JP2020159487A - Stacked-joint structure and automobile frame component - Google Patents

Abstract

To provide a stacked-joint structure of stacked-joint members capable of suppressing breakage of a plate member starting from a hole formed in a non-fused joint when a stacked portion formed by stacking a plurality of plate members together is joined by non-fused joining means.SOLUTION: A stacked-joint structure according to one aspect of the present invention includes: a plurality of stacked plate members; and a plurality of joints arranged in a stacked portion of the plurality of stacked members, the joints being formed by mechanical joining means or friction-agitation point joining means. The plurality of joints have holes through which the mechanical joining means is inserted or holes formed by the friction-agitation point joining. Among the plurality of plate members, a main plate member having the largest product of the plate thickness and the tensile strength has, between the plurality of joints in the stacked portion, a soft portion with a hardness of 80% or less of the hardness of the plate member which includes main soft portions.SELECTED DRAWING: Figure 1

Description

The present invention relates to a lap joint structure and an automobile frame component.

In order to achieve both improved collision safety and improved fuel efficiency, the application of high-strength steel sheets to structural members (hereinafter referred to as "structural members for automobiles") that form the skeleton of the monocoque body that constitutes the automobile body has expanded. There is. Currently, high-tensile steel sheets having a tensile strength of 980 MPa class are used for structural members for automobiles, and recently, application of high-tensile steel sheets having a tensile strength of 1180 MPa class or more is also being considered. Further, by using a hot stamping method in which quenching is performed at the same time as press molding, a high-strength structural member for automobiles having a tensile strength of 1500 MPa or more is being manufactured. According to the hot stamping method, since the steel sheet is press-formed at a high temperature and soft, there are few problems related to dimensional accuracy after forming, and the press forming can be performed at a high temperature and high ductility. It has the great advantage of being excellent in sex.

However, in a spot welded joint containing a steel plate having a tensile strength of 780 MPa or more, the toughness of the nugget decreases, and the stress in the peeling direction concentrates the stress on the nugget end, so that the tensile strength of the steel plate increases. However, there is a problem that the cross tensile strength (CTS) does not increase or decreases.

As one of the techniques for solving this problem, there is a technique for mechanically joining a plurality of metal plates by using a mechanical joining means such as a rivet or a screw without melting the base metal. By using this technology, there is a possibility that automobile parts with higher strength and reliability than before can be manufactured.

Further, in an automobile body or the like, a combination of different materials such as a steel plate and an aluminum plate or a steel plate and a carbon fiber reinforced plastic (CFRP) plate may be joined for the purpose of weight reduction or the like. As described above, when the materials to be combined are materials having different physical properties such as melting point and coefficient of linear expansion, they are fastened and joined by mechanical joining means as described in Patent Documents 1 and 2, for example. .. Further, in an aluminum plate having a low electric resistance, friction stir welding may be used instead of resistance spot welding. Hereinafter, the mechanical joining means and the friction stir welding point joining means may be collectively referred to as a non-melt joining means.

In order to provide this non-melt bonding means in the lap bonding structure, it is inevitably necessary to provide holes in the plate member. For example, when the overlapped portions of a plurality of stacked plate members are joined by a mechanical joining means such as a blind rivet at the joint portion, a hole through which the rivet is inserted is formed in the joint portion of the plate members. Further, when the overlapped portions are point-bonded by the friction joining means, a hole due to a press-fitting mark of the probe at the tip of the rotating tool remains at the joint portion of the plate member on the rotating tool side.

In the study of the present inventor, in the lap joining member in which the lap portion is joined by mechanical joining means or friction joining means, when the entire lap joining member is subjected to tensile deformation, strain is concentrated in the holes formed in the joining portion. As a result, there was a problem that the plate member was broken due to a small deformation starting from the hole. In the prior arts such as Patent Documents 1 and 2, no study has been made on this problem.

Japanese Unexamined Patent Publication No. 2000-272541 Japanese Unexamined Patent Publication No. 2005-119757

The present invention suppresses breakage of a plate member starting from a hole formed in the non-melt joint portion when the overlapped portion formed by superimposing a plurality of plate members is joined by a non-melt joint means. It is an object of the present invention to provide a lap joint structure of a lap joint member capable of being capable of.

The gist of the present invention is as follows.
(1) The lap joining structure according to one aspect of the present invention is composed of a plurality of lapped plate members and a mechanical joining means or a friction stir welding point joining means provided in the lap portion of the plurality of plate members. The plurality of joints are provided with, and the plurality of joints have a hole through which the mechanical joining means is inserted or a hole formed by friction stir welding, and among the plurality of plate members. One or more sheets have a soft portion between the plurality of joints in the overlapped portion, and the hardness of the soft portion is 80% or less of the hardness of the plate member provided with the soft portion. ..
(2) In the lap joint structure according to (1) above, the length L1 of the soft portion, the width W1 of the soft portion, the hardness H1 of the soft portion, and the hardness H2 of the plate member having the soft portion. , And the diameter K of the hole 131 may satisfy the following formulas 1 and 2.
L1> K (Equation 1)
(H2-H1) × W1> H2 × K (Equation 2)
(3) In the lap joint structure according to (1) or (2) above, the shortest distance D between the end of the hole and the end of the soft portion and the diameter K of the hole 131 are the following formulas. 3 may be satisfied.
D ≧ K (Equation 3)
(4) In the lap joint structure according to any one of (1) to (3) above, the hole may penetrate one or more of the plurality of plate members.
(5) In the lap joint structure according to any one of (1) to (4) above, the soft portion may be provided on the plate member having the holes.
(6) In the lap joint structure according to any one of (1) to (5) above, the soft portion may be provided on the main plate member having the largest product of the plate thickness and the tensile strength.
(7) In the lap joint structure according to any one of (1) to (6) above, the plate member has a second soft portion that surrounds the joint portion and is separated from the soft portion. , The hardness H1 of the soft portion, the hardness H2 of the plate member having the soft portion, the hardness H3 of the second soft portion, the width W1 of the soft portion, the width W3 of the second soft portion, and the above. The diameter K of the hole 131 may satisfy the following equation 4.
(H2-H1) × W1> H2 × K + (W3-K) × (H2-H3) (Equation 4)
(8) In the lap joint structure according to any one of (1) to (7) above, the plate member having the soft portion has a tensile strength of 980 MPa or more, and its metal structure forms martensite. It may be a steel plate containing.
(9) The automobile skeleton component according to another aspect of the present invention has the lap joint structure according to any one of (1) to (8) above.
(10) The automobile frame component according to (9) above may be an A pillar, a B pillar, or a roof rail.

