COMPONENT FOR ABSORBING IMPACT FORCE

Abstract

A component in the form of a crash element is made of a fibre composite material, the wall of which is constructed at least predominantly from bundles of carbon fibres. The carbon fibre filaments are arranged parallel to one another within the fibre bundles, and the bundles are embedded in a polymer matrix. Within the wall of the component the bundles are distributed uniformly and have a substantially isotropic orientation as considered perpendicularly to a first and/or second surface.

Claims

1. Three-dimensional body-shaped component formed from a fibre composite material based on carbon fibres for arrangement between a first impact element and a second impact element and for absorbing impact energy as a result of an impact load acting between the first impact element and the second impact element, which has an impact direction, p1 the component comprising: at least a first end and a second end, a longitudinal direction extending between the ends, which is arranged substantially in the impact direction, a first surface and a second surface and a wall with a wall thickness extending between the first surface and the second surface, wherein the wall is constructed at least predominantly from bundles of carbon fibres, within which the carbon fibre filaments which form the carbon fibres are arranged parallel to one another, wherein the bundles and the carbon fibres making up the bundles are embedded in a polymer matrix, which predominantly comprises one or more crosslinked polymers, wherein the bundles are distributed substantially uniformly over the wall thickness, when viewed in a direction perpendicular to the first surface and/or the second surface are oriented substantially isotropically, and when viewed parallel to the first and/or second surface the bundles form intersection angles with a part of the first surface and/or the second surface, wherein the bundles, viewed parallel to the first surface and/or the second surface, are distributed within the component so that the predominant portion of the intersection angles lie in a range in which the intersection angles are substantially distributed between 0 and 90 up to predominantly existing intersection angles greater than 1, wherein a fibre volume fraction of the carbon fibres in the wall is between 35 vol. % and 70 vol. %, wherein the bundles of carbon fibres have a length between 3 mm and 100 mm and wherein the component is obtainable by a method comprising the production of a fibre preform from the bundles of carbon fibres, and by subsequently introducing a matrix system into the fibre preform by injection, infusion, infiltration or pressing and crosslinking the matrix system, wherein the matrix system consists substantially of one or more crosslinked polymers.

2. Component according to claim 1, wherein the carbon fibres are stretched in the wall when viewed perpendicular to the first and/or second surface.

3. Component according to claim 1, wherein the fracture toughness of the polymer matrix changes by a maximum of 100% when the temperature changes from 20 C. to 100 C. measured according to ISO13586.

4. Component according to claim 1, wherein the inner and/or the outer cross section of the body has a corrugated shape, a zig-zag shape, an angular shape, a curve or mixtures of the forms mentioned above.

5. Component according to claim 1, wherein the component has a closed or open hollow profile as a body, which has an interior space extending between the first and second ends, wherein the first end and the second end are connectable to the first and second impact elements, and wherein the body has an outer cross section and an inner cross section and the first surface faces away from the interior space and the second surface faces toward the interior space.

6. Component according to claim 5, wherein the inner cross section and/or the outer cross section has a circular, elliptical, square or rectangular contour or a polygonal contour.

7. Component according to claim 5, wherein the inner cross section and/or the outer cross section is constant along the extension in the longitudinal direction.

8. Component according to claim 5, wherein the inner cross section and/or the outer cross section increases in an area between the first end and the second end from the first to the second end of the composite material component.

9. Component according to claim 1, wherein the wall thickness increases in an area between the first end and the second end from the first end to the second end of the component.

10. Component according to claim 1, wherein the polymer matrix, which embeds the bundles of carbon fibres and/or the matrix system, is a duromeric resin.

11. Component according to claim 1, wherein the component has at the first end an area for introducing the impact energy.

12. Component according to claim 1, wherein the component is constructed from two partial bodies which are connected to one another in the longitudinal direction to form the component.

13. Component according to claim 12, wherein the partial bodies have flanges laterally in the longitudinal extension, by which the partial bodies are connected to one another.

14. Component according to claim 1, wherein the wall on the first surface and/or the second surface has reinforcing elements which extend in the longitudinal direction of the component.

