Patent Application
20200340544
The invention relates to a three-dimensional body-shaped component made of a fibre composite material 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 and second impact element.
The protection of vehicle occupants of a motor vehicle and the protection of people and objects in the vicinity of the vehicle in the event of a collision is an important aspect in the design and manufacture of a motor vehicle. In the case of a safe design of a motor vehicle in the event of a collision, it is important that a vehicle deceleration or a force which acts on the vehicle occupants while occupant restraint systems are in effect does not exceed certain threshold values in the course of the collision. In the event of a collision of the motor vehicle, there is a relationship between an effective mass of the colliding vehicle, a deceleration of the colliding vehicle and a force, in which a body structural support, which is often also referred to in this context as a crash structure or deformation element, progressively fails due to plastic, elastic deformation or brittle fracture. Such a deformation element can be attached, for example, between a bumper crossmember and a frame side member of the motor vehicle.
A possible reduction of the collision energy by the deformation element is determined by a force curve over an available deformation path. At the start of a collision, the vehicle's speed is high, so that a relatively high kinetic collision energy or impact energy has to be reduced and the body structure including a body structural support or deformation element has to be designed in such a way that the body structural support fails with an adapted level of force.
Body structural supports or deformation elements are often designed in such a way that they fail to absorb collision energy in the event of a collision load of the motor vehicle. Body structural supports made of metallic materials are designed in such a way that they plastically deform at a certain force level over a specified distance.
Body structural supports are widespread which use metal pipes that are compressed in the longitudinal direction in the event of an impact. The metal tubes, for example aluminium tubes, ensure a strong connection between the bumper crossmember and the vehicle. However, the specific energy absorption (kJ/kg) of metal pipes when compressed is not particularly high. Furthermore, the initial force required to compress a metal pipe in the longitudinal direction may be too great for many situations.
In the case of a body structural support or deformation element made of carbon fibre-reinforced plastic or another fibre-reinforced plastic, for example, hollow profiles have been proposed which have, for example, a rectangular profile. Such a hollow profile made of carbon fibre reinforced plastic fails due to so-called “crushing”. In the “crushing” failure mechanism, the body structural support is disintegrated to a greater or lesser extent (pulverisation or fragmentation, also known as splintering), primarily in the brittle fracture. This failure mechanism functions particularly in the event of a frontal impact, in which the force on the carrier is perpendicular to a cross-section of the carrier. The amount of force occurring in this failure mechanism per surface of the deformation profile cross section in the plane perpendicular to the direction of force is referred to as the crash failure stress.
Documents DE 102012019923 A1, DE 102014016024 A1, DE 102014206610, or EP 1366960 B1 disclose components for energy absorption or for the absorption of impact energy made from fibre composite materials, in particular composite materials based on carbon fibres. These body structural supports or deformation elements can be produced, for example, by braiding, pultruding or winding or, as is described in EP 1366960 B1, by laminating a plurality of fibre layers, for example a plurality of fabric layers, onto one another, preferably starting from continuous fibres. The components for energy absorption described in the cited documents sometimes have a layered structure or laminate structure, but can also be made from discontinuous fibres according to DE 102014016024 A1 or contain regions with randomly oriented fibres, as is described in EP 1366960 B1. Overall, the components described in the aforementioned documents have a complex component structure. US 2005/0147804 A1 also describes elements for energy absorption, these elements having a layered structure of fibre layers made of bundled filament yarns. The fibres are arranged so that their direction of extension is parallel or oblique to the pressure load due to the impact, i.e. that the fibres have a component in the direction of the impact load. In addition, in the elements for energy absorption in US 2005/0147804 Al, the density of the fibres increases from one end of the element to the other.
JP 06-264949 describes elements for energy absorption which are made up of fibre-reinforced synthetic resins, into which short fibres are mixed. The elements for energy absorption in JP 06-264949 have a cylindrical shape, the wall of a cylindrical section being designed such that the wall thickness increases from one end to another end. In the examples, JP 06-264949 starts from elements produced by an injection moulding process with a polypropylene matrix into which glass fibres with a fibre length of 3 mm and in a concentration of 30 wt. % have been mixed.
