RU2818055C1 - Method of creating a composite angular connecting element based on solid-woven 3d preform with change in reinforcement structure - Google Patents

Abstract

FIELD: moulding materials.

SUBSTANCE: can be used to create angular connecting element in form of bracket based on composite material with polymer thermosetting matrix. Reinforced 3D solid-woven preform with reinforcing structure forming transition from preform base is made. Preform comprises intertwined four layers of warp threads, five layers of weft threads and a piercing system of threads passing through four layers of the preform base due to change of the reinforcement structure to the outgoing layer. Outgoing layer includes intertwining one layer of warp and one layer of weft threads. Future stiffening rib of the composite material includes four bonded woven layers due to the fact that zones of the outgoing layer are staggered relative to each other when folded. At the first stage, three-dimensional solid-woven 3D preform is made on the basis of continuous carbon threads. At the same time transition from base of solid-woven 3D preform to outgoing layer for future stiffening rib is made with change of reinforcement structure so that the orthogonal weave warp threads, lying horizontally in a straight line in the upper fourth layer of the base of solid-woven 3D preform, change the trajectory, are separated from the middle of the fourth layer of the base of the preform and enter the linen weave of the outgoing layer, preventing pull-out of warp threads and shedding of weft threads of exit layer during further cutting of auxiliary weft threads located at edges and centre of outgoing layer. At the second stage, auxiliary weft threads are cut, enveloping the side parts of the preform, by means of which the transition from the fourth layer of the base of the preform to the fifth outgoing layer is made, and bonding the outgoing layer zones of the preform to each other, along three cutting lines. As a result, the outgoing layer of the preform is divided into four zones. At the third stage, 3D preform is folded twice into the final shape of the article. In the process of the first folding along the first fold line, four zones of the outgoing layer obtained as a result of cuts of auxiliary weft threads at the second stage are opened and preliminary pairwise combination is performed. In the process of the second folding along the second bending line the opened zones of the outgoing layer of the preform are turned in a staggered order. At the fourth stage, tooling mould is made for formation of angular connecting element in the form of bracket. At the fifth stage, folded 3D preform is laid in the tooling mould and impregnated with the binder by the RTM method. At the same time four zones of outgoing layer are transformed into stiffening rib consisting of four woven layers. At the sixth stage, after hardening by the binder, the finished product is removed from the tooling mould. Flash of the outer contour is removed. Through technical holes are formed. Stiffening rib shape is transformed. Chamfers are stitched in angular zones of the bracket.

EFFECT: disclosed is a method of making a composite angular connecting element based on solid-woven 3d preform with a change in the reinforcement structure.

1 cl, 11 dwg

Description

The present invention relates to a method for creating a corner connecting element based on a composite material with a polymer thermosetting matrix, reinforced with a three-dimensional solid-woven 3D preform, forming a transition from the base of the preform, due to a change in the structure of the reinforcement to the outgoing layer, which represents the future stiffener of the composite material, including four bonded woven layers, due to the fact that the zones of the outgoing layer, when folded, are staggered relative to each other.

In particular, the creation method involves the development of a carbon fiber-reinforced composite bracket, increased strength provided by using a change in the structure of the reinforcement. This corner connecting element has a wide range of applications, which can be used in mechanical engineering, the production of satellites and spacecraft, the railway and aviation industries and other industries for connecting and fixing structural elements that are flat panels. However, it should be understood that the composite can be used to fasten a wide variety of structures.

The composite bracket contains a matrix material and reinforcement with carbon continuous threads, while the volumetric reinforcement of the base of the solid woven preform runs in three axial directions.

A seamless 3D preform is a three-dimensional reinforcing lattice woven from carbon threads that matches the size and shape of the future product made of a polymer composite material. In a volumetric seamless 3D preform, all reinforcing elements, which are carbon threads intertwined into a single volumetric structure, are always in the calculated locations, in the designed design position, which ensures constant quality of products and uniformity of physical and mechanical characteristics.

By reinforcing threads we mean continuous carbon threads.

The thermosetting polymer matrix according to this method preferably consists of curable synthetic resins: epoxy, phenol-formaldehyde, not subject to carbonization. Another suitable matrix-forming material is carbon, for example, for creating a carbon-carbon composite material.

The RTM (RESIN TRANSFER MOLDING) method - “transporting resin to tooling”, is a technology for the production of composite products based on impregnation of the reinforcing material with a thermosetting binder.

