JPH07276513A - Fiber reinforced plastic cylindrical body - Google Patents

Abstract

PURPOSE:To obtain excellent bending characteristics and flat crushing strength by a method wherein reinforcing fibers are employed respectively for the outermost, middle and innermost layers under the condition that the ratios of the thicknesses of the outermost, middle and innermost layers to the wall thickness of cylindrical body are specified, and the reinforcing fiber employed for the outermost layer has the compressive strength at least of a specified value, that employed for the middle layer has the compressive strength and modulus of tensile elasticity at least of a specified values and that employed for the innermost layer has the modulus of tensile elasticity at least of a specified value. CONSTITUTION:A cylindrical body consists of the outermost, middle and innermost layers, in which reinforcing fibers are arranged normal, axial and normal to its cylindrical axis in the order named. For the outermost layer, reinforcing fiber having the compressive strength of 100kgf/mm<2> or higher is employed for flat crushing strength. For the middle layer, reinforcing fiber having the compressive strength of 80kgf/mm<2> or higher and the modulus of tensile elasticity of 50,000kgf/mm<2> or higher is employed for improving bending characteristics. For the inner most layer, reinforcing fiber having the modulus of tensile elasticity of 50,000kgf/ mm<2> or higher is employed for obtaining dynamic balance as a whole. The ratios of the thicknesses of the respective layers to the wall thickness of the cylindrical body are set to be 12-20% for the outermost layer, 74-85% for the middle layer and 10-20% for the innermost layer for optimizing bending, flat crushing strength and modulus of flexural elasticity, because the too much thin outermost layer brings the lowering of the flat crushing strength, the too much thin middle layer brings the lowering of the modulus of flexural elasticity and even either thin one of the layers brings the bending strength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an aircraft,
The present invention relates to a fiber-reinforced plastic cylindrical body suitable as various frames, pipes, shafts for automobiles, bicycles, etc., and also as various leisure products such as fishing rods, golf club shafts, ski poles, and tent columns.

[0002]

2. Description of the Related Art A cylindrical body made of fiber reinforced plastic (hereinafter abbreviated as FRP) has a reinforcing fiber in the outermost layer and the innermost layer in the axial direction of the cylinder, as described in, for example, JP-A-59-73683. Layers arranged at right angles to each other, so-called 90 ° layers,
The intermediate layer often has a structure in which reinforcing fibers are arranged in the axial direction of the cylinder, that is, a so-called 0 ° layer. Where 90
The 0 ° layer mainly acts to improve the crushing property of the cylinder, and the 0 ° layer mainly acts to improve the bending property.

In particular, in the case of a cylinder having a wall thickness ratio to the average radius of the cylinder of 0.1 or less (hereinafter referred to as a thin-walled cylinder), the bending strength and the bending elastic modulus when a bending force is originally applied are not always sufficient. Therefore, measures have been taken to improve the maximum bending strength and bending elastic modulus.
Although the maximum bending strength and bending elastic modulus are improved, there is a problem that the crushing reaction force in the diametrical direction of the cylinder, so-called crush strength, is significantly reduced. In particular, in the case of a fishing rod or the like which is a thin-walled cylindrical body, it is required to improve the bending characteristics without lowering the crush strength. That is, in the conventional cylinder described above, it is difficult to simultaneously satisfy the bending strength, the bending elastic modulus, and the crushing strength of the cylinder in the thin cylinder.

[0004]

The object of the present invention is to solve the above-mentioned problems of the conventional FRP thin-walled cylindrical body, and to have excellent bending characteristics such as bending strength and bending elastic modulus, and crushing strength in the cylindrical diameter direction. It is to provide a thin-walled cylinder made of FRP.

[0005]

In order to achieve the above object, the present invention has the following constitution. That is, the outermost layer in which the reinforcing fibers are arranged at right angles to the cylinder axis direction, the intermediate layer arranged in the cylinder axis direction, and the cylindrical body composed of the innermost layer arranged at right angles to the cylinder axis direction, The ratio of the thickness of each layer to the thickness of the cylinder is respectively the outermost layers 12 to 2
0%, middle layer 74 to 85%, innermost layer 5 to 12%,
The outermost layer, the reinforcing fiber compressive strength is 100 kgf / mm ² or more, the intermediate layer, the reinforcing fiber compressive strength is 80 kgf / mm ² or more and a tensile modulus of 50000kgf / mm ² or more, the innermost layer A fiber-reinforced plastic cylindrical body comprising a reinforcing fiber having a tensile elastic modulus of 50,000 kgf / mm ² or more.

