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] The present invention relates to a bent pipe having a braided structure. [Background technology]

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

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

[0004] [Patent Document 1] JP 1992-327910 A [Patent Document 2] Patent Publication No. 2021-094739 [Patent Document 3] JP 2018-038463 A [Patent Document 4] JP 1995-223271 A DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

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

[0006] Specifically, the tubular preform of Patent Document 1 has layers with braiding angles of 0° (a braided sleeve combining unidirectional fibers and elastic yarns (nylon crimped yarns)), layers with ±α°, and layers with 0°, stacked from the inside, and since there are two 0° layers, it is difficult to bend the tubular preform in the axial direction. Even if it is 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, and fiber undulations may occur, which may reduce the axial tensile properties and bending properties of the bent tubular preform.

[0007] In addition, with regard to the tubular preforms and curved pipes of Patent Documents 2 to 4, the laminated prepreg UD sheets (0° yarns) have such rigidity that they cannot be bent. If they are forcibly bent, the laminated prepreg UD sheets (0° yarns) will not follow the axial direction, and fiber undulations will occur, which may reduce the axial tensile properties and bending properties of the curved pipe.

[0008] In this way, when it comes to curved pipes that have high levels of mechanical properties in the axial direction, there are conflicting factors in terms of both physical properties and manufacturing, so some ingenuity is required to achieve both.

[0009] Therefore, an object of the present invention is to provide a curved pipe having a cylindrical braided structure, which does not suffer from orientation disturbance such as fiber undulation even when bent in the axial direction, and which maintains a high level of mechanical properties in the axial direction. [Means for solving the problem]

[0010] The present invention provides a curved pipe having a cylindrical braided structure, the curved pipe including an inner layer, an outer layer, and an intermediate layer disposed between the inner layer and the outer layer, The intermediate layer is An axial yarn formed of a high-strength fiber and oriented in a central axis direction of the curved pipe; The curved tube has an orientation angle in the range of ±5 to 85° with respect to the central axis direction, and the intermediate layer braid is made of elastic yarn. The curved tube has a configuration in which one or more cylindrical braids are stacked together. The inner layer is Located on the inner circumferential side of the intermediate layer, The bent pipe has an orientation angle in the range of ±5 to 85° with respect to the central axis direction, and is configured by stacking one or more cylindrical braids without an axial thread, which are formed by combining inner layer braids made of high-strength fibers, The outer layer is The intermediate layer is disposed on an outer peripheral side thereof. The curved tube has an orientation angle in the range of ±5 to 85° with respect to the central axis direction, and is characterized by having one or more stacked cylindrical braids without an axial thread, which are formed by combining outer layer braids made of high-strength fibers.

[0011] According to the above configuration, in the intermediate layer, the high-strength axial thread is fixed to the soft elastic thread, forming a flexible braid, which makes it easier to bend the curved tube while maintaining the orientation of the axial thread (the axial thread remains aligned along the central axis of the curved tube). In addition, when bending a curved pipe, the axial yarn in the middle layer is covered by the inner and outer layers, so the axial yarn does not come apart and can be bent while maintaining its orientation along the central axis. 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 made not to interfere with the bending process of the curved pipe (making it easier to follow the shape changes when the curved pipe is bent). That is, even if the bent pipe is bent in the direction of its central axis, there is no disturbance in the orientation of the fibers, such as undulation, and it is possible to obtain a bent pipe in which the mechanical properties in the direction of the central axis are maintained at a high level.

[0012] Further, the present invention provides the inner layer and the outer layer of the bent pipe, The width of the inner layer yarn or the width of the outer layer yarn is b f [mm] The number of the inner layer yarns or the outer layer yarns is n [pieces] 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 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 ratio of the surface area of ​​the inner layer occupied by the inner layer yarn or the ratio of the surface area of ​​the outer layer occupied by the outer layer yarn, on the inner side of the bent portion of the curved pipe, calculated by the following (Equation 1) when is set as above, is 60% or more and not more than 100%, and the value of an outer cover factor cf1(out), which indicates the ratio of the surface area of ​​the inner layer occupied by the inner layer yarn or the ratio of the surface area of ​​the outer layer occupied by the outer layer yarn, on the outer side of the bent portion of the curved pipe, calculated by the following (Equation 1) when is set as above, is 50% or more and not more than 100%.

number

[0013] As in the above configuration, in the inner and outer layers formed only of yarns (inner layer yarns, outer layer 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 bias of the curved pipe and to increase the torsional strength of the curved pipe itself.

[0014] Further, the present invention provides a bent pipe having an intermediate layer, The width of the intermediate layer yarn is b f[mm] The number of yarns for the intermediate layer is n [pieces] The inner diameter of the intermediate layer is D [mm] The orientation angle of the intermediate layer yarn is θ [°] The width of one cell in the intermediate 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 intermediate layer occupied by the intermediate layer yarn and the axial yarn on the inner side of the bent portion of the curved tube, calculated by the following (Equation 2) when the above is set, is 60% or more and 100% or less, and the value of an outer cover factor cf3(out), which indicates the proportion of the surface area of ​​the intermediate layer occupied by the intermediate layer yarn and the axial yarn on the outer side of the bent portion of the curved tube, calculated by the following (Equation 2) when the above is set, is 50% or more and 100% or less.

number

[0015] In the intermediate layer formed by combining the intermediate 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 tube and the value of the outer cover factor cf3(out) on the outer side of the bent portion of the curved tube satisfy the above conditions, it is possible to prevent a decrease in strength or strength bias of the curved tube and to increase the torsional strength of the curved tube itself.

