JPH06123322A - Energy absorbing member - Google Patents

Abstract

PURPOSE:To provide an energy absorbing member having excellent energy absorbing efficiency per unit weight of member without generating a sudden load at the time of deformation due to a collision. CONSTITUTION:An energy absorbing member 11 is made of the fiber reinforced resin, in which short fiber is mixed, and formed into a cylindrical shape having the bottom, which consists of a cylindrical part 2 and a bottom part 3 having a round cross section. The tip of the cylindrical part 2 is formed with a taper part 2a so that the outer diameter thereof is gradually reduced as it comes close to the tip. The angle theta of the taper part 2a is formed at 60 degrees. The inner surface of the cylindrical part 2 and the inner surface of the bottom part 3 are connected through a circular surface 4. The cylindrical part 2 is formed into a slight taper-shape so as to be made thick gradually toward the bottom part 3. The angle of this taper is remarkably small (in ordinary, 3 degrees or less) different from the angle 6' of the taper part 2a.

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 supporting 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 an occupant at the time of a collision, an automobile is generally provided with bumpers at the front and rear of the vehicle body for absorbing impact energy at the time of a collision. The bumper needs to irreversibly absorb energy against a large load applied when the vehicle collides with an obstacle. In order to increase the absorbed energy, various improvements have been made to the material and structure of the support member that supports the bumper body.

In addition, a member having a light weight and a high energy absorbing function is required in order to soften the impact when the aircraft lands on the lower floor of the seat of the helicopter due to an accidental failure, and especially to reduce the influence on passengers. Has been.

For example, German Patent (3626150) published on February 18, 1988 discloses a bumper attached to a stay of a vehicle body through an elastically deformable damping molded body made of fiber reinforced plastic. . The damping molded body is formed in a substantially ring shape, and the reinforcing fibers of the fiber-reinforced plastic forming the damping molded body 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.

Further, in Japanese Patent Laid-Open No. 57-124142, as a shock-protecting structural material used for a bumper, a strip 21 made of a fiber composite material (eg, epoxy resin-impregnated glass fiber) is used as shown in FIG. A structure 22 having a cylindrical shape formed of a network structure has been proposed. The structure 22 is used in a state in which a compressive load is applied in the axial direction of the cylinder, and when an axial load acts on the structure 22, the opposing node points 2 of the network structure 2
3 causes delamination, and shear yield occurs at the interface between the fiber and the matrix to absorb energy stepwise. The strip 21 is inclined at an inclination angle of 30 to 60 degrees with respect to the longitudinal axis of the structure 22. Further, each knot 23 is formed by about 10 layers of the strip 21 made of a fiber composite material.

Further, in USP 3143321, etc., FIG.
As shown in FIG. 3, an energy absorbing member including a cylindrical body 24 and a fixing member 25 having a convex portion 25a that bites into the inner surface of the cylindrical body 24 is proposed. This energy absorbing member is also used in a state where a compressive load is applied in the axial direction of the cylinder.
Then, when the cylindrical body 24 is subjected to axial compression, the convex portion 25a acts so as to expand the cylindrical body 24 outward, and the cylindrical body 2
4 is continuously destroyed.

[0007]

However, when a substantially ring-shaped fiber reinforced plastic as disclosed in the above-mentioned German Patent is broken by applying an external force from its side surface,
The deformed part is broken only in the part in the same direction as the load, and the part in the direction perpendicular to the external force remains substantially in its original shape and is not broken. Therefore, the energy represented by the product of the stress and the deformation amount (specifically, the area between the compression load-displacement amount curve and the axis indicating the displacement amount) generated in the compressive deformation process when a load is applied to the member. There is a problem that the absorption amount is extremely small and the efficiency per member weight is poor.

On the other hand, the tubular impact protection structural material disclosed in JP-A-57-124142 is used with the bumper being supported so that a compressive load is applied from the axial direction of the tube. Therefore, when a compressive load is applied for destruction, all parts are destroyed, so that the energy absorption efficiency per member weight can be increased compared to the case where a compressive load is applied from the side. However, the crossing angle of the strip 21 is 3
Since it is composed of a mesh structure of 0 to 60 degrees, there is a problem that when a compressive load in the axial direction acts, the cylindrical body is easily compressed and deformed by a small load due to the deformation of the mesh structure. Also, if there is a condition to reduce the impact on the human body like a bumper support member, it is necessary to suppress the maximum value of the load to a level that has a low effect on the human body. The energy absorption amount of becomes smaller. Therefore,
In order to meet the requirements of reducing the impact on the human body and increasing the amount of energy absorbed during deformation, sudden load is prevented from occurring and the compression load-displacement amount curve is set to a flat level with minimal load fluctuation. It is important to keep However, this structural member for shock protection has a problem that the amount of energy absorption is difficult to increase because the load is gradually reduced as the amount of 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 tubular body in addition to the tubular body, and the fitting between the convex portion and the tubular body is required. The combined state greatly affects the fracture behavior. Since the tubular body and the fixing member are manufactured separately, the fracture behavior may become unstable due to manufacturing errors between them.
Further, if a load is applied from an oblique direction, the cylindrical body may be broken from the vicinity of the fitting portion with the fixing member, and a sufficient energy absorbing function may not be exhibited.