In a cylindrical body composed of an outermost layer in which reinforcing fibers are arranged at right angles to the cylinder axis direction, an intermediate layer arranged in the cylinder axis direction, and an innermost layer arranged at right angles to the cylinder axis direction. , The ratio of the thickness of each layer to the thickness of the cylindrical body is 12 to 20% of the outermost layer, 74 to 85% of the intermediate layer, and 5 to 12% of the innermost layer, and the outermost layer has a tensile elastic modulus of 300.
00~50000kgf / mm ² at a carbon fiber, the intermediate layer, carbon fiber tensile modulus of 50000~70000kgf / mm ^2, the innermost layer has a tensile modulus of 50000Kgf /
A fiber reinforced plastic cylinder characterized by using carbon fibers having a size of mm ² or more.

The FRP cylindrical body of the present invention will be described in detail below.

(Shape of Cylindrical Body) In the cylindrical body of the present invention, when the ratio of the wall thickness to the average radius of the cylinder is larger than 0.1, the bending strength of the cylindrical body becomes the rate-determining property of the compressive strength of the cylindrical intermediate layer. Therefore, the ratio of the wall thickness to the average radius of the cylindrical body is preferably 0.1 or less, more preferably 0.08,
It is more preferable that the cylindrical body has a diameter of 0.05 or less. Here, the average radius of the cylinder means the distance from the center of the cylinder to the center of the wall thickness of the cylinder.

(Matrix resin) In the present invention,
As the FRP matrix resin, a thermosetting resin such as an epoxy resin or an unsaturated polyester resin, or a thermoplastic resin such as nylon, polypropylene, polyester, polyimide, or polyether ether ketone can be used. Among them, the epoxy resin is preferably used in the present invention because it has excellent heat resistance, water resistance, and adhesiveness with the reinforcing fiber.

(Reinforcing fiber) The outermost layer mainly acts on the crush strength, the intermediate layer mainly acts on the bending characteristics, and the bending characteristics are determined by the synergistic effect of each layer. Therefore, for example, in the case of carbon fiber, if reinforcing fibers having high tensile properties and super high elastic modulus yarns are used for each layer in order to improve bending properties, the compressive strength of the outermost layer is low, and the crushing strength is reduced. Sometimes.

As the reinforcing fibers used for each layer, it is necessary to use reinforcing fibers having high compressive strength for the outermost layer and the intermediate layer and reinforcing fibers having high tensile elastic modulus for the intermediate layer and the innermost layer. That is, in order to improve the crush strength, it is necessary to use reinforcing fibers with high compressive strength in the outermost layer, and to improve bending properties, use reinforcing fibers with high elastic modulus in the intermediate layer, and Since it is important to balance the mechanical properties of the reinforcing fibers, it is necessary to use reinforcing fibers having a high elastic modulus also in the innermost layer, and it is desirable that the outermost layer also has a certain tensile elastic modulus.

The compressive strength of the reinforcing fiber in the present invention is JI
It is the composite compressive strength according to SK7076, and the tensile strength and tensile modulus are the strand tensile strength and tensile modulus measured according to JIS-R7601.

Carbon fibers, glass fibers, polyamide fibers, and other high-strength and high-modulus fibers can be used as the reinforcing fibers. These reinforcing fibers may be of different types, or the same type may have different mechanical properties. Of these, carbon fibers having excellent specific strength and specific elastic modulus are preferable.

In the cylindrical body of the present invention, the outermost layer has a compressive strength of 100 kgf / mm ² or more, preferably 120 kgf / mm ^2.
The reinforcing fibers having the above high compressive strength are arranged. Such a reinforcing fiber has a tensile modulus of 30.
000 to 50,000 kgf / mm ² , preferably 38,000 to
Carbon fiber of 50,000 kgf / mm ² can be used. As the reinforcing fiber of the outermost layer, a polyacrylonitrile (PAN) -based carbon fiber that can maintain a relatively high compressive strength even when the tensile modulus is high is more preferably used. In the case of carbon fiber, the crystal size is 20-5.
5 angstrom, the crystal orientation degree is 83 to 92%, more preferably the crystal size is 44 to 55 angstrom,
Carbon fiber having a crystal orientation of 90 to 92% has compressive strength,
It is preferably used in order to obtain the desired tensile modulus.