According to the present invention, when a laminated portion formed by superimposing a plurality of plate members is joined by a non-melt joining means, it is possible to prevent the plate member from breaking starting from a hole formed at the time of joining. Therefore, it is possible to provide a lap joint structure of a lap joint member capable of increasing the elongation (strain amount) until the plate member breaks.

It is a perspective view of the lap joint structure which concerns on this embodiment. It is sectional drawing of the joint part. It is a conceptual diagram of the mechanical joining means formed by the resistance element welding. It is a conceptual diagram of the mechanical joining means formed by the resistance element welding. It is a conceptual diagram of the friction stir point welding means formed by friction stir welding. It is a figure which outlines the hardness of a soft part and its surroundings. It is a schematic diagram which shows the length L1 of a soft part, the width W1 of a soft part, and the diameter K of a hole. It is a perspective view of the lap joint structure having a second soft part. It is the schematic explaining the measuring method of the hardness H3 and the width W3 of a second soft part. It is a perspective view which illustrates the variation of the shape of a soft part. It is a perspective view which illustrates the variation of the shape of a soft part. It is a perspective view which illustrates the variation of the shape of a soft part. It is a perspective view which illustrates the variation of the shape of a soft part. It is a perspective view of the B pillar which is an automobile skeleton component which concerns on this embodiment. It is XI-XI sectional view of the B pillar of FIG. It is a perspective view of the A pillar and the roof rail which are an example of the automobile frame parts which concerns on this embodiment. It is sectional drawing of the roof rail of FIG. It is a perspective view of the hinge reinforcement of the B pillar which is an example of the automobile frame component which concerns on this embodiment. It is a top view and a side view of a test piece simulating a conventional lap joint structure. It is a top view and a side view of the test piece which simulated the lap joint structure of this invention. It is a photograph of the test piece of FIG. 15 after the tensile test.

The present inventors suppress the breakage of the plate members starting from the holes formed at the time of joining when the overlapped portions formed by superimposing a plurality of plate members are joined by non-melt joining means. We have repeatedly studied a method for providing a lap-joining structure of lap-joining members. As a result, it was conceived that it would be better to provide a means to disperse the strain so that the strain does not concentrate on the end of the hole formed in the joint. Then, in the laminated portion of the plate members, a soft portion is formed between the joint portion and the joint portion adjacent to the joint to disperse the strain due to the tensile load, and the laminated joint member starting from the hole has a structure. We obtained the finding that destruction is suppressed.

Hereinafter, the lap joint structure 1 according to the present embodiment will be described with reference to the drawings as appropriate. As an example of the lap joint structure 1, the plate member 11 having the flange 12 is shown in the figure, but the lap joint structure 1 according to the present embodiment does not have to include the flange 12. Further, although the lap joint structure according to the present embodiment will be described with reference to the configuration in which the number of plate members 11 is 2 or 3 in the drawing, the number of plate members 11 may be 4 or more.

As shown in FIG. 1, the lap-join structure 1 according to one aspect of the present invention obtained from the above findings is provided on a plurality of stacked plate members 11 and a stack portion of the plurality of plate members 11. A plurality of joints 13 (not shown in FIG. 1) configured by a mechanical joining means or a friction stir welding point joining means, and the plurality of joinings 13 are holes 131 through which the mechanical joining means are inserted. Alternatively, it has a hole 131 formed by friction stir welding, and one or more of the plurality of plate members 11 has a soft portion 14 between the plurality of joint portions 13 in the overlapping portion, and the hardness of the soft portion 14 is hard. The hardness is 80% or less of the hardness of the plate member 11 provided with the soft portion 14. Further, although the overlapping portion is the flange portion 12 in FIG. 1, the flange portion 12 is not essential as described above.

(1) Plate member 11
The material of the plate member 11 is not particularly limited. The plate member 11 is, for example, a resin plate, a CFRP (Carbon Fiber Reinforced Plastic) plate, or a metal plate such as an aluminum plate, an aluminum alloy plate, a stainless plate, a titanium plate, or a steel plate. The plate member 11 may include a coating film and a surface treatment layer such as plating. The lap joint structure according to the present embodiment is formed by stacking a plurality of plate members 11, but the materials of the plurality of plate members 11 may be the same or different. The plate thickness and mechanical strength (tensile strength, hardness, etc.) of the plate member 11 are also not particularly limited. For example, when the plate member 11 is a steel plate, the thickness of the plate member 11 may be, for example, 0.5 to 2.6 mm. When the plate member 11 is a CFRP plate, the thickness of the plate member 11 may be, for example, 0.3 to 4.0 mm. The plate thickness and mechanical strength of the plurality of plate members 11 may be the same or different.

Of the plurality of plate members 11 constituting the lap joint structure, the plate member having the largest product of the plate thickness and the tensile strength has the greatest effect on the mechanical strength of the lap joint structure. In the lap joint structure according to the present embodiment, the plate member 11 having the largest product of the plate thickness and the tensile strength is referred to as a main plate member, and the other plate members 11 are referred to as sub plate members. When the lap joint structure has two or more plate members 11 having the same product of plate thickness and tensile strength, and the product of these plate thickness and tensile strength is the maximum among the plurality of plate members 11. Both of these can be regarded as main plate members.

