WO2023153517A1

WO2023153517A1 - Frp plate spring

Info

Publication number: WO2023153517A1
Application number: PCT/JP2023/004875
Authority: WO
Inventors: 孝充佐野; 勝今村; 昌威木下
Original assignee: 日本発條株式会社
Priority date: 2022-02-14
Filing date: 2023-02-14
Publication date: 2023-08-17
Also published as: JP2023117715A

Abstract

The present invention pertains to an FRP plate spring (1) provided with a resin material (R) and a plurality of reinforcing fibers (F) that are embedded in the resin material (R) and that extend in one direction (X). The diameter of each of the plurality of reinforcing fibers (F) is 1-100 μm. The amount of the plurality of reinforcing fibers (F) contained in the resin material (R) is 50-70 vol%. In a cross-sectional view orthogonal to the one direction (X), when a plurality of divided regions (x1, x2) including a portion of the plurality of reinforcing fibers (F) is magnified 300 times, the standard deviation of the area proportion of the reinforcing fibers (F) included in each of the divided regions (x1, x2) is 3% or less.

Description

FRP leaf spring

The present invention relates to FRP leaf springs. This application claims priority based on Japanese Patent Application No. 2022-020431 filed in Japan on February 14, 2022, the contents of which are incorporated herein.

Conventionally, an FRP leaf spring as shown in Patent Document 1 below, for example, has been known. In such an FRP leaf spring, a plurality of reinforcing fibers extending in one direction are embedded in a resin material.

Japanese Patent Publication No. 59-45858

However, the conventional FRP leaf spring has a problem that it is difficult to improve the fatigue limit. Therefore, the inventors of the present application have made intensive studies on solutions to solve the problem, and found that a plurality of reinforcing fibers are arranged in a cross section orthogonal to one direction in which the reinforcing fibers extend, so as to reduce variations. In other words, the inventors have found that uniform provision is effective in improving the fatigue limit.

The present invention has been made in consideration of such circumstances, and an object of the present invention is to provide an FRP leaf spring capable of improving the fatigue limit.

A first aspect of the present invention comprises a resin material and a plurality of reinforcing fibers embedded in the resin material and extending in one direction, wherein each reinforcing fiber of the plurality of reinforcing fibers has a diameter of 1 μm or more and 100 μm or less. The plurality of reinforcing fibers are contained in the resin material at 50% by volume or more and 70% by volume or less, and in a cross-sectional view orthogonal to the one direction, each of the plurality of divided fibers includes a part of the plurality of reinforcing fibers The FRP leaf spring has a standard deviation of 3% or less of the area ratio of the reinforcing fibers in each of the plurality of divided regions when the region is magnified 300 times.

In this case, in the cross-sectional view, even when a plurality of divided regions each containing a plurality of reinforcing fibers are enlarged at a high magnification of 300 times, the standard deviation of the area ratio of the reinforcing fibers in each divided region is 3% or less. kept to a low value. As a result, a plurality of reinforcing fibers can be provided in a cross section perpendicular to the one direction with less variation, that is, evenly. Therefore, when a bending stress is repeatedly applied to the FRP leaf spring in the plate thickness direction, it becomes possible to make it difficult for cracks to occur, and the fatigue limit of the FRP leaf spring can be improved.

A second aspect of the present invention is obtained by a box counting method at a resolution such that the length of 1 pixel is 0.15 μm or more and 2.3 μm or less based on an image obtained by enlarging the cross section orthogonal to the one direction by 100 times. The FRP leaf spring according to the first aspect, wherein the resin material has a fractal dimension of 1.98 or more and 2.01 or less.

