Bent pipe

Abstract

To provide an FRP bent pipe in which a cylindrical braided structure is embedded in a cylindrical resin molded body, orientation disturbance such as fiber waviness does not occur even when bending is performed in an axial direction, and mechanical characteristics in the axial direction are maintained at a high level.SOLUTION: In an FRP bent pipe 1, a braided structure 11 in which a braided sleeve 13 for an outer layer and a braided sleeve 12 for an outer layer are arranged in an overlapping manner is embedded in a resin molded body 15. The braiding sleeve (13) for the inner layer is a tubular braiding body formed by combining an axial yarn (132) oriented in the central axis direction (X) and formed from a high-strength fiber and an inner layer braiding yarn (131) oriented at an orientation angle within the range of ± 5-85 ° and formed from an elastic yarn, and the braiding sleeve (12) for the outer layer is a tubular braiding body having no axial yarn and formed by combining outer layer braiding yarns (121) oriented at an orientation angle within the range of ± 5-85 ° with respect to the central axis direction (X) and formed from a high-strength fiber.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a bent pipe made of FRP in which a braided structure is embedded inside a resin molding. [Background technology]

[0002] Next-generation mobility such as large drones (large unmanned aerial vehicles) and flying cars is made up of components such as the main body frame, propellers, propeller guards, arms, skids (legs), etc. These components are made of tubular materials to reduce weight, and because high rigidity is required, it is expected that tubular braids made of fiber reinforced plastic (FRP) will be used, which are made using braiding technology using fiber materials (braided yarns) and resin molding.

[0003] In order to improve the mechanical properties of such a cylindrical braid in the axial direction, it is conceivable to orient a high-strength (high-elastic modulus) fiber material in the axial direction. For example, Patent Documents 1 to 4 disclose tubular preforms and curved pipes manufactured by laminating cylindrical braids, and Patent Documents 5 to 7 disclose tubular preforms and curved pipes manufactured by laminating reinforcing fiber sheets (prepreg UD sheets). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 1992-327910 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-025807 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-167776 [Patent Document 4] Japanese Patent Application Laid-Open No. 2009-034885 [Patent Document 5] Japanese Patent Publication No. 2021-094739 [Patent Document 6] Japanese Patent Application Publication No. 2018-038463 [Patent Document 7] Japanese Patent Application Laid-Open No. 1995-223271 DISCLOSURE OF THE INVENTION [Problem to be solved by the invention]

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

[0006] For example, the tubular preform of Patent Document 1 is stacked from the inside with a layer having a braiding angle of 0° (a braided sleeve combining unidirectional fibers and elastic yarns (crimped nylon yarns)), a layer having a braiding angle of ±α°, and a layer having a braiding angle of 0°. Because there are two 0° layers, it is difficult to bend the tubular preform in the axial direction. Even if the tubular preform can be bent, the yarns in the 0° layer on the outside of the tubular preform may come apart. As a result, the yarns in the 0° layer do not follow the axial direction, causing fiber waviness, which may reduce the axial tensile and bending properties of the bent tubular preform.

[0007] Furthermore, with regard to the tubular preforms and curved pipes of Patent Documents 5 to 7, 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, and fiber undulations will occur, which may reduce the axial tensile and bending properties of the curved pipe.

[0008] As described above, in the case of curved pipes, those with high levels of axial mechanical properties involve conflicting factors in terms of both physical properties and manufacturing, so some ingenuity is required to achieve both.

[0009] Therefore, the object of the present invention is to provide a curved pipe made of FRP in which a cylindrical braided structure is embedded inside a cylindrical resin molding, which does not suffer from orientation disturbances such as fiber undulations even when bent in the axial direction, and which maintains a high level of axial mechanical properties. [Means for solving the problem]

[0010] The present invention provides a bent pipe made of FRP, in which a braided structure in which an inner layer and an outer layer are overlapped is embedded inside a cylindrical resin molding, The inner layer is an axial thread formed of high-strength fibers and oriented in the central axis direction of the curved pipe; and an inner layer braided yarn made of elastic yarn, the orientation angle of which with respect to the central axis direction of the curved pipe is in the range of ±5 to 85°. The outer layer is is disposed on the outer circumferential side of the inner layer, The curved tube is characterized by having one or more stacked cylindrical braided sleeves without an axial thread, which are formed by combining outer layer braided yarns made of high-strength fibers and whose orientation angle with respect to the central axis direction of the curved tube is within the range of ±5 to 85°.

[0011] According to the above configuration, in the inner layer, the high-strength axial yarn is fixed to the soft elastic yarn, forming a flexible braid, which makes it easier to bend the curved tube while maintaining the orientation of the axial yarn (the axial yarn remains aligned along the central axis of the curved tube). Furthermore, when bending a curved pipe, the axial yarns in the inner layer are covered by the outer layer, so the axial yarns do not come apart and can be bent while maintaining their orientation in the central axis direction. Furthermore, since the outer layer does not contain axial threads oriented in the direction of the central axis, the outer layer does not interfere with the bending process of the curved pipe (it can easily follow the shape changes when the curved pipe is bent). That is, even when bending the curved pipe in the direction of its central axis, there is no disturbance in the orientation of the fibers, such as undulation, and a curved pipe can be obtained in which the mechanical properties in the direction of the central axis are maintained at a high level.

[0012] Further, the present invention provides a method for manufacturing a bent pipe, comprising: The width of the outer layer yarn is b f [mm] The number of outer layer yarns is n [pieces] The inner diameter of the outer layer is D [mm] The orientation angle of the outer layer yarn is θ [°] The present invention may be characterized in that the value of an inner cover factor cf1(in), which indicates the proportion of the surface area of ​​the outer layer occupied by the outer layer yarns on the inner side of the bent portion of the curved pipe, calculated by the following (Equation 1) when the above equation is met, is 60% or more and 100% or less, and the value of an outer cover factor cf1(out), which indicates the proportion of the surface area of ​​the outer layer occupied by the outer layer yarns on the outer side of the bent portion of the curved pipe, calculated by the following (Equation 1) when the above equation is met, is 50% or more and 100% or less.

number

[0013] As in the above configuration, in an outer layer formed only of braided yarns (outer layer braided yarns) without including an axial yarn, if the value of the inner cover factor cf1(in) on the inner side of the bent portion of the curved pipe and the value of the outer cover factor cf1(out) on the outer side of the bent portion of the curved pipe satisfy the above conditions, it is possible to prevent a decrease in strength or strength imbalance of the curved pipe and to increase the torsional strength of the curved pipe itself.

