Cylindrical body and method for manufacturing a cylindrical body

Abstract

The cylindrical body (1) made of fiber-reinforced resin, used as a structural material for vehicles, has corners (4) extending along the axis of the cylindrical body (1) on its outer peripheral surface. The cylindrical body (1) is a cylindrical laminate consisting of multiple fabric layers (12) and multiple unidirectional material layers (11, 13). Each fabric material comprises a fabric woven from reinforcing fibers and resin impregnated in the fabric. Each unidirectional material layer (11, 13) comprises unidirectionally oriented reinforcing fibers and resin impregnated in the reinforcing fibers. The reinforcing fibers of each unidirectional material layer (11, 13) are oriented along the axis of the cylindrical laminate. The multiple unidirectional material layers (11, 13) include: an outer unidirectional material layer (13) laminated on the outer peripheral surface of the fabric layer (12); and an inner unidirectional material layer (11) laminated on the inner peripheral surface of the fabric layer.

Description

Technical Field

[0001] This disclosure relates to a cylindrical body made of fiber-reinforced resin and a method for manufacturing the cylindrical body. Background Technology

[0002] Although lightweight, fiber-reinforced resin tubular structures possess excellent strength, making them widely used as structural materials in automobiles, aircraft, and sporting goods such as golf clubs and tennis rackets. Even within tubular structures, for example, a square tube with a polygonal radial cross-section has a larger moment of inertia compared to a circular tube with a circular radial cross-section. Therefore, they exhibit excellent bending stiffness, making them useful as structural materials.

[0003] As such a square tube, there are molded articles using a unidirectional material, which is a fiber-reinforced resin sheet containing unidirectionally oriented reinforcing fibers. This molded article is formed by laminating multiple layers of unidirectional material around a core material and then curing it by heating. Such unidirectional material is laminated while appropriately adjusting the orientation direction of the reinforcing fibers according to the required properties of the square tube. The flexural stiffness of the square tube is improved by the reinforcing fibers oriented along the axis of the square tube, thereby achieving the strength required for the structural material.

[0004] When using unidirectional materials in square tubes, large pores tend to form at the corners. This is because during the molding process, reinforcing fibers oriented orthogonally to the axis are difficult to shape along the corners, resulting in a propped-up state. Consequently, voids easily form between layers. Furthermore, due to heating during molding, the volume of these voids increases, or multiple voids connect, or they appear as pores in the molded product. When fracture originates from these pores, the strength of the square tube decreases. Additionally, the amount of resin increases at the corners, and sometimes uneven resin distribution occurs throughout the entire square tube.

[0005] As a structural material for vehicles, aircraft, and the like, there are molded products using fiber-reinforced resin sheets, which are fabrics made by impregnating reinforcing fibers with resin. Because the reinforcing fibers in fiber-reinforced resin sheet fabrics curl at the intersections of warp and weft threads, they easily follow curved surfaces. Therefore, fabrics using fiber-reinforced resin sheets are advantageous when molding complex shapes.

[0006] Patent Document 1 discloses a resin fuel tank for mounting on a car body. The fuel tank has a fiber reinforcement layer formed by laminating fabric material. By having a fiber reinforcement layer, the fuel tank can be made lightweight and given high rigidity.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2017-1618 Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] Therefore, the inventors considered that if a square tube is formed from a fabric material, the formation of corner voids can be suppressed, thereby suppressing the reduction in bending stiffness. Assuming a square tube is used as a structural material for reinforcing automotive roofs, etc., and a square tube is formed from a fabric material, it can be confirmed that: in a square tube formed from a fabric material, the formation of corner voids can be suppressed, and the bending stiffness is improved compared to the case where it is formed from a unidirectional material.

[0012] However, it is understood that while increased bending stiffness increases the risk of breakage, it also presents a problem when the square tube fractures. This refers to the phenomenon where, when a large bending load is applied to the square tube, causing it to begin to fracture, the tube may be completely severed. Assuming this occurs in a scenario such as a car colliding with a utility pole, the impact of the collision applies a large bending load to the square tube, which is a structural material. The tube may then be unable to withstand the bending load and completely sever. This could result in undesirable consequences, such as the severed tube fragment embedding itself in an unexpected location.

[0013] Solution for solving the problem

[0014] One aspect of the disclosed cylindrical body is a fiber-reinforced resin cylindrical body used as a structural material for vehicles, the cylindrical body having one or more corner portions extending along the axis of the cylindrical body on its outer peripheral surface. The cylindrical body is a cylindrical laminated body formed by laminating a fabric layer and multiple unidirectional material layers. The fabric layer is a fabric layer formed by laminating multiple fabric materials, each fabric material comprising a fabric woven from reinforcing fibers and resin impregnated in the fabric. Each of the multiple unidirectional material layers comprises unidirectionally oriented reinforcing fibers and resin impregnated in the reinforcing fibers. The reinforcing fibers of each unidirectional material layer are oriented along the axis of the cylindrical laminated body. The multiple unidirectional material layers include: an outer unidirectional material layer laminated on the outer peripheral surface of the fabric layer; and an inner unidirectional material layer laminated on the inner peripheral surface of the fabric layer.

