JPH1045023A - Energy absorbing member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain the cracking of a wall and prevent the deterioration of energy absorbing ability by forming the outer wall corner R of a sectionally hollow extruded material to be thinner than original. SOLUTION: In sectionally square with cross inside-shaped extrusion molding, the thickness t1 of a corner R and a joint between a center cross section and a outer wall are made smaller than an original thickness (t). The corner R is made thinner (a) at the inside or outside of at both sides, e.g. The joint between the center cross section and the outer wall is made thinner (b) at the center cross section or at the outer face side of the joint between the cross section and the outer wall, e.g. In this way, the cracking of the wall is restrained and the deterioration of energy absorbing ability is prevented.

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, such as a side member at a front portion of an automobile, for preventing an entire structure from being broken by converting an impact load applied from an axial direction into deformation energy.

[0002]

2. Description of the Related Art As shown in FIG. 13, an energy absorbing member at a front portion of an automobile includes a bumper 1, a front side member (hereinafter referred to as a side member) 2 and the like. It is mainly the side member 2 that absorbs energy. Therefore, the side member 2 is required to absorb more energy in a limited space.

[0003] As a side member of an automobile, a rectangular steel plate having a rectangular cross section made of a steel plate press is often used, but a light alloy such as an aluminum alloy which can be expected to be lighter in light of recent demands for a lighter weight can be considered. It has become These side members have a hollow column shape as a whole, and FIG.
As schematically shown in FIG. 4, when compressed in the axial direction, the wall surface deforms while forming a bellows shape, and absorbs energy by converting impact energy into plastic deformation energy of metal. In addition, in the case of aluminum alloy, since it has low strength and rigidity as compared with steel, it easily collapses plastically and has good energy absorbing ability.

A conventional energy absorbing member used for a side member or the like is well-known when it is subjected to a compressive force in the axial direction and plastically collapses, as disclosed in JP-A-4-50083 or JP-A-02-175452. The main focus is on whether to collapse the bellows. That is, by intentionally disintegrating in a bellows shape, Euler buckling (the side member itself is broken) is prevented, and stable energy absorption is obtained. However, these technologies can stabilize energy absorption but cannot increase the amount of energy absorption itself, and in order to increase the energy absorption, it is inevitable to increase the diameter and thickness of the cross section. Therefore, in order to secure a larger amount of energy absorption in a limited space and a limited weight like an automobile, these conventional technologies are not enough.

In order to reduce the weight, use of a light metal such as aluminum is conceivable. However, a light metal mainly made of an aluminum alloy has a drawback that it has a smaller elongation than steel and that even a small amount of deformation causes cracking. . In particular, when trying to give a large amount of energy absorption capacity with a small volume, a treatment to increase the material strength by heat treatment or adjustment of alloy components is performed, but such a treatment loses the ductility (elongation) of the material. In many cases, the material may be broken at the time of crushing and energy may not be absorbed effectively. Also, when not using a high-strength material, it is necessary to increase the thickness of the energy absorbing member, and when the profile wall deforms in a bellows shape during crushing, the wall surface distortion due to the thickening becomes too large,
There is a disadvantage that the energy absorption ability is reduced due to cracks.

[0006]

The use of a light alloy mainly composed of an aluminum alloy makes it possible to reduce the weight and obtain a good energy absorption capacity. However, it has been attempted to provide a large energy absorption capacity as described above. In this case, there is a possibility that the material may be broken and a predetermined energy absorbing ability may not be obtained. An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and an object of the present invention is to suppress cracks generated on a wall surface to prevent a reduction in energy absorption ability, and to use a material having a small elongation even in a limited space and weight. An object of the present invention is to obtain an energy absorbing member having a high energy absorbing ability.

[0007]

One of the energy absorbing members according to the present invention is an extruded member having a hollow cross section having an R (curvature) at a corner portion of an outer wall. An energy absorbing member characterized in that it is formed thinner than the plate thickness, or a hollow cross-section extruded material having a web at the corner portion of the outer wall and having an R at the corner portion of the outer wall, the corner R portion or the web An energy absorbing member characterized in that at least one of the joints with the outer wall is formed thinner than the original plate thickness.
Examples of such extruded shapes include a mouth shape having no web inside, a Japanese shape having one web inside (one web), an eye shape (two webs), and a cross-shape (web is a cross section). Etc. can be exemplified. FIG. 1 shows an example of a cross shape. In addition, it is assumed that the cross-section having a cross-section includes a cross-section having a cross-section substantially cross-section as shown in FIG. 2 in which the cross sections do not intersect at the center.