[0014] Further, the present invention provides the inner layer of the curved pipe, The width of the inner layer yarn is b f [mm] The number of inner layer yarns is n [pieces] The inner diameter of the inner layer is D [mm] The orientation angle of the inner layer yarn is θ [°] The width of one cell in the inner layer is f [mm] The width of the axon is b m [mm] The number of axonemes is n m [Books] The present invention may be characterized in that the value of an inner cover factor cf3(in), which indicates the proportion of the surface area of ​​the inner layer occupied by the inner layer yarn and the axial yarn on the inner peripheral side of the bent portion of the curved pipe, calculated by the following (Equation 2) when

number

[0015] In the inner layer formed by combining the inner layer braiding yarn and the axial yarn as in the above configuration, if the value of the inner cover factor cf3(in) on the inner side of the bent portion of the curved pipe and the value of the outer cover factor cf3(out) on the outer side of the bent portion of the curved pipe satisfy the above conditions, it is possible to prevent a decrease in strength or strength imbalance of the curved pipe and to increase the torsional strength of the curved pipe itself.

[0016] Furthermore, in the above-mentioned curved pipe, the present invention may be characterized in that the braided structure is a structure in which multiple sets of braided sleeve groups, each set consisting of the inner layer and the outer layer arranged in order from the inner periphery side, are stacked on top of each other.

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

[0018] Regarding a curved pipe made of FRP in which a cylindrical braided structure is embedded inside a cylindrical resin molding, it is possible to provide a curved pipe in which no orientation disturbance such as fiber waviness occurs even when bending in the axial direction, and in which mechanical properties in the axial direction are maintained at a high level. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 2 is an explanatory diagram of a curved pipe according to the present embodiment. [Figure 2] 1A is a cross-sectional view of a curved pipe according to the present embodiment, and FIG. 1B is an explanatory diagram of a two-layer braided structure of the curved pipe according to the present embodiment. [Figure 3] FIG. 2 is an explanatory diagram of the braided structure (one cell) of the outer layer braided sleeve. [Figure 4] (A) An explanatory diagram of a braided structure (1 cell) formed only with inner layer braid yarns in an inner layer braided sleeve. (B) An explanatory diagram of a braided structure (1 cell) formed with inner layer braid yarns and an axial yarn in an inner layer braided sleeve. [Figure 5] 4A and 4B are explanatory diagrams illustrating the braided structure of the bent portion of the bent pipe according to the present embodiment. [Figure 6] 1A is an explanatory diagram of a sleeve braiding process, and FIG. 1B is an explanatory diagram of a spindle track in the sleeve braiding process. [Figure 7] FIG. 2 is an explanatory diagram of a manufacturing process of a preform. [Figure 8] FIG. 10 is an explanatory diagram illustrating placement of a preform in a mold. [Figure 9] FIG. 1 is an explanatory diagram regarding a resin molding process for a preform. [Figure 10] FIG. 10 is an explanatory diagram illustrating removal of the mandrel from the preform after resin molding. [Figure 11] 10 is a photograph of the appearance of the manufactured bent pipe. [Figure 12] FIG. 10 is a cross-sectional view of a bent pipe according to another embodiment. [Figure 13] FIG. 1 is an explanatory diagram of a method for measuring the breaking strength of a curved pipe. [Figure 14]FIG. 2 is an explanatory diagram of the inside and outside of the bent portion (central curved portion) of the curved pipe, which is the subject of measurement of the tensile modulus of elasticity. DETAILED DESCRIPTION OF THE INVENTION

[0020] (Embodiment) Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0021] (Bent pipe 1) As shown in Figures 1 and 2, the curved pipe 1 is a cylindrical pipe with a circular cross section made of fiber reinforced plastic (FRP) consisting of a braided structure 11 made of braided yarn (carbon fiber material, etc.) and a cylindrical resin molded body 15, and is curved 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), the propeller, the propeller guard, the arm that connects the propeller to the main frame, and the skid (legs) that make up the large drone). The main frame, propeller, propeller guard, arm, and skid that make up these large drones have curved parts in their shapes, and in addition to being lightweight, highly rigid, and having excellent vibration damping properties, they are required to maintain a high level of mechanical properties in the central axis direction X without causing orientation disturbances such as fiber undulations even when bending the curved pipe 1 in the central axis direction X.

[0023] The braided structure 11 of the bent pipe 1 has a cylindrical shape and is embedded inside the resin molded body 15. The braided structure 11 has a structure in which two layers of cylindrical braided sleeves are arranged one on top of the other. Specifically, as shown in Figure 2(A), the braided structure 11 of the curved pipe 1 has a two-layer structure consisting of a cylindrical outer layer braided sleeve 12 (corresponding to the outer layer) placed on the outer peripheral side of the curved pipe 1, and a cylindrical inner layer braided sleeve 13 (corresponding to the inner layer) layered (placed) on the inner peripheral side of the outer layer braided sleeve 12.

[0024] (Outer layer braid sleeve 12) The outer layer braid sleeve 12 is laminated on the outer peripheral side of the inner layer braid sleeve 13 . 2(B) and 3, the outer layer braided sleeve 12 is formed by combining outer layer braided yarns 121 made of high-strength (high elastic modulus) fibers so that they intersect and are oriented at an orientation angle (θ) in the range of ±5 to 85° with respect to the central axial direction X of the curved pipe 1. Here, the outer layer braided sleeve 12 does not have an axial yarn that is oriented in the central axial direction X of the curved pipe 1. In addition, examples of high-strength (high elastic modulus) fibers that can be used to form the outer layer braided yarn 121 of the outer layer braided sleeve 12 include carbon fiber, glass fiber, aramid fiber, boron fiber, silicon carbide fiber, steel fiber, polyethylene fiber, nylon fiber, alumina fiber, Tyranno fiber, basalt fiber, and amorphous fiber.

[0025] (Inner layer braided sleeve 13) The inner layer braided sleeve 13 is laminated on the inner circumferential side of the outer layer braided sleeve 12 . As shown in Figures 2(B) and 4, the inner layer braided sleeve 13 is formed by combining, in a crossing manner, an axial yarn 132 that is oriented in the central axis direction X of the curved pipe 1 (the orientation angle with respect to the central axis direction X is 0°) and is made of high-strength (high elastic modulus) fibers, and an inner layer braided yarn 131 that is oriented at an orientation angle with respect to the central axis direction X in the range of ±5 to 85° and is made of elastic yarn.

[0026] Examples of high-strength (high elastic modulus) fibers that can be used to form the axial thread 132 of the inner layer braided sleeve 13 include carbon fiber, glass fiber, aramid fiber, boron fiber, silicon carbide fiber, steel fiber, polyethylene fiber, nylon fiber, alumina fiber, Tyranno fiber, basalt fiber, and amorphous fiber.

