JP3385798B2 - Automotive frame material and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is used as front side frames, rear side frames, etc. of various vehicles.
The present invention relates to a frame material for an automobile, which effectively absorbs a shock such as a collision as a plastic deformation and protects a driver or a passenger.

[0002]

2. Description of the Related Art Various types of shock absorbing members are incorporated in automobiles to absorb the impact when they collide with or come into contact with other automobiles or objects. The shock absorption mode includes a method of incorporating a liquid damper or the like into a structural material such as a bumper, a method of using the structural material itself as an energy absorber, and a method of interposing a spring between the structural body and the vehicle body. Above all, the method of absorbing the collision energy by plastic deformation of the structural material can absorb a large amount of energy, and is therefore expected to be developed as a shock absorbing member. For example, Japanese Laid-Open Patent Publication No. 6-247337 discloses, as this type of shock absorbing member, a fragile portion is provided by compression processing or overhanging processing so as to be a starting point of crushing due to energy at the time of collision.

The structural material having improved shock absorbing performance is used as the front side frame 3 or the rear side frame 3'as shown in the schematic view of the perimeter frame of FIG. 1, for example. The front side frame 3 or the rear side frame 3'is provided with deformation starting portions 4 and 4'which are the starting points of buckling deformation, and the connecting members 2 and 2'are provided with impact dispersion portions 5 and 5 '. There is. When a shock is applied to the bumper 1 from the front due to a vehicle collision or the like, or a shock is applied to the rear bumper 1'from the rear, the shock absorbing frames 3 and 3'are folded as shown schematically in FIG. It continuously buckles and deforms and absorbs the applied impact. As a result, the impact transmitted to the intermediate frame M is reduced, and the occupant is protected.

[0004]

In a structural material that absorbs impact energy by plastic deformation, the applied impact causes the structural material to buckle and deform. If this buckling is repeated regularly and proceeds continuously, a large impact energy is dispersed and absorbed in each buckling deformation, so that the impact on the occupant is reduced. On the other hand, during normal use and when an impact less than the maximum load that causes buckling deformation is applied, it is necessary to maintain the strength required as a normal structural material.
Moreover, in order to reduce the weight of the vehicle body, a structural material that satisfies these requirements and is lightweight is desired. The present invention has been devised to meet such a demand, and by specifying the shape and size of a rectangular cross section in consideration of tensile strength, proof stress, Young's modulus, etc., the impact energy absorption performance can be improved. It is an object of the present invention to provide a structural member which has a sufficient strength in a steady state and is suitable for weight reduction as well as heightening.

[0005]

In order to achieve the object, the method of manufacturing an automobile frame according to the present invention includes a partition wall 7.
The energy amount U (KN) to be absorbed by one frame when manufacturing an automobile frame material formed of an aluminum extruded profile having a plurality of rectangular hollow portions (N = 1 to n) partitioned by From m), the amount of energy U _n absorbed by each virtual extruded shape member composed of an outer peripheral portion surrounding each rectangular hollow portion sharing the partition wall 7 as each outer wall
By absorbing the impact at the time of collision by regular buckling by defining the cross-sectional shape and material so that the total sum U _t [U _t = ΣU _n (n = 1 to n)] is large or equal This is a car frame material that can be manufactured.

[0006]

Specifically, a plurality of rectangular hollow portions (1 to
n), a frame for automobiles made of extruded aluminum made of aluminum has a value U calculated by the following formula from the amount of energy U (KN · m) to be absorbed by one frame.
_The cross-sectional shape and material were determined so that _T (KN · m) was large or equal. U _n = [{4.72 × (B + H) ^0.3 × t ^1.81 × E ^0.15 × ((σ _B + σ _0.2 ) / 2)} / 1000] × L (1) U _T = ΣU _n (n = 1 to n) (2) where U _n is the amount of energy (KN) absorbed by each virtual extruded shape member composed of an outer peripheral portion surrounding each hollow portion n sharing the partition wall as each outer wall. -M) B: Width in cross section of each hollow part n (mm) H: Height in cross section of each hollow part n (mm) L: Length capable of buckling deformation (mm) t: Each hollow part Thickness of n profile (mm) E: Young's modulus of extruded profile (GPa) σ _B : Tensile strength (MPa) σ _0.2 : 0.2% proof stress (MPa)