Structures made of fibre composite materials with a thermoplastic matrix for shock absorption or for energy absorption are described in EP 3104036 A1. The structures are usually designed as hollow profiles and can have bundle-shaped reinforcing fibres. The fibres can be carbon fibres that are embedded in the thermoplastic matrix. The fibres can preferably be randomly oriented in two dimensions in a surface plane. To produce the fibre composite materials, reinforcing fibres can be cut, then opened and the opened reinforcing fibres can then be mixed with a fibrous or particulate thermoplastic. The mixture is then pressed under pressure and heat into a fibre-reinforced thermoplastic semifinished product. One or more such layers of semifinished products are stacked on top of one another in layers to form the hollow profile.
Because of the high viscosities of thermoplastic matrices, the uniform impregnation of the fibres with the thermoplastic matrix and the homogeneous distribution of the fibres in the matrix as the basis for uniform mechanical properties can be difficult during processing. In addition, the layered structure can lead to delamination of the layers in the event of an impact load in a direction parallel to the layers, combined with the detachment of large, contiguous material areas, which significantly reduces the specific absorption of impact energy, or in connection with the buckling of areas of the component weakened in this way, which leads to the sudden failure of the component and extremely low impact force absorption.
The object of the present invention is to provide a structurally simple and easy-to-manufacture component for energy absorption in the event of impact load. The component should have a high specific energy absorption when subjected to impact loads. In addition, in the event of an impact load in the component, the initial peak loads, as can be observed in particular in the case of deformation elements made of metallic materials, should be reduced and certain threshold values should not be exceeded in the course of the collision/impact load.
The object is achieved by a three-dimensional, body-shaped component made of a fibre composite material based on carbon fibres for arrangement between a first impact element and a second impact element and for absorption of impact energy as a result of an impact load, which has an impact direction, acting between the first and second impact element, wherein the component has
The component should be designed as a body in a viewing direction parallel to the longitudinal extension. The term body includes both a profile, half profiles or other geometries, the cross section of which can change along the longitudinal axis. The body can be hollow, solid and/or partially filled and/or its longitudinal extension can be divided by means of intermediate pieces. Furthermore, the body can have different wall thicknesses, contain reinforcing elements and/or have recesses. The body that forms the component can be constructed from one piece (in one piece) or from a plurality of partial bodies. The partial bodies can likewise have different cross sections, be hollow, solid and/or partially filled, and have different wall thicknesses and/or geometries.
The component can also be referred to as a deformation element. The bundles of carbon fibres can also be referred to as carbon fibre bundles, reinforcing fibre bundles or just as bundles.
The component can also be formed without the subsequent introduction of the components of a matrix system (for example a duromer matrix resin). In this embodiment, the fibre bundles and thus the component itself already have so much polymer matrix that an additional introduction of matrix material (a matrix system) is not necessary for component production. In such a case, the component can be produced, for example, by activating the components of the polymer matrix using pressure and heat.
The polymer matrix (in which the fibre bundles are embedded) predominantly consists of one or more crosslinked polymers. To a lesser extent, the polymer matrix can also have a minor portion of partially crosslinked polymers. For example, the polymer matrix can have a predominant portion of a fully crosslinkable duromer and a minor portion of a thermoplastic resin system and/or additives. Thermoplastic duromers are preferably used. In another embodiment, the polymer matrix consists of a conglomerate of epoxy with thermoplastic portions.
In the optional embodiment, the matrix system is preferably a polymer matrix system which predominantly consists of one or more crosslinked polymers (for example a duromeric matrix resin). For component production, the matrix system preferably cures. The matrix system (which can optionally be added in addition to component production) preferably also consists predominantly of one or more crosslinked polymers. To a lesser extent, the matrix system can have fully or at least partially crosslinked polymers. For example, the matrix system can have a predominant portion of a fully crosslinkable duromer and a minor portion of a thermoplastic resin system and/or additives. Thermoplastic duromers can also be used. In a further embodiment, the matrix system consists of a conglomerate of epoxy with thermoplastic portions.
