JPH06160257A - Method for measuring orientation angle of fiber in continuous fiber reinforced plastic - Google Patents

Abstract

PURPOSE:To determe orientation angle of fiber accurately by polishing a fiber reinforced plastic to provide a cross-section inclining at an angle within a predetermined range with respect to the reinforcing direction and measuring long and short diameters of fiber on the polished surface. CONSTITUTION:Reinforcing fiber 2 and basic material 3 may be combined arbitrarily so long as an FRP 1 is reinforced at least partially in one direction by continuous fibers. The fiber 2 has preferably right circular cross-section. The FRP 1 is polished to make an angle of 5-60 deg. with respect to the reinforcing direction. The FRP 1 may be polished solely or while being embedded in a resin. Polished FRP 1 is observed by means of a microscope. The microscope is selected from optical microscope, stereoscopic microscope, electronic microscope, etc., depending on the fiber diameter or sample profile. The fiber has elliptical cross-section and lond and short diameters (b), (a) thereof are measured. Assuming the inclination angle of the cross-section of the FRP 1 is theta, inclination angle (alpha) of the fiber with respect to the reinforcing direction can be determined according to the following formula alpha=¦theta-cos<-1>(a/b)¦. The angle alpha is measured for a plurality of fibers 2 and processed statistically thus determining the orientation angle of fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the orientation angle of fibers in a fiber reinforced plastic.

[0002]

2. Description of the Related Art Fiber reinforced plastics (FRP) are used in various fields by taking advantage of characteristics such as light weight, high strength and corrosion resistance. As the reinforcing fibers, inorganic fibers such as carbon fibers, glass fibers and boron fibers, and organic fibers such as aramid fibers and polyethylene fibers are used, and the reinforcing forms of the fibers include short fiber reinforcement and continuous fiber reinforcement. In order to produce a high performance FRP, it is necessary to orient the reinforcing fibers continuously in the reinforcing direction. Therefore, the highest performance FRP is unidirectional continuous fiber reinforced plastic (hereinafter, unidirectional FRP).

However, it is difficult to precisely orient the fibers in one direction, and waviness of the fibers and deviation of the orientation angle are often found in the molded product, which causes deterioration of the physical properties. That is, since the swell portion does not receive the load in the initial stage of the load, the fibers are sequentially broken, and the material is unexpectedly broken at a low load. Therefore, from the viewpoint of quality control, it is important to examine the degree of orientation of the fibers in the FRP during manufacturing.

Regarding the prepreg sheet, which is an intermediate raw material for the production of unidirectional FRP, a method of measuring the waviness of fibers by X-ray or the like is disclosed. However, since this method is limited to the measurement of a thin sheet, it cannot be measured without using FRP or prepreg sheet after molding. Moreover, it was difficult to quantify the measurement results.

As a means for measuring the waviness of the fiber in the unidirectional FRP after molding, a method of observing a cross section of the unidirectional FRP in the strengthening direction (L direction) with a microscope is known. However, this method was able to evaluate only a small part of the fibers in FRP, and could only quantitatively evaluate the twist.

As a method for quantitatively evaluating the orientation angle of the fibers, for example, Adv. Polym. Technol.
(2), 135 (1990), there is a method of obtaining from a micrograph of a cross section. This is a method for predicting the strength of a molded product or estimating the flow of plastic during injection molding, for example. When the fiber is a perfect circle, the cross-sectional shape of the fiber that appears on any cross section of the FRP is an ellipse unless it is cut at right angles to the fiber. The orientation angle of the fiber is
It is calculated from the aspect ratio of the ellipse appearing on the cross section. That is, as shown in FIGS. 2 and 3, the orientation angle β is represented by the formula (1) from the major axis b and the minor axis a. β = cos ^-1 (a / b) (1)

