CH717056A1 - Flat body made of fiber-reinforced plastic as part of a piece of sports equipment. - Google Patents

Abstract

A flat body made of fiber-reinforced plastic as part of a piece of sports equipment for power transmission is shown and described. The flat body has a plastic matrix and fibers received in the plastic matrix and is manufactured using an injection molding process. According to the invention, the surface of at least one of the two flat sides (21) of the body is formed at least in some areas by a unidirectional fiber fabric (25).

Description

TECHNICAL FIELD OF THE INVENTION

The invention relates to a flat body made of fiber-reinforced plastic as part of a sports device for power transmission according to the preamble of claim 1. The invention also relates to a method for producing a flat plastic body as part of a sports device.

BACKGROUND OF THE INVENTION

It is generally known that fiber reinforcements increase the mechanical properties of plastics and thus improve the use of plastics under stress in the use of sports articles. Functional layers of fabric have also been attached for a long time, which reinforce the surface and thus generate a general increase in bending resistance.

These reinforcements by pre-impregnated with thermosetting or thermoplastic fiber fabrics, so-called pre-pregs consisting of fiber fabrics with longitudinal and transverse weft fibers, are usually applied over the entire surface and are expensive to use and especially to process. A targeted control of the mechanical properties is only possible to a limited extent, since the fiber direction not required for reinforcement has a disruptive influence on the pressure side of a system that is subject to bending due to the longitudinal and transverse fiber direction of the fiber fabric. The current solutions on the market exclusively use fiber fabrics which, like a matrix, provide all or parts of a plastic sports device with a reinforcing fiber fabric on both sides close to the surface. Various solutions are in use for this, such as in water sports in the use of wave boards as surfing fins for demanding use at high speeds and rapid changes of direction and curve radii.

In EP 3102482A1 a surfboard is disclosed which has fins made with fiber-reinforced plastic. The outer surface of the fin comprises a so-called pre-preg, which has a fiber fabric with longitudinal and transverse weft fibers. The fin is manufactured in an injection process, whereby the injected polymer is a different polymer than the polymer impregnated in the fiber fabric. The inner core of the fin is formed by a further third material with a lower density. The use of fiber fabrics as the outer surface for the fin leads to the use of fibers which, due to their orientation, make no contribution to the flexural rigidity of the fin and thus only ensure higher material and manufacturing costs. At the same time, the use of different polymers leads to a multi-layer structure of the fin with different material properties.

TASK

It is therefore an object of the present invention to propose an alternative flat body made of fiber-reinforced plastic as part of a piece of sports equipment for power transmission with lower manufacturing costs. Furthermore, it is an object of the invention to make targeted use of the mechanical properties of the fibers in a flat body made of fiber-reinforced plastic as part of a piece of sports equipment for power transmission. Another object of the invention is to provide a method for manufacturing such a body.

DESCRIPTION

The object is achieved with a flat body made of fiber-reinforced plastic as part of a sports device for power transmission with the features of claim 1. Further developments and / or advantageous design variants are the subject of the dependent claims.

The invention relates to a flat body made of fiber-reinforced plastic as part of a sports device for power transmission, the flat body having a plastic matrix and fibers received in the plastic matrix and being manufactured by injection molding. According to the invention, the surface of at least one of the two flat sides of the body is formed at least in some areas by a unidirectional fiber structure. The direction of a flat body, which is mainly subjected to bending, is usually that which is perpendicular to the flat side of the body. The introduction of continuous fibers in the surface of these flat sides enables the bending behavior of the body to be changed. The use of unidirectional fiber scrim, which at least partially forms the surface of the flat sides, enables the optimal use of the fiber properties to improve the bending behavior of a flat body. The bending stress of a flat body causes tensile stress on one flat side, while the opposite side is stressed in compression. The fibers embedded in plastics show a pronounced anisotropic behavior for absorbing forces and have excellent properties for absorbing tensile forces in the direction of the fibers. The subject matter of the invention aims, among other things, at making maximum use of this property of the fibers embedded in a plastic by choosing, among other things, the direction of the fibers in the plastic body in such a way that the fibers bear the tensile forces resulting from the bending of the plastic body be able to record. The targeted alignment of the fibers leads to the most effective possible use of the fibers and thus to the lowest possible manufacturing costs for a fiber-reinforced plastic body which is used as part of a piece of sports equipment for power transmission.

