curved pipe

Abstract

To provide a curved pipe having a cylindrical braided structure, which is free from orientation disturbance such as fiber undulation even when curving processing is performed in an axial direction and maintains a mechanical property at a high level in the axial direction.SOLUTION: There is provided a curved pipe 1 having a cylindrical braided structure, comprising: an inner layer braided sleeve 11; an intermediate layer braided sleeve 13; and an outer layer braided sleeve 12. The intermediate layer braid sleeve 13 is configured as a tubular braid formed by combining an axial yarn 132 formed of high strength fiber and oriented in a central axis direction X with an intermediate layer braid yarn 131 formed of elastic yarn and oriented at an orientation angle in a range of ±5 to 85°. The inner layer braid sleeve 11 (outer layer braid sleeve 12) is configured as a tubular braid without an axial thread, which is formed by combining an inner layer braid yarn 111 (outer layer braid yarn 121) made of high-strength fiber and oriented at an angle relative to the central axis direction X in a range of ±5 to 85°.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to a bent pipe with a braided structure. [Background technology]

[0002] Next-generation mobility devices such as large drones (large unmanned aerial vehicles) and flying cars are composed of components such as the main frame, propellers, propeller guards, arms, and skids (legs). To reduce weight, cylindrical components are used for these parts, and furthermore, because high rigidity is required, it is envisioned that cylindrical assemblies made of fiber-reinforced plastic (FRP), which are constructed using braiding technology with fibrous materials (braided yarn) and resin molding, will be used.

[0003] To improve the axial mechanical properties of such tubular structures, it is conceivable to orient high-strength (high modulus of elasticity) fiber materials in the axial direction. For example, Patent Document 1 discloses a tubular preform manufactured by laminating cylindrical assemblies. Patent Documents 2 to 4 disclose tubular preforms and curved pipes manufactured by laminating reinforced fiber sheets (prepreg UD sheets). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 1992-327910 [Patent Document 2] Japanese Patent Publication No. 2021-094739 [Patent Document 3] Japanese Patent Publication No. 2018-038463 [Patent Document 4] Japanese Patent Publication No. 1995-223271 [Disclosure of the Invention] [Problems that the invention aims to solve]

[0005] However, in the case of a straight pipe, it is sufficient to simply orient a high-strength (high modulus of elasticity) fiber material in the axial direction. But in the case of a curved pipe with a bent shape, if the axial mechanical properties are too high, it becomes difficult to process it for bending. Even if it can be bent, the axial orientation of the fiber material becomes disordered.

[0006] Specifically, the tubular preform described in Patent Document 1 has layers of weaving angles from the inside out: a layer with a 0° weaving angle (a braided sleeve combining unidirectional fibers and elastic yarn (nylon crimped yarn)), a layer with ±α° weaving angles, and a layer with a 0° weaving angle. Because there are two layers with a 0° weaving angle, it is difficult to bend the tubular preform in the axial direction. Even if it is bent, the yarn in the outer 0° layer of the tubular preform may unravel. As a result, the yarn in the 0° layer does not follow the axial direction, causing fiber waviness, which can reduce the axial tensile and bendable properties of the bent tubular preform.

[0007] Furthermore, regarding the tubular preforms and curved pipes described in Patent Documents 2 to 4, the laminated prepreg UD sheets (0° yarn) have such rigidity that they cannot be bent. If they are forcibly bent, the laminated prepreg UD sheets (0° yarn) will not follow the axial direction, causing fiber waviness to occur, which may reduce the axial tensile and bendable properties of the curved pipe.

[0008] Thus, in the case of curved pipes, curved pipes with high-level axial mechanical properties involve conflicting factors in terms of physical properties and manufacturing, requiring ingenuity to achieve a balance between them.

[0009] Therefore, the object of the present invention is to provide a curved tube with a tubular braided structure in which there is no orientation disorder such as fiber waviness even when bent in the axial direction, and in which the axial mechanical properties are maintained at a high level. [Means for solving the problem]

[0010] The present invention relates to a curved tube having a tubular braided structure comprising an inner layer, an outer layer, and an intermediate layer disposed between the inner layer and the outer layer, The aforementioned intermediate layer is An axial thread formed of high-strength fibers and oriented in the direction of the central axis of the curved tube, The curved tube is oriented at an orientation angle within the range of ±5 to 85° with respect to its central axis, and the structure consists of one or more stacked tubular braids formed by combining it with an intermediate layer braid made of elastic yarn. The aforementioned inner layer is It is arranged on the inner circumference side of the intermediate layer, The curved tube is oriented at an orientation angle within the range of ±5 to 85° with respect to its central axis, and the structure consists of one or more stacked tubular braids without an axis thread, formed by combining inner layer braids made of high-strength fibers. The aforementioned outer layer is It is arranged on the outer periphery side of the intermediate layer, The curved tube is oriented at an orientation angle of ±5 to 85° with respect to its central axis, and is characterized by having one or more tubular braids without axial threads, formed by combining braided outer layers made of high-strength fibers.

[0011] According to the above configuration, in the intermediate layer, the high-strength axolus threads are fixed to the flexible elastic threads, resulting in a flexible braid. This makes it possible to easily bend the curved tube while maintaining the orientation of the axolus threads (the axolus threads remain aligned along the central axis of the curved tube). Furthermore, when bending a curved tube, the axial threads of the intermediate layer are covered by the inner and outer layers, allowing the axial threads to remain unraveled and maintain their orientation toward the central axis while the tube is bent. Furthermore, since the inner and outer layers do not contain axial threads oriented in the direction of the central axis, the inner and outer layers can be designed so as not to hinder the bending process of the curved tube (making it easier to follow the shape changes when the curved tube is bent). That is, even when bending is performed in the central axis direction of the bent pipe, no orientation disturbance such as fiber undulation occurs, and a bent pipe in which the mechanical properties in the central axis direction are maintained at a high level can be obtained.

[0012] Further, in the present invention, in the inner layer and the outer layer of the bent pipe, the width of the braided yarn for the inner layer or the width of the braided yarn for the outer layer is b f [mm] the number of braided yarns for the inner layer or the number of braided yarns for the outer layer is n [sheets] the inner diameter of the inner layer or the inner diameter of the outer layer is D [mm] the orientation angle of the braided yarn for the inner layer or the orientation angle of the braided yarn for the outer layer is θ [°] when defined as above, the value of the inner cover factor cf1(in), which is obtained by the following (Formula 1) and represents the ratio of the area occupied by the inner layer braided yarn to the surface area of the inner layer or the ratio of the area occupied by the outer layer braided yarn to the surface area of the outer layer on the inner circumferential side of the bent portion of the bent pipe, is 60% or more and 100% or less, and the value of the outer cover factor cf1(out), which is obtained by the following (Formula 1) and corresponds to the outer circumferential side of the bent portion of the bent pipe and represents the ratio of the area occupied by the inner layer braided yarn to the surface area of the inner layer or the ratio of the area occupied by the outer layer braided yarn to the surface area of the outer layer, is 50% or more and 100% or less. [Numerical formula] ···(Formula 1)

[0013] As in the above configuration, in a case where the inner layer and the outer layer are formed only of braided yarns (inner layer braided yarns and outer layer braided yarns) without including axial yarns, and the value of the inner cover factor cf1(in) on the inner circumferential side of the bent portion of the bent pipe and the value of the outer cover factor cf1(out) on the outer circumferential side of the bent portion of the bent pipe satisfy the above conditions, a decrease in strength and uneven strength of the bent pipe can be prevented, and the torsional strength of the bent pipe itself can be increased.

