JPS5847580B2 - Arc cross section steel plate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circular arc section steel plate used for leaf springs etc. that undergo bending deformation, and has higher bending rigidity and fatigue strength per unit weight than conventional flat steel plates for springs. The purpose is to provide a steel plate with an excellent circular arc cross section.

Conventionally, the steel plates for extremely common leaf springs, such as leaf springs used for vehicle axle suspensions, have generally been made of rolled flat steel having an approximately rectangular cross section perpendicular to the length direction, as shown in Figure 1. In some cases, rolled flat steel has been used in which the cross section perpendicular to the length direction has a grooved cross section with grooves formed on the bottom surface as shown in FIG. 2, or a rolled flat steel having a trapezoidal cross section as shown in FIG.

The reason why the steel plates for leaf springs having the cross sections shown in FIGS. 2 and 3 are used is that, compared to the steel sheets for leaf springs having the rectangular cross section shown in FIG. By making the width of the receiving side wider than the width of the side receiving compressive stress, the bending neutral axis of the cross section is moved to the tensile stress side, and the unit weight is reduced by reducing the tensile stress (increasing the compressive stress) when a bending moment is applied. The aim is to increase the amplitude of the repeated bending moment that can be borne by the joint.

By the way, stacked leaf springs, etc., which are made by stacking several leaf springs with cross sections shown in Figures 2 and 3, which are often used for axle suspension, have an average bending moment as a static load and a bending moment amplitude as a dynamic load. However, the fatigue strength per unit weight is improved by utilizing the property that the cyclic fatigue strength is higher on the average bending compression side due to static load than on the average bending tension side.

However, rolling a steel sheet for leaf springs with the cross-sectional shapes shown in FIGS. 2 and 3 to a predetermined dimensional tolerance is more difficult than rolling a steel sheet for leaf springs with a simple rectangular cross section as shown in FIG. This is extremely difficult and leads to an increase in rolling costs.

In steel plates for leaf springs having the cross-sectional shapes shown in Figures 1 to 3, a common problem is that fatigue failure occurs at corners where stress is concentrated during bending on the surface on the bending tensile stress side. This remains an unresolved issue, and when compared with round bars for springs of the same material, the fatigue strength of flat steel is greater than that of round bars without corners, as shown in Figure 4. It is normal for it to drop by nearly 20%.

That is, Fig. 4 is a diagram in which the vertical axis shows the durability limit and the horizontal axis shows the hardness. (Indicated by white circles in the figure)
It is shown in comparison.

The present invention can follow the forming process from rolled flat steel that is commonly used in the manufacture of leaf springs, and is easier to form than the leaf springs having the cross-sectional shapes shown in Figs. 2 and 3, and is lightweight, low cost, and highly As a result of various studies in an attempt to obtain steel plates for leaf springs with high fatigue strength,
The stress on the bending tension side is lower than the stress on the bending compression side, and this is a steel plate for leaf springs that can solve the problem of stress concentration at the corners, which caused a decrease in fatigue strength in conventional steel sheets for leaf springs. , the cross-sectional shape of the steel plate in a plane perpendicular to the length direction is such that the surface on the bending tension side is bulged in an arc shape and the surface on the bending compression side is concave in an arc shape, so that the neutral axis of the cross-sectional bending is It was detected that the stress on the tensile side when a bending moment is applied is reduced by moving it to the compressive stress side, and furthermore, the width of the arc-shaped steel plate with arc-shaped surfaces on both sides is b, and the center line in the thickness direction is The radius is r.

By setting 2.0≧r c / b≧0.64, it is possible to obtain a circular cross-section steel plate that has higher bending rigidity than a flat plate and has the best bending rigidity and fatigue strength per unit weight. and the radius r at the time of manufacturing the steel plate.

This has the excellent effect of reducing the variation in bending rigidity due to variations in the weight and achieving weight reduction.

In addition, in the present invention, when the plate thickness in the above cross section is t, by setting 0.2≧t/b≧0.05, it is possible to improve the formability of the arc cross section steel plate and improve the reliability and efficiency of processing. It is designed to effectively utilize the fatigue strength on the average stress compression side.