In the cylindrical body of the present invention, the compressive strength of the reinforcing fiber of the intermediate layer is 80 kgf / mm ² or more, preferably 90 kgf /
mm ² or more, and the tensile elastic modulus of the reinforcing fiber of the intermediate layer is 50,000 kgf / mm ² or more, preferably 60,000 kgf / mm
^Two or more reinforcing fibers. Such a reinforcing fiber has a tensile modulus of 50,000 to 70,000 kgf /
It is possible to use carbon fibers of mm ² , preferably 60,000 to 70,000 kgf / mm ² . As the reinforcing fiber of the outermost layer, a polyacrylonitrile (PAN) -based carbon fiber that can maintain a relatively high compressive strength even when the tensile modulus is high is more preferably used. In the case of carbon fiber, the crystal size is 55 to 62 angstroms, the crystal orientation is 92 to 95%, and more preferably the crystal size is 60 to 62 angstroms and the crystal orientation is 94 to 95.
% Carbon fiber is preferably used in order to obtain desired properties such as compressive strength and tensile modulus.

Further, in the cylindrical body of the present invention, the reinforcing fiber of the innermost layer has a tensile elastic modulus of 50000 kgf / mm ² or more, preferably 60,000 kgf / mm ² or more.
As such a reinforcing fiber, a PAN-based or pitch-based carbon fiber can be used. Further, the tensile strength of the reinforcing fiber of the innermost layer is preferably 260 kgf / mm ² or more.

(Ratio of thickness of each layer) Regarding the ratio of the thickness of each layer to the cylindrical wall thickness, if the outermost layer is too thin, the crushing strength decreases, and if the intermediate layer is too thin, the bending elastic modulus decreases, and Since the bending strength will decrease even if any of them is thinned, the outermost layer has a thickness ratio of 12 to 2 in order to make the bending strength, bending elastic modulus, and crushing strength optimal for the current situation (as a fishing rod).
0%, 74-85% for the intermediate layer, 5-12% for the innermost layer, preferably 12-14% for the outermost layer, and 74-78 for the intermediate layer.
%, And the innermost layer is 10 to 12%. That is, since reinforcing fibers having different mechanical properties are used for the outermost layer and the innermost layer, a cylindrical body having a so-called asymmetric structure with respect to the intermediate layer is formed.

The content of the reinforcing fiber in each layer is preferably in the range of 40 to 70% by volume in order to make the mechanical properties of the cylinder higher.

(FRP manufacturing method) In order to manufacture the cylindrical body of the present invention, a conventionally known mandrel having the same outer diameter as the inner diameter of the cylindrical body is wrapped with a prepreg in the order of the innermost layer, the intermediate layer and the outermost layer, and lapping is performed. A method such as winding and molding a tape can be used.

[0020]

Example The following prepreg was produced.

Prepreg A: PAN-based carbon fiber A (average single yarn diameter: 4.7 μm, strand tensile strength: 400 kgf /
mm ² , Strand Tensile Elastic Modulus: 60000 kgf / mm ² , Crystal Size: 62 Å, Crystal Orientation: 94
%) Parallel to each other and aligned in a sheet shape to prepare a unidirectional prepreg impregnated with B stage epoxy resin (composite compression strength: 90 kgf / m
m ² ). The carbon fiber content was 49% by volume.

Prepreg B: PAN carbon fiber B (average single yarn diameter: 4.6 μm, strand tensile strength: 380 kgf /
mm ² , Strand Tensile Modulus: 65000 kgf / mm ² , Crystal Size: 61 Å, Crystal Orientation: 95
%) Parallel to each other and aligned in a sheet shape to prepare a unidirectional prepreg impregnated with a B-stage epoxy resin (composite compression strength: 85 kgf / m
m ² ). The carbon fiber content was 66% by volume.

Prepreg C: PAN-based carbon fiber C (average single yarn diameter: 5.2 μm, strand tensile strength: 450 kgf /
mm ² , Strand Tensile Modulus: 38500 kgf / mm ² , Crystal Size: 32 Å, Crystal Orientation: 88
%) In parallel with each other and aligned in a sheet form to prepare a unidirectional prepreg impregnated with B-stage epoxy resin (composite compressive strength: 120 kgf / m
m ² ). The carbon fiber content was 51% by volume.

Prepreg D: PAN-based carbon fiber D (average single yarn diameter: 5.0 μm, strand tensile strength: 400 kgf /
mm ² , Strand Tensile Elastic Modulus: 48500 kgf / mm ² , Crystal Size: 50 Å, Crystal Orientation: 91
%) In parallel with each other in a sheet shape and impregnated with B-stage epoxy resin to prepare a unidirectional prepreg (composite compression strength: 100 kgf / m
m ² ). The carbon fiber content was 49% by volume.