The basic principle of the method is the injection of resin under pressure into the cavity of a mold containing a blank package made of “dry” reinforcing fiber. During the injection process, the resin spreads throughout the entire volume of the mold cavity, displacing the air present there, and impregnates the fiber.

The RTM method allows you to achieve optimal impregnation characteristics, while improving the lightness, thermal resistance and strength characteristics of the final product.

The bracket obtained by this method is based on a composite material with a polymer thermosetting matrix, reinforced with a three-dimensional solid-woven 3D preform with a reinforcing structure that forms a transition from the base of the preform, including four layers of warp threads intertwined, five layers of weft threads and a stitching system of threads passing through four base layer of the preform, due to a change in the reinforcement structure to the outgoing layer, which includes one layer of warp and one layer of weft threads intertwined with each other, which represents the future stiffener of the composite material, including four bonded woven layers, due to the fact that the areas of the outgoing layer when folded are staggered relative to each other.

In the production technology of a composite corner connecting element, in the form of a bracket, using the RTM method, a composite blank was created based on a volumetric seamless 3D preform in such a way that the transition from the base of the seamless 3D preform to the outgoing layer for the future stiffener was made with a change in the reinforcement structure so that warp threads, orthogonal weave, located horizontally in a straight line in the upper fourth layer of the base of a solid-woven 3D preform change trajectory, are separated from the middle of the fourth layer of the preform base and enter the plain weave of the outgoing layer, preventing the main threads from being pulled out and the weft threads of the outgoing layer fraying during further cutting of the auxiliary weft threads threads located along the edges and center of the outgoing layer.

A seamless preform consists of five seamless layers. The first four layers form the base of the preform, which implies an orthogonal weave formed by intertwining four layers of warp threads, five layers of weft threads and a stitching system of threads passing through the four layers of the preform base, stitching these layers in the vertical direction. The top fifth layer of the preform forms an outgoing layer, intended to form a future stiffener, consisting of four woven layers formed by cutting the auxiliary weft threads connecting the base and the outgoing layer.

The auxiliary weft threads are supposed to be connecting weft threads that go around the side parts of the preform, with the help of which only the transition from the fourth layer of the preform base to the fifth outgoing layer is made, as well as fastening the zones of the outgoing layer of the preform together.

By "orthogonal" here we mean a three-dimensional weave, where each system is mutually perpendicular to the other, corresponding to a rectangular Cartesian coordinate system. There are longitudinal (warp), transverse (weft) and vertical (stitching) systems of threads that form three-dimensional reinforcement in preforms.

The plain weave of the outgoing layer implies the main threads of the preform running perpendicular to the interlacing threads of the weft.

To give the final shape to a seamless 3D preform, the auxiliary weft threads located along the edges and center of the outgoing layer, securing the outgoing layer to the fourth layer of the preform base, are cut along three cut lines, due to which the outgoing layer of the preform is divided into four zones and two folds. In the process of the first fold along the first fold line, the opening and preliminary pairwise alignment of the four zones of the outgoing layer, obtained as a result of cuts of the auxiliary weft threads at the second stage, are performed; in the process of the second fold along the second fold line, the open zones of the outgoing layer of the preform are rotated and combined in a checkerboard pattern. .

Subsequently, during the molding process, the folded 3D preform is placed in the manufactured tooling mold and impregnated with the RTM binding method, in which the four zones of the outgoing layer are converted into a stiffener consisting of four woven layers;

After curing with a binder, the finished product is removed from the mold-equipment, the flash of the external contour is removed, through technical holes are formed, the shape of the stiffener is transformed, and chamfers are ground in the corner areas of the bracket.

Often the connecting elements of many structures used in the production of satellites and spacecraft, the railway and aviation industries, including the construction industry, are made of metal. However, the use of metal has disadvantages - weight and strength of structures.

Modern methods of obtaining materials for the production of aerospace vehicles (satellites) require a significant reduction in weight, resistance to chemical reagents and an increase in strength while maintaining its basic functions, and currently new lightweight composite materials with increased strength and performance characteristics are increasingly used for the manufacture of elements for reliable fixation of node connections and other parts of the device.

The latest scientific developments in the field of composite materials reinforced with special fibers and threads: glass, carbon and organic, have a number of unique properties. For example, the use of carbon fiber in structures can reduce weight by up to 60%. Carbon fiber reinforced plastics are also characterized by: high specific strength, rigidity and impact resistance; low coefficients of thermal expansion and friction; high wear resistance and resistance to aggressive environments, thermal and radiation exposure.

