioning plants, desalination equipment domestic or industrial radiators, water heaters, kettle elements, boilers, steam generating units, heat sinks, where it is critical to dissipate heat at a high transfer rate or in solar energy panels. Similarly the large surface area may be used to support insulating materials, hot water tanks, jackets, lagging jackets, insulated clothing, bed filling down, duvets, sleeping bags clothing or within vehicle body or housing cavities. Preferably in all the aforementioned uses the angle included between any two axially adjacent linear ridge sections is 60°. However, this may be varied especially where fluids are required to flow along a channel defined by a portion of the structure. Clearly different angles may be used. The erected tessellated parallelogram structure could be arranged in the form of a fan. That is channels adjacent one edge of the structure could be closer together than those on a different edge. Such a structure permits fluids to flow through adjacent channels at different velocities and could be used in heat transfer situations where a differential temperature gradient is required wound a curved object. The sheet forming the structure may be of paper, card, metal, plastics or other material and may be formed by folding, moulding or fabrication from individual panels, vapour deposition onto a substrate or drop forging. The sheet may be laminated with a plane sheet on one face thereof or sandwiched between two such plane sheets. Suitable edge strips may be placed around the tessellated parallelogram structure when formed. It may even be possible to place the tessellated parallelogram structure in a box, as a loose fitting device and a suitably sized lid or cover placed on the box so as to close it. The advantage of this arrangement is that the structure is able to move laterally under any transverse or vertically applied force. Accordingly the structure will by its very nature adopt a configuration to absorb and transmit applied forces equidirectionally. Additional sheet or sheets may be formed from similar material to that of the corrugated structure or of different material from that of the corrugated structure. Different layers of corrugated structure may be placed on top of one another. Further aspects of the invention will be apparent from the detailed description below. The invention also relates to methods and apparatus for shaping material, and in particular for shaping a uniaxially foldable sheet material such for example as paper, card and metal foil or sheet metal. Such materials are currently shaped in a variety of ways and for a variety of reasons. Suitably shaped material can be used in a honeycomb configuration for reinforcement in a sandwich construction, or in any of the above mentioned uses. Shaped metal sheet can also be used as rigidised material as compared to the unprocessed sheet in free-standing i.e. non-sandwiched applications. In this configuration the structure may be used in inductive lighting equipment. A silver or reflective metallic substrance may be deposited on the surface and used as a reflector in lighting equipment. Holes may be formed in the structure and fluorescent tubes placed therethrough so as to provide an effective and attractive light housing. A member comprising a corrugated tessellated parallelogram structure wherein the ridges on one face thereof are coplanar and of saw-tooth shape extending in axially spaced parallel relationship, the intermediate nadirs (which form the ridges on the opposite side of the sheet) being of identical saw-tooth shape, there being two panels of identical parallelogram shape joining any two transversely adjacent linear ridge sections; and the manufacture thereof will be described below. Such a tessellated parallelogram structure, when suitably constrained about its edges or otherwise against flattening, constitutes theoretically a very compression resistant, if not indeed the most compression resistant, form of sandwich composite reinforcement. Initial samples of such material have been made by manual folding. This may be achieved on a large scale in industrial preforming, folding a controlled compression. It could also be achieved by suggestion of the shape to a sheet in much the same way as newspaper is folded at high speed off a printing press. Sheet metal is rigidised in a variety of ways usually involving deformation between embossing or deforming rollers or by stamping. Such methods involve thinning of metal pressed out from the body of the sheet and whilst these methods do in fact strengthen and rigidise the sheet they do not, on account of the thinning as well in many cases as a result of metallurgical disturbances, achieve the maximum possible rigidity or resistance to compression. The present invention provides a plurality of methods and apparatus by which the aforementioned structure can be manufactured. The invention comprises a method for shaping a uniaxially foldable sheet material comprising initiating an area pattern of fold lines constituting incipient folds oppositely directed with regard to the faces of the material and reducing the lateral sheet dimension while constraining the material depthwises to permit controlled deformation based on the pattern of fold lines across the area. The pattern may comprise a two-dimensional array of apexes each formed of three coincident like-facing fold lines and intermediate nadirs likewise formed of three coincident like-facing fold lines facing in the opposite direction to the fold lines of the apexes. The pattern may comprise parallel zig-zag lines alternate ones of which face in