JP2023117715A - Frp plate spring - Google Patents

Abstract

To achieve improved fatigue limit.SOLUTION: The present invention pertains to an FRP plate spring including a resin material R with a plurality of reinforcing fibers F embedded therein, the reinforcing fibers extending in one direction X. The diameters of the reinforcing fibers range from 1 μm to 100 μm inclusive. The amount of the reinforcing fibers contained in the resin material is 50 vol.% to 70 vol.% inclusive. In a cross-sectional view orthogonal to the one direction, when a plurality of divided regions each including the plurality of reinforcing fibers is magnified 300 times, the standard deviation of the area proportion of the reinforcing fibers included in each of the divided regions is 3% or less.SELECTED DRAWING: Figure 3A

Description

The present invention relates to FRP leaf springs.

Conventionally, there has been known an FRP leaf spring in which a plurality of reinforcing fibers extending in one direction are embedded in a resin material, as disclosed in Patent Document 1 below.

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 extensive studies and found that it is effective to improve the fatigue limit by evenly disposing a plurality of reinforcing fibers in a cross section orthogonal to one direction in which the reinforcing fibers extend.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an FRP leaf spring capable of improving the fatigue limit.

In order to solve the above problems and achieve such objects, the FRP leaf spring of the present invention has a plurality of reinforced fibers extending in one direction embedded in a resin material, and the diameter of the reinforced fibers is 1 μm or more and 100 μm. The 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, the plurality of divided regions each including a plurality of reinforcing fibers are enlarged 300 times. In this state, the standard deviation of the area ratio of the reinforcing fibers in each divided region is 3% or less.

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 suppressed to 3% or less. Therefore, a plurality of reinforcing fibers can be evenly provided with little variation in the cross section orthogonal to the one direction. 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.

The fractal dimension of the resin material is 1.98, which is obtained by a box counting method with a resolution of 0.15 μm or more and 2.3 μm or less for the length of one pixel based on the image of the cross section orthogonal to the one direction magnified 100 times. It may be greater than or equal to 2.01 or less.

Even when the cross section orthogonal to the one direction is enlarged at a low magnification of 100 times, the fractal dimension of the resin material is suppressed to 2.01 or less, and the pattern expressed by the reinforcing fiber and the resin material in the cross section is It is possible to make the cross section uniform with little variation, and it is possible to reliably prevent the occurrence of starting points where cracks occur when repeated bending stress is applied in the plate thickness direction.
Since the fractal dimension of the resin material is 1.98 or more when the cross section orthogonal to the one direction is magnified at a low magnification of 100 times, it is possible to suppress the occurrence of interlaminar shear fracture, It is possible to reliably improve the fatigue limit of the FRP leaf spring. 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.

In the cross-sectional view, the standard deviation of each fractal dimension of the resin material obtained based on each image obtained by enlarging a plurality of divided regions each containing a plurality of reinforcing fibers by 100 times is 0.3% or less. good too.

In the cross-sectional view, the standard deviation of each fractal dimension of the resin material in the plurality of divided regions is 0.3% or less even when the plurality of divided regions, each containing a plurality of reinforcing fibers, is enlarged at a low magnification of 100 times. , it is possible to ensure that the pattern expressed by the reinforcing fibers and the resin material in the cross section is uniform with little variation in the cross section.

According to this 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, and is formed in a plate shape having front and back surfaces facing in the vertical direction Z and having a long rectangular shape in one direction X when viewed from the vertical direction Z. 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 reinforcing fibers F have a diameter of 1 μm or more and 100 μm or less, preferably 10 μm or more and 30 μm or less.