[0027] Examples of elastic yarns that can be used to form the inner layer braided yarn 131 of the inner layer braided sleeve 13 include multifilament yarns made of thermoplastic resins such as nylon resin, polybutylene terephthalate resin, and polyester resin, and false twisted yarns (also called crimped yarns or woolly yarns) obtained by processing monofilament yarns, urethane fibers, etc.

[0028] (Resin molded body 15 of bent pipe 1) Resin materials used for the resin molded body 15 of the curved pipe 1 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. Resin molding methods include resin transfer molding (RTM: vacuum suction and pressure impregnation), VaRTM (vacuum impregnation method), and internal pressure molding.

[0029] (Braided structure 11 of bent portion 2 of bent pipe 1) When forming a curved pipe 1, as shown in Fig. 5, it is necessary to braid the braided structure 11 in a curved shape at the curved portion 2. However, compared to when braiding in a straight line, the braided structure 11 shrinks on the inner circumferential side 21 of the curved portion 2, while it stretches on the outer circumferential side 22 of the curved portion 2, which can cause unevenness (differences in strength) in the braided structure 11 of the curved pipe 1. If such unevenness occurs in the braided structure 11 of the curved pipe 1, the high rigidity and impact resistance of the curved pipe 1 will be reduced.

[0030] Therefore, the braided structures of each bent portion of the outer layer braided sleeve 12 and the inner layer braided sleeve 13 that constitute the braided structure 11 of the curved pipe 1 are formed using an index (value) called the cover factor cf (Equations 1 to 3), which indicates the proportion of the surface area of ​​each braided structure of the outer layer braided sleeve 12 and the inner layer braided sleeve 13 that constitute the braided structure 11 of the curved pipe 1 that is an index of strength of the curved pipe 1 having a braided structure 11 with a circular cross section.

[0031] As shown in Figures 3 to 5, the width f [mm] per cell (one section surrounded by braided yarns) of the braided structure is the same on the inner and outer sides of each bent portion of the outer layer braided sleeve 12 and the inner layer braided sleeve 13 that make up the braided structure 11 of the curved pipe 1, but the orientation angle θ [°] with respect to the central axis direction X of the curved pipe 1 is different. Therefore, it is necessary to calculate the inner cover factor cf(in) of the inner side of each bent portion of the outer layer braided sleeve 12 and the inner layer braided sleeve 13 that make up the braided structure 11 of the curved pipe 1, and the outer cover factor cf(out) of the outer side of each bent portion of the outer layer braided sleeve 12 and the inner layer braided sleeve 13 that make up the braided structure 11 of the curved pipe 1. In addition, the calculation of the cover factor cf must take into consideration the following cases: a case where the cells of the braided structure are composed only of braid yarns (outer layer braid yarns 121) (cf1), as in the outer layer braided sleeve 12 shown in Figure 3; and a case where the cells (see Figure 4(A)) include a braided structure (cf1) composed only of braid yarns (inner layer braid yarns 131) and a braided structure (cf2) (see Figure 4(B)) having a braid yarn (inner layer braid yarn 131) and an axial yarn (axial yarn 132), as in the inner layer braided sleeve 13 shown in Figure 4.

[0032] (Cover factor of outer layer braid sleeve 12) When the braided cell is made up of only the outer layer braid yarn 121, as in the outer layer braided sleeve 12 shown in FIG. 3, the width b fFrom values ​​based on two-dimensional data such as the length n [mm] of the outer layer braided sleeve 12, the number n [pieces] of outer layer braided yarns 121, the inner diameter D [mm] of the outer layer braided sleeve 12, and the orientation angle θ [°] of the outer layer braided yarns 121 with respect to the central axis direction X of the curved pipe 1, the value of the inner cover factor cf1(in) on the inner side of the curved portion of the outer layer braided sleeve 12 and the value of the outer cover factor cf1(out) on the outer side of the curved portion of the outer layer braided sleeve 12 are calculated using the following (Equation 1):

[0033]

number

[0034] Furthermore, when the braided structure is composed only of the outer layer braided yarn 121 (when the braided structure does not include an axial yarn), as in the outer layer braided sleeve 12, by satisfying the condition that the value of the inner cover factor cf1(in) calculated by the above (Equation 1) is in the range of 100% or less and 60% or more, and the value of the outer cover factor cf1(out) calculated by the above (Equation 1) is in the range of 100% or less and 50% or more, it is possible to prevent a decrease in strength or strength imbalance in the bent portion 2 of the curved pipe 1, and to increase the torsional strength of the curved pipe 1 itself.

[0035] The outer layer braided sleeve 12 prevents buckling failure of the axial threads 132 of the inner layer braided sleeve 13 due to bending load, and can increase the torsional strength of the curved pipe 1 itself. Furthermore, with the outer layer braided sleeve 12, by restraining the axial yarns 132 of the inner layer braided sleeve 13, it is possible to prevent bending and displacement of the axial yarns 132 at the bent portion 2. Furthermore, it is possible to prevent a decrease in strength or unevenness of strength of the curved pipe 1, thereby increasing the torsional strength of the curved pipe 1 itself.

[0036] (Cover factor of inner layer braid sleeve 13) When the cover factor cf3 is calculated for a braided structure having a cell (see FIG. 4(A)) composed only of an inner layer braid 131, as in the case of the inner layer braided sleeve 13 shown in FIG. 4, and a cell (see FIG. 4(B)) composed of a braided structure having an inner layer braid 131 and an axial yarn 132, the cover factor cf3 is calculated taking into account the cover factor cf1 (calculated in the same manner as for the outer layer braided sleeve 12: see Equation 1) for the cell shown in FIG. 4(A) whose braided structure is composed only of the inner layer braid 131, and the cover factor cf2 for the cell shown in FIG. 4(B) whose braided structure is composed of the inner layer braid 131 and an axial yarn 132.

[0037] Here, as shown in FIG. 4(B), when the braided cell includes an inner layer braid 131 and an axial thread 132, the width b f [mm], the number n [pieces] of the inner layer braided yarns 131, the inner diameter D [mm] of the inner layer braided sleeve 13, and the orientation angle θ [°] of the inner layer braided yarns 131 with respect to the central axis direction X, in addition to the width f [mm] per cell of the braided structure (one section surrounded by the inner layer braided yarns 131: see FIG. 4(B)), the width b m [mm] and the number n of the axial threads 132 m From values ​​based on two-dimensional data such as [book], the value of the inner cover factor cf2(in) on the inner side of the bent portion of the inner layer braid sleeve 13, and the value of the outer cover factor cf2(out) on the outer side of the bent portion of the inner layer braid sleeve 13 are calculated using the following (Equation 2).