[0015] Here, the "corner extending along the axis" of the "fiber-reinforced resin cylindrical body" is defined as follows: When the outer peripheral surface of the cylindrical body comprises multiple planes, it refers to a corner where, in a radial section, the straight-line intersection of adjacent planes extends along the axis. Furthermore, when the outer peripheral surface of the cylindrical body comprises both planes and curved surfaces, it refers to a corner where, in a radial section, the intersection of planes and curved surfaces, and the portion where the inclination of the tangent in the radial section changes discontinuously, extends along the axis. Further, when the outer peripheral surface of the cylindrical body comprises multiple curved surfaces, it refers to a corner where, in a radial section, the intersection of adjacent curved surfaces, and the portion where the inclination of the tangent in the radial section changes discontinuously, extends along the axis. In addition, "corner" also includes a portion that is chamfered and bent. A chamfered portion refers to a curved shape with a smaller curvature compared to the planes or curved surfaces of the outer peripheral surface of the cylindrical body.

[0016] According to the above structure, the tubular body comprises multiple layers of fabric material, each fabric material including a woven fabric of reinforcing fibers and a resin impregnated in the fabric. In the fabric layers, the reinforcing fibers are curled at the intersections of the warp and weft threads, thus allowing the reinforcing fibers to easily conform to the shape of the corners of the tubular body. Therefore, the formation of pores in the interlayers of the fabric material can be suppressed. Furthermore, the tubular body exhibits excellent bending rigidity.

[0017] Furthermore, unidirectional material layers are laminated on both the inner and outer circumferential surfaces of the fabric layer. Each unidirectional material layer includes unidirectionally oriented reinforcing fibers and resin impregnated with the reinforcing fibers. Such a tubular body can prevent complete shearing even under bending loads. Therefore, the tubular body has excellent bending stiffness and can prevent complete shearing.

[0018] This disclosure discloses a method for manufacturing a cylindrical body, specifically a fiber-reinforced resin cylindrical body used as a structural material for vehicles, wherein the cylindrical body has one or more corner portions extending along the axis of the cylindrical body on its outer peripheral surface. The method includes laminating four or more molded substrates around a core material. The four or more molded substrates comprise: a plurality of unidirectional materials, each unidirectional material comprising unidirectionally oriented reinforcing fibers and resin impregnated with the reinforcing fibers; and a plurality of fabric materials, each fabric material comprising a fabric woven from reinforcing fibers and resin impregnated with the fabric. The method further comprises heating the four or more molded substrates disposed around the core material. The lamination includes: disposing at least one of the unidirectional materials around the core material such that the reinforcing fibers are oriented along the axis of the core material; disposing the plurality of fabric materials around the at least one unidirectional material; and disposing at least one of the unidirectional materials around the plurality of fabric materials such that the reinforcing fibers are oriented along the axis of the core material.

[0019] According to the above structure, multiple fabric materials, including a fabric woven from reinforcing fibers and a resin impregnated in the fabric, are arranged around a unidirectional material. In the fabric material, the reinforcing fibers are curled at the intersections of the warp and weft threads, so even if the core material or mold has corners, the reinforcing fibers easily conform to the shape of the inner surface of the mold. Therefore, the corners have good shapeability, enabling the formation of a cylindrical body that suppresses the formation of porosity at the corners. Thus, a cylindrical body with excellent bending rigidity is obtained.

[0020] Furthermore, unidirectional materials are placed before and after the fabric materials. Thus, unidirectional material layers are deposited on both the inner and outer circumferential surfaces of the multiple fabric layers. The reinforcing fibers of the unidirectional material are oriented along the axis of the core material. Therefore, in the formed tubular body, the unidirectional material layers are exposed on both the inner and outer circumferential surfaces. Therefore, even under bending loads, complete cutting of the tubular body can be prevented. Thus, a tubular body with excellent bending rigidity and the ability to prevent complete cutting can be manufactured. Attached Figure Description

[0021] Figure 1 This is a perspective view of the square tube that serves as the cylindrical body in this embodiment.

[0022] Figure 2 Yes Figure 1 The diagram illustrates the manufacturing method of the square tube.

[0023] Figure 3 Figure 3A This is a sectional view of the first modified example of the square tube. Figure 3B This is a sectional view of the second modified example of the square tube. Figure 3C This is a cross-sectional view of the third variation of the square tube.

[0024] Figure 4This is a diagram illustrating the three-point bending test.

[0025] Figure 5 This is a coordinate graph showing the results of the three-point bending test.

[0026] Figure 6A The photograph shows the results of the three-point bending test of the square tube in Example 1. Figure 6B This is a photograph showing the results of the three-point bending test of the square tube in Comparative Example 2. Detailed Implementation

[0027] Hereinafter, one embodiment of the cylindrical body will be described.

[0028] like Figure 1 As shown, one example of the cylindrical body disclosed herein is a square tube 1 with a rectangular or rectangular radial cross-section. Cylindrical bodies commonly used as structural materials in vehicles include circular tubes with a circular radial cross-section or irregularly shaped tubes. In addition to straight-lined cylindrical bodies, there are also cylindrical bodies that extend in a curved manner, or cylindrical bodies that extend with a partial bend.