In a cross-sectional view perpendicular to one direction X, as shown in FIGS. 3% 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 size (for example, 250 μm × 250 μm or more) each containing a plurality of reinforcing fibers F, and for the images of the divided regions x1 and x2, It is obtained by dividing the number of pixels where the reinforcing fibers F are located by the total number of pixels. The standard deviation of the area ratio of the reinforcing fibers F in each of the divided regions x1 and x2 is 3% or less when the 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 region A in the cross section is equally divided into 6 (1160 μm × 870 μm), and the image of each divided region x1 is 100 times as shown in FIGS. 3A to 3F. (SEM, backscattered electron image, accelerating voltage 21 kV), and in this image, by setting the length of 1 pixel to 0.15 μm or more and 2.3 μm or less, enhancement occupying each of the six divided regions x1 Each area ratio of the fiber F 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, if the length of one pixel is 1.13 μm, for example, the standard deviation of the area ratio of the reinforcing fibers F occupying each of the six divided regions x1 is 1.1. 14%.

Further, for example, as shown in FIG. 2, the predetermined area A in the cross section is equally divided into 54 pieces (387 μm×290 μm), and the image of each divided area x2 is magnified 300 times (SEM, Backscattered electron image, acceleration voltage 21 kV). In this image, by setting the length of 1 pixel to 0.15 μm or more and 2.3 μm or less, each area ratio of the reinforcing fiber F occupying each of the 54 divided regions x2 can be obtained. be done.
At this time, for example, if the length of one pixel is 0.38 μm, the standard deviation of each 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 count method with a resolution of 0.15 μm or more and 2.3 μm or less in length of 1 pixel based on a cross-sectional view image orthogonal to the one direction X. .01 or less. The fractal dimension of the resin material R is 1.98 or more and 2.01 or less when the divided regions x1 and x2 are enlarged at least 100 times or more and 300 times or less.

In the fractal dimension of the resin material R, the number of pixels in which the resin material R is positioned in the image of the same area included in the cross section orthogonal to the one direction X is different from each other within the range of 0.15 μm or more and 2.3 μm or less in length. It is the slope of the approximate straight line calculated by the least-squares method based on a log-log graph (horizontal axis: pixel size, vertical axis: number of pixels where the resin material R is located) plotted for each pixel size, that is, for each resolution. ing.

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 pattern expressed by the reinforcing fiber F and the resin material R in the cross section becomes uniform with little variation in the cross section, even if the pixel size fluctuates greatly, the number of pixels where the resin material R is located does not fluctuate. can be kept small.

In the cross-sectional view, the standard deviation of each fractal dimension of the resin material R obtained based on each image of a plurality of divided regions x1 and x2 each including a plurality of reinforcing fibers F is 0.3% or less. there is 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 region A in the cross section is equally divided into 6, and the image of each divided region x1 is 100 times as shown in FIGS. 3A to 3F. Using a magnified image, the number of pixels in which the resin material R is located is plotted for each of three different pixel sizes of 0.57 μm, 1.13 μm, and 2.27 μm in length on a log-log graph. obtained based on
In this case, the fractal dimension in the six divided regions x1 is 1.998 or more and 2.003 or less, and as shown in Table 1 and FIG. is 0.18%.

For the fractal dimension, for example, as shown in FIG. 2, the predetermined area A in the cross section is equally divided into 54 areas, and the image of each divided area x2 is magnified 300 times (SEM, reflection electron image, acceleration voltage 21 kV), in which the number of pixels in which the resin material R is located is plotted for each of three different pixel sizes of 0.19 μm, 0.38 μm, and 0.76 μm in length. It is obtained based on the graph.
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 is immersed in a pool in which the molten resin material R is stored while letting out the reinforcing fibers F wound around the bobbin, and then pulled out from the pool and coated with the molten resin material R. After forming a plate-shaped intermediate by winding the reinforcing fibers F around the outer peripheral surface of the rotating body over a plurality of turns, this intermediate is heated while being pressed in the plate thickness direction (pressing process). Obtainable.
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 are evenly provided in a cross section orthogonal to the one direction X with little variation.

