JP3246041B2 - Energy absorbing material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an energy absorbing member used for a support member of a bumper mounted on an automobile or a lower floor of a helicopter.

[0002]

2. Description of the Related Art In order to protect a vehicle body and a passenger at the time of a collision, an automobile is generally provided with a bumper for absorbing impact energy at the time of a collision in front and rear of the vehicle body. Bumpers need to irreversibly absorb energy in the event of a large load applied when the vehicle collides with an obstacle. In order to increase the absorbed energy, various improvements in the material and structure of the support member for supporting the bumper body have been conventionally made.

[0003] Impact absorbing members are also used below the seat floor of helicopters. As this shock absorbing member, the shock when the aircraft lands due to an accidental failure is moderated even a little,
Particularly, in order to reduce the influence on passengers, there is a demand for a member that is lightweight and has a high energy absorption function.

[0004] For example, German Patent (3262150) published February 18, 1988 discloses a bumper attached to a stay of a vehicle body via an elastically deformable damping molded body made of fiber reinforced plastic (FRP). Have been. The damping molding is formed substantially in a ring shape, and the reinforcing fibers of the fiber-reinforced plastic forming the damping molding are arranged in the circumferential direction. The damping molded body is used in a state where an impact force is applied from its side surface, that is, in a state where the axis of the damping molded body is orthogonal to the direction in which the impact force is applied.

Japanese Unexamined Patent Publication No. 57-124142 discloses an impact protection structural material used for a bumper, as shown in FIG. 11, comprising a strip 21 made of a fiber composite material (for example, an epoxy resin impregnated glass fiber). A structure 22 formed in a cylindrical shape with a network structure has been proposed. The strip 21 is the structure 2
Each of the nodes 23 is formed by about ten layers of fiber composite material strips 21 arranged at an angle of inclination of 30 to 60 degrees with respect to the two longitudinal axes. Structure 2
No. 2 is used in a state where a compressive load is applied in the axial direction of the cylinder, and when an axial load acts on the structure 22, delamination occurs at the opposing nodes 23 of the network, and the shear yield occurs at the interface between the fiber and the matrix. As a result, energy is absorbed stepwise.

[0006] In addition, US Pat. No. 3,143,321 discloses FIG.
As shown in (2), an energy absorbing member including a cylindrical body 24 and a fixing member 25 having a convex portion 25a that cuts into the inner surface of the cylindrical body 24 has been proposed. This energy absorbing member is also used in a state where a compressive load is applied in the axial direction of the cylinder.
When the cylindrical body 24 is subjected to axial compression, the projection 25a acts to expand the cylindrical body 24 outward, and the cylindrical body 2
4 is destroyed continuously.

[0007]

However, when an external force is applied to the substantially ring-shaped fiber-reinforced plastic as disclosed in the above-mentioned German patent from the side thereof, the material is broken.
The deformed part is destroyed only at the part extending in the same direction as the load,
The portion perpendicular to the external force remains substantially intact and is not destroyed. Therefore, the amount of energy absorbed during the compression deformation process when a load is applied to the member (specifically, represented by the area between the compression load-displacement curve and the axis representing the displacement) is extremely small, and the weight of the member is small. There is a problem that the hit efficiency is poor.

On the other hand, a cylindrical impact protection structural material disclosed in Japanese Patent Application Laid-Open No. 57-124142 is used with a bumper supported so that a compressive load is applied from the axial direction of the cylinder. Therefore, when a compressive load is applied to break, all parts are broken, so that the energy absorption efficiency per member weight can be increased as compared with a case where a compressive load is applied from the side. However, the intersection angle of the strip 21 is 30
Since it is composed of a mesh structure of up to 60 degrees, there is a problem that when a compressive load is applied in the axial direction, the tubular body is easily compressed and deformed with a small load due to deformation of the mesh structure. Also, when there is a condition such as a bumper support member that reduces the impact on the human body, it is necessary to suppress the maximum value of the load to a low level that does not affect the human body. Energy absorption is reduced. Therefore, in order to satisfy the requirement of reducing the impact on the human body and increasing the amount of energy absorption during deformation, it is necessary to prevent the occurrence of sudden loads and to set the compressive load-displacement curve as flat as possible with as little load fluctuation as possible. It is important to keep it at an appropriate level. However, this impact protection structural material has a problem that the amount of energy absorption is unlikely to increase because the load gradually decreases as the displacement increases.