If t/b exceeds 0.2, the utilization of fatigue strength will be insufficient, and if t/b is 0.05 or less, forming will become difficult due to the limit of hot working.

Roughly speaking, in the present invention, the radius of curvature of the arcuate (bulging side) surface of the steel material is r.

, When the radius of curvature of the side concave in a circular arc is ri, 1.2≧ro/ri≧1.0, when a plurality of circular arc cross-section steel plates of the present invention are stacked and used for a stacked leaf spring, etc. A gap within a predetermined range is formed at the center of the steel plate in the width direction between the protruding surface and the concave surface of adjacent steel members, thereby preventing fillet sautéing and corrosion at the body fastening end, child plate end position, etc. This can prevent the occurrence of fatigue and have an excellent effect on fatigue strength.

This r. When the value of /r s is less than 10, the central part of the bulging surface comes into contact with the recessed surface of the adjacent steel plate that is in contact with the surface, and when the value exceeds 1.2, the gap becomes too large and damping occurs. The effect fades.

Furthermore, in the present invention, the central apex of the bulging side surface of the circular arc cross-section steel plate is truncated in a plane parallel to the line connecting both ends in the width direction to form a flat part, and the amount of truncation relative to the plate thickness t is By setting 0.35≧h/t≧O, where h is 0.35≧h/t≧O, the moment of inertia of area can be lowered with almost the same section modulus as when no truncations are applied, and the bending rigidity can be increased without changing stress, that is, fatigue strength. The chisel can be adjusted to a lower value, and by grinding or cutting the truncated surface, surface scratches and decarburized layers can be removed, which has the practical effect of further improving fatigue strength.

As described above, the arc cross-sectional steel plate of the present invention can have higher bending rigidity per unit weight than the conventional flat steel plate for springs, and has a flat cross-sectional shape as shown in conventional figures 2 and 3. Stress on the bending and tensile side (average stress, stress amplitude) as with steel plates
By lowering the stress on the bending compression side, the allowance for fatigue strength on the static bending compression side can be effectively utilized.Furthermore, unlike conventional flat steel plates, the risk of fatigue failure is lower than the stress on the tensile stress side due to the average bending load. Because the top of the surface bulges out in an arc shape, there is no notch effect seen in the tensile side corners of conventional flat steel plates during bending loads, and the tolerance for fatigue is as high as can be expected from the material. It is designed to absorb stress.

FIG. 5 is a diagram showing a cross section of the steel plate according to the first embodiment of the present invention along a plane perpendicular to the length direction, and the radius of the upper surface 1 and the lower surface 2 of the arc-section steel sheet is the difference of the plate thickness t. It is formed into concentric circles with .

FIG. 6 is a cross-sectional view of a steel plate according to a second embodiment of the present invention taken along a plane perpendicular to the length direction, and the upper surface 3 and lower surface 4 of the arc-shaped cross-section steel plate form six circular arcs with equal radii. It is something.

FIG. 7 is a cross-sectional view of a steel plate according to a third embodiment of the present invention taken along a plane perpendicular to the length direction, and the upper surface 5 and lower surface 6 of the arc-shaped steel plate are defined within the same cross section. Thickness {It is formed by an arbitrary arcuate line so that there is no significant difference.

The radius r of the center line in the thickness direction of the arc cross-section steel plate in Embodiment 6.

can be calculated as the radius of the top surface 1 minus half the plate thickness t.

It can also be calculated in the case of the second embodiment, but generally the third
As shown in the example, the plate thickness t at the center of the steel plate
center point P, center point Q of plate thickness t' at both ends of the steel plate,
A circle passing through the three points H may be drawn and its radius may be set as the radius of the center line in the thickness direction.

The reason for setting the upper limit of the r c / b ratio to 2.0 is that if the ratio is 2.0 or less, it is superior to conventional rolled flat steel plate springs in terms of spring constant and weight ratio. 2.
This is because if it is more than 0, the effect will be almost the same as that of the conventional plate spring, and r.