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

[0017] According to the above-described configuration, by changing the number of sets of the braided sleeve group that constitutes the curved pipe, the flexibility and strength of the curved pipe can be changed according to the required specifications. Effect of the Invention

[0018] To provide a curved pipe having a cylindrical braided structure that maintains a high level of mechanical properties in the axial direction without fiber undulation or other orientation disturbances even when bent in the axial direction. [Brief description of the drawings]

[0019] [Figure 1] FIG. 4 is an explanatory diagram of a curved pipe according to the embodiment. [Diagram 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 three-layer structure of the curved pipe according to the present embodiment. [Diagram 3] FIG. 2 is an explanatory diagram of the braided structure (one cell) of an inner layer braided sleeve and an outer layer braided sleeve. [Figure 4] 1A is an explanatory diagram of a braided structure (1 cell) formed only with intermediate layer braid yarns in an intermediate layer braided sleeve, and FIG. 1B is an explanatory diagram of a braided structure (1 cell) formed with intermediate layer braid yarns and an axial yarn in an intermediate layer braided sleeve. [Diagram 5] 4 is an explanatory diagram of a braided structure of a bent portion of a curved pipe according to the embodiment. FIG. [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. 2 is an explanatory diagram showing the placement of a preform in a mold. [Figure 9] FIG. 2 is an explanatory diagram regarding a resin molding process for a preform. [Figure 10] FIG. 11 is an explanatory diagram regarding removal of the mandrel from the preform after resin molding. [Figure 11] 1 is a photograph showing the appearance of the manufactured bent pipe. [Figure 12] FIG. 11 is a cross-sectional view of a bent pipe according to another embodiment. [Figure 13] FIG. 2 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 a bent portion (central curved portion) of a curved pipe that is the subject of measurement of the tensile modulus of elasticity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[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) that is constructed by a braided structure of yarn (carbon fiber material, etc.) and resin molding, 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 constitute the large drone). The main frame, propeller, propeller guard, arm, and skid that constitute these large drones have curved parts in their shapes, and in addition to being lightweight, having high rigidity, and 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 bent pipe 1 has a structure in which at least three layers of cylindrical braided sleeves are stacked. Specifically, as shown in FIG. 2(A), the curved pipe 1 has a three-layer structure consisting of an inner layer braided sleeve 11 (corresponding to the inner layer) that forms the inner circumference of the curved pipe 1, an outer layer braided sleeve 12 (corresponding to the outer layer) that forms the outer circumference of the curved pipe 1, and an intermediate layer braided sleeve 13 (intermediate layer) that is stacked (arranged) between the inner layer braided sleeve 11 and the outer layer braided sleeve 12.

[0024] (Inner layer braided sleeve 11) The inner layer braided sleeve 11 is laminated on the inner peripheral side of the intermediate layer braided sleeve 13 . 2(B) and 3, the inner layer braided sleeve 11 is formed by combining inner layer braided yarns 111 made of high strength (high elastic modulus) fibers so as to cross and be 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 inner layer braided sleeve 11 does not have an axial yarn that is oriented in the central axial direction X of the curved pipe 1.

[0025] Examples of high strength (high elastic modulus) fibers that can be used to make up the inner layer yarns 111 of the inner layer braided sleeve 11 include carbon fibers, glass fibers, aramid fibers, boron fibers, silicon carbide fibers, steel fibers, polyethylene fibers, nylon fibers, alumina fibers, Tyranno fibers, basalt fibers, and amorphous fibers.

[0026] (Outer layer braid sleeve 12) The outer layer braid sleeve 12 is laminated on the outer peripheral side of the intermediate layer braid sleeve 13 . 2(B) and 3, 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 elastic modulus) fibers so as to be oriented and cross over 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, like the inner layer braided sleeve 11, 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. The high strength (high elastic modulus) fibers constituting the outer layer braided yarns 121 of the outer layer braided sleeve 12 are the same as those of the inner layer braided sleeve 11 .

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

[0028] Examples of high strength (high elastic modulus) fibers that can be used to form the axial threads 132 of the intermediate layer braided sleeve 13 include carbon fibers, glass fibers, aramid fibers, boron fibers, silicon carbide fibers, steel fibers, polyethylene fibers, nylon fibers, alumina fibers, Tyranno fibers, basalt fibers, and amorphous fibers.

[0029] The elastic yarn constituting the intermediate layer braided yarn 131 of the intermediate layer braided sleeve 13 may be, for example, a false twisted yarn (also called a crimped yarn or woolly yarn) obtained by processing a multifilament yarn or a monofilament yarn made of a thermoplastic resin such as nylon resin, polybutylene terephthalate resin, or polyester resin, or a urethane fiber.