For the injection molding process with which the flat body is produced, a polymer is used which is similar to the polymer impregnated on the fibers of the unidirectional fiber structure.

In order to increase the flexural rigidity of a flat body, the axial moment of area of the 2nd degree and thus also the moment of resistance must be increased. The following relationship applies to rectangular elements: I: moment of area 2 degrees, b = width h = height of the rectangle.

Because of the aspect ratios, for the devices of this invention the relationship I device ~ a <3> applies in a simplified manner, where a is the distance between the edge fiber or surface of the continuous fiber reinforcement and the bending axis.

When the flat body is bent, the modulus of elasticity also plays an important role in addition to the moment of area. The deflection is determined by solving the following differential equation: M = -E · I · ω '', with M = bending moment, E = modulus of elasticity and ω = deflection

This equation states that the higher the modulus of elasticity and the axial moment of area, the lower the curvature of the flat body. A slight curvature means a slight deflection over a certain length. This is achieved with a high level of flexural rigidity. A high level of flexural rigidity is achieved by arranging continuous fibers that are parallel to the bending axis but also as far away from it as possible. Accordingly, in a flat body, the fibers must come to lie as close as possible to the surface of the flat sides of the body.

Advantageously, both flat sides of the flat body are formed by a unidirectional fiber structure. This makes it possible to make use of the properties of the fibers on both flat sides of a flat body. This increases the section modulus in both directions perpendicular to the flat side.

The bending properties of a body can be specifically influenced by the predetermination of the displacement ω with the help of the following formula:

The flexural rigidity of the entire device E · I is composed of the flexural rigidity of the plastic used as a matrix and that of the continuous fiber reinforcement in a linear combination.

In a preferred embodiment, the area of the flat side of the body, which is formed by a unidirectional fiber structure, forms at least 40%, preferably at least 60%, of the area of the flat side. The flexural rigidity of the flat body is controlled in a targeted manner by geometrically reducing the surface areas of the unidirectional fiber structure. The ratio of the areas with a unidirectional fiber structure to the total area of the flat side defines a geometry factor which is multiplied by the bending stiffness to determine the bending behavior of a flat body. The selection of the areas on the flat side, which are formed from unidirectional fiber fabric, also influences the torsional strength of the flat body. In addition to a desired flexural strength, a desired torsional strength can also serve as the basis for determining the areas that are to be covered by unidirectional fiber fabrics.

The flat body advantageously has a thermoplastic matrix. The use of a thermoplastic polymer enables the flat body to be produced more easily. The thermoplastic polymer is the ideal plastic for use in an injection molding process. As already mentioned above, the flexural rigidity is formed by the product of the modulus of elasticity E and the moment of area I. The selection of the polymer has a direct influence on the flexural rigidity of the flat body. Ideally, the polymer used in the flat body has a modulus of elasticity of 1000 MPa to 20,000 MPa.

In a preferred embodiment, the unidirectional fiber scrim is provided in each case as a tape. Ideally, the tape is a flexible tape. The use of a tape as the starting material for the unidirectional fiber structure allows the use of standard products that are common and readily available on the market. The simple accessibility and great availability of such tapes reduce the costs for the production of the flat body. The thickness of the tape is chosen so that flexibility of the tape is always guaranteed and the tape can be rolled up on a roll. The thickness of the tape and thus also that of the unidirectional fiber structure is between 0.1 and 1.0 mm.