Brackets implementing this invention are not limited to any particular shapes or sizes.

From the existing state of the art, many devices are known for angular connection of parts and flat surfaces. Metal brackets are widely known. Examples of such designs are indicated in patents RU 170021 U1 (F16B 12/44; published 04/11/2017, Patentee Ilya Valerievich Butsaev (RU); “Fasting device”), RU 105382 U1 (F16B 12/44; published 06/10/2011; Patent holder Limited Liability Company "GRANDIS" (RU); “Furniture fastening kit”), RU 155066 U1 (F16B 12/44; published 09/20/2015; Patent holder Fedor Petrovich Shevelev (RU); “Device for connecting furniture parts”) . Currently, metal connecting elements are used as fasteners in a variety of areas, in particular in aggressive environments, in chemical plants or water treatment plants, but there are a number of serious problems that arise during their operation. For example, it can be noted that metal brackets are unsuitable for use in marine structures: boats, artificial reef structures, since constant contact with sea water leads to corrosion and rust, and subsequently to the destruction of structures.

Another approach is to weave a two-dimensional fabric and fold it into a three-dimensional shape so that the panel is rigid as a single unit, that is, the threads are continuously intertwined between the flat base or part of the panel and the stiffening element.

In the prior art, a preform is known for forming a structure having a three-dimensional shape, said preform containing: warp and weft fibers that are intertwined in the woven portion of the preform; a plurality of adjacent warp fibers and a plurality of adjacent weft fibers in a non-woven portion of the preform, where the warp and weft fibers are not interlocked with each other and can move independently of each other; and whereas folding the fabric in a first direction parallel to the warp fibers and in a second direction parallel to the weft fibers causes the non-woven part to collapse, causing the warp and weft fibers in the non-woven part to align with each other so that they are parallel to each other. (patent US6733862B2, IPC B29C70/22; D03D23/00; D03D25/00; D06C7/02, publ. 2004-05-11, Patent holder ALBANY INT TECHNIWEAVE INC [US], “Reinforced product and method of its manufacture”).

The option of giving a shape to the finished product using additional operations of bending, introducing and removing sacrificial fibers into the structure is shown in the example of the invention (patent RU No. 2409712, IPC D03D 15/06, Application: 2008116872/12, 10/16/2006, publ. 20.01. 2011, Patentee: Albany Engineered Composites, Inc. (US), "Angle fitting and a method for forming an angle fitting using fiber transfer." A corner fitting made of folded flat fabric, which includes: a first woven portion having fibers arranged in first and second directions; a second woven portion located adjacent the first woven portion and having fibers located in a first direction and sacrificial fibers located in a second direction; and a third semi-woven portion having fibers located in a first direction and selectively interlocked with sacrificial fibers located in a second direction, wherein when the sacrificial fibers located in the second direction are removed, they are replaced in the second portion by fibers of the third semi-woven portion located in the first direction , to form a corner fitting having continuous fibers connecting all sides.

Compared to the previously discussed analogues, this useful model does not require additional reinforcement of the structure, taking into account the fact that during assembly there is minimal mechanical intervention in the form of cuts in the transition (auxiliary) weft threads, which do not affect the strength of the preform, excluding subsequent possible shedding of the threads , by using a tight plain weave to create the top layer of a 3D woven preform for the stiffener assembly.

There is also no need for additional manual thread pulling operations, since the composite panel is based on a seamless 3D preform.

Known are corner connecting elements made of composite materials obtained by layer-by-layer laying out reinforcing fabrics to obtain a given thickness of the product.

Other methods of solving this problem are based on the concept of introducing high-strength fibers across the joint by using techniques such as stitching the components together, with the expectation that such stitching threads will introduce reinforcing fibers within and across the joint. One such method is disclosed in US Pat. No. 4,331,495 and US Pat. No. 4,256,790, divisional application thereof. These patents disclose connections made between first and second composite panels made of bonded fiber layers. The first panel is bifurcated at one end in a known manner to form two diverging panel contact surfaces located in the same plane, which are connected to the second panel by stitches of an uncured flexible composite thread passing through both panels. The panels and filament are then cured together at the same time.

The disadvantage of this technical solution is the possibility of delamination of the material, since a polymer composite is created on a woven basis by overlapping layers of fabric or fibers made using traditional 2D weaving technology, held together only by a polymer binder. During operation, this composite, made using the prepreg press method, is subject to interlayer shear stress, which causes the layers of the composite to separate under load.