[0030] (Resin molding of bent pipe 1) In addition, examples of resin materials used in resin molding for the braided structure of the curved pipe 1 (the inner layer braided sleeve 11, the outer layer braided sleeve 12, and the middle layer braided sleeve 13) 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. In addition, resin molding methods that are used include resin transfer molding (RTM: vacuum suction and pressure impregnation), VaRTM (vacuum impregnation method), and internal pressure molding.

[0031] (Braided structure of bent portion 2 of bent pipe 1) When forming a curved pipe 1, it is necessary to braid the curved portion 2 in a curved shape as shown in Fig. 5, but compared to when braiding in a straight line, the braided structure on the inner peripheral side 21 of the curved portion 2 shrinks, while the braided structure on the outer peripheral side 22 of the curved portion 2 stretches, which may cause unevenness (difference in strength) in the braided structure of the curved pipe 1. If unevenness occurs in the braided structure of the curved pipe 1, the high rigidity and impact resistance of the curved pipe 1 will decrease.

[0032] Therefore, the braided structures of the respective bent portions of the inner layer braided sleeve 11, the outer layer braided sleeve 12, and the intermediate layer braided sleeve 13 constituting the curved pipe 1 are formed using an index (value) called a cover factor cf (Equations 1 to 3) which indicates the proportion of the surface area of ​​each braided structure of the inner layer braided sleeve 11, the outer layer braided sleeve 12, and the intermediate layer braided sleeve 13 constituting the curved pipe 1 that is accounted for by the braided yarns (inner layer braided yarns 111, outer layer braided yarns 121, intermediate layer braided yarns 131) and the axial yarns (axial yarns 132), and which serve as an index of strength of the curved pipe 1 having a braided structure with a circular cross section.

[0033] Here, as shown in FIGS. 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 inner layer braided sleeve 11, the outer layer braided sleeve 12, and the intermediate layer braided sleeve 13 that constitute the curved pipe 1. However, the orientation angle θ [°] with respect to the central axial 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 inner layer braided sleeve 11, the outer layer braided sleeve 12, and the intermediate layer braided sleeve 13 that constitute the curved pipe 1, and the outer cover factor cf(out) of the outer side of each bent portion of the inner layer braided sleeve 11, the outer layer braided sleeve 12, and the intermediate layer braided sleeve 13 that constitute the curved pipe 1. In addition, the calculation of the cover factor cf must take into consideration the following cases: a case in which the cells of the braided structure are composed only of braid yarns (inner layer braid yarns 111, outer layer braid yarns 121) (cf1), as in the inner layer braided sleeve 11 and the outer layer braided sleeve 12 shown in FIG. 3; and a case in which the cells (see FIG. 4(A)) include a braided structure (cf1) composed only of braid yarns (middle layer braid yarns 131), as in the middle layer braided sleeve 13 shown in FIG. 4, and a case in which the cells (see FIG. 4(B)) include a braided structure (cf2) having a braid yarn (middle layer braid yarn 131) and an axial yarn (axial yarn 132) (cf3).

[0034] (Cover factor of inner layer braided sleeve 11 and outer layer braided sleeve 12) In the case where the braided cell is composed only of the inner layer braid 111 (outer layer braid 121) as in the inner layer braid sleeve 11 (outer layer braid 12) shown in FIG. 3, the width b f From values ​​based on two-dimensional data such as the number n [pieces] of the inner layer braided yarns 111 (outer layer braided yarns 121), the inner diameter D [mm] of the inner layer braided sleeve 11 (outer layer braided sleeve 12), and the orientation angle θ [°] of the inner layer braided yarns 111 (outer layer braided sleeve 121) with respect to the central axial direction X of the curved tube 1, the value of the inner cover factor cf1(in) on the inner side of the curved portion of the inner layer braided sleeve 11 (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 inner layer braided sleeve 11 (outer layer braided sleeve 12) are calculated using the following (Equation 1):

[0035]

number

[0036] Furthermore, when the braided structure is composed only of the inner layer braided yarn 111 (outer layer braided yarn 121) (when the braided structure does not include an axial yarn), as in the inner layer braided sleeve 11 (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, a decrease in strength or strength bias in the bent portion 2 of the curved pipe 1 can be prevented, and the torsional strength of the curved pipe 1 itself can be increased.

[0037] The above-described braided sleeve 11 for the inner layer can prevent buckling damage of the axial threads 132 of the braided sleeve 13 for the intermediate layer due to bending load, and can increase the torsional strength of the curved pipe 1 itself. Furthermore, with the above-described outer layer braided sleeve 12, by restraining the axial yarns 132 of the intermediate 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 in strength of the curved pipe 1, thereby increasing the torsional strength of the curved pipe 1 itself.

[0038] (Cover factor of braid sleeve 13 for mid layer) When the cell (see FIG. 4(A)) includes a braided structure composed only of an intermediate layer yarn 131, and the cell (see FIG. 4(B)) includes a braided structure having an intermediate layer yarn 131 and an axial yarn 132, as in the case of the intermediate layer braided sleeve 13 shown in FIG. 4, the value of the cover factor cf3 is calculated taking into consideration the cover factor cf1 (calculated in the same manner as the inner layer braided sleeve 11: see formula 1) in the cell shown in FIG. 4(A) whose braided structure is composed only of 131, and the cover factor cf2 in the cell shown in FIG. 4(B) whose braided structure is composed of an intermediate layer yarn 131 and an axial yarn 132.