[0008] In the above energy absorbing member,
The original thickness is the thickness of the outer wall or the portion of the web that is not formed thin. Further, in the energy absorbing member, preferably, the corner R formed to be thinner than the original plate thickness.
When the ratio of the plate thickness of the joint portion between the inner or inner web and the outer wall and the original plate thickness (hereinafter, referred to as the plate thickness ratio) is k, k = 0.
Set it to 45-0.7.

Another energy absorbing member according to the present invention is a shape member having a hollow rectangular cross section, wherein a convex portion having a rectangular cross section is provided outside a wall portion. (See FIG. 8). Here, the profile having a rectangular cross section refers to a profile having a rectangular or square cross section. This includes not only a mouth shape in cross section, but also a shape material having a web inside such as an eye shape, a Japanese shape, and a Tagata shape. For this profile,
It is preferable that a convex portion is provided on the outside of the facing wall portion. Each of the above types of energy absorbing members is preferably formed using an extruded aluminum alloy material. In particular, by converting an impact load applied from the axial direction into a deformation energy like a side member of an automobile, the entire structure is formed. Applied to prevent destruction.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS.
The configuration and operation of the energy absorbing member according to the present invention will be described more specifically.

(1) Energy absorbing member having a cross section in a cross section FIG. 1 shows an extruded section having a cross section in a cross section in a cross section of a cross section of a corner R and / or a central section and an outer wall. The thickness t ₁ is made thinner than the original thickness t. FIG. 3A shows an example in which the corner R portion is thinned, that is, a thinner portion from the inside, a thinner portion from the outer portion, and a thinner portion from both sides.
FIG. 2B shows an example in which the thickness of the junction between the center cross section and the outer wall is reduced. In this example, the thickness of the center cross section is reduced (in this example, the inner surface of the outer wall at the portion where the cross section is joined is formed in an arc shape). The end of the thinned cross section and the arc-shaped portion are continuous with each other), and the thinned outer surface of the joint between the cross section and the outer wall is described. In each case, both ends of the thinned portion are formed in an arc shape in order to prevent concentration of strain. In this type of energy absorbing member, cracking is prevented by reducing the strain in the thinned portion, the portion to be thinned is specified, and the plate thickness ratio k (= t ₁ / t) of the portion is appropriately adjusted. By setting to a value, the energy absorbing ability can be improved without an extreme decrease in the axial strength.

In this type of energy absorbing member, the wall thickness at the time of collapse in a bellows shape is reduced by reducing the thickness of the joint between the corner R and / or the central cross section of the profile and the outer wall. Has the effect of preventing cracking of the material itself. In addition, concentration of strain can be prevented by connecting a portion to be thinned and another portion in an arc shape. This prevents the energy absorbing ability from being reduced due to the cracking of the material, and allows a material having a small elongation to be used as an energy absorbing member.

The reason that the material is prevented from cracking in the energy absorbing member is that bending strain is reduced in the thinned portion. That is, when the wall surface is crushed in a bellows shape, the wall surface is deformed by bending as shown in FIG. 3, and when the wall surface is thick, a high strain region (illustrated by an arrow)
In this case, the bending strain on the surface increases, which causes cracking. However, since the bending strain is proportional to the square of the wall thickness in the elastic region of the material, in the thinned portion, for example, the sheet thickness ratio k = 0.5, the bending strain is reduced to 1/4. Actually, since the cracking occurs in a plastic state, the above proportional relationship does not strictly hold, but the strain is surely reduced by thinning.

On the other hand, in the case of axial crushing, as shown in FIG.
Portion and the joint between the cross section and the outer wall) bear a larger load than the central portion. However, by thinning the end portions of the plate such as the corner R portions as in the present invention, FIG. As shown in (1), the load distribution becomes uniform, and the central portion, which did not significantly contribute to the absorption of the crushing load due to the impact, can also contribute to the energy absorption. For this reason, it is possible to sufficiently compensate for the decrease in the reaction force at the time of crushing due to the thinning.

(Embodiment) Next, the operation and effect of this type of energy absorbing member will be described more specifically. Extruded aluminum material having a cross section (50 mm × 50 mm, original plate thickness of 2 mm) and length (200 mm) as shown in FIG. 5 and joining to the outer wall of four corners R and four central cross sections The thickness ratio k of the thinned portion is 1-0.
The pressure-displacement curve shown in FIG. 6 (illustrated up to around a stroke of 140 mm) was obtained by changing the pressure in several steps to 3 and compressing each at a speed of 1 mm / s in the axial direction. However, the vertical axis in FIG. 6 is made dimensionless by the crushing load P of the profile by the load P (σ0.2) assuming that the entire cross section of the profile has yielded.
Note that 6061-T6 was used as the extruded aluminum material. It has a proof stress of 28 kgf / mm ² and a tensile strength of 31.5 kg.
It is f / mm ² and the elongation at break is 12%, which means that the material has a relatively small elongation and is brittle.

