WO2020075739A1 - 骨格部材 - Google Patents
骨格部材 Download PDFInfo
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- WO2020075739A1 WO2020075739A1 PCT/JP2019/039758 JP2019039758W WO2020075739A1 WO 2020075739 A1 WO2020075739 A1 WO 2020075739A1 JP 2019039758 W JP2019039758 W JP 2019039758W WO 2020075739 A1 WO2020075739 A1 WO 2020075739A1
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- WIPO (PCT)
- Prior art keywords
- hardness
- softening layer
- plate thickness
- skeleton member
- thickness direction
- Prior art date
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Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D29/00—Superstructures, understructures, or sub-units thereof, characterised by the material thereof
- B62D29/007—Superstructures, understructures, or sub-units thereof, characterised by the material thereof predominantly of special steel or specially treated steel, e.g. stainless steel or locally surface hardened steel
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
- B21D22/20—Deep-drawing
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D22/00—Shaping without cutting, by stamping, spinning, or deep-drawing
- B21D22/20—Deep-drawing
- B21D22/26—Deep-drawing for making peculiarly, e.g. irregularly, shaped articles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D47/00—Making rigid structural elements or units, e.g. honeycomb structures
- B21D47/01—Making rigid structural elements or units, e.g. honeycomb structures beams or pillars
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D53/00—Making other particular articles
- B21D53/88—Making other particular articles other parts for vehicles, e.g. cowlings, mudguards
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60R—VEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR
- B60R19/00—Wheel guards; Radiator guards, e.g. grilles; Obstruction removers; Fittings damping bouncing force in collisions
- B60R19/02—Bumpers, i.e. impact receiving or absorbing members for protecting vehicles or fending off blows from other vehicles or objects
- B60R19/04—Bumpers, i.e. impact receiving or absorbing members for protecting vehicles or fending off blows from other vehicles or objects formed from more than one section in a side-by-side arrangement
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D21/00—Understructures, i.e. chassis frame on which a vehicle body may be mounted
- B62D21/15—Understructures, i.e. chassis frame on which a vehicle body may be mounted having impact absorbing means, e.g. a frame designed to permanently or temporarily change shape or dimension upon impact with another body
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D25/00—Superstructure or monocoque structure sub-units; Parts or details thereof not otherwise provided for
- B62D25/06—Fixed roofs
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D25/00—Superstructure or monocoque structure sub-units; Parts or details thereof not otherwise provided for
- B62D25/20—Floors or bottom sub-units
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60R—VEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR
- B60R19/00—Wheel guards; Radiator guards, e.g. grilles; Obstruction removers; Fittings damping bouncing force in collisions
- B60R19/02—Bumpers, i.e. impact receiving or absorbing members for protecting vehicles or fending off blows from other vehicles or objects
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60Y—INDEXING SCHEME RELATING TO ASPECTS CROSS-CUTTING VEHICLE TECHNOLOGY
- B60Y2304/00—Optimising design; Manufacturing; Testing
- B60Y2304/03—Reducing weight
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60Y—INDEXING SCHEME RELATING TO ASPECTS CROSS-CUTTING VEHICLE TECHNOLOGY
- B60Y2306/00—Other features of vehicle sub-units
- B60Y2306/01—Reducing damages in case of crash, e.g. by improving battery protection
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D25/00—Superstructure or monocoque structure sub-units; Parts or details thereof not otherwise provided for
- B62D25/02—Side panels
- B62D25/025—Side sills thereof
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D25/00—Superstructure or monocoque structure sub-units; Parts or details thereof not otherwise provided for
- B62D25/04—Door pillars ; windshield pillars
Definitions
- the present invention relates to a skeleton member.
- the present application claims priority based on Japanese Patent Application No. 2018-193175 filed in Japan on October 12, 2018 and Japanese Patent Application No. 2019-025366 filed on February 15, 2019 in Japan. , The contents of which are incorporated herein.
- a metal plate-shaped member processed into a predetermined cross-sectional shape has been used as a frame member of an automobile.
- These skeletal members are required to have a light weight and a sufficient load resistance. Therefore, in recent years, a material having high strength such as a high-tensile steel plate may be used.
- the skeleton member is required to realize a desired deformation mode and efficiently absorb the impact.
- Patent Document 1 describes that a technique of partially changing the hardness of a member is used to provide a low hardness region and a high hardness region in a product made of sheet metal.
- the present invention has been made in view of the above problems, and an object of the present invention is to be able to achieve both the guarantee of deformability at the time of collision and the improvement of load resistance, which is new and improved.
- a first aspect of the present invention is a skeleton member including a corner portion extending in a longitudinal direction and a vertical wall portion extending from an end portion in the lateral direction of the corner portion, wherein A softening layer is provided in the plate thickness direction from at least one surface of the bending inner side and the bending outer side, and the softening layer has a length of 1 ⁇ 2 or more of a short-side direction length of the vertical wall portion from the corner portion.
- the hardness of the central portion in the plate thickness direction in the portion where the softening layer is provided is 400 Hv or more, and the softening layer is the portion where the softening layer is provided.
- the thickness of the softening layer is 2% or more and less than 20% of the plate thickness in the portion where the softening layer is provided.
- the hardness of the softening layer on the surface is 0.5 times or more and less than 0.9 times the hardness of the central portion in the plate thickness direction in the portion where the softening layer is provided, and the softening layer is the thickness of the softening layer from the surface in the plate thickness direction.
- a first hardness change region which is a region of up to 40% of the hardness
- a second hardness change region which is a region of the softening layer which is not the first hardness change region
- the absolute value ⁇ Hv1 of the hardness change in the plate thickness direction in the one hardness change region is larger than the absolute value ⁇ Hv2 of the hardness change in the plate thickness direction in the second hardness change region, and the bending radius of the corner portion is larger.
- R is a skeleton member with R / t ⁇ 2.5 with respect to the plate thickness t of the corner portion.
- the absolute value ⁇ Hv1 of the hardness change in the plate thickness direction of the first hardness change region may be 100 Hv or more and less than 200 Hv.
- the softening layer may be provided outside the bend of the corner portion.
- the softening layer may be provided on both the inside and the outside of the bend of the corner portion.
- the vertical wall portion extends from one end of the corner portion, and the skeleton member includes other corner portions.
- the softening layer further includes a flat plate portion extending from an end portion, and the softening layer extends from the corner portion to the flat plate portion over a region having a length of 1 ⁇ 2 or more of a short-side length of the flat plate portion.
- the vertical wall portion extends from one end of the corner portion, and the skeleton member includes other corner portions.
- the hardness at a position at a depth of 70 ⁇ m from the surface of the flat plate part further includes a flat plate part extending from an end, and the hardness of the center part in the plate thickness direction is It may be 0.9 times or less.
- the surface of the flat plate portion may be a surface that is continuous with the inside of the corner portion of the flat plate portion that is bent.
- a skeletal member that has both improved deformability at the time of collision and improved load bearing capacity.
- FIG. 5 is a cross-sectional view taken along the line XZ of a region including a corner portion of the skeleton member according to the same embodiment.
- FIG. 3B is a cross-sectional view taken along the line XZ of the skeleton member according to the same embodiment.
- FIG. 3B is a cross-sectional view taken along the line XZ of the skeleton member according to the same embodiment.
- FIG. 3B is a cross-sectional view taken along the line XZ of the skeleton member according to the same embodiment.