Here, the energy amount U to be absorbed is
It is the amount of energy that needs to be absorbed by one frame designed from the design. The energy amount U is a value obtained by subtracting the amount of energy absorbed in a portion other than the frame from the amount of energy calculated at the total vehicle weight (vehicle body + occupant) and the expected velocity V at the time of collision. For example, in a frame used in front of a vehicle body, members other than the frame, such as exterior parts such as fenders and bonnets, bumpers, wheels, and the like, come into contact with parts other than the frame. The expected limit collision speed is JIS as a range that can be effectively used in industry.
A speed conforming to FMVSS-204 (American Motor Vehicle Safety Standard) indicated by D1060, specifically 50 km /
The time is right. The amount of energy absorbed by parts other than the frame cannot be unconditionally determined because it varies depending on the design concept of the vehicle body, and it is necessary to accurately measure the amount of energy absorbed in the prototype car model destruction test. In a test conducted by the present inventors using an existing passenger car in which the engine room is located in front of the passenger compartment, at least 70% of the collision energy under the above conditions is the exterior parts such as fenders, bonnets, bumpers, and engines. The structure was such that it was absorbed by members other than the frame, such as wheels, located in front of the vehicle body.

From the results of this test, in the case of the front part side impact absorbing frame of a passenger car in which the engine room is arranged in front of the passenger compartment which is usually manufactured, the speed is 50 km / h.
It is effective in actual design to design the frame shape based on the above equation, with a standard value being a value obtained by dividing 30% or more of the energy generated when the vehicle collides at / hour by the number of used frames. From these results, it is necessary to design the value U _T defined by the equation (2) equal or larger than the energy amount U ₁ to be absorbed in one frame defined by the equation (A). U ₁ = 28.8 × W × N ⁻¹ × 10 ⁻³ (A) U _n = [{4.72 × (B + H) ^0.3 × t ^1.81 × E ^0.15 × ((σ _B + σ _0.2 )) / 2)} / 1000] × L ... (1) U _T = ΣU _n (n = 1 to n) ... (2) Since the frame material is also used as a structural material, Naturally, it has the strength required as a structural material.

[0010]

When an impact is applied to the impact absorbing member provided with the buckling deformation starting portion, overhang and folding are periodically repeated as shown in FIG. 3 (a), and this regular buckling deformation causes the impact. Be absorbed. The overhanging and folding cycles are shifted by a half cycle between the adjacent side surfaces L ₁ and L ₃ and the adjacent side surfaces L ₂ and L ₄ . As a result of investigations and studies on a method of absorbing shock by such buckling deformation, the present inventors have found that the hollow part of the shock absorbing frame is simply separated by a wall formed in the hollow part to obtain an outer diameter It has been found that even extruded profiles of the same size absorb a very large amount of impact energy. For example, in a frame in which the hollow portion is divided into three by partition walls, regular buckling deformation as shown in FIG. 3B occurs. That is, the side surfaces L ₁ , L ₂₂ ,
L _3, L ₄₂ and the side surface _{L 21, L 23, L 41} , L 43 and projecting and shifted by a half period in Orekomi is periodically repeated in the longitudinal direction, a large amount of impact energy is absorbed.

Further, as shown in FIG. 4 (a), the partition wall 7
When an impact is applied to the extruded shape member having the hollow portion divided by, the partition wall 7 is also deformed due to the buckling deformation of the outer surface.
It buckles and deforms as shown in. The partition wall 7 is associated with the deformation of the hollow portions A and B. For example, in the hollow portion A, since the upper surface and the lower surface are deformed into a concave shape, the partition wall 7
Deforms in the overhang direction. These buckling deformations occur periodically and continuously in the longitudinal direction of the extruded profile, and
The shape is as shown in (c). The absorbed energy at this time is represented by the sum of the absorbed energy by the hollow portion A and the absorbed energy by the hollow portion B, as shown in FIG. It was found that the amount was significantly larger than that of the extruded profile having the same outer shape. As a result of the research, the impact energy absorbed by the extruded profile as shown in FIG. 3A in which the interior is divided into a plurality of hollow parts by the partition wall is formed by the extruded profile S _N having a shape surrounding each hollow part. It was found that the impact energy absorbed by each frame was equal to the added value. Further, the absorbed energy at this time absorbs an extremely large amount of impact energy as compared with an extruded shape member having the same outer shape and a single hollow portion by simply forming a partition wall that divides the hollow portion into a plurality. It is considered that this is because the partition wall acted extremely effectively for absorbing energy.