The present invention has been made in view of the above problems, and its purpose is to soften the impact at the time of landing due to a collision of an automobile or a rotor failure of a helicopter, and to reduce the influence on passengers. An object of the present invention is to provide an energy absorbing member that does not generate a sudden load at the time of collision deformation and has high energy absorbing efficiency per member weight.

[0011]

In order to achieve the above-mentioned object, in the invention according to claim 1, a fiber-reinforced resin mixed with short fibers is molded into a bottomed tubular shape, and the inner surface and the bottom portion of the tubular portion are formed. The inner surface is connected by an arcuate surface, and the tubular portion is formed so that its cross-sectional area becomes smaller toward the tip end side and continuously changes in the axial direction from the tip end to the middle.

According to the second aspect of the present invention, a fiber-reinforced resin mixed with short fibers is molded into a bottomed tubular shape, and the inner surface of the tubular portion and the inner surface of the bottom portion are connected by an arc surface to form a tubular shape. The cross-sectional area is formed so as to become smaller toward the tip side and continuously change in the axial direction over the entire length from the tip side of the part to the connection part with the bottom part.

[0013]

The energy absorbing member of the present invention is attached so as to receive a compressive load from the axial direction of the tubular portion. When a load is applied to the energy absorbing member in the axial direction, the fracture starts gradually from the tip of the tubular portion having a small cross-sectional area, and the fracture site propagates to the bottom side successively. Since the inner surface of the cylindrical portion and the inner surface of the bottom portion are connected by the arcuate surface, breakage due to stress concentration does not occur at the connection portion, and continuous stable breakage continues and large energy is absorbed. The breakage occurs at all parts over the entire circumference of the tubular part and absorbs energy, so that the energy absorption efficiency per member weight is improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment embodying the present invention will now be described with reference to FIGS.
This will be described with reference to FIG. As shown in FIGS. 1 and 2, the energy absorbing member 1 is formed in a bottomed tubular shape including a tubular portion 2 having a circular cross section and a bottom portion 3. At the tip of the tubular portion 2, a tapered taper portion 2a is formed, the outer diameter of which is gradually reduced toward the tip side. The cylindrical portion 2 has a constant outer diameter except for the tapered portion 2a, and an inner diameter of the bottom portion 3
It is formed so that it becomes smaller toward the sides. That is, the tubular portion 2 is formed in a slightly tapered shape that gradually becomes thicker toward the bottom portion 3. The angle of this taper is an angle θ (approximately 30 to 60) of the taper portion 2a provided at the tip of the tubular portion 2.
It is an extremely small angle (usually about 3 degrees or less) that is completely different from (degree). By providing such a slight taper, it is possible to ensure that the portion closer to the bottom portion 3 will be destroyed by a larger load, and continuous destruction from the tip will be promoted. The inner surface of the continuous portion of the tubular portion 2 and the bottom portion 3, that is, the inner surface of the tubular portion 2 and the inner surface of the bottom portion 3 are connected by an arc surface 4. Although the bottom portion 3 is used for mounting on a vehicle frame or the like, it is not destroyed and does not contribute to energy absorption. Therefore, it is not preferable to make the bottom portion 3 too thick to have a large weight, contrary to weight reduction. Therefore, the bottom portion 3 only needs to have a thickness that can withstand the load that breaks the tubular portion 2.

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 more time for molding and curing than the thermoplastic resin, and is generally expensive because the cost is high. Resin is preferred. The length and content of the mixed short fibers can be freely selected, but a longer fiber length and a higher fiber content both generate a large breaking load and a large energy absorption effect. Is preferable because it has The molding is mainly performed by injection molding. However, the tapered portion at the tip may be formed by cutting.