- FIG. 3B is a cross-sectional view taken along the line XZ of the skeleton member according to the same embodiment.
- FIG. 6 is a load-stroke diagram for explaining the effect of the skeleton member according to the present embodiment.
- FIG. 11 is a cross-sectional view taken along the line XZ of a region including a corner portion according to a modified example of the same embodiment. It is a partial perspective view showing an example of a frame member concerning other modifications of the embodiment.
- FIG. 14 is a cross-sectional view taken along the line XZ of a skeleton member according to another modification of the same embodiment.
- FIG. 9 is a cross-sectional view taken along the line XZ of a skeleton member according to the modification. It is an enlarged view of the portion P of FIG. 12A. It is a figure which shows an example of the mode of deformation
- FIG. 13B is a cross-sectional view taken along the line I-I ′ of FIG. 13A. It is a partial perspective view which shows an example of the skeleton member which concerns on the 2nd Embodiment of this invention.
- FIG. 9 is a cross-sectional view taken along the line XZ of a skeleton member according to the modification. It is an enlarged view of the portion P of FIG. 12A. It is a figure which shows an example of the mode of deformation
- 3B is a cross-sectional view taken along the line XZ of the skeleton member according to the same embodiment. It is a figure showing an automobile skeleton as an example to which a skeleton member concerning an embodiment of the present invention is applied. An example of a load-stroke diagram obtained as a result of the simulation according to the present embodiment is shown. An example of a load-stroke diagram obtained as a result of the simulation according to the present embodiment is shown.
- FIG. 1 is a partial perspective view showing an example of a skeleton member according to the present embodiment.
- the skeleton member 10 is, for example, a member that extends in the Y direction shown in FIG. 1 as the longitudinal direction and has a substantially hat-shaped cross-section in the longitudinal direction (XZ plane) opened in the X direction.
- the skeleton member 10 includes a flat plate portion 11, a vertical wall portion 15 as a wall portion extending from the flat plate portion 11 via a corner portion 13, and a corner portion 13 of the vertical wall portion 15 on the opposite side. And a flange portion 17 bent from the end portion. Further, in the skeleton member 10, at least the corner portion 13 and the vertical wall portion 15 have a softening layer 20 described later.
- the skeleton member 10 forms a skeleton of the whole or a part of the product by being fixed or connected with other members. For example, when a load is applied to the skeleton member 10 in a direction perpendicular to the longitudinal direction (X direction or Z direction in FIG. 1), bending deformation may occur. Further, for example, when an axial load is applied to the skeleton member 10 in the longitudinal direction (Y direction in FIG. 1), deformation due to axial crushing may occur.
- the skeleton member 10 may be composed of various metal plate-shaped members.
- the skeleton member 10 may be composed of a steel plate.
- a steel material having a tensile strength of 1470 MPa or higher for example, 1.5 GPa class, 1.8 GPa class or higher
- the plate thickness of the steel plate used for the skeleton member 10 is about 0.5 to 3.5 mm, or about 1.0 to 2.9 mm.
- the skeleton member 10 can be formed by applying various known processing techniques to a metal plate-shaped member (blank material).
- FIG. 2 is an XZ plane sectional view of a region including the corner portion 13 according to the present embodiment.
- 3 to 5 are XZ plane cross-sectional views of the skeleton member according to the present embodiment.
- the corner portion 13 is a bent portion existing between the flat plate portion 11 and the vertical wall portion 15, and has a predetermined bending radius R described later.
- the corner portion 13 is formed in a region defined by the R stop points A1 and A2 on the inner side of the bend and the R stop points A3 and A4 on the outer side of the bend in the XZ plane sectional view.
- the bending radius R is set to a value that satisfies the relational expression of R / t ⁇ 2.5 with respect to the plate thickness t in the corner portion 13.
- R / t ⁇ 2.5 or less the vertical wall portion 15 is less likely to bend during bending deformation at the time of collision, and the withstand load of the corner portion 13 particularly increases at the beginning of the stroke.
- a high withstand load can be maintained in the middle of the stroke and the latter half of the stroke.
- the softening layer 20 described later is formed in the corner portion 13, it is possible to exhibit an excellent load resistance particularly in the latter stage of the stroke, and it is possible to improve the deformability and the load resistance at the time of collision. Become.
- the lower limit of R / t is not particularly limited, but from the viewpoint of moldability, R / t ⁇ 0.5 is preferable, and R / t ⁇ 0.9 is more preferable.
- the bending radius R is determined from the image of the cross section of the corner portion 13 on the inner side of the bending to the R stop points A1 and A2 and the bending center point of the corner portion 13 (half the distance between the R stop points A1 and A2 in the corner portion 13). It can be obtained by obtaining three points (positioned points) and obtaining the curvature from the three points by a known mathematical method.
- the skeletal member 10 having a tensile strength of 1470 MPa or higher (for example, 1.5 GPa class, 1.8 GPa class or higher), in order to obtain the corner portion 13 satisfying R / t ⁇ 2.5, It is preferable to use the hot stamping method.
- the corner portion 13 has a softening layer 20.
- the softening layer 20 may be provided on the front surface side of the skeleton member 10 on either the bending inner side or the bending outer side of the corner portion 13, or on both the bending inner side and the bending outer side. In particular, as shown in FIG. 4, the softening layer 20 may be provided outside the bend of the corner portion 13. Further, as shown in FIG. 5, the softening layer 20 may be provided on the entire surface of the skeleton member 10.
- the vertical wall portion 15 extends from the end portion including the R stop of the corner portion 13 in a direction orthogonal to the plate thickness direction.
- An end portion of the vertical wall portion 15 opposite to the corner portion 13 may be bent outward, and the flange portion 17 may extend through the bent portion. That is, the skeleton member 10 can be formed in a substantially hat shape in the XZ section in FIG.
- the vertical wall portion 15 has the softening layer 20.
- the softening layer 20 is a half of the length in the lateral direction of the vertical wall portion 15 from the R stop which is a connection portion of the corner portion 13 with the vertical wall portion 15. It extends over the region of the above length.
- the reason why the softening layer 20 is a region having a length of 1 ⁇ 2 or more of the length in the lateral direction of the vertical wall portion 15 is that the skeleton member 10 by the present inventors shown in FIGS. 6A and 6B has three points. Based on the results of bending simulation. That is, when the three-point bending simulation is performed from the initial state of FIG. 6A, as shown in FIG.
- the corner portion 13 and the region from the R stop to the half of the length in the lateral direction of the vertical wall portion 15 are obtained. It was found that the maximum principal strain was higher than that in other regions. Therefore, by providing the softening layer 20 at least in a region having a length from the R stop to half the length in the short-side direction of the vertical wall portion 15, cracking in this region can be less likely to occur at the time of collision.
- the lateral direction of the vertical wall portion 15 is the extending direction of the vertical wall portion 15 when the longitudinal direction of the skeletal member 10 (Y direction in FIG. 1) is the longitudinal direction of the vertical wall portion 15. Is a direction orthogonal to the longitudinal direction (generally the X direction in FIG. 1).
- the length in the lateral direction of the vertical wall portion 15 means the R stop on the vertical wall portion 15 side of the corner portion 13 in the XZ plane cross section, and the vertical wall of the bent portion between the vertical wall portion 15 and the flange portion 17. It indicates the distance between the R stops on the part 15 side.