[0038]

number

[0039] As shown in Figures 4(A) and 4(B), in (Equation 2), A is the area of ​​one cell of the braided structure of the inner layer braided sleeve 13, and A S is the area of ​​the voids in one cell of the braided structure of the inner layer braided sleeve 13 excluding the inner layer braid 131 portion, and A ais the area of ​​the axial yarn 132 (excluding the portion overlapping with the inner layer braid 131) in one cell of the braided structure of the inner layer braided sleeve 13.

[0040] In the case of the braided sleeve for inner layer 13, in which the cell (see FIG. 4(A)) includes a braided structure composed only of the inner layer braid yarn 131, and in which the cell (see FIG. 4(B)) includes a braided structure having the inner layer braid yarn 131 and the axial yarn 132, the cover factor cf3 is calculated by using the cover factor cf1 of the cell in which the braided structure is composed only of the inner layer braid yarn 131 shown in FIG. 4(A) and the cover factor cf2 of the cell in which the braided structure is composed only of the inner layer braid yarn 131 and the axial yarn 132 shown in FIG. By satisfying the condition 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 constituent cells, is in the range of 100% or less and 60% or more, and the value of the outer cover factor cf3(out), calculated by the following (Equation 3), is in the range of 100% or less and 50% or more, it is possible to prevent a decrease in strength or strength imbalance in the bent portion 2 of the curved pipe 1, and to increase the torsional strength of the curved pipe 1 itself.

[0041] In the above-mentioned braided sleeve for the inner layer 13, elastic yarn is used for the braided yarn for the inner layer 131, and therefore the braided sleeve for the inner layer 13 itself can be made flexible, and therefore the axial yarn 132 can be arranged seamlessly and uniformly along the central axis direction X in the bent portion 2 of the curved pipe 1.

[0042]

number

[0043] As described above, the outer layer braided sleeve 12 and the inner layer braided sleeve 13 that constitute the braided structure 11 of the curved pipe 1 are designed to satisfy the condition that the value of the inner cover factor cf(in) is in the range of 100% or less and 60% or more, and the value of the outer cover factor cf(out) is in 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%, the surface area will be greater than or equal to the surface area of ​​the outer layer braided sleeve 12 and the inner layer braided sleeve 13, which are formed by the braided structure of the outer layer braid 121 and the braided structure of the inner layer braid 131 and the axial yarn 132, and therefore part of the outer layer braid 121, the inner layer braid 131, and the axial yarn 132 will float on the surface of the curved pipe 1, and loads will be applied to the floated parts or their surroundings, which may reduce the rigidity and impact resistance of the curved pipe 1. Also, 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 11 between the inner peripheral side 21 and the outer peripheral side 22 of the bent portion 2 of the curved pipe 1, which may reduce the rigidity and impact resistance of the curved pipe 1.

[0044] In order to further enhance the rigidity and impact resistance of the curved pipe 1, it is more preferable that the inner cover factor cf(in) of the outer layer braided sleeve 12 and the inner layer braided sleeve 13 constituting the braided structure 11 of the curved pipe 1 satisfy the condition that the value of the inner cover factor cf(in) is in the range of 100% to 70% and the value of the outer cover factor cf(out) is in the range of 100% to 60%.Moreover, it is most preferable that the value of the inner cover factor cf(in) is in the range of 100% to 80% and the value of the outer cover factor cf(out) is in the range of 100% to 70%.

[0045] (Manufacturing method of curved pipe 1) Next, a method for manufacturing the curved pipe 1 will be described.

[0046] (1) Sleeve braiding process First, as shown in FIG. 6(a), the braided sleeve 12 for the outer layer and the braided sleeve 13 for the inner layer are manufactured using a braiding machine.

[0047] For example, in the case of the outer layer braided sleeve 12, braided yarns (outer layer braided yarns 121) wound around a spindle are combined on the outer periphery of a cylindrical mandrel to form the outer layer braided sleeve 12. As shown in Fig. 6(b), the spindle moves along the track, so that the braided yarns (outer layer braided yarns 121) are combined, and a seamless outer layer braided sleeve 12 is formed on top of the mandrel, and is then wound up by a winding device.

[0048] In the case of the inner layer braided sleeve 13, the braided yarn (inner layer braided yarn 131) wound around the spindle and the axial yarn 132 supplied from the bottom of the braiding machine (supplied from a fixed cylinder) are combined on the outer periphery of a cylindrical mandrel to form the inner layer braided sleeve 13. As shown in Fig. 6(b), the spindle moves along the track, so that the braided yarn (inner layer braided yarn 131) and the axial yarn 132 are combined, and a seamless inner layer braided sleeve 13 is formed on the top of the mandrel, which is then wound up by a winding device.

[0049] Here, when the braided structure is composed only of the outer layer braid yarn 121 (when the braided structure does not include an axial yarn), as in the outer layer braided sleeve 12, the width b f The values ​​of various parameters, such as the inner diameter D [mm] of the outer layer braided sleeve 12, the number n [pieces] of outer layer braided yarns 121, the inner diameter D [mm] of the outer layer braided sleeve 12, and the orientation angle θ [°] of the outer layer braided yarns 121 with respect to the central axis direction X of the curved tube 1, must satisfy the condition that the value of the inner cover factor cf1(in) calculated by the above (Equation 1) is in the range of 100% to 60%, and the value of the outer cover factor cf1(out) calculated by the above (Equation 1) is in the range of 100% to 50%.

[0050] In addition, in the case of the inner layer braided sleeve 13, in which the cell (see FIG. 4(A)) includes a braided structure composed only of the inner layer braid yarn 131 and the cell (see FIG. 4(B)) includes a braided structure having the inner layer braid yarn 131 and the axial yarn 132, the width b f[mm], the number n [pieces] of the inner layer braided yarns 131, the inner diameter D [mm] of the inner layer braided sleeve 13, and the orientation angle θ [°] of the inner layer braided yarns 131 with respect to the central axis direction X, in addition to the width f [mm] per cell of the braided structure (one section surrounded by the inner layer braided yarns 131: see FIG. 4(B)), the width b m [mm] and the number n of the axial threads 132 m The values ​​of various parameters such as [Book] must satisfy the condition that the value of the inner cover factor cf3(in) calculated by the above (Equation 3) is in the range of 100% or less and 60% or more, and the value of the outer cover factor cf3(out) calculated by the above (Equation 3) is in the range of 100% or less and 50% or more.

[0051] (2) Manufacturing of preforms Next, as shown in FIG. 7, a cylindrical mandrel made of wax and having a small coefficient of friction is covered in this order with the inner layer braided sleeve 13 and the outer layer braided sleeve 12 to produce a preform (hereinafter referred to as a preform) in which two cylindrical braided sleeves are stacked. In this embodiment, a mandrel made of wax is used for the shaft portion (rod) of the preform, but the material used for the mandrel is not particularly limited as long as it has a small coefficient of friction.