In this case, the fractal dimension of the resin material is suppressed to a low value of 2.01 or less even when the cross section perpendicular to the one direction is enlarged at a low magnification of 100 times. This makes it possible to reduce variations in the pattern expressed by the reinforcing fibers and the resin material in the cross section, that is, to make it uniform. Therefore, when a bending stress is repeatedly applied to the FRP leaf spring in the plate thickness direction, it is possible to reliably prevent the origin of cracks from occurring.
In addition, the fractal dimension of the resin material is 1.98 or more when the cross section perpendicular to the one direction is enlarged at a low magnification of 100 times. As a result, it is possible to suppress the occurrence of interlaminar shear fracture in the FRP leaf spring, and the fatigue limit of the FRP leaf spring can be reliably improved. That is, when the fractal dimension of the resin material is smaller than 1.98, the resin material is visually recognized as a clear and wide region containing no reinforcing fibers in the cross section.

A third aspect of the present invention is a resin material obtained based on each of a plurality of images obtained by enlarging the plurality of divided regions each containing the part of the plurality of reinforcing fibers in the cross-sectional view by 100 times. The FRP leaf spring according to the second aspect, wherein the standard deviation of the fractal dimension of is 0.3% or less.

In this case, in the cross-sectional view, even in a state in which the plurality of divided regions each including the part of the plurality of reinforcing fibers is enlarged at a low magnification of 100 times, the resin material in each divided region of the plurality of divided regions The standard deviation of the fractal dimension is suppressed to a low numerical value of 0.3% or less. As a result, it is possible to reliably realize that the patterns expressed by the reinforcing fibers and the resin material in the cross section are made uniform within the cross section.

According to the present invention, the fatigue limit can be improved.

1 is a cross-sectional photograph of an FRP leaf spring of one embodiment; 1 is a cross-sectional photograph of an FRP leaf spring of one embodiment; FIG. 2 is a SEM photograph showing a plurality of divided regions in FIG. 1; FIG. FIG. 2 is a SEM photograph showing a plurality of divided regions in FIG. 1; FIG. FIG. 2 is a SEM photograph showing a plurality of divided regions in FIG. 1; FIG. FIG. 2 is a SEM photograph showing a plurality of divided regions in FIG. 1; FIG. FIG. 2 is a SEM photograph showing a plurality of divided regions in FIG. 1; FIG. FIG. 2 is a SEM photograph showing a plurality of divided regions in FIG. 1; FIG. 4 is a SEM photograph showing a plurality of divided regions in Comparative Example 1; 4 is a SEM photograph showing a plurality of divided regions in Comparative Example 1; 4 is a SEM photograph showing a plurality of divided regions in Comparative Example 1; 4 is a SEM photograph showing a plurality of divided regions in Comparative Example 1; 4 is a SEM photograph showing a plurality of divided regions in Comparative Example 1; 4 is a SEM photograph showing a plurality of divided regions in Comparative Example 1; 10 is an SEM photograph showing a plurality of divided regions in Comparative Example 2; 10 is an SEM photograph showing a plurality of divided regions in Comparative Example 2; 10 is an SEM photograph showing a plurality of divided regions in Comparative Example 2; 10 is an SEM photograph showing a plurality of divided regions in Comparative Example 2; 10 is an SEM photograph showing a plurality of divided regions in Comparative Example 2; 10 is an SEM photograph showing a plurality of divided regions in Comparative Example 2; 11 is an SEM photograph showing a plurality of divided regions in Comparative Example 3; 11 is an SEM photograph showing a plurality of divided regions in Comparative Example 3; 11 is an SEM photograph showing a plurality of divided regions in Comparative Example 3; 11 is an SEM photograph showing a plurality of divided regions in Comparative Example 3; 11 is an SEM photograph showing a plurality of divided regions in Comparative Example 3; 11 is an SEM photograph showing a plurality of divided regions in Comparative Example 3; It is a figure which shows the result of a verification test.