[0014] Further, in the present invention, in the intermediate layer of the bent pipe, the width of the braided yarn for the intermediate layer is b f[mm] The number of braided yarns for the intermediate layer is n [threads] The inner diameter of the aforementioned intermediate layer is D[mm] The orientation angle of the braided yarn for the intermediate layer is θ[°] The width of each cell in the intermediate layer is f [mm] The width of the aforementioned axial thread is b m [mm] The number of the aforementioned axial threads is n m [Book] In this case, the inner cover factor cf3(in), which indicates the ratio of the braided yarn for the intermediate layer and the axle yarn to the surface area of ​​the intermediate layer on the inner circumference side of the bent portion of the bent tube, is 60% or less and is determined by the following (Equation 2), and the outer cover factor cf3(out), which indicates the ratio of the braided yarn for the intermediate layer and the axle yarn to the surface area of ​​the intermediate layer on the outer circumference side of the bent portion of the bent tube, is 50% or less and is determined by the following (Equation 2).

number

[0015] As described above, in the intermediate layer formed by combining the braided yarn for the intermediate layer and the axis yarn, if the value of the inner cover factor cf3(in) on the inner circumference side of the bent portion of the curved tube and the value of the outer cover factor cf3(out) on the outer circumference side of the bent portion of the curved tube satisfy the above conditions, it is possible to prevent a decrease in strength or uneven distribution of strength of the curved tube and to increase the torsional strength of the curved tube itself.

[0016] Furthermore, the present invention may be characterized in that, in the curved pipe described above, multiple sets of assembled sleeves, each consisting of an inner layer, an intermediate layer, and an outer layer arranged in order from the inner circumference, are stacked on top of each other.

[0017] According to the above configuration, the flexibility and strength of the curved pipe can be changed according to the required specifications by changing the number of sets of assembled sleeves that make up the curved pipe. [Effects of the Invention]

[0018] Regarding curved pipes with a tubular braided structure, it is possible to provide curved pipes in which there is no orientation disorder such as fiber waviness even when bending in the axial direction, and in which the axial mechanical properties are maintained at a high level. [Brief explanation of the drawing]

[0019] [Figure 1] This is an explanatory diagram of a curved pipe according to this embodiment. [Figure 2] (A) A cross-sectional view of the curved pipe according to this embodiment. (B) An explanatory diagram of the three-layer structure of the curved pipe according to this embodiment. [Figure 3] This is an explanatory diagram of the braided structure (1 cell) of the inner layer braided sleeve and the outer layer braided sleeve. [Figure 4] (A) An explanatory diagram of a braided structure (1 cell) formed only of the braided yarn for the intermediate layer in a braided sleeve for the intermediate layer. (B) An explanatory diagram of a braided structure (1 cell) formed of the braided yarn for the intermediate layer and the core yarn in a braided sleeve for the intermediate layer. [Figure 5] This is an explanatory diagram of the braided structure of the bent portion of the curved pipe according to this embodiment. [Figure 6] (a) This is an explanatory diagram of the sleeve braiding process. (b) This is an explanatory diagram of the spindle trajectory in the sleeve braiding process. [Figure 7] This is an explanatory diagram of the manufacturing process for preforms. [Figure 8] This is an explanatory diagram regarding the installation of the preform into the mold. [Figure 9] This is an explanatory diagram regarding the resin molding process for preforms. [Figure 10] This is an explanatory diagram regarding the removal of preforms from a mandrel after resin molding. [Figure 11] This is a photograph of the exterior of a manufactured curved pipe. [Figure 12] This is a cross-sectional view of a curved pipe according to another embodiment. [Figure 13] This is an explanatory diagram of a method for measuring the fracture strength of a bent pipe. [Figure 14]This is an explanatory diagram of the inner and outer sides of the bent portion (central curve) of a curved pipe, which is the subject of measurement for the tensile modulus of elasticity. [Modes for carrying out the invention]

[0020] (Embodiment) Embodiments of the present invention will be described below with reference to the drawings.

[0021] (Bent pipe 1) As shown in Figures 1 and 2, the curved pipe 1 is a cylindrical tube with a circular cross-section, made of fiber-reinforced plastic (FRP), constructed by a braided structure using braided threads (such as carbon fiber material) and resin molding, and is bent at a certain bending angle.

[0022] For example, the curved pipe 1 is used as a component of a large drone (large unmanned aerial vehicle) that transports cargo unmanned (the main frame (which forms the space for storing the cargo to be transported), propellers, propeller guards, arms connecting the propellers to the main frame, and skids (legs) that make up the large drone). The main frame, propellers, propeller guards, arms, and skids that make up these large drones have curved sections in their shape and are required to be lightweight, highly rigid, and have excellent vibration damping properties. In addition, even when the curved pipe 1 is bent in the central axis direction X, there should be no orientation disturbance such as fiber waviness, and the mechanical properties in the central axis direction X should be maintained at a high level.

[0023] The curved pipe 1 has a structure in which at least three layers of cylindrical assembled sleeves are stacked on top of each other. Specifically, as shown in Figure 2(A), the curved pipe 1 has a structure in which three layers are stacked: an inner layer assembly sleeve 11 (corresponding to the inner layer) that constitutes the inner circumference of the curved pipe 1, an outer layer assembly sleeve 12 (corresponding to the outer layer) that constitutes the outer circumference of the curved pipe 1, and an intermediate layer assembly sleeve 13 (intermediate layer) that is stacked (placed) between the inner layer assembly sleeve 11 and the outer layer assembly sleeve 12.

[0024] (Inner layer assembly sleeve 11) The inner layer assembly sleeve 11 is laminated on the inner circumference side of the intermediate layer assembly sleeve 13. As shown in Figures 2(B) and 3, the inner layer braided sleeve 11 is formed by combining inner layer braided yarns 111, which are made of high-strength (high modulus) fibers, oriented at an orientation angle (θ) of ±5 to 85° with respect to the central axis X of the curved tube 1, and intersecting each other. Here, the inner layer braided sleeve 11 does not have axial yarns that are oriented in the central axis X of the curved tube 1.

[0025] High-strength (high modulus) fibers that make up the inner layer yarn 111 of the inner layer braided sleeve 11 can include, for example, carbon fibers, glass fibers, aramid fibers, boron fibers, silicon carbide fibers, steel fibers, polyethylene fibers, nylon fibers, alumina fibers, tyranno fibers, basalt fibers, amorphous fibers, etc.