Another method is to weave a two-dimensional ("2D") structure and fold it into a three-dimensional ("3D") form. However, this usually causes deformation of the parts when folding the workpiece. The deformation occurs due to the fact that the length of the fibers when weaving is different from the length of the fibers that is required when folding. As a consequence, wavy folds are formed in areas where the length of the woven fibers is too short, and ties are formed in areas where the length of the fibers is too long. An example of a woven configuration of a three-dimensional blank that can cause folds or loops to occur in areas where the blank is folded is disclosed in US Pat. No. 6,874,543. Fiber blanks with specific structural shapes, such as, for example, 'T', 'I', 'H' or 'P' cross sections, can be woven on a traditional shuttle loom, and several known patents disclose the method weaving such structures (for example, in US patents No. 6446675 and No. 6712099). However, all known blanks have been designed such that the cross-section is constant in the direction of the warp fibers and the weft fibers, i.e. The intersections of the shelves and vertical legs are always in the same position across the width and length of the workpiece.

The closest to the claimed technical solution is a corner insert blank (patent RU 2604444 C2, IPC C08J 5/00, publ. 12/10/2016, Patent holder ALBANY ENGINEERED COMPOSITES, INC. (US), “Corner insert blanks and method of their manufacture” ). According to one aspect of the invention, there is provided a method for forming a corner insert blank, comprising the steps of completely interweaving a base or base material with one or more elongated elements that extend from the base. The flattened woven preform contains specially designed areas within the cores and flanges that contain continuous warp yarns that are not interlaced. The non-intertwined areas provide a hinge structure that allows the elongated workpiece elements to be bent around a corner. After folding, the excess unwoven warp threads are pulled back through the woven portion of the rods and flanges to produce a reinforcement of continuous reinforcing warp threads around the corner.

Disadvantages of this technical solution:

The stiffener obtained in this way has a line of stress concentrators at the points of reversal (inflection) of the reinforcing threads by 90 ^° .

When an extension load is applied to this corner insert, along this line of concentrating points, the load on the rupture of the stiffener will be concentrated, going along the weakest points, where, due to the geometry of the product, a small bending force will turn into several times a greater load on the rupture going exactly along the line Inflection points of the reinforcing threads (stress concentrator points) result in a technologically generated rupture line. In addition, manually pulling threads does not provide consistent quality and is a labor-intensive and unstable technological operation.

Thus, the main disadvantages can be called: the weakness of the structure to mechanical loads; high labor intensity and instability of technological operations of pulling threads and forming the final shape of the workpiece.

Also distinguished from the existing state of the art is a method of weaving a fiber preform with legs in such a way that the legs are not necessarily straight, extending in the direction of the warp and/or weft. An exemplary embodiment of the invention provides a U-shaped blank with sinusoidal legs, that is, vertical legs extend along a sinusoid in the direction of the warp and/or weft.

For example, a sine wave is formed by selectively removing some warp fibers from portions of the workpiece forming one of the vertical legs while adding warp fibers to the other vertical leg. For example, to move the legs to the left in the weft direction, warp fibers are removed from the base of one vertical leg and simultaneously added to the base of the adjacent vertical leg. Likewise, the reverse action can be performed to move the legs to the right. (patent RU 2530378 C2, IPC D03D 25/00, publ. 10-10-2014, Patentee ALBANY ENGINEERED COMPOSITES, INC. (US), “U-shaped blank”).

The disadvantage of this technical solution is the high labor intensity and complexity of manual operations of adding and removing warp threads when forming the workpiece. As well as instability of the physical and mechanical characteristics of the product as a result of complex and unique manual operations.

This invention eliminates all of the above-mentioned disadvantages of analogues, since the reinforcing solid-woven 3D preform is completely formed by an automatic 3D weaving machine in a uniform automatic mode for solid-woven bulk-reinforcing preforms, and has such physical and mechanical characteristics as no delamination, increased resistance to damage, improved impact resistance, high durability, high strength near holes and fasteners.

Also, the main condition for obtaining high-quality composite materials is the preservation of the strength properties of the reinforcing threads, because they are the main load-bearing element of the material.

A feature of three-dimensional reinforcement is to ensure the continuity of fibers in the preform. Thus, it is possible to minimize the loss of structural strength in the nodal zones where the ribs intersect, while maintaining the integrity of the reinforcement during the transition from one structural element to another. In a three-dimensional fabric, fibers of one type run perpendicular to other fibers, that is, the fibers are located along the X, Y and Z axes.