As described above, according to the FRP leaf spring 1 according to the present embodiment, in a cross-sectional view perpendicular to the one direction X, a plurality of divided regions x2 each including a plurality of reinforcing fibers F can be viewed at a high magnification of 300 times. Even in the enlarged state, the standard deviation of the area ratio of the reinforcing fibers F occupying each divided region x2 is suppressed to a low level of 3% or less, so that the plurality of reinforcing fibers F in the cross section orthogonal to the one direction X are dispersed less. can be set 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.

The fractal dimension of the resin material R is suppressed to a low level of 2.01 or less even when the cross section perpendicular to the one direction X is enlarged at a low magnification of 100 times, and is expressed by the reinforcing fiber F and the resin material R in the cross-sectional view. It is possible to make the pattern uniform within this cross section with little variation, and it is possible to reliably prevent crack initiation points from occurring when bending stress is repeatedly applied in the plate thickness direction.

Since the fractal dimension of the resin material R is 1.98 or more when the cross section orthogonal to the one direction X is magnified at a low magnification of 100 times, it is possible to suppress the occurrence of interlaminar shear fracture. , 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 clear and wide region containing no reinforcing fibers F in the cross-sectional view.

In the cross-sectional view, the standard deviation of each fractal dimension of the resin material R in the plurality of divided regions x1 is 0 even when the divided regions x1 each including a plurality of reinforcing fibers F are enlarged at a low magnification of 100 times. Since it is kept as low as 0.3% or less, it is possible to ensure that the pattern expressed by the reinforcing fibers F and the resin material R in the cross section is made uniform with little variation in the cross section.

Next, the verification test will be explained.
As an example, the FRP leaf spring 1 shown in FIGS. 1, 2, and 3A to 3F was adopted, and FRP leaf springs 101 to 103 of Comparative Examples 1 to 3 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 the embodiment. Images of the FRP leaf spring 101 of Comparative Example 1 corresponding to FIGS. 3A to 3F of the example are shown in FIGS. 4A to 4F.
In Comparative Example 1, as shown in FIGS. 4A to 4F, a bundle in which a plurality of reinforcing fibers F are bundled includes a portion surrounded by a layer of resin material R. FIG.

In the FRP leaf spring 102 of Comparative Example 2, a plurality of sheets in which reinforcing fibers F are woven are set in a cavity of a molding die in a laminated state, and a resin material R in a molten state is poured into the cavity and cured. formed by Images of the FRP leaf spring 102 of Comparative Example 2 corresponding to FIGS. 3A to 3F of the example are shown in FIGS. 5A to 5F.
The FRP leaf spring 103 of Comparative Example 3 was formed by pressing and heating the prepreg sheets in which the reinforcing fibers F were embedded in the uncured resin material R in a state of being laminated. Images of the FRP leaf spring 103 of Comparative Example 3 corresponding to FIGS. 3A to 3F of the embodiment are shown in FIGS. 6A to 6F.
In Comparative Examples 2 and 3, as shown in FIGS. 5A to 5F and FIGS. 6A to 6F, a fiber layer made of a plurality of reinforcing fibers F includes a portion laminated via a layered resin material R. there is

In each of Comparative Examples 1 to 3, similarly to Example, 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 were obtained. The average value of each fractal dimension of the resin material R and the standard deviation of each fractal dimension were obtained.
Results are shown in Table 1 and FIG.

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

Next, for Examples and Comparative Examples 1 to 3 (thickness 2 mm, width 15 mm, length (one direction X) 60 mm), three-point bending fatigue test (distance between fulcrums (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. . In addition, when the life cycle number is reached, in Example, Comparative Example 1 and Comparative Example 3, the reinforcing fiber F is, for example, tensile fractured, and the cross section perpendicular to the one direction X is magnified 100 times. In Comparative Example 2 in which the fractal dimension of the resin material R was less than 1.98, 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 can be improved if the deviation is 3% or less.

The technical scope of the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist 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 each 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 embodiments with known components without departing from the scope of the present invention, and the above-described embodiments and modifications may be combined as appropriate.

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

Claims (3)

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

Images