[0026] (Outer layer assembly sleeve 12) The outer layer assembly sleeve 12 is laminated on the outer circumference side of the intermediate layer assembly sleeve 13. The outer layer braided sleeve 12, like the inner layer braided sleeve 11, is formed by combining outer layer braided yarns 121 made of high-strength (high modulus) fibers, which are oriented at an orientation angle (θ) of ±5 to 85° with respect to the central axis X of the curved tube 1, and intersecting each other, as shown in Figures 2(B) and 3. Here, the outer layer braided sleeve 12, like the inner layer braided sleeve 11, does not have axial yarns oriented in the central axis X of the curved tube 1. Furthermore, the high-strength (high modulus of elasticity) fibers that make up the outer layer yarn 121 of the outer layer braided sleeve 12 are the same as those used in the inner layer braided sleeve 11.

[0027] (Intermediate layer assembly sleeve 13) The intermediate layer assembly sleeve 13 is laminated between the inner layer assembly sleeve 11 and the outer layer assembly sleeve 12. As shown in Figures 2(B) and 4, the intermediate layer braided sleeve 13 is formed by combining an axis yarn 132 made of high-strength (high modulus) fibers, which is oriented in the direction of the central axis X of the curved tube 1 (orientation angle with respect to the central axis X is 0°), and an intermediate layer braided yarn 131 made of elastic yarn, which is oriented in the direction of the central axis X within a range of ±5 to 85°, so as to intersect.

[0028] High-strength (high modulus) fibers that constitute the axial thread 132 of the intermediate layer braided sleeve 13 can include, for example, carbon fibers, glass fibers, aramid fibers, boron fibers, silicon carbide fibers, steel fibers, polyethylene fibers, nylon fibers, alumina fibers, tyranno fibers, basalt fibers, amorphous fibers, etc.

[0029] As the elastic yarn constituting the intermediate layer yarn 131 of the intermediate layer braided sleeve 13, for example, false-twist yarn (also called crimped yarn or woolly yarn) obtained by processing multifilament yarn or monofilament yarn made of thermoplastic resins such as nylon resin, butylene terephthalate resin, or polyester resin, or urethane fibers can be used.

[0030] (Resin molding of curved pipe 1) Furthermore, as resin materials used for resin molding of the braided structure of the curved pipe 1 (inner layer assembly sleeve 11, outer layer assembly sleeve 12, intermediate layer assembly sleeve 13), examples include thermosetting resins (matrix resins) such as epoxy resin, polyester resin, vinyl ester resin, phenolic resin, and polyurethane resin, as well as thermoplastic resins such as nylon resin, polyethylene resin, polypropylene resin, polyphenylene sulfide resin, polyether ether ketone resin, polycarbonate resin, acrylonitrile-butadiene-styrene copolymer resin (ABS resin), polyacetal resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polystyrene resin, acrylonitrile-styrene resin, polyvinyl chloride resin, and acrylic resin. Furthermore, resin molding methods include resin transfer molding (RTM: vacuum suction and pressure impregnation), VaRTM (vacuum impregnation method), and internal pressure molding.

[0031] (Braided structure of the bent portion 2 of the curved pipe 1) When forming a curved pipe 1, as shown in Figure 5, it is necessary to braid the bent portion 2 in a curved shape. However, compared to braiding in a straight line, the braided structure is compressed on the inner circumference 21 of the bent portion 2, while it is stretched on the outer circumference 22 of the bent portion 2, which can cause an imbalance (difference in strength) in the braided structure of the curved pipe 1. If such an imbalance occurs in the braided structure of the curved pipe 1, the rigidity and impact resistance of the curved pipe 1 will decrease.

[0032] Therefore, using an index (value) called cover factor cf (Equations 1 to 3), which is an indicator of the strength of the curved pipe 1 having a braided structure with a circular cross-section, the braided structure of each bent portion of the inner layer braided sleeve 11, outer layer braided sleeve 12, and intermediate layer braided sleeve 13 that constitute the curved pipe 1, the braided structure of each bent portion of the inner layer braided sleeve 11, outer layer braided sleeve 12, and intermediate layer braided sleeve 13 is formed.

[0033] Here, as shown in Figures 3 to 5, the width f [mm] per cell (one section surrounded by braided threads) of the braided structure is the same on the inner and outer sides of the bent portions of the inner layer braided sleeve 11, outer layer braided sleeve 12, and intermediate layer braided sleeve 13 that constitute the bent pipe 1. However, the orientation angle θ [°] with respect to the central axis X of the bent pipe 1 is different. Therefore, it is necessary to calculate the inner cover factor cf (in) on the inner side of the bent portion of the inner layer braided sleeve 11, outer layer braided sleeve 12, and intermediate layer braided sleeve 13 that constitute the bent pipe 1, and the outer cover factor cf (out) on the outer side of the bent portion of the inner layer braided sleeve 11, outer layer braided sleeve 12, and intermediate layer braided sleeve 13 that constitute the bent pipe 1. Furthermore, when calculating the cover factor cf, it is necessary to take into account cases where the cells of the braided structure are composed only of braided yarns (braided yarn for the inner layer 111, braided yarn for the outer layer 121), as shown in Figure 3, as in the case of the inner layer braided sleeve 11 and outer layer braided sleeve 12 (cf1), and cases where the cells (see Figure 4(A)) are composed only of braided yarns (braided yarn for the intermediate layer 131), as in the case of the intermediate layer braided sleeve 13 shown in Figure 4, as in the case of the braided structure (cf2) which includes both a braided structure (see Figure 4(B)) having braided yarns (braided yarn for the intermediate layer 131) and axle yarns (axle yarns 132) (cf3).

[0034] (Cover factor of inner layer assembly sleeve 11 and outer layer assembly sleeve 12) As shown in Figure 3, when the cells of the braided structure are composed only of inner layer braid yarn 111 (outer layer braid yarn 121), the width b of the inner layer braid yarn 111 (outer layer braid yarn 121) f Based on two-dimensional data such as the diameter [mm], the number of inner layer braids 111 (outer layer braids 121) n [strands], the inner diameter D [mm] of the inner layer braid sleeve 11 (outer layer braid sleeve 12), and the orientation angle θ [°] of the inner layer braid 111 (outer layer braid 121) with respect to the central axis X of the bent tube 1, the value of the inner cover factor cf1(in) on the inner circumference side of the bent portion of the inner layer braid sleeve 11 (outer layer braid sleeve 12) and the value of the outer cover factor cf1(out) on the outer circumference side of the bent portion of the inner layer braid sleeve 11 (outer layer braid sleeve 12) are calculated using the following (Equation 1).