The most preferable example of the plate member 11 is a high-strength steel sheet, specifically, a steel sheet having a tensile strength of 1200 MPa or more and having a metal structure containing martensite. A high-strength steel sheet containing martensite can be easily formed into a soft portion, which will be described later, by subjecting it to a local heat treatment using laser irradiation or the like. On the other hand, it is not hindered that the steel plate having a tensile strength of 1200 MPa or less is used as the plate member 11. For example, a high-strength steel plate having a tensile strength of 1200 MPa or more and a steel plate having a tensile strength of 270 MPa to 980 MPa may be combined. ..

When the plate member 11 is a steel plate, the steel plate may be a non-plated steel plate whose surface is not plated, and may be alloyed hot-dip galvanizing (GA plating), hot-dip galvanizing (GI plating), or electrozinc plating (EG). ), Zn-Al plating, Zn-Al-Mg plating, Zn-Mg plating, or other zinc-based plating, or a steel sheet coated with chromate, resin, etc., and an aluminum-plated steel sheet. May be. When the plate member 11 is a hot stamping material, the plate member 11 is made of a non-plated steel plate, aluminum plating, an intermetallic compound of iron and aluminum, or a composite layer composed of an iron-zinc solid solution layer and a zinc oxide layer. It may be a coated steel plate or a steel plate coated with a composite layer composed of a solid solution layer of zinc iron-zinc nickel and a zinc oxide layer.

According to the mechanical joining means described later, it is possible to join the plate member 11 which is not suitable for welding. For example, the mechanical joining means can be applied to a lap joining structure 1 in which a plurality of aluminum materials are combined, a lap joining structure 1 in which an aluminum material and a steel material are combined, and the like. Further, the mechanical joining means can be applied to the lap joining structure 1 in which a CFRP material is used instead of the metal plate. It is also possible to join materials that are not suitable for welding by the friction stir welding means described later. For example, the friction stir welding point joining means can be applied to a lap joining structure 1 in which a plurality of aluminum materials are combined, a lap joining structure 1 in which an aluminum material and a steel material are combined, and the like. For the above reasons, the material of the plate member 11 is not particularly limited.

(2) Joint portion 13 and hole 131
A part or all of the plurality of plate members 11 are overlapped with each other, and are joined to each other at the overlapped portion. The joining portion 13 is a non-melt joining means, that is, a mechanical joining means 132, a friction stir point joining means 133, and the like.

The mechanical joining means 132 includes, for example, blind rivets, self-piercing rivets (self-perforated rivets, SPR), hollow rivets, flat rivets, drill screws, bolts, EJOWELD (registered trademark), FDS (registered trademark) and the like. According to these, the plate members 11 are joined by plastic working cold or hot. The plate member 11 may be joined by a combination of these descriptive joining means and energization heating and pressurization. The mechanical joining means 132 includes one that penetrates all the stacked metal plate members 11 such as a blind rivet and one that does not penetrate a part of the stacked metal plate members 11 such as a self-piercing rivet. However, all of them can be used in the superposition structure 1 according to the present embodiment. In the example of the joint portion 13 shown in FIG. 2, the mechanical joining means 132 is composed of rivets.

As the mechanical joining means 132, Resistance Element Welding (REW) may be used. As shown in FIGS. 3A and 3B, the REW includes a plate member 11 (for example, an aluminum alloy plate) in which a hole 131 penetrating in the plate thickness direction is formed, and another plate member 11 (for example, boron steel or the like). (Steel plate) is overlapped, the mechanical joining means 132 which is a rivet with a steel flange is inserted into the hole 131, and further, the two plate members 11 are sandwiched by the electrode X (see FIG. 3A). ), A joining means for forming a nugget 132'by melting the contact portion between the tip portion of the mechanical joining means 132 and the plate member 11 by energizing the two plate members 11 at a predetermined current value. (See FIG. 3B). As described above, although REW partially uses the melt joining means, it is essentially a joining means using a mechanical element called a flanged rivet, so such a joining means is also a mechanical joining means. As 132, it can be suitably used in the present invention.

When the plate member 11 is joined by the mechanical joining means 132, it is necessary to provide a hole 131 in the plate member 11 for inserting the mechanical joining means 132. That is, the joining portion 13 formed by the mechanical joining means 132 has a hole 131 through which the mechanical joining means 132 is inserted. The hole 131 through which the mechanical joining means 132 is inserted may or may not penetrate the plate member 11.

The joint portion 13 is a joint portion formed by friction stir welding. Here, Friction Stir Spot Welding (FSSW) is, as shown in FIG. 4, press-fitting into the base metal while rotating the rotation tool Y, which is relatively harder than the base metal, and melts the base metal. It is a kind of solid-state bonding that joins without causing. In friction stir welding, the deformation resistance of the plate member 11 is reduced by the frictional heat generated by the rotation of the rotary tool Y, and the plate member 11 around the rotary tool Y is plastically flowed and stirred by the movement of the rotary tool Y. Integrate (see FIG. 4B). The rotary tool Y used in these series of steps usually has a probe with a threaded tip. When the rotary tool is press-fitted into the plate member 11, friction stir welding is performed, and then the rotary tool Y is pulled out from the base material, the plate member 11 into which the rotary tool Y is press-fitted inevitably has a press-fitting mark of the probe. Occurs (see FIG. 4C). That is, the joint portion formed by the friction stir welding point joining means has a hole 131 which is a press-fitting mark of the probe. The lap bonding structure 1 according to the present embodiment is preferably applied when a hole having a depth of 80% or more of the plate thickness is formed by press-fitting the probe.

It should be noted that the combination of these non-melt bonding means and other bonding means (for example, resin or the like) is not hindered. For example, an adhesive (for example, an epoxy resin-based adhesive) may be interposed on the overlapping surfaces, and the adhesive bonding may be used in combination with the non-melt bonding means. A sealing resin (sealer, electrodeposition coating, etc.) may be interposed on the overlapping surfaces to waterproof or insulate the seams. It is a preferable form of the superposition structure 1 according to the present embodiment that a structural adhesive, an impact-resistant adhesive or the like is interposed on the superposition surface and the bonding by the adhesive is used in combination with the non-melt bonding means. is there. In particular, in the case of a structural member in which an aluminum material and a steel material are combined, it is preferable to use a resin and an adhesive having a sealing function capable of electrically insulating and a non-melt bonding means in combination.