[0039] Here, as shown in FIG. 4B, when the braided cell includes an intermediate layer yarn 131 and an axial yarn 132, the width b fIn addition to the number n [pieces] of intermediate layer braid yarns 131, the inner diameter D [mm] of the intermediate layer braid sleeve 13, and the orientation angle θ [°] of the intermediate layer braid yarns 131 with respect to the central axis direction X, the width f [mm] of one cell of the braided structure (one section surrounded by the intermediate layer braid yarns 131: see FIG. 4(B)), the width b [mm] of the axial yarn 132, m [mm] and the number n of the axle threads 132 m From values ​​based on two-dimensional data such as [pieces], the value of the inner cover factor cf2(in) on the inner side of the curved portion of the intermediate layer braid sleeve 13, and the value of the outer cover factor cf2(out) on the outer side of the curved portion of the intermediate layer braid sleeve 13 are calculated using the following (Equation 2).

[0040]

number

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

[0042] In the case of the intermediate layer braided sleeve 13, in which the cell (see FIG. 4(A)) includes a braided structure composed only of the intermediate layer braid 131, and in which the cell (see FIG. 4(B)) includes a braided structure having the intermediate layer braid 131 and an axial yarn 132, the cover factor cf3 is calculated by using the cover factor cf1 in the cell in which the braided structure is composed only of the intermediate layer braid 131 shown in FIG. 4(A) and the cover factor cf2 in the cell in which the braided structure is composed only of the intermediate layer braid 131 shown in FIG. 4(B). 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 cell composed of the above, 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 bias in the bent portion 2 of the curved pipe 1, and to increase the torsional strength of the curved pipe 1 itself.

[0043] In the above-mentioned braided sleeve for intermediate layer 13, elastic yarn is used for the braided yarn 131 for the intermediate layer, so that the braided sleeve for intermediate 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 curved portion 2 of the curved tube 1.

[0044]

number

[0045] As described above, the inner layer braided sleeve 11, the outer layer braided sleeve 12, and the intermediate layer braided sleeve 13 constituting the curved pipe 1 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%, it will exceed the surface area of ​​the inner layer braided sleeve 11, the outer layer braided sleeve 12, and the intermediate layer braided sleeve 13 formed by the braided structure of the inner layer braid 111 (outer layer braid 121) and the braided structure of the intermediate layer braid 131 and axial yarn 132, and as a result, part of the inner layer braid 111 (outer layer braid 121), the intermediate layer braid 131, and the axial yarn 132 will float on the surface of the curved tube 1, and loads will be applied to the floated parts or their surroundings, which may reduce the high rigidity and impact resistance of the curved 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%, a bias in strength (difference in strength) will occur in the braided structure between the inner side 21 and the outer side 22 of the bent portion 2 of the curved pipe 1, which may reduce the high rigidity and impact resistance of the curved pipe 1.

[0046] In order to further enhance the high rigidity and impact resistance of the curved pipe 1, it is more preferable that the inner cover factor cf(in) value is within the range of 100% to 70% and the outer cover factor cf(out) value is within the range of 100% to 60% in the inner layer braided sleeve 11, the outer layer braided sleeve 12, and the intermediate layer braided sleeve 13 constituting the curved pipe 1. Furthermore, it is most preferable that the inner cover factor cf(in) value is within the range of 100% to 80% and the outer cover factor cf(out) value is within the range of 100% to 70%.

[0047] (Manufacturing method of curved pipe 1) Next, a method for manufacturing the curved pipe 1 will be described.

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

[0049] For example, in the case of an inner layer braided sleeve 11 (outer layer braided sleeve 12), braided yarns (inner layer braided yarns 111 and outer layer braided yarns 121) wound around a spindle are combined on the outer periphery of a cylindrical mandrel to form the inner layer braided sleeve 11 (outer layer braided sleeve 12). As shown in Fig. 6(b) , the spindle moves along a track, so that the braided yarns (inner layer braided yarns 111 and outer layer braided yarns 121) are combined to form a seamless inner layer braided sleeve 11 (outer layer braided sleeve 12) on the upper part of the mandrel, and the seamless inner layer braided sleeve 11 (outer layer braided sleeve 12) is wound up by a winding device.

[0050] In the case of the braided sleeve for intermediate layer 13, the braided yarn (braided yarn for intermediate layer 131) wound around the spindle and the axial yarn 132 supplied from the lower part of the braiding machine (supplied from a fixed cylinder) are combined on the outer periphery of a cylindrical mandrel to form the braided sleeve for intermediate layer 13. As shown in Fig. 6(b) , the spindle moves along the track, so that the braided yarn (braided yarn for intermediate layer 131) and the axial yarn 132 are combined to form a seamless braided sleeve for intermediate layer 13 on the upper part of the mandrel, which is then wound up by a winding device.

[0051] Here, in the case where the braided structure is composed only of the inner layer braid yarn 111 (outer layer braid yarn 121) (where the braided structure does not include an axial thread), as in the case of the inner layer braided sleeve 11 (outer layer braided sleeve 12), the width b f The values ​​of various parameters, such as the number n [pieces] of the inner layer braided yarns 111 (outer layer braided yarns 121), the inner diameter D [mm] of the inner layer braided sleeve 11 (outer layer braided sleeve 12), and the orientation angle θ [°] of the inner layer braided yarns 111 (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% 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.