By selecting the polymer matrix and the matrix system, the component advantageously has approximately constant properties over a large temperature range. Temperature-dependent fluctuations in energy absorption (such as occur, for example, when using thermoplastics) can advantageously be avoided.
If one considers a theoretical linear extension of the fibre bundles beyond the first and/or second surface of the component, this line forms angles with the first and/or second surface of the component. When considering a sufficiently small and flat area of the first and/or second surface of the component (part of the first and/or second surface), the majority of the bundles between the first and/or second surface form so-called intersection angles with the first and/or second surface. The intersection angles of the fibre bundles lie in a range in which the intersection angles are in the west evenly distributed between 0° and 90° up to an arrangement of the fibre bundles in which the intersection angles predominantly have an angle of greater than 1°, preferably greater than 2° and most preferably have greater than 3°. With a distribution of the fibre bundles that is predominantly isotropic when viewed parallel to the first and/or second surface, the intersection angles essentially all have a value between 0° and 90°, whereby no value should be represented much more often or less often. If the fibre bundles are relatively parallel to the first and/or second surface, the predominant portion of the fibre bundles have intersection angles that are greater than 1°. As a result, the majority of the fibre bundles is essentially not exactly parallel to the surfaces of the component in the component. It should be made clear that the fibre bundles can assume any arrangement within the defined range, wherein the majority of the fibre bundles within the component, however, have the selected arrangement.
A “predominant portion” should be understood to mean a portion of approximately 70% to 100%, preferably 80% to 95% and most preferably 85% to 90%.
The expression “essentially all” means that this applies to 80% to 100%, preferably 85% to 95%.
The fibre bundles are, for example, isotropic in the component and also isotropic with regard to the surfaces if the fibres of the fibre bundles are short and the wall thickness of the component is greater than the fibre length. An example of this could be the use of fibre lengths of 3 mm for a component with a wall thickness of 5 mm. A non-isotropic distribution of the intersection angles between the bundles of carbon fibres and the surfaces of the component, in which the intersection angles of the predominant portion of the bundles are greater than 1°, results in particular when the fibre length of the bundles is relatively large in relation to the wall thickness, for example with a fibre length of 50 mm and a wall thickness of 2 mm. Since the component can have different bundles with different fibre lengths and, in addition, different wall thicknesses within a component or also are conceivable with different components, the arrangement of the bundles parallel to the surfaces fluctuates between these two possibilities.
The extension of the component in the longitudinal direction is preferably greater than its extension perpendicular to the longitudinal direction.
The three-dimensional, body-shaped component made of a fibre composite material according to the invention can be between a first impact element and a second impact element, thus, for example, between a bumper crossmember and a frame side member of a motor vehicle, and absorb impact energy in the event of a collision or in the event of an impact load acting between the first and second impact element. This shows that the component according to the invention leads to a uniform absorption behaviour, which can be seen from the force curve over the deformation path, wherein the peak loads in the initial phase of an impact load are comparatively low. At the same time, a high specific energy absorption (kJ/kg) can be achieved with the component according to the invention in comparison to components or deformation elements made of metallic materials.
The component according to the invention thus provides a solution which enables defined energy absorption at a level which is as constant as possible over an adjustable long deformation path. The actual energy level can be set, inter alia by the geometrical design of the component (especially by the wall thickness). In addition, the isotropic material structure of the component offers a defined, constant energy absorption even with impact loads that do not run axially to the longitudinal expansion of the component.
A comparable or higher level of specific energy absorption is also shown in comparison to deformation elements made of fibre composite materials, which have a layered structure of layers of a fibre composite material laminated on top of one another. In the case of failure, with components or deformation elements having a layered structure, the layers are at least partially delaminated, i.e. the layers are peeled or broken apart, accompanied by a lower resulting force level. In contrast to such components or deformation elements with a layered structure, such a failure cannot take place in the present component or deformation element, since when viewed in a direction perpendicular to the thickness of the wall or parallel to the first and/or second surface of the component, the majority of the bundles are arranged between an isotropic alignment and an alignment in which the bundles essentially do not fall below an intersection angle greater than 1° to the first and/or second surface of the component. This means that there is no layered structure, but penetration of different levels of the wall of the component by the bundles, that is, an entanglement of the fibre structures.