15. Component according to claim 1, wherein the wall further comprises at least one layer of unidirectionally oriented long fibres, wherein the at least one layer is arranged on at least one of the surfaces or in the interior of the wall and extends between the first end and the second end of the component.

16. Component according to claim 1, wherein the fibre volume fraction of the carbon fibres in the wall is from 45 vol. % to 65 vol. %.

17. Component according to claim 1, wherein the carbon fibres have a length of 5 mm and to 70 mm.

Description

[0081] The invention is described below by means of examples, wherein the examples and figures represent merely embodiments of the invention and are not to be understood as restrictive.

[0082] FIG. 1 schematically shows a comparison of the voltage-path profiles between components not according to the invention and an exemplary embodiment of the component according to the invention in a crash.

[0083] FIGS. 2, 2a, 2b, 2c and 2d schematically show possible embodiments of the component. FIGS. 1 and 3 to 11 show various crash data in curves for exemplary embodiments of the component. The X axis respectively represents the path measured in mm. The Y axis indicates the force measured in kN.

[0084] FIG. 1 shows a comparison of the pressure or stress-displacement profiles of an aluminium component (curve A) compared to components made of fibre-reinforced plastics. The X axis describes the path in mm, the Y axis the pressure or stress in MPa. The components made of fibre-reinforced plastics are an example of a thermoplastic material with carbon fibres (curve B) and a component, according to an exemplary embodiment of the invention (curve C), which is not according to the invention, wherein the carbon fibres with an average cut length of the fibre bundles of 50 mm are present in an isotropic fibre bundle distribution in the component. Both components made of fibre-reinforced plastic had the same geometry and were made up of half shells. The aluminium component consisted of a tube with an inner diameter of 66 mm and a wall thickness of 2 mm. The geometries of the components have been coordinated so that the results are comparable.

[0085] It can be seen that the amplitude fluctuation in relation to the path of the aluminium component is much more pronounced than the amplitude fluctuations in the components made of fibre-reinforced plastics. In comparison to the component made of fibre-reinforced plastic not according to the invention, the initial stress amplitude of the failing component according to one exemplary embodiment of the invention is significantly lower. As a result, kinetic energy is already converted into deformation energy at lower initial forces, and the following vehicle structures or vehicle occupants are protected, for example, from the effects of high forces.

[0086] FIG. 2 shows an exemplary embodiment of a component 1 that can be used for impact energy absorption. The component 1 has a first end E1 and a second end E2 and, for example, a semicircular cross section, wherein the cross-section changes along the longitudinal direction L. The component 1 can have a rib 2 (or a plurality of ribs), which can be provided, for example, on a first surface 8. The rib can be made in one piece from the component 1 or can be attached to component 1 as a further element. For example, the rib 2 can be formed by placement of one or more fibre bands on the component 1. The component 1 can furthermore preferably have recesses 3, such as holes. By means of these recesses 3, the weight of the component 1 can advantageously be reduced without reducing the length or width of the component 1. Flaps or covers 5 can be provided within the component, which subdivide the component 1 in its longitudinal extension L. The covers 5 can be designed such that they extend from one wall to the other wall and thus form a closure, or they can only extend inside the component 1 without the cover 5 having contact with the other (opposite) wall side. The lids or flaps 5 can advantageously stabilise the component 1 and, for example, prevent the body 1 from buckling in the event of an impact. In the exemplary embodiment in FIG. 2, the body 1 has a semicircular profile 7, wherein the first end E1 has a smaller diameter than the second end E2. The component 1 can be connected to other parts by means of flanges 6. The other parts can be, for example, further components 1 for absorbing impact energy (of the same type or of a different type) or can be impact elements. By means of the flanges 6, the component 1 can be positively and/or non-positively connected to the other parts, wherein an irreversible connection is preferred.

[0087] FIG. 2a shows an exemplary embodiment of component 1, as was used for example 1.