[0029] As described above, one example of a cylindrical body has corners extending along the axis of the cylindrical body on its outer circumferential surface. The cylindrical bodies disclosed herein do not include circular tubes, but include square tubes and irregularly shaped tubes. The cylindrical bodies disclosed herein include not only straight-extending cylindrical bodies, but also cylindrical bodies such as those that extend in a curved manner, and cylindrical bodies such as those that extend with a partial bend. In the following description, for convenience, an example of a square tube 1 with a rectangular radial cross-section and straight extension will be used for illustration.

[0030] The square tube 1 has two long sidewalls 2 corresponding to the long side in a rectangular cross-section, and two short sidewalls 3 corresponding to the short side in the same cross-section. The corner portion 4, extending along the axis of the square tube 1, is located at the boundary between the long sidewalls 2 and the short sidewalls 3.

[0031] The length of the square tube 1 along its axis is, for example, approximately 700 mm. In the radial section of the square tube 1, the length of the long sidewall 2 is, for example, approximately 50 mm, and the length of the short sidewall 3 is, for example, approximately 30 mm. The thickness t of the long sidewall 2 is the same as the thickness t of the short sidewall 3. The thickness t can be approximately 0.8 mm to 3.0 mm, or approximately 1.2 mm to 2.2 mm. When the thickness t is within this range, although lightweight, it possesses the strength required as a structural material for vehicles.

[0032] like Figure 1As shown, the square tube 1 is a cylindrical laminate consisting of an inner unidirectional material layer 11, a fabric layer 12, and an outer unidirectional material layer 13 sequentially laminated from the inner layer side. The inner unidirectional material layer 11, fabric layer 12, and outer unidirectional material layer 13 are formed from four or more molding substrates that are fiber-reinforced resin materials. Each of the inner unidirectional material layer 11 and the outer unidirectional material layer 13 is formed from a molding substrate containing unidirectionally oriented reinforcing fibers and resin impregnated with those reinforcing fibers. The fabric layer 12 is formed from a molding substrate containing a fabric woven from reinforcing fibers and resin impregnated with that fabric.

[0033] There are no particular limitations on the material of the fiber-reinforced resin constituting the molding substrate. Both the reinforcing fiber and the resin can be conventionally known materials. Examples of reinforcing fibers include carbon fiber, glass fiber, and polyamide fiber. Additionally, the resin can be a thermosetting resin, such as epoxy resin or polyester resin. Commercially available unidirectional materials or fabric materials can be appropriately selected for the molding substrate.

[0034] The reinforcing fibers contained in the inner unidirectional material layer 11 and the outer unidirectional material layer 13 are oriented along the axis of the square tube 1. The inner unidirectional material layer 11 can be formed from a single unidirectional material or from a layer of two or more unidirectional materials. Similarly, the outer unidirectional material layer 13 can be formed from a single unidirectional material or from a layer of two or more unidirectional materials.

[0035] In the square tube 1, the ratio of the thickness of the inner unidirectional material layer 11 to the thickness t of the long sidewall 2 and the short sidewall 3 can be, for example, less than 10% or less, or less than 5%. Similarly, the ratio of the thickness of the outer unidirectional material layer 13 to the thickness t can be, for example, less than 10% or less, or less than 5%. When the ratio of the thicknesses of the inner unidirectional material layer 11 and the outer unidirectional material layer 13 is within this range, the square tube 1 can be given appropriate bending rigidity, and the complete cutting of the square tube 1 can be prevented when a bending load is applied. The thicknesses of the inner unidirectional material layer 11 and the outer unidirectional material layer 13 can be the same or different.

[0036] Fabric layer 12 has a laminated structure in which multiple fabric materials are stacked. The fabrics included in fabric layer 12 are, for example, plain weave, twill weave, or shoji weave, but are not limited to these, and can be appropriately selected from conventionally known fabrics. The multiple fabrics included in fabric layer 12 can all be the same weave, or they can be a combination of fabrics with different weaves.

[0037] In fabric layer 12, reinforcing fibers are woven as warp and weft yarns, extending in mutually orthogonal directions. In fabric layer 12, the warp or weft yarns can be oriented along the axis of the square tube 1 or in a direction intersecting the axis. Furthermore, multiple fabric materials can be layered either with warp and weft yarns extending in the same direction or with warp and weft yarns extending in different directions. When the warp or weft yarns are oriented along the axis, the bending rigidity of the square tube 1 can be improved. Additionally, when the warp or weft yarns are oriented in a direction intersecting the axis, for example, at a 45° angle to the axis, the blocking rigidity of the square tube 1 can be improved. In this embodiment, in a portion of the fabric material included in fabric layer 12, the warp or weft yarns of the square tube 1 are oriented along the axis of the square tube 1.

[0038] The amount of fabric material contained in the fabric layer 12 is not particularly limited, for example, it can be more than 5 and less than 15. When the amount of fabric material is within this range, it can impart appropriate bending stiffness to the square tube 1 and make the square tube 1 lighter.

[0039] The tensile modulus of elasticity of the reinforcing fibers included in the inner unidirectional material layer 11, the fabric layer 12, and the outer unidirectional material layer 13 can be 70 GPa or higher, or 200 GPa or higher. When the reinforcing fibers constituting the fiber-reinforced resin material are glass fibers or polyamide fibers, they can also be high-strength glass fibers or high-strength polyamide fibers with a tensile modulus of elasticity of 70 GPa or higher. Furthermore, if the reinforcing fibers are carbon fibers, a tensile modulus of elasticity of 200 GPa or higher can be obtained.