Finally, the distribution of the bundles, which is essentially uniform over the wall thickness, and in particular their essentially isotropic alignment when viewed in a direction perpendicular to the first and/or second surface, ensures that in the event of an impact load, uniform failure without peak loads occurs in the initial phase of an impact load.
Without wishing to be bound by theory, it is assumed that the fact that the fibre composite material and thus the wall of the component according to the invention is at least predominantly made up of bundles of carbon fibres and the orientation of the fibre bundles required according to the invention is the cause of a high specific energy absorption. In the event of an impact load and a resulting failure of the component in the failure zone initiated thereby the impact energy is dissipated from the continuously acting impact force in such a way that it is converted into degradation energy to generate new surfaces between the fibres and the matrix. Due to the reinforcing fibre structure of the fibre composite material according to the invention, which not only has an isotropy parallel to the component surface, but also ensures a strong entanglement of the fibre bundles through the thickness, a high degradation energy density, and thus a high specific energy absorption, can be guaranteed as the failure zone progresses over the entire component volume.
Likewise, the high fibre volume fraction of the carbon fibres in the wall in the range between 35 vol. % and 70 vol. % is the reason for a high specific energy absorption of the component under impact load. It should be noted that with fibre volume fractions below 35 vol. %, the failure behaviour of the component under impact load is dominated by the matrix failure, i.e. the failure behaviour is determined by a break or crack in the matrix and thus by an intermediate fibre break. In the case of fibre volume fractions above 35 vol. %, the failure behaviour is primarily determined by a failure at the interface between the fibre and the matrix, i.e. by a fibre break. The higher failure forces of the latter two failure modes compared to the first failure mode generate a high degradation energy density and thus a high specific dissipated energy and thus a high specific energy absorption in the material. Above 70 vol. %, on the other hand, a sufficient distribution of the matrix in the component and wetting on the filament surfaces of the fibre bundles can no longer be ensured. It is also assumed that the fibre volume fraction at very high values is limited by the filament geometry, since in the case of circular filament cross-sections a densest circular packing in the cross-sectional plane along the fibre direction in the fibre bundle cannot be exceeded. Above 70 vol. % this fibre volume fraction ensures a poor fibre matrix connection and thus a low specific energy dissipation in the component. In a preferred embodiment of the component according to the invention, the fibre volume fraction of the carbon fibres in the wall of the component is in the range from 45 vol. % to 65 vol. %.
According to the invention, the bundles of carbon fibres, i.e. the reinforcing fibre bundles, consist of carbon fibre filaments aligned parallel to one another and have a length of between 3 mm and 100 mm. The length is preferably in the range from 5 mm to 70 mm and most preferably in the range from 10 mm to 50 mm. With a view to the attainable fibre volume fractions of carbon fibres in the wall of the component, in particular in order to achieve portions above 45 vol. %, it is advantageous if the wall of the component according to the invention has several groups of reinforcing fibre bundles with lengths that differ from one another, so that the length of the reinforcing fibre bundles has a distribution overall. For example, reinforcing fibre bundles with a length of 20 mm, 30 mm and 50 mm can be combined with one another.
The bundles of carbon fibres, i.e. the reinforcing fibre bundles, can consist of conventional carbon fibre filament yarns with, for example, 500 to 50,000 fibre filaments. However, it is advantageous if each reinforcing fibre bundle consists of 500 to 24,000 reinforcing fibre filaments. The number of filaments in the bundles is most preferably in the range from 500 to 6,000 and very preferably in the range from 1,000 to 3,000 in order to achieve the most homogeneous possible distribution of the reinforcing fibre bundles in the component wall and to achieve the highest possible fibre volume fractions.
In one embodiment, a multifilament reinforcing yarn can be used as a carbon fibre yarn with a strength of at least 5000 MPa measured according to JIS-R-7608 and a tensile modulus of at least 260 GPa measured according to JIS-R-7608.
In order to achieve high fibre volume fractions in the component wall, in particular to achieve portions of carbon fibres above 45 vol. %, it has also proven to be advantageous if the wall has several groups of reinforcing fibre bundles with different numbers of filaments, since this results in high packing densities of the bundles in the wall. For example, reinforcing fibre bundles with 3,000, 6,000 and 12,000 filaments can be combined.
In order to achieve the required fibre volume fractions in the wall, the bundles that form the wall of the component according to the invention preferably have a width in the range from 1 mm to 20 mm and most preferably a width in the range from 1 mm and 10 mm. Likewise, in order to achieve high packing densities of the bundles, that is to say to achieve high fibre volume fractions in the component wall of above 45 vol. %, it is also advantageous if the bundles have a cross section that is as flat as possible perpendicular to the extent of the carbon fibre filaments in the bundle. The bundles are preferably in the form of a band and have a ratio of bundle width to bundle thickness of at least 25. The ratio of bundle width to bundle thickness is most preferably in the range from 30 to 150.
Through a suitable selection of reinforcing fibre bundles with regard to their ratio of bundle width to bundle thickness, with regard to their length and with regard to the number of reinforcing fibre filaments, particularly high packing densities of the reinforcing fibre bundles and thus particularly high fibre volume fractions in the component wall can be achieved. In a very particularly preferred embodiment of the component, the bundles arranged in the wall of the component have, in addition to a flat cross section, different lengths and different numbers of filaments. This leads to particularly high fibre volume fractions in the wall of the component.
For the use of the component according to the invention for the absorption of impact energy, i.e. as a deformation or crash element, a uniform material behaviour over the widest possible range of environmental conditions, such as temperature or humidity, is required. Depending on the manufacturer and area of application, different continuous operating temperatures apply to applications in the automobile. A temperature window of −40° C. to 120° C. has been established for applications in areas close to the engine or exhaust system. The glass transition temperatures of most thermoplastics that are relevant for automotive engineering are in this temperature range. For example, the glass transition temperatures of the polyamides widely used in the automotive sector are in the range of approx. 35° C. and 60° C. Such thermoplastics are consequently difficult to use in a component for absorbing impact energy with the same properties.
Of course, there are also thermoplastics with higher glass transition temperatures, for example thermoplastics from the PAEK family, such as polyether ether ketones (PEEK) etc. However, these matrix materials are too expensive for applications in large series in the automotive industry. On the one hand, the costs of the materials are too high, on the other hand, the high processing temperatures due to the high melting temperatures mean considerable follow-up costs. Thermoplastics with a melting point above 250° C. (preferably 220° C.) are not suitable. In addition, all matrix materials which have a water absorption of greater than 5 wt. %, preferably greater than 3 wt. %, are unsuitable for structural components in a vehicle. With increasing water absorption, the components swell and the mechanical performance decreases. Consistent properties, for example constant energy absorption values, cannot therefore be achieved with changing environmental conditions.
The bundles in the component and the carbon fibres making up the bundles are therefore preferably embedded in a polymer matrix, which predominantly consists of one or more partially or fully crosslinked polymers. The polymer matrix preferably consists of at least 60 vol. %, based on the matrix fraction, and most preferably at least 75 vol. %, of one or more partially or fully crosslinked polymers. Other components of the polymer matrix can be thermoplastics, for example, in order to increase the impact resistance of the component or other additives which, for example, influence the processability or the service life of the component. In an advantageous embodiment, the polymer matrix has a matrix material based on acrylate or methacrylate. In addition, polyester resins, vinyl ester resins or phenol-formaldehyde resins can be contained in the polymer matrix.
The carbon fibres in the wall of the component are preferably stretched when viewed perpendicular to the first and/or second surface of the wall (see
As stated, the wall is at least predominantly made up of bundles of carbon fibres, within which the carbon fibre filaments that make up 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 consists of one or more crosslinked polymers. This means that the bundle structure in the finished component is actually preserved. Advantageously, the carbon fibres are stretched in the bundles, as a result of which a high level of compressive rigidity values can be achieved for the component according to the invention.
This property of the component according to the invention is advantageous in application because, when the component or the deformation element is subjected to an impact load, which causes the component to fail while forming a crash zone, the material located below the crash zone must withstand the compressive forces and must not fail. This high pressure rigidity is necessary because it keeps the deformation in the support zone not yet damaged by failure (crushing) low and thus prevents the premature failure of the component due to buckling. If the compressive stiffness is comparatively low in relation to the crash failure stress, the component would otherwise have to be made very thick or, in the worst case, it would always fail due to buckling processes.
In the context of the present invention, a stretched configuration of the carbon fibres in the component is understood to mean that the carbon fibres are not bent or buckled by themselves and that a change in the longitudinal extension of the carbon fibres is only due to the geometry of the component. The fibre bundles therefore have no buckles or corrugations either in the longitudinal extension or transversely to the longitudinal extension, which would not be caused by the geometry of the component.
In conventional fibre composite materials, such as those based on fabrics, nonwovens or sheet moulded compounds (SMC), the fibres are curved or undulating, so that the stiffness values (modulus of elasticity) for tensile and in particular for compressive loads are reduced. These reduced properties are disadvantageous for both static and dynamic loads. Such curved or corrugated arrangements of the fibres can be made visible, for example, by means of X-ray examinations. For example, the Handbuch der Faserverbundwerkstoffe/Composites, Springer Verlag, 2014, 4th Edition, page 253 in
In comparison, the carbon fibre bundles according to the invention are distributed homogeneously over the component cross section. In the present case, a homogeneous distribution is understood to mean that the fluctuation in the fibre volume fraction is less than ±10 vol. % for each sample of the component with a size of at least half the fibre bundle length of the component (for example for a cylindrical sample of 25 mm in diameter and 2 mm thickness with a component wall thickness of 2 mm and a fibre bundle length of 50 mm). In addition, the bundles are already stored in essentially the final geometry when the preform is manufactured. Only the flowable components of the polymer matrix are added during the injection and infusion process. A displacement of the carbon fibre bundle is excluded due to the fixing of the preform. Additionally, the carbon fibre bundles keep their stretched orientation. In this way, high compressive rigidity values are achieved and undesired failure at weak points, such as resin-rich zones or particularly strongly deformed areas of the component, is avoided.
The component can be manufactured in a simple manner by first producing a fibre preform, often also referred to as a preform, from the bundles of carbon fibres. The fibre preform, which is already close to the final contour, is placed in a tool which has the negative or positive shape of the component close to the final contour. If the reinforcing fibre bundles already have enough matrix material, the addition of further matrix material is not necessary. In such a case, the matrix material can be activated with pressure and heat, for example for component production. However, it can also be provided that additional matrix material (matrix system) is supplied to the fibre preform by means of conventional methods. For example, the matrix material, i.e. the matrix resin which has not yet been fully or partially hardened, can be introduced into the tool and thus into the fibre preform via infusion, infiltration, injection or pressing. The component is then formed with full or partial crosslinking of the polymeric matrix material (for example by curing a duromeric matrix resin).
The fibre preform can be produced inexpensively and in a simple manner by the method as described, for example, in EP 2727693 B1, the disclosure of which is expressly incorporated by reference. The method of EP 2727693 B1 comprises the following steps:
Bundles of carbon fibres in which the carbon fibres are provided with a binder are preferably used to produce the fibre preform. This binder is a material by means of which the fibre preform can be brought into a stable state, for example by heat activation and subsequent cooling, which allows the fibre preform to be handled in subsequent process steps.
The binder can then be a fibre preparation, as is usually applied to the filaments of the carbon fibres, in order to achieve improved processability and good fibre closure, that is to say an at least partial connection of the filaments to one another. Such preparations are often based on epoxy resins or polyurethane resins. The polymer matrix (in which the fibre bundles are embedded) preferably represents the binder or the preparation for the carbon fibre bundles. For the production of the fibre preform for the component according to the invention, however, an increased content compared to the commonly used concentrations of the preparation is required, preferably in the range from 2 wt. % to 14 wt. % and most preferably in the range from 3 wt. % to 7 wt. %, based on the total weight of the carbon fibre yarn provided with binder.
Suitable binders here are thermoplastic or uncured or partially cured duromeric polymers or polymer compositions composed of these polymers. Suitable thermoplastic polymers are, for example, polyethyleneimine, polyether ketone, polyether ether ketone, polyphenylene sulphide, polysulfone, polyether sulfone, polyether ether sulfone, aromatic polyhydroxy ethers, thermoplastic polyurethane resins or mixtures of these polymers. Examples of suitable uncured or partially cured thermosetting polymers are epoxies, isocyanates, phenolic resins or unsaturated polyesters.
It is advantageous if the carbon fibres provided with the binder or the carbon fibre bundles are not tacky at processing temperatures such as those used to produce the fibre preform, that is to say when the bundles are deposited on the fibre preform, that is to say generally at room temperature. At elevated temperatures, however, the binder or the carbon fibres provided with the binder should be tacky and lead to good adhesion of the fibre bundles produced therefrom. Such reinforcing fibre yarns or strands of reinforcing fibres are described, for example, in WO 2005/095080, the disclosure of which is expressly referred to here. The filament yarns there are infiltrated with a binder composed of several different epoxy resins, wherein these epoxy resins differ from one another in a defined manner in terms of their properties, such as epoxy value and molecular weight, and in terms of their concentration. WO 2013/017434, the disclosure of which is expressly referred to, also describes carbon fibres preimpregnated with a binder.
In an advantageous embodiment of the component according to the invention, the polymer matrix and/or the matrix system used in the component has a fracture toughness which increases by a maximum of 100% when the temperature changes from 20° C. to 100° C., measured according to ISO 13586. Components with such a matrix property have a high matrix brittleness. (The more brittle the matrix, the lower the fracture toughness.)
It is assumed that by selecting the matrix material with such a fracture toughness, the component delaminates when force is applied to the individual fibre bundles, as a result of which a large inner surface is formed in the component, which contributes to the eventual conversion of the collision energy into heat. The polymer matrix used in the component can be the polymer matrix of the reinforcing fibre bundle and/or the matrix system optionally added for the production of the component.
As stated, the component is designed as a body in a viewing direction parallel to the longitudinal direction. By designing as a body, a self-supporting structure that is stable against buckling loads is obtained. In this way, the impact energy can be dissipated evenly over the deformation path and buckling of the component, which ends further energy dissipation, can be at least largely avoided.
In a preferred embodiment, when viewed parallel to the longitudinal direction of the component, the body can be a profile, more preferably a corrugated profile, a zig-zag profile, an angle profile or a profile which has a mixture of the aforementioned profiles. However, it can also be any, even irregular, profiles. The inner and/or outer cross section of the body preferably has a corrugated shape, a zig-zag shape, an angular shape, a curve or a mixture of the aforementioned shapes.
In a further preferred embodiment, the component can have a closed hollow profile as a body, which has a cavity 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 hollow profile has an outer and an inner cross section and the first surface faces away from the cavity and the second surface faces towards the cavity. Hollow profiles are preferred in which the inner and/or the outer cross-section has a circular, elliptical, square or rectangular contour or a polygonal contour. Examples of such hollow profiles can be found, for example, in EP 3104036 Al or also in US 2005/0147804 A1.
The component can have more than one first and one second end. For example, the component can have three or more ends. To simplify matters, a first and a second end are referred to below, without the component being restricted to these.
In a preferred embodiment, the wall thickness of the component according to the invention is constant over the extension in the longitudinal direction (see
In the event that the inner and outer cross sections are constant, a wall with a wall thickness constant from the first to the second end of the component is obtained. In this embodiment, the cross-sectional area of the wall is also constant over the extension of the component in the longitudinal direction. Likewise, a constant wall thickness can be obtained if the inner and outer cross sections increase in the same way along the extension in the longitudinal direction from the first to the second end. In this case, however, the cross-sectional area of the wall increases over the extension of the component in the longitudinal direction from the first to the second end of the component. Further advantageous embodiments of the component according to the invention are those in which the wall thickness increases in a range between the first and the second end from the first to the second end of the component. Further designs of the component provide that the wall of the component is only thicker and/or thinner in partial areas. Partial areas, whose wall is thicker within the partial area can have ribs, for example. Partial areas whose wall is thinner within the partial area can, for example, be trigger areas which can be used to apply force.
The component is preferably constructed from a plurality of partial bodies. For example, the component can consist of two body shells which, when put together (for example by means of connection by flanges), form the component. In the final application (for example in the vehicle), the component can be used individually or with several components as an absorption element for impact energy. When using a plurality of components, the components used can be constructed identically or differently and/or can be arranged in a row next to one another, one above the other and/or concentrically around a centre point.
In a preferred embodiment, in the event that the component as a body is a closed hollow profile, this component is constructed from two partial profiles which are connected to one another in the longitudinal direction to form the hollow profile. Such partial profiles, for example in the form of half-shells, can be produced in a particularly simple manner by means of a process for producing a fibre preform or a preform, since the reinforcing fibre bundles can be placed in an open form during the manufacture of the preform. The partial profiles preferably have lateral flanges in the longitudinal direction, by means of which the partial profiles are connected to one another. The connection can preferably be made using an adhesive, for example using a 2-component construction adhesive. The connection can also be made by means of a clamping, screwing, welding and/or riveting surrounding the flanges or by means of an auxiliary construction surrounding the flanges, as described for example in EP 3104036 A1. The partial profiles are preferably connected to one another in a positive and/or non-positive manner.
It is advantageous if the component has at least on its first and/or second end an area for introducing the impact energy. When using the component according to the invention, it is important that, in the event of an impact load, a failure zone is formed in a controlled manner, with as much energy as possible being absorbed by the component as it progresses. This can advantageously be achieved in that the impact force or impact energy is first introduced into the component, which is often also referred to as a crash element, into an area at the end of the crash element for introducing the impact energy, the so-called trigger area, which, for example, can be a sloping section of the cross-sectional area (chamfer). The precise geometric design of this area has proven to be less important. However, it must include a reduction in the wall thickness or the cross-sectional area of the wall and is above all a predetermined breaking point for targeted failure. An increased tension acts in the trigger area, since the same force acts on less material in the area of the bevelled tips, and the material fails.
According to the invention, the wall of the present component is constructed at least predominantly from bundles of carbon fibres, within which the carbon fibre filaments that make up the carbon fibres are arranged parallel to one another. In a preferred case, however, the wall can additionally comprise at least one layer of unidirectionally oriented long fibres, wherein the at least one layer can be arranged on at least one of the surfaces or in the interior of the wall and extend between the first and the second end of the component. Such layers of unidirectionally oriented long fibres can be used, for example, to further stabilise the component against buckling. The long fibres preferably extend from the first to the second end of the component. If there are more than two ends, the long fibres preferably extend between at least two ends of the component. Such long fibres preferably have fibres with a length of more than 10 mm and a width of more than 3 mm.
In an advantageous embodiment of the component according to the invention, the wall on the first and/or second surface has reinforcing elements which extend in the direction of the longitudinal direction of the component. Such reinforcing elements can have, for example, the shape of ribs or lamellae which are applied to the surface, for example by gluing separately manufactured elements (see also
In a further preferred embodiment, a permanently load-bearing element is integrated into the component, which can be connected to the first or the second impact element.
In the event of an impact load, this permanently load-bearing element is not destroyed together with the component, but rather shifted and/or deformed. Such elements can be used to ensure that a connection remains between the first and the second impact element even after the component has been destroyed after an impact load, that is to say, for example, the bumper crossmember is still held on the frame side member of the motor vehicle. For example, the permanently load-bearing element can be a steel tube that is telescopically displaced in the component in the event of a crash or in the event of an impact load. It is also possible for several permanently load-bearing elements to be integrated into the component.
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.
a, 2b, 2c and 2d schematically show possible embodiments of the component.
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.
A section of the component 1 is shown schematically in
A further embodiment of component 1 is shown schematically in
For Example 1, a body according to an exemplary embodiment of the invention was produced as a crash component, as shown in
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
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
The X axis of
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.
Comparative Example 2 from Table 1 is an aluminium tube, as was also used for the experiment in
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
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
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
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
| Number | Date | Country | Kind |
|---|---|---|---|
| 17199076.5 | Oct 2017 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/079466 | 10/26/2018 | WO | 00 |