[0052] (3) Installation in the mold Next, as shown in FIG. 8, the mandrel on which the preforms are stacked is bent and fitted into the cavity of a mold, and the lid is then placed.

[0053] In this embodiment, in manufacturing the preform, two layers of tubular braided sleeves (braided sleeve 13 for the inner layer and braided sleeve 12 for the outer layer) are stacked on a cylindrical mandrel, and then the mandrel is bent. However, it is also possible to first prepare a bent mandrel, and then stack two layers of tubular braided sleeves (braided sleeve 13 for the inner layer and braided sleeve 12 for the outer layer) on this bent mandrel.

[0054] (4) Resin molding process Next, as shown in Figure 9, thermosetting resin (matrix resin) is pressure-injected into the cavity of the mold using resin transfer molding (RTM), impregnating the preform with the thermosetting resin, and the excess thermosetting resin is vacuum-sucked out. The resin molding method may be Vacuum Reverse Transfer Molding (VaRTM) or internal pressure molding.

[0055] (5) Removing the mandrel Next, as shown in FIG. 10, after the thermosetting resin impregnated in the preform has hardened, the mandrel is removed.

[0056] (6) Finishing Finally, the bent pipe 1 is obtained by removing burrs, cutting, and painting (see FIG. 11).

[0057] According to the configuration of the curved pipe 1, in the inner layer braid sleeve 13, the high-strength axial yarn 132 is fixed to the soft inner layer braid 131, resulting in a flexible braid, which makes it easier to bend the curved pipe 1 while maintaining the orientation of the axial yarn 132 (while the axial yarn 132 remains aligned along the central axis direction X of the curved pipe 1). Furthermore, when bending the curved pipe 1, the axial yarns 132 of the inner layer braided sleeve 13 are covered by the outer layer braided sleeve 12, so the axial yarns 132 do not come apart and can be bent while maintaining their orientation in the central axis direction X. Furthermore, since the outer layer braided sleeve 12 does not include axial threads oriented in the central axis direction X, the outer layer braided sleeve 12 does not interfere with the bending process of the curved pipe 1 (it can easily follow the shape changes when the curved pipe 1 is bent). That is, even when bending the curved pipe 1 in the central axis direction X, there is no orientation disorder such as fiber undulation, and a curved pipe 1 can be obtained in which the mechanical properties in the central axis direction X are maintained at a high level.

[0058] Furthermore, when the curved pipe 1 is used for the main body frame, propeller, propeller guard, arm, and skid that make up a large drone, which is a large unmanned aerial vehicle, the curved pipe 1 not only has excellent light weight, high rigidity, and vibration damping properties, but also does not cause orientation disturbances such as fiber undulations even when the curved pipe 1 is bent in the central axis direction X, and the mechanical properties in the central axis direction X are maintained at a high level.

[0059] (Other embodiments) In the above embodiment, the braided structure 11 of the curved pipe 1 has been described as a two-layer structure having one inner layer braided sleeve 13 as the inner layer and one outer layer braided sleeve 12 as the outer layer, but considering the balance between the flexibility and strength of the curved pipe 1, each layer may also be configured by stacking multiple braided sleeves of the same type. For example, the inner layer may be configured by stacking a plurality of inner layer braid sleeves 13, or the outer layer may be configured by stacking a plurality of outer layer braid sleeves 12. In this way, by changing the number of braided sleeves to be layered on the inner layer and the outer layer, the flexibility and strength of the curved pipe 1 can be changed according to the required specifications.

[0060] Furthermore, in the above embodiment, when a set of braided sleeves is made up of an inner layer braided sleeve 13 (one piece) and an outer layer braided sleeve 12 (one piece), which are stacked in order from the inner periphery side, the braided structure 11 of the curved pipe 1 is made up of one set of braided sleeves, but this configuration is not limited to this, and a braided structure may be made up of multiple sets of braided sleeves stacked on top of each other. 12, a curved pipe 101 includes a braided structure 111 in which two sets of braided sleeve groups 10 (10A, 10B) are stacked. That is, the braided structure 111 of the curved pipe 101 is configured such that, from the inner circumferential side, an inner layer braided sleeve 13, an outer layer braided sleeve 12, an inner layer braided sleeve 13, and an outer layer braided sleeve 12 are stacked. In this way, by changing the number of sets of braided sleeve groups 10 that make up the braided structure 111 of the curved pipe 101, the flexibility and strength of the curved pipe 101 can be changed according to the required specifications.

[0061] In addition, in the above embodiment, the curved pipe 1 is described as being used in the main body frame, propeller, propeller guard, arm, and skid that make up a large drone, which is a large unmanned aerial vehicle, but the curved pipe 1 may also be used in a manned aircraft (for example, a large drone-type flying taxi, etc.).

[0062] Although the embodiments of the present invention have been described above, they are merely illustrative examples and do not particularly limit the present invention, and the specific configurations of each means etc. can be appropriately modified in design. Furthermore, the effects described in the embodiments of the present invention are merely a list of the most preferable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the embodiments of the present invention. [Example]

[0063] [Verification based on Examples 1 to 17 and Comparative Examples 1 to 3] The FRP bent pipe of the present invention includes a braided structure consisting of two layers: an "inner layer" that is a braided sleeve formed from an axial yarn composed of high-strength fibers and braided yarns composed of elastic yarns oriented at an angle of ±5 to 85°; and an "outer layer" that is a braided sleeve formed from braided yarns composed of high-strength fibers oriented at an angle of ±5 to 85°. This bent pipe does not experience any disturbance in the orientation of the fibers even when bent, and maintains a high level of mechanical properties in the axial direction.

[0064] Therefore, in this example, curved pipes according to Examples 1 to 17 and Comparative Examples 1 to 3 were fabricated, and comparative verification was carried out by measuring the tensile modulus of the curved pipes and straight pipes and measuring the breaking strength of the curved pipes. The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0065] (Structure of bent pipe made of fiber reinforced plastic (FRP)) <High-strength fiber used in the braided structure of curved pipes> Table 1 lists the high-strength fibers (carbon fibers) used in the braided structure of the curved pipe. [Table 1]

[0066] <Elastic thread used in the braided structure of a curved pipe> Table 2 lists the elastic threads (polyamide fibers) used in the braided structure of the curved pipe. [Table 2]

[0067] <Resin composition used in resin molded curved pipe> Thermosetting resin: Vinyl ester resin (brand CBZ500LM-AS, viscosity 200-350 mPa·s, manufactured by Japan U-Pica) Accelerator: PR-CBZ01 (made by U-Pica Japan) Hardener: 328E (manufactured by Nouryon Chemical Co., Ltd.)