[0035]

number

[0036] Furthermore, in cases where the braided structure consists only of inner braided yarn 111 (outer braided yarn 121), such as the inner braided sleeve 11 (outer braided sleeve 12) (where the braided structure does not include the axis yarn), by satisfying the conditions that the value of the inner cover factor cf1(in), calculated by (Equation 1) above, is within the range of 100% or less and 60% or more, and the value of the outer cover factor cf1(out), calculated by (Equation 1) above, is within the range of 100% or less and 50% or more, it is possible to prevent a decrease in strength or uneven distribution of strength in the bent portion 2 of the bent tube 1 and increase the torsional strength of the bent tube 1 itself.

[0037] With the inner layer assembly sleeve 11 described above, it is possible to prevent buckling failure of the axial thread 132 of the intermediate layer assembly sleeve 13 due to bending load, thereby increasing the torsional strength of the bent pipe 1 itself. Furthermore, with the outer layer assembly sleeve 12 described above, the axial thread 132 of the intermediate layer assembly sleeve 13 can be restrained, preventing bending and misalignment of the axial thread 132 at the bent portion 2. In addition, it is possible to prevent a decrease in strength or uneven distribution of strength of the bent tube 1 and increase the torsional strength of the bent tube 1 itself.

[0038] (Cover factor of the intermediate layer assembly sleeve 13) As shown in Figure 4, in the case where a cell (see Figure 4(A)) is composed only of the intermediate layer yarn 131 and a cell (see Figure 4(B)) is composed of the intermediate layer yarn 131 and a core yarn 132, the value of the cover factor cf3 is calculated by considering the cover factor cf1 in the cell where the braided structure is composed only of 131 (calculated in the same way as the inner layer braided sleeve 11: see Equation 1) as shown in Figure 4(A), and the cover factor cf2 in the cell where the braided structure is composed of the intermediate layer yarn 131 and a core yarn 132 as shown in Figure 4(B).

[0039] Here, as shown in Figure 4(B), if the cells of the braided structure include the intermediate layer yarn 131 and the core yarn 132, the width b of the intermediate layer yarn 131 f[mm], the number n of interlayer braided yarns 131 [pieces], the inner diameter D [mm] of the interlayer braided sleeve 13, and the orientation angle θ [°] of the interlayer braided yarn 131 relative to the central axis direction X, and further, the width f [mm] per cell of the braided structure (one compartment surrounded by the interlayer braided yarns 131: see FIG. 4(B)), the width b of the axial yarn 132 m [mm], and the number n of axial yarns 132 m Based on values derived from two-dimensional data such as [pieces], the value of the inner cover factor cf2(in) on the inner circumferential side of the bent portion of the interlayer braided sleeve 13 is calculated by the following (Formula 2), and the value of the outer cover factor cf2(out) on the outer circumferential side of the bent portion of the interlayer braided sleeve 13 is calculated by the following (Formula 2).

[0040] [Formula] ···(Formula 2)

[0041] As shown in FIGS. 4(A) and 4(B), in (Formula 2), A is the area of one cell of the braided structure of the interlayer braided sleeve 13, and A S is the area of the void portion excluding the interlayer braided yarn 131 portion in one cell of the braided structure of the interlayer braided sleeve 13, and A a is the area of the axial yarn 132 portion (excluding the portion overlapping with the interlayer braided yarn 131) in one cell of the braided structure of the interlayer braided sleeve 13.

[0042] Furthermore, to calculate the value of the cover factor cf3 when the braided structure includes a cell (see Figure 4(A)) composed solely of the intermediate layer braid yarn 131 and a braided structure (see Figure 4(B)) composed of the intermediate layer braid yarn 131 and the core yarn 132, as shown in Figure 4(A), the cover factor cf1 for a cell in which the braided structure is composed solely of the intermediate layer braid yarn 131 and the cover factor cf1 for a cell in which the braided structure is composed solely of the intermediate layer braid yarn 131 and the core yarn 132 By satisfying the conditions that the value of the inner cover factor cf3(in), calculated by the following (Equation 3) taking into account the cover factor cf2 in the cell composed of the above, is within the range of 60% or less and the value of the outer cover factor cf3(out), calculated by the following (Equation 3), is within the range of 50% or less and the value of the outer cover factor cf3(out), which is within the range of 50% or less, it is possible to prevent a decrease in strength or uneven distribution of strength in the bent portion 2 of the bent pipe 1 and to increase the torsional strength of the bent pipe 1 itself.

[0043] In the case of the braided sleeve 13 for the intermediate layer described above, since elastic yarn is used in the braided yarn 131 for the intermediate layer, the braided sleeve 13 for the intermediate layer itself can be made flexible, so that the axis yarn 132 can be uniformly arranged without seams along the central axis direction X in the bent portion 2 of the curved tube 1.

[0044]

number

[0045] Here, as described above, in the inner layer assembly sleeve 11, outer layer assembly sleeve 12, and intermediate layer assembly sleeve 13 that constitute the curved pipe 1, the inner cover factor cf(in) is within the range of 100% or less and 60% or more, and the outer cover factor cf(out) is within the range of 100% or less and 50% or more. This is because if the value of the inner cover factor cf(in) or the value of the outer cover factor cf(out) exceeds 100%, it will exceed the surface area of ​​the inner layer braided sleeve 11, outer layer braided sleeve 12, and intermediate layer braided sleeve 13, which are formed by the braided structure of the inner layer braided yarn 111 (outer layer braided yarn 121) and the braided structure of the intermediate layer braided yarn 131 and axis yarn 132. As a result, some of the inner layer braided yarn 111 (outer layer braided yarn 121), intermediate layer braided yarn 131, and axis yarn 132 will float on the surface of the bent tube 1, and loads may be placed on the floating part or its surroundings, potentially reducing the rigidity and impact resistance of the bent tube 1. Furthermore, if the value of the inner cover factor cf(in) is less than 60% or the value of the outer cover factor cf(out) is less than 50%, an imbalance (difference in strength) will occur in the strength of the braided structure between the inner circumference 21 and the outer circumference 22 of the bent portion 2 of the bent pipe 1, which may reduce the rigidity and impact resistance of the bent pipe 1.

[0046] Furthermore, in the inner layer assembly sleeve 11, outer layer assembly sleeve 12, and intermediate layer assembly sleeve 13 that constitute the curved pipe 1, from the viewpoint of further enhancing the rigidity and impact resistance of the curved pipe 1, it is more preferable that the value of the inner cover factor cf(in) is within the range of 100% or less and 70% or more, and the value of the outer cover factor cf(out) is within the range of 100% or less and 60% or more. Moreover, it is most preferable that the value of the inner cover factor cf(in) is within the range of 100% or less and 80% or more, and the value of the outer cover factor cf(out) is within the range of 100% or less and 70% or more.

[0047] (Manufacturing method for curved pipe 1) Next, we will explain the manufacturing method of the curved pipe 1.

[0048] (1) Sleeve braiding process First, as shown in Figure 6(a), the inner layer braided sleeve 11, the outer layer braided sleeve 12, and the intermediate layer braided sleeve 13 are manufactured using a braiding machine.