Prepreg E: PAN-based carbon fiber E (average single yarn diameter: 6.9 μm, strand tensile strength: 500 kgf /
mm ² , Strand Tensile Modulus: 23500 kgf / mm ² , Crystal Size: 19 Å, Crystal Orientation: 80
%) Parallel to each other and aligned in a sheet form to prepare a unidirectional prepreg impregnated with B-stage epoxy resin (composite compressive strength: 150 kgf / m
m ² ). The carbon fiber content was 50% by volume.

Prepreg F: A prepreg was prepared in the same manner using PAN-based carbon fiber E. The carbon fiber content of this prepreg was 65%.

The crystal size of the carbon fiber was measured as follows.

The X-ray source was obtained by scanning the peak of the plane index (002) observed near 2θ = 26.0 ° in the equatorial direction using Cu Kα rays monochromated by a Ni filter. The full width at half maximum was obtained from the peak, and the crystal size (Lc) was calculated by the following formula.

Lc = λ / (β ₀ cos θ) β ₀ ² = β _e ² −β ₁ ² (λ: wavelength of X-ray, θ: diffraction angle, β ₀ : true half width, β
_e : Apparent half width, β ₁ : Device constant) The degree of crystal orientation was measured as follows.

The degree of crystal orientation π ₀₀₂ (%) was obtained from the half width (H) of the spread of the profile in the meridional direction containing the highest intensity of (002) diffraction obtained by the same analysis method as the crystal size using the following formula. I asked.

Π ₀₀₂ = [(180−H) / 180] × 100 (Example 1) A prepreg A was placed on a mandrel having an outer diameter of 20 mm and a length of 1000 mm, and its carbon fiber direction was 90 ° with respect to the mandrel. Winding, then prepreg B
Wrap it so that it becomes 0 °, and then prepreg D 90
It was wound so as to be at a temperature of 0 °, and further wrapped with a wrapping tape and heated at 130 ° C. for 120 minutes for molding to obtain a cylindrical body having an inner diameter of 20 mm, an outer diameter of 20.5 mm and a length of 850 mm. The carbon fiber content of this cylinder was 51% by volume in the outermost layer, 66% by volume in the intermediate layer, and 49% by volume in the innermost layer.
The thickness of each layer was 15.2% of the outermost layer, 76% of the intermediate layer, and 8.8% of the innermost layer with respect to the thickness of the cylinder, and the ratio of the thickness to the average radius of the cylinder was 0.03.

The distance between the branches of this cylinder is 750 m.
When a 4-point bending test was performed at m, span length of 200 mm, and load speed of 10 mm / min, the bending strength was 68 kgf / mm ² , and the bending elastic modulus was 30800 kgf / mm ² .

Further, a cylindrical body manufactured in the same manner is used to have a length of 15
When a test piece cut into mm was subjected to a uniform compression test (hereinafter, crush test) in the radial direction of the cylinder, the crush strength was 4.0 kgf.

(Comparative Example 1) Outer diameter 20 mm, length 1000 mm
Wrap the prepreg D around the mandrel at 90 ° with respect to the carbon fiber direction, then wrap the prepreg B at 0 °, and then wrap the prepreg A at 90 °. Then, a wrapping tape was further wound and heated at 130 ° C. for 120 minutes for molding to obtain a cylindrical body having an inner diameter of 20 mm, an outer diameter of 20.5 mm and a length of 850 mm. The carbon fiber content of this cylinder is 49% by volume in the outermost layer, 66% by volume in the intermediate layer, and 51% by volume in the innermost layer.
And the thickness of each layer relative to the cylinder thickness is the outermost layer 12.
2%, middle layer 76.3%, innermost layer 11.5%, and the ratio of the wall thickness to the cylinder average radius was 0.03.

The distance between the branches of this cylinder is 750 m.
When a 4-point bending test was performed at m, span length of 200 mm, and load speed of 10 mm / min, the bending strength was 68 kgf / mm ² , and the bending elastic modulus was 30800 kgf / mm ² .

Further, a cylindrical body manufactured in the same manner is used as a length 15
The test piece cut into mm was subjected to a uniform compression test (hereinafter, crush test) in the radial direction of the cylinder, and the crush strength was 2.7 kgf.