The lower limit of the /b ratio was set at 0.64 because when forming rolled flat steel into an arc shape, if the ratio is less than 0.64, the change in the moment of inertia of area due to dimensional errors in the radius of curvature during forming will be large. This is because the probability of obtaining a leaf spring with the desired effect decreases.

Fig. 8 shows a steel plate according to the second embodiment, the plate width b is 69.5 mm, the plate thickness t at the center in the width direction is 6.48 mm,
A steel plate 7 of 1 meter in diameter and 91 mm in diameter on the upper and lower surfaces 3 and 4 is prepared, and one end is fixed to a support base 8 so that bending tensile stress is applied to the upper surface to form a cantilever beam with a length of 600 mm. , shows a cantilever bending test with a static load applied to the tip.

In the figure, points A to E are the points where the amount of deflection was measured in the cantilever bending test, and point A is 600 mm, point B is 580 mm, and point C is 600 mm from the bearing end.
The point is 475 mm, and the point D is 350 mm E.
The points are 60 mm apart.

The above test results are as shown in Table 1, and are in good agreement with the calculated value of the deflection amount (represented by line F) separately obtained using beam theory and shown in FIG.

In addition, in the above test, strain gauges were glued to the surface of the arc-section steel plate along one cross-section in a plane perpendicular to the length direction as shown in Figure 10, and the stress at these positions was measured. In Fig. 11, the distance from the neutral axis of bending is plotted at point G, and this measured value also agrees well with the calculated value of the stress distribution obtained from beam theory 6 (this is shown by line H). There is.

From these results, it has become clear that the steel plate of the present invention can be handled as an elastic beam in the same way as the conventional steel plate having the cross-sectional shapes shown in FIGS. 1 to 3.

Next, the usefulness of the arc-shaped steel plate of the present invention as a spring material will be discussed.

Fig. 12 is a diagram showing the change in the moment of inertia of the cross section when the radius of curvature of the cross section of the steel plate of the present invention is formed into an arc-shaped cross section with a thickness of 7 mm and a width of 70 mm. Figure 13 is a diagram showing the change in the ratio of the maximum compressive stress to the maximum tensile stress when the radius of curvature of the cross section of the same inventive arc cross section steel plate is changed, and point J is a flat steel plate with a cross section of the same size. For comparison, point J' represents the value of a flat steel plate shown in FIG. 2, which has grooves formed on the compressive stress acting surface and has approximately the same cross-sectional area as these steel plates.

According to Fig. 12, the moment of inertia of area is higher than about 2000 for the flat cross-section steel plate and about 2400 for the grooved cross-section steel plate, indicating a high spring constant. The ratio of the maximum compressive stress to the maximum tensile stress (σ
.

/σ1) can be set higher than 10 for a flat cross-section steel plate, as well as about 1.22 for a grooved cross-section steel plate, and this is the maximum stress σ on the bending compression side.

is higher than the maximum stress σ1 on the tensile side, so as shown in Table 5 below, the margin of fatigue strength on the bending compression side during bending load compared to the tensile side must be fully utilized. I can do it.

Furthermore, since the position of the maximum tensile stress due to bending is at the top of the surface that bulges out in an arc shape, there is no reduction in fatigue strength due to the notch effect of the tension side corner seen in the grooved cross section of the flat plate.

Therefore, the arc cross-section steel plate of the present invention has a higher spring constant than a flat cross-section steel plate or a grooved cross-section steel plate with the same width and same cross-sectional area, but σ.

/σ1 value and fatigue strength are high, so when replacing the conventionally used stacked plate springs of flat cross-section steel plates, use circular arc cross-section steel plates with the same width and cross-sectional area to form a stacked plate spring. You can reduce the number of leaves.

Also, in Figure 12 I, the moment of inertia of area with a radius of curvature of 120 mm is approximately 3200 (mm
4), and since the plate thickness of a flat cross-sectional steel plate with a width of 70 mm and a cross-sectional moment of inertia that is approximately the same as this is approximately 10 mm, the steel plate of the present invention is applied to a flat cross-sectional steel plate with approximately the same spring constant. When replacing, the plate thickness can be reduced by approximately 30%, and as can be seen from Fig. 13, the stress ratio is approximately 30% higher than that of a flat cross-section steel plate with the same dimensions. With almost the same spring characteristics, the spring weight per load can be significantly reduced compared to flat cross-section steel plates and grooved cross-section steel plates.