[0049] For example, in the case of an inner layer braided sleeve 11 (outer layer braided sleeve 12), the braided threads (inner layer braided threads 111 and outer layer braided threads 121) wound around a spindle are combined on the outer circumference of a cylindrical mandrel to form the inner layer braided sleeve 11 (outer layer braided sleeve 12). As shown in Figure 6(b), the spindle moves along a track, causing the braided threads (inner layer braided threads 111 and outer layer braided threads 121) to combine, forming a seamless inner layer braided sleeve 11 (outer layer braided sleeve 12) on the top of the mandrel, which is then wound up by a winding device.

[0050] In the case of an intermediate layer braided sleeve 13, the braided yarn (intermediate layer braided yarn 131) wound around the spindle and the shaft yarn 132 supplied from the bottom of the braiding machine (supplied from a fixed cylinder) are combined on the outer circumference of a cylindrical mandrel to form the intermediate layer braided sleeve 13. As shown in Figure 6(b), as the spindle moves along the track, the braided yarn (intermediate layer braided yarn 131) and the shaft yarn 132 are combined, forming a seamless intermediate layer braided sleeve 13 on the top of the mandrel, which is then wound up by a winding device.

[0051] Here, in the case where the braided structure consists only of inner layer braided yarn 111 (outer layer braided yarn 121), as in the inner layer braided sleeve 11 (outer layer braided sleeve 12) (the braided structure does not include the axis yarn), the width b of the inner layer braided yarn 111 (outer layer braided yarn 121) f The values ​​of various parameters such as the diameter [mm], the number of inner layer braids 111 (outer layer braids 121) n [strands], the inner diameter D [mm] of the inner layer braid sleeve 11 (outer layer braid sleeve 12), and the orientation angle θ [°] of the inner layer braids 111 (outer layer braids 121) with respect to the central axis X of the curved tube 1 must satisfy the conditions that the value of the inner cover factor cf1(in), calculated by (Equation 1) above, is within the range of 100% or less and 60% or more, and the value of the outer cover factor cf1(out), calculated by (Equation 1) above, is within the range of 100% or less and 50% or more.

[0052] Furthermore, in cases such as the braided sleeve 13 for the intermediate layer, where the cells (see Figure 4(A)) consist only of the braided yarn 131 for the intermediate layer, and the cells (see Figure 4(B)) include a braided structure having both the braided yarn 131 for the intermediate layer and the core yarn 132, the width b of the braided yarn 131 for the intermediate layer f [mm], n [number] intermediate layer yarns 131, inner diameter D [mm] of the intermediate layer braid sleeve 13, and orientation angle θ [°] of the intermediate layer yarns 131 with respect to the central axis X, in addition, f [mm] of one cell of the braided structure (one section surrounded by the intermediate layer yarns 131: see Figure 4(B)), and b [width] of the axis yarn 132. m [mm], and the number n of the axial threads 132. m The values ​​of various parameters such as [Book] must satisfy the following conditions: the value of the inner cover factor cf3(in), calculated by (Equation 3) above, is within the range of 100% or less and 60% or more; and the value of the outer cover factor cf3(out), calculated by (Equation 3) above, is within the range of 100% or less and 50% or more.

[0053] (2) Manufacturing of preforms Next, as shown in Figure 7, a preform is manufactured by stacking three layers of cylindrical assembly sleeves on a cylindrical silicone resin mandrel, in the order of inner layer assembly sleeve 11, intermediate layer assembly sleeve 13, and outer layer assembly sleeve 12. In this embodiment, a silicone resin mandrel is used for the shaft (rod) of the preform. However, the material used for the mandrel may be an elastic thermosetting resin or thermoplastic resin. Furthermore, by using materials such as wax, polystyrene foam, gypsum, or a low-melting-point alloy, it is possible to remove the shaft portion from the molded product even after molding.

[0054] (3) Installation into the mold Next, as shown in Figure 8, the mandrel with the stacked preforms is bent and fitted into the mold cavity, and then the lid is closed.

[0055] In this embodiment, regarding the manufacturing of the preform, three layers of cylindrical assembly sleeves (inner layer assembly sleeve 11, intermediate layer assembly sleeve 13, and outer layer assembly sleeve 12) are stacked on a cylindrical mandrel, and then the mandrel is bent. However, it is also possible to prepare a bent mandrel first, and then stack three layers of cylindrical assembly sleeves (inner layer assembly sleeve 11, intermediate layer assembly sleeve 13, and outer layer assembly sleeve 12) on this bent mandrel.

[0056] (4) Resin molding process Next, as shown in Figure 9, thermosetting resin (matrix resin) is pressure-injected into the mold cavity by resin transfer molding (RTM), impregnating the preform with the thermosetting resin, and any excess thermosetting resin is removed by vacuum suction. Furthermore, methods such as VaRTM (vacuum impregnation molding) or internal pressure molding may be used as resin molding methods.

[0057] (5) Removal of the mandrel Next, as shown in Figure 10, the mandrel is removed after the thermosetting resin impregnated into the preform has hardened.

[0058] (6) Finishing process Finally, deburring, cutting, and painting are performed to obtain the bent pipe 1 (see Figure 11).

[0059] According to the above configuration of the curved tube 1, in the intermediate layer braid sleeve 13, the high-strength shaft thread 132 is fixed to the flexible intermediate layer braid thread 131, resulting in a flexible braid. This makes it possible to easily bend the curved tube 1 while maintaining the orientation of the shaft thread 132 (the shaft thread 132 remains aligned along the central axis X of the curved tube 1). Furthermore, when bending the curved pipe 1, the axial thread 132 of the intermediate layer assembly sleeve 13 is covered by the inner layer assembly sleeve 11 and the outer layer assembly sleeve 12, so the axial thread 132 does not unravel and can be bent while maintaining its orientation toward the central axis X. Furthermore, since the inner layer assembly sleeve 11 and the outer layer assembly sleeve 12 do not contain axial threads oriented in the central axis direction X, the inner layer assembly sleeve 11 and the outer layer assembly sleeve 12 can be made so as not to hinder the bending process of the curved pipe 1 (making it easier to follow the shape changes when the curved pipe 1 is bent). In other words, even when bending the curved pipe 1 in the direction of its central axis X, there is no orientation disorder such as fiber waviness, and a curved pipe 1 can be obtained in which the mechanical properties in the direction of its central axis X are maintained at a high level.

[0060] Furthermore, when the above-mentioned curved pipe 1 is used in the main frame, propellers, propeller guards, arms, and skids of a large drone, which is a large unmanned aerial vehicle, it exhibits excellent lightness, high rigidity, and vibration damping properties. In addition, even when the curved pipe 1 is bent in the direction of its central axis X, there is no orientation disturbance such as fiber waviness, and the mechanical properties in the direction of its central axis X are maintained at a high level.