[0040] Furthermore, the tensile strength of the reinforcing fiber can be 3000 MPa or higher, or 3500 MPa or higher. When the reinforcing fiber constituting the fiber-reinforced resin material is glass fiber or polyamide fiber, it can also be high-strength glass fiber or high-strength polyamide fiber with a tensile strength of 3000 MPa or higher. Alternatively, if the reinforcing fiber is carbon fiber, a tensile strength of 3500 MPa or higher can be obtained.

[0041] When the tensile modulus of elasticity and tensile strength are within the aforementioned ranges, a square tube 1 with excellent tensile strength can be obtained. The tensile modulus of elasticity of the reinforcing fibers can be equal or different in the inner unidirectional material layer 11, the fabric layer 12, and the outer unidirectional material layer 13. Similarly, the tensile strength of the reinforcing fibers can be equal or different in the inner unidirectional material layer 11, the fabric layer 12, and the outer unidirectional material layer 13.

[0042] In this embodiment, the square tube 1 has a rectangular radial cross-section, so the two opposing sidewalls 3, namely the first sidewall 3 and the second sidewall 3, extend parallel to each other. Similarly, the two opposing sidewalls 2, namely the first sidewall 2 and the second sidewall 2, extend parallel to each other. In this case, for example, at least one of the tensile modulus of elasticity or tensile strength of the reinforcing fibers in the first sidewall 3 and the second sidewall 3 may be different. In this case, for example, due to the bending load during a vehicle collision, the reinforcing fibers oriented along the axis of the square tube 1 are respectively arranged on the compression side and the tension side of the two opposing sidewalls 3. By making the tensile strength on the tension side higher than the tensile strength on the compression side, the cutting of the square tube 1 can be better controlled.

[0043] <Regarding the manufacturing method of square tube 1>

[0044] Next, the manufacturing method of square tube 1 will be described. The following describes the case where square tube 1 is manufactured using a molding substrate made by impregnating carbon fiber with epoxy resin, which is a thermosetting resin.

[0045] like Figure 2 As shown, the square tube 1 is manufactured using a hydroforming method via a forming system S. The forming system S includes a mold 50 and a bag 40, which serves as the core material disposed inside the mold 50, and is configured to circulate superheated steam inside the bag 40.

[0046] The molding system S includes a cold water circulation device 20, a temperature control circulation device 30, a bag 40, and a mold 50. The molding system S is configured such that water, as a fluid, flows between the devices constituting the molding system S while undergoing a state change. The square tube 1 is formed by laminating four or more molding substrates inside the cavity of the mold 50 and then curing them by heating inside the mold 50.

[0047] Water is stored inside the cold water circulation device 20. A supply pump 21 is built into the cold water circulation device 20, and water is supplied from the cold water circulation device 20 to the temperature control circulation device 30 by driving the supply pump 21.

[0048] The temperature-controlled circulation device 30 includes a heating device 31, a pressure pump 32, and a temperature sensor 33. The heating device 31 heats water supplied from the cold water circulation device 20 to above 100°C, generating superheated steam. The pressure pump 32 regulates the supply pressure when supplying the superheated steam generated by the heating device 31 to the bag 40. The pressure pump 32 is equipped with a pressure regulating unit (not shown) for adjusting the supply pressure of the superheated steam. The temperature sensor 33 detects the temperature of the superheated steam generated by the heating device 31.

[0049] The bag 40 is placed inside the mold 50 before molding. The mold 50 defines the outer shell shape of the square tube 1 by closing the mold. During molding, the molding substrate is placed inside the mold 50. In addition, during molding, superheated steam generated by the heating device 31 is supplied to the inside of the bag 40 via the pressure pump 32, and the superheated steam circulates between the superheated steam and the temperature control circulation device 30. Therefore, the bag 40 is formed into a cylindrical shape from a synthetic resin with excellent heat resistance and flexibility.

[0050] The manufacturing method of square tube 1 includes a molding substrate preparation process, a mold closing process, a molding process, a finishing process, and a post-process.

[0051] In the molding substrate preparation process, a molding substrate is prepared within the cavity of the mold 50, more specifically the lower mold. At this time, one or more unidirectional materials constituting the outer unidirectional material layer 13 of the square tube 1 are first prepared. The unidirectional materials are arranged such that the reinforcing fibers are aligned along the long side of the cavity of the mold 50. That is, the reinforcing fibers are oriented along the axis of the bag 40, which forms the core material. Next, multiple fabric materials constituting the fabric layer 12 of the square tube 1 are prepared. At least one of the fabric materials has its warp or weft threads aligned along the long side of the cavity. Next, one or more unidirectional materials forming the inner unidirectional material layer 11 of the square tube 1 are prepared. The unidirectional materials are arranged such that the reinforcing fibers are aligned along the long side of the cavity of the mold 50. The process of preparing the unidirectional materials forming the outer unidirectional material layer 13 is the first process. The process of preparing the multiple fabric materials forming the fabric layer 12 is the second process. The process of preparing the unidirectional materials forming the inner unidirectional material layer 11 is the third process.

[0052] In the mold closing process, the bag 40 is placed inside the mold 50 and the mold is closed. More specifically, the bag 40 is placed on a molding substrate disposed in the cavity of the lower mold, such that the molding substrate surrounds the bag 40. The upper mold is then assembled onto the lower mold and the mold is closed.