Further, the energy absorbing member disclosed in US Pat. No. 3,143,321 requires a fixing member having a convex portion for breaking the cylindrical member in addition to the cylindrical member, and the fitting between the convex portion and the cylindrical member is required. The combined state greatly affects the fracture behavior. And since a cylindrical body and a fixing member are manufactured separately, there exists a possibility that destructive behavior may become unstable by the manufacturing error of both.

The present invention has been made in view of the above problems, and an object of the present invention is to reduce the impact on a passenger by reducing the impact at the time of a collision of a car or landing due to a rotor failure of a helicopter. An object of the present invention is to provide an energy absorbing member which does not generate a sudden load during collision deformation and has good energy absorbing efficiency per member weight.

[0011]

In order to achieve the above object, an energy absorbing member according to the present invention is formed into a tubular shape with a fiber reinforced resin mixed with short fibers, and a wall of the tubular portion is formed at a first end portion. The second end portion is formed so as to be thicker on the second end side, and the wall surface of the first end portion is formed so as to be curved outward so that its tip protrudes outward from the outer peripheral surface of the cylindrical portion.

It is preferable that a bottom wall is formed at the second end of the cylindrical portion, and the inner surface of the cylindrical portion and the inner surface of the bottom wall are connected by an arc surface.

[0013]

The energy absorbing member of the present invention is used in a state where it is mounted so as to receive a compressive load from the axial direction of the cylindrical portion. When a load is applied in the axial direction of the energy absorbing member, the first portion having a small cross-sectional area, that is, the first portion having a small thickness, is formed.
The destruction starts gradually from the end, and the destruction site gradually propagates to the two ends. Then, continuous stable destruction is sustained, and large energy is absorbed. Since the destruction occurs at all portions over the entire circumference of the cylindrical portion and absorbs energy, the energy absorbing member has improved energy absorption efficiency per member weight.

Since the first end of the cylindrical body, that is, the thin-walled end is curved outwardly in a trumpet shape, a sudden large load does not occur when the load rises at the beginning of the collision. The second of the cylindrical part
In the case of a configuration in which a bottom wall is formed at the end, a small-diameter hole is formed in the bottom wall, and the bottom wall can be directly attached to an automobile frame or the like by means such as bolting. In addition, since the inner surface of the cylindrical part and the inner surface of the bottom wall are connected by an arc surface, no breakage due to stress concentration occurs at the connection part, and continuous stable breakage continues to the final stage and large energy is absorbed Is done.

[0015]

【Example】

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.

As shown in FIGS. 1 and 2, the energy absorbing member 1 is formed in a cylindrical shape. The wall of the tubular portion 2 is formed so as to become gradually thicker from the first end to the second end. The outer diameter of the cylindrical portion 2 is constant, and the inner diameter is the first.
It is formed so as to continuously reduce from the end to the second end.

The shape of the wall surface of the first end of the cylindrical portion 2 is a trumpet shape that curves outward so that the tip protrudes outward from the outer peripheral surface of the cylindrical portion. As shown in FIG. 2B, the curved portion 3 is formed so that both the inner and outer surfaces are curved, and the radius of curvature of the outer surface 3a is set smaller than the radius of curvature of the inner surface 3b. That is, the energy absorbing member 1
Has a gradually increasing cross-sectional area from the first end to the second end.

As a material of the energy absorbing member 1, a resin mixed with short fibers, that is, a fiber reinforced resin (FRP) is used. The resin may be either a thermoplastic resin or a thermosetting resin, but the thermosetting resin generally requires a longer time for molding and curing than the thermoplastic resin, and is expensive because of the high cost. Resins are preferred. The molding is mainly performed by injection molding. The length and content of the short fibers to be mixed can be freely selected, but the longer the fiber length or the higher the fiber content, the larger the breaking load and the greater the energy absorption effect. Is preferred.
However, an excessive fiber content has a limit due to poor dispersion in the resin, and it is usually difficult to increase the fiber content to about 40% or more. When glass fiber having a fiber length of 3 mm was used and a fiber reinforced resin having a fiber content of about 30% was used, good results were obtained.