(Example 2) Outer diameter 20 mm, length 1000 mm
Wrap the prepreg A around the mandrel so that its carbon fiber direction is 90 ° with respect to the mandrel, then wrap the prepreg B at 0 °, and then prepreg C at 90 °. Wrapping, further wrapping with a wrapping tape, heating at 130 ° C. for 120 minutes to mold, and forming according to the present invention, inner diameter 20 mm, outer diameter 20.5
A cylindrical body having a length of 850 mm and a length of 850 mm was obtained. The carbon fiber content of this cylinder is 51% by volume for the outermost layer and 66% by volume for the intermediate layer.
The innermost layer is 49% by volume, and the ratio of the thickness of each layer to the cylindrical wall thickness is 12.5% in the outermost layer, 75.5% in the middle layer, and 12% in the innermost layer, and the ratio of the wall thickness to the cylinder average radius is Was 0.03.

When this cylinder was subjected to the same bending test as in Example 1, the bending strength was 68 kgf / mm ² and the bending elastic modulus was 30800 kgf / mm ² . Further, when a crush test was conducted on a test piece obtained by cutting a cylindrical body produced in the same manner to a length of 15 mm, the crush strength was 4.4 kgf.

(Comparative Example 2) Outer diameter 20 mm, length 1000 mm
Wrap the prepreg A around the mandrel so that its carbon fiber direction is 90 ° to the mandrel, then wrap the prepreg B at 0 °, and then prepreg E at 90 °. , Further wrapped with wrapping tape and heated at 130 ° C. for 120 minutes to be molded, according to the present invention, inner diameter 20 mm, outer diameter 20.5 mm,
A cylinder having a length of 850 mm was obtained. The carbon fiber content of this cylinder is 50% by volume in the outermost layer, 66% by volume in the intermediate layer, and 49% by volume in the innermost layer, and the ratio of the thickness of each layer to the cylindrical wall thickness is 12.2% in the outermost layer. The middle layer is 75.6% and the innermost layer is 12%, and the ratio of the wall thickness to the cylinder average radius is
It was 0.03.

When this cylinder was subjected to the same bending test as in Example 1, the bending strength was 62 kgf / mm ² and the bending elastic modulus was 30900 kgf / mm ² . Furthermore, when a crush test was conducted on a test piece obtained by cutting a cylindrical body produced in the same manner to a length of 15 mm, the crush strength was 5.1 kgf.

(Comparative Example 3) Outer diameter 20 mm, length 1000 mm
Wrap the prepreg A around the mandrel so that its carbon fiber direction is 90 ° with respect to the mandrel, then wrap the prepreg F at 0 °, and then prepreg C at 90 °. Wrapping, further wrapping with a wrapping tape, heating at 130 ° C. for 120 minutes to mold, and forming according to the present invention, inner diameter 20 mm, outer diameter 20.5
A cylindrical body having a length of 850 mm and a length of 850 mm was obtained. The carbon fiber content of this cylinder is 49% by volume of the outermost layer, 65% by volume of the intermediate layer, and 49% by volume of the innermost layer, and the ratio of the thickness of each layer to the thickness of the cylinder is 12.4% of the outermost layer and 75% of the intermediate layer. .6%, innermost layer 1
1.9%, and the ratio of the wall thickness to the cylinder average radius is
It was 0.03.

When this cylinder was subjected to the same bending test as in Example 1, the bending strength was 54 kgf / mm ² and the bending elastic modulus was 10100 kgf / mm ² . Furthermore, when a crush test was conducted on a test piece obtained by cutting a cylindrical body produced in the same manner to a length of 15 mm, the crush strength was 4.3 kgf.

(Comparative Example 4) Outer diameter 20 mm, length 1000 mm
Wrap the prepreg E around the mandrel of 90 ° so that the carbon fiber direction is 90 ° with respect to the mandrel, then wrap the prepreg B at 0 °, and then prepreg C above 90 °. Wrapping, further wrapping with a wrapping tape, heating at 130 ° C. for 120 minutes to mold, and forming according to the present invention, inner diameter 20 mm, outer diameter 20.5
A cylindrical body having a length of 850 mm and a length of 850 mm was obtained. Furthermore, length 15mm
The test piece of was also obtained. The carbon fiber content of this cylinder was 49% by volume in the outermost layer, 66% by volume in the intermediate layer, and 50% by volume in the innermost layer. The thickness of each layer relative to the cylinder thickness was 12.5% in the outermost layer. The intermediate layer had 75.5% and the innermost layer had 12%, and the ratio of the wall thickness to the cylinder average radius was 0.03.