Further, from the results of FIG. 6, the energy absorption amount U of each section (based on the section of k = 1) and Pcr / P of each section are shown.
Means are obtained, and the relationship between them and k is shown in FIG. here,
The energy absorption U is represented by the area (up to a stroke of 160 mm) surrounded by each curve and the horizontal axis in FIG.
Is the maximum value of the initial crushing load (also referred to as the initial reaction force), and Pmean represents the average value of the crushing load up to a stroke of 160 mm (energy absorption / stroke).

According to the results of this experiment, the plate thickness ratio k = 1, that is, when the corner R portion is made thinner than in the original uniform plate thickness state, the overall energy absorption capacity is reduced while suppressing the initial reaction force Pcr. It can be seen that there is a region where is larger.
Further, when the plate thickness ratio k is set to 0.5, the amount of energy absorption is largest, and when it is more than this, the effect of cracking of the material (the crack itself cannot be completely prevented) is obtained. There is a decrease in the amount of energy absorbed, which may be due to the decrease in strength. That is, it is considered that k = 0.5 where the effect of cracking and the effect of strength reduction are balanced.

FIG. 7 shows that k = 0.45 to 0.7 as a desirable range of the thickness ratio k. This lower limit value k
= 0.45 is the lower limit value where the energy absorption exceeds the original thickness, and when the upper limit exceeds k = 0.7, the energy absorption is lower than the original thickness and the initial crushing load The ratio between the maximum value Pcr and the average crushing load Pmean exceeds 2.0. Normally, in the case of transportation structural members, the safety factor adopts a value near 2.0, so Pcr / Pmean
Is 2.0 or more, the maximum input expected compared to the load Pmean to be considered in the design becomes Pcr ≧ 2.0 × Pmean, so that the balance of the entire structure is broken and the entire structure may be destroyed. is there. From the above, 0.45 ≦ k ≦ 0.7
Is a preferable range.

FIG. 6 shows the results of an experiment in which a depression (crush initiator) is provided on the wall surface to make it easier to collapse in a bellows-like manner, as in a conventional energy absorbing member. This is the same as in the case of k = 1 described above except that there is a depression, and the maximum value Pcr of the initial crushing load can be reduced as compared with the case of k = 1. The subsequent load-displacement curve is almost the same as that of k = 1, and it can be seen that it does not lead to an increase in energy absorption. In contrast, the energy absorbing member according to the present invention has a higher energy absorption than the conventional one.

(2) Energy Absorbing Member with Hollow Rectangular Cross Section FIG. 8 shows a shape having a hollow rectangular cross section having a rectangular cross section having a height αt and a width (B / β) outside the wall surface. It is provided. FIG. 3A shows an example in which a convex portion is provided on one of the wall portions, FIG. 3B shows an example in which a convex portion is provided on two facing wall portions, FIG. 3C shows three examples, and FIG. This is an example in which the convex portions are provided on the four wall portions. However, from the viewpoint of the balance of the load distribution that the profile receives at the time of crush, the convex portions are provided outside the facing wall portions (b) or (d). More preferred.

When a conventional profile having a rectangular cross section is crushed in the axial direction, energy absorption due to the movement of the plastic hinge line at the corners (circled portions) shown in FIG. It is known that the amount of bending deformation energy consumed when a wall surface (a portion sandwiched between corners) is folded in a bellows shape is not so large. This indicates that increasing the number of corners increases the amount of energy absorption. In other words, in this energy absorbing member, a plastic hinge line is formed there by providing a convex corner portion on a wall surface portion that has not conventionally contributed much to energy absorption, and the impact energy is absorbed by the movement of the hinge line. As a result, it is possible to absorb more impact energy than a simple rectangular cross-section member without causing a significant increase in weight.

(Embodiment) Next, the operation and effect of this type of energy absorbing member will be described more specifically based on simulation analysis results. As shown in FIGS. 8A to 8D, a cross section B × H, a plate thickness t, and a height h (= 180 mm)
Of aluminum extruded profile of height αt on the outside of the wall,
Each of the projections having a rectangular cross section with a width (B / β) is compressed 80% of the height h at a speed of 1 mm / s in the axial direction, respectively.
A relationship diagram between the energy absorption amount and the convex portion height parameter α or the convex portion width parameter β shown in FIGS. 10 and 11 was obtained. The vertical axes in FIGS. 10 and 11 represent the present invention type (FIGS. 8A to 8A).
FIG. 1D shows the ratio of the energy absorption amount E ₂ of the conventional type (with no convex portion) to the energy absorption amount E ₁ of the conventional type (with no convex portions).
At 0, the convex portion width parameter β = 3, and in FIG. 11, the convex portion height parameter α = 5. The extruded aluminum material was 6N01-T5.