[0052] In addition, in the case of the intermediate layer braided sleeve 13, in which the cell (see FIG. 4(A)) includes a braided structure composed only of the intermediate layer braid 131, and the cell (see FIG. 4(B)) includes a braided structure having the intermediate layer braid 131 and the axial yarn 132, the width b f In addition to the number n [pieces] of intermediate layer braid yarns 131, the inner diameter D [mm] of the intermediate layer braid sleeve 13, and the orientation angle θ [°] of the intermediate layer braid yarns 131 with respect to the central axis direction X, the width f [mm] of one cell of the braided structure (one section surrounded by the intermediate layer braid yarns 131: see FIG. 4(B)), the width b [mm] of the axial yarn 132, m [mm] and the number n of the axle 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 formula 3 is in the range of 100% to 60% and the value of the outer cover factor cf3(out) calculated by the above formula 3 is in the range of 100% to 50%.

[0053] (2) Manufacturing of preforms Next, as shown in FIG. 7, an inner layer braided sleeve 11, a middle layer braided sleeve 13, and an outer layer braided sleeve 12 are placed in that order onto a cylindrical silicone resin mandrel to produce a preform having three layers of cylindrical braided sleeves. In this embodiment, a mandrel made of silicone resin is used for the shaft portion (rod) of the preform. However, the material used for the mandrel may be an elastic thermosetting resin or thermoplastic resin. Also, by using, for example, wax, polystyrene foam, plaster, or a low melting point alloy, it is possible to remove the shaft portion from the molded product even after molding.

[0054] (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 a lid is placed.

[0055] In the present embodiment, in manufacturing the preform, three layers of tubular braided sleeves (braided sleeve 11 for the inner layer, braided sleeve 13 for the middle layer, and braided sleeve 12 for the outer layer) are stacked around a cylindrical mandrel, and then the mandrel is bent. However, it is also possible to first prepare a bent mandrel, and then stack three layers of tubular braided sleeves (braided sleeve 11 for the inner layer, braided sleeve 13 for the middle layer, and braided sleeve 12 for the outer layer) around this bent mandrel.

[0056] (4) Resin molding process Next, as shown in Figure 9, thermosetting resin (matrix resin) is pressurized and injected into the cavity of the mold by 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 Resistant Molding (VaRTM) or internal pressure molding.

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

[0058] (6) Finishing Finally, the bent pipe 1 is obtained by removing burrs, cutting and painting (see FIG. 11).

[0059] According to the configuration of the curved pipe 1, in the intermediate layer braid sleeve 13, the high-strength axial threads 132 are fixed to the soft intermediate layer braid yarns 131, resulting in a flexible braid, which makes it easier to bend the curved pipe 1 while maintaining the orientation of the axial threads 132 (while the axial threads 132 remain aligned along the central axis direction X of the curved pipe 1). In addition, when bending the curved pipe 1, since the axial yarn 132 of the intermediate layer braided sleeve 13 is covered by the inner layer braided sleeve 11 and the outer layer braided sleeve 12, the axial yarn 132 does not come apart and can be bent while maintaining its orientation in the central axis direction X. Furthermore, since the inner layer braided sleeve 11 and the outer layer braided sleeve 12 do not include axial yarns oriented in the central axis direction X, the inner layer braided sleeve 11 and the outer layer braided sleeve 12 can be made not to interfere with the bending process of the curved pipe 1 (they can easily follow the shape change when the curved pipe 1 is bent). That is, even if the curved pipe 1 is bent in the central axis direction X, there is no orientation disturbance such as fiber waviness, 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.

[0060] Furthermore, when the curved pipe 1 is used for the main body frame, propeller, propeller guard, arm, and skid that constitute a large drone, which is a large unmanned aerial vehicle, in addition to being lightweight, having high rigidity, and excellent vibration damping properties, even when the curved pipe 1 is bent in the central axis direction X, no orientation disturbance such as fiber undulation occurs, and the mechanical properties in the central axis direction X are maintained at a high level.

[0061] (Other embodiments) In the above embodiment, the curved pipe 1 has been described as having a three-layer structure with one inner layer braided sleeve 11 as the inner layer, one outer layer braided sleeve 12 as the outer layer, and one intermediate layer braided sleeve 13 as the intermediate layer. However, taking into account the flexibility and strength of the curved pipe 1, each layer may be configured by stacking multiple braided sleeves. For example, the inner layer may be configured by stacking multiple inner layer braid sleeves 11, the outer layer may be configured by stacking multiple outer layer braid sleeves 12, or the intermediate layer may be configured by stacking multiple intermediate layer braid sleeves 13. In this way, by changing the number of braided sleeves layered in the inner layer, outer layer, and intermediate layer, the flexibility and strength of the curved pipe 1 can be changed according to the required specifications.