The essence of the work of reinforcing threads is to strengthen and strengthen the internal bonds of the future composite due to the uniform distribution of the load throughout the entire volume of the product.

Thus, the strength and rigidity of the composite itself is determined by the properties of the reinforcing filler, in this case, a three-dimensional seamless 3D preform made of carbon threads. Therefore, the advantages of this invention include the fact that the auxiliary weft threads used also form the structure and reinforcement system of a voluminous whole-woven preform. The change in the reinforcement structure is made in such a way that when cutting these auxiliary weft threads, the structure does not weaken; in addition, due to the addition of the formed upper zones of the preform, the stiffening rib is formed from four layers, which is comparable to the four layers of the whole-woven base of the preform, which in turn is connected with each zone to create a stiffener by changing the reinforcement structure.

The technical problem to be solved by the claimed invention is the development of a method for creating a lightweight structure of a composite corner connecting element, in the form of a bracket, with increased shear and shear strength, by creating a 3D reinforcement structure that strengthens the stiffener rib of the finished product, preventing pulling out of the main threads and fraying weft threads of the outgoing layer.

This problem is solved due to the fact that the claimed method of creating a corner connecting element in the form of a bracket based on a composite material with a polymer thermosetting matrix is reinforced with a three-dimensional all-woven 3D preform with a reinforcing structure that forms a transition from the base of the preform, including four layers of main threads intertwined with each other, five layers of weft threads and a stitching system of threads passing through four layers of the base of the preform, due to a change in the reinforcement structure to the outgoing layer, which includes one layer of main and one layer of weft threads intertwined, which represents the future stiffener of the composite material, including four fastened woven layer, due to the fact that the zones of the outgoing layer, when added, are staggered relative to each other.

A volumetric seamless 3D preform, based on continuous carbon threads, is made in such a way that the transition from the base of the preform to the outgoing layer, for the future stiffener, is made with a change in the reinforcement structure so that the warp threads, orthogonal weave, are located horizontally in a straight line in the upper fourth layer of the base whole-woven 3D preforms change trajectory, separate from the middle of the fourth layer of the preform base and enter the plain weave of the outgoing layer, preventing the main threads from being pulled out and the weft threads of the outgoing layer fraying during further cutting of the auxiliary weft threads located along the edges and center of the outgoing layer.

With further cutting of the auxiliary weft threads that go around the side parts of the preform, with the help of which the transition is made from the fourth layer of the base of the preform to the fifth outgoing layer, and fastening the zones of the outgoing layer of the preform to each other, along three cut lines, the outgoing layer of the preform is divided into four zones.

Next, two folds of the 3D preform are made into the final shape of the product; in the process of the first fold, along the first fold line, the opening and preliminary pairwise alignment of the four zones of the outgoing layer are performed, obtained as a result of cuts of the auxiliary weft threads at the second stage; in the process of the second fold, along the second fold line, turning and combining the open zones of the outgoing layer of the preform in a checkerboard pattern.

Afterwards, a mold-equipment is made to form a corner connecting element in the form of a bracket and a folded 3D preform is placed in it, impregnated with the RTM binding method, during which the four zones of the outgoing layer are converted into a stiffener consisting of four woven layers.

After curing with a binder, the finished product is removed from the mold-equipment, the flash of the external contour is removed, through technical holes are formed, the shape of the stiffener is transformed, and chamfers are ground in the corner areas of the bracket.

The technical result provided by the given set of features is a method of creating a lightweight structure from a polymer composite material, in the form of a bracket, based on a volumetric seamless 3D preform, a corner connecting element of increased structural integrity, impact resistance and load resistance, preventing weakening of the reinforcing structure of the product with minimal mechanical stress processing and ensuring higher strength of the finished product.

The technical result is achieved due to the fact that the finished reinforcing structure of the claimed composite element, consisting of a volumetric seamless 3D preform based on carbon threads and a polymer matrix, contains five seamless layers, in the spatial (volumetric) structure of which a change in the reinforcement structure is provided, strengthening the solid woven rib rigidity and preventing the warp threads from being pulled out of the sections of the upper layer of the 3D woven preform when cutting the connecting weft threads, and thereby providing the possibility of introducing reinforcement in the form of a stiffener rib.

The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the accompanying drawings. For purposes of illustrating the invention, the drawings show an embodiment which is currently preferred. However, it should be understood that the invention is not limited to the precise circuits and tools shown.