An embodiment of the FRP leaf spring will now be described with reference to FIG.
The FRP leaf spring 1 is used, for example, in a suspension system of a vehicle. The FRP leaf spring 1 is formed in a plate shape having front and back surfaces facing in the vertical direction Z and having a rectangular shape elongated in one direction X when viewed from the vertical direction Z. As shown in FIG. The FRP leaf spring 1 is constructed by embedding a plurality of reinforcing fibers F extending in one direction X in a resin material R, as shown in FIGS. 3A to 3F. The diameter of the reinforcing fiber F is 1 μm or more and 100 μm or less, preferably 10 μm or more and 30 μm or less. The reinforcing fibers F are contained in the resin material R in an amount of 50% by volume or more and 70% by volume or less.

In a cross-sectional view orthogonal to one direction X shown in FIGS. % or less.
The area ratio of the reinforcing fibers F is obtained by equally dividing the predetermined region A in the cross-sectional view into a plurality of divided regions x1 and x2 each having a size (for example, 250 μm × 250 μm or more) containing a plurality of reinforcing fibers F, and dividing each divided region It is obtained by dividing the number of pixels where the reinforcing fibers F are located in the images of the regions x1 and x2 by the total number of pixels. The standard deviation of the area ratio of the reinforcing fibers F in each of the plurality of divided regions x1 and x2 is 3% or less when the plurality of divided regions x1 and x2 are enlarged at least 100 times or more and 300 times or less.

For example, as shown in FIG. 1, the predetermined area A in the cross section is equally divided into six divided areas x1 (1160 μm×870 μm), and the image of each divided area x1 is magnified 100 times (SEM, backscattered electron image, acceleration voltage 21 kV), and the length of one pixel in the enlarged image (images shown in FIGS. 3A to 3F) is 0.15 μm or more and 2.3 μm or less. As a result, the area ratio of the reinforcing fibers F in each of the six divided regions x1 is obtained. 3A to 3F, white portions indicate the reinforcing fibers F, and black portions indicate the resin material R. As shown in FIG. At this time, for example, if the length of one pixel is 1.13 μm, the standard deviation of the area ratio of the reinforcing fibers F occupying each of the six divided regions x1 is as shown in Table 1 and FIG. 14%.

Further, for example, as shown in FIG. 2, the predetermined area A in the cross section is equally divided into 54 divided areas x2 (387 μm×290 μm), and the image of each divided area x2 is enlarged 300 times (SEM, Backscattered electron image, accelerating voltage 21 kV), the length of one pixel in the enlarged image is 0.15 μm or more and 2.3 μm or less. As a result, the area ratio of the reinforcing fibers F to each of the 54 divided regions x2 is obtained. At this time, for example, if the length of one pixel is 0.38 μm, the standard deviation of the area ratio of the reinforcing fibers F occupying each of the 54 divided regions x2 is 1, as shown in Table 1 and FIG. .90%.

The fractal dimension of the resin material R is 1.98 or more, which is obtained by the box counting method at a resolution where the length of one pixel is 0.15 μm or more and 2.3 μm or less based on the cross-sectional image orthogonal to the one direction X. 2.01 or less. The fractal dimension of the resin material R is 1.98 or more and 2.01 or less when the plurality of divided regions x1 and x2 are enlarged at least 100 times or more and 300 times or less.

The fractal dimension of the resin material R is defined as the number of pixels in which the resin material R is positioned in an image of the same region included in a cross section perpendicular to the one direction X, with the length of one pixel being in the range of 0.15 μm or more and 2.3 μm or less. Approximate straight line calculated by the method of least squares based on a double logarithmic graph (horizontal axis: pixel size, vertical axis: number of pixels where resin material R is located) plotted for each of a plurality of different pixel sizes (that is, for each resolution) becomes the slope of

Note that as the pixel size increases, the number of pixels in which the resin material R is positioned decreases, and as the pixel size decreases, the number of pixels in which the resin material R is positioned increases. In addition, when the patterns expressed by the reinforcing fibers F and the resin material R in the cross-section view have less variation in the cross-section, that is, become uniform, even if the pixel size fluctuates greatly, the resin material R The variation in the number of pixels where is located is kept small.