opposite directions. By the term opposite, it is intended that alternate sets of zig-zag lines may define a first plane and "opposite" alternate sets of zig-zag lines, defining a second plane, point in an opposite direction. Similar to opposite facing chevrons. The pattern may be initiated by pressing a linear projection against the material which is in turn against a resislient backing. Such linear projection may comprise a wire or edge projecting from the surface of one of a pair of rollers of which the other constitutes the resilient backing. Each roller may have wires or edges. It could be achieved by stamping, punching, etching, laser cutting, engraving or scoring. The lateral sheet dimension may be reduced by lateral compression, which may effect the lateral compression after the fashion of rolling mill rollers. The material may make multiple passes through the same set of edge rollers, or may make passes through multiple sets of edge rollers. The material may be constrained depthwise, during reduction of the lateral sheet dimension, between depth-limiting rollers, or similarly controlled hydraulic plates, which may have a fixed separation, which may, however, depend upon the extent of lateral sheet dimension reduction. The controlled deformation may be determined by correlating the degree of constraint of the material depthwise with the reduction in lateral sheet dimension. The material may be constrained to a maximum depth corresponding to the maximum possible lateral sheet dimension reduction consistent with folding purely on the area pattern of fold lines, formed as aforedescribed. The lateral sheet dimension, measured along the zig-zag lines direction, may be reduced by a factor of about 0.58. The invention also comprises apparatus for shaping a uniaxially foldable sheet material comprising fold line pattern initiating means adapted to initiate on the material an area pattern of fold lines constituting incipient folds oppositely directed with regard to the faces of the material, and lateral sheet dimension reducing means together with material depth constraining means adapted to permit controlled deformation of the patterned material on reduction of the lateral sheet dimension. Said pattern initiating means may comprise opposed rollers between which the sheet material can be fed with linear projections from the surfaces of the rollers which are pressed against opposite faces of the sheet material. The rollers may be of resilient material. Said lateral sheet dimension reducing means may comprise edge rollers, which may be progressively adjustable, with means adapted to pass the sheet material multiple times therethrough. There may, however, be a plurality of edge roller arrangements arranged with progressively reducing separation. The material depth constraining means may comprise depth limiting rollers associated with the edge rollers - a primary function of the depth constraining means is to level out the increase in depth across the material. Control means may be provided operative to correlate the depth constraining means with the sheet lateral dimension reducing means. Apparatus for forming a corrugated sheet comprising a die, corrugation suggestion means placed adjacent the die such that a sheet passing across the corrugation suggestion means has formed within it the corrugations, prior to passing through an orifice in the die. Preferably the sheet passes through the die by way of a suitable drawing means such as a pulling force or by way of pushing force. In either case the force may be applied by rollers. Preferably the die and the corrugation suggestion means are arranged so as to form a structure the structure having ridges on one face thereof which are coplanar and of saw-tooth shape extending in an axially spaced parallel relationship, the intermediate nadirs (which form the ridges on the opposite side of the sheet) being of identical saw-tooth shape, there being two panels of identical parallelogram shaped joining any two transversely adjacent linear ridge sections. In an alternative embodiment the die and the corrugation suggestion means may be so arranged as to suggest a shape of a structure which comprises a plurality of cells arranged in an array, the cells comprising first, second, third and fourth sub-groups of planar regions, each region being in the form of a parallelogram, the sub-groups being arranged in groups such that in a transverse direction a first group of regions comprises alternating members of a first and second sub-group; and a second group of regions comprises alternating members of the third and fourth sub-groups; and in a transverse direction a third group of regions comprises alternating members of the second and third sub-groups; and a fourth group of regions comprises members of the first and fourth sub-groups, each member of each group sharing a common interface with members of two different sub-groups along alternating edges. The drawing of the structure through the die is such that a plain sheet of synthetic plastics, paper, card or even metal, such as sheet steel, may be urged through the die across the corrugation suggestion means so as to pass through a series of phases from an original planar sheet through the die to a final tessellated parallelogram structure. Of course lines of weakness may be suggested in the material prior to it passing through the die. Similarly some compression may be achieved by urging lateral edges of the material together by juddering lateral edges of the die. The die and the corrugation suggestion means may comprise several separate stages and accordingly could extend over some distance