- a softening layer 20 is formed on at least the corner portion 13 and the vertical wall portion 15 on the front surface side of the skeleton member 10.
- the softening layer 20 may be formed continuously or partially over the longitudinal direction (Y direction in FIG. 1) of the skeleton member 10.
- the softening layer 20 is formed from the surface of the skeletal member 10 to a predetermined depth in the plate thickness direction.
- the thickness of the softening layer 20 is 2% or more and less than 20% of the plate thickness of the skeleton member 10.
- the plate thickness refers to the total thickness of the skeleton member 10 in the plate thickness direction, including the softening layer 20 and the center portion 30 in the plate thickness direction described later.
- the thickness of the softening layer 20 is preferably 17% or less, more preferably 14% or less of the plate thickness of the skeleton member 10.
- the thickness of the softening layer 20 is preferably 5% or more, and more preferably 8% or more of the plate thickness of the skeleton member 10.
- the center side in the plate thickness direction of the skeleton member 10 (the region in the plate thickness direction excluding the softening layer 20 of the skeleton member 10) is a center portion 30 in the plate thickness direction.
- the softening layer 20 is a region having a hardness that is at least 10 Hv lower than the hardness of the central portion 30 in the plate thickness direction.
- the softening layer 20 has a hardness of 0.5 times or more and less than 0.9 times the hardness of the central portion 30 in the plate thickness direction on the surface of the skeleton member 10.
- the surface of the skeleton member 10 refers to the surface of the base material of the skeleton member 10 excluding the coating film and the plating layer.
- the hardness of the surface of the skeleton member 10 is measured by the Vickers hardness test described in JIS Z 2244: 2009 on the cross section of the base material. At that time, the measurement point is within a depth of 20 ⁇ m from the surface of the base material and the indentation is 10 ⁇ m or less.
- the softening layer 20 has a hardness of 0.6 times or more the hardness of the central portion 30 in the plate thickness direction on the surface of the skeleton member 10.
- the softening layer 20 preferably has a hardness less than 0.8 times the hardness of the central portion 30 in the plate thickness direction on the surface of the skeleton member 10.
- the hardness of the central portion 30 in the plate thickness direction is 400 Hv or more in Vickers hardness.
- the Vickers hardness of the central portion 30 of the skeleton member 10 in the plate thickness direction is preferably 500 Hv or more, and more preferably 600 Hv or more.
- the upper limit of the hardness of the central portion 30 in the plate thickness direction is not particularly specified, but considering the formability of the skeleton member 10 and the like, it is preferably 800 Hv, and more preferably 700 Hv.
- the hardness of the softening layer 20 on the surface of the skeleton member 10 can be set to Vickers hardness of 250 Hv or more.
- the hardness of the softening layer 20 on the surface of the skeleton member 10 can be 500 Vv or less in Vickers hardness. The details of the method for measuring the hardness of the surface of the softened layer 20 of the skeleton member 10 and the center portion 30 in the plate thickness direction will be described later.
- the softening layer 20 can be formed on the surface side of the skeleton member 10 by applying various surface treatments, surface treatments, or heat treatment techniques which are known techniques. As an example of a method of forming the softened layer 20, laser heating to a region corresponding to the corner portion 13 and the vertical wall portion 15 or partial tempering by high frequency heating can be given. Further, the skeleton member 10 having the softening layer 20 in a predetermined region can be formed by processing the blank material having the softening layer previously formed on the surface layer.
- FIG. 7 is a diagram showing an example of a change in hardness between B-B ′ in FIG. 2 of the softening layer 20 of the skeletal member 10 according to the present embodiment.
- FIG. 7 shows the skeleton member 10 according to the present embodiment, which is formed by hot-pressing a steel material for hot stamping into a hat shape having a tensile strength of 2.0 GPa, and the softening layer 20 in the plate thickness direction. It is the result of plotting the Vickers hardness.
- the softening layer 20 is provided between the first hardness change region 21 existing on the surface side of the skeleton member 10, the first hardness change region 21 and the center portion 30 in the plate thickness direction. And a second hardness change region 22 existing in the.
- the second hardness change region 22 is a region of the softening layer 20 that is not the first hardness change region 21. Both the first hardness change region 21 and the second hardness change region 22 are regions in which the hardness in the plate thickness direction changes at a predetermined gradient, and the first hardness change region 21 and the second hardness change region 21 The second hardness change region 22 has different absolute values ⁇ Hv1 and ⁇ Hv2 of hardness change.
- the first hardness change region 21 extends from the surface of the skeletal member 10 to 40% of the total thickness of the softening layer 20.
- the second hardness change region 22 is continuous from the first hardness change region 21 of the softening layer 20 and extends to the central portion 30 of the skeleton member 10 in the plate thickness direction. That is, the second hardness change region 22 is a region of the softening layer 20 that is not the first hardness change region 21.
- the absolute value ⁇ Hv1 of hardness change in the first hardness change region 21 is larger than the absolute value ⁇ Hv2 of hardness change in the second hardness change region 22. This is because if ⁇ Hv2 is larger than ⁇ Hv1, the skeleton member 10 is excessively softened and sufficient load characteristics cannot be obtained.
- the absolute value ⁇ Hv1 of the hardness change in the first hardness change region 21 is 100 Hv or more and less than 200 Hv.
- ⁇ Hv1 is 100 Hv or more
- stress concentration during bending deformation can be further alleviated, and bending characteristics can be further improved.
- ⁇ Hv1 is less than 200 Hv
- the effect of relaxing the stress concentration during bending deformation is further enhanced, and better bending characteristics can be obtained. Therefore, when ⁇ Hv1 is 100 Hv or more and less than 200 Hv, good bending characteristics are obtained, and the deformability of the skeleton member 10 can be improved.
- the absolute value ⁇ Hv1 of the hardness change in the first hardness change region 21 is preferably 100 Hv or more and less than 200 Hv.
- the method of measuring the hardness of the central portion 30 in the plate thickness direction is as follows. A cross section perpendicular to the plate surface of the sample is taken, the sample of the measurement surface is prepared, and the hardness test is performed.
- the method for preparing the measurement surface is according to JIS Z 2244: 2009. After polishing the measurement surface using # 600 to # 1500 silicon carbide paper, a diamond surface having a particle size of 1 ⁇ m to 6 ⁇ m is mirror-finished using a liquid such as alcohol diluted with pure water or pure water.
- the hardness test is performed by the method described in JIS Z 2244: 2009.
- a cross section perpendicular to the plate surface of the sample is sampled, and a sample for the measurement surface is prepared, and then subjected to a hardness test.
- the measurement surface is prepared so that the hardness in the vicinity of the surface of the sample is accurately measured so that the unevenness is as small as possible and no sagging occurs in the vicinity of the surface.
- the measurement surface is sputtered with an argon ion beam using a cross-section polisher manufactured by JEOL.
- a sample rotation holder manufactured by JEOL is used to irradiate the measurement surface with an argon ion beam from the 360-degree direction.
- the hardness of the sample whose measurement surface has been prepared is measured using the Micro Vickers hardness tester.
- a region corresponding to the softened layer of the sample is measured from the surface of the sample in a direction perpendicular to the plate surface (plate thickness direction) with a load of 1 kgf at intervals of three times or more the indentation.
- the total number of measurement points differs depending on the plate thickness of the sample, but the number of measurement points for calculating ⁇ Hv1 and ⁇ Hv2 described later is based on the description in JIS Z 2244: 2009 and is not affected by the indentation. Set as many measurement points as possible while ensuring the intervals.