Next, the operation of the energy absorbing member 1 configured as described above will be described. This energy absorbing member 1
Is used as a support member for a bumper or as an impact protection member to which a load acts directly under a compressive load from the axial direction.

Since the breaking load is usually proportional to the wall thickness, when the energy absorbing member 1 receives a compressive load in the axial direction, the cylindrical portion 2 starts to break at the first end having the thinnest wall. Since the thin portion at the tip (first end) is easily broken with a small load, no sudden large load occurs and no impact is given to the occupant.

If the load at the tip of the cylindrical portion 2 is large, if the load is at a large level, it spreads to the adjacent thick portion requiring a larger breaking load, and the breaking progresses one after another. And absorb a lot of energy. The cylindrical portion 2 absorbs energy by breaking at all portions over the entire circumference of the cylindrical portion. Therefore, despite the small weight of the material constituting the cylindrical portion 2, it absorbs a large amount of energy and becomes an extremely efficient and excellent energy absorbing member.

If the entire cylindrical portion 2 is composed of portions having equal strength, that is, if the wall thickness is constant,
The entire cylindrical portion is subject to destruction due to the compressive load, and destruction (buckling) occurs in the weakest portion (usually the central portion) of the portion, so that the cylindrical shape cannot be maintained. As a result, the load is not propagated to the remaining portion and no continuous destruction occurs, so that the final overall absorbed energy is at a very small level.

Also, the fact that the curved end portion 3 of the cylindrical portion 2 expands outwardly in a trumpet shape is extremely necessary for crushing the cylindrical portion 2 and continuing the destruction toward the thick side. Plays an important function. Due to the presence of the curved portion 3, the initial stage of destruction causes the wall of the tubular portion 2 to be directed outward and torn by several cracks, and just the flower buds outward to several petals one by one. Destruction progresses as it divides and spreads all at once. At this time, the wall does not tear prior to the destruction, but simultaneously or slightly after the destruction of the wall. That is, the wall opens in a petal shape while being torn by the load from the axial direction, transmitting the pattern of its destruction to the adjacent part,
It leads to reproducible and stable fracture behavior.

If the wall thickness merely changes along the axial direction of the cylindrical portion 2, stable and continuous breaking behavior cannot be obtained. It changes variously, and the absorbed energy with respect to the breaking load greatly varies.

In this embodiment, since the inner surface of the cylindrical portion 2 is formed in a tapered shape in one direction, that is, the diameter is reduced toward the second end portion, it is difficult to manufacture by injection molding. There is also a merit that work such as die cutting is easy.

As shown in FIGS. 1 and 2, injection molding is carried out using a polypropylene resin (fiber content 30%) mixed with glass fibers (fiber length: 3 mm) as short fibers for reinforcement.
Was manufactured. FIG. 3 shows the result of measuring the relationship between the compressive load and the amount of displacement when a compressive load is applied to the energy absorbing member 1 in the axial direction. The compression was performed until the distance between both ends of the energy absorbing member 1 became approximately 70 mm. The dimensions of each part are as follows.

The thickness t 1 of the bending start portion of the bending portion 3: 5 mm The outer diameter φ of the cylindrical portion 2: 60 mm The thickness t 2 of the second end of the cylindrical portion 2: 10 mm The length L of the energy absorbing member 1: 100 mm Curvature radius R1 of the curved portion outer surface 3a: 2.5 mm Curvature radius R2 of the curved portion inner surface 3b: 7 mm Projection length p of the curved portion tip: 1 mm Also, for comparison, the first portion of the cylindrical portion 2 is curved. The same measurement was performed on an energy absorbing member having the same structure and dimensions as those described above except that the portion 3 was not present. FIG. 4 shows the results.