in an industrial production line. An embodiment of the tessellated parallelogram structure together with a method of its production will now described, by way of example only, and with reference to the figures in which: Figure 1 shows a plan view of a corrugated sheet which forms part of a tessellated parallelogram structure; Figure 2 shows a cross-section through the structure on the line II-II of Figure 1; Figure 3 ' shows an end view of the structure of Figure 1 sandwiched between plane covering sheets to form the structural member; Figure 3A shows an isometric view of the structure in part section; Figure 4 is a view of one face of a sheet of material suitable for producing the structure of Figures 1 to 3A with an area pattern of fold lines; Figure 5 is a view like Figure 4 of the same sheet shaped by reducing the laterial dimension of the same; Figure 6 is a section on the line III-III of Figure 5; Figure 7 is a perspective view of one embodiment of apparatus for shaping the sheet material; Figure 8 is a plan view of another embodiment of apparatus ; Figure 9 is a view of a pair of rollers used to initiate the area patterning of Figure 4; and Figure 10 is a developed view of the surfaces of the rollers of Figure 9. A description of one embodiment will now be made with reference to Figures 1, 2, 3 and 3A. From Figures 1 and 2 of the drawings, it will be seen that the corrugated sheet 100 formed into a tessellated parallelogram structure, has ridges 110 on its upper face which lie in a common plane and which are of a regular saw-tooth shape. The ridges 110 extend in axially spaced relationship. The intermediate nadirs 120 which are of identical saw-tooth shape form the ridges on the opposite face of the sheet. Fig 3A shows an isometric view in part section of an assembled tessellated parallelogram structure 501 enclosed within a box 500. The box 500 comprises front and back walls 502 and 505, top and bottom layers 507 and 506 and side walls 503 and 504. The slab formed by this arrangement is incredibly strong and very lightweight. Two panels 130 of identical parallelogram shape join any pair of transversely adjacent linear ridge sections such as those labelled A and B. The included angle between any two axially adjacent linear ridge sections such as those labelled C and D is 60°. The sheet 100 is sandwiched between covering sheets 140 and 150, which are laminated therewith by joining along the ridges 11. It will be understood that the internal structure combines with the covering sheets to define a multiplicity of tetrahedral shapes whence exceptional strength derives. The corrugated sheet 100 may be of paper, card, metal, plastics or other material and formed by folding, moulding or fabrication as appropriate. Structural members of paper or card will find application in the packaging industry, those of metal in the motor body, aerospace and construction industries. A particular application might be panels for access floors. Outer sheets of wood veneer may be applied to a corrugated core of card to form members for use in the furniture industry. The range of possibilities are legion. Detailed descriptions of embodiments of the machine are described below. Embodiments of apparatus and methods for shaping material according to the invention will now be described with reference to the accompanying drawings, in which:- A detailed description of one type of machine for producing the above mentioned structure will now be described with reference to Figures 4 to 11 inclusive. The drawings illustrate methods and apparatus for shaping a uniaxially foldable sheet material 11 comprising initiating an area pattern 12 of fold lines 13 constituting incipient folds oppositely directed with regard to the faces of the material 11, and reducing the lateral dimension LD of the sheet while constraining the material 11 depthwise to permit controlled deformation based on the pattern 12 across the area thereof. The pattern comprises a two-dimensional array of apexes 14 each formed of three coincident like-facing fold lines 13a and intermediate nadirs 15 likewise formed of three coincident like-facing fold lines 14b facing in the opposite direction to the fold lines 13a of the apexes 14. The pattern comprises parallel zig-zag lines 16 alternate ones of which face is opposite directions. In the method of the invention, the fold lines which constitute the parallel zig-zags lines 16 may be regarded as more important to form than the lines 13c which span between the lines 16 and which are shown in dashed line against the solid line of the lines 16. The lined 13c may not (depending perhaps on the nature of the material 11) need to be present at all, or at least not completely - it will become apparent that so long as the zig-zag lines 16 are present as incipient fold lines, further treatment of the material according to the invention to be described below will automatically tend to fold the material along the lines 13c due simply to the geometry of the arrangement. The pattern 12 is initiated by pressing linear projections against the material 11 which is in turn against a resilient backing. Such linear projections are shown in Figures 6 and 7 as wires 17 or edges of metal strips set into and projecting from the surfaces 18 of rollers 19 between which the material 11 is passed while pressure is applied between the rollers 19, the surfaces being resilient depending, again, on the nature of the material 11. Lubrication may be provided, in the form of a powder such as carbon or talc, or a liquid such as an oil, between relatively moving surfaces. As best seen in Figure 10, the wires 17 are