The areas of the flat sides of the flat body together are preferably at least 5 times larger than the total area of the remaining sides combined. The influence of the fibers of a unidirectional fiber structure, which at least partially forms a flat side of a body, comes into play as long as this flat side takes on a dominant side in terms of size in the body. This dominance is guaranteed if the sum of the area of the flat sides together is at least 5 times larger than the total area of the remaining sides.

Preferably, the ratio of the length to the thickness of the flat body is at least 5. Since it is a flat body, the maximum extent of a flat side represents the length of the flat body. The thickness of the flat body is the extent perpendicular to the flat side of the body. The unidirectional fiber scrim, which forms at least one of two flat sides of a flat body at least in some areas, has a greater influence on the flexural rigidity of a flat body if it has a ratio of its length to its thickness of at least 5.

In a further preferred embodiment, the wall thickness of the flat body is a maximum of 20 mm, in particular a maximum of 15 mm. The application of the invention is limited to flat bodies which, in one possible embodiment, can have a limited wall thickness.

The fibers of the unidirectional fiber structure are advantageously carbon fibers. The carbon fibers have the advantage over other materials that they can have a smaller diameter. In addition, due to their low density, they have a low mass, which can have a beneficial effect on the weight of the flat body. It is conceivable that the fibers can be glass fibers or natural fibers. The selection of the material for the fibers can also influence the thickness of the unidirectional fiber structure.

The unidirectional fiber fabric preferably has a fiber content of 30% to 70%, in particular from 50% to 70%. Most of the fibers absorb the forces acting on the flat body, while the plastic matrix ensures that the fibers are bonded and held together within the plastic body. The aim is to achieve an optimal range of the proportion of fibers compared to the matrix in which the advantages of both materials come into play.

The direction of the fibers in the unidirectional fiber structure preferably runs in such a way that a desired flexural rigidity of the flat body is achieved. A setting of the fiber angle α, which represents an angle between the main axis and the fibers in the unidirectional fiber structure, is dependent on the contour of the flat body and the main load direction of the bending stress on the flat body. The desired bending properties by setting the fiber angle α can be determined by finite element simulation or by empirical tests.

The present invention also relates to a method for producing a flat plastic body as part of a sports device, in which at least one of the two opposite flat sides of the plastic body is formed at least in some areas by a unidirectional fiber fabric. The production has the following process steps; the unidirectional fiber scrim is cut out of a flexible tape in the form of the flat side of the flat plastic body, an injection mold preferably consisting of two halves with a cavity corresponding to the plastic body to be produced is produced, the cut-out fiber fabric is placed in the injection mold and placed against one of the mold halves, the injection mold is closed and injected with a thermoplastic material and then the plastic body is removed.

The method is characterized in that the fibers in the flexible tape are unidirectional and are preferably carbon fibers.

Advantageously, both opposite flat sides of the plastic body to be produced are formed by a unidirectional fiber fabric.

Said optional features can be realized in any combination as long as they are not mutually exclusive. In particular where preferred ranges are given, further preferred ranges result from combinations of the minima and maxima mentioned in the ranges.

BRIEF DESCRIPTION OF THE FIGURES

Further advantages and features of the invention emerge from the following description of exemplary embodiments of the invention with reference to schematic representations. In a schematic representation not true to scale: FIG. 1: a side view of a surfboard fin with a side surface which is formed in some areas by a unidirectional fiber fabric; FIG. 2: the same view of the fin as in FIG. 1 with a symbolic representation of the direction of the fibers; FIG. 3: a horizontal section through the surfboard fin from FIGS. 1 and 2; FIG. 4: a side view of a further fin with two areas on the flat side without unidirectional fiber layers; FIG. 5: a plan view of a paddle blade with a receiving device for a shaft; FIG. 6: a side view of the paddle blade from FIG. 5 showing the area of the unidirectional fiber structure and the direction of the fibers; and FIG. 7: a side view of a hockey stick with a trowel, which in some areas has a unidirectional fiber structure.

DETAILED DESCRIPTION OF THE FIGURES

In the following, the same reference numbers stand for the same or functionally identical elements (in different figures). An additional apostrophe can be used to differentiate between similar or functionally identical or functionally similar elements in a further embodiment.