[0053] Before the molding process, the molding system S is started. The supply pump 21 and the pressure pump 32 of the molding system S are turned on, and the outlet 31a of the fluid channel connected to the cold water circulation device 20 in the heating device 31 is opened. At this time, heating of the heating device 31 is not performed. Water in the cold water circulation device 20 is supplied to the heating device 31 by the supply pump 21, and water in the heating device 31 is supplied to the bag 40 by the pressure pump 32. In addition, water in the bag 40 returns to the cold water circulation device 20 via the heating device 31. Thus, a first fluid circulation path R1 is formed between the cold water circulation device 20, the temperature-controlled circulation device 30, and the bag 40 in the mold 50. By circulating the water supplied from the cold water circulation device 20 in the first path R1, the interior of the temperature-controlled circulation device 30, the interior of the bag 40, or the interior of the fluid channel connecting the cold water circulation device 20, the temperature-controlled circulation device 30, and the bag 40 is filled with water before molding. Thus, air present inside the fluid channel, etc., is expelled.

[0054] In the molding process, the square tube 1 is formed by heating the molding substrate through the molding system S. More specifically, firstly, the supply pump 21 is turned off, and the outlet 31a is closed. As a result, the fluid within the heating device 31 is supplied into the bag 40 by the drive of the pressurization pump 32, forming a second fluid circulation path R2 between the temperature-controlled circulation device 30 and the bag 40 within the mold 50. The molding process is performed using the second path R2.

[0055] In the molding process, the pressure pump 32 on the second path R2 is first turned off. In this state, the heating device 31 starts heating, and superheated steam at a predetermined temperature and pressure is generated from the water in the heating device 31. The temperature of the superheated steam is set to be slightly higher than the thermosetting temperature of the thermosetting resin contained in the molding substrate made of fiber-reinforced resin.

[0056] If the superheated steam in the heating device 31 reaches a predetermined temperature, the pressure pump 32 is turned on, supplying superheated steam into the bag 40 and circulating the superheated steam via the second path R2. In the bag 40 supplied with superheated steam, the internal pressure increases due to the pressure of the superheated steam, pressing the molding substrate against the inner surface of the cavity in the mold 50. Furthermore, due to the heat of the superheated steam, the thermosetting resin, such as epoxy resin, contained in the molding substrate begins to thermocure.

[0057] The temperature of the superheated steam within the heating device 31 is adjusted based on the temperature readings detected by the temperature sensor 33 at regular intervals. If the detected value is determined to be lower than the target value for the superheated steam, the heating device 31 continues heating. If the detected value is determined to be higher than the target value, the first path R1 is temporarily selected, and the temperature of the superheated steam is adjusted by supplying water from the cold water circulation device 20 to the temperature regulation circulation device 30.

[0058] In the molding process, the epoxy resin constituting the molding substrate is thermocured within the mold 50, and the square tube 1 is formed. By applying high pressure based on superheated steam, the molding substrate is pressed against the inner surface of the mold 50 cavity, thus suppressing the formation of gaps between the layers of the molding substrate. The square tube 1 formed in this way has its porosity suppressed.

[0059] In the final step of the molding system S, the first path R1 in the molding system S is selected. The supply pump 21 and the pressurization pump 32 are turned on, and the outlet 31a is opened. The superheated steam present in the fluid channels of the heating device 31, the bag 40, and the second path R2 is discharged from the outlet 31a and transported to the cold water circulation device 20. The superheated steam gradually dissipates heat and decreases in temperature in the fluid channels leading to the cold water circulation device 20. In the cold water circulation device 20, it is appropriately mixed with the water in the cold water circulation device 20 and discharged to the outside.

[0060] In the subsequent process, the mold 50 is opened, and the square tube 1 and the bag 40 are removed together from inside the mold 50. If necessary, the bag 40 is removed from inside the square tube 1 or cut off at both ends of the square tube 1. Thus, the square tube 1 is obtained.

[0061] <Regarding the function of square tube 1>

[0062] Next, the function of the square tube 1 as a cylindrical body will be explained.

[0063] The radial cross-section of the square tube 1 is rectangular. At the boundary between the long sidewall 2 and the short sidewall 3, there is a corner 4 extending along the axis of the square tube 1.

[0064] The middle layer of the square tube 1 is a fabric layer 12 composed of multiple layers of fabric material. Fabric layer 12 is one of multiple layers in the square tube 1, and the reinforcing fibers contained in the fabric material are oriented in a direction along the axis of the square tube 1 and in a direction orthogonal to the axis. In this layer, the reinforcing fibers oriented orthogonal to the axis of the square tube 1 originate from the fabric material, and therefore, at the corners 4, the reinforcing fibers are shaped to follow the shape of the corners 4. Therefore, voids can be suppressed between the layers of the fabric material, and consequently, the formation of pores in the corners 4 can be suppressed. Furthermore, the corners 4 have good shapeability, thus suppressing the retention of resin contained in the fabric material at the corners 4. As a result, uneven resin content across the entire square tube 1 can be suppressed.