- the measurement position on the outermost surface side of the sample should be within 20 ⁇ m from the plate surface (immediately below the plating layer or immediately below the alloy layer between the plating layer and the base metal, if a plating layer exists). To do. This is because the outermost surface portion of the base material surface has many soft phase structures.
- the same measurement is performed from the first surface side of the sample, and the second surface side opposite to the first surface side. Also do from.
- ⁇ Hv1 a method of calculating ⁇ Hv1 will be described. That is, from all the measurement points included in the region (first hardness change region 21) from the surface of the sample to the thickness of the entire softened layer of 40%, the first hardness change region 21 The hardness gradient ⁇ a is calculated.
- a i is the ratio (%) of the distance from the surface at the i-th measurement point to the total thickness of the softened layer
- c i is the Vickers hardness (Hv) at a i
- n the softened layer from the surface. It is the total of all the measurement points included in the region (first hardness change region 21) up to the total thickness of 40%.
- ⁇ a Gradient (Hv /%) of change in hardness in the plate thickness direction in the first hardness change region
- a i Ratio of the distance from the surface at the i-th measurement point to the total thickness of the softening layer (%)
- c i Vickers hardness (Hv) at a i n: Total of all measurement points included in the first surface side first hardness change region.
- ⁇ a1 on the first surface side is calculated based on the hardness measurement result from the first surface side, and further, Based on the hardness measurement result from the second surface side, ⁇ a2 on the second surface side is calculated.
- the arithmetic average of ⁇ a1 and ⁇ a2 can be set to ⁇ a.
- ⁇ Hv1 can be calculated by multiplying ⁇ a calculated by the equation (1) by the ratio of the thickness of the first hardness change region 21 in the thickness direction of the entire softened layer.
- the second hardness is calculated by the formula (2).
- the hardness gradient ⁇ A of the change area 22 is calculated.
- a i is the ratio (%) of the distance from the surface at the i-th measurement point to the total thickness of the softening layer
- C i is the Vickers hardness (Hv) in A i
- N is the softening on the surface side. It is the sum of all the measurement points contained in the area
- ⁇ A Gradient (Hv /%) of change in hardness in the plate thickness direction in the second hardness change region
- a i Ratio of the distance from the surface at the i-th measurement point to the total thickness of the softening layer (%)
- C i Vickers hardness (Hv) at A i N: Total of all measurement points included in the first surface side second hardness change region.
- ⁇ A1 on the first surface side is calculated based on the hardness measurement result from the first surface side, and further, Based on the hardness measurement result from the second surface side, ⁇ A2 on the second surface side is calculated.
- the arithmetic average of ⁇ A1 and ⁇ A2 can be set to ⁇ A.
- ⁇ Hv2 can be calculated by multiplying ⁇ A calculated by the equation (2) by the ratio of the thickness of the second hardness change region 22 in the plate thickness direction to the total thickness of the softened layer.
- FIG. 8 is a load-stroke diagram for explaining the function and effect of the skeleton member 10 according to the present embodiment.
- Curve a is a load-stroke diagram assuming a skeleton member in which an appropriate softening layer is provided, R / t is set to 2.0, and absolute value ⁇ Hv1 is set to 150 Hv.
- a curve b is a load-stroke diagram assuming a skeleton member provided with an appropriate softening layer, R / t set to 2.0, and absolute value ⁇ Hv1 set to 70Hv.
- a curve c is a load-stroke diagram assuming a skeleton member in which an appropriate softening layer is provided, R / t is set to 5.0, and absolute value ⁇ Hv1 is set to 150 Hv.
- a curve d is a load-stroke diagram assuming a skeleton member in which R / t is set to 2.0 without providing a softening layer.
- the R / t is set to 2.5 or less, and the corner portion 13 and at least a part of the vertical wall portion 15 are provided with the softening layer 20, whereby the curve a
- the curve b the bending characteristic at the time of collision is improved from the early stage of the stroke to the latter stage of the stroke, and the load can be reduced with a gentle curve in the latter stage of the stroke. That is, the deformability can be improved.
- the hardness of the center portion 30 in the plate thickness direction is set to 400 Hv or more in Vickers hardness, a high load resistance is maintained especially in the latter part of the stroke.
- the absolute value ⁇ Hv1 of the hardness change in the first hardness change region is made larger than the absolute value ⁇ Hv2 of the hardness change in the second hardness change region, the softened portion on the surface side of the skeletal member 10 Is ensured and the bending characteristics are improved.
- ⁇ Hv2 smaller than ⁇ Hv1
- ⁇ Hv1 is 100 Hv to 200 Hv
- the softened portion on the surface side of the skeleton member 10 is sufficiently secured, so that the softening layer 20 can sufficiently improve the bending characteristics. That is, comparing the curve a with ⁇ Hv1 of 150 Hv and the curve b with ⁇ Hv1 of 70 Hv, by setting ⁇ Hv1 in the range of 100 Hv to 200 Hv in the curve a, the drop of the withstand load from immediately after the peak in the latter part of the stroke is reduced. It can be made more gradual.
- the skeleton member 10 by setting the R / t of the corner portion 13 to be 2.5 or less, it is possible to maintain a high withstand load from the initial stroke to the latter stroke.
- the latter part of the stroke in combination with the effect that the softening layer 20 is formed in the corner portion 13 described above, a particularly excellent load resistance can be exhibited, and the deformability and the load resistance at the time of collision can be improved. It will be possible.
- the skeleton member 10 according to the present embodiment can maintain a high withstand load against a collision, can be less likely to be cracked by a collision, and can sufficiently secure the deformability. This makes it possible to achieve both high levels of load resistance and bending characteristics compared to conventional frame members.
- the wall portion 15 may be buckled and deformed.
- the softening layer 20 extends from the corner portion 13 over a region having a length of 1 ⁇ 2 or more of the length in the lateral direction of the vertical wall portion 15, The vertical wall portion 15 is effectively deformed. That is, when an external force is applied to the skeletal member 10 due to a collision in a direction including the X-direction component, the corner portion 13 side portion of the vertical wall portion 15 is bent and deformed.
- the portion includes a region where the softening layer 20 is provided. Therefore, when the softening layer 20 is provided in the region, the skeleton member 10 is flexibly bent by the softening layer 20, and thus the buckling deformation of the vertical wall portion 15 at a small pitch is promoted. Thereby, the deformability of the skeleton member 10 can be improved and the impact absorption energy can be increased.
- the softening layer 20 both inside and outside the bend of the corner portion 13, the bending characteristics can be further improved and the deformability can be improved.
- Modification 1 The skeleton member according to the first embodiment of the present invention has been described above. From here, a modification of the present embodiment will be described with reference to FIG. 9. This modification is characterized in that the flat plate portion 11 extending between the corner portions 13 of the skeleton member 10 has the softening layer 20.
- FIG. 9 is an XZ plane cross-sectional view of a region including a corner portion according to a modified example of the present embodiment.
- the flat plate portion 11 As shown in FIG. 9, in the corner portion 13, from the other end portion on the opposite side to the one end portion where the vertical wall portion 15 as the first wall portion extends, the flat plate portion 11 as the second wall portion. Is extended, and the softening layer 20 is also formed on the flat plate portion 11.