However, it is difficult to apply the above method to unidirectionally reinforced plastics. That is, one-way FR
Since P has its performance enhanced to the utmost limit, the fibers are not randomly oriented from 0 ° to 90 ° unlike the random direction reinforced product. In the unidirectional FRP, the fibers are oriented in almost the same direction, and even if the fibers have undulations, the orientation angle is deviated by at most several degrees. Therefore, even if a micrograph of a cross section orthogonal to one direction FRP is measured, the cross-sectional shape of the fiber is almost a perfect circle, and it is difficult to detect the deviation of the orientation angle. , A / b is 0.996, and it is almost impossible to detect the difference. However, this slight deviation in orientation angle may affect the physical properties of FRP, and it is desirable to detect this difference from the viewpoint of quality control. In other words, if this difference can be detected, it can be used as one of the quality control standards to detect non-standard products at an early stage, and to omit the time-consuming, time-consuming, and costly physical property test of FRP. it can.

[0008]

SUMMARY OF THE INVENTION The present invention provides a method for accurately measuring the orientation angle of fibers in a unidirectional continuous fiber reinforced plastic.

[0009]

DISCLOSURE OF THE INVENTION According to the present invention, in a continuous fiber reinforced plastic reinforced in one direction, the fiber reinforced plastic is processed so as to obtain a cross section at an angle of 5 ° or more and 60 ° or less with respect to the reinforced direction. Then, the polishing surface of the cross section is observed, and the major axis and the minor axis of the fiber observed on the polishing surface are measured to measure the orientation angle of the fiber-reinforced plastic.

The method of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a conceptual diagram for explaining the method of the present invention. The FRP1 to be measured is partially or wholly reinforced in one direction. As reinforced in one direction, unidirectional prepreg sheets (sheet-shaped intermediate material in which fibers are aligned in one direction and impregnated with resin) are laminated in the same direction, unidirectional material, pultrusion material, resin Impregnated strand material, etc. Partly reinforced in one direction includes quasi-isotropic materials in which unidirectional prepreg sheets are laminated in different directions, angle ply materials, etc., as well as mixed products of unidirectional materials and mat materials and cloth (woven fabric) materials. and so on.

The reinforcing fiber 2 used in the FRP may be any as long as it is used in ordinary unidirectional continuous fiber reinforced plastic. Examples thereof include inorganic fibers such as carbon fiber, glass fiber and boron fiber, organic fibers such as aramid fiber, polyethylene fiber, vinylon fiber and polyarylate fiber, metal fibers such as stainless fiber and amorphous fiber, and a mixture thereof. .

The resin used for the base material 3 may be any resin used for ordinary unidirectional continuous fiber reinforced plastics. For example, thermosetting resin such as epoxy resin, unsaturated polyester resin, phenol resin, polyimide resin, urethane resin, polyamide (nylon) resin, polypropylene resin, polyether ether ketone (PEEK) resin, polyphenylene sulfide (PPS) resin Thermoplastic resins such as polyimide resin, urethane resin and polystyrene resin, rubbers such as neoprene rubber, isoprene rubber and silicone rubber, and mixtures or modified products thereof are used.

As long as a part of the FRP is unidirectionally reinforced as continuous fibers, any combination of the reinforcing fibers and the base material may be used. However, the cross-sectional shape of the fiber is preferably a perfect circle. An irregular cross section, especially an elliptical cross section, is not suitable because the measurement of the orientation angle becomes inaccurate.

The FRP is polished after being processed into an angle of 5 ° or more and 60 ° or less with respect to the strengthening direction to be measured. This angle corresponds to the angle θ in FIG. Processing is a method of cutting to a predetermined angle,
It is carried out by a method of grinding FRP cut at an appropriate angle so as to have a predetermined angle. The polishing may be performed by a commonly used device such as a rotary polishing machine or a vibration polishing machine. At that time, polishing may be performed only with FRP or further by embedding FRP in a resin and polishing. Polishing only with FRP is easier in terms of measurement, but when the sagging of the edge portion occurs during polishing, which is not preferable in terms of measurement, a method of embedding in resin and polishing is preferable.

The above-mentioned angle is preferably a small angle because the purpose is to increase the ratio of the major axis and the minor axis of the cross section of the fiber. However, if the angle is too small, the major axis becomes too long and measurement becomes difficult. An angle of 5 ° or more and 60 ° or less, more preferably 10 ° or more and 40 ° or less is particularly preferable.