Next, the operation of the energy absorbing member 1 constructed as described above will be described. This energy absorbing member 1
Is used as a support member of a bumper or as a shock protection member to which a load is directly applied while receiving a compressive load from the axial direction. The attachment to an automobile frame or the like is performed by providing a small-diameter hole in the bottom portion 3 and bolting or the like. When the energy absorbing member 1 receives a compressive load in the axial direction, the tubular portion 2 has a taper portion 2a formed at the tip thereof and becomes thinner toward the tip thereof, so that the tubular portion 2 is easily broken with a small load. Therefore, it is destroyed even at a low collision speed, no sudden load is generated, and the passenger is not impacted.

The tapered portion 2a at the tip of the tubular portion 2 is the tubular portion 2
If it is provided on the outer surface side of the, the propagation of fracture tends to occur continuously and smoothly. When the taper portion 2a is provided on the inner surface side of the tubular portion 2, the central portion of the tubular portion 2 is deformed outward due to compression from the tip, so to speak, to form a bulge, and as a result, a crack is generated near the central portion and the seat Give in. Then, the load is reduced all at once, not only the occupant is impacted, but also the continuous fracture behavior is not maintained, and the energy absorption amount is also reduced, which is not preferable.

The area of the tip end surface of the energy absorbing member 1 and the angle θ of the tapered portion 2a are determined by the maximum load allowed during compression deformation. In order to reduce the maximum load generated, it is preferable to make the area of the tip end face small and to increase the inclination angle. The taper angle θ is preferably 30 to 60 degrees because the sharper the tip, the more smoothly the fracture starts and continues, but the energy absorption amount decreases.

The breakage generated at the tip of the tubular portion 2 spreads to the adjacent part, and the breakup progresses continuously and absorbs a large amount of energy. Upon compression failure, the tubular body causes buckling failure at all parts along the entire circumference of the tubular body to absorb energy. Therefore, although the weight of the material forming the tubular portion 2 is small, it absorbs a large amount of energy and becomes an excellent energy absorbing member with extremely high efficiency. If the entire tubular portion 2 is composed of parts having equal strength, a compressive load causes breakage (buckling) at the weakest portion of the entire tubular portion and maintains the tubular shape. become unable.
As a result, the load is not propagated to the remaining portion and continuous destruction is not performed, so that the final total absorbed energy becomes a very small level.

When a compressive load is applied to the tubular portion 2, the breakage of the tip portion gradually propagates and moves to the bottom portion 3 side. If the connecting portion between the cylindrical portion 2 and the bottom portion 3 is not a circular arc surface but a square shape, stress concentration occurs in the connecting portion in the above process, and a crack is generated before the fracture reaches, and the fracture easily occurs. However, when the connecting portion between the tubular portion 2 and the bottom portion 3 is connected by the arcuate surface 4, stress concentration does not occur at the connecting portion, and the tubular portion 2 is surely directed from the tip portion to the bottom portion 3. It is destroyed one after another and absorbs a large amount of energy.

An axial compressive load was applied to the energy absorbing member 1 produced by injection molding using polypropylene in which glass fibers having different lengths were mixed at a content ratio of 30% as short fibers for reinforcement. The results of measuring the relationship between the compressive load and the amount of displacement in this case are shown in FIGS. However,
FIG. 3 shows the case where the glass fiber length is 3 mm, and FIG. 4 shows the case where the glass fiber length is 12 mm. The dimensions of each part of the energy absorbing member 1 are as follows.

The most advanced wall thickness t0: 1.5 mm, the wall thickness t1: 5 mm of the cylindrical portion on the bottom side from the base end of the tapered portion, the wall thickness t2 at a position 80 mm away from the tip: 6 mm, outside the tubular portion. Diameter φ: 60 mm, energy absorbing member length L: 100 m
m, bottom wall thickness t3: 10 mm, radius of curvature R of connecting portion between tubular portion and bottom portion: 5 mm, angle θ of tip tapered portion: 60
Every time.

For comparison, the wall thickness of the tubular portion 2 on the bottom 3 side from the base end of the taper portion 2a is fixed to 5 mm, and other conditions are the same as the energy absorbing member 1 of FIG. FIG. 5 shows the measurement results of the relationship between the compressive load and the displacement amount when an axial compressive load is applied to the absorbing member. However, the length of the glass fiber is 3 mm. Further, in FIG. 6, when the angle θ of the tip tapered portion 2a is set to 10 degrees, in FIG. 7, when the connecting portion between the cylindrical portion 2 and the bottom portion 3 is formed at a right angle instead of an arc surface, in FIG. 10 shows the measurement results of the relationship between the compressive load and the displacement amount when the tip tapered portion 2 is formed inside as shown in FIG. However, the length of each glass fiber is 2m
m.