By the way, the impact energy U _n (KN · m) absorbed by the frame formed of the extruded frame member having a single hollow portion is calculated by the above-mentioned formula (1) from the results of many experiments and verifications. It turned out to be calculated. That is, when the impact energy is to be absorbed by regular buckling in the axial direction of the frame, the elements that influence the amount of absorbed energy are the sectional shape (B, H, t) and the strength of the material (E, σ _B , σ). _0.2 ). The present inventors have found that the amount of impact energy U absorbed from the experimental data under this assumption is U.
_This is a formula (1) that approximates _n . Formula (1)
Assumes that the limit collision speed required for the vehicle body in order to ensure the safety of occupants during a vehicle collision is 50 km / hour as described above, and therefore the collision speed is also assumed to be 50 km / hour. On the other hand, the amount of energy U _T (KN · m) absorbed by the frame made of the extruded aluminum frame having a plurality of rectangular hollow portions that share the partition wall 7 as each outer wall is determined by numerous experiments and verifications. From the result, it was found that the sum of the absorbed energy amount U _n of each hollow portion is calculated by the above-mentioned formula (2). Also in this case, the collision speed is assumed to be 50 km / hour.

Since the expressions (1) and (2) accurately represent the amount of absorbed energy, it is possible to easily design the shape and size of the shock absorbing frame member by calculation without trial and error. To Formula (1) is derived from the following experimental results. Aluminum alloy JIS
A6063 was used to manufacture an extruded shape member having a rectangular cross section shown in FIG. 5 (a) having a side length of 50 mm and a wall thickness of 3 mm. 50mm from the end face of the extruded profile,
As shown in Fig. 5 (b), the depth of 2m
A buckling start portion 6 was formed by forming a recess of m. A 400 mm long test piece is cut out from the extruded shape member with the buckling start part 6 applied, and an axial compressive load is applied by a hammer test in which a 4.8 KN weight is dropped to investigate the relationship between the load and the amount of displacement. did. As shown in FIG. 5C showing the examination result, it is understood that the displacement-compression load curve changes continuously and regularly, and the test piece undergoes periodic buckling deformation. Displacement amount-
The total area under the compressive load curve indicates the total energy absorbed by the frame. In this test and the following collisions, the speed of the weight was measured at 27 km / h, but it was confirmed that there was no difference in the results for the same energy amount even at speeds up to at least 60 km / h. There is.

Extruded profiles having the same cross-sectional shape (FIG. 5a) were prepared from various aluminum alloys, and the average value of tensile strength and 0.2% proof stress (σ _B +
The relationship between σ _0.2 ) / 2 and the average load P _AV was investigated. As a result, the average load P _AV is (σ _B +
It was found to be expressed as a linear function of σ _0.2 ) / 2.
The relationship of FIG. 6 was similarly established for extruded shape members having different cross-sectional aspect ratios, plate thicknesses, and the like. Also, aluminum alloy J
From IS A6063, plate thickness t is 2.9 mm, 2.4 mm
An extruded shape member having a rectangular cross section was manufactured by using, and the influence of the shape of the frame member on the average load P _AV was investigated. As the shape element, the sum B + H of the long side B and the short side H was adopted. As shown in FIG. 7 showing the survey result, the average load P _AV is
It was found to be proportional to the (B + H) th power of 0.3. This proportional relationship was similarly established for extruded shape members having different cross-sectional aspect ratios, plate thicknesses, and the like.

The plate thickness t, which is a factor of material strength, has the relationship shown in FIG. 8 with the average load P _AV . Note that FIG.
Has a square hollow cross section, B + H = 100 and 20
0 is the result of testing the extrudate JIS A6063-T ₅ and the frame members cut from steel angle pipe.
It can be seen from FIG. 8 that the average load P _AV is proportional to the 1.81th power of the plate thickness t. Further, this proportional relationship was similarly established in extruded shape members having different cross-sectional aspect ratios, plate thicknesses, and the like. The Young's modulus E, which is a factor of material strength, has the relationship shown in FIG. 9 with the average load P _AV . In addition, in FIG.
Four types of extruded shapes J with different rectangular cross-section sizes and thicknesses
It is the result of testing the frame member which is cut out from the IS A6063-T ₅ and iron square pipe. From FIG. 9, it can be seen that the average load P _AV is proportional to the Young's modulus E to the 0.15th power. Further, this proportional relationship was similarly established in extruded shape members having different cross-sectional aspect ratios, plate thicknesses, and the like.