[0068] (Manufacturing method of bent pipes) Using the "method for manufacturing a curved pipe" described in the above embodiment, curved FRP pipes including the braided structures described in Examples 1 to 17 and Comparative Examples 1 to 3 shown in Tables 3 to 6 were produced. As an example, the dimensions and shape of the curved pipe of Example 1 are shown in Figure 13. The method for manufacturing a straight pipe is the same as that for the "method for manufacturing a curved pipe" except that the shape of the cavity of the mold used in resin transfer molding (RTM) is straight.

[0069] (Evaluation of laminated structure) [Table 3] [Table 4] [Table 5] [Table 6]

[0070] (Test Method) <Method for measuring the tensile modulus of elasticity of curved and straight pipes> Test pieces measuring L 50 mm × W 5 mm × 1.5 mm were taken from the bent portion (central curved portion) of the bent pipe produced by the above manufacturing method using the water jet method, one from the inside and one from the outside (see Figure 14). In addition, test pieces with the same dimensions as the bent pipe were taken from the center of the straight pipe in the longitudinal direction by the water jet method at two locations facing each other in the circumferential direction. Then, test pieces taken from the bent part (central curved part) of the curved pipe and the central part of the straight pipe were subjected to tensile tests at a speed of 1 mm / min in an environment of a temperature of 23±2°C and a humidity of 50±10% in accordance with JIS K7164 (2005), and the tensile modulus of elasticity E was calculated from the obtained stress-strain curve using (Equation 4).

[0071]

number

[0072] In this test, the area where the slope is linear is used as the strain reading range. σ1: Tensile stress measured at strain ε1 = 0.0025 (MPa) σ2: Tensile stress measured at strain ε2 = 0.0050 (MPa) The tensile modulus E is calculated by the above formula (4). The tensile modulus of the test piece taken from the inside of the bent part (central curved part) of the bent pipe was defined as E(in), and the tensile modulus of the test piece taken from the outside was defined as E(out). The average of E(in) and E(out) was defined as the tensile modulus of the bent pipe. The tensile modulus of the straight pipe was defined as the average of the values ​​from the two locations.

[0073] <Method for measuring the breaking strength of bent pipes> For the curved pipes manufactured by the above manufacturing method, the tensile test method was performed in accordance with the above-mentioned "Method for measuring the tensile modulus of elasticity of curved pipes and straight pipes." The chuck portion shown in Figure 13 was gripped with a chuck, and the tensile stress (test force: F) until the test piece broke was measured at a test speed of 6 mm / min, and the breaking strength was calculated using the following (Equation 5) (the number of tests was 3 for each).

[0074] <Settings for measuring the breaking strength of curved pipes> ·Equipment Autograph: Amsler Strain gauge: KFGS-2-120-C1-11LIM3R Kyowa Electric Strain gauge adhesive: CC-33A Kyowa Electronics Conditioning 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: 6mm / min Number of tests: 3 Chuck part: A core bar is inserted to prevent crushing by the chuck

[0075]

number

[0076] (Regarding test results) <Acceptance / rejection criteria for bent pipes> FRP curved pipes were deemed to pass if they maintained a high level of axial mechanical properties without any disruption to the fiber orientation even after bending, and if they showed only a small decrease in tensile modulus even after bending, i.e., if they maintained a value close to that of a straight pipe. The tensile modulus of elasticity (E st) and the tensile modulus of elasticity (E in ) and the tensile modulus of elasticity of the outer periphery (E out ) and the tensile modulus of elasticity of the inner periphery (E in ) and the tensile modulus of elasticity of the straight pipe (E st ) and the tensile modulus of elasticity of the outer periphery (E out ) and the tensile modulus of elasticity of the straight pipe (E st ) was calculated as the retention rate of the tensile modulus. The geometric mean value of these two retention rates was calculated using the following formula (6), and the results were ranked according to the following criteria. The closer this geometric mean value is to 1, the higher the tensile modulus of elasticity (E st ) is maintained. Geometric mean value = (E in E out / E st 2 ) 1 / 2 ...(Formula 6) a: The geometric mean value of the retention rate of the tensile modulus is 0.998 or more and 1.002 or less b: The geometric mean value of the retention rate of the tensile modulus is 0.990 or more and less than 0.998, or more than 1.002 and less than 1.012 C: The geometric mean value of the retention rate of the tensile modulus is less than 0.990 or more than 1.012

[0077] In addition, since FRP bent pipes are expected to be used as structural components for large drones and other applications, breaking strength is important. The breaking strength of the center of the straight pipe (F st ) and the fracture strength of the inner periphery of the bent part (central curved part) of the bent pipe (F in ) and outer peripheral breaking strength (F out ) and the inner periphery breaking strength (F in ) and the breaking strength of the straight pipe (F st ) and the fracture strength of the outer periphery (F out ) and the breaking strength of the straight pipe (F st ) was calculated as the retention rate of breaking strength. The geometric mean value of these two retention rates was calculated using the following formula (7), and the results were ranked according to the following criteria. The closer this geometric mean value is to 1, the higher the fracture strength (F in ) is maintained. Geometric mean value = (F in F out / F st 2 ) 1 / 2 ...(Formula 7) a: The geometric mean value of the fracture strength retention rate is 0.998 or more and 1.002 or less b: The geometric mean value of the retention rate of breaking strength is 0.990 or more but less than 0.998, or is greater than 1.002 but less than 1.012 C: The geometric mean value of the fracture strength retention rate is less than 0.990 or more than 1.012

[0078] The overall evaluation was ranked as A (pass), B (pass), C (pass), or D (fail) according to the evaluation criteria in Table 7 below.

[0079] (Judgment criteria) [Table 7]

[0080] <Test results for curved and straight pipes> (Layer structure evaluation (Table 3)) [Comparative Example 1: Example of a two-layer structure in which the inner layer is formed only with axial yarn (no braiding yarn)] The inner layer used carbon fiber 1 as the axon thread. The outer layer used carbon fiber 1 as the braided thread. During the sleeve braiding process, there was no braided thread to secure the axon thread in the inner layer, so the orientation of the axon thread in the inner layer was disturbed, the sleeve was unable to maintain its shape, and it was not possible to produce curved or straight pipes.

[0081] Comparative Example 2: Example of a two-layer structure in which the inner layer of braided yarn is made of high-strength fibers The inner layer used carbon fiber 1 as the axon and braiding yarn. The outer layer used carbon fiber 1 as the braiding yarn. The inner layer sleeve, in which both the axon and braiding yarns are made of high-strength fiber (carbon fiber), is inflexible. Therefore, a straight pipe could be produced, but the preform could not be bent when it was placed in the mold, and a curved pipe could not be produced.