Next, a leaf spring of the present invention and a flat steel leaf spring were manufactured under the same conditions, and fatigue tests were conducted under the same tensile stress conditions to determine and compare the average lives of the two.

The dimensions and number of leaf springs used in the test are shown in Table 2, and all conform to Japanese Industrial Standards SU. P6 material was molded to the required dimensions, and the average tensile stress was measured using a Spring Association type fatigue testing machine with an average stress of 65k9/i and a stress amplitude of 55kg/r.
A partial vibration fatigue test was conducted under the stress conditions of ILIj.

The steel plates used in the test were quenched and tempered under the same conditions, then subjected to surface shot peening treatment, and the hardness after heat treatment was BHD 3.05.

Further, the steel plate of the present invention used in the test had a shape in which the upper and lower surfaces in the cross section shown in the first example had a circular shape.

The results of this fatigue test are as shown in Figure 14, and by comparing the number of repetitions, it was found that the arc-section steel plate in which the present invention was applied had a service life four times longer than that of the conventional flat-section steel plate. .

In addition, in this fatigue test, the steel plate on which the present invention was applied was
Of course, the arcuate bulging surface was positioned on the tensile stress side and displacement was applied repeatedly.

Further, in FIG. 14, a line connecting symbols with black dots inside white circles indicates the probability of failure for all the products according to the present invention.

The 50% fracture probability in this test is shown on the repeated bending S-N diagram (Figure 15) of the round bar decarburized material and the flat decarburized material, which were evaluated using a known method considering the hardness of the decarburized layer on the sample surface. When calculating the number of repeated fractures in , the average of all the products of the present invention is located on the line of the round bar decarburized material represented by the solid line, as shown by the white circle, and that of the flat cross-section steel plate (represented by the black circle) is on the line of the flat decarburized material. It can be seen that it lies well on the line of charcoal material.

From the above results, the arc cross-section steel plate of the present invention has a tensile stress side surface bulged in an arc shape and the position of maximum tensile stress is moved to near the top of the arc-shaped bulge. By eliminating the notch effect of the edge part on the surface on the tensile stress side, which is the starting point of fatigue cracks, fatigue strength comparable to that of nine bars can be obtained, and after heat treatment of hot rolled steel for springs. When performing peening on the surface on the average stress tensile side in order to strengthen the black skin decarburized layer, it is difficult to perform shot peening on the edge part in the case of a flat cross-section steel sheet, whereas in the case of the arc cross-section steel sheet of the present invention. Since the risk area for fatigue failure is the top of the circular arc-shaped bulging surface with a dog radius of curvature, the shot hits the risk area at an angle close to right angle during shot peening processing, and the advantage is that a sufficient peening effect can be obtained. It turns out that there is.

It is clear from the above that the arc cross-section steel plate of the present invention has better bending rigidity and fatigue strength than conventional rolled flat steel plate springs, but it is necessary to improve the bending rigidity and fatigue strength per unit weight. It is necessary to appropriately determine the cross-sectional shape of the steel plate and consider the spring characteristics per unit weight.

In particular, the arc cross-section steel plate of the present invention has a cross-sectional shape that can be formed from a rolled flat steel plate, but if the plate thickness is thicker than the plate width, dimensional errors in the radius of curvature of the arc-shaped surfaces on both the front and back surfaces of the leaf spring occur during manufacturing. It is clear that this causes a large change in the moment of inertia of area.

Therefore, by taking the plate thickness (t/b), which is expressed dimensionlessly by dividing it by the plate width, as a parameter, the second moment of inertia (I/b), which is expressed dimensionlessly, of the steel plates of the first and second embodiments of the present invention is
') and the radius (ro) of the arc passing through the center of the plate thickness (
If you draw a line diagram between the radius of curvature (ro/b) and the dimensionless representation of dividing by t/b)
It can be seen that when ro/b is small, a range of about ro/b≧0.64 is desirable.