As is apparent from FIG.
In the case of the energy absorbing member 1 in which the load is present, the load tends to increase slightly with an increase in the amount of displacement, but the load is kept stable by generating a substantially constant load. As a result, the absorbed energy represented by the area between the load curve and the axis representing the displacement is also large.

On the other hand, in the case of the energy absorbing member having no curved portion 3, since a buckling break occurs in a part of the thin portion of the cylindrical portion 2, a sudden large deformation occurs at the beginning of compression as shown in FIG. After the load occurred, a relatively small load continued intermittently. As a result, the absorbed energy was also at a small level. When the state of destruction of the energy absorbing member was observed, no petal-shaped destruction was observed.

(Embodiment 2) Next, a second embodiment will be described with reference to FIGS.
It will be described according to. In this embodiment, the bottom wall 4 is formed integrally with the second end of the tubular portion 2 and the thickness of the tubular portion 2 is formed so as to change in two stages in the axial direction macroscopically. This is greatly different from the first embodiment.

The cylindrical portion 2 is formed so that its outer diameter is constant and its thickness changes macroscopically in two stages. That is,
The cylindrical portion 2 includes a relatively thin first stage 2a and a thick second stage 2b, and a curved portion 3 is formed at the tip of the first stage 2a. The inner surface of each of the first stage 2a and the second stage 2b is formed in a slightly tapered shape so as to be thicker on the side closer to the bottom wall 4. The continuous portion of the first stage 2a and the second stage 2b is formed in a tapered shape connected by a small arc surface.

Inner surface of a continuous portion between the second stage 2b and the bottom wall 4,
That is, the inner surface of the cylindrical portion 2 and the inner surface of the bottom portion 3 are arc-shaped surfaces 4a.
Connected by A small diameter hole 5 is formed in the center of the bottom wall 4. The hole 5 serves as a bolt insertion hole when the energy absorbing member 1 is attached to a frame of an automobile or the like. Since the bottom wall 4 is not destroyed and does not contribute to energy absorption, it is not preferable to make the bottom wall 4 too thick and have a large weight in spite of weight reduction. Therefore, the bottom wall 4 only needs to be thick enough to withstand the load at which the tubular portion 2 is broken.

The energy absorbing member 1 is also used in a state where it receives a compressive load from the axial direction. There are roughly two types of methods for attaching the energy absorbing member 1 to an automobile frame or the like. The first method is to insert a bolt through the hole 5 in the bottom wall 4 and directly fix the bottom wall 4 by means such as bolting. In a second method, as shown in FIG. 7, a lid 6 is attached to the first end of the energy absorbing member 1, and a bolt 7 penetrating through the hole 5 of the bottom wall 4 and the hole 6a of the lid 6, This is a method of fixing with a nut 8 which is screwed to the nut 7. In this method, the energy absorbing member 1 is fixed to the automobile with the bottom wall 4 in contact with the frame 9 and the lid 6 in contact with the bumper reinforcement 10.

The lid 6 is attached to the energy absorbing member 1 in a state where a pair of projections 6b formed inside the lid 6 are positioned so as to engage with the inner surface of the tubular portion 2 at a position deeper than the curved portion 3. . The lid 6 does not need to be particularly adhered to the cylindrical portion 2, but may be lightly adhered in advance for convenience of handling or the like.

When the energy absorbing member 1 receives a compressive load in the axial direction, as in the case of the first embodiment, the breakage progressively progresses from the distal end side of the tubular portion 2. If the connection between the cylindrical portion 2 and the bottom wall 4 is not a circular arc but a square, stress concentration occurs in the connection during the process of fracture, and a crack occurs before the fracture reaches the connection, resulting in fracture. Easier to do. If this break occurs during the break, the energy absorption function is significantly impaired.
However, since the connecting portion between the tubular portion 2 and the bottom wall 4 is connected by an arc surface, stress concentration does not occur at the connecting portion, and the tubular portion 2 is surely successively moved from the front end portion toward the bottom wall 4. It is destroyed and absorbs large amounts of energy.