[0061] (Other embodiments) In the above embodiment, the curved pipe 1 was described as having a three-layer structure, with one inner layer assembly sleeve 11 as the inner layer, one outer layer assembly sleeve 12 as the outer layer, and one intermediate layer assembly sleeve 13 as the intermediate layer. However, depending on the balance between the flexibility and strength of the curved pipe 1, each layer may be constructed by stacking multiple assembly sleeves. For example, the inner layer may consist of multiple inner layer assembly sleeves 11 stacked on top of each other, the outer layer may consist of multiple outer layer assembly sleeves 12 stacked on top of each other, or the intermediate layer may consist of multiple intermediate layer assembly sleeves 13 stacked on top of each other. In this way, by changing the number of each assembly sleeve layered in the inner, outer, and intermediate layers, the flexibility and strength of the curved pipe 1 can be changed according to the required specifications.

[0062] Furthermore, in the above embodiment, if a set of assembled sleeves consists of an inner layer assembled sleeve 11 (1 piece), an intermediate layer assembled sleeve 13 (1 piece), and an outer layer assembled sleeve 12 (1 piece), which are stacked in order from the inner circumference side, then the bent pipe 1 is composed of one set of assembled sleeves. However, the configuration is not limited to this, and a bent pipe may be constructed by stacking multiple sets of assembled sleeves. For example, as shown in Figure 12, the curved pipe 101 has a configuration in which two sets of assembly sleeve groups 10 (10A, 10B) are stacked. That is, the curved pipe 101 has a configuration in which, from the inner circumference side, the inner layer assembly sleeve 11, the intermediate layer assembly sleeve 13, the outer layer assembly sleeve 12, the inner layer assembly sleeve 11, the intermediate layer assembly sleeve 13, and the outer layer assembly sleeve 12 are stacked in that order. In this way, by changing the number of sets of the assembled sleeve group 10 that make up the bent pipe 101, the flexibility and strength of the bent pipe 101 can be changed according to the required specifications.

[0063] Furthermore, although the above embodiment described the use of the bent pipe 1 in the main frame, propeller, propeller guard, arms, and skids that constitute a large drone, which is a large unmanned aerial vehicle, the bent pipe 1 may also be used in a manned aircraft (for example, a large drone-type flying taxi).

[0064] Although embodiments of the present invention have been described above, these are merely illustrative examples and do not particularly limit the present invention. The specific configurations of each means, etc., can be modified as appropriate. Furthermore, the effects described in the embodiments of the present invention are merely a list of the most preferred effects resulting from the present invention, and the effects of the present invention are not limited to those described in the embodiments. [Examples]

[0065] [Verification based on Examples 1-15 and Comparative Examples 1-4] The curved tube according to the present invention has a braided structure consisting of three layers: an "intermediate layer" formed from an axis yarn made of high-strength fibers and a braided yarn made of elastic fibers oriented at an orientation angle in the range of ±5 to 85°, and an "inner layer" and an "outer layer" which do not have an axis yarn and are made from braided yarn made of high-strength fibers oriented at an orientation angle in the range of ±5 to 85°. Even when bent, the orientation of the fibers is not disturbed and the axial mechanical properties are maintained at a high level.

[0066] Therefore, in this embodiment, curved pipes according to Examples 1 to 15 and Comparative Examples 1 to 4 were fabricated, and the tensile modulus of the curved pipes and straight pipes was measured, and the fracture strength of the curved pipes was measured, and a comparative verification was performed. The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0067] (Structure of a curved pipe made of fiber-reinforced plastic (FRP)) <High-strength fibers used in the braided structure of curved pipes> Table 1 lists the high-strength fibers used in the braided structure of curved pipes. [Table 1]

[0068] <Elastic yarn used in the braided structure of curved tubes> Table 2 lists the elastic yarns used in the braided structure of the curved tube. [Table 2]

[0069] <Resin composition for use in curved pipes> • Thermosetting resin: Vinyl ester resin (Brand name CBZ500LM-AS, viscosity 200-350 mPa·s, manufactured by Nippon Yupika) • Accelerator: Brand PR-CBZ01 (manufactured by Nippon Yupika) • Hardener: 328E (manufactured by Kayaku Nurion)

[0070] (Manufacturing method for curved pipes) Using the "Method for Manufacturing Curved Pipes" described in the above embodiments, FRP curved pipes with braided structures as shown in Examples 1 to 15 and Comparative Examples 1 to 4 in Tables 3 to 6 were manufactured. As an example, the dimensions and shape of the curved pipe of Example 1 are shown in Figure 13. The method for manufacturing straight pipes is the same as that for curved pipes, except that the shape of the mold cavity used for resin transfer molding (RTM) is straight.

[0071] (Evaluation of layered structure) [Table 3]

[0072] (Variable evaluation of orientation angle) [Table 4]

[0073] (Random evaluation of the coverage factor) [Table 5]

[0074] (Variable evaluation of the number of sleeve sets) [Table 6]

[0075] (Test method) <Method for measuring the tensile modulus of curved and straight pipes> Test specimens with dimensions of L50mm × W5mm × 1.5tmm were taken from the bent portion (central curved section) of the curved pipe manufactured using the above manufacturing method, one from the inside and one from the outside, using the water jet method (see Figure 14). Furthermore, two test specimens of the same dimensions as those of the curved pipe were collected from the center of the straight pipe in the longitudinal direction, facing each other in the circumferential direction, using the water jet method. Then, tensile tests were performed on test specimens taken from the bent portion (central curve) of the curved pipe and the central portion of the straight pipe, in accordance with JIS K7164 (2005), under conditions of 23±2°C and 50±10% humidity, at a speed of 1 mm / min. The tensile modulus E was calculated from the obtained stress-strain curves using (Equation 4).

[0076]

number

[0077] In this test, the region where the slope is a straight line is used as the strain reading range. σ1: Tensile stress (MPa) measured at strain ε1 = 0.0025 σ²: Tensile stress (MPa) measured at strain ε² = 0.0050 The tensile modulus E is calculated using the above (Equation 4). The tensile modulus of elasticity of the specimen taken from the inside of the bent section (central curve) of the curved pipe was defined as E(in), and the tensile modulus of elasticity of the specimen taken from the outside was defined as E(out). The average of E(in) and E(out) was taken as the tensile modulus of elasticity of the curved pipe. The tensile modulus of elasticity of the straight pipe was the average of the two values.

[0078] <Method for measuring the fracture strength of bent pipes> For the curved pipes manufactured using the above manufacturing method, the tensile test was performed in accordance with the tensile test method described in "Method for Measuring the Tensile Modulus of Curved and Straight Pipes" above. The chuck portion shown in Figure 13 was gripped with the chuck, and the test speed was set to 6 mm / min. The tensile stress (test force: F) until the test piece broke was measured, and the breaking strength was calculated using the following formula (Equation 5) (each test was performed 3 times).