In the cross-sectional view, the standard deviation of the fractal dimension of the resin material R obtained based on each of the plurality of images of the plurality of divided regions x1 and x2 each including the plurality of reinforcing fibers F is 0.3% or less. It's becoming This standard deviation is 0.3% or less when the divided regions x1 and x2 are enlarged at least 100 times or more and 300 times or less.

For the fractal dimension, for example, as shown in FIG. 1, the predetermined area A in the cross section is equally divided into six divided areas x1, the image of each divided area x1 is magnified 100 times, and in the enlarged image The number of pixels in which the resin material R is located is obtained based on a double-logarithmic graph plotted for each of three different pixel sizes, where the length of one pixel is 0.57 μm, 1.13 μm, and 2.27 μm. In this case, the fractal dimensions of the six divided regions x1 are 1.998 or more and 2.003 or less. Also, as shown in Table 1 and FIG. 7, the average value of the fractal dimension in the six divided regions x1 is 1.9999, and the standard deviation is 0.18%.

For the fractal dimension, for example, as shown in FIG. 2, the predetermined region A in the cross section is equally divided into 54 divided regions x2, and the image of each divided region x2 is magnified 300 times (SEM, reflection electron image, acceleration voltage 21 kV), the number of pixels where the resin material R is located in the magnified image for each of three different pixel sizes, where the length of one pixel is 0.19 μm, 0.38 μm, and 0.76 μm. is obtained based on the log-log graph plotted on In this case, as shown in Table 1 and FIG. 7, the average value of the fractal dimensions in the 54 divided regions x2 is 1.9927 and the standard deviation is 0.15%.

The FRP leaf spring 1 can be obtained as follows. First, while the reinforcing fibers F wound around the bobbin are let out, the reinforcing fibers F are submerged in a pool in which the molten resin material R is stored. After that, the reinforcing fibers F coated with the molten resin material R are pulled out from the pool and wound around the outer peripheral surface of the rotating body over a plurality of turns to form a plate-shaped intermediate. After that, the FRP leaf spring 1 can be obtained by heating the molded intermediate while pressurizing it in the plate thickness direction (pressing step). During the pressurizing step, the reinforcing fibers F flow through the resin material R in a molten state, so that the plurality of reinforcing fibers F become uniform within the cross section orthogonal to the one direction X so that the variation is reduced. is provided as follows.

As described above, according to the FRP leaf spring 1 according to the present embodiment, in a cross-sectional view orthogonal to the one direction X, a plurality of divided regions x2 each including a plurality of reinforcing fibers F are magnified at a high magnification of 300 times. , the standard deviation of the area ratio of the reinforcing fibers F occupying each divided region x2 is suppressed to a low numerical value of 3% or less. In other words, a plurality of reinforcing fibers F can be provided in a cross section orthogonal to the one direction X so as to reduce variations, that is, evenly. Therefore, when a bending stress is repeatedly applied to the FRP leaf spring 1 in the plate thickness direction, it is possible to make it difficult for cracks to occur, and the fatigue limit of the FRP leaf spring 1 can be improved.

In addition, even when the cross section orthogonal to the one direction X is enlarged at a low magnification of 100 times, the fractal dimension of the resin material R can be kept low at 2.01 or less. By this. The pattern expressed by the reinforcing fiber F and the resin material R in the cross-sectional view can be made uniform within the cross-section, that is, it can be made uniform, and repeated bending stress is applied in the plate thickness direction. It is possible to reliably make it difficult to generate the starting point where cracks are generated when it is crushed.

In addition, the fractal dimension of the resin material R is 1.98 or more when the cross section orthogonal to the one direction X is enlarged at a low magnification of 100 times. As a result, it is possible to suppress the occurrence of interlaminar shear fracture, and the fatigue limit of the FRP leaf spring 1 can be reliably improved. That is, when the fractal dimension of the resin material R becomes smaller than 1.98, the resin material R is visually recognized as a region containing no reinforcing fibers F, ie, a clear and wide region in the cross section.