In the energy absorbing member 1 of this embodiment, since the thickness of the cylindrical portion 2 changes in two steps, the first level 2a, which is the thin portion, is not removed until the first stage 2a is destroyed. Then, the second stage 2b, which is a thick portion, is broken, and the load rises to the second level. That is, the energy absorbing member 1 exhibits two stages of load change behavior according to the wall thickness, and one member can cope with two different levels of collision speed. This behavior is extremely important as a tuner function of the sensor for the operation of a so-called airbag used for protection of a vehicle occupant. The wall thicknesses of the first stage 2a and the second stage 2b are set depending on up to what collision speed is targeted.

For example, the second stage 2b in which the destruction of the second stage 2b occurs
Is set to a load level acting on the energy absorbing member 1 at the time of a collision at a speed equal to or higher than a certain speed at which there is a risk that the occupant may be obstructed, and the destructive load level of the second stage 2b is detected. Can be configured to open. In this case, for a low collision speed, the first stage 2a is destroyed and energy is absorbed, but the airbag does not open and the collision occurs at a speed higher than a certain speed that may hinder the occupant. The airbag opens while absorbing more energy. Therefore, when this energy absorbing member 1 is used as the tuner member, it becomes a lightweight, reliable and inexpensive functional member.

As in the case of the first embodiment, a polypropylene resin (fiber content: 30%) mixed with glass fiber (fiber length: 3 mm) was used as a short fiber for reinforcement by injection molding. The energy absorbing member 1 having the following shape was manufactured. FIG. 6 shows the result of measuring the relationship between the compressive load and the amount of displacement when a compressive load is applied to the energy absorbing member 1 in the axial direction. The dimensions of each part are as follows.

The thickness t 1 of the bending start portion of the bending portion 3: 5 mm The outer diameter φ of the cylindrical portion 2: 60 mm The thickness t 3 of the base end of the first stage 2 a: 6 mm The thickness of the tip of the second stage 2 b t4: 8 mm Thickness of base end of second stage 2b t5: 9mm Length L of energy absorbing member 1: 100mm Length L1 of first stage 2a: 40mm, Thickness of bottom wall 4 t6: 9mm Hole 5 Radius d: 11 mm Curvature radius R3 of the connecting portion between the second step 2b and the bottom wall 4: 5m
m, radius of curvature R1 of the outer surface 3a of the curved portion: 2.5 mm Radius of curvature R2 of the inner surface 3b of the curved portion: 7 mm Projection length p of the tip of the curved portion: 1 mm As is clear from FIG. The energy absorption level is 2 in response to the two-step change.
It is changing in stages. This confirms that the load is almost proportional to the wall thickness.

It should be noted that the present invention is not limited to the two embodiments described above. For example, the thickness of the cylindrical portion 2 is not necessarily limited to the second thickness.
It is not necessary to continuously increase the thickness toward the end. FIG.
As shown in (a), the thickness changes intermittently, that is, it has a continuously changing portion and a constant portion,
When the thickness changes in two stages as shown in FIG. 8 (b), depending on the length of the first stage 2a and the second stage 2b, one or both of the thicknesses are kept constant. You may.
Further, as shown in FIG. 9, the change in the thickness may be changed intermittently in multiple stages. That is, if the thickness gradually increases from the first end to the second end, the change may be continuous, intermittent, or stepwise. However, it is preferable that the wall thickness is changed little by little, rather than being constant and long.

The shape of the cylindrical portion 2 is preferably cylindrical, but may be rectangular. However, in order to break the wall of the cylindrical portion evenly, a cylinder or an elliptical cylinder formed with a smooth curved surface is preferable. In the case of a rectangular tube shape, it is preferable to make the joint portion a curved surface in order to prevent the joint portion on each surface from becoming square and causing abnormal stress concentration. For example, in the case of a hexagonal cylindrical shape, both the inner and outer surfaces of the cylindrical portion 2 have no corners as shown in FIGS. 10 (a) and 10 (b), and each surface is smoothly connected by a curved surface. Further, in connection to an automobile or the like, since those members have many square cross sections, it is often necessary to select a square tube and achieve aesthetic harmony with peripheral members. Even in such a case, it is preferable that the corners be smoothly connected in an arc shape and that no sharp bends be provided in order to cause the breakage continuously. It is easily guessed that the cylindrical shape is a particularly preferable shape, because the curved portions 3 are uniformly distributed in the circumferential direction, and it is easy to lead to a uniform petal-like destruction without bias.