The pictures show:

Fig. 1a – Photograph of the finished composite connecting element, in the form of a bracket, front view;

Fig.1b – Photograph of the finished composite connecting element, in the form of a bracket, isometric;

Fig. 2a – Photograph of a three-dimensional solid-woven 3D preform removed from the machine, top view;

Fig. 2b – Scheme of a three-dimensional solid-woven 3D preform removed from the machine, with pre-designated zones and cut lines, top view;

Fig. 3a – Photograph of a three-dimensional seamless 3D preform at the first stage of folding;

Fig. 3b – Scheme of a three-dimensional seamless 3D preform at the first stage of folding;

Fig.4a – Photograph of a three-dimensional seamless 3D preform at the second stage of folding, front view;

Fig.4b – Scheme of a three-dimensional seamless 3D preform at the second stage of folding, front view;

Fig. 5a – Photograph of a three-dimensional seamless 3D preform at the second stage of folding, isometric;

Fig. 5b – Scheme of a volumetric seamless 3D preform at the second stage of isometric folding;

Fig.6 – Diagram of the longitudinal section of a three-dimensional seamless preform.

One embodiment involves creating a corner connecting element 1 (Fig. 1a, Fig. 1b), in the form of a bracket, based on a composite material with a polymer thermosetting matrix, which is an epoxy resin, reinforced with a three-dimensional seamless 3D preform 2 (Fig. 2a), in a predetermined structure comprising multiple interlocking woven layers made using continuous carbon filaments.

The corner connecting element 1 (Fig. 1) has a stiffener 4, designed to accept the load in order to maintain the strength of the entire structure.

Also in figure 1 there are four through technical holes 3 located in the corner parts of the structure, intended for fastening the parts to be connected. And also four ground chamfers in the corner areas of the composite for smooth structural contours and weight reduction.

Figure 2a is a photograph of a three-dimensional seamless 3D preform2. Figure 2b shows a refinement diagram to figure 2a.

In Fig. 2a and Fig. 2b, the outgoing layer of the volumetric seamless 3D preform 2 is divided into four zones 5,6,7,8 for clarity. Red lines mark three cutting lines of 11 auxiliary weft threads to subsequently give the final shape of the product before molding, which are located parallel to the main threads.

Fig. 3a is a photograph of the preform after cutting the auxiliary weft threads, which allows the first fold to be formed by opening the areas 5,6,7,8 of the outgoing layer.

Fig. 3b is an explanatory diagram for Fig. 3a, where a blue line marks the line of the first fold 9, at which the opening of zones 5,6,7,8 of the outgoing layer of the volumetric seamless 3D preform 2 and their separation from the base 12 occurs. second addition 11, highlighted in blue, and refers to the base 12 of the preform, this can be seen more clearly in Fig. 4b and Fig. 5b. The arrows indicated by the dotted line show the direction of the first addition of zones 5,6,7,8, by first combining zone 5 with zone 6, and, accordingly, zone 7 with zone 8. The diagram also shows explanatory lines corresponding to the direction of the main threads X (orange arrows ), weft threads Y (black arrows) and stitching threads Z (green arrows).

Fig. 4a – Photograph of a three-dimensional solid-woven 3D preform 2 at the second stage of folding, at which the base of the preform 12 is folded along line 11, as well as the rotation of zones 5 and 6 and the parallel alignment of the open zones of the outgoing layer of the preform in a checkerboard pattern, that is, in numerical order 7,5,8,6.

Fig. 4b more clearly demonstrates the folding structure of the photograph in Fig. 4a.

The photograph (Fig. 5a) and its clarifying diagram (Fig. 5b) show an isometric view of a volumetric seamless 3D preform 2.

Figure 6 shows a longitudinal section of a volumetric seamless 3D preform.

As a result of the development of the technological process for manufacturing a preform for a future product, a filling map was drawn up, which took into account the features of the formation of volumetric structures for the reinforcement of the corner connecting element. Based on the developed technological map, a model of the reinforcement structure was compiled, in which the reinforcing carbon fibers are located in the X-Y-Z directions (Fig. 6), that is, the threads of the X axis in weaving correspond to the system of warp threads, the threads of the Y axis - the system of weft threads, and the threads of the Z axis - stitching thread system.