The position of the joint portion 13 is not particularly limited, but by separating the position of the hole 131 formed in the joint portion 13 from the end portion of the plate member 11, the possibility of breakage starting from the hole 131 can be further suppressed. it can. For example, it is preferable that the shortest distance L between the end of the hole 131 and the end of the plate member 11 and the diameter K of the hole 131 satisfy the following equation.
L ≧ 0.8K

The pitch of the joints 13 (distance between adjacent joints 13) is also not particularly limited. The pitch may be appropriately set according to the structure to which the lap joint structure 1 is applied and the application site. When the lap joint structure 1 is applied to an automobile part, for example, the pitch of the joint portion 13 may be about 20 mm to 100 mm.

In the lap joint structure 1 according to the present embodiment, the hole 131 is not limited to a hole (through hole) that penetrates the plate member 11, but a hole (blind hole) that does not penetrate the plate member 11 and a step on the inner surface. It may be a hole (stepped hole), a hole having a conical inner surface (tapered hole), a hole having a thread on the inner surface (female screw hole), or the like. Further, the hole 131 may be provided in either the main plate member or the sub plate member.

(3) Soft part 14
As described above, in the lap joining member 1 in which the lap portions are joined by the mechanical joining means 132 or the friction stir welding point joining means, a hole formed in the joining portion 13 when the entire lap joining member 1 is subjected to tensile deformation. When the strain is concentrated on the 131, the plate member 11 starting from the hole 131 may be broken. Therefore, the present inventors have studied a means for dispersing the strain so that the strain does not concentrate on the end of the hole 131 formed in the joint portion 13. As a result, in the overlapped portion of the plate member 11, the soft portion 14 is formed between the adjacent joint portions 13, so that the strain due to the tensile load is dispersed, and the overlapped joint member 1 starting from the hole 131 is broken. Was found to be suppressed.

Based on the above findings, the lap joint structure 1 according to the present embodiment has a soft portion 14 between a plurality of joint portions 13 in the lap portion. The soft portion 14 is a region having a hardness of 80% or less of the hardness H2 of the plate member 11 provided with the soft portion 14. An example of the means for identifying the soft portion 14 is shown in FIG. FIG. 5 is a graph showing the hardness distribution of the plate member 11 between the holes 131. In this graph, the region where the hardness is 80% or less of the hardness H2 of the plate member 11 is the soft portion.

The soft portion 14 needs to be provided on one or more of the plurality of plate members 11 constituting the lap joint structure 1, but which plate member 11 to be arranged can be appropriately selected. Preferably, the soft portion 14 is provided on the main plate member. As described above, since the main plate member is a member that most affects the mechanical properties of the lap joint structure 1, by providing the soft portion 14 on the main plate member, the effect of reducing the concentration of strain in the hole 131 is maximized. be able to. Further, preferably, the soft portion 14 is provided in the plate member 11 in which the hole 131 is present. Hereinafter, the lap joint structure 1 according to the present embodiment will be described with a configuration in which the soft portion 14 is provided on the main plate member having the hole 131. However, the soft portion 14 may be provided on the sub-plate member, or may be provided on the plate member 11 having no hole 131.

The size and shape of the soft portion 14 are not particularly limited, but for example, the length L1 of the soft portion 14, the width W1 of the soft portion 14, the hardness H1 of the soft portion 14, the hardness H2 of the plate member 11, and the hole 131. It is preferable to determine the size and shape of the soft portion 14 so that the diameter K of the above satisfies the following formulas 1 and 2.
L1> K (Equation 1)
(H2-H1) × W1> H2 × K (Equation 2)

As shown in FIG. 6, the length L1 of the soft portion 14 is the distance between the line connecting the centers of the adjacent holes 131 and the two intersections of the outer edge of the soft portion 14. The measurement of L1 is performed by continuously measuring the hardness of the plate member 11 along the line connecting the centers of the adjacent holes 131 to create a hardness-position graph as shown in FIG. In the hardness-position graph, the width of the region below 0.8 × H2 is the length L1 of the soft portion 14.

As shown in FIG. 6, the width W1 of the soft portion 14 is the width of the soft portion 14 measured in the direction perpendicular to the line connecting the centers of the adjacent holes 131. When the soft portion is bent as shown in FIG. 9B, the width W1 of the soft portion 14 is a value measured along the bent portion of the soft portion 14.

The hardness H1 of the soft portion 14 is the smallest value in the soft portion 14 among a plurality of hardness values obtained by measuring the hardness of the plate member 11 along a line connecting the centers of adjacent holes 131. It is the average value of the third smallest value. Taking FIG. 5 as an example, the average value of hardness at the three measurement points surrounded by the dotted line is H1.

The hardness H2 of the plate member 11 is the hardness of a region other than the joint portion 13, the soft portion 14, and the second soft portion 15 described later, among the plate members 11 provided with the soft portion 14. The average value of the hardness measured at at least three points in this region is regarded as the hardness H2 of the plate member 11.

The diameter K of the hole 131 is the diameter of the hole 131 when the plate member 11 is viewed in a plan view when the hole 131 is cylindrical. When the hole 131 has a non-cylindrical shape such as a cone, the diameter of a cylinder having the same volume and depth as the actual volume of the hole 131 and the actual depth of the hole 131 is regarded as the diameter K of the hole 131. .. When the diameters of the holes 131 on both sides of the soft portion 14 are different, the larger diameter of the holes 131 on both sides of the soft portion 14 is regarded as the diameter K of the hole 131. For example, as shown in FIG. 6, in evaluating whether or not the soft portion 14 between the hole having a diameter K and the hole 131 having a diameter K'smaller than K satisfies the equation 2, the equation is used. Substitutes the value of K. When the shape of the hole 131 in a plan view is not a circle, the diameter corresponding to the circle is regarded as the diameter K of the hole 131. In the case of a female screw hole, the diameter with the wider uneven pitch is regarded as K.