- the softening layer 20 since the softening layer 20 is also present in the flat plate portion 11, the surface portion of the flat plate portion 11 is also softened, so that the bending characteristics at the time of collision can be improved and the deformability can be improved. it can.
- the softening layer 20 may be formed over the entire flat plate portion 11. Thereby, the bending characteristics of the flat plate portion 11 are improved, so that the deformability of the skeleton member 10 can be further improved.
- the configuration in which the softening layer 20 is provided over the entire area of the flat plate portion 11 is also effective when the skeleton member 10 is used as a shock absorbing skeleton. This is particularly effective when the input to the skeleton member 10 is axial compression. In this case, the skeletal member 10 is crushed by the load in the longitudinal direction (Y direction shown in FIG. 1), but since the flat plate portion 11 has the softening layer 20 as a whole, the flat plate portion 11 is buckled. It is possible to prevent the flat plate portion 11 from cracking.
- the softening layer 20 may be provided over the entire area of the flat plate portion 11, the vertical wall portion 15, and the flange portion 17. This improves the bending characteristics of the skeleton member 10 as a whole, so that the deformability of the skeleton member 10 can be further improved.
- Modification 2 Heretofore, one modification example according to the first embodiment of the present invention has been described. From here, another modification of the present embodiment will be described with reference to FIGS. 10 and 11. This modification is characterized in that the patch material 40 is attached to the inside of the bend of the corner portion 13.
- FIG. 10 is a partial perspective view showing an example of a skeleton member according to this modification.
- FIG. 11 is an XZ plane sectional view of a skeleton member according to the present modification.
- the patch member 40 which is a component separate from the skeleton member 10
- the patch material 40 is a member having an L-shaped cross section.
- the patch material 40 may be made of the same material as the skeleton member 10 or may be made of a different material.
- the length of the patch material 40 in the longitudinal direction may be equal to or shorter than that of the skeleton member 10.
- the patch material 40 is attached so as to cover at least the bending inner side portion of the corner portion 13.
- the patch material 40 can be attached to the bending inner side of the corner portion 13 by various known techniques.
- Modification 3 (Modification 3)
- the hardness is set in a predetermined range at a position of a depth of 70 ⁇ m from the surface in the plate thickness direction at the center of the flat plate portion 11.
- FIG. 12A is a cross-sectional view taken along the line XZ of the skeleton member 10 according to this modification.
- 12B is an enlarged view of a portion including the central position S of the flat plate portion 11 (that is, a portion P of FIG. 12A) in the XZ plane cross section of the skeleton member 10 according to the present modification.
- FIG. 13A is a diagram showing an example of how the skeleton member 10 according to the present modification is deformed.
- 13B is a cross-sectional view taken along the line I-I ′ of FIG. 13A. As shown in FIG.
- the hardness is set in a predetermined range at the center position S of the flat plate portion 11 in the lateral direction of the skeleton member (X direction in FIG. 12A).
- the center position S is a position separated from both ends of the flat plate portion 11 in the lateral direction by the same distance L.
- the hardness is within a predetermined range at a position at a predetermined depth from the surface at the center position S.
- the depth (distance in the plate thickness direction) d from the surface of the flat plate portion 11 at the position C where the hardness is set within a predetermined range is 70 ⁇ m.
- the hardness at the position C is set to 0.9 times or less the hardness of the central portion 30 of the flat plate portion 11 in the plate thickness direction.
- the hardness at a position of a depth of 70 ⁇ m from the surface of the center position S of the flat plate portion 11 is set to be 0.9 times or less the hardness of the center portion 30 in the plate thickness direction. .
- the hardness is reduced at the center position S of the flat plate portion 11, so that the progress of cracks is suppressed.
- the occurrence of cracks during deformation of the skeleton member 10 is suppressed, the amount of energy absorbed by the skeleton member 10 is increased, and the impact absorption characteristics are further improved.
- the hardness of the flat plate portion 11 is set to be 0.9 times or less the hardness of the central portion 30 in the plate thickness direction at a position of a depth of 70 ⁇ m from the surface continuous with the bending inner side of the corner portion 13.
- the hardness of the surface that is continuous from the inside of the bend of the corner portion 13 where a tensile load that propagates a crack is generated is controlled.
- the occurrence of cracks during deformation of the skeleton member 10 is suppressed, the amount of energy absorbed by the skeleton member 10 is increased, and the impact absorption characteristics are further improved.
- the hardness at the position C where the hardness is controlled may be set to be 0.1 times or more the hardness of the central portion 30 of the flat plate portion 11 in the plate thickness direction.
- the hardness ratio in the flat plate portion 11 is set to a predetermined value or more, so that a high load resistance can be maintained.
- a skeleton member according to the second embodiment of the present invention will be described with reference to FIGS. 14 and 15.
- the skeleton member according to the present embodiment and the skeleton member according to the first embodiment differ in the shape of the cross-section in the lateral direction of the skeleton member.
- FIG. 14 is a partial perspective view showing an example of the skeleton member according to the present embodiment.
- FIG. 15 is a cross-sectional view taken along the XZ plane of the skeleton member according to this embodiment.
- the skeleton member 100 according to the present embodiment has a shape in which the cross-section (XZ plane) in the lateral direction of the skeleton member 100 is a closed cross section.
- the skeleton member 100 is a so-called rectangular tube-shaped member, and the cross-sectional shape is a hollow rectangular shape.
- the skeleton member 100 extends, for example, with the Y direction shown in FIG. 14 as the longitudinal direction. As shown in FIG. 15, the skeleton member 100 is a member having a hollow rectangular cross-section in the lateral direction (XZ plane).
- the skeletal member 100 has a flat plate portion 151, a vertical wall portion 153, and a corner portion 130 that is bent so as to connect the vertical wall portion 153 adjacent to the flat plate portion 151. That is, the skeletal member 100 includes a vertical wall portion 153 extending from one end of the corner portion 130 having an R stop and a flat plate portion 151 extending from the other end of the corner portion 130 having an R stop. Composed of.
- At least the corner portion 130 has the softening layer 200.
- the softening layer 200 does not need to be provided in all the corner portions 130, but may be provided in at least one corner portion 130.
- the softening layer 200 extends from the corner portion 130 to the vertical wall portion 153.
- the softening layer 200 extends over a length of 1 ⁇ 2 or more of the length of the vertical wall portion 153 in the lateral direction.
- the softening layer 200 may be formed over the entire area of the vertical wall portion 153.
- the softening layer 200 may extend over a length of 1 ⁇ 2 or more of the length of the flat plate portion 151 in the widthwise direction. Further, the softening layer 200 may be formed over the entire area of the flat plate portion 151.
- the softening layer 200 may be formed on the entire surface of the skeleton member 100.
- the skeletal member 100 has the softening layer 200 in the corner portion 130 and the vertical wall portion 153, so that it is possible to further improve the deformability while ensuring a load bearing capacity.
- the portion where the softening layer 200 is provided is selected according to the application target of the skeleton member 100.
- FIG. 16 is a diagram showing an automobile skeleton as an example to which the skeleton members 10 and 100 according to the embodiment of the present invention are applied.
- the skeleton members 10, 100 may constitute an automobile skeleton as a cabin skeleton or a shock absorbing skeleton.
- Examples of application of the skeleton members 10 and 100 as the cabin skeleton are roof center reinforcements 201, roof side rails 203, B pillars 207, side sills 209, tunnels 211, A pillar lowers 213, A pillar uppers 215, kick clean forces 227, floors.