In Fig.6. the orange lines, indicated by the letter X, represent the main fibers, running parallel to the observer’s eye and along the length of the preform, and the black circles, also located parallel to the plane of the preform, but in the direction along its width, represent the weft fibers - Y. And the third reinforcing system of stitching threads, located along the height, perpendicular to the plane of the preform, is depicted in figure 6 in the form of vertical green lines, and is designated by the letter Z.

Also in Fig.6 it is shown that, for example, in this preform there are four layers of main threads X at the base 12 and one additional layer, which is the zone of the outgoing layer for the future stiffener 4 of the finished product.

Additional layers may be added to increase the thickness of the base 12, as may be apparent to one skilled in the art.

Volumetric seamless preform 2 (Fig. 2a) was created using an automated 3D weaving complex. The preform has a base of four layers and a solid-woven layer extending from it, which corresponds to the future stiffening rib of the finished product, initially connected to each other and the base by one layer of auxiliary weft threads.

After the production of a three-dimensional solid-woven 3D preform, one layer of auxiliary weft threads is cut, connecting the zones of the outgoing layer of the future edge of the preform with each other and between the solid-woven base of the preform.

For clarity (Fig. 3b, Fig. 4b, Fig. 5b), the base 12 of the preform was divided into parts 13,14,15,16.

The reinforcement of the preform is implemented in such a way that the main threads X from each part 13-16 of the fourth layer of the base 12 pass into the main threads of zones 5,6,7,8 of the outgoing layer. In this case, there is a transition from orthogonal to plain weave.

Accordingly, the warp threads X from the part 13 of the base 12 formed by the orthogonal weave pass into the warp threads of the plain weave zone 6; the main threads X from part 14 of the base 12, , pass into the main threads of zone 5; the main threads X from part 15 of the base 12 pass into the main threads of zone 8; and the warp threads X from part 16 of the base 12, , pass into the warp threads of zone 7.

That is, the first four layers of the base 12 of the preform 2 are made using an orthogonal weave, and the fifth layer of the 3D woven preform is formed by a plain one, which is an interweaving of only two systems of threads: warp X and weft Y, located perpendicular to each other.

To give the volumetric whole-woven 3D preform the shape of the final product, three longitudinal cuts 10 are made (red lines in Figs. 2a, 2b), auxiliary weft threads located only in the transition layer, between the fourth base layer and single-layer whole-woven zones 5,6,7,8 outgoing layer.

To give the final form of this invention, two additions are made.

The first stage of folding consists of opening and preliminary combining zones 5 and 6, and zones 7 and 8 along the first fold line 9, parallel to the weft threads Y, as shown in figure 3b.

The second stage of folding occurs along the fold line 11, due to the placement of sections 13,14, base 12, perpendicular to sections 15 and 16. The line of the second fold is parallel to the main fibers X and perpendicular to the weft fibers Y (Fig. 3b).

During the second stage of folding, the opened zones of the upper layer of the preform are also folded and rotated in a checkerboard pattern, that is, in order of numbers 7,5,8,6 (Fig. 4b). When laying such a configuration of zones of a preform layer with a plain weave, the reinforcement structure is doubled (increased in strength), since in zones 5, 6 when folded, the warp threads X run perpendicular to the main threads X running at the base 12 of the preform in the X-Y plane. weft Y also become perpendicular to the weft threads of base 12, but already relative to the Y-Z plane.

As for zones 7, 8, when folded, the main threads X become perpendicular to the main threads X of the base 12 of the preform 2 relative to the X-Z plane, and the weft threads Y remain parallel to the weft threads Y of the base 12 of the preform 2, as shown in figures 3b, 4b ,5 B.

The dense fabric structure of zones 5-8 of the future rib prevents fraying of the weft threads during the folding stages.

In the technology for the production of a composite corner connecting element, in the form of a bracket, using the RTM method, a composite blank was created based on a volumetric seamless 3D preform 2, which was placed in a mold-equipment and impregnated with a binder using the RTM method, in which, by changing the structure of the reinforcement, zones are transformed 5-8 preforms into a full-fledged stiffener 4 by opening them and combining them in a checkerboard pattern and compacting them during the molding process in the tooling, using minimal mechanical processing, without damaging the integrity of the reinforcing structure.

By minimal mechanical processing we mean removing the flash of the external contour, forming through technical holes 3 intended for fastening various flat surfaces, transforming the shape of the stiffener and bringing it to a rational minimum size. In corner areas, chamfers are ground to ensure smooth structural contours and reduce weight.