[0062] In addition, in the above embodiment, if a set of braided sleeves is made up of an inner layer braided sleeve 11 (1 piece), an intermediate layer braided sleeve 13 (1 piece), and an outer layer braided sleeve 12 (1 piece), which are stacked in order from the inner circumference side, the curved pipe 1 is made up of one set of braided sleeves, but this is not limited to the configuration, and a curved pipe may be made up of multiple sets of braided sleeves stacked on top of each other. 12, for example, the curved pipe 101 is configured by stacking two sets of braided sleeve groups 10 (10A, 10B). That is, the curved pipe 101 is configured by stacking, in order from the inner periphery, an inner layer braided sleeve 11, an intermediate layer braided sleeve 13, an outer layer braided sleeve 12, an inner layer braided sleeve 11, an intermediate layer braided sleeve 13, and an outer layer braided sleeve 12. In this manner, by changing the number of sets of the braided sleeve group 10 constituting the bent pipe 101, the flexibility and strength of the bent pipe 101 can be changed according to the required specifications.

[0063] 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; however, the curved pipe 1 may also be used in a manned aircraft (for example, a large drone-type flying taxi).

[0064] Although the embodiments of the present invention have been described above, they are merely illustrative examples and do not 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. EXAMPLES

[0065] [Verification based on Examples 1 to 15 and Comparative Examples 1 to 4] The curved pipe of the present invention has a braided structure consisting of three layers: an "intermediate layer" formed of an axial yarn made of high-strength fibers and a braided yarn made of elastic yarns oriented at an orientation angle in the range of ±5 to 85°; and an "inner layer" and "outer layer" which do not have an axial yarn and are formed of a braided yarn made of high-strength fibers oriented at an orientation angle in the range of ±5 to 85°. Even when bending, the orientation of the fibers does not become disturbed and the mechanical properties in the axial direction 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 comparative verification was performed 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 with reference to examples, but the present invention is not limited to these examples.

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

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

[0069] <Resin composition used for bent pipe> Thermosetting resin: Vinyl ester resin (brand CBZ500LM-AS, viscosity 200-350 mPa·s, made by Japan U-Pica) Accelerator: PR-CBZ01 (made by Japan U-Pica) Hardener: 328E (made by Nouryon Chemical)

[0070] (Manufacturing method of curved pipes) Using the "manufacturing method for curved pipe" described in the above embodiment, curved FRP pipes having a braided structure described in Examples 1 to 15 and Comparative Examples 1 to 4 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 Fig. 13. The manufacturing method for straight pipes is the same as that of the "manufacturing method for curved pipes" except that the shape of the cavity of the mold used in resin transfer molding (RTM) is straight.

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

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

[0073] (Variable evaluation of cover factor) [Table 5]

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

[0075] (Test Method) <Method for measuring tensile modulus of elasticity of curved and straight pipes> Test pieces measuring L50mm x W5mm x 1.5tmm were taken from the bent portion (central curved portion) of the curved pipe produced by the above manufacturing method using the water jet method, one each on the inside and outside (see Figure 14). In addition, test pieces of the same dimensions as the curved 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, for test pieces taken from the bent part (central curved part) of the curved pipe and from the center of the straight pipe, tensile tests were performed at a speed of 1 mm / min in an environment of a temperature of 23±2°C and a humidity of 50±10% according to a method in accordance with JIS K7164 (2005), and the tensile modulus of elasticity E was calculated from the obtained stress-strain curve using (Equation 4).

[0076]

number

[0077] In this test, the area where the slope is linear is set 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 curved pipe was defined as E(in), and the tensile modulus of the test piece taken from the outside was defined as E(out), and the average of E(in) and E(out) was defined as the tensile modulus of the curved pipe. The tensile modulus of the straight pipe was defined as the average of the values ​​at the two locations.

[0078] <Method of measuring the breaking strength of curved 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 part 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 formula 5 (the number of tests was 3 for each).

[0079] <Settings for measuring the breaking strength of curved pipes> ·Equipment Autograph: Amsler Strain gauge: KFGS-2-120-C1-11LIM3R Kyowa Electric Industries Strain gauge adhesive: CC-33A Kyowa Electric Industries 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: A core bar is inserted to prevent crushing by the chuck

[0080]

number

[0081] (Regarding test results) <Determining the pass / fail criteria for bent pipes> FRP curved pipes were deemed to pass if they maintained a high level of axial mechanical properties without any disturbance in 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. As an index value, the ratio of the tensile modulus of elasticity between the bent part (central curved part) of the curved pipe and the central part of the straight pipe, calculated using the above-mentioned method for measuring the tensile modulus of elasticity, was calculated as the retention rate, and ranked according to the following criteria. A rating: The retention rate of tensile elastic modulus (ratio of tensile elastic modulus of curved pipe to straight pipe) is 0.8 or more. B: The retention rate of the tensile modulus (ratio of the tensile modulus of the curved pipe to that of the straight pipe) is less than 0.8.

[0082] In addition, since FRP curved pipes are expected to be used as structural components for large drones and other devices, their breaking strength is important. The breaking strength of the bent pipes was calculated using the breaking strength measuring method described above, and was ranked according to the following criteria. A rating: Breaking strength is 500 MPa or more B: Breaking strength is 400MPa or more and less than 500MPa C: Breaking strength is less than 400MPa

[0083] The overall evaluation was ranked into A (pass), B (pass), C (pass), and D (fail) based on the evaluation criteria in Table 7 below.