In the cross-sectional view, even when the plurality of divided regions x1 each including a plurality of reinforcing fibers F is enlarged at a low magnification of 100 times, the fractal dimension of the resin material R in each divided region x1 of the plurality of divided regions x1 The standard deviation of is suppressed to a low numerical value of 0.3% or less. As a result, it is possible to ensure that the patterns expressed by the reinforcing fibers F and the resin material R in the cross section are made uniform within the cross section.

Next, I will explain the verification test. As an example, the FRP leaf spring 1 shown in FIGS. 1, 2, and 3A to 3F was adopted, and as comparative examples 1 to 3, FRP leaf springs 101 to 103 were prepared.

The FRP leaf spring 101 of Comparative Example 1 was formed by a manufacturing method that does not include the pressing process, in contrast to the manufacturing method of the FRP leaf spring 1 of Example. Images of the FRP leaf spring 101 of Comparative Example 1 are shown in FIGS. 4A to 4F. 4A to 4F correspond to FIGS. 3A to 3F showing images of the FRP leaf spring 1 of the embodiment. In the FRP leaf spring 101 of Comparative Example 1, a bundle in which a plurality of reinforcing fibers F are bundled includes a portion surrounded by layers of the resin material R, as shown in FIGS. 4A to 4F.

The FRP leaf spring 102 of Comparative Example 2 is set in a cavity of a molding die in a state in which a plurality of sheets in which reinforcing fibers F are woven are laminated, and in such a state, a molten resin material R is placed in the cavity. Formed by pouring and curing. Images of the FRP leaf spring 102 of Comparative Example 2 are shown in FIGS. 5A to 5F. 5A to 5F correspond to FIGS. 3A to 3F showing images of the FRP leaf spring 1 of the embodiment.
The FRP leaf spring 103 of Comparative Example 3 was formed by laminating prepreg sheets in which reinforcing fibers F were embedded in an uncured resin material R, and then pressing and heating the prepreg sheets. Images of the FRP leaf spring 103 of Comparative Example 3 are shown in FIGS. 6A to 6F. 6A to 6F correspond to FIGS. 3A to 3F showing images of the FRP leaf spring 1 of the embodiment. In the FRP leaf springs 102 and 103 of Comparative Examples 2 and 3, as shown in FIGS. 5A to 5F and FIGS. 6A to 6F, fiber layers composed of a plurality of reinforcing fibers F are laminated via a layered resin material R. includes the part that is

In each of Comparative Examples 1 to 3, similarly to Example, based on the standard deviation of the area ratio of the reinforcing fibers F in each of the plurality of divided regions x1 and x2 and the images of each of the plurality of divided regions x1 and x2 The average value of the fractal dimension and the standard deviation of the fractal dimension of the resin material R obtained by The results are shown in Table 1 and FIG.

In Comparative Examples 1 to 3, the standard deviation of the area ratio of the reinforcing fibers F occupying each divided region x2 was higher than 3% when each of the plurality of divided regions x2 was magnified 300 times in the cross-sectional view. there is In Comparative Examples 1 and 3, the fractal dimension of the resin material R obtained based on the image obtained by enlarging the cross section perpendicular to the one direction X by 100 times is greater than 2.01. In Comparative Example 2, the fractal dimension of the resin material R obtained based on the image obtained by enlarging the cross section perpendicular to the one direction X by 100 times is smaller than 1.98.

Next, for Examples and Comparative Examples 1 to 3 (thickness 2 mm, width 15 mm, length (length in one direction X) 60 mm), three-point bending fatigue test (distance between fulcrums (distance in one direction X) 45 mm , indenter radius 7.5 mm, fulcrum radius 5.0 mm, frequency 6 Hz, load control).

As a result, it was confirmed that the life cycle number of the example was about 16 times longer than that of Comparative Example 1, about 100 times longer than that of Comparative Example 2, and about 22 times longer than that of Comparative Example 3. was done. In addition, in Example, Comparative Example 1, and Comparative Example 3, for example, tensile breakage or the like occurred in the reinforcing fibers F when the life cycle number was reached. In Comparative Example 2, in which the fractal dimension of the resin material R is less than 1.98, which is obtained based on the image obtained by enlarging the cross section perpendicular to the one direction X by 100 times, cracks occurred in the resin material R (interlaminar shear fracture). From the above, as in the embodiment, when the plurality of divided regions x2 each including a plurality of reinforcing fibers F are magnified 300 times in the cross-sectional view, the standard of the area ratio of the reinforcing fibers F occupying each divided region x2 It was confirmed that the fatigue limit of the FRP leaf spring can be improved if the deviation is 3% or less.

One aspect of the present invention includes a resin material and a plurality of reinforcing fibers embedded in the resin material and extending in one direction, and the diameter of each reinforcing fiber of the plurality of reinforcing fibers is 1 μm or more and 100 μm or less. , the plurality of reinforcing fibers are contained in the resin material at 50% by volume or more and 70% by volume or less, and in a cross-sectional view perpendicular to the one direction, a plurality of divided regions each including a part of the plurality of reinforcing fibers is magnified 300 times, the standard deviation of the area ratio of the reinforcing fibers in each divided region of the plurality of divided regions is 3% or less.

In the FRP leaf spring, the resin is obtained by a box counting method with a resolution such that the length of one pixel is 0.15 μm or more and 2.3 μm or less based on an image obtained by enlarging a cross section orthogonal to the one direction by 100 times. The fractal dimension of the material may be between 1.98 and 2.01.

In the FRP leaf spring, in the cross-sectional view, the resin material is obtained based on each of a plurality of images obtained by enlarging the plurality of divided regions each containing the part of the plurality of reinforcing fibers by 100 times. A standard deviation of the fractal dimension may be 0.3% or less.

It should be noted that the technical scope of the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

For example, the fractal dimension of the resin material R obtained by the box counting method with a resolution of 0.15 μm or more and 2.3 μm or less in length of one pixel based on a 100-fold enlarged image of a cross section orthogonal to one direction X is calculated as follows: , may be less than 1.98 or greater than 2.01. Further, in the cross-sectional view, the standard deviation of the fractal dimension of the resin material R obtained based on an image obtained by enlarging each of the plurality of divided regions x1 by 100 times may be larger than 0.3%.

In addition, it is possible to appropriately replace the components in the above-described embodiment with known components within the scope of the present invention, and the above-described embodiments and modifications may be combined as appropriate.

According to the present invention, the fatigue limit can be improved.

1 FRP leaf spring F Reinforcement fiber R Resin material X One direction x1, x2 Divided area

Claims

a resin material;
a plurality of reinforcing fibers embedded in the resin material and extending in one direction;
with
The diameter of each reinforcing fiber of the plurality of reinforcing fibers is 1 μm or more and 100 μm or less,
The plurality of reinforcing fibers are contained in the resin material in an amount of 50% by volume or more and 70% by volume or less,
In a cross-sectional view orthogonal to the one direction, in a state in which the plurality of divided regions each including a part of the plurality of reinforcing fibers are magnified 300 times, the area ratio of the reinforcing fibers in each divided region of the plurality of divided regions A FRP leaf spring with a standard deviation of 3% or less.
The fractal dimension of the resin material, which is obtained by a box counting method at a resolution where the length of one pixel is 0.15 μm or more and 2.3 μm or less, based on an image obtained by enlarging the cross section perpendicular to the one direction by 100 times, 2. The FRP leaf spring according to claim 1, which is 1.98 or more and 2.01 or less.
3. The method according to claim 2, wherein the standard deviation of the fractal dimension of the resin material obtained based on each of a plurality of images obtained by enlarging the plurality of divided regions by 100 times is 0.3% or less. FRP leaf spring.