arranged, circumferentially of the rollers 19, alternately on one roller and the other so as to give the required alternately facing zig-zag lines 16 across the material 11. Also shown on Figures 9 and Figure 10 are wires 17a which may nor may not need to be present depending on the nature of the material 11 and which, if present, may be required to extend only a short distance away from the wires 17 that produce the zig-zag lines 16 since all that may be required is some "encouragement" for ' the material to fold on these intermediate lines and indeed the material depending again on its nature may in any event automatically fold on these lines in consequence of the folding on the zig-zag lines 16 without any such encouragement at all. Such as the way in which the shape is suggested to folding newspapers. The folding results from lateral compression and this is effected by edge rollers 41, Figure 4 and 5, after the fashion of rolling mill rollers. In Figure 4, one arrangement of edge rollers 41 is shown comprising four such rollers, two each side of a strip of thematerial 11 passing between them. The rollers 41 are arranged on adjustable framework 42 which can be controlled so as to move the opposed rollers in towards each other. The strip of material 11 may as indicated by arrow A make multiple passes between the rollers 41 with their spacing progressively reduced so as to reduce the lateral sheet dimension gradually. It is possible to have the zig-zag lines 16 running circumferentially of the rollers 19, but as will be seen from Figure 5, the edges of the material then compress to a complex form. The material 11 is constrained depthwise during such reduction in its lateral dimension between depth-limiting rollers 43. The rollers 43 have, at any one time, a fixed separation determining the maximum depth of the material 11 - the depth, of course, increases as the lateral dimension decreases - but this fixed separation is adjustable in correlation with the spacing between the edge rollers 41 so that the depth to which the material 11 deforms is constrained to be uniform across the width of the strip. The correlation can be under the control of a computer (not shown) which ' adjusts the roller spacings via stepper motors 44. Figure 8 illustrates a different arrangement in which there are multiple sets of edge rollers 41 with permanently set spacing and each such set being associated with a pair of depth constraining rollers 43. In any event, the depth constraining rollers 43 are ultimately set to a spacing equal to the maximum depth of the material 11 which corresponds to the maximum possible lateral sheet dimension reduction consistent with folding purely on the area pattern of fold lines - it is, of course, possible to reduce the lateral dimension further, but such further reduction would be accompanied by unplanned and excessive crumpling which would in no way further enhance the mechanical properties of the material. The geometry will depend upon the thickness of the sheet material 11, but the width will be found to be reducible by a factor of 0.58 to produce a material with desirable mechanical properties imparting the ability to serve in place of conventional honeycomb reinforcement and rigidised metal panelling. Depending, furthermore, on the nature of the material 11, shaping as above described can be used to fashion springy material which may have useful resilience lengthwise of widthwise. It will be appreciated that it is not intended to limit the invention to the above example only, many variations, such as might readily occur to one skilled in the art, being possible, without departing from the scope thereof. For example other uses of the structure, when suitably modified include: Absorbency products, Ski equipment, Marine equipment, Buoyancy products, Lifts and lift shafts, Floor coverings (carpets/underlays/tiles/fabrics), Tyres, Inductive lighting, Handle (shock absorbent) , Artificial lungs, Insulated glass, Glass reinforced materials (such as GRP) , Baby changing mats and Linear springs. Other uses of the structure include as a heater for runways; as a foldable mat, which may be used for babies and as an insulator for vacuum flasks and insulated containers.

Claims: CLAIMS 1. A structural member comprising a corrugated sheet wherein the ridges on one face thereof are coplanar and of saw-tooth shape extending in an axially shaped parallel relationship, the intermediate nadirs, being in the form of ridges on the opposite side of the sheet, are of identical saw-tooth shape, there being two panels of identical parallelogram shape joining any two transversely adjacent linear ridge sections. 2. A structure comprising a plurality of cells arranged in an array, the cells comprising first, second, third and fourth sub-groups of planar regions, each region being in the form of a parallelogram, the sub-groups being arranged in groups such that in a transverse direction a first group of regions comprises alternating members of a first and second sub-group; and a second group of regions comprises alternating members of a third and fourth sub-group; and in a transverse direction a third group of regions comprises alternating members of the second and third sub-groups ; and a fourth group of regions comprises members of the first and fourth sub-groups, each member of each sub-group sharing a common interface with members of two different sub-groups along alternating edges. 3. A structure according to claim 1 or claim 2 formed from a substantially planar sheet by arranging each planar region of a sub-group to be displaced so as to form alternating peaks and troughs defined by the parallelogram elements, wherein points defining the upper and lower regions can join so as to define zig-zag lines. 