[0082] Comparative Example 3: Example of a two-layer structure in which the outer layer is formed of an axon yarn and braided yarns and the inner layer is formed of braided yarns only The inner layer used carbon fiber 1 as the braiding yarn. The outer layer used carbon fiber 1 as the axial yarn. The geometric mean value of the retention rate of tensile modulus was 0.681 (rating c), and the geometric mean value of the retention rate of breaking strength was 0.675 (rating c), both of which were small, resulting in an overall rating of D rank (failure).

[0083] [Example 1: Example of a two-layer structure consisting of an inner layer formed of an axon yarn and braided yarns and an outer layer formed only of braided yarns] The inner layer used carbon fiber 1 as the axial thread. The outer layer used carbon fiber 1 as the braided thread. The geometric mean value of the retention rate of tensile modulus was 1.002 (a rating), and the geometric mean value of the retention rate of breaking strength was 1.002 (a rating), giving an overall rating of A rank (pass).

[0084] Example 2: Example in which the number of stacked inner layers in Example 1 was changed from 1 to 2 (inner layer 1, inner layer 2) The inner layer used carbon fiber 1 as the axial thread. The outer layer used carbon fiber 1 as the braided thread. The geometric mean value of the retention rate of tensile modulus was 1.001 (a rating), and the geometric mean value of the retention rate of breaking strength was 0.998 (a rating), resulting in an overall rating of A rank (pass).

[0085] (Variable evaluation of inner layer orientation angle (Table 4)) [Example 3: Example in which the inner orientation angle of the braided yarn in the inner layer in Example 1 was changed from 50° to 6° and the outer orientation angle was changed from 42° to 5°] The inner layer used carbon fiber 1 as the axial thread. The outer layer used carbon fiber 1 as the braided thread. The geometric mean value of the retention rate of tensile modulus was 1.001 (a rating), and the geometric mean value of the retention rate of breaking strength was 1.001 (a rating), giving an overall rating of A rank (pass).

[0086] [Example 4: Example in which the inner orientation angle of the braided yarn in the inner layer in Example 1 was changed from 50° to 17° and the outer orientation angle was changed from 42° to 13°] The inner layer used carbon fiber 1 as the axial thread. The outer layer used carbon fiber 1 as the braided thread. The geometric mean value of the retention rate of tensile modulus was 0.999 (a rating), and the geometric mean value of the retention rate of breaking strength was 0.998 (a rating), resulting in an overall rating of A rank (pass).

[0087] [Example 5: Example in which the inner orientation angle of the braided yarn in the inner layer in Example 1 was changed from 50° to 80° and the outer orientation angle was changed from 42° to 78°] The inner layer used carbon fiber 1 as the axial thread. The outer layer used carbon fiber 1 as the braided thread. The geometric mean value of the retention rate of tensile modulus was 1.001 (a rating), and the geometric mean value of the retention rate of breaking strength was 1.002 (a rating), resulting in an overall rating of A rank (pass).

[0088] Example 6: Example in which the inner orientation angle of the inner layer braided yarn in Example 1 was changed from 50° to 85° and the outer orientation angle was changed from 42° to 83° The inner layer used carbon fiber 1 as the axial thread. The outer layer used carbon fiber 1 as the braided thread. The geometric mean value of the retention rate of tensile modulus was 1.001 (a rating), and the geometric mean value of the retention rate of breaking strength was 0.999 (a rating), resulting in an overall rating of A rank (pass).

[0089] (Variable evaluation of outer layer orientation angle (Table 4)) [Example 7: Example in which the inner orientation angle of the braided yarns in the outer layer in Example 1 was changed from 50° to 6° and the outer orientation angle was changed from 42° to 5°] The inner layer used carbon fiber 1 as the axial thread. The outer layer used carbon fiber 1 as the braided thread. The geometric mean value of the retention rate of tensile modulus was 1.001 (a rating), and the geometric mean value of the retention rate of breaking strength was 0.998 (a rating), resulting in an overall rating of A rank (pass).

[0090] Example 8: Example in which the inner orientation angle of the braided yarns in the outer layer in Example 1 was changed from 50° to 34° and the outer orientation angle was changed from 42° to 27° The inner layer used carbon fiber 1 as the axial thread. The outer layer used carbon fiber 1 as the braided thread. The geometric mean value of the retention rate of tensile modulus was 0.998 (a rating), and the geometric mean value of the retention rate of breaking strength was 0.999 (a rating), resulting in an overall rating of A rank (pass).

[0091] [Example 9: Example in which the inner orientation angle of the braided yarns in the outer layer in Example 1 was changed from 50° to 59° and the outer orientation angle was changed from 42° to 51°] The inner layer used carbon fiber 1 as the axial thread. The outer layer used carbon fiber 1 as the braided thread. The geometric mean value of the retention rate of tensile modulus was 0.998 (a rating), and the geometric mean value of the retention rate of breaking strength was 0.999 (a rating), resulting in an overall rating of A rank (pass).

[0092] [Example 10: Example in which the inner orientation angle of the braided yarns in the outer layer in Example 1 was changed from 50° to 85° and the outer orientation angle was changed from 42° to 82°] The inner layer used carbon fiber 1 as the axial thread. The outer layer used carbon fiber 2, which is thinner than carbon fiber 1, as the braided thread in order to increase the orientation angle. The geometric mean value of the retention rate of tensile modulus was 0.999 (a rating), and the geometric mean value of the retention rate of breaking strength was 0.998 (a rating), resulting in an overall rating of A rank (pass).

[0093] (Variable evaluation of inner layer cover factor (Table 5)) Example 11: Example in which the inner cover factor cf3(in) of the inner layer in Example 1 was changed from 99% to 33%, and the outer cover factor cf3(out) was changed from 99% to 33% The inner layer used carbon fiber 1 as the axial thread. The outer layer used carbon fiber 1 as the braided thread. The geometric mean value of the retention rate of tensile modulus was 1.005 (rating b), and the geometric mean value of the retention rate of breaking strength was 1.023 (rating c), resulting in an overall rating of C rank (pass).

[0094] Example 12: Example in which the inner cover factor cf3(in) of the inner layer in Example 1 was changed from 99% to 50%, and the outer cover factor cf3(out) was changed from 99% to 50%. The inner layer used carbon fiber 1 as the axial thread. The outer layer used carbon fiber 1 as the braided thread. The geometric mean value of the retention rate of tensile modulus was 1.006 (rating b), and the geometric mean value of the retention rate of breaking strength was 1.003 (rating b), resulting in an overall rating of B rank (pass).