In Figure 1, a fin 11 is shown, which is ideally attached to a surfboard (not shown here). The side view of the fin 11 in FIG. 1 indicates a triangular shape of the fin 11. The longest edge of the fin 11 is the attack edge 13. Of the two shorter edges, that is the base edge 15, which comes to rest on the surfboard. The rear edge 17 is almost the same length as the base edge and almost forms a right angle with it. The fin 11 is attached to its base on the surfboard. The base side of the fin 11 is that side on which the base edge 15 is located and is perpendicular to the plane of the drawing. On the base of the fin 11, two lip-like projections of different lengths are provided, which engage in recesses provided for this purpose on a surfboard and ensure that the fin 11 is attached to the surfboard. The rear edge 17 has a bend in the direction inward of the triangular surface. The attack edge 11 also has a bend in the area in front of the point of intersection with the rear edge 17, as a result of which the rear edge 17 is shorter than if the attack edge 13 were straight.

The area which is spanned by the three edges 13,15,17 described above represents the flat side 21 and thus the largest area of the fin 11. A region 23 of this flat side 21 is formed by a unidirectional fiber fabric. In the following, the area which forms the surface of the flat side with the unidirectional fiber fabric is referred to as the fiber-reinforced area 23.

In Figure 2, the fin 11 is shown in the same view as in Figure 1, but the direction of the fibers 25 in the fiber-reinforced area 23 of the flat side 21 is also shown. The fibers 25 shown do not correspond to the total number of fibers in the fiber-reinforced area 23, but are only intended to represent the direction of the fibers 25. Contrary to the illustration in FIG. 2, the fiber-reinforced area 23 of the flat side 21 is completely offset with fibers. The fibers 25 run parallel to one another and ideally extend from one edge to the other edge of the fiber-reinforced area 23. Depending on the orientation of the fibers, a fiber can run from one edge to the opposite edge or to the adjacent edge of the fiber-reinforced area 23.

The fiber-reinforced area 23 covers a certain area of the flat side 21 of the fin 11. This area is selected in such a way that both the flexural rigidity and the torsional rigidity of the fin 11 exhibit a desired behavior. In the fin 11 shown in FIGS. 1 and 2, this area, along with the attack edge 13 and the base edge 15, is spanned by an additional edge 27. The additional edge 27 defines the separation from the fiber-reinforced area 23 to the non-fiber-reinforced area of the flat side 21 of the fin. The additional edge 27 is arranged almost parallel to the rear edge 17 and intersects the base edge 15.

In FIG. 3, a section through the fin 11 that is parallel to the base side and is applied approximately in the center is shown. The fiber-reinforced area 23 extends over the longer edge 13 on both flat sides 21, 21 'of the fin 11. The dividing line in FIG real object not to be found like this. The reason for this is that the plastic matrix of the fiber-reinforced area 23 is the plastic from which the flat body is also made.

In FIG. 4, the same fin is shown as in FIG. 1, with the unidirectional fiber structure in this fin 11 covering a different area of the flat side of the fin 11. In this embodiment there are two edges 27, 27 'which form a separation between the fiber-reinforced area and the non-fiber-reinforced area. The first edge 27 also runs in this embodiment from the rear edge 17 to the base edge 15. It assumes a shape similar to a quarter circle with the point of intersection of the two short edges 15, 17 as its center. The second edge 27 'also has a shape similar to a circular arc, but it runs from the attack edge 13 to the rear edge 17 and the point of intersection of these edges roughly defines the center of this circular arc. The selection of a different area for covering the flat side 21 of a fin 11 with a unidirectional fiber structure leads to a different behavior of the fin 11 with regard to bending and torsion. This is because both the flexural strength and torsional strength of the fin 11 are changed in their surface by the fiber-reinforced plastic layer. With the direction of the fibers 25 and the area 23 of the flat side 21 of a body with a unidirectional fiber structure to be covered, a specific flexural and torsional strength can be achieved in a targeted manner.