[0065] The inner layer of the square tube 1 is an inner unidirectional material layer 11, and the outer layer of the square tube 1 is an outer unidirectional material layer 13. In both the inner and outer unidirectional material layers 11 and 13, the reinforcing fibers contained in each unidirectional material are oriented along the axis of the square tube 1. Therefore, the square tube 1 is given bending stiffness, and its strength is increased relative to bending load. In addition, because the inner and outer layers of the square tube 1 are unidirectional materials, even if the square tube 1 begins to fracture under a large bending load, complete shearing can be prevented by the presence of the unidirectional materials.

[0066] Next, the effects of square tube 1 and its manufacturing method will be explained.

[0067] (1) The square tube 1 is a cylindrical body used as a structural material for the vehicle. Furthermore, the square tube 1 has a fabric layer 12 in the middle of its sidewall in the thickness direction.

[0068] Therefore, the reinforcing fibers readily follow the shape of the corner 4 of the square tube 1, suppressing the formation of pores at the corner 4. This prevents pores from becoming the fracture initiation point of the square tube 1. Consequently, the bending stiffness of the square tube 1 is improved.

[0069] (2) An inner unidirectional material layer 11 and an outer unidirectional material layer 13 are respectively laminated on the inner and outer peripheral surfaces of the fabric layer 12. The inner unidirectional material layer 11 and the outer unidirectional material layer 13 include reinforcing fibers extending along the axis of the square tube 1.

[0070] Therefore, the bending stiffness of the square tube 1 can be improved. Furthermore, by laminating unidirectional material layers 11 and 13 onto the inner and outer circumferential surfaces of the fabric layer 12, even when a strong bending load is applied to the square tube 1, complete severing of the square tube 1 can be prevented. Thus, in the event of a cylindrical body, which is a structural material of a vehicle, being severed during a vehicle collision, the severed square tube can be prevented from embedding in an unexpected location.

[0071] (3) By having the fabric layer 12, the shapeability of the corner 4 of the square tube 1 becomes good, and the excessive resin retention at the corner 4 can be suppressed. Thus, a square tube 1 with homogeneous and stable properties is obtained.

[0072] (4) In the square tube 1, in the fabric material contained in the fabric layer 12, the warp or weft threads are oriented along the axis of the square tube 1.

[0073] Therefore, by reinforcing the fabric material with fibers oriented along the axis of the square tube 1, the bending stiffness is improved.

[0074] (5) The manufacturing method of the square tube 1 includes a molding substrate preparation step of placing a molding substrate around the bag 40 and a molding step of heating the molding substrate in the mold 50. The molding substrate preparation step places the fabric material in the cavity of the mold 50.

[0075] Therefore, it is not necessary to align the molding substrate with reinforcing fibers oriented along the axis of the square tube 1 and the molding substrate with reinforcing fibers oriented in a direction orthogonal to the axis. Compared with the case where the square tube 1 is formed from only unidirectional material, the alignment of reinforcing fibers can be easily performed.

[0076] (6) In the molding substrate preparation process, a fabric material is prepared as the molding substrate.

[0077] Therefore, by using a soft fabric, the reinforcing fibers can easily follow the corners within the cavity. The shapeability of the corners becomes good, which can suppress the formation of pores at the corners 4 of the square tube 1.

[0078] (7) The fabric material is woven into a molded substrate by weaving warp and weft.

[0079] Therefore, compared to the case of unidirectional material lamination, the slippage of orthogonal reinforcing fibers between layers can be suppressed. As a result, the substrate preparation process can be simplified.

[0080] (8) The square tube 1 is formed by hydraulic forming.

[0081] Therefore, not only is the temperature required for molding the square tube 1 obtained, but also a high pressure based on superheated steam can be applied within the bag 40. This allows the molding substrate to be pressed against the inner surface of the mold 50 with stronger pressure. Consequently, gaps between the multiple layers of the molding substrate can be suppressed, and porosity in the square tube 1 can be prevented. As a result, a square tube 1 with excellent bending rigidity can be manufactured.

[0082] (9) The temperature control circulation device 30 includes a heating device 31 for generating superheated steam and a temperature sensor 33 for detecting the temperature of the superheated steam. The temperature sensor 33 detects the temperature of the superheated steam and adjusts the temperature of the superheated steam in the heating device 31 based on the detected value.

[0083] Therefore, under the condition that the changes in molding temperature and molding pressure are suppressed, superheated steam at the desired temperature and pressure can be continuously supplied into the bag 40.

[0084] (10) The molding system S of the above embodiment includes a cold water circulation device 20 that circulates fluid between itself and the temperature control circulation device 30.

[0085] Therefore, at the start of molding, water can be circulated between the cold water circulation device 20 and the bag 40 via the temperature control circulation device 30, allowing water to fill the interior of each device or the fluid channel before molding. Furthermore, at the end of molding, the superheated steam generated during the molding process can be discharged to the outside along with the water in the cold water circulation device 20. This facilitates easy fluid supply at the start of molding and fluid discharge at the end of molding.

[0086] Furthermore, the above embodiments can be implemented in the following variations. The above embodiments and the following variations can be combined with each other within the scope of technical non-contradiction.

[0087] In the above embodiment, a square tube 1 with a rectangular radial cross-section was described as a cylindrical body; however, the shape of the cylindrical body is not limited to this. For example, as... Figure 3A As shown, the radial cross-section of the cylindrical body can also be trapezoidal. Or, as... Figure 3B As shown, the radial cross-section of the cylindrical body can also be an irregular pentagon. Additionally, as... Figure 3C As shown, the cylindrical body can also have curved sidewalls, and its radial cross-section includes both straight and curved portions. Furthermore, the radial cross-section of the cylindrical body can also be polygonal.