[0088] A section of the component 1 is shown schematically in FIG. 2b. A part of a wall of the component 1 with the first surface 8 is shown. When considering a perpendicular S to the first surface 8, fibre bundles for forming the component 1 are essentially isotropic. Furthermore, when considering a parallel W to the first surface 8, the fibre bundles form intersection angles to the surfaces 8, 9.

[0089] FIG. 2c schematically illustrates an embodiment of component 1 in a simplified manner. In this exemplary embodiment, an outer cross section 11 of the component at the first end E1 is smaller than the outer cross section 11 at the second end E2. The cross section of the component 1 has consequently increased over the longitudinal direction L. An inner cross section 11 of the component 1 may have changed from the first to the second end E1, E2 or may have remained the same. With a constant inner cross section 11, there is a change in the wall thickness of the component 1.

[0090] A further embodiment of component 1 is shown schematically in FIG. 2d in a simplified manner. In this exemplary embodiment, the outer cross section (not shown) of the component 1 remains constant from the first end E1 to the second end E2. However, a wall thickness 10 of the component 1 at the first end E1 is greater than the wall thickness 10 of the component at the second end E2.

[0091] FIG. 12 shows an X-ray image of a component with an elongated fibre bundle. The component should preferably have at least 20% of the fibre bundles in areas that are not already determined to be curved by the predetermined component geometry, which deviate from this by a maximum of 5 mm (preferably by 2 mm) compared to an applied straight line. Curvatures in the fibre bundles that do not result from the preform production, but rather from the geometry of the component, which are forced and desired dimensions, are determined by using the closest component edge as a reference.

EXAMPLE 1

[0092] For Example 1, a body according to an exemplary embodiment of the invention was produced as a crash component, as shown in FIG. 2a. For the test result, the component was tested in a dynamic impact test. For this purpose, preforms were first produced. For this step, a carbon fibre yarn (Tenax HTS 40 X 030 12k 800 tex) with obstructions (according to the documents WO 2005/095080, WO 2013/017434) was cut into fibre bundles in the transverse and longitudinal directions. The fibre bundles were given a length of 50 mm and a width between 1 mm and 5 mm. These fibre bundles were formed into preforms close to the final contour. For this purpose, the fibre bundles are applied to a preform tool, which already largely depicts the geometry of the end component. The method of application (manually or by means of a regulated moving unit, for example a robot) is of subordinate importance as long as a uniform application of the bundles is generated. In the example, a fibre application is set which leads to a fibre volume content in the component of 50 vol. % with a maximum deviation of 5 vol. %. In order to fix the fibre bundles at the respective application location, the preform tool can be designed with many small holes which are subjected to a suction flow. In this way, the fibre bundles are suctioned in and fixed at the respective point. In the next step, this structure is heated and the binder develops its adhesive effect. Under certain circumstances, the structure can be compacted by an additional force perpendicular to the respective surface. After the binder has cooled down again, the entire preform but also the individual fibre bundles are fixed in their local locations. The preforms were made in a steel tool using a resin infusion process (resin transfer moulding, RTM) to form two half-shell-shaped profile components (partial bodies) with a constant wall thickness of 2 mm in the longitudinal direction and a partially semicircular cross section. The fibre volume fraction of the partial bodies was 50%. An epoxy resin system (Huntsman Araldite LY 1564/Aradur AD 22962) was used as the matrix system for the resin infusion. After the demoulding of the profile components or the partial bodies, they were annealed. The partial bodies were trimmed with a diamond circular saw. Two of these half-shell-shaped partial bodies were joined together in an adhesive clamp and glued to flat longitudinal flanges with a two-component onstruction adhesive (3M DP490). Subsequently, a force introduction structure (so-called trigger) in the form of a circumferential 45 chamfer was introduced on one side of the component.