- the cross member 229, the under lean force 231, the front header 233, etc. are mentioned.
- examples of application of the skeleton members 10 and 100 as a shock absorbing skeleton include a rear side member 205, an apron upper member 217, a bumper reinforcement 219, a crash box 221, and a front side member 223.
- the skeleton members 10 and 100 are used as a cabin skeleton or a shock absorbing skeleton, the skeleton members 10 and 100 have a sufficient load resistance, and thus deformation during collision can be reduced. Further, the skeleton members 10 and 100 have improved deformability, and even when an input such as a side collision is applied to the skeleton of the automobile, the skeleton members can absorb the impact by sufficient deformation and protect the inside of the skeleton.
- the shape of the analysis model is "hat material” and "square tube".
- the “hat material” means a closed cross-section hat member having a closed cross section by joining a closing plate to the flange portion 17 of the skeleton member 10 shown in FIGS. 1 and 4.
- “Square tube” means a rectangular member as shown in FIGS. 14 and 15.
- the length of the "hat material” and the “square tube” in the longitudinal direction was 500 mm.
- the height of each model (corresponding to the height of the vertical wall portions 15 and 153) was 60 mm, and the length in the width direction (corresponding to the length of the flat plate portions 11 and 151 in the width direction) was 80 mm.
- the plate thickness was 1.6 mm.
- the “corner portion” means a region corresponding to the corner portions 13 and 130 in the “hat material”.
- the “vertical wall” means a region having a length of 1 ⁇ 2 of the lateral length of the vertical wall portion 15 from the R stop of the corner portion 13.
- the “flat plate” means a region having a length that is 1 ⁇ 2 of the lateral length of the flat plate portion 151 from the R stop of the corner portion 130.
- “entire” means that the softening layer is provided on the entire surface including the corner portion.
- Double-sided means that the softening layers are provided on both sides, and “single-sided” means that the softening layers are provided on the bending outside surface of the corner portion.
- Table 1 shows R / t, the thickness of the softening layer, ⁇ Hv1, ⁇ Hv2, and the ratio of the surface hardness to the central hardness.
- Load characteristics A first peak is shown in the early stage of the stroke, a high withstand load is maintained in the middle of the stroke and the second half of the stroke, and a second peak is shown in the latter half of the stroke. After the second peak, the withstand load gradually decreases.
- B The first peak is shown in the early stage of the stroke, the high withstand load is maintained in the middle of the stroke and the latter period of the stroke, and the second peak is shown in the latter stage of the stroke.
- -C A high load is maintained in the middle of the stroke and the latter part of the stroke, and a peak is shown in the latter part of the stroke.
- ⁇ D Maintains high load in the middle of the stroke and the latter part of the stroke.
- E Low load is shown in any period, or maximum load is low due to cracking. In addition, A to C were regarded as acceptable levels.
- ⁇ A A level where sufficient energy can be absorbed as a result of maintaining a high load over the entire stroke.
- B A level at which high energy cannot be absorbed as a result of being unable to maintain a high load over the entire stroke.
- ⁇ C A level at which a low load is maintained over the entire stroke or energy is not sufficiently absorbed due to cracking. In addition, A was made into the acceptance level.
- Example 9 As shown in Table 1, in Examples 1 to 9, peaks were obtained in the early and late stages of the stroke, and overall sufficient load characteristics and energy absorption characteristics were shown. Further, in Example 9, sufficient load characteristics and energy absorption characteristics were obtained even when the softening layer was provided only on one side.
- FIG. 17 shows an example of the load-stroke diagram obtained as a result of the simulation according to this embodiment.
- the first peak was exhibited at the early stage of the stroke, the high load was maintained during the middle period of the stroke and the latter period of the stroke, and the second peak was exhibited at the latter stage of the stroke.
- Comparative Example 11 since R / t was 5.0, no peak was seen at the beginning of the stroke.
- the softening layer is present, the second peak in the latter half of the stroke is lower than that in Example 2.
- Comparative Example 3 since the softening layer was provided only at the corners, the vertical wall portion was cracked before reaching the maximum load. As a result, sufficient load characteristics and energy absorption characteristics could not be obtained. In Comparative Example 4, since the softening layer was provided only at 1% of the plate thickness, cracking occurred before reaching the maximum load. Therefore, sufficient load characteristics and energy absorption characteristics could not be obtained.
- Comparative Example 8 since the surface hardness was not sufficiently lower than the hardness of the central portion, cracking occurred in the vertical wall portion before reaching the maximum load. As a result, sufficient load characteristics and energy absorption characteristics could not be obtained.
- Comparative Examples 9 to 11 since R / t was more than 2.5, it was not possible to maintain a high load from the initial stroke to the latter stroke.
- Comparative Example 12 although R / t was 2.5 or less, it did not have a softening layer, so cracking occurred in the latter half of the stroke, and a high maximum load could not be secured. As a result, sufficient load characteristics and energy absorption characteristics could not be obtained.
- Comparative Example 1 the maximum load could not be obtained because cracking occurred in the middle of the stroke. Further, in Comparative Example 5, it was shown that although a crack did not occur until the latter half of the stroke, a sufficient load could not be maintained.
- the depth from the surface indicates the value of the depth d in FIG. 12B.
- the surface is defined as "inside” and the hardness is determined at the position of a predetermined depth from the surface that is continuous to the outside of the bend of the corner. If is controlled, the surface is “outside”.
- the hardness is controlled at a predetermined depth position from both surfaces, it is defined as "both sides”.
- the ratio of the hardness at the predetermined depth position C at the center position S to the hardness of the center portion 30 in the plate thickness direction is as shown in Table 2.
- FIG. 18 shows an example of the load-stroke diagram obtained as a result of the simulation according to the embodiment shown in Table 2. As shown in FIG. 18, in Example 10, a high load was maintained over the latter part of the stroke, and the second peak was exhibited in the latter part of the stroke.
- a skeleton member that has both improved deformability at the time of collision and improved load bearing capacity.
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Abstract
Description
本願は、2018年10月12日に、日本に出願された特願2018-193175号と、2019年2月15日に、日本に出願された特願2019-025366号に基づき優先権を主張し、その内容をここに援用する。
(1)本発明の第一の態様は、長手方向に延びるコーナ部と、当該コーナ部の短手方向の端部から延在する縦壁部とを含む骨格部材であって、前記コーナ部の曲げ内側または曲げ外側の少なくともいずれか一方の表面から板厚方向に軟化層が設けられ、前記軟化層は、前記コーナ部から前記縦壁部の短手方向長さの1/2以上の長さの領域に亘って前記縦壁部に延在し、前記軟化層が設けられた部分における板厚方向の中心部の硬度は400Hv以上であり、前記軟化層は、前記軟化層が設けられた部分における前記板厚方向の中心部の硬度よりも少なくとも10Hv低い硬度を有する領域であり、前記軟化層の厚さは、前記軟化層が設けられた部分における前記板厚の2%以上20%未満であり、前記表面における前記軟化層の硬度が、前記軟化層が設けられた部分における前記板厚方向の中心部の硬度の0.5倍以上0.9倍未満であり、前記軟化層は、前記板厚方向において、前記表面から前記軟化層の厚さの40%までの領域である第一の硬さ変化領域と、前記軟化層のうち前記第一の硬さ変化領域ではない領域である第二の硬さ変化領域とを有し、前記第一の硬さ変化領域における板厚方向の硬さ変化の絶対値ΔHv1は、前記第二の硬さ変化領域における板厚方向の硬さ変化の絶対値ΔHv2よりも大きく、前記コーナ部の曲げ半径Rが、前記コーナ部の板厚tに対して、R/t≦2.5である骨格部材である。
(2)上記(1)に記載の骨格部材では、前記第一の硬さ変化領域の前記板厚方向の硬さ変化の絶対値ΔHv1は、100Hv以上200Hv未満であってもよい。
(3)上記(1)又は(2)に記載の骨格部材では、前記軟化層は、前記コーナ部の前記曲げ外側に設けられてもよい。
(4)上記(1)~(3)のいずれか一項に記載の骨格部材では、前記軟化層は、前記コーナ部の前記曲げ内側と前記曲げ外側の両方に設けられてもよい。
(5)上記(1)~(4)のいずれか一項に記載の骨格部材では、前記縦壁部は、前記コーナ部の一端部から延在され、前記骨格部材は、前記コーナ部の他端部から延在された平板部をさらに含み、前記軟化層は、前記コーナ部から前記平板部の短手方向長さの1/2以上の長さの領域に亘って前記平板部に延在してもよい。
(6)上記(1)~(5)のいずれか一項に記載の骨格部材では、前記縦壁部は、前記コーナ部の一端部から延在され、前記骨格部材は、前記コーナ部の他端部から延在された平板部をさらに含み、前記平板部の中心の板厚方向において、前記平板部の表面から70μmの深さの位置における硬度が、前記板厚方向の中心部の硬度の0.9倍以下であってもよい。
(7)上記(6)記載の骨格部材では、前記平板部の表面は、前記平板部における、前記コーナ部の曲げ内側と連続する表面であってもよい。
[骨格部材の全体構造]
まず、図1を参照して、本発明の第1の実施形態に係る骨格部材の一例の部分構造について説明する。図1は、本実施形態に係る骨格部材の一例を示す部分斜視図である。骨格部材10は、一例として、図1に示すY方向を長手方向として延在され、長手方向断面(X-Z平面)が、X方向に開口された略ハット形状となっている部材である。骨格部材10は、一例として、平板部11と、平板部11からコーナ部13を介して延在された壁部としての縦壁部15と、縦壁部15のコーナ部13とは反対側の端部から屈曲されたフランジ部17とを含んでいる。また、骨格部材10において、少なくともコーナ部13および縦壁部15は、後述する軟化層20を有する。
次に、図2~図5、図6A、図6Bを参照して、本実施形態に係るコーナ部13を含む領域の構成について説明する。図2は、本実施形態に係るコーナ部13を含む領域のX-Z平面断面図である。図3~5は、本実施形態に係る骨格部材のX-Z平面断面図である。コーナ部13は、平板部11と縦壁部15との間に存在する屈曲部であり、後述する所定の曲げ半径Rを有する。コーナ部13は、図2に示すように、X-Z平面断面視で、曲げ内側におけるR止まり点A1、A2、曲げ外側におけるR止まり点A3、A4により区画される領域に形成されている。
尚、引張強度で1470MPa以上(例えば1.5GPa級、1.8GPa級またはそれ以上)の骨格部材10を製造する場合には、R/t≦2.5を満たすコーナ部13を得るために、ホットスタンプ工法を用いることが好ましい。
縦壁部15は、コーナ部13のR止まりを含む端部から板厚方向と直交する方向に延在されている。縦壁部15のコーナ部13と反対側の端部は、外方に屈曲されており、屈曲部を介してフランジ部17が延在されていてもよい。すなわち、骨格部材10は、図1におけるX-Z断面において、略ハット形状に形成され得る。
骨格部材10の表面側において、少なくともコーナ部13および縦壁部15には軟化層20が形成されている。軟化層20は、骨格部材10の長手方向(図1のY方向)に亘って、連続的に形成されていてもよいし、部分的に形成されていてもよい。また、軟化層20は、骨格部材10の表面から板厚方向に所定の深さに亘って形成されている。本実施形態に係る骨格部材10では、軟化層20の厚さは、骨格部材10の板厚の2%以上20%未満である。ここで、板厚とは、軟化層20と後述する板厚方向の中心部30とを含めた、骨格部材10の板厚方向の全体厚さを指す。
一方、軟化層20の厚さが、骨格部材10の板厚の2%未満になると、骨格部材10における軟化層20の割合が少なく、変形能が十分に発揮されない。軟化層20の厚さは、骨格部材10の板厚の5%以上であることが好ましく、8%以上であることが更に好ましい。
一方、表面の硬度が板厚方向の中心部30の硬度に対して0.9倍以上となると、変形能を十分に向上させることが困難となる。軟化層20は、骨格部材10の表面において、板厚方向の中心部30の硬度に対して、0.8倍未満の硬度を有していることが好ましい。
板厚方向の中心部30の硬度の上限は特に規定しないが、骨格部材10の成形性等を鑑みれば、800Hvであることが好ましく、700Hvであることが更に好ましい。
板厚方向の中心部30の硬度の測定方法は以下の通りである。試料の板面に垂直な断面を採取し、測定面の試料調製を行い、硬さ試験に供する。測定面の調製方法は、JIS Z 2244:2009に準じて実施する。#600から#1500の炭化珪素ペーパーを使用して測定面を研磨した後、粒度1μmから6μmのダイヤモンドパウダーをアルコール等の希釈液や純水に分散させた液体を使用して鏡面に仕上げる。硬さ試験は、JIS Z 2244:2009に記載の方法で実施する。マイクロビッカース硬さ試験機を用いて、試料の板厚の1/2位置に、荷重1kgfで、圧痕の3倍以上の間隔で10点測定し、その平均値を板厚方向の中心部30の硬度とする。
Δa:第一の硬さ変化領域における板厚方向の硬さの変化の勾配(Hv/%)
ai:i番目の測定点における表面からの距離が軟化層全体の厚さに占める割合(%)
ci:aiにおけるビッカース硬さ(Hv)
n:第一の表面側第一の硬さ変化領域に含まれる全ての測定点の合計
である。
ΔA:第二の硬さ変化領域における板厚方向の硬さの変化の勾配(Hv/%)
Ai:i番目の測定点における表面からの距離が軟化層全体の厚さに占める割合(%)
Ci:Aiにおけるビッカース硬さ(Hv)
N:第一の表面側第二の硬さ変化領域に含まれる全ての測定点の合計
である。
図8は、本実施形態に係る骨格部材10の作用効果を説明するための荷重-ストローク線図である。
曲線aは、適切な軟化層を設け、R/tを2.0に設定し、絶対値ΔHv1を150Hvに設定した骨格部材を想定した荷重-ストローク線図である。