[0084] [Table 7]

[0085] <Test results for curved and straight pipes> (Evaluation of laminated structure (Table 3)) [Comparative Example 1: Example of a three-layer structure in which the middle layer is formed only with axial yarn (no braiding yarn)] In the sleeve braiding process, since there was no braiding yarn to fix the axial threads of the middle layer, the orientation of the axial threads of the middle layer was disturbed, the sleeve was unable to maintain its shape, and curved or straight tubes could not be produced.

[0086] [Comparative Example 2: Example of a three-layer structure in which the middle layer of braided yarn is made of high-strength fiber] Because the sleeve of the middle layer, in which both the axial thread and the braiding thread are made of high-strength fibers, is inflexible, it was possible to produce a straight pipe, but when placing the preform in the mold, it was not possible to bend the preform, and therefore it was not possible to produce a curved pipe.

[0087] [Comparative Example 3: An example of a three-layer structure in which the inner layer is formed of an axon and braided yarn, and the middle layer is formed only of braided yarn] In the manufacture of preforms, the frictional force between the inner sleeve and the silicone resin mandrel was so large that the inner sleeve could not be placed over the mandrel, making it impossible to manufacture curved or straight pipes.

[0088] [Comparative Example 4: An example of a three-layer structure in which the outer layer is formed of an axon and braided yarn, and the middle layer is formed only of braided yarn] In the manufacture of the preform, since there was no layer to fix the axial yarns of the outer layer on the outer periphery side of the outer layer, the orientation of the axial yarns on the outer periphery side of the outer layer was disturbed, and the cover factor cf3(out) on the outer periphery side of the outer layer was small at 43%, which was a large difference from the cover factor cf3(in) on the inner periphery side of 93%. As a result, the retention rate of the tensile modulus was small at 0.56 (b judgment), and the overall judgment was D rank (failure).

[0089] [Example 1: An example of a three-layer structure consisting of a middle layer formed of an axial yarn and a braided yarn, and an inner layer and an outer layer formed only of a braided yarn] The retention rate of the tensile modulus of elasticity was 0.94 (a rating), and the breaking strength of the curved pipe was 650 MPa (a rating), giving an overall rating of A rank (pass).

[0090] [Example 2: Example in which the number of stacked intermediate layers in Example 1 was changed from 1 to 2] The retention rate of the tensile modulus of elasticity was 0.84 (a rating), and the breaking strength of the bent pipe was 740 MPa (a rating), giving an overall rating of A rank (pass).

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

[0092] [Example 4: Example in which the inner orientation angle of the braided yarn in the middle layer in Example 1 was changed from 47° to 15°, and the outer orientation angle was changed from 45° to 13°] The retention rate of the tensile modulus of elasticity was 0.94 (a rating), and the breaking strength of the curved pipe was 620 MPa (a rating), giving an overall rating of A rank (pass).

[0093] [Example 5: Example in which the inner orientation angle of the braided yarn in the middle layer in Example 1 was changed from 47° to 80°, and the outer orientation angle was changed from 45° to 77°] The retention rate of the tensile modulus of elasticity was 0.94 (a rating), and the breaking strength of the bent pipe was 630 MPa (a rating), giving an overall rating of A rank (pass).

[0094] [Example 6: Example in which the inner orientation angle of the braided yarn in the middle layer in Example 1 was changed from 47° to 85°, and the outer orientation angle was changed from 45° to 84°] The retention rate of the tensile modulus of elasticity was 0.94 (a rating), and the breaking strength of the bent pipe was 630 MPa (a rating), giving an overall rating of A rank (pass).

[0095] (Variable evaluation of outer layer orientation angle (Table 4)) [Example 7: Example in which the inner orientation angle of the braided yarn in the middle layer in Example 1 was changed from 48° to 34°, and the outer orientation angle was changed from 46° to 27°] The retention rate of the tensile modulus of elasticity was 0.89 (a rating), and the breaking strength of the curved pipe was 630 MPa (a rating), giving an overall rating of A rank (pass).

[0096] [Example 8: Example in which the inner orientation angle of the braided yarn in the middle layer in Example 1 was changed from 48° to 60°, and the outer orientation angle was changed from 46° to 53°] The retention rate of the tensile modulus of elasticity was 0.86 (a rating), and the breaking strength of the curved pipe was 500 MPa (a rating), giving an overall rating of A rank (pass).

[0097] (Variable evaluation of cover factors for the middle class (Table 5)) [Example 9: Example in which the inner cover factor cf3(in) of the intermediate layer in Example 1 was changed from 93% to 52%, and the outer cover factor cf3(out) was changed from 80% to 40%] The retention rate of the tensile modulus of elasticity was 0.84 (grade a), and the breaking strength of the bent pipe was 380 MPa (grade c), giving an overall grade of C (pass).

[0098] [Example 10: Example in which the inner cover factor cf3(in) of the intermediate layer in Example 1 was changed from 93% to 64%, and the outer cover factor cf3(out) was changed from 80% to 52%] The retention rate of the tensile modulus of elasticity was 0.86 (grade a), and the breaking strength of the curved pipe was 460 MPa (grade b), giving an overall grade of B (pass).