In Figure 5, a paddle blade 31 is shown. The paddle blade 31 has a device 33 for receiving a shaft (not shown here). The receiving device 33 is arranged such that the shaft of the paddle can be inserted into the receiving device 33 in the longitudinal direction of the paddle blade 31. The paddle blade 31 has a slight curvature. The inner side of the curved paddle is the bottom 35, whereupon the outer side of the curved paddle defines the top 37 of the paddle.

FIG. 6 shows a top view of the paddle blade 31 from FIG. 5, the side shown being the underside 35 of the paddle blade. The plan of the paddle blade 31 has a rectangular shape with rounded corners. The receiving device 33 for the shaft is arranged on a broad side in approximately the middle thereof. The paddle blade 31 makes a constant reduction in its width in the direction of the receiving device 33.

The bottom 35 is divided into two areas. The larger area is hatched and forms the area 23 in which the outer surface is formed by a unidirectional fiber structure. The hatching in this area indicates the direction of the fibers 25 running parallel to one another. They generally run in the longitudinal direction of the paddle blade 31, but have a small angle with respect to the longitudinal direction of the paddle blade, the longitudinal direction of the paddle blade being determined by the central axis 39 of the cylindrically shaped receiving device 33. On the opposite side of the receiving device 33 of the paddle blade 31, areas are provided which do not have a surface reinforced with fibers. Depending on the areas that comprise a surface with or without a unidirectional fiber structure, the object has different flexural rigidity, which in turn leads to a different flexural behavior. By selecting the areas on the flat side 21 of an object, the outer surface of which is formed by a unidirectional fiber structure, its bending and torsional behavior can be controlled in a targeted manner.

In Figure 7, a part of a piece of sports equipment is shown, which, in contrast to the previous exemplary embodiments, is not intended for use in water. This is a hockey stick 41, the shaft 43 of the hockey stick 41 only partially shown. The trowel 45 has a rectangular shape with rounded corners. A receiving device 47 for the shaft 43 is provided at one corner of the trowel. This takes up the shaft 43 in such a way that the shaft 43 and the longitudinal axis of the trowel 45 come to an angle of approximately 120 °. In certain areas of its flat side 21, the trowel 45 has a fiber-reinforced layer 23 as an outer surface. These areas are marked in FIG. 7 by hatching. The lines of hatching show the direction of the fibers 25.

The trowel 45 has at all of its corners except for the one to which the receiving device 47 is attached, areas in which the outer surface is not formed by a unidirectional fiber structure. Also within the flat side 21 there are three narrow areas of the outer surface which are free of a unidirectional fiber structure. These areas are shaped as narrow rectangles, the width of which is formed by a semicircle. The long side of the narrow rectangles run parallel to the long side of the trowel 45. The three narrow areas are all of the same length and are arranged one below the other.

A fin as shown in FIGS. 1-4 is produced as follows: unidirectional fiber layers which have the shape of the flat sides 21 of the fin 11 are cut from a flexible tape. When cutting out the pieces, care must be taken to ensure that the direction of the fibers 25 in the cut-out pieces runs as later desired on the fin 11. A thermoplastic polymer is impregnated on at least one side of the cut-out pieces.

If not already available, an injection mold is produced which ideally consists of two halves and has a cavity corresponding to the fin 11 to be produced. With the aid of holding devices, the fiber layers previously cut out from a flexible tape are arranged in the injection mold, so that the sides of the fiber layers with the impregnated thermoplastic polymer are oriented opposite one another. The injection mold is closed when the two halves come to rest on top of one another. The same thermoplastic polymer as is impregnated on the layers is injected into the injection mold. The plasticization of the thermoplastically impregnated layer on the layers leads to a bond with the injected thermoplastic polymer. After the polymer has cooled, a uniform body is created in the form of a fin 11, the flat sides 21 of which are formed in some areas by unidirectional fiber fabrics. Opening the injection mold enables the finished fin 11 to be removed and thus closes the manufacturing process.