As is clear from the above definition, the evaluation of whether or not each of the plurality of soft portions 14 that can be provided in the lap joint structure 1 satisfies the equations 1 and 2 is made by the soft portion 14 and the holes 131 on both sides thereof. It is based on relationships. When the soft portion 14 and the hole 131 are provided in different plate members 11, the soft portion 14 and the hole 131 when the plate member 11 is viewed in a plan view with the plurality of plate members 11 joined. The above values may be specified based on the positional relationship. It is recommended to measure the hardness with a Vickers hardness tester. The measured load at the time of measuring the Vickers hardness may be appropriately selected according to the material of the plate member 11. In Equation 2, the value obtained by multiplying the Vickers hardness by a coefficient is compared. Therefore, if H1 and H2 are measured with the same measured load, the soft portion 14 is expressed by the equation without being affected by the measured load. It is possible to evaluate whether or not 2 is satisfied. This also applies to Equation 4 described later.

Since the soft portion 14 satisfying the formula 1 is sufficiently long with respect to the diameter K of the hole 131, when stress is applied to the lap joint structure 1, the amount of elongation of the lap joint structure 1 until fracture is increased. be able to. In order to obtain this effect, the length L1 of the soft portion 14 is preferably longer. For example, the length L1 of the soft portion 14 is twice or more (that is, L1 ≧ 2 × K), three times or more (that is, L1 ≧ 3 × K), or four times or more (that is, L1 ≧ 4) the diameter K of the hole 131. It may be specified as × K). However, if the length L1 of the soft portion 14 is too large, the shortest distance D between the end of the hole 131 and the end of the soft portion 14, which will be described later, will be narrowed. The length L1 of the soft portion 14 may be determined in consideration of the shortest distance D between the end of the hole 131 and the end of the soft portion 14, the distance between the holes 131, and the like.

The right side “H2 × K” of the equation 2 indicates the effect of the strength decrease of the plate member 11 due to the hole 131, and the left side “(H2-H1) × W” of the equation 2 indicates the effect of the strength decrease due to the soft portion 14. .. When tensile stress (tensile stress along the line connecting the centers of adjacent holes 131) is applied to the lap joint structure 1 provided with the soft portion 14 satisfying the formula 2, the soft portion 14 is more than the periphery of the hole 131. Priority is given to deformation. Therefore, the soft portion 14 satisfying the equation 2 has an effect of alleviating strain concentration.

The distance between the soft portion 14 and the hole 131 is not particularly limited, but a larger distance is preferable. For example, it is preferable that the shortest distance D between the end of the hole 131 and the end of the soft portion 14 and the diameter K of the hole 131 satisfy the following formula 3.
D ≧ K (Equation 3)
As shown in FIG. 6, the shortest distance D between the end of the hole 131 and the end of the soft portion 14 is the intersection of the line connecting the centers of the adjacent holes 131 and the edge of the soft portion 14, and The distance between this line and the intersection of the edges of the holes 131. The size of the holes 131 on both sides of the soft portion 14 may differ on the left and right, and the distance between the hole 131 and the soft portion 14 may also differ on the left and right, but whether or not Equation 3 is satisfied. The determination may be made for each hole 131. For example, in the example of FIG. 6, whether or not the right side of the soft portion 14 satisfies the formula 3 is determined based on D and K, and whether or not the left side of the soft portion 14 satisfies the formula 3 is determined based on D'and K'. It should be judged based on.

According to the lap joint structure 1 satisfying the formula 3, the fracture strain (the amount of strain of the lap joint structure 1 until the lap joint structure 1 is broken) can be further improved. This is because when the lap joint structure 1 in which the distance between the soft portion 14 and the hole 131 is secured so as to satisfy the equation 3 is deformed, the growth of cracks from the hole 131 toward the soft portion 14 is effectively prevented. Because it is done. In order to obtain this effect, the longer the distance between the soft portion 14 and the hole 131, the more preferable. For example, the shortest distance D between the end of the hole 131 and the end of the soft portion 14 is twice or more the diameter K of the hole 131 (that is, D ≧ 2 × K) and three times or more the diameter K of the hole 131 (that is, that is). D ≧ 3 × K), or 4 times or more the diameter K of the hole 131 (that is, D ≧ 4 × K). However, if the shortest distance D between the end of the hole 131 and the end of the soft portion 14 is too large, the length L1 of the soft portion 14 described above becomes short. It is preferable to determine the shortest distance D between the end of the hole 131 and the end of the soft portion 14 while considering the length L1 of the soft portion 14 and the distance between the holes 131.

As shown in FIG. 7, the plate member 11 of the lap joint structure 1 may have a second soft portion 15 that surrounds the joint portion 13 (not shown in FIG. 7) and is separated from the soft portion 14. Here, the hardness H1 of the soft portion 14, the hardness H2 of the plate member 11 having the soft portion, the hardness H3 of the second soft portion 15, the width W1 of the soft portion 14, the width W3 of the second soft portion 15, and so on. The diameter K of the hole 131 may satisfy the following equation 4.
(H2-H1) × W1> H2 × K + (W3-K) × (H2-H3) (Equation 4)