The FRP after polishing is subjected to microscopic observation. As the microscope, an optical microscope, a stereoscopic microscope, an electron microscope, or the like may be selected according to the fiber diameter, sample properties, and the like. Further, it is not particularly required to be a microscope, and any device such as a CCD camera which can magnify and observe an object may be used.

The cross section of the observed fibers is elliptical. The major and minor axes of this elliptical shape are measured. Assuming that the length of the major axis is b, the length of the minor axis is a, and the inclination of the cross section with respect to the reinforcing direction of the FRP is θ, the inclination α of the fiber from the reinforcing direction is α = | θ− cos ⁻¹ (a / b ) | Is represented by (2). The orientation angle and the state of waviness can be measured by measuring α for all fibers or a part of the fibers and performing statistical processing.

The length of the observation surface is measured by, for example, photographing the observation surface with a photograph or a laser printer and measuring the length with a caliper, or measuring the length on a computer by an image processing device. and so on.

Regarding the statistical processing, a method suitable for the purpose may be adopted, for example, a method of calculating the standard deviation is performed. In addition, when θ cannot be accurately determined and polishing cannot be performed, β can be calculated according to the equation (1) and the average of all β can be used as θ.

[0021]

By using the method of the present invention, one-way FR
It is possible to accurately measure the orientation angle of P. It was almost impossible to detect a slight angular deviation within 10 ° by observing an orthogonal cross section, but in the case of this method, it is easy to detect the angular deviation by giving an angle to the cross section in advance. ing. For example, if it was polished to 20 ° in advance,
At an orientation angle of 0 °, the minor axis is 1 and the major axis is 2.92. The deviation of ± 1 ° is 2.79 (21 °) and 3.07 (19
.Degree.), A minute change in the angle can be easily detected.

[0022]

Example: A carbon fiber having a diameter of 10 μm and a tensile strength of 300 kgf / mm ² was used, and an FRP rod (diameter 3 mm, fiber volume content 60%) manufactured by pultrusion using an epoxy resin as a base material was used in the axial direction. Was processed and polished to an angle of about 20 °. This cross section was processed by an image processing device (manufactured by Toray Engineering Co., Ltd.), and the ratio of the major axis and the minor axis of the fiber observed in an elliptical shape was calculated for 1000 points of fiber, and the angle was calculated according to the above formula (1). It was calculated. The total average angle of 1000 points was taken as the polishing angle θ of this sample, and the deviation of each point from θ was taken as the orientation angle α of that point. the standard deviation of α,
The breaking load of the rod is shown in Table 1. The breaking load is
FRP tabs are attached to both ends of the rod, and the load at break is the result of a tensile test using a tensile tester.

[0023]

[Table 1]

From this, it was revealed that the tensile strength was lowered when the standard deviation of α was 10 ° or more. Therefore, in the subsequent manufacturing, the tensile strength was decreased for the samples having the standard deviation of α of 10 ° or more. It was made into a nonstandard product without performing a test.

For the comparative example, the same measurement was carried out on the cross section orthogonal to the axial direction of the sample, but the angle could not be calculated.

[0026]

By using the method of the present invention, it is possible to easily and quantitatively measure the orientation angle of the unidirectional FRP without requiring a special device. This measurement is useful for quality control at the manufacturing site, and in some cases, it is possible to omit the tensile test and the like.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a method of the present invention.

FIG. 2 is a perspective view conceptually showing a method for measuring an orientation angle.

FIG. 3 is a conceptual diagram showing a fiber shape appearing on a cross section.

[Explanation of symbols]

 1 FRP 2 Reinforcing fiber 3 Base material

Claims (1)

[Claims] 1. A continuous fiber reinforced plastic reinforced in one direction, the fiber reinforced plastic is processed so as to obtain a cross section at an angle of 5 ° or more and 60 ° or less with respect to the reinforced direction, and the polished surface of the cross section is processed. A method for measuring an orientation angle of a fiber-reinforced plastic, which comprises observing and measuring a major axis and a minor axis of a fiber cross section observed on the polished surface.