曲線bは、適切な軟化層を設け、R/tを2.0に設定し、絶対値ΔHv1を70Hvに設定した骨格部材を想定した荷重-ストローク線図である。
曲線cは、適切な軟化層を設け、R/tを5.0に設定し、絶対値ΔHv1を150Hvに設定した骨格部材を想定した荷重-ストローク線図である。
曲線dは、軟化層を設けず、R/tを2.0に設定した骨格部材を想定した荷重-ストローク線図である。
本実施形態に係る骨格部材10によれば、R/tを2.5以下とし、且つ、コーナ部13と、縦壁部15の少なくとも一部とに軟化層20を設けたことで、曲線a又は曲線bに示すように、ストローク初期からストローク後期に亘り、衝突時の曲げ特性が向上し、ストローク後期において緩やかなカーブで荷重を落とすことができる。すなわち、変形能を向上させることができる。
以上、本発明の第1の実施形態に係る骨格部材について説明した。ここから、図9を参照しながら本実施形態の一の変形例について説明する。本変形例では、骨格部材10のコーナ部13の間に延設された平板部11が軟化層20を有する点に特徴がある。
以上、本発明の第1の実施形態に係る一の変形例について説明した。ここから、図10および図11を参照しながら、本実施形態の他の変形例について説明する。本変形例では、コーナ部13の曲げ内側にパッチ材40が取り付けられている点に特徴がある。
以上、本発明の第1の実施形態に係るいくつかの変形例について説明した。ここから、図12A、図12B、図13A、および図13Bを参照しながら、本実施形態のその他の変形例について説明する。本変形例では、平板部11の中心の板厚方向において、表面から70μmの深さの位置において硬度が所定の範囲に設定されている点に特徴がある。
続いて、本発明の第2の実施形態に係る骨格部材について図14および図15を参照しながら説明する。本実施形態に係る骨格部材と第1の実施形態に係る骨格部材とは、骨格部材の短手方向断面の形状で相違する。
以上、本発明の好適な実施の形態について詳細に説明した。ここから、図16を参照して本発明の実施形態に係る骨格部材の適用例について説明する。図16は、本発明の実施形態に係る骨格部材10、100が適用される一例としての自動車骨格を示す図である。骨格部材10、100は、キャビン骨格または衝撃吸収骨格として自動車骨格を構成し得る。キャビン骨格としての骨格部材10、100の適用例は、ルーフセンタリーンフォース201、ルーフサイドレール203、Bピラー207、サイドシル209、トンネル211、Aピラーロア213、Aピラーアッパー215、キックリーンフォース227、フロアクロスメンバ229、アンダーリーンフォース231、フロントヘッダ233等が挙げられる。
骨格部材10、100の平板部11、151の反対側において、支点間距離を600mmとして骨格部材10、100を支持し、平板部11、151側に対して半径150mmのインパクタを準静的に押し込み、押し込み量と荷重の値を算出し、エネルギー吸収量を得た。また、押し込みの際に、後述するストローク中期において縦壁部に割れが生じたか否かを併せて判定した。耐荷重の指標である荷重特性、および耐荷重と変形能の指標であるエネルギー吸収特性の評価基準は以下のとおりである。
・A:ストローク初期に第1のピークを示し、ストローク中期、ストローク後期にわたって高い耐荷重を維持し、ストローク後期において第2のピークを示す。第2のピーク後は耐荷重が緩やかに低下する。
・B:ストローク初期に第1のピークを示し、ストローク中期、ストローク後期にわたって高い耐荷重を維持し、ストローク後期において、第2のピークを示す。
・C:ストローク中期、ストローク後期に高い荷重を維持し、ストローク後期においてピークを示す。
・D:ストローク中期、ストローク後期に高い荷重を維持する。
・E:いずれの期においても低い荷重を示す、または割れの発生により最大荷重が低い。
尚、A~Cを合格水準とした。
・A:ストローク全体にわたって高い荷重を維持した結果、十分にエネルギー吸収できる水準。
・B:ストローク全体にわたって高い荷重を維持できなかった結果、十分にエネルギーを吸収できない水準。
・C:ストローク全体にわたって低い荷重を維持、または割れの発生により十分にエネルギーを吸収できない水準。
尚、Aを合格水準とした。
また、実施例9においては、片面側のみに軟化層を設けた場合であっても、十分な荷重特性およびエネルギー吸収特性が得られた。
比較例4においては、軟化層が板厚の1%しか設けられなかったため、最大荷重に到達する前に割れが生じた。このため、十分な荷重特性およびエネルギー吸収特性が得られなかった。
比較例9~11においては、R/tが2.5超であったため、ストローク初期からストローク後期に亘り高い荷重を維持することができなかった。
比較例12においては、R/tが2.5以下であるものの軟化層を有さないため、ストローク後期において割れが生じ、高い最大荷重を確保することができなかった。その結果、十分な荷重特性およびエネルギー吸収特性が得られなかった。
11 平板部
13 コーナ部
15 縦壁部
17 フランジ部
20 軟化層
21 第一の硬さ変化領域
22 第二の硬さ変化領域
30 板厚方向の中心部
Claims (7)
- 長手方向に延びるコーナ部と、当該コーナ部の短手方向の端部から延在する縦壁部とを含む骨格部材であって、
前記コーナ部の曲げ内側または曲げ外側の少なくともいずれか一方の表面から板厚方向に軟化層が設けられ、
前記軟化層は、前記コーナ部から前記縦壁部の短手方向長さの1/2以上の長さの領域に亘って前記縦壁部に延在し、
前記軟化層が設けられた部分における板厚方向の中心部の硬度は400Hv以上であり、前記軟化層は、前記軟化層が設けられた部分における前記板厚方向の中心部の硬度よりも少なくとも10Hv低い硬度を有する領域であり、
前記軟化層の厚さは、前記軟化層が設けられた部分における前記板厚の2%以上20%未満であり、
前記表面における前記軟化層の硬度が、前記軟化層が設けられた部分における前記板厚方向の中心部の硬度の0.5倍以上0.9倍未満であり、
前記軟化層は、前記板厚方向において、前記表面から前記軟化層の厚さの40%までの領域である第一の硬さ変化領域と、前記軟化層のうち前記第一の硬さ変化領域ではない領域である第二の硬さ変化領域とを有し、
前記第一の硬さ変化領域における板厚方向の硬さ変化の絶対値ΔHv1は、前記第二の硬さ変化領域における板厚方向の硬さ変化の絶対値ΔHv2よりも大きく、
前記コーナ部の曲げ半径Rが、前記コーナ部の板厚tに対して、R/t≦2.5である、
骨格部材。 - 前記第一の硬さ変化領域の前記板厚方向の硬さ変化の絶対値ΔHv1は、100Hv以上200Hv未満である、請求項1に記載の骨格部材。
- 前記軟化層は、前記コーナ部の前記曲げ外側に設けられる請求項1または2に記載の骨格部材。
- 前記軟化層は、前記コーナ部の前記曲げ内側と前記曲げ外側の両方に設けられる、請求項1~3のいずれか一項に記載の骨格部材。
- 前記縦壁部は、前記コーナ部の一端部から延在され、
前記骨格部材は、前記コーナ部の他端部から延在された平板部をさらに含み、
前記軟化層は、前記コーナ部から前記平板部の短手方向長さの1/2以上の長さの領域に亘って前記平板部に延在する、請求項1~4のいずれか一項に記載の骨格部材。 - 前記縦壁部は、前記コーナ部の一端部から延在され、
前記骨格部材は、前記コーナ部の他端部から延在された平板部をさらに含み、
前記平板部の中心の板厚方向において、前記平板部の表面から70μmの深さの位置における硬度が、前記板厚方向の中心部の硬度の0.9倍以下である、請求項1~5のいずれか一項に記載の骨格部材。 - 前記平板部の表面は、前記平板部における、前記コーナ部の曲げ内側と連続する表面である、請求項6に記載の骨格部材。
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