Note that in FIG. 16, the broken line is for the steel plate of the first embodiment, and the solid line is for the steel plate of the second embodiment.

Therefore, the width 70, which is actually used for truck axle suspensions, is
mm, plate thickness 8 mm rolled flat steel plate spring (spring constant 10 kg/mm, stress normal use 42 kg/IILI7I)
In order to compare with the above, the spring constant and stress of the leaf spring made of the circular arc cross section steel plate according to the present invention with the specifications shown in Table 3 are estimated, and the weight ratio with the rolled flat steel plate spring is shown in the figure.
As shown in the figure and FIG. 18.

That is, under the condition that the tensile side stress is almost the same as that of a conventional flat spring, the arc cross section steel plate according to the present invention has a higher spring constant than a flat flat spring, a weight smaller than a conventional flat spring, and a plate thickness (t).
/b) and the radius of curvature r6/b approaches a flat spring as it becomes more dog-like.

From FIG. 17 and FIG. 18, when the radius of curvature (rC/b) becomes 2.0, the spring constant and weight ratio become almost the same as that of the known rolled flat steel plate spring. ※※( rC/b
) must have an upper limit of 2.0, and ro/b is 2.0.
If it exceeds 0, no weight reduction effect is required compared to conventional leaf springs.

Figures 19 to 21 show three types of surface properties that undergo repeated bending with average bending (see Table 4). A durability limit diagram evaluated by a known method based on the following is shown.

Figure 19 shows the nine-bar smooth bar material, Figure 20 shows the black-skinned decarburized nine-bar material, and Fig. 21 shows the shot-peened black-skinned decarburized round bar material.
This is what I tried to show.

In these figures, the range surrounded by the fatigue durability limit line and the bending deformation limit line is the stress range that can be put to practical use.

As shown in the figure, the average stress compression side has more fatigue strength than the tension side.

Suspension springs and the like are generally used in a partial vibration state.

Therefore, on the durability limit diagram, the ratio of stress amplitude σ3 to average stress σ (stress ratio) σa/σ - ±1, ±0.5, and the ratio of stress amplitude σ3 to average stress σ are
(The positive line corresponds to the tensile stress due to average bending, and the negative line corresponds to the compressive stress side.) A line indicating the stress situation was drawn.

Between these lines and two types of damage limit lines (endurance limit line, bending deformation limit line), the stress of the lower stress level as the failure limit was read as a stress amplitude value and is shown in Table 5.

Based on these stress values, the failure stress σ of the surface on the tensile stress side is
Ratio of failure stress σ′0 on the compressive stress side surface to ′1 σ′
o/σ't is calculated and recorded in Table 5. Then, for the circular arc cross-section steel plate of the present invention, the radius of curvature (rC/b) and stress ratio (σ
C/σ1) as shown in FIG. 22 for the steel plate of the first example and as shown in FIG. 23 for the steel plate of the second example.

Line KL in Figure 22 and line PQ in Figure 23
is the limit line determined from the relationship between the change in the second moment of area due to the radius of curvature, and the line LM in FIG. 22 and the line QR in FIG. 23 are the desirable σ determined from the durability limit diagram.

The limit line showing /σ1 is the line MN in FIG. 22 and the line MN in FIG.
The line RS in the figure is the limit line determined from the calculation results of the degree of weight reduction, and the line KN in Figure 22 and the line PS in Figure 23 are the limits of the plate thickness ratio (t/b) determined from the rolling limit of the leaf spring. A preferred embodiment of the present invention is shown at the point KLM, respectively.
It is within the range surrounded by N and point PQRS.

That is, the plate thickness t is 0.05b to 0.2b. Note that the limit of the plate thickness ratio determined from the rolling limit of the plate spring (t/b=
0.0 5) means that the rolling limit of a rolled flat steel plate with a width of 70 mm, which is currently not in practical use, is said to be up to 3.5 mm.
) was set as 3.5/70-0.05.

FIG. 24 6 shows a cross section of a steel plate with an arcuate cross section according to another embodiment of the present invention along a plane perpendicular to the longitudinal direction. The top of the tensile stress side surface 11 of the steel plate, which was formed into an arc concentric with the arc of the bulged surface 11, was removed and truncated in a plane parallel to a line connecting both ends in the width direction to form a flat portion 13. It is something.