4. A structure according to claim 3 wherein the zig-zag lines defining the peaks and troughs are of identical length, the interspacing between adjacent zig-zag lines being defined by the characteristic length of an edge of the parallelogram. 5. A structure according to any of claims 1 to 3 wherein parallelograms of the array are congruous. 6. A structure according to any of claims 1 to 3 wherein the parallelograms in the array are of different sizes and are arranged in a predetermined pattern. 7. A structure according to claim 6 wherein the pattern of parallelograms is such that when the structure is assembled so that they form a fan. 8. A structure according to any of claims 2 to 7 wherein the first and second groups of parallelograms in the array are substantially parallel to one another so as to define a corrugated sheet which in longitudinal and transverse cross sections define a saw tooth like profile . 9. A structure according to any preceding claim which is deformed about an axis parallel to the axis defining a first sub group so as to form a cylindrical or part cylindrical structure. 10. A structure according to any of claims 1 to 6 wherein the structure is deformed about two non linear axes so as to form compound curves. 11. A tessellated parallelogram structure for use in processing vessels so as to promote mixing of substances within the vessel. 12. A structure according to claim 11 for use in closed processing vessels. 13. A tessellated parellelogram structure for use as a separating medium between a first and a second fluid, the first fluid being of a higher temperature than the second fluid, into position of the tessellated structure between the two fluids so as to promote effective heat transfer from the hotter fluid to the colder fluid. 14. A tessellated parallelogram structure for use as a shock absorber. 15. A structure according to claim 14 wherein different cell sizes are provided within the structure. 16. A structure according to claim 14 or 15 wherein the thickness of the membrane of the structure is varied so as provide different strengths of material . 17. A tessellated parallelogram structure for use as a sound absorber. 18. A tessellated parallelogram structure for use as an energy absorber. 19. A tessellated parallelogram structure adapted to be sandwiched between first and second planar structures so as to provide a slab for use in buildings. 20. A tessellated parallelogram structure wherein the angle included between any two axially adjacent linear ribbed sections is 60 . 21. A tessellated parallelogram structure formed from a metal . 22. A tessellated parallelogram structure formed from a synthetic plastics material. 23. A tessellated parallelogram structure formed from card . 24. A tessellated parallelogram structure formed from card for use as a package. 25. Apparatus for producing a tessellating parallelogram structure comprising a die and means for urging a preform through the die. 26. Apparataus according to claim 25 wherein at least one roller is arranged to urge the preform through the die. 27. Apparatus according to claim 25 to 26 wherein means is provided to form lines of weakness onto a sheet of material. 28. Apparatus for producing a tessellating parallelogram structure comprising means for urging an edge of a preform towards an opposite edge of the preform. 29. Apparatus according to claim 28 wherein the means * comprises a pneumatic ram. 30. Apparatus according to claim 28 or 29 wherein a height restrictor means is provided ' , so as to limit the height of the structure. AMENDED CLAIMS [received by the International Bureau on 13 Apri l 1992 ( 13.04.92) ; original claims 20 deleted; original claims 1 and 2 amended ; new claims 3-6,9,23,25,26,31 added; remaining claims unchanged but renumbered (7 pages )] 1. A structure comprising a corrugated sheet wherein the ridges on one face thereof are coplanar and of saw-tooth shape extending in an axial ly shaped paral lel relationship , the intermediate nadirs , being in the form of ridges on the opposite side of the sheet, are of identical saw-tooth shape , there being two panels of identical paral lelogram shape joining any two transversely adjacent linear ridge sections characterised in that an angle , included between any two axial ly adjacent linear ribbed sections is substantially 60 . 2 . A structure comprising a plurality of cel ls arranged in an array, the cells comprising first, second, third and fourth sub-groups of planar regions , each region being in the form of a paral lelogram, the sub-groups being arranged in groups such that in a transverse direction a first group of regions comprises alternating members of a first and second sub-group ; and a second group of regions comprises alternating members of a third and fourth sub-group ; and in a transverse direction a third group of regions comprises alternating members of the second and third sub-groups ; and a fourth group of regions comprises members of the first and fourth sub-groups , each member of each sub-group sharing a common interface with members of two different sub-groups along alternating edges characterised in that an angle, included between any two axially adjacent linear ribbed sections is substantially 60 . 3. A structural member comprising a corrugated sheet wherein the ridges on one face thereof are coplanar and of saw-tooth shape extending in an axially shaped parallel relationship, the intermediate nadirs, being in the form of ridges on the opposite side of the sheet, are of identical saw-tooth shape, there being two panels of identical parallelogram shape joining any two transversely adjacent linear ridge sections characterised in that means is provided to restrain lateral movement of the structure within a housing. 