[0093] The component manufactured in this way was attached to a flat, non-compliant baffle plate made of steel, so that the longitudinal axis was perpendicular to the plate and the force application point was facing outwards. Subsequently, a carriage, which had a mass of 61 kg and a flat steel baffle plate in the direction of the component, was driven onto the component at 10 m/s in such a way that it was destroyed along its longitudinal axis. During the destruction process, the path of the carriage in the event of an impact was absorbed with a magnetic displacement sensor and a magnetostrictive position measurement system (Temposonics R-Series of the Fa. MTS with max. 1000 mm path length) and the force acting on the component was absorbed with a load cell (Piezo-KMD 9091A from Kistler with a max. 400 kN) on the component. A course of the force and the path over time was recorded with a sampling period of 4 ps and frequency of 250 kHz. In FIG. 3, the recorded force-displacement relationship of the various components is shown averaged (X-axis displacement in mm, Y-axis force in kN), wherein both the displacement and the force data were filtered numerically in terms of time using a Channel Frequency Classes (CFC) 600 filter algorithm (according to SAE J211). A force plateau at (50 +/ 5) kN was shown in this curve. The absorbed energy per mass of the component material (dissipated energy density) was 71 J/g. The result showed that in the failure zone initiated by the trigger, the impact energy from the continuously acting impact force was dissipated by converting it into degradation energy to create the new surfaces between fibre and matrix. Due to the largely time-constant course of the failure zone, a uniform course of the failure force and the associated uniform energy consumption was created. There are no large fluctuations in amplitude, which lead to a hazard to, for example, vehicle occupants. The value of the dissipated energy density was within the range of the values of other materials which represent the prior art, or exceeded them, as shown in Table 1.

TABLE-US-00001 Material: dissipated energy density in J/g Example 1, 50 mm 71 Cut length Comparative Example 1, 75 Thermoplastic CF-PA6 Comparative Example 2, 42 aluminium

[0094] Comparative Example 1 from Table 1 is a component made of carbon fibres with a cut length of 50 mm, wherein the component is produced as described in Example 1, with the difference that polyamide 6 was used as the matrix material. As explained in relation to FIG. 1, such a component has the disadvantage that the initial amplitude is significantly higher than for a component according to an exemplary embodiment of the invention. In addition, thermoplastic matrix systems show temperature-dependent crash behaviour, which is not desirable. In addition, components with a high portion of thermoplastics tend to absorb water, which reduces the lifespan of such components by swelling of the components. It is easy to see that the shortening of the service life, especially at the end of the life cycle, influences and reduces the crash properties of the component. The temperature dependence of components with a thermoplastic matrix is shown in FIG. 11.

[0095] The X axis of FIG. 11 describes the path in mm, the Y axis describes the force in kN. Curve

[0096] D describes the crash behaviour of a component constructed according to Comparative Example 1 at 30 C. Curve E describes the crash behaviour of a component constructed according to Comparative Example 1 at 20 C., the F curve at 50 C. and the G curve at 90 C. Such a temperature range is particularly common in the case of components as crash elements in the automotive sector. Consistent failure behaviour, which is largely independent of the temperature, can therefore not be achieved with thermoplastics as the main matrix material.

[0097] Comparative Example 2 from Table 1 is an aluminium tube, as was also used for the experiment in FIG. 1.

EXAMPLE 2

[0098] As described in Example 1, a component was produced from preforms which contained fibre bundles 25 mm long and 1 mm to 5 mm wide. In contrast to Example 1, fibre lengths of 25 mm were used instead of 50 mm. The wall thickness of the component corresponded to that of Example 1. The component was destroyed as indicated in Example 1. This resulted in a force curve similar to that shown in FIG. 3 with a force plateau at (55 +/ 5) kN. The absorbed energy per mass of the component material was 72 J/g. The course of the force-displacement curve and the specific energy density did not differ significantly from the case in Example 1 with a cut length of 50 mm. A separate figure for example 2 was therefore not created.