[0095] Example 13: Example in which the inner cover factor cf3(in) of the inner layer in Example 1 was changed from 99% to 82%, and the outer cover factor cf3(out) was changed from 99% to 82% The inner layer used carbon fiber 1 as the axial thread. The outer layer used carbon fiber 1 as the braided thread. The geometric mean value of the retention rate of tensile modulus was 1.002 (a rating), and the geometric mean value of the retention rate of breaking strength was 1.002 (a rating), giving an overall rating of A rank (pass).

[0096] (Variable evaluation of outer layer cover factor (Table 5)) Example 14: Example in which the inner cover factor cf3(in) of the outer layer in Example 1 was changed from 96% to 46%, and the outer cover factor cf3(out) was changed from 90% to 41%. The inner layer used carbon fiber 1 as the axial thread. The outer layer used carbon fiber 1 as the braided thread. In order to make the thickness equivalent to that of other Examples, the outer layer was made of four braided sleeves for the outer layer. The geometric mean value of the retention rate of tensile modulus was 1.017 (rating c), and the geometric mean value of the retention rate of breaking strength was 1.009 (rating b), resulting in an overall rating of C rank (pass).

[0097] Example 15: Example in which the inner cover factor cf3(in) of the outer layer in Example 1 was changed from 96% to 50% and the outer cover factor cf3(out) was changed from 90% to 42% The inner layer used carbon fiber 1 as the axial thread. The outer layer used carbon fiber 2 as the braided thread. In order to make the thickness equivalent to that of other examples, the outer layer was made of three braided sleeves for the outer layer. The geometric mean value of the retention rate of tensile modulus was 1.012 (rating b), and the geometric mean value of the retention rate of breaking strength was 1.005 (rating b), resulting in an overall rating of B rank (pass).

[0098] Example 16: Example in which the inner cover factor cf3(in) of the outer layer in Example 1 was changed from 96% to 78% and the outer cover factor cf3(out) was changed from 90% to 71% The inner layer used carbon fiber 1 as the axial thread. The outer layer used carbon fiber 1 as the braided thread. In order to make the thickness equivalent to that of other examples, two outer layer braided sleeves were stacked on top of each other to form the outer layer. The geometric mean value of the retention rate of tensile modulus was 1.002 (a rating), and the geometric mean value of the retention rate of breaking strength was 1.002 (a rating), resulting in an overall rating of A rank (pass).

[0099] (Variable evaluation of the number of sleeve group sets (Table 6)) Example 17: Example in which the number of sets of braided sleeves in Example 1 was changed from 1 set (inner layer 1, outer layer 1) to 2 sets (inner layer 1, inner layer 2, outer layer 1, outer layer 2). The inner layer used carbon fiber 1 as the axial thread. The outer layer used carbon fiber 1 as the braided thread. The geometric mean value of the retention rate of tensile modulus was 0.998 (a rating), and the geometric mean value of the retention rate of breaking strength was 0.998 (a rating), resulting in an overall rating of A rank (pass).

[0100] From the above results, it was confirmed that an FRP bent pipe formed of a two-layer braided structure consisting of an inner layer formed from a high-strength fiber axial yarn and a braided elastic yarn, and an outer layer formed from a braided high-strength fiber yarn, with the braided yarns of the inner and outer layers oriented at an angle ranging from ±5° to 85°, does not experience any disruption in the fiber orientation even when bent, and maintains a high level of mechanical properties in the axial direction. [Explanation of symbols]

[0101] 1. Bend pipe 11 Braided structure 12 Braided sleeve for outer layer 15 Resin molding 121 Outer layer braid 13 Braided sleeve for inner layer 131 Inner layer braid 132 Axoneme 2 Bent part 21 Inner side 22 Outer periphery X center axis direction

Claims

1. A bent pipe made of FRP, in which a braided structure in which an inner layer and an outer layer are overlapped is embedded inside a cylindrical resin molding, The inner layer is an axial thread formed of high-strength fibers and oriented in the central axis direction of the curved pipe; and an inner layer braided yarn made of elastic yarn, the inner layer braided yarn having an orientation angle in the range of ±5 to ±85° with respect to the central axis direction of the curved pipe, and one or more cylindrical braided sleeves stacked together, The outer layer is is disposed on the outer circumferential side of the inner layer, The curved pipe is characterized by being configured by stacking one or more cylindrical braided sleeves without an axial thread, which are formed by combining outer layer braided yarns made of high-strength fibers and whose orientation angle with respect to the central axis direction of the curved pipe is in the range of ±5 to 85°.

2. In the outer layer, The width of the outer layer yarn is b f [mm] The number of outer layer yarns is n [pieces] The inner diameter of the outer layer is D [mm] The orientation angle of the outer layer yarn is θ [°] In this case, an inner cover factor cf is calculated by the following (Equation 1), which indicates the ratio of the surface area of ​​the outer layer to the surface area of ​​the outer layer on the inner circumferential side of the bent portion of the curved pipe. 1 The outer cover factor cf (in) is 100% or less and 60% or more, and indicates the ratio of the outer layer braid to the surface area of ​​the outer layer corresponding to the outer peripheral side of the bent portion of the curved pipe, and is calculated by the following (Equation 1): 1 2. The bent pipe according to claim 1, wherein the value of (out) is 100% or less and 50% or more. [Equation 1] ...(Formula 1)

3. In the inner layer, The width of the inner layer yarn is b f [mm] The number of inner layer yarns is n [pieces] The inner diameter of the inner layer is D [mm] The orientation angle of the inner layer yarn is θ [°] The width of one cell in the inner layer is f [mm] The width of the axon is b m [mm] The number of the axons is n m [Books] In this case, an inner cover factor cf is calculated by the following (Equation 2) to indicate the ratio of the surface area of ​​the inner layer on the inner circumferential side of the bent portion of the curved pipe to the surface area of ​​the inner layer occupied by the inner layer braid yarns and the axial yarns. 3 The value of (in) is 100% or less and 60% or more, and the outer cover factor cf indicates the ratio of the surface area of ​​the inner layer on the outer circumferential side of the bent portion of the curved pipe that is occupied by the inner layer braid yarns and the axial yarns, which is calculated by the following (Equation 2): 3 2. The bent pipe according to claim 1, wherein the value of (out) is 100% or less and 50% or more. [Equation 2] ...(Formula 2)

4. The bent pipe according to any one of claims 1 to 3, characterized in that the braided structure is a structure in which multiple sets of braided sleeve groups, each set consisting of the inner layer and the outer layer arranged in order from the inner circumferential side, are stacked.

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