As is clear from FIGS. 3 and 4, when the length of the glass fiber is 3 mm or 12 mm, a large load is not generated at the initial stage of compression and a substantially constant load is generated and stable until the end of fracture. And the absorbed energy is large. Further, when the glass fiber length is long (FIG. 4), the load fluctuation is gentler and the absorbed energy is larger than when the glass fiber length is short (FIG. 3).

On the other hand, when the wall thickness of the cylindrical portion 2 is constant except for the taper portion 2a (FIG. 5), the load fluctuation is smaller than that when the wall thickness gradually increases toward the bottom portion 3 side. The absorbed energy was also large and small. That is, by gradually increasing the wall thickness of the tubular portion 2 toward the bottom portion 3 side, it is confirmed that the fracture is surely propagated from the tip end side of the tubular member 2 to the bottom portion 3 side in order.

Further, when the angle θ of the tip tapered portion 2a is reduced to 10 degrees, a sudden load change occurs as shown in FIG. 6 and the tubular portion 2 is broken in the middle. As a result, the absorbed energy until the end of destruction became small. Further, when the connecting portion between the tubular portion 2 and the bottom portion 3 was at a right angle (FIG. 7), the tubular portion 2 near the bottom face was cracked during the compression process, and thereafter the load was drastically reduced. Further, when the tapered portion 2a at the tip is provided inside (Fig. 8), a part of the tubular portion 2 expands outward due to a compressive load and a crack is generated, so the load decreases after a sudden load occurs. However, it was confirmed that the high level could not be maintained continuously.

The present invention is not limited to the above-described embodiments. For example, instead of forming the tip of the tubular portion 2 in a tapered shape, the tubular portion 2 as shown in FIG. It may be formed in a shape in which the tip of is cut obliquely at an angle of 30 degrees or less with respect to the axis. There may be one or more cutout points. Even in this shape, the cross-sectional area of the distal end portion of the tubular portion 2 gradually decreases toward the distal end side and continuously changes in the axial direction. Therefore, also in the case of the energy absorbing member 1 having such a shape, if a compressive load is applied to the tip end surface of the tubular portion 2 via the flat member orthogonal to the axis, the tubular portion 2 having the smallest cross-sectional area can be obtained. The fracture continuously progresses from the tip to the bottom 3 side. Further, the tip of the tubular portion 2 may be cut off obliquely, and the tip may be tapered.

Further, instead of gradually increasing the wall thickness of the tubular portion 2 excluding the taper portion 2a up to the connecting portion with the bottom portion 3, the wall thickness of the tubular portion 2 is gradually increased to a constant value thereafter. You may do it.

Further, when the bumper is supported by the energy absorbing member 1, in order to facilitate the support of the bumper, FIG.
As shown in (b), the lid 5 may be attached to the tip of the tubular portion 2 and the bumper 6 (illustrated by a chain line) may be supported via the lid 5. The shape of the lid 5 is the bottom portion 3 of the energy absorbing member 1.
The reason why the bumper 6 is inclined obliquely with respect to the bumper 6 is that since the bumper 6 is slightly bent backward due to its design, the bumper 6 has a shape along the inclination. The bumper 6, the lid 5 and the energy absorbing member 1 are provided with a single bolt 7 that penetrates from the outside of the bumper 6.
It is fixed to the body frame 8 by.

The shape of the cylindrical portion 2 is preferably a cylindrical shape from the viewpoint of easy manufacturing, but may be a rectangular cylindrical shape. However, in the case of the rectangular tube shape, it is preferable that the joint portion is a curved surface in order to prevent the joint portion of each surface from being angular and cause abnormal stress concentration. Further, as the reinforcing fiber constituting the FRP of the material, various functional fibers having high strength physical properties such as carbon fiber and aramid fiber may be used instead of the glass fiber.

Further, the energy absorbing member 1 may be applied to a shock absorbing member directly receiving an impact load or a seat floor of a helicopter. When the energy absorbing member 1 is used in a moving body such as an automobile in a state in which the energy absorbing member 1 directly receives a load without a bumper or the like, the tip of the energy absorbing member 1 is directed in the direction in which the load is most easily applied. It is preferably installed. That is, the energy absorbing member 1 is installed parallel to the forward or backward direction when it is installed near the center of the front or rear of the moving body, and the tip is directed diagonally forward or diagonally backward when installed on the side. It is preferably installed.