From the above, the sum of the long side and the short side (B +
H), plate thickness t, Young's modulus E and material strength (σ _B + σ _0.2 ).
Considering the effect of the load on the average load P _AV , the average load P _AV
AV has a proportional relationship with the product of each element which is made into a multiplier. That is, (B + H) ^0.3 × t ^1.81 × E ^0.15 ×
Looking at the average load P _{AV in} relation to ((σ _B + σ _0.2 ) / 2), FIG. 10 is obtained for Samples 1 to 9 shown in Example 1 described later.
As shown in, the average load P _AV is (B + H) ^0.3 × t
^1.81 × E ^0.15 × ((σ _B + σ _0.2 ) / 2) with a coefficient of 4.72
It was found that it was approximated by the value multiplied by. That is, the amount of impact energy absorbed by the frame made of the aluminum extruded shape member having one hollow portion is represented by the above-mentioned formula (1). In addition, as shown in FIG.
Average load P of the frame material with the hollow part divided by the partition wall 7
_It was clarified from the experimental results that the _AV becomes equal to the value obtained by adding the average load of the virtual extruded shape members surrounding the hollow portions a and b.
Similarly, in the frame material in which the hollow part is divided into three parts by the partition walls 7 and 7, it is equal to the value obtained by adding the average load of the virtual extruded shape members surrounding the hollow parts a, b and c shown in FIG. 11 (b). Become. In any case, compared with a frame material having the same outer shape and wall thickness and having a single hollow portion, a significantly larger average load P _AV is exhibited and the absorbed energy becomes larger. In this way, the amount of energy U _T (K _T absorbed by the frame made of the extruded aluminum frame having a plurality of rectangular hollow portions that share the partition wall 7 as each outer wall.
It was verified / confirmed that N · m) is represented by the sum of the absorbed energy amount U _n of each hollow portion, that is, the above-mentioned formula (2). Although the above-described shock absorbing mechanism has been mainly described with respect to the extruded material of the aluminum alloy, it is similarly applied to the iron material. In addition, the above-mentioned formula (A)
As described above, the amount of collision energy to be absorbed by one of the N shock absorbing frames used is 50 k / h.
It is a value in which the amount of energy corresponding to 30% of the amount of energy generated at the time of a collision of a passenger car having a vehicle body weight W (kgf) at m / hour is arranged in a formula.

[0017]

【Example】

Example 1: An aluminum alloy JIS A6063 was used to manufacture an extruded profile having a cross section having a size shown in Table 1. At a position 50 mm from the end face of the extruded shape member, as shown in FIG.
As shown in (b), a recess having a depth of 2 mm was formed by press working to form the buckling start portion 6. In Table 1, the strength of the used material is also shown as (σ _B + σ _0.2 ) / 2.

[0018]

A 400 mm long test piece was cut out from the extruded shape member to which the buckling start part 6 was attached, and an axial compressive load was applied by a falling hammer test in which a 4.8 KN weight was dropped from a height of 3 m to give a test piece. Compressive load (average value) when is deformed
Was actually measured. In this hammer test, the falling velocity of the weight reaches 27.6 km / hour when it reaches the frame material, and as described above, results equivalent to the impact at the time of a vehicle collision are obtained. When the measured value was compared with the calculated value calculated by the above-mentioned formula (1), as shown in Table 2, high agreement was observed between the two. From this, it was confirmed that the formula (1) is effective in previously obtaining the characteristics required as the shock absorbing frame material.

[0020]

Example 2: In order to investigate the effect of the partition wall on the increase in shock absorption energy, a test piece having the following cross-sectional shape was extruded from an aluminum alloy JIS A6.
It was prepared from 061-T ₄ . Sample 10: [corresponding to an extruded profile forming the space b in FIG. 11 (b)] Length H = 80 mm, width B = 35.5 mm, plate thickness t = 2.3
mm Specimen 11: [corresponding to an extruded shape member that forms the space B in FIG. 11 (b)] Length H = 80 mm, width B = 53 mm, plate thickness t = 2.3 mm Specimen 12: [Fig. 11 (b) Corresponding to an extruded shape member forming a space portion c] Vertical H = 80 mm, width B = 43 mm, plate thickness t = 2.3 mm Sample 13: [Extrusion shape having space portions a, b, and c of FIG. 11 (b)] Equivalent to material] Vertical H = 80 mm, width B = 125 mm, plate thickness t = 2.3 m
m Specimen 14: [equivalent to an extruded shape member having spaces B and C in FIG. 11B] Length H = 80 mm, width B = 96 mm, plate thickness t = 2.3 mm Specimen 15: [partition wall from specimen 13 Equivalent to extruded profile excluding the material] Vertical H = 80 mm, width B = 125 mm, plate thickness t = 2.3 m
m Sample 16: [corresponding to an extruded shape member obtained by removing the partition wall from Sample 14] Vertical H = 80 mm, width B = 96 mm, plate thickness t = 2.3 mm Results of a drop hammer test of each test piece as in Example 1 Is shown in Table 3. From Table 3, it can be seen that the frame material in which the space parts a to c are formed by the partition wall has extremely high impact absorption energy characteristics corresponding to the total amount of the virtual extruded shape members forming the space parts a to c.

[0022]

Third Embodiment A case of actually designing a vehicle body frame will be described. Table 4 shows the relationship between the total weight of the vehicle body and the amount of energy that should be absorbed by one frame.

[0024]

FIG. 12 shows an aluminum alloy JIS
FIG. 14 is a graph showing applicable vehicle body weights for a profile made of A6063-T ₅ and having a typical double-hollow cross-sectional shape (FIG. 13). In the range of the bar graph in the right column of FIG. 12, the shock absorbing frame used for the front part of the passenger car having the total vehicle body weight exceeds the U ₁ value shown in Table 4 and satisfies the performance required for other frames. Under these conditions, it can be seen that it is used for a suitable automobile shock absorbing frame.

[0026]

As described above, the structural member of the present invention has a rectangular cross section so that the absorbed energy calculated by a relational expression incorporating tensile strength, proof stress, Young's modulus and the like falls within a certain range. , Width, plate thickness, etc. The calculated value of the absorbed energy has a high degree of agreement with the actual measured value, which facilitates the design of a structural member for a vehicle having excellent impact energy absorption performance. The structural member thus obtained exhibits sufficient strength in a steady state, and absorbs impact energy by plastic deformation when the vehicle collides or comes into contact with the vehicle to protect the occupant. Moreover, a design suitable for a narrow internal space of a vehicle, which is greatly restricted due to a positional conflict with other devices, can be obtained, and a lightweight structural member can be obtained by using an aluminum extruded profile.

[Brief description of drawings]

FIG. 1 is a schematic perspective view in which a shock absorbing frame attached to a front side frame or a rear side frame is used as a perimeter frame.

[Fig. 2] Shock absorbing frame buckled and deformed by shock

FIG. 3 is a perspective view showing a state in which a frame (a) having one space portion and a frame (b) having three space portions are buckled and deformed.

FIG. 4 is a diagram illustrating that the partition wall increases the amount of impact energy absorbed, and is a cross-sectional view of an extruded shape member provided with a partition wall (a) and a cross-sectional view of the buckled and deformed extruded shape member (b). , A cross-sectional view of the buckling deformation in the longitudinal direction (c), and the absorbed energy of the extruded profile provided with partition walls is the space A.
And graph (d) showing that it is represented as the sum of B and B.

FIG. 5 is a cross-sectional view (a) of an extruded frame member having one space portion, a sectional view (b) showing a buckling start portion attached to the extruded frame member, and a displacement amount and a compression load of the extruded frame member. Graph showing the relationship (c)

FIG. 6 is a graph showing the relationship between the mechanical properties of various aluminum alloys and the average load.

FIG. 7 is a graph showing the relationship between the average load and the sum of the long and short sides of each frame material.

FIG. 8 is a graph showing the relationship between the plate thickness of each frame material and the average load.

FIG. 9 is a graph showing the relationship between the Young's modulus of each frame material and the average load.

FIG. 10 is a graph showing that the average load is calculated by the formula (1) specified in the present invention.

FIG. 11 shows that the impact absorption energy of a frame made from an extruded profile obtained by dividing a hollow part into a plurality of partitions by partition walls is expressed as the sum of the impact absorption energies of each virtual extruded profile forming each space. Illustration for illustration

FIG. 12 is a chart showing impact absorption energy in Example 3 using a frame having a double follow cross section.

FIG. 13 is a cross-sectional view of the frame used in Example 3.

[Explanation of symbols]

1: Bumper 1 ': Rear bumper 2, 2': Connecting member 3: Front side frame 3 ': Rear side frame 4, 4': Deformation start part 5,
5 ': Impact dispersion part 6: Buckling start part 7: Partition wall

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Haruno Jindo 1-34-1, Kambara, Kambara-machi, Anbara-gun, Shizuoka Prefecture Nippon Light Metal Co., Ltd. Group Technology Center (72) Inventor Takashi Sasamoto Kambara-cho, Anbara-gun, Shizuoka Prefecture 1-31 Kambara Nippon Light Metal Co., Ltd. Within the Group Technology Center (56) References JP-A-5-65076 (JP, A) Fukuihei 5-12361 (JP, U) (58) Fields investigated ( Int.Cl. ⁷ , DB name) B62D 21/15

Claims (3)

(57) [Claims] 1.A plurality of rectangles divided by a partition wall (7)
Aluminum extruded profile with hollow section (N = 1 to n)
It is a method of manufacturing automobile frame material formed by
Energy to be absorbed in one frame U (KN
・ From m), use the partition wall (7) as each outer wall.
Individual rectangular hollows that are used to
Energy amount U absorbed in extruded profile _n The sum of U
_t [U _t = ΣU _n (N = 1 to n)] is large or equal
The cross-sectional shape and material are determined so that
Self-absorbing impact during collisions due to regular longitudinal buckling
Manufacturing method of frame material for motor vehicle. 2. A plurality of rectangles partitioned by a partition wall (7)
Aluminum extruded profile with hollow section (1 to n)
Amount U of energy that is formed and should be absorbed in one frame
From (KN · m), the value U _T (KN · calculated by the following equation
The cross-sectional shape and material should be
Impact due to regular longitudinal buckling characterized by defined
Frame material for automobiles that absorbs the impact of a collision. U _n = [{4.72 × (B + H) ^0.3 × t ^1.81 × E ^0.15 × ((σ _B + σ _0.2 ) / 2)} / 1000] × L ... (1) U _T = ΣU _n (n = 1 to n) ... (2) However, U _n : The partition wall is shared as each outer wall
Individual provisional consisting outer peripheral portion surrounding the individual hollow portion n that
The amount of energy absorbed by the virtual extruded shape members (KN · m) B: width of the cross section of each hollow section n (mm) H: height of the cross section of each hollow section n (mm) L: buckling Possible length (mm) t: Plate thickness (mm) of the shape of each hollow part E: Young's modulus of the extruded shape (GPa) σ _B : Tensile strength (MPa) σ _0.2 : 0.2% Proof strength (MPa) 3. A plurality of rectangles partitioned by a partition wall (7)
Aluminum extruded profile with hollow section (1 to n)
A more form, provided the engine Le chromatography beam in front of the passenger compartment
Which is a front frame material for a passenger car having the formula (A)
Energy to be absorbed in one frame defined by
From U ₁ (KN · m), the value U _T (K
N ・ m) Cross section shape and
Regular buckling in the longitudinal direction characterized by defining the material
A frame material for automobiles that absorbs the impact of a collision. U ₁ = 28.8 × W × N ^-1 × 10 ^-3 ... (A) W: gross weight of vehicle body (kgf) N: number of frames used U _n = [{4.72 x (B + H) ^0.3 x t ^1.81 x E ^0.15 x ((σ _B + σ _0.2 )) / 2)} / 1000] × L ···· (1) U T = ΣU n (n = 1~n) ···· (2) provided that U _n: to share the partition wall as a respective outer wall
Individual provisional consisting outer peripheral portion surrounding the individual hollow portion n that
The amount of energy absorbed by the virtual extruded shape members (KN · m) B: width of the cross section of each hollow section N (mm) H: height of the cross section of each hollow section N (mm) L: buckling Possible length (mm) t: Plate thickness (mm) of the shape of each hollow portion E: Young's modulus (GPa) of extruded shape σ _B : Tensile strength (MPa) σ _0.2 : 0.2% Proof strength (MPa)