When this cylinder was subjected to the same bending test as in Example 1, the bending strength was 59 kgf / mm ² and the bending elastic modulus was 30900 kgf / mm ² . Furthermore, when a crush test was conducted on a test piece obtained by cutting a cylindrical body produced in the same manner to a length of 15 mm, the crush strength was 4.3 kgf.

(Comparative Example 5) Outer diameter 20 mm, length 1000 mm
Wrap the prepreg A around the mandrel so that its carbon fiber direction is 90 ° to the mandrel, then wrap the prepreg B at 0 °, and then prepreg C at 90 °. , Further wrapped with wrapping tape and heated at 130 ° C. for 120 minutes to be molded, according to the present invention, inner diameter 20 mm, outer diameter 20.5 mm,
A cylinder having a length of 850 mm was obtained. The carbon fiber content of this cylinder is 49% by volume of the outermost layer, 66% by volume of the intermediate layer, and 51% by volume of the innermost layer, and the ratio of the thickness of each layer to the thickness of the cylinder is 23.6% of the outermost layer and the intermediate layer. 61.9%, innermost layer 1
4.5%, and the ratio of the wall thickness to the average radius of the cylinder is
It was 0.03.

When this cylinder was subjected to the same bending test as in Example 1, the bending strength was 62 kgf / mm ² and the bending elastic modulus was 24000 kgf / mm ² . Further, when a crush test was conducted on a test piece obtained by cutting a cylindrical body produced in the same manner to a length of 15 mm, the crush strength was 6.0 kgf.

[0047]

EFFECTS OF THE INVENTION The cylindrical body of the present invention is bent by arranging an intermediate layer and an innermost layer having a high elastic modulus inside the outermost layer having a high compressive strength and setting the thickness of each layer within a specific range. When subjected to stress, the bending properties of the entire cylindrical body are improved and the crush strength in the radial direction of the cylinder is improved. Furthermore, even if the bending characteristics are the same as the current one, the thickness of each layer can be reduced and the wall thickness of the cylinder can be reduced, so that the weight of the cylinder can be reduced. With such a cylindrical body, it is possible to further reduce the weight of various frame members, structural members such as pipes and shafts, and fishing rods, golf club shafts, ski poles, stanchion columns, and the like in aircraft, automobiles, bicycles, and the like.

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Claims (4)

[Claims] 1. A cylinder comprising an outermost layer in which reinforcing fibers are arranged at right angles to the cylinder axis direction, an intermediate layer arranged in the cylinder axis direction, and an innermost layer arranged at right angles to the cylinder axis direction. In the body, the ratio of the thickness of each layer to the thickness of the cylindrical body is 12 to 20% of the outermost layer, 74 to 85% of the intermediate layer, and 5 to 12% of the innermost layer, and the compressive strength of the outermost layer is 100 kg.
Reinforcing fibers of f / mm ² or more, the intermediate layer has a compressive strength of 8
Reinforcing fibers 0 kgf / mm ² or more and a tensile elastic modulus is 50000kgf / mm ² or more, the innermost layer, a tensile modulus of 5000
A fiber reinforced plastic cylinder characterized by using a reinforcing fiber of 0 kgf / mm ² or more. 2. A cylinder comprising an outermost layer in which reinforcing fibers are arranged at right angles to the cylinder axis direction, an intermediate layer arranged in the cylinder axis direction, and an innermost layer arranged at right angles to the cylinder axis direction. In the body, the ratio of the thickness of each layer to the thickness of the cylindrical body is 12 to 20% in the outermost layer, 74 to 85% in the intermediate layer, and 5 to 12% in the innermost layer, and the outermost layer has a tensile elastic modulus of 300.
00~50000kgf / mm ² at a carbon fiber, the intermediate layer, carbon fiber tensile modulus of 50000~70000kgf / mm ^2, the innermost layer has a tensile modulus of 50000Kgf /
A cylinder made of fiber reinforced plastic, characterized in that carbon fiber having a size of mm ² or more is used. 3. The fiber-reinforced plastic cylindrical body according to claim 2, wherein the carbon fibers of the outermost layer and the intermediate layer are polyacrylonitrile-based carbon fibers. 4. The outermost carbon fiber has a crystal size of 20-.
55 angstrom, the degree of crystal orientation is 83-92%, and the carbon fiber of the intermediate layer has a crystal size of 55-62 angstrom and the degree of crystal orientation of 92-95%. Fiber reinforced plastic cylinder.