[0088] In the radial cross-section of the cylindrical body, the angle of corner 4 is acute or closer to acute, and the more easily the effect of laminating the fabric layer 12 in the intermediate layer occurs. That is, the more easily pores are formed at corner 4 in a cylindrical body formed with a unidirectional material, the more significant the effect of suppressing pore formation by forming with fabric material becomes.

[0089] The manufacturing method of the square tube 1 is not limited to hydroforming. For example, a method can also be used where multiple molding substrates are wound around a mandrel as a core material and then heated and cured in a mold. In this case, firstly, a unidirectional material that will become the inner unidirectional material layer 11 is wound around the mandrel. Next, multiple fabric materials that will become fabric layers 12 are wound around the outer peripheral surface of the unidirectional material that will become the inner unidirectional material layer 11. Then, a unidirectional material that will become the outer unidirectional material layer 1 is wound around the outer peripheral surface of the fabric materials that will become fabric layers 12. It is then placed in a mold and the mold is closed, and it is heated at a predetermined temperature for a predetermined time to cure. When it is removed from the mold and the mandrel is removed, a cylindrical body is obtained.

[0090] In this case, the process of winding the unidirectional material into the inner unidirectional material layer 11 is the first process. Furthermore, the process of winding the multiple fabric materials into the fabric layer 12 is the second process. And the process of winding the unidirectional material into the outer unidirectional material layer 13 is the third process.

[0091] Example

[0092] An example of a cylindrical body is described.

[0093] <Molding of cylindrical body>

[0094] (Example 1)

[0095] The square tube 1, which is a cylindrical body, is formed according to the above-described hydroforming method. The square tube 1 is a rectangular cylindrical body with a radial cross-section of 28 mm × 48 mm and a length of 700 mm. The inner unidirectional material layer 11 and the outer unidirectional material layer 13 each include a unidirectional material arranged such that the orientation direction of the reinforcing fibers is along the axis of the square tube 1. The unidirectional material uses a sheet prepreg (P3252S-10, manufactured by Toray Industries, Inc.) as a sheet substrate impregnated with epoxy resin and carbon fiber.

[0096] The fabric material constituting the fabric layer 12 is sequentially layered from the outer periphery of the square tube 1 in two layers with the orientation direction of the reinforcing fibers intersecting the axis of the square tube 1 at ±45°, one layer with the orientation direction at 0° / 90° relative to the axis of the square tube 1, and two layers with the orientation direction intersecting the axis of the square tube 1 at ±45°. All fabric materials use a sheet prepreg (F6343B-05P, manufactured by Toray Industries, Inc.) as a sheet substrate impregnated with epoxy resin and carbon fiber.

[0097] The types of molding substrates, sidewall thicknesses t (mm), and orientation angles (°) of the reinforcing fibers relative to the axis of the square tube 1 for each of the inner unidirectional material layer 11, fabric layer 12, and outer unidirectional material layer 13 are shown in Table 1. The sidewall thickness t of the square tube 1 is 1.55 mm. The square tube 1 obtained in this way is used as Example 1.

[0098] [Table 1]

[0099]

[0100] (Comparative Example 1)

[0101] Except that all the molding substrates are made of unidirectional material, the square tube 1 of Example 1 was molded in the same manner. Fourteen layers of unidirectional material were laminated with the reinforcing fibers aligned along the axis of the square tube 1, in a direction orthogonal to it, and at a 45° angle to it. All the unidirectional material used was a sheet prepreg (P3252S-10, manufactured by Toray Industries, Inc.) that was an epoxy resin impregnated with carbon fiber sheet substrate. The types of molding substrates for each layer, the sidewall thickness t (mm), and the orientation angle (°) of the reinforcing fibers relative to the axis of the square tube 1 are shown in Table 2. The sidewall thickness t of the square tube 1 was 1.60 mm. The square tube 1 obtained in this way was used as Comparative Example 1.

[0102] [Table 2]

[0103]

[0104] (Comparative Example 2)

[0105] Except that all the molding substrates are made of fabric material, the square tube 1 is molded in the same manner as in Example 1. The fabric material is laminated in seven layers with the orientation direction of the reinforcing fibers at 0° and 90° relative to the axis of the square tube 1, and at ±45°. All the fabric materials used are sheet prepreg (F6343B-05P, manufactured by Toray Industries, Inc.) which is an epoxy resin impregnated sheet substrate of carbon fiber. The type of molding substrate for each layer, the sidewall thickness t (mm), and the orientation angle (°) of the reinforcing fibers relative to the axis of the square tube 1 are shown in Table 3. The sidewall thickness t of the square tube 1 is 1.80 mm. The square tube 1 obtained in this way is used as Comparative Example 2.

[0106] [Table 3]

[0107]

[0108] <Evaluation of Bending Stiffness>

[0109] For the square tubes 1 of Examples 1, 1, and 2, a three-point bending test was performed to evaluate their bending stiffness. The three-point bending test was performed according to JIS K 7074.