The second soft portion 15 is a region having a hardness of 80% or less of the hardness H2 of the plate member 11 provided with the second soft portion 15. The width W3 of the second soft portion 15 is the distance of the width of the second soft portion 15 measured along the direction perpendicular to the direction in which the joints are lined up.
The hardness H3 of the second soft portion 15 is the hardness H3 of the second soft portion 15 among a plurality of hardness values obtained by measuring the hardness of the plate member 11 along a line connecting the centers of adjacent holes 131. It is the average value of the smallest value to the third smallest value. When the holes 131 are not arranged in a straight line, the hardness H3 of the second soft portion 15 is a plurality of hardness values of the plate member 11 measured along the line BAC shown in FIG. Of these, it is the average value of the smallest value to the third smallest value in the second soft portion 15. Note that A in FIG. 8 is the center of the hole 131 surrounded by the second soft portion 15 for which the hardness H3 is to be specified. FIG. 8B is an intersection of the line connecting the center of the hole 131 adjacent to the second soft portion 15 for which the hardness H3 is to be specified to the above-mentioned A and the edge of the second soft portion 15. B in FIG. 8 is an intersection of a line connecting the center of one of the holes 131 on both sides of the second soft portion 15 for which hardness H3 is to be specified to the above-mentioned A and the edge of the second soft portion 15. is there. C in FIG. 8 is an intersection of the line connecting the other center of the holes 131 on both sides of the second soft portion 15 for which the hardness H3 is to be specified to the above-mentioned A and the edge of the second soft portion 15. is there.

The second soft portion 15 has an effect of facilitating the formation of the joint portion 13 when the second soft portion 15 is provided on the plate member before joining the plurality of plate members 11. For example, when the hot stamp material having a tensile strength of more than 1500 MPa is the plate member 11, the plate member 11 may be too hard to drive the mechanical joining means 132 such as a self-piercing rivet. By providing the second soft portion 15 on the plate member 11 in advance, it is possible to facilitate the joining of the plurality of plate members 11.

Here, in order to effectively prevent the growth of cracks from the hole 131 toward the soft portion 14, the soft portion 14 and the second soft portion 15 are separated from each other. Further, the second soft portion 15 preferably has a shape and hardness satisfying the formula 4. The left side “(H2-H1) × W1” of the formula 4 shows the influence of the strength reduction due to the soft portion 14 as in the left side of the formula 2. The right side “H2 × K + (W3-K) × (H2-H3)” of the formula 4 indicates the effect of the strength reduction of the plate member 11 due to the hole 131 and the second soft portion 15. When tensile stress (tensile stress along the line connecting the centers of adjacent holes 131) is applied to the lap joint structure 1 provided with the soft portion 14 and the second soft portion 15 satisfying the formula 4, the periphery of the hole 131. (That is, the soft portion 14 is preferentially deformed over the second soft portion 15). Therefore, the soft portion 14 satisfying the equation 4 exerts a higher strain concentration relaxation effect on the hole 131.

The method for producing the lap joint structure 1 according to the present embodiment, particularly the method for forming the soft portion 14 (and the second soft portion 15 if necessary) is not particularly limited. The step of forming the soft portion 14 and the second soft portion 15 may be performed before or after the step of joining the plate members 11. When the step of forming the second soft portion 15 is performed before the step of joining the plate members 11, it is preferable because the joining portion 13 can be easily formed.

The means for forming the soft portion 14 (and the second soft portion 15 if necessary) can be appropriately selected according to the material of the plate member 11. For example, when the plate member 11 is a high-strength steel plate containing martensite, bainite, etc., the local hardness is determined by tempering by laser irradiation or high-frequency heating (local heating and slow cooling of the plate member 11). The drop can easily occur. Preferably, tempering with a laser beam is desirable. This is because the energy of the laser beam is stable. For example, as the laser beam, any one of a disk laser, a fiber laser, a direct diode laser, a YAG laser, a carbon dioxide gas laser, etc. is used, the beam diameter is in the range of 5 to 25 mm, the output is in the range of 1 to 10 kW, and the soft portion. 14 may be formed. More preferably, it is desirable to apply an optical system capable of rectangular condensing and having a rectangular energy distribution.

Further, when the plate member 11 is formed by hot stamping, the soft portion 14 and the second soft portion 15 can be formed by using a mold for hot stamping. In a normal hot stamp, the steel sheet is first heated to point A3 or higher, and then the steel sheet is heated using a water-cooled die (a die having a flow path for flowing a refrigerant such as water and having a function of cooling the work material). Martensite is produced by molding and then quenching the steel sheet using a water-cooled die. Here, the parts to be rapidly cooled by the water cooling mold are limited to the parts other than the soft part 14 and the second soft part 15, and the parts where the soft part 14 and the second soft part 15 are provided are slowly cooled. The type can be constructed. Further, when heating the steel sheet, the maximum heating temperature may be set to A3 or lower at the locations where the soft portion 14 and the second soft portion 15 are provided, and the maximum heating temperature may be set to A3 or higher at other locations. A soft portion 14 and a second soft portion 15 can be formed.

A specific example of the lap joint structure 1 according to the present embodiment described above will be described below with reference to FIGS. 9A to 9D. 9A to 9D show various lap joint structures 1 in which the plate member 11 has a bent portion and a flange portion 12, and the plate members 11 are overlapped with each other at the flange portion 12 and are joined by the joint portion 13. In any of the examples, the soft portion 14 is provided between the joint portions 13, but the shape of the soft portion 14 can be various.

FIG. 9A is an example in which the soft portion 14 has a rectangular shape along the end portion of the flange portion 12 and is provided only inside the flange portion 12.

FIG. 9B is an example in which the soft portion 14 has a rectangular shape along the end portion of the flange portion 12 and extends beyond the bent portion of the plate member 11. Specifically, in the lap joint structure 1 illustrated in FIG. 9B, the soft portion 14 extends not only inside the flange portion 12 but also beyond the bent portion to the outside of the flange portion 12. In this case, the width W1 of the soft portion 14 is measured along the bending of the plate member 11. Further, in the lap joint structure 1 illustrated in FIG. 9B, the soft portion 14 extends to the end portion of the flange portion 12.

FIG. 9C shows an example in which the soft portion 14 has a shape that extends from the bent portion toward the end portion of the flange portion 12. In this case, the length L1 of the soft portion 14 is defined as the distance between the line connecting the centers of the adjacent holes 131 and the two intersections of the outer edge of the soft portion 14.

FIG. 9D is an example in which the soft portion 14 has a rectangular shape with rounded corners (two parallel lines of equal length and a shape consisting of two semicircles provided at both ends of these parallel lines). In this case, as described above, the length L1 of the soft portion 14 is defined as the distance between the two intersections of the line connecting the centers of the adjacent holes 131 and the outer edge of the soft portion 14, and the width of the soft portion 14. W1 is defined as the width of the soft portion 14 measured in a direction perpendicular to the line connecting the centers of adjacent holes 131.

In the lap joint structure 1 according to the present embodiment, it is not necessary to provide the soft portion 14 between all the holes 131. This is because in the lap joint structure 1, the susceptibility to deformation is not always uniform. For example, the soft portion 14 may be provided only in a place where deformation is particularly likely to occur and strain concentration in the hole 131 is feared, and the soft portion 14 may not be provided in other places. That is, the lap joint structure 1 in which the soft portion 14 is provided only between a part of the holes 131 also corresponds to the lap joint structure 1 according to the present embodiment.

The use of the lap joint structure 1 according to the present embodiment is not particularly limited. One of the preferred uses of the lap-bonded structure 1 is an automobile part composed of a plurality of joined steel plates, particularly an automobile skeleton part. Since the automobile skeleton part is composed of a high-strength steel plate containing martensite, the lap joint structure 1 according to the present embodiment can be easily applied, and in this case, it is remarkable that the collision safety of the automobile is enhanced. The effect is obtained. On the other hand, it is possible to apply the lap joining structure 1 according to the present embodiment to any plate member 11 joined by the mechanical joining means 132 and / or the friction stir welding point joining means. For example, even for bridge members joined by rivets or high-strength bolts, aluminum railroad vehicle structures joined by friction stir welding, etc., breakage can be suppressed by applying the lap joint structure 1 according to the present embodiment. Is considered possible. It is also conceivable to apply the lap joint structure 1 according to the present embodiment to home appliances such as fittings, beams, link members, simple warehouses, furniture, refrigerators, televisions, copiers, cooler outdoor units, and fixtures for construction.

Next, an automobile frame component according to another aspect of the present invention will be described. The automobile skeleton part according to the present embodiment is an automobile skeleton part having the lap joint structure 1 according to the present embodiment. The automobile frame parts are, for example, A pillars, B pillars, side sills, bumpers, floor members, front side members, rear side members or roof rails. Hereinafter, an example of the automobile frame parts according to the present embodiment will be described.

FIG. 10 is a perspective view of the B-pillar 2, which is an example of the automobile frame component according to the present embodiment. In this figure, the side panel outer is omitted. The B-pillar 2 of FIG. 10 has a mechanical joint 13 (not shown) having a hole 131 and a soft portion 14 provided between adjacent mechanical joints 13 (that is, between the holes 131). .. However, no soft portion is provided between some of the mechanical joints 13 (the region surrounded by the dotted line in FIG. 10). This is because the occurrence of distortion at the time of a side collision of the vehicle body differs depending on the part of the B pillar, and it is not always necessary to provide a soft part at the part where the amount of distortion is small, where breakage from the hole is unlikely to occur at the time of collision. For some reason.

FIG. 11 is a cross-sectional view taken along the line XI-XI of the B pillar 2 of FIG. The B-pillar 2 is composed of a B-pillar inner 22 which is a normal steel plate, a B-pillar reinforcement 21 which is a high-strength steel plate, and a side panel outer 23 which is aluminum or mild steel. These correspond to the plate member 11, and in particular, the B-pillar reinforcement 21 corresponds to the main plate member. The B-pillar reinforcement 21, the B-pillar inner 22, and the side panel outer 23 are joined at both ends thereof, and the B-pillar reinforcement 21 corresponding to the main plate member is provided with a soft portion 14.

FIG. 12 is a perspective view of the A pillar 3 and the roof rail 4 which are examples of the automobile frame parts according to the present embodiment. Even in the parts shown in FIG. 12, the soft portion 14 is provided only between some holes.

FIG. 13 is a sectional view taken along line XIII-XIII of the roof rail 4 shown in FIG. This automobile frame component is composed of a roof rail inner 42 which is a high-strength steel plate, a roof rail outer reinforcement 41 which is a high-strength steel plate, and a side panel outer 43 which is aluminum or mild steel. These correspond to the plate member 11, and in particular, the roof rail outer ring force 41 corresponds to the main plate member. The roof rail inner 42, the roof rail outer line force 41, and the side panel outer 43 are joined at both ends thereof, and the roof rail outer line force 41 corresponding to the main plate member is provided with a soft portion 14.

FIG. 14 is a perspective view of a hinge reinforcement 5 of a B-pillar, which is an example of an automobile frame component according to the present embodiment. In this automobile frame component, the hat-shaped member 52 and the high-strength steel plate 51 arranged along the inside of the hat-shaped member are joined by a joint portion 13 which is a mechanical joining means, and the joint portion of the high-strength steel plate is joined. A soft portion 14 is provided between 13 (that is, between holes 131). The configuration shown in FIG. 14 can also be used for the floor members.

In the description of the lap joint structure 1 according to the present embodiment, a lap joint structure in which a joint portion is formed in a lap portion obtained by superimposing two or three plate members 11 is exemplified, but four or more plate members 11 May be overlapped. Further, in the description of the lap joint structure 1 according to the present embodiment, a case where a soft portion is formed on one plate member 11 or two plate members 11 out of two or three plate members 11 will be described. However, for example, a joint portion may be formed in a superposed portion in which four or more (plural) plate members 11 are superposed to form a superposed joint structure. In such a case, a plate member in which a soft portion is formed is formed. The number of 11 sheets can be set arbitrarily. Further, it is not necessary to use the overlapped portion formed by superimposing the plate members 11 as the flange portion. Needless to say, the lap joining structure according to the present embodiment also includes a lap joining structure in which plate members 11 having no flange are overlapped and joined for the purpose of partial reinforcement or the like.

Sample No. 15 in which the plate member A and the plate member B having no soft portion are joined as shown in FIG. 1 and No. Sample No. 8 and the plate member A having a soft portion and the plate member B not having a soft portion, which are shown in FIG. 2-No. 7 and No. 9 to No. 11 was created. Here, (A) of FIGS. 15 and 16 is a plan view of the sample (rivet-bonded), and FIG. 15 and 16 (B) are side views of the sample (rivet-bonded). In addition, in FIGS. 15 and 16, the plate member A is a plate having a length of 200 mm (score interval 50 mm) having a parallel portion having a width of 20 mm and holding portions (shoulders) having a width of 35 mm provided at both ends of the parallel portion. Is. In FIGS. 15 and 16, the plate member B is a plate having a width of 20 mm and a length of 60 mm, which is overlapped with parallel portions of the plate member A. The type, plate thickness, and hardness of the plate member A were the same for all the samples, and the contents were as shown in Table 1. The type, plate thickness, and hardness of the plate member B were two types, B1 and B2 shown in Table 1. The metal structure of the plate member A was almost all martensite.

The joining means of the plate member A and the plate member B was any one of rivets, SRP (self-piercing rivets), and friction stir welding. Among the samples in which the joining means was SRP, No. In No. 6, a second soft portion was formed in the SRP portion of the plate member A. The width W3 of the second soft portion was 10 mm, and the hardness H3 of the second soft portion was HV270. The diameter K of the holes of the plate members A and B and the shape of the soft portion are as shown in Table 2. The soft portion has a rectangular shape along both ends of the parallel portion of the test piece, and the width W1 of the soft portion is the width of the soft portion measured along the direction perpendicular to both ends of the parallel portion. The length L1 of the portion was defined as the length of the soft portion measured along the direction parallel to both ends of the parallel portion.

Then, the sample No. of Table 2 Tensile tests were performed on 1 to 11 and the breaking strain was measured. The measurement results are shown in Table 2.

As shown in Table 2, the sample No. of the lap joint structure composed of a plate member having no soft portion. 1 and No. Compared with No. 8, the sample No. of the lap joint structure including the plate member A having a soft portion. 2-No. 7 and No. 9 to No. In No. 11, the starting point of fracture was not a hole (at the joint) but a soft portion, and the fracture strain had excellent fracture strain.

When each sample after the tensile test was confirmed in detail, the test piece without the soft portion was fractured starting from the hole as shown as the fracture portion Z in FIG. For reference, No. 1 which had a mechanical joint but did not have a soft part. The photograph after the test of No. 1 is shown in FIG. On the other hand, the test piece provided with the soft portion was broken at the soft portion 14 as shown in FIG. 16 as the fractured portion Z.

According to the present invention, when an overlapping portion formed by superimposing a plurality of plate members is joined by a non-melt joining means, it is possible to prevent the plate member from breaking starting from a hole formed at the time of joining. It is possible to provide a lap joint structure of a lap joint member capable of increasing the elongation until breaking. For example, when the present invention is applied to an automobile, the occupant protection performance at the time of a collision can be dramatically improved. Therefore, the present invention has high industrial applicability.

1 Lap joint structure 11 Plate member 12 Flange part 13 Joint part 131 Hole 132 Mechanical joining means 132'Nugget 133 Friction stirring point joining means 14 Soft part 15 Second soft part 2 B pillar 21 B pillar Reinforce 22 B pillar inner 23 Side Panel Outer 3 A Pillar 4 Roof Rail 41 Roof Rail Outer Linforce 42 Roof Rail Inner 43 Side Panel Outer 5 Hinge Reinforce 51 High Strength Steel Plate 52 Hat-shaped Member X Electrode Y Rotating Tool

Claims (10)

With multiple superposed plate members,
A plurality of joints formed by mechanical joining means or friction stir welding point joining means provided in the overlapping portions of the plurality of plate members, and
With
The plurality of joints have holes through which the mechanical joining means are inserted, or holes formed by friction stir welding.
One or more of the plurality of plate members have a soft portion between the plurality of joint portions in the overlapping portion.
A lap joint structure characterized in that the hardness of the soft portion is 80% or less of the hardness of the plate member provided with the soft portion. The length L1 of the soft portion, the width W1 of the soft portion, the hardness H1 of the soft portion, the hardness H2 of the plate member having the soft portion, and the diameter K of the hole are the following equations 1 and. The lap joint structure according to claim 1, wherein the lap joint structure is characterized by satisfying 2.
L1> K (Equation 1)
(H2-H1) × W1> H2 × K (Equation 2) The lap joint structure according to claim 1 or 2, wherein the shortest distance D between the end portion of the hole and the end portion of the soft portion and the diameter K of the hole satisfy the following formula 3.
D ≧ K (Equation 3) The lap joint structure according to any one of claims 1 to 3, wherein the hole penetrates one or more of the plurality of plate members. The lap joint structure according to any one of claims 1 to 4, wherein the soft portion is provided on the plate member having the hole. The lap joint structure according to any one of claims 1 to 5, wherein the soft portion is provided on a main plate member having the largest product of plate thickness and tensile strength. The plate member has a second soft portion that surrounds the joint and is separated from the soft portion.
The hardness H1 of the soft portion, the hardness H2 of the plate member having the soft portion, the hardness H3 of the second soft portion, the width W1 of the soft portion, the width W3 of the second soft portion, and the hole. The lap joint structure according to any one of claims 1 to 6, wherein the diameter K of 1 satisfies the following formula 4.
(H2-H1) × W1> H2 × K + (W3-K) × (H2-H3) (Equation 4) The lap joint according to any one of claims 1 to 7, wherein the plate member having the soft portion has a tensile strength of 980 MPa or more and the metal structure thereof is a steel plate containing martensite. Construction. An automobile skeleton component having the lap joint structure according to any one of claims 1 to 8. The automobile frame component according to claim 9, wherein the A-pillar, the B-pillar, the side sill, the bumper, the floor member, the front side member, the rear side member, or the roof rail.