FIG. 25 shows the plate width b-70, plate thickness t=35 mm, and the radius r of the arc passing through the center of the plate thickness.

= An example of a leaf spring of 90 mm in which the center C of the tensile stress side surface 11 is truncated by hmm in the radial direction. Figure 26 shows a circular arc passing through the center of the plate thickness, where the plate width is b - 70 mm and the plate thickness t is 7 mm. radius r.

In the example of a plate spring having a diameter of 90 cm and having a radial h77Xm truncated at the center of the tensile stress side surface 11, the truncated depth h is taken on the horizontal axis, and the truncated depth O, that is, both sides 11 is taken on the vertical axis.
．． 12 is the measured value of the original plate spring with concentric circular arcs as 1, and the stress ratio σ.

FIG. 2 is a diagram showing the ratio of /σ1, section modulus Z, and second moment of area ■.

From FIGS. 25 and 26, it is possible to reduce the moment of inertia of the plate of this example to 80% compared to the one without truncations without changing the section modulus Z much. I understand that.

In the above explanation, the arc cross-section steel plate of the present invention can be treated as an elastic beam, and by effectively utilizing the margin of fatigue strength on the average bending compression side with respect to the tension side, the position of maximum tensile stress can be roughly adjusted to the arc-shaped expansion. By moving the steel plate near the top of the protruding part, it is possible to obtain fatigue strength comparable to that of nine-bar steel, and explain that it is an excellent steel plate for use in leaf springs, etc. due to its excellent spring properties per unit weight. did.

In the present invention, when the load per unit area of the flat cross-section steel plate normally used for leaf springs is small, the surface bulges in an arc shape and the arc shape It is possible to bundle several arc-section steel plates by overlapping the concave surfaces and use this as a single elastic beam.

In this case, by making the radius of curvature of the bulging surface smaller than the radius of curvature of the concave surface, or by using a truncated circular arc section steel plate as shown in Fig. 24, it is possible to It is possible to make them contact each other only at the ends and bundle them without contact at the center in the width direction.

In this way, filleting and corrosion can be prevented from occurring on the overlapping surfaces of the arc-section steel plates that are in adjacent contact with each other at the end positions of the body clamping terminal plates and the like.

As explained above, the present invention can have higher bending rigidity per unit weight than conventional rolled flat steel plate springs,
As with conventional leaf springs with grooved or trapezoidal cross sections, by lowering the stress on the bending tension side (average stress, stress amplitude) than the stress on the compression side, the fatigue strength margin on the static bending compression side is effectively utilized. Moreover, in conventional leaf springs, fatigue damage tends to occur at the corners of the cross section of the leaf spring when subjected to bending loads, whereas in the present invention, the parts at risk of fatigue failure are caused by tensile stress due to the average bending load. Since the cross-sectional shape is at the apex of the side bulging arcuate cross-section, the damage seen at the corners of the plate panel during the above bending load is eliminated, and the fatigue tolerance is as high as expected from the material. It has excellent features such as being able to absorb stress.

In the present invention, the forming process is almost the same as the conventional rolling process for rolled flat steel plate springs, and by adding a single-step forming process using a 6-caliber instead of the final process, the required dimensions, Since it can be rolled into a shape, it can be processed extremely easily.

In addition, when using a plurality of leaf springs according to the present invention 6, if the arcs on the compressive stress side that contact each other are made to have a slightly smaller radius than the arc on the tensile stress side, there is a risk of fatigue failure. The bulging top portion of the surface on the tensile stress side, which is a portion, is prevented from coming into contact with each other, and it is possible to prevent a decrease in fatigue strength due to fresotyping, corrosion, and the like.

The arc-shaped steel plate of the present invention is not only useful as a constituent material for stacked leaf springs, but also useful when fixing and supporting a workpiece 15 on a base 14, as shown in FIG. 27, for example. In this case, the matsuba 16 made of a steel plate with an arcuate cross section according to the present invention is bridged between the workpiece 15 and the support 17, and is tightened to the base 14 with bolts 18 or the like, thereby utilizing its elasticity and damping between the plates. Needless to say, the present invention can also be effectively applied to tools for fixing and fixing belt-shaped objects, or to metal fittings for positioning belt-like objects.