Further, various functional fibers having high-strength physical properties such as carbon fibers and aramid fibers may be used as the reinforcing fibers constituting the FRP of the material, instead of the glass fibers. Further, the energy absorbing member 1 may be applied to an impact absorbing member that receives an impact load directly, a lower part of a seat floor of a helicopter, or the like. The energy absorbing member 1 is mounted on a moving body such as an automobile without using a bumper or the like.
When the device is used in a state where it is directly subjected to a load, it is preferable that the energy absorbing member 1 is installed such that the tip of the energy absorbing member 1 is directed in a direction in which the load is most easily applied. That is, when the energy absorbing member 1 is installed near the center of the front or rear portion of the moving body, the energy absorbing member 1 is installed parallel to the forward or backward direction, and when installed on the side, the tip is directed obliquely forward or obliquely rearward. Preferably, it is installed.

[0043]

As described in detail above, when the energy absorbing member of the present invention is destroyed, it gradually starts to break from the end of the cylindrical portion having the smaller cross-sectional area, and the entirety of the cylindrical portion is destroyed. The energy generated at all the parts over the circumference is absorbed, and the stable destruction continues, and large energy is absorbed, and the energy absorption efficiency per member weight is improved.

[Brief description of the drawings]

FIG. 1 is a sectional view of an energy absorbing member according to a first embodiment of the present invention.

FIG. 2A is a plan view of an energy absorbing member, and FIG.
FIG. 4 is a partially enlarged cross-sectional view of the tip of the energy absorbing member.

FIG. 3 is a graph showing a relationship between a compressive load and a displacement amount when an axial load is applied to the energy absorbing member.

FIG. 4 is a graph showing a relationship between a compressive load and a displacement when an axial load is applied to the energy absorbing member of the comparative example.

FIG. 5 is a sectional view of an energy absorbing member according to a second embodiment.

FIG. 6 is a graph showing a relationship between a compressive load and a displacement amount when an axial load is applied to the energy absorbing member of the second embodiment.

FIG. 7 is a partial cross-sectional view showing the energy absorbing member attached to the frame of the vehicle.

FIG. 8 is a cross-sectional view of an energy absorbing member of a modified example.

FIG. 9 is a sectional view of an energy absorbing member of another modification.

10A is a cross-sectional view of an energy absorbing member according to another modification, and FIG. 10B is a plan view thereof.

FIG. 11 is a schematic perspective view showing a conventional impact protection structural material.

FIG. 12 is a sectional view showing a conventional energy absorbing member.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Energy absorption member, 2 ... Cylindrical part, 2a ... 1st stage, 2b ... 2nd stage, 3 ... Bending part, 3a ... Outer surface, 3b ...
Inner surface, 4 ... bottom wall, 4a ... arc surface, 5 ... hole.

Continuation of the front page (56) References JP-A-56-131849 (JP, A) Japanese Utility Model Application Showa 59-1946 (JP, U) Japanese Utility Model Application Showa 64-1167 (JP, U) (58) Fields investigated (Int) .Cl. ⁷ , DB name) F16F 7/12

Claims (2)

(57) [Claims] 1. A cylindrical member formed of a fiber reinforced resin mixed with short fibers, wherein a wall of the cylindrical portion is formed so as to be thicker on a second end side than on a first end portion. An energy absorbing member in which a wall at one end is curved outward so that a tip of the wall protrudes outward from an outer peripheral surface of the cylindrical portion. 2. A bottomed cylindrical shape made of a fiber reinforced resin mixed with short fibers, the inner surface of the cylindrical portion and the inner surface of the bottom portion are connected by an arc surface, and the wall of the cylindrical portion is formed from the first end to the first end. The energy absorbing member is formed so as to be thicker toward the second end, and the outer wall of the first end is curved outward so that the tip protrudes outward from the outer peripheral surface of the cylindrical portion. .