4. A structure comprising a plurality of cells arranged in an array, the cells comprising first, second, third and fourth sub-groups of planar regions, each region being in the form of a parallelogram, the sub-groups being arranged in groups such that in a transverse direction a first group of regions comprises alternating members of a first and second sub-group; and a second group of regions comprises alternating members of a third and fourth sub-group; and in a transverse direction a third group of regions comprises alternating members of the second and third sub-groups ; and a fourth group of regions comprises members of the first and fourth sub-groups, each member of each sub-group sharing a common interface with members of two different sub-groups along alternating edges characterised in that means is provided to restrain lateral movement of the structure within a housing. 5. A structure according to claim 1 or claim 2 wherein means is provided to restrain lateral movement of the structure within a housing. 6. A structure according to claim 3 or 4 wherein an angle included between two adjacent linear ribbed sections is substantially 60 . 7. A structure according to any preceding claim wherein the zig-zag lines defining the peaks and troughs are of identical length, the interspacing between adjacent zig-zag lines being defined by the characteristic length of an edge of the parallelogram. 8. A structure according to any preceding claim wherein parallelograms of the array are congruous. 9. A structure according to any preceding claim wherein apertures are provided in the material from which • the structure is formed. 10. A structure according to any claims 1 to 9 wherein the parallelograms in the array are of different sizes and are arranged in a predetermined pattern. 11. A structure according to claim 10 wherein the pattern of parallelograms is such that when the structure is assembled so that they form a fan. 12. A structure according to claim 2 or 4 wherein the first and second groups of parallelograms in the array are substantially parallel to one another so as to define a corrugated sheet which in longitudinal and transverse cross sections define a saw tooth like profile. 13. A structure according to any of claims 1 to 4 which is deformed about an axis parallel to the axis defining a first sub group so as to form a cylindrical or part cylindrical structure. 14. A structure according to any of claims 1 to 4 wherein the structure is deformed about two non linear axes so as to form compound curves. 15. A tessellated parallelogram structure for use in processing vessels so as to promote mixing of substances within the vessel. 16. A structure according to claim 14 for use in closed processing vessels. 17. A tessellated parellelogram structure for use as a separating medium between a first and a second fluid, the first fluid being of a higher temperature than the second fluid, interposition of the tessellated structure between the two fluids so as to promote effective heat transfer from the hotter fluid to the colder fluid. 18. A tessellated parallelogram structure for use as a shock absorber. 19. A structure according to claim 18 wherein different cell sizes are provided within the structure. 20. A structure according to claim 18 or 19 wherein the thickness of the membrane of the structure is varied so as provide different strengths of material. 21. A tessellated parallelogram structure for use as a sound absorber. 22. A tessellated parallelogram structure for use as an energy absorber. 23. A tessellated parallelogram structure for use as an insulator. 24. A tessellated parallelogram structure adapted to be sandwiched between first and second planar structures so as to provide a slab for use in buildings. 25. A tessellated parallelogram structure according to claim 24 wherein the sides of the slab have means arranged to restrain lateral movement of the tessellated parallelogram structure. 26. A tessellated parallelogram structure according to claim 23 wherein the means arranged to restrain comprises planar walls. 27. A tessellated parallelogram structure formed from a metal. 28. A tessellated parallelogram structure formed from a synthetic plastics material. 29. A tessellated parallelogram structure formed from card. J 30. A tessellated parallelogram structure formed from card for use as a package. 31. A tessellated parallelogram structure formed from an absorbant material. 32. Apparatus for producing a tessellated parallelogram structure comprising a die and means for urging a preform through the die. 33. Apparataus according to claim 25 wherein at least one roller is arranged to urge the preform through the die. 34. Apparatus according to claim 27 to 28 wherein means is provided to form lines of weakness onto a sheet of material. 35. Apparatus for producing a tessellated parallelogram structure comprising means for urging an edge of a preform towards an opposite edge of the preform. 36. Apparatus according to claim 30 wherein the means comprises a pneumatic ram. 37. Apparatus according to claim 32 or 33 wherein a height restrictor means is provided, so as to limit the height of the structure.

Inventors: ELLIS COLIN MARK RICHARD, ELLIS, COLIN, MARK, RICHARD
Applicants: ELLIS COLIN MARK RICHARD, ELLIS, COLIN, MARK, RICHARD
Application year: 1991
Main classification: E04C2
IPC codes: B21D13, B31D3, B65D65, E04C2