The diameter and thickness of each of the X, Y, Z reinforcing continuous carbon filament systems constituting the elongated woven material of the bulk woven 3D preform can be varied in accordance with the mechanical strength required for the corner connector (Fig. 1a).

As the composite matrix used in the present utility model, epoxy resins, unsaturated polyester resins, vinyl ester resins, epoxy acrylate resins, phenolic resins and the like may be mentioned. Epoxy resins are preferred for various desirable properties such as bond strength, tensile strength, flexural strength, electrical insulation properties and non-cure shrinkage.

As can be seen from the above, a composite corner connector having physical strength sufficient for practical use can be easily manufactured from a 3D solid woven resin-impregnated preform.

Thus, the bracket member of the present invention can be manufactured at a lower cost than the traditional prepreg press method, which requires not only the step of preparing prepreg sheets, but also the step of laying multiple prepreg sheets into a stack of a predetermined thickness.

The claimed corner connecting element is manufactured in an industrial environment using equipment for the production of composite products.

In addition to high strength, brackets made in accordance with this invention are characterized by excellent corrosion resistance, and carbon matrix composite brackets are additionally characterized by high heat resistance. Accordingly, the present invention is particularly suitable for use in joining elements consisting of composite materials, ceramics, carbon or graphite, which are subject to high thermal stress or are exposed to chemical attack. Such corner connectors are very important in key areas such as aerospace and defense engineering.

The promising nature of the three-dimensional weaving method is indicated by the fact that the production of highly and complexly loaded parts from polymer composite materials is difficult, and in some cases impossible, without the use of three-dimensional reinforcing structures.

Thus, if the technologies for manufacturing polymer composites based on woven preforms can be considered mainly implemented in various areas of industry using products from polymer composite materials, then volumetric seamless 3D preforms are used more rarely, although they are extremely promising. The implementation of volumetric woven preforms in modern high-tech production leads to the production of products with specified physical and mechanical properties, reducing the labor intensity of manufacturing products, with the prospect of production automation. The development and application of these solutions in high-tech sectors of Russian industry will provide additional impetus for the production of new types of equipment.

Claims (7)

A method for creating a corner connecting element in the form of a bracket based on a composite material with a polymer thermosetting matrix, reinforced with a three-dimensional solid-woven 3D preform with a reinforcing structure that forms a transition from the base of the preform, including four layers of warp threads intertwined, five layers of weft threads and a stitching system of threads, passing through four layers of the preform base, due to a change in the reinforcement structure to the outgoing layer, which includes one layer of warp and one layer of weft threads intertwined, which represents the future stiffener of the composite material, including four bonded woven layers, due to the fact that the zones When folded, the outgoing layer is staggered relative to each other, differing in that it includes the following stages: at the first stage, a three-dimensional all-woven 3D preform is made on the basis of continuous carbon threads in such a way that the transition from the base of the all-woven 3D preform to the outgoing layer for the future stiffener is made with a change in the reinforcement structure so that the warp threads, orthogonal weave, are located horizontally in a straight line in the upper fourth base layer of a seamless 3D preform, change trajectory, separate from the middle of the fourth layer of the preform base and enter the plain weave of the outgoing layer, preventing the main threads from being pulled out and the weft threads of the outgoing layer fraying during further cutting of the auxiliary weft threads located along the edges and center of the outgoing layer; at the second stage, the auxiliary weft threads are cut, going around the side parts of the preform, with the help of which the transition is made from the fourth layer of the preform base to the fifth outgoing layer, and fastening the zones of the outgoing preform layer to each other, along three cut lines, due to which the outgoing layer of the preform is divided into four zones; at the third stage, two folds of the 3D preform are made into the final shape of the product; during the first fold, along the first fold line, the opening and preliminary pairwise combination of four zones of the outgoing layer are performed, obtained as a result of cuts of the auxiliary weft threads at the second stage, during the second fold, along the second line the fold is rotated and the open zones of the outgoing layer of the preform are combined in a checkerboard pattern; at the fourth stage, a mold-equipment is made to form a corner connecting element in the form of a bracket; at the fifth stage, the folded 3D preform is placed in a tooling mold and impregnated with the RTM binding method, during which the four zones of the outgoing layer are converted into a stiffener consisting of four woven layers; at the sixth stage, after curing with a binder, the finished product is removed from the mold-equipment, the flash of the external contour is removed, through technical holes are formed, the shape of the stiffener is transformed, and chamfers are ground in the corner areas of the bracket.