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

[0100] (Variable evaluation of outer layer cover factor (Table 5)) [Example 12: Example in which the inner cover factor cf3(in) of the outer layer in Example 1 was changed from 94% to 47%, and the outer cover factor cf3(out) was changed from 93% to 41%] The retention rate of the tensile modulus of elasticity was 0.94 (grade a), and the breaking strength of the bent pipe was 360 MPa (grade c), giving an overall grade of C (pass).

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

[0102] [Example 14: Example in which the inner cover factor cf3(in) of the outer layer in Example 1 was changed from 94% to 79%, and the outer cover factor cf3(out) was changed from 93% to 72%] The retention rate of the tensile modulus was 0.95 (a rating), and the breaking strength of the curved pipe was 520 MPa (a rating), giving an overall rating of A rank (pass).

[0103] (Variable evaluation of the number of sleeve group sets (Table 6)) [Example 15: Example in which the number of sets of braided sleeve groups in Example 1 was changed from 1 set to 2 sets] The retention rate of the tensile modulus of elasticity was 0.93 (a rating), and the breaking strength of the bent pipe was 640 MPa (a rating), giving an overall rating of A rank (pass).

[0104] Regarding the variable evaluation regarding the range of the orientation angle of the inner layer yarn, since it is clear that the results are similar to those of the variable evaluation regarding the range of the orientation angle of the outer layer yarn, no verification was performed. In addition, the variable evaluation regarding the range of the cover factor of the inner layer was not verified because it is clear that the results are similar to the variable evaluation regarding the range of the cover factor of the outer layer.

[0105] From the above results, it was confirmed that a three-layer curved pipe consisting of an intermediate layer formed from an axial yarn of high-strength fiber and a braided yarn of elastic yarn, and inner and outer layers formed from braided yarns of high-strength fiber, with the braided yarns of the intermediate, inner and outer layers oriented at angles ranging from ±5° to 85°, does not experience any disturbance in the fiber orientation even when subjected to bending processing, and maintains a high level of mechanical properties in the axial direction. [Explanation of symbols]

[0106] 1 Bend Pipe 11 Braided sleeve for inner layer 111 Inner layer braid 12 Braided sleeve for outer layer 121 Outer layer yarn 13 Braided sleeve for intermediate layer 131 Intermediate layer yarn 132 Axon 2 Bent part 21 Inner side 22 Outer circumference X Center axis direction

Claims

1. A cylindrical curved pipe having a circular cross section, made of FRP and configured by a braided structure in which an inner layer, an outer layer, and an intermediate layer disposed between the inner layer and the outer layer are overlapped and resin molding, The intermediate layer is an axial thread formed of high-strength fibers and oriented in the central axis direction of the curved pipe; and an intermediate layer braided yarn made of elastic yarn, the intermediate layer braided yarn having an orientation angle in the range of ±5 to ±85° with respect to the central axis direction of the curved tube, and one or more cylindrical braided sleeves stacked together, The inner layer is is disposed on the inner circumferential side of the intermediate layer, The bent pipe has an orientation angle in the range of ±5 to 85° with respect to the central axis direction, and the braided sleeve is formed by combining inner layer braided yarns made of high-strength fibers, and the braided sleeve is configured by stacking one or more cylindrical braided sleeves without an axial yarn, The outer layer is and disposed on the outer peripheral side of the intermediate 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 inner layer and the outer layer, The width of the inner layer braiding yarn or the width of the outer layer braiding yarn is b f [mm] The number of the inner layer yarns or the outer layer yarns is n [pieces] 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 orientation angle of the outer layer yarn is θ [°] an inner cover factor cf, which indicates the ratio of the inner layer braiding yarn to the surface area of ​​the inner layer or the ratio of the outer layer braiding yarn to the surface area of ​​the outer layer on the inner circumferential side of the bent portion of the curved pipe, calculated by the following (Equation 1) when 1 The value of (in) is 100% or less and 60% or more, and the outer cover factor cf indicates the ratio of the inner layer braiding yarn to the surface area of ​​the inner layer or the ratio of the outer layer braiding yarn to the surface area of ​​the outer layer, which corresponds 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 intermediate layer, The width of the intermediate layer yarn is b f [mm] The number of intermediate layer yarns is n [pieces] The inner diameter of the intermediate layer is D [mm] The orientation angle of the intermediate layer yarn is θ [°] The width of one cell in the intermediate layer is f [mm] The width of the axon is b m [mm] The number of the axons is n m [Books] An inner cover factor cf, which indicates the ratio of the surface area of ​​the intermediate layer on the inner circumferential side of the bent portion of the curved pipe to the surface area of ​​the intermediate layer that is occupied by the intermediate layer braid yarns and the axial yarns, is calculated by the following (Equation 2) when 3 The outer cover factor cf (in) is 100% or less and 60% or more, and indicates the ratio of the surface area of ​​the intermediate layer on the outer circumferential side of the bent portion of the curved tube that is occupied by the intermediate layer braid yarns and the axial yarns, and 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. A curved pipe as described in any one of claims 1 to 3, characterized in that multiple sets of braided sleeve groups, each set consisting of the inner layer, the intermediate layer, and the outer layer arranged in order from the inner circumferential side, are stacked on top of each other.

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