The production of all other conceivable design options is analogous to the procedure described above. If only one flat side of an object is to have a unidirectional fiber lay-up, only one fiber lay-up cut from the flexible, unidirectional tape is placed in one of the two holding devices of the injection mold during production. The remaining process steps remain the same.

While the invention has been described above with reference to specific embodiments, it is apparent that changes, modifications, variations and combinations can be made without departing from the spirit of the invention.

REFERENCE CHARACTERISTICS LIST:

11 fin 13 longitudinal edge of fin 15 first short edge of fin 17 second short edge of fin 21, 21 'flat side of a flat body 23 fiber-reinforced area of flat side 25 fibers 27, 27', 27 "edge of fiber-reinforced area 31 paddle blade 33 receiving device 35 Underside of the paddle blade 37 Upper side of the paddle blade 39 Center axis of the receiving device 41 Hockey stick 43 Shaft of the hockey stick 45 Blade of the hockey stick 47 Receiving device for the shaft

Claims (13)

1. Flat body (11,31,41) made of fiber-reinforced plastic as part of a piece of sports equipment for power transmission, the flat body (11,31,41) having a plastic matrix and fibers received in the plastic matrix and being manufactured by injection molding, characterized, that the surface of at least one of the two flat sides (21) of the body is at least partially formed by a unidirectional fiber structure. 2. Flat body (11,31,41) according to claim 1, characterized in that the surface of both flat sides (21) of the flat body (11,31,41) is formed by a unidirectional fiber fabric. 3. Flat body (11,31,41) according to claim 1 or 2, characterized in that the area of the flat side (21) of the flat body (11,31,41), which is formed by a unidirectional fiber fabric, is at least 40% , preferably at least 60%, of the area of the flat side (21). 4. Flat body (11,31,41) according to one of claims 1 to 3, characterized in that the flat body (11,31,41) has a thermoplastic matrix. 5. Flat body (11,31,41) according to one of claims 1 to 4, characterized in that the unidirectional fiber scrim is provided in each case as a tape. 6. Flat body (11,31,41) according to one of claims 1 to 5, characterized in that the area of the flat sides (21) of the flat body (11,31,41) together are at least 5 times larger than the total area the remaining pages together. 7. Flat body (11,31,41) according to one of claims 1 to 6, characterized in that the ratio of the length to the thickness of the flat body (11,31,41) is at least 5. 8. Flat body (11,31,41) according to one of claims 1 to 7, characterized in that the maximum wall thickness of the flat body (11,31,41) is 20 mm, in particular 15 mm. 9. Flat body (11,31,41) according to one of claims 1 to 8, characterized in that the fibers of the unidirectional fiber structure are carbon fibers. 10. Flat body (11,31,41) according to one of claims 1 to 9, characterized in that the unidirectional fiber structure has a fiber content of 30% to 70%. 11. Flat body (11,31,41) according to one of claims 1 to 10, characterized in that the direction of the fibers in the unidirectional fiber structure runs in such a way that a desired flexural strength of the flat body (11,31,41) is achieved. 12. A method for producing a flat plastic body (11,31,41) as part of a piece of sports equipment, in which at least one of the two opposite flat sides (21) of the plastic body is formed at least in some areas by a fiber fabric, and has the following method steps; the layer of fibers is cut out of a flexible tape in the form of the flat side (21) of the flat plastic body (11,31,41), an injection mold preferably consisting of two halves with a cavity corresponding to the plastic body to be produced is produced, the cut-out layer of fibers is placed in the injection mold and placed against a mold half, the injection mold is closed and injected with a thermoplastic material and then the plastic body is removed, characterized, that the fibers in the flexible tape are unidirectional and are preferably carbon fibers. 13. The method according to claim 12, characterized in that both opposite flat sides (21) of the plastic body (11,31,41) are formed by a unidirectional fiber fabric.