[0032]

As described above in detail, when the energy absorbing member of the present invention is broken, the breaking gradually starts from the end portion of the tubular body having the smaller area, and the load level is substantially constant as a whole. The energy absorption amount is increased and the energy absorption efficiency per member weight is improved because the energy is absorbed and the energy is absorbed by buckling and breaking at all parts of the energy absorption member.

[Brief description of drawings]

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

FIG. 2 is a schematic perspective view of an energy absorbing member.

FIG. 3 Energy absorbing member (glass fiber length 3 mm)
5 is a graph showing the relationship between the compressive load and the amount of displacement when an axial load is applied to the.

FIG. 4 Energy absorbing member (glass fiber length 12 m
It is a graph which shows the compressive load-displacement amount relationship at the time of adding an axial load to m).

FIG. 5 is a graph showing a relationship between a compression load and a displacement amount when an axial load is applied to an energy absorbing member (glass fiber length 3 mm) of a comparative example (constant wall thickness of a tubular portion).

FIG. 6 is a graph showing the relationship between the compression load and the amount of displacement when an axial load is applied to the energy absorbing member (glass fiber length 2 mm) of another comparative example (taper angle of 10 degrees).

FIG. 7 is a graph showing the relationship between the compressive load and the amount of displacement when an axial load is applied to the energy absorbing member (glass fiber length 2 mm) of another comparative example (perpendicular to the connecting portion).

FIG. 8 is a graph showing the relationship between the compression load and the amount of displacement when an axial load is applied to the energy absorbing member (glass fiber length 2 mm) of another comparative example (inside the taper portion).

FIG. 9 is a cross-sectional view of an energy absorbing member of a comparative example.

FIG. 10A is a schematic perspective view of an energy absorbing member of a modified example, and FIG. 10B is a cross-sectional view of a state in which the energy absorbing member and the bumper are assembled via a lid.

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

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

[Explanation of symbols]

1 ... Energy absorption member, 2 ... Cylindrical part, 2a ... Tapered part, 3 ... Bottom part, 4 ... Arc surface.

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[Procedure amendment]

[Submission date] January 21, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Correction content]

For comparison, the wall thickness of the tubular portion 2 on the bottom 3 side from the base end of the taper portion 2a is fixed to 5 mm, and other conditions are the same as the energy absorbing member 1 of FIG. FIG. 5 shows the measurement results of the relationship between the compressive load and the displacement amount when an axial compressive load is applied to the absorbing member. However, the length of the glass fiber is 3 mm. Further, in FIG. 6, when the angle θ of the tip tapered portion 2a is set to 10 degrees, in FIG. 7, when the connecting portion between the cylindrical portion 2 and the bottom portion 3 is formed at a right angle instead of an arc surface, in FIG. 10 shows the measurement results of the relationship between the compressive load and the displacement amount when the tip tapered portion 2 is formed inside as shown in FIG. However, the length of each glass fiber is 3m
m.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 6

[Correction method] Change

[Correction content]

FIG. 6 is a graph showing a relationship between a compression load and a displacement amount when an axial load is applied to an energy absorbing member (glass fiber length: 3 mm) of another comparative example (tapered portion angle: 10 degrees).

[Procedure 3]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 7

[Correction method] Change

[Correction content]

FIG. 7 is a graph showing the relationship between the compressive load and the amount of displacement when an axial load is applied to the energy absorbing member (glass fiber length 3 mm) of another comparative example (perpendicular to the connecting portion).

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] Figure 8

[Correction method] Change

[Correction content]

FIG. 8 is a graph showing the relationship between the compressive load and the amount of displacement when an axial load is applied to the energy absorbing member (glass fiber length 3 mm) of another comparative example (inside the taper portion).

Claims (2)

[Claims] 1. A fiber-reinforced resin mixed with short fibers, which is molded into a tubular shape with a bottom, and the inner surface of the tubular portion and the inner surface of the bottom portion are connected by an arcuate surface, at least from the tip to the middle of the tubular portion. An energy absorbing member formed so that the area becomes smaller toward the tip side and continuously changes in the axial direction. 2. A fiber-reinforced resin mixed with short fibers, which is molded into a tubular shape with a bottom, and an inner surface of the tubular portion and an inner surface of the bottom portion are connected by an arc surface, and a connecting portion from a tip end side of the tubular portion to the bottom portion. An energy absorbing member formed such that its cross-sectional area becomes smaller toward the distal end side over the entire length and continuously changes in the axial direction.