As shown in FIGS. 10 and 11, the shapes (a) to (d) of the type according to the present invention have energy absorption in all the regions α and β compared to the conventional type by providing a convex portion on the wall surface. The amount is increasing. Further, FIG. 11 is the ratio of the energy absorption amount (E ₂ / E _1), the ratio of A ₁ of the cross-sectional area of the cross-sectional area A ₂ and the conventional profile of the present invention type profiles of (A ₂ / A ₁ ) Indicates that the actual energy absorption of the shaped material of the present invention increases at a rate higher than the area of the protrusion increases. That is, a larger increase in energy absorption can be achieved with a small weight increase.

[0024]

According to the present invention, the thickness of the corner R of the hollow section and / or the joint between the inner web and the outer wall is made thinner than the original thickness, so that the initial thickness can be reduced. Greater energy absorbing ability can be obtained while suppressing the reaction force, and even a fragile material can be used as an energy absorbing member. In addition, by providing a convex portion having a rectangular cross section outside the wall portion of the shape member having a hollow rectangular cross section,
A larger increase in energy absorption can be achieved with a small increase in weight.

[Brief description of the drawings]

FIG. 1 is a view showing various forms of a cross-sectional shape of an energy absorbing member having a cross-shaped cross section according to the present invention.

FIG. 2 is a view showing another embodiment of the cross-sectional shape of the energy absorbing member also having a cross-section in a cross shape.

FIG. 3 is a bellows-like crush diagram of the energy absorbing member.

FIGS. 4A and 4B show the distribution of compression load of an energy absorbing member having a cross section in a cross-section, in which FIG. 4A shows a conventional example and FIG. 4B shows an example of the present invention.

FIGS. 5A and 5B are a side view and a cross-sectional view, respectively, of an energy absorbing member having a cross-shaped cross section used in Examples.

FIG. 6 is a graph showing the load (Pcr / P (σ0.2))-displacement (crushing slot talk).

FIG. 7 is a curve of the energy absorption (U) -plate thickness ratio (k) and the ratio of the maximum crushing load to the average crushing load (Pcr / Pmea).
n) -plate thickness ratio (k) curve.

FIG. 8 is a view showing various forms of a cross-sectional shape of the energy absorbing member having a rectangular cross-section according to the present invention.

FIG. 9 is a view showing a cross-sectional shape of a conventional energy absorbing member having a rectangular cross section.

FIG. 10 is a diagram showing a relationship between the energy absorption amount and a convex portion height parameter α.

FIG. 11 is a diagram showing the relationship between the energy absorption amount and the convex portion width parameter β.

FIG. 12 is a diagram showing a relationship between an absorption energy ratio (E ₂ / E ₁ ) and a sectional area ratio (A ₂ / A ₁ ).

FIG. 13 is a diagram showing a structure of a front portion of the automobile.

FIG. 14 is a schematic view of axial compression deformation of a rectangular cross-sectional shape member.

[Explanation of symbols]

 1 Bumper reinforcement 2 Front side member

Claims (8)

[Claims] 1. An extruded profile having a hollow cross section having an R (curvature) at a corner portion of an outer wall, wherein a thickness of a corner R portion is formed smaller than an original thickness. Element. 2. An extruded profile having a hollow section having an R (curvature) at a corner portion of an outer wall and a web therein, wherein at least one of a corner R portion and a joint portion between the web and the outer wall has a thickness of at least one. An energy absorbing member characterized by being formed thinner than the original plate thickness. 3. The energy absorbing member according to claim 2, wherein the cross section of the extruded member has a cross-section. 4. The ratio of the thickness of the corner R portion or the joint portion between the web and the outer wall formed to be smaller than the thickness of the base plate to the base plate thickness is k.
Wherein k = 0.45 to 0.7.
The energy absorbing member according to any one of the above. 5. An energy-absorbing member having a hollow rectangular cross-sectional shape, wherein a projection having a rectangular cross-section is provided outside a wall portion. 6. The energy absorbing member according to claim 5, wherein a convex portion is provided outside the facing wall portion. 7. The energy absorbing member according to claim 1, which is formed using an extruded aluminum alloy. 8. The energy absorbing member according to claim 1, wherein the energy absorbing member is used for a side member of an automobile.