[Brief explanation of the drawing]

Figures 1 to 3 are cross-sectional views of conventionally used spring steel plates, and Figure 4 shows the rotational bending durability limits of various spring steel materials and the bioscillatory plane bending durability limits of flat plate test pieces, depending on the hardness. Figures 5 to 7 are cross-sectional diagrams of the first, second, and third embodiments of the arc cross-section steel materials of the present invention, respectively, and Figure 8 is a cross-sectional view of the cantilever bending test. Diagram showing measurement points,
Fig. 9 is a diagram showing the amount of deflection during cantilever bending of the steel plate of the present invention, Fig. 10 is a diagram showing the gage attachment points on a half cross section of the steel plate of the present invention, and Fig. 11 is a diagram showing the stress on the cross section. Figure 12 is a diagram showing the second moment of area with respect to the radius of curvature of the steel plate of the present invention, Figure 13 is a diagram showing the ratio of maximum compressive stress to maximum tensile stress with respect to the radius of curvature of the steel plate of the present invention, Figure 14 is a diagram showing the distribution. The figure shows the fatigue test results, and Figure 15 shows the S
-N diagram, Figure 16 is a diagram showing the change in the second moment of area with respect to the radius of curvature with plate thickness as a parameter, Figure 17
The figure is a diagram showing changes in spring constant and stress with respect to radius of curvature, Figure 18 is a diagram showing changes in weight ratio with respect to radius of curvature, Figures 19 to 21 are diagrams showing repeated bending durability limits of various steel materials, 22 and 23 are diagrams showing changes in stress ratio to radius of curvature with plate thickness as a parameter in the first and second embodiments of the present invention, and FIG. 24 is a cross section of another embodiment of the present invention. 25 and 26 are diagrams showing the influence of the truncated depth on the moment of inertia, section modulus and stress ratio in the examples, and FIG. 27 is one use of the arc-section steel plate of the present invention. FIG. In the figure, numerals 1, 3, 5, and 11 indicate the tensile stress side surfaces in the cross section of the arc-shaped steel plate of the present invention, 2, 4, 6, and 12 indicate the compressive stress side surfaces, and 13 indicates the truncated flat portion, respectively. be.

Claims (1)

[Claims] 1. In a steel plate that is composed of a spring steel plate whose length is larger than its width and which is substantially perpendicular to the length direction and subjected to bending deformation in the thickness direction, The in-plane cross section has a shape in which the surface on the side that receives tensile stress during bending load bulges out in an arc shape, and the surface on the side that receives compressive stress is concave in an arc shape, and bulges out in the arc shape. The curvature of the side surface and the curvature of the side surface recessed into the arc shape are approximately the same in the longitudinal direction of the steel plate, and the length of the width in the cross section is b, and a line passing through the center of the thickness. The radius of r. A circular arc cross-sectional steel plate characterized in that when it is closed, 2.0≧ro/b≧0.64. 2. The steel plate has a cross-sectional thickness in a plane perpendicular to its length direction, where t is 0.2≧t/b≧0.05, as set forth in claim 1. arc cross section steel plate. 3 In the cross section of the steel plate in a plane perpendicular to its length direction, when the radius of curvature of the surface on the side that bulges out in an arc shape is ro, and the radius of curvature on the surface on the side that is concave in an arc shape is ri, 1 .2≧ro/r i≧1.0 The arc-shaped steel plate according to claim 1 or 2, characterized in that: .2≧ro/ri≧1.0. 4 The steel plate is cut in a plane parallel to a line connecting both ends in the width direction at the top of the surface of the side that bulges out in an arc shape that receives tensile stress during bending load in a cross section in a plane perpendicular to the length direction. A flat section with a flat head is formed, and the plate thickness at the cross section is set to t1.
The arc cross-section steel plate according to any one of claims 1 to 3, characterized in that, where h is the truncated amount with respect to the plate thickness t, 0.35≧h/t.