[0110] like Figure 4 As shown, square tube 1 is supported by two fulcrums 61 and 62. The distance between fulcrums 61 and 62 is set to 500 mm. Square tube 1 is supported by its short sidewall 3 along the vertical direction. A pressure head 63 is applied from the upper part of the center position along the long side of square tube 1, and the bending load (N) and deflection (mm) of square tube 1 are measured. Measurements are continued even after square tube 1 begins to break to confirm whether square tube 1 is ultimately cut off.

[0111] The deflection (mm) curves of each tube 1 in Examples 1, 1, and 2 relative to the bending load (N) are plotted on... Figure 5 The image is shown in Figure 6. Additionally, Figure 6 shows photographs of the square tubes 1 of Example 1 and Comparative Example 2 after the bending stiffness evaluation. Figure 6A This refers to the appearance of the square tube 1 in Example 1. Figure 6B The appearance of square tube 1 in Comparative Example 2 is shown.

[0112] according to Figure 5 As a result, the square tube 1 of Comparative Example 1, which uses unidirectional materials as the molding substrate, has lower bending stiffness compared to other square tubes 1. Furthermore, the square tube 1 of Comparative Example 2, which uses fabric materials as the molding substrate, has higher bending stiffness compared to the square tube 1 of Comparative Example 1. However, when the deflection becomes a certain value, the bending load suddenly becomes zero. At this time, as... Figure 6B As shown, the square tube 1 of Comparative Example 2 is completely cut off.

[0113] On the other hand, in the square tube 1 of Example 1, where unidirectional material layers 11 and 13 are respectively deposited on the inner and outer peripheral surfaces of the fabric layer 12 as the molding substrate, the bending stiffness is higher than that of the square tube 1 of Comparative Example 1, but lower than that of the square tube 1 of Comparative Example 2. This is believed to be because the sidewall thickness t of the square tube 1 of Comparative Example 2 is 1.80 mm, while the sidewall thickness t of the square tube 1 of Example 1 is as thin as 1.55 mm. In this respect, when comparing the values ​​obtained by dividing the bending load by the thickness t of the respective sidewall, it can be seen that the square tube 1 of Example 1 and the square tube 1 of Comparative Example 2 have the same bending stiffness.

[0114] Furthermore, even if the deflection of the square tube 1 in Example 1 becomes higher than a certain value and the bending load decreases, it will not immediately become zero, but will continue to decrease with a certain bending load. At this time, as... Figure 6A As shown, in Example 1, the square tube 1 is not completely cut off, and remains connected across the fracture site.

Claims

1. A cylindrical body made of fiber-reinforced resin, used as a structural material for vehicles, the cylindrical body having one or more corner portions extending along the axis of the cylindrical body on its outer peripheral surface. The cylindrical body is a cylindrical laminate composed of a fabric layer and multiple unidirectional material layers. The fabric layer is a fabric layer composed of multiple layers of fabric materials, each fabric material comprising a fabric woven from reinforcing fibers and a resin impregnated in the fabric. Each of the plurality of unidirectional material layers comprises unidirectionally oriented reinforcing fibers and resin impregnated with the reinforcing fibers. The reinforcing fibers of each unidirectional material layer are oriented along the axis. The plurality of unidirectional material layers include: An outer unidirectional material layer is deposited on the outer peripheral surface of the fabric layer; and An inner unidirectional material layer is deposited on the inner circumferential surface of the fabric layer.

2. The cylindrical body according to claim 1, wherein, The fabric layer comprises one or more fabric materials in which the warp or weft threads of the fabric are oriented along the axis.

3. The cylindrical body according to claim 1 or 2, wherein, The cylindrical laminate has a first sidewall and a second sidewall that are opposite each other. The first sidewall and the second sidewall extend parallel to each other. The unidirectional material layer in the first sidewall contains reinforcing fibers with a higher tensile strength than the unidirectional material layer in the second sidewall.

4. A method for manufacturing a cylindrical body according to any one of claims 1 to 3, comprising manufacturing a cylindrical body made of fiber-reinforced resin used as a structural material for vehicles, the cylindrical body having one or more corner portions extending along the axis of the cylindrical body on its outer peripheral surface, the method comprising: Four or more molded substrates are laminated around the core material; and The four or more molded substrates arranged around the core material are heated. The four or more molded substrates include: Multiple unidirectional materials, each unidirectional material comprising unidirectionally oriented reinforcing fibers and resin impregnated with the reinforcing fibers; and Multiple fabric materials, each fabric material comprising a fabric woven from reinforcing fibers and a resin impregnated in the fabric, The layering includes: At least one of the unidirectional materials is disposed around the core material in such a way that the reinforcing fibers are oriented along the axis of the core material; The plurality of fabric materials are arranged around at least one of the unidirectional materials; and At least one of the unidirectional materials is disposed around the plurality of fabric materials in such a manner that the reinforcing fibers are oriented along the axis of the core material.

5. The method for manufacturing a cylindrical body according to claim 4, wherein, Configuring the plurality of fabric materials includes aligning the warp or weft of at least one of the fabric materials along the axis of the core material.

6. A method for manufacturing a cylindrical body according to any one of claims 1 to 3, comprising: A molding substrate made of fiber-reinforced resin is placed inside the cavity of the mold; A bag is placed inside the mold and the mold is closed; Superheated steam is supplied into the bag; as well as The molding substