JPH04372436A - Fiber-reinforced composite material and energy absorbing member for bumper - Google Patents

Abstract

PURPOSE:To provide an energy absorbing member for a bumper having a high impact absorbing ability to a diagonally applied alod, having only a small stress fluctuation for compression deformation, and having a large energy absorbing ability to a constant quantity of deformation CONSTITUTION:An energy absorbing member 1 comprises two cylinder parts 2 disposed in parallel to be applied to each other, and an oval cylinder part 3 is integrally formed on their outer side to be circumscribed with the cylinder parts 2. For the cylinder parts 2 and the oval cylinder parts 3, mixed fibers of glass fibers and polyethylene fibers or polyester fibers are used for reinforcement fibers, and they are formed of fiber-reinforced composite material where the fibers (or fila-ments) are wound along the circumference and which is hardened by resin.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber-reinforced composite material and an energy-absorbing member for a bumper made of a fiber-reinforced composite material used as a shock-absorbing member for a bumper installed in an automobile.

0002

BACKGROUND OF THE INVENTION In recent years, there has been a strong desire to improve exercise function and reduce energy consumption by reducing weight. The replacement of metal components with fiber-reinforced composite materials such as fiber-reinforced plastics (FRP) can be said to be the star of this process, and FRP is being used extensively in a large number of fields, and this trend appears to be expanding more and more. There is.

[0003] There are various grades of FRP, and the one in which cut fibers called short fibers are mixed into the resin as reinforcing fibers and the short fibers are arranged completely randomly is a general-purpose grade and is used for general household use. . On the other hand, fibers in which the fibers are not cut but are integrated with reinforcing resin as filaments are ranked as high grade for use in industrial products that require high strength and high elasticity. When filaments are used as reinforcing fibers, the fibers are usually laminated into sheets, impregnated with resin, and cured, which is called a laminated composite material. Conventionally, a mixture of multiple types of fibers has not been used as reinforcing fibers.

[0004] The laminated composite material exhibits extremely high strength and rigidity against loads in the plane where the fibers are arranged, but when an out-of-plane load that generates bending stress or shear stress is applied,
It has the disadvantage that the layers easily peel off, causing separation and destruction with weak force. Figure 7 shows stress-displacement curves during bending and shear failure of plate-like laminated composite materials when glass filaments are used as reinforcing fibers and when carbon filaments are used.
and FIG. 8, respectively. However, in (a), the bending stress is
(b) shows the case where shear stress is applied. In both cases, the stress increases almost linearly in response to an increase in load up to a certain point, but after that the stress decreases rapidly, leading to failure. That is, in conventional laminated composite materials that use one type of fiber as reinforcing fibers, when minute peeling occurs between layers, it grows all at once, resulting in separation between the layers, resulting in destruction of the composite material. The energy absorption (area between the stress-displacement curve and the axis representing the displacement) is extremely small, and it can be said to be a brittle material.

[0005] Furthermore, in order to protect the vehicle body and passengers in the event of a collision, bumpers are generally attached to the front and rear of the vehicle body to absorb impact energy in the event of a collision. Bumpers need to irreversibly absorb energy from the large load that is applied when a car collides with an obstacle. In order to increase absorbed energy, various improvements have been made to the materials and structures of the support members that support the bumper body.

For example, a German patent (3626150) published on February 18, 1988 discloses a bumper 22 attached to a stay 23 of a vehicle body via an elliptical annular damping molded body 21, as shown in FIG. has been done. The damping molded body 21 is formed of FRP (fiber-reinforced plastic) in which fibers are arranged in the circumferential direction, and is attached so that its long elliptical side surfaces are in contact with the bumper 22 and the stay 23, respectively.

[0007] In addition, Japanese Patent Application Laid-Open No. 57-124142 discloses a structural material for absorbing energy used in a bumper as shown in FIG.
As shown in FIG. 0, a structure 25 formed into a cylindrical shape with a network structure consisting of strips 24 made of a fiber-reinforced composite material (for example, epoxy resin-impregnated glass fiber) has been proposed. Structure 2
5 is used with a compressive load applied in the axial direction of the cylinder, and when the axial load is applied to the structure 25, delamination occurs at opposing node points 26 of the network structure, and shear yield occurs at the interface between the fibers and the matrix. It is designed to absorb energy step by step. Additionally, each node 26 is formed of approximately ten layers of fiber composite material strips 24.

[0008]

[Problems to be Solved by the Invention] As mentioned above, when a laminated composite material is subjected to bending stress or shear stress, delamination occurs suddenly, and it does not exhibit yielding behavior like metals.
Fracture occurs instantaneously and the stress reaches zero. That is, when destruction occurs, it becomes impossible to maintain the shape in a short period of time. Therefore, it is common practice to use laminated composite materials within a range that does not exceed the limit load. However, if the margin is increased, safety is high, but the weight reduction effect is lost, and if the margin is small, there is always a risk of destruction.

[0009]Also, the German patent discloses the use of a damping molded body 21 made of FRP in which fibers are arranged in the circumferential direction as an energy absorbing member, but when a load is applied to the member, There is no mention of the stress caused, its fluctuation, absorbed energy, etc. The manufacturing method for an annular structure made of FRP in which long fibers are arranged in the circumferential direction is filament winding (FW), which involves impregnating (adhering) filaments with resin and winding them around a mandrel (core material) in multiple layers, and then heating and curing them. The law is commonly used. When a homogeneous structure fabricated using the FW method is compressed by a load applied from its side, the compression energy accumulates because there is no trigger for fracture, and when it can no longer withstand, the fibers suddenly delaminate and fracture. , the deformation stress is drastically reduced instantly. At the initial stage of compression, this severe stress fluctuation is repeated, delamination progresses, and the stress tends to gradually decrease. When the deformation becomes larger and exceeds the breaking limit of the fiber, the stress is further attenuated. The product of the stress generated in this compressive deformation process and the amount of deformation (specifically, the area between the compressive load-displacement curve and the axis representing the amount of displacement) becomes the absorbed energy at that time. If there is a condition to reduce the impact on the human body, such as with bumper support members, it is necessary to suppress the maximum value of stress to a level that has a low impact on the human body, and if stress fluctuations are severe, the overall energy Absorption amount becomes smaller. Therefore, in order to satisfy the requirements of reducing the impact on the human body and increasing the amount of energy absorbed during deformation,
The important point is to keep the compressive load-displacement curve constant at the lowest possible level.

Similar to the one disclosed in the German patent, an elliptical annular structure made of FRP with glass fibers arranged in the circumferential direction and having a constant thickness was produced, and compressed by a load from the longitudinal side of the ellipse. When the relationship between the load and the amount of displacement was measured, the results shown in FIG. 11 were obtained. In this case, a sudden change in load occurs at the point where separation first begins, and the fluctuation is very drastic. It becomes small and is insufficient as an energy absorbing member of a bumper.

On the other hand, the cylindrical energy absorbing structural material disclosed in JP-A-57-124142 exhibits its function when a compressive load is applied in the axial direction of the cylinder.
It can barely handle loads from diagonal directions. In addition, as mentioned above, in order to increase the absorbed energy, it is important that the load is kept at a constant level even when the amount of displacement increases, but this energy absorbing structural material There is a problem that the amount of energy absorbed fluctuates drastically and it is difficult to increase the amount of energy absorbed.

The present invention has been made in view of the above-mentioned problems, and the first object is to prevent the sudden occurrence of delamination, suppress the drastic change in stress at the time of fracture, and improve the quality of the metal. The objective is to provide a fiber-reinforced composite material that exhibits similar behavior and can absorb large amounts of energy.

[0013] The second purpose is to suppress the impact when a car collides and to reduce the transmission of the impact to the human body, so that stress above a certain level is not generated during collision deformation, and when the deformation exceeds a certain amount. To provide an energy absorbing member for a bumper that absorbs a large amount of energy, has a high shock absorbing ability even for loads applied in an oblique direction, and is lighter in weight than metal.

[0014]

[Means for Solving the Problem] In order to achieve the first object, the invention according to claim 1 uses at least two types of fibers as fiber materials arranged in a laminated state within the matrix of the fiber reinforced composite material. Then, these fibers were arranged in a mixed state.

The combination of fibers is preferably a combination of inorganic fibers and organic fibers, or a combination of materials having different surface bonding strengths to the matrix. In addition, as for the mixed state of the fibers, it is preferable that the two types of fibers are finely dispersed and evenly mixed, and substantially non-twisted fiber bundles are arranged in a uniform manner in each layer throughout the entire layer. In some cases, fibers of different types are arranged alternately in each layer, but if you look at the interlayers, the two types of fabric are evenly distributed throughout the fabric. be.

Further, in order to achieve the second object, the energy absorbing member of the invention according to claim 2 is a fiber reinforced composite material in which filaments are wound in the circumferential direction so as to have an annular cross section and are cured with a resin. It is formed into a cylindrical shape,
At least two types of fibers are mixed as the filament.

[0017] The finer the fiber mixture, the less the stress fluctuation during compressive deformation, so by winding the rovings of the multiple types of fibers in a uniform state, each fiber can be randomly distributed. Can be mixed and arranged. However, as long as the fibers are divided into thin layers in which substantially different types of fibers are mixed, they may be laminated so that different types of fibers are arranged in each layer.

As for the combination of fiber materials, a combination of dissimilar fibers such as an inorganic fiber and an organic fiber is preferable to a combination of similar inorganic fibers such as a carbon fiber and a glass fiber. In particular, a combination of using glass fiber as the inorganic fiber and polyethylene fiber or polyester fiber as the organic fiber is preferred.

[0019]

[Operation] The fiber-reinforced composite material of the invention according to claim 1 has the following features:
Since different types of fibers are arranged in the matrix, when an external load such as elongation or compression is applied, the stress generated by the same deformation will differ due to the difference in the physical properties of each fiber, and the stress at the interface with the matrix resin will vary. Due to the difference in the bonding strength of the two, there are differences in the peeling behavior of each,
As fracture progresses as small amounts of energy are released one after another in many minute locations, even after stress exceeding the maximum allowable stress occurs in the composite material, it withstands the stress through minute peeling that gradually occurs at many locations. The material absorbs more energy and becomes sticky, like a metal material.

The energy absorbing member for a bumper according to the invention described in claim 2 is attached so as to receive a compressive load from the side surface of the cylindrical portion, and has a high impact absorption ability even against a load from an oblique direction. The stress fluctuations that occur when subjected to stress are significantly reduced compared to when one type of fiber is used as the reinforcing fiber, resulting in an extremely gentle compressive load-displacement curve. Therefore, the absorbed energy with respect to the maximum load becomes very large, and the impact load caused by the collision of the automobile is not applied to the human body, and the impact on the occupant is extremely mild.

The reason why the above phenomenon occurs is not clear, but if only one type of reinforcing fiber is used in the energy absorbing member, the adhesive force (interfacial bonding force) between the fiber and the resin is uniform, and the energy absorption Because there is no trigger for destruction when the absorbent material undergoes compression deformation, the compression energy accumulates, and when it can no longer withstand, fiber delamination occurs all at once, and the delamination immediately progresses to large deformation, resulting in a sudden and severe delamination. On the other hand, when multiple fibers are mixed, the adhesion effect to the resin differs depending on the type of fiber, so minute peeling easily occurs at the interface of fibers with low adhesion effect, and when deformed. This is presumed to be due to the fact that the energy is not accumulated excessively and is gradually released.

When polyethylene fibers and glass fibers are mixed, as the mixing ratio of polyethylene fibers is increased,
Load fluctuations in the compression load-displacement curve gradually subside, and when about 10% (volume ratio) of polyethylene fibers are mixed, sudden fluctuations in load almost no longer occur. but,
When the mixing ratio of polyethylene fibers is increased, the load level itself also tends to decrease and the absorbed energy also tends to decrease, so it is not preferable to increase the mixing ratio too much. Therefore, when combining organic fibers and inorganic fibers as a combination of different types of fibers, the mixing ratio of organic fibers varies depending on the type of fibers, but is preferably about 30% or less.

[0023]

【Example】

(Example 1) Next, a first example embodied in a plate-shaped laminated composite material will be described with reference to FIG. Virtually untwisted glass fiber roving (filament) and high strength polyethylene fiber (
After mixing and aligning fiber bundles with Dyneema (trade name: Dyneema, manufactured by Toyobo Co., Ltd.) and arranging them in layers, they were impregnated and cured with epoxy resin to form a plate-like laminated composite material. Figure 1 shows the results of measuring the relationship between load and displacement when a shear load is applied to a plate-like laminated composite material in which the volume ratio of glass fibers and polyethylene fibers is 90/10.

Unlike the case where the reinforcing fibers are 100% glass fibers, even after the maximum load is reached, the deformation continues while the stress is maintained at a substantially constant level, and the absorbed energy against the maximum load becomes very large. In addition, since the destruction progresses gradually, no thorns (hangnails) occur in the damaged area.

[0025] Applications of such plate-shaped laminated composite materials include automobile bodies, ship hulls, guardrails, etc. Cylindrical materials made by filament winding are used as bicycle frames. It is important for these members to minimize damage to the human body in the event of a collision, and the plate-like laminated composite material, which absorbs a large amount of energy in the event of a collision and does not generate splinters in the damaged portion, satisfies this requirement. Furthermore, when used in a member such as an aircraft wing, the shape is maintained without sudden breakage even if there is a problem in which an impact load exceeding the permissible range is applied during flight. Therefore, the aircraft can survive until landing, increasing the return rate and preventing major accidents. (Example 2) Substantially untwisted glass fiber rovings and carbon fiber rovings were alternately arranged layer by layer, and then impregnated with epoxy resin and cured to form a plate-like laminated composite material. FIG. 2 shows the results of measuring the relationship between load and displacement when a shear load is applied to the plate-like laminated composite material.

[0026] In this example, 100% carbon fiber is also used.
Unlike the case of , even after the maximum load is reached, deformation continues with a small change in stress, and the absorbed energy against the maximum load increases. However, unlike the case of the previous embodiment, after reaching the maximum load, the stress is not kept constant but gradually decreases. This is considered to be due to both the physical properties of the two types of fibers and the difference in the mixing state. In other words, in this example, both the two types of fibers are surface-activated as materials for composite materials, and both have a high adhesive effect with the resin, and the two types of fibers are alternately used in each layer. Therefore, compared to the case of the above embodiment in which each layer of the laminated fiber layer was constructed by aligning two types of fibers, the mixing unit of both fibers is not fine, and the separation point between the layers is finely divided. This is thought to be due to insufficient conversion.

(Third Embodiment) Next, a third embodiment of the energy absorbing member for a bumper will be described with reference to FIG. A fiber bundle made by mixing glass fiber roving and high-strength polyethylene fiber (product name: Dyneema, manufactured by Toyobo Co., Ltd.) is used as a reinforcing fiber, and a mandrel is attached to the filament (fiber bundle) while resin is attached. A cylindrical energy absorbing member with a constant wall thickness was produced by a filament winding (FW) method in which the resin was wound on top and cured by heating. Epoxy resin is used as the resin, and the fiber bundle is wound approximately at right angles to the rotating shaft. When compressive load is applied from the side of each energy absorbing member manufactured under the same conditions except that the mixing ratio of polyethylene fiber and glass fiber is changed to 0%, approximately 5%, and approximately 10% by volume. Figure 3 shows the results of measuring the relationship between the load and the amount of displacement.

The compressive loads in the respective compressive load-displacement curves shown in FIG. 3 correspond to the stress generated during compressive deformation of the energy absorbing member. As shown in Figure 3(a), in an energy absorbing member using only glass fiber as the reinforcing fiber,
At the initial stage of compression, the stress generated by compression deformation fluctuates rapidly, and the stress suddenly decreases dramatically. On the other hand, when polyethylene fibers are mixed with glass fibers as reinforcing fibers, the severe fluctuations in stress caused by compressive deformation are reduced, and when the mixing ratio of polyethylene fibers is approximately 10%, as shown in Figure 3 ( As shown in c), sudden fluctuations in stress almost no longer occur. The reason for this is that the adhesion effect to resin differs depending on the type of fiber, so minute peeling easily occurs at the interface of fibers with low adhesion effect.
It is presumed that this is because the energy during deformation is not sufficiently accumulated.

[0029] Increasing the mixing ratio of polyethylene fibers suppresses load fluctuations, but if the ratio of polyethylene fibers is increased too much, the load level itself tends to decrease and the absorbed energy also tends to decrease, so it is not recommended to increase the mixing ratio too much. I don't like that.

(Embodiment 4) Next, the fourth embodiment is shown in FIGS. 4 and 5.
Explain according to the following. Energy absorbing member 1 of this example
The energy absorbing member differs greatly from the energy absorbing member of the first embodiment in that it has a structure in which a plurality of annular cylindrical portions are combined. As shown in FIG. 4, the energy absorbing member 1 has two cylindrical parts 2 of the same shape arranged in parallel with each other in contact with each other, and an elliptical cylindrical part 3 outside of the cylindrical parts 2 is integrally connected with both cylindrical parts 2. It is formed. In addition, both the cylindrical portions 2 and the elliptical cylindrical portions 3 are reinforced with mixed fibers of polyester fibers and glass fibers (about 10% polyester fibers by volume).
%) is used.

The energy absorbing member 1 is manufactured by first manufacturing a cylinder corresponding to the cylindrical portion 2 by the FW method in the same manner as in the third embodiment, and then arranging the two cylinders in parallel so as to abut each other. The resin is attached to the mixed fiber of polyester fiber and glass fiber around the outer periphery, and it is wrapped using the FW method.
Produced by heating and curing resin.

FIG. 5 shows the results of measuring the relationship between load and displacement when a compressive load is applied to this energy absorbing member 1 from its side. In this case, although some load fluctuations are seen, the level of absorbed energy relative to the weight of the energy absorbing member is quite high.

(Embodiment 5) Next, a fifth embodiment will be explained with reference to FIG. In this example, the structure of the energy absorbing member 1 was the same as that of the fourth example, and a mixed fiber of polyethylene fiber and glass fiber (about 10% by volume polyethylene fiber) was used as the reinforcing fiber. This is different from the fourth embodiment in this point. FIG. 6 shows the results of measuring the relationship between load and displacement when a compressive load is applied to this energy absorbing member 1 from its side. In this case, there is a slight variation in the load compared to the case where 10% polyethylene fiber was mixed in the first example, but the load was slightly different from the case where 5% polyethylene fiber was mixed or the case where polyester fiber was mixed with 10% glass fiber. Compared to the fourth example, the variation in load during compressive deformation was significantly reduced. In addition, the load level increased as the number of fractured areas increased due to the two cylindrical portions in contact with each other being compressed and strongly crimped together. In other words, although the mixing ratio of polyethylene fibers has been increased to such an extent that a simple cylindrical energy absorbing member has an insufficient load level, it is possible to combine a plurality of cylindrical portions 2 and elliptical cylindrical portions 3 as in this example. By combining these, you can easily increase the load level sufficiently. Therefore, the absorbed energy with respect to the maximum load during compressive deformation can be made very large, and the absorbed energy per weight of the energy absorbing member can be made sufficiently large. Furthermore, since the material is FRP with a specific gravity of around 2, it is much smaller and lighter than metal.

It should be noted that the present invention is not limited to the above-mentioned embodiments; for example, the number of reinforcing fibers may be two or more, or the reinforcing fibers may be interlaced (interlaced) in fiber units. When using interlaced threads (mixed weave) or arranging different types of fibers in layers, it is best to divide and arrange a small amount of fibers between the large fiber layers. Alternatively, instead of arranging the fibers in layers, a three-dimensional fabric woven so that a plurality of types of fibers are dispersed within the plane may be impregnated with a matrix resin and cured. In addition, the resin constituting the FRP material is not limited to epoxy resin, but thermosetting resins such as phenol resin and unsaturated polyester may also be used, and as reinforcing fibers, carbon fibers, aramid fibers, etc. can be used instead of glass fibers. Various functional fibers with physical properties such as elasticity and high strength are used.

The cross-sectional shape of the cylindrical portion of the energy absorbing member 1 is not limited to circular or elliptical shapes, but may be substantially annular, such as a combination of circular arcs with different curvatures. Furthermore, in the case of a structure in which a plurality of cylindrical parts are combined as in the fourth embodiment, the number of cylindrical parts may be increased or the diameters of the cylindrical parts may be changed. or,
In the case of the energy absorbing member 1, resins other than epoxy resins are used, and various functional fibers other than glass fibers are used, but in the case of bumper members, reinforcing fibers are cost-effective due to the required level of weight reduction and heat resistance. Preferably, the main component thereof is glass fiber.

[0036]

[Effects of the Invention] As detailed above, according to the invention described in claim 1, delamination of reinforcing fibers does not occur suddenly, and even after stress exceeding the maximum allowable stress is generated in the composite material. The result is a composite material that deforms while withstanding stress due to minute peeling that gradually occurs between each layer, and exhibits tough behavior similar to that of metal against external loads. In addition, since the amount of energy absorbed during breakage is large, the breakage does not progress rapidly even under impact loads, allowing continued use and increasing the time required for repair. Furthermore, even after destruction, the protrusions (thorns) of the broken fibers are not exposed, and when used for car bodies, guardrails, etc., damage to the human body in the event of a collision can be minimized.

Furthermore, according to the invention as set forth in claim 2, the energy absorbing member is formed to have an annular cross section and is used while receiving a compressive load from the side surface thereof. Has high shock absorption ability. Furthermore, stress fluctuations during compressive deformation are significantly reduced compared to when one type of fiber is used as reinforcing fibers, and energy absorption is performed stably. Therefore, it is possible to reduce the impact on the human body when a car collides, and also absorb a large amount of energy.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the shear deformation behavior of a plate-like laminated composite material of a first example.

FIG. 2 is a diagram showing the shear deformation behavior of the plate-like laminated composite material of the second example.

FIG. 3 is a diagram showing compressive load-displacement curves of energy absorbing members manufactured by changing the mixing ratio of polyethylene fibers and glass fibers constituting reinforcing fibers in the third example.

FIG. 4 is a schematic perspective view of an energy absorbing member according to a fourth embodiment.

FIG. 5 is a diagram showing a compressive load-displacement curve of the energy absorbing member.

[Fig. 6] Compressive load of the energy absorbing member of the fifth embodiment -
It is a figure showing a displacement amount curve.

FIG. 7 is a diagram showing a load-displacement curve of a laminated composite material using glass filaments as reinforcing fibers.

FIG. 8 is a diagram showing a load-displacement curve of a laminated composite material using carbon filaments as reinforcing fibers.

FIG. 9 is a schematic plan view showing a state in which a bumper is supported by a conventional bumper support member.

FIG. 10 is a schematic perspective view showing a conventional energy absorbing structural member.

FIG. 11 is a compressive load-displacement curve of a conventional bumper support member.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1... Energy absorption member, 2... Cylindrical part, 3... Oval cylindrical part.

Claims (2)

[Claims] 1. A fiber-reinforced composite material in which at least two types of fibers are used as fiber materials arranged in a layered state in a matrix, and these fibers are arranged in a mixed state. 2. A bumper in which a filament is wound in the circumferential direction so as to have an annular cross section and is formed into a cylindrical shape of a fiber-reinforced composite material cured with a resin, in which at least two types of fibers are mixed as the filament. Energy absorbing member for use.