EXAMPLE 3

[0099] As described in Example 1, components were produced from preforms which contained fibre bundles 50 mm long and 1 mm to 5 mm wide. In contrast to Example 1, however, two components were manufactured that had a wall thickness of 3 mm or 4 mm. The components were destroyed as indicated in Example 1 and the results worked up as indicated for Example 1. This resulted in a force curve as in FIG. 4 for the component with 3 mm wall thickness and in FIG. 5 for the component with 4 mm wall thickness with a force plateau at (70 +/ 5) kN for 3 mm wall thickness and (90 +/ 7) kN for 4 mm wall thickness. The absorbed energy per mass of the component material was 70 J/g for 3 mm wall thickness and 73 J/g for 4 mm wall thickness. This showed that the failure force was adjustable through the wall thickness of the component and scaled largely linearly with the cross-sectional area of the wall, whereby the dissipated energy density remained largely constant. An adjustable force curve is thus advantageously possible during the deformation of the component.

EXAMPLE 4

[0100] As described in Example 1, components were produced from preforms which contained fibre bundles with a length of 50 mm and a width of 1 mm to 5 mm and a wall thickness of 2 mm. The components were destroyed as indicated in Example 1 and the data were processed as indicated for Example 1. Unlike in Example 1, however, the components were tempered to 30 C., 70 C. and 110 C. up to 30 s before the tests. This resulted in component temperatures of 30 C., 50 C. and 90 C. in the crash test. The force curves shown here resulted in the curves in FIG. 6 (30 C.), FIG. 7 (50 C.) and FIG. 8 (90 C.) with a force plateau at (40 +/ 5) kN for a component temperature of 30 C., (45 +/ 5) kN for a component temperature of 50 C., and (45 +/ 5) kN for a component temperature of 90 C. The absorbed energy per mass of the component material was 54 J/g for a component temperature of 30 C., 60 J/g for a component temperature of 50 C., and 60 J/g for a component temperature of 90 C. It turned out to be advantageous that the temperature dependence of the failure force and the dissipated energy density is not very pronounced. This was particularly evident in comparison to carbon fibre composite materials with thermoplastics, as can be found in the prior art and as they were investigated in Comparative Example 1, FIG. 11.

EXAMPLE 5

[0101] As described in Example 1, components were produced from preforms which had fibre bundles 50 mm long and 1 mm to 5 mm wide with a wall thickness of 2 mm. However, the fibre volume fraction of the components according to Example 5 was once 40% and once 45%. The components were destroyed as indicated in Example 1 and the data prepared as described in Example 1. This resulted in the force curves of the curves shown in FIG. 9 for 40% fibre volume fraction and FIG. 10 with 45% fibre volume fraction with a force plateau at (45 +/ 10) kN for a fibre volume fraction of 40% and at (45 +/ 5) kN for a fibre volume fraction of 45%. The absorbed energy per mass of the component material was 64 J/g for a fibre volume fraction of 40% and 61 J/g for a fibre volume fraction of 45%. While the fluctuations in the plateau area of the force-displacement curve were still relatively large with a fibre volume fraction of 40%, a relatively flat plateau was already formed at 45%. So here the advantageous failure of the material took place. The respectively higher force level of the plateau value of the test with a fibre volume content of 50% from Example 1 in comparison with the value at 45% and in comparison with the value at 40% fibre volume fraction showed that a smaller fibre volume fraction reduced the failure properties (force and dissipated energy density), since there were fewer detachment processes between fibre and matrix material per component volume.

LIST OF REFERENCE NUMERALS

[0102] A Curve component aluminium [0103] B Curve component carbon fibres with thermoplastic [0104] C Curve component according to an embodiment of the invention [0105] D Curve Comparative Example component with thermoplastic [0106] E Curve Comparative Example component with thermoplastic [0107] F Curve Comparative Example component with thermoplastic [0108] G Curve Comparative Example component with thermoplastic [0109] 1 Component (impact element, crash structure) [0110] 2 Rib [0111] 3 Recess/hole [0112] 4Corrugated profile [0113] 5 Lid/flap [0114] 6 Flange [0115] 7 Semicircular profile [0116] 8 First surface [0117] 9 Second surface [0118] 10, 10 Wall thickness [0119] 11 Outer cross section [0120] 11 Inner cross section [0121] E1 First end [0122] E2 Second end [0123] L Longitudinal direction [0124] S Perpendicular to surface 8, 9 [0125] W Parallel to surface 8, 9