[0079] <Settings for measuring the fracture strength of curved pipes> ·Equipment Autograph: Amsler Strain Gauge: KFGS-2-120-C1-11LIM3R, manufactured by Kyowa Electric Industry Co., Ltd. Strain gauge adhesive: CC-33A Kyowa Electric Industry • Condition adjustment Temperature 23±2℃, humidity 50±10%, 16 hours or more • Test conditions Test environment: Temperature 23±2℃, Humidity 50±10% Load cell capacity: 100kN Test speed: 6 mm / min Number of attempts: 3 Chuck section: Core metal inserted to prevent crushing by the chuck.

[0080]

number

[0081] (Regarding the test results) <Determination of pass / fail criteria for curved pipes> For FRP curved pipes, the requirement was that the fiber orientation remained undisturbed even after bending, and that the axial mechanical properties were maintained at a high level. Specifically, the decrease in tensile modulus after bending was small; in other words, it was considered acceptable if it maintained a value close to that of a straight pipe. As an index value, the ratio of the tensile modulus of the bent portion (central curve) of a curved pipe to the central portion of a straight pipe, calculated using the tensile modulus measurement method described above, was used as the retention rate, and the pipes were ranked according to the following criteria. Grade A: Tensile modulus retention rate (ratio of tensile modulus of curved pipe to straight pipe) is 0.8 or higher. Grade B: Tensile modulus retention rate (ratio of tensile modulus of curved pipe to straight pipe) is less than 0.8

[0082] Furthermore, since FRP curved pipes are expected to be used as structural components in large drones and other applications, fracture strength is crucial. The fracture strength of the bent pipes was calculated using the fracture strength measurement method described above and ranked according to the following criteria. Grade A: Breaking strength of 500 MPa or higher Grade B: Breaking strength between 400 MPa and less than 500 MPa C rating: Breaking strength is less than 400 MPa

[0083] Based on the overall assessment, candidates were ranked as follows: A (Pass), B (Pass), C (Pass), and D (Fail) according to the criteria in Table 7 below.

[0084] [Table 7]

[0085] <Test results for curved and straight pipes> (Evaluation of the laminated structure (Table 3)) [Comparative Example 1: An example of a three-layer structure in which the intermediate layer is formed only of axial yarn (without braided yarn)] In the sleeve braiding process, the absence of braiding threads to fix the axial threads of the intermediate layer disrupted the orientation of the axial threads, preventing the sleeve from maintaining its shape and making it impossible to manufacture curved and straight tubes.

[0086] [Comparative Example 2: An example of a three-layer structure in which the intermediate layer is composed of high-strength fibers] Because the intermediate sleeve, composed of high-strength fibers for both the core and braid threads, lacks flexibility, straight tubes could be manufactured. However, during the placement of the preform into the mold, the preform could not be bent, making it impossible to manufacture curved tubes.

[0087] [Comparative Example 3: An example of a three-layer structure in which the inner layer is formed from axial yarn and braided yarn, and the intermediate layer is formed from braided yarn alone] In the manufacturing of preforms, the frictional force between the inner sleeve and the silicone resin mandrel was so large that the inner sleeve could not be fitted onto the mandrel, making it impossible to manufacture curved and straight pipes.

[0088] [Comparative Example 4: An example of a three-layer structure in which the outer layer is formed from axial yarn and braided yarn, and the intermediate layer is formed from braided yarn alone] In the manufacturing of the preform, the absence of a layer to fix the outer filament of the outer layer on its outer circumference resulted in disordered orientation of the filament on the outer circumference. This led to a small cover factor cf3(out) of 43% on the outer circumference and a large difference compared to the 93% cover factor cf3(in) on the inner circumference. As a result, the retention rate of the tensile modulus was low at 0.56 (grade B), and the overall rating was D (fail).

[0089] [Example 1: An example of a three-layer structure consisting of an intermediate layer formed from core yarn and braided yarn, and an inner layer and outer layer formed solely from braided yarn.] The tensile modulus retention rate was 0.94 (grade A), and the fracture strength of the bent pipe was 650 MPa (grade A), resulting in an overall rating of A (pass).

[0090] [Example 2: An example in which the number of intermediate layers in Example 1 is changed from 1 to 2 layers] The tensile modulus retention rate was 0.84 (grade A), and the fracture strength of the bent pipe was 740 MPa (grade A), resulting in an overall rating of A (pass).

[0091] (Variable evaluation of the orientation angle of the intermediate layer (Table 4)) [Example 3: An example in which the orientation angle of the inner yarn of the intermediate layer in Example 1 is changed from 47° to 6°, and the orientation angle of the outer yarn is changed from 45° to 5°.] The tensile modulus retention rate was 0.94 (grade A), and the fracture strength of the bent pipe was 640 MPa (grade A), resulting in an overall rating of A (pass).

[0092] [Example 4: An example in which the orientation angle of the inner yarn of the intermediate layer in Example 1 is changed from 47° to 15°, and the orientation angle of the outer yarn is changed from 45° to 13°.] The tensile modulus retention rate was 0.94 (grade A), and the fracture strength of the bent pipe was 620 MPa (grade A), resulting in an overall rating of A (pass).

[0093] [Example 5: An example in which the orientation angle of the inner yarn of the intermediate layer in Example 1 is changed from 47° to 80°, and the orientation angle of the outer yarn is changed from 45° to 77°.] The tensile modulus retention rate was 0.94 (grade A), and the fracture strength of the bent pipe was 630 MPa (grade A), resulting in an overall rating of A (pass).

[0094] [Example 6: An example in which the orientation angle of the inner yarn of the intermediate layer in Example 1 is changed from 47° to 85°, and the orientation angle of the outer yarn is changed from 45° to 84°.] The tensile modulus retention rate was 0.94 (grade A), and the fracture strength of the bent pipe was 630 MPa (grade A), resulting in an overall rating of A (pass).

[0095] (Variable evaluation of the orientation angle of the outer layer (Table 4)) [Example 7: An example in which the orientation angle of the inner yarn of the intermediate layer in Example 1 was changed from 48° to 34°, and the orientation angle of the outer yarn was changed from 46° to 27°.] The tensile modulus retention rate was 0.89 (grade A), and the fracture strength of the bent pipe was 630 MPa (grade A), resulting in an overall rating of A (pass).

[0096] [Example 8: An example in which the orientation angle of the inner yarn of the intermediate layer in Example 1 was changed from 48° to 60°, and the orientation angle of the outer yarn was changed from 46° to 53°.] The tensile modulus retention rate was 0.86 (grade A), and the fracture strength of the bent pipe was 500 MPa (grade A), resulting in an overall rating of A (pass).

[0097] (Random evaluation of the coverage factor of the hidden layer (Table 5)) [Example 9: An example in which the value of the inner cover factor cf3(in) of the intermediate layer in Example 1 is changed from 93% to 52%, and the value of the outer cover factor cf3(out) is changed from 80% to 40%.] The tensile modulus retention rate was 0.84 (grade A), and the fracture strength of the bent pipe was 380 MPa (grade C), resulting in an overall grade of C (pass).

[0098] [Example 10: An example in which the value of the inner cover factor cf3(in) of the intermediate layer in Example 1 is changed from 93% to 64%, and the value of the outer cover factor cf3(out) is changed from 80% to 52%.] The tensile modulus retention rate was 0.86 (grade A), and the fracture strength of the bent pipe was 460 MPa (grade B), resulting in an overall grade of B (pass).

[0099] [Example 11: An example in which the value of the inner cover factor cf3(in) of the intermediate layer in Example 1 is changed from 93% to 75%, and the value of the outer cover factor cf3(out) is changed from 80% to 63%.] The tensile modulus retention rate was 0.88 (grade A), and the fracture strength of the bent pipe was 540 MPa (grade A), resulting in an overall rating of A (pass).

[0100] (Random assessment of outer layer coverage factor (Table 5)) [Example 12: An example in which the value of the inner cover factor cf3(in) of the outer layer in Example 1 is changed from 94% to 47%, and the value of the outer cover factor cf3(out) is changed from 93% to 41%.] The tensile modulus retention rate was 0.94 (grade A), and the fracture strength of the bent pipe was 360 MPa (grade C), resulting in an overall grade of C (pass).

[0101] [Example 13: An example in which the value of the inner cover factor cf3(in) of the outer layer in Example 1 is changed from 94% to 65%, and the value of the outer cover factor cf3(out) is changed from 93% to 58%.] The tensile modulus retention rate was 0.95 (grade A), and the fracture strength of the bent pipe was 440 MPa (grade B), resulting in an overall grade of B (pass).

[0102] [Example 14: An example in which the value of the inner cover factor cf3(in) of the outer layer in Example 1 is changed from 94% to 79%, and the value of the outer cover factor cf3(out) is changed from 93% to 72%.] The tensile modulus retention rate was 0.95 (grade A), and the fracture strength of the bent pipe was 520 MPa (grade A), resulting in an overall rating of A (pass).

[0103] (Variable evaluation of the number of sleeve sets (Table 6)) [Example 15: An example in which the number of sets of assembled sleeves in Example 1 was changed from 1 set to 2 sets] The tensile modulus retention rate was 0.93 (grade A), and the fracture strength of the bent pipe was 640 MPa (grade A), resulting in an overall rating of A (pass).

[0104] Furthermore, regarding the random evaluation of the range of orientation angles of the inner layer's braided yarns, it has been clear that the results are similar to those of the random evaluation of the range of orientation angles of the outer layer's braided yarns, therefore no verification was performed. Furthermore, since the results of the random assessment regarding the range of the inner layer's coverage factor are clearly similar to those of the random assessment regarding the range of the outer layer's coverage factor, no verification was performed.

[0105] From the above results, it was confirmed that a three-layer bent tube, consisting of an intermediate layer formed from high-strength fiber axle yarn and elastic yarn braid, and an inner and outer layer formed from high-strength fiber braid, with the braids of the intermediate, inner, and outer layers oriented at an orientation angle in the range of ±5° to 85°, maintains a high level of axial mechanical properties without disruption of fiber orientation even after bending. [Explanation of Symbols]

[0106] 1. Bent pipe 11. Inner layer assembly sleeve 111 Braided yarn for inner layer 12 Outer layer assembly sleeve 121 Braided yarn for the outer layer 13 Intermediate layer assembly sleeve 131 Braided yarn for the intermediate layer 132 Axle yarn 2 Bent part 21 Inner side 22 Outer perimeter X Center axis direction

Claims

1. A cylindrical curved pipe made of FRP, having a circular cross-section, is constructed by a braided structure in which an inner layer, an outer layer, and an intermediate layer placed between the inner and outer layers are stacked and arranged, and by resin molding. The aforementioned intermediate layer is An axial thread formed of high-strength fibers and oriented in the direction of the central axis of the curved tube, The structure consists of one or more stacked tubular braided sleeves, each formed by combining an intermediate layer braid made of elastic yarn with an orientation angle of ±5 to 85° relative to the central axis of the curved tube. The aforementioned inner layer is It is arranged on the inner circumference side of the intermediate layer, The structure consists of one or more stacked tubular braided sleeves, which do not have an axis thread, formed by combining inner layer braided threads made of high-strength fibers, with an orientation angle of ±5 to 85° relative to the central axis of the curved tube. The aforementioned outer layer is It is arranged on the outer periphery side of the intermediate layer, A curved tube characterized by having a configuration in which one or more tubular braided sleeves without axial threads are stacked, each sleeve being formed by combining braided outer layer threads made of high-strength fibers, with an orientation angle of ±5 to 85° with respect to the central axis of the curved tube.

2. In the inner layer and the outer layer, The width of the inner layer braid or the width of the outer layer braid is b f [mm] The number of inner layer braids or the number of outer layer braids is n [number of strands] The inner diameter of the inner layer or the inner diameter of the outer layer is D [mm] The orientation angle of the inner layer yarn or the outer layer yarn is θ [°] The inner cover factor cf, which is calculated by the following (Equation 1) for the ratio of the braided yarn for the inner layer to the surface area of ​​the inner layer or the ratio of the braided yarn for the outer layer to the surface area of ​​the outer layer, is obtained on the inner circumference side of the bent portion of the curved tube. 1 The value of (in) is 60% or less and is less than or equal to 100%, and the outer cover factor cf indicates the ratio of the braided yarn for the inner layer to the surface area of ​​the inner layer or the ratio of the braided yarn for the outer layer to the surface area of ​​the outer layer, which corresponds to the outer circumference of the bent portion of the curved tube, as determined by the following formula (Formula 1). 1 The curved pipe according to claim 1, characterized in that the value of (out) is 50% or less and less than or equal to 100%. [Math 1] ...(Formula 1)

3. In the aforementioned intermediate layer, The width of the braided yarn for the intermediate layer is b f [mm] The number of braided yarns for the intermediate layer is n [threads]. The inner diameter of the intermediate layer is D [mm] The orientation angle of the braided yarn for the intermediate layer is θ [°] The width of each cell in the intermediate layer is f [mm] The width of the aforementioned shaft thread is b m [mm] The number of the aforementioned axial threads is n m [Book] In this case, the inner cover factor cf, which is calculated by the following (Equation 2), represents the ratio of the intermediate layer yarn and the axis yarn to the surface area of ​​the intermediate layer on the inner circumference side of the bent portion of the curved tube. 3 The value of (in) is 60% or less and is less than or equal to 100%, and the outer cover factor cf, which indicates the ratio of the intermediate layer yarn and the axis yarn to the surface area of ​​the intermediate layer on the outer circumference of the bent portion of the curved tube, is determined by the following (Formula 2). 3 The curved pipe according to claim 1, characterized in that the value of (out) is 50% or less and less than or equal to 100%. [Math 2] ...(Formula 2)

4. A curved pipe according to any one of claims 1 to 3, characterized in that multiple sets of assembled sleeves, each consisting of an inner layer, an intermediate layer, and an outer layer arranged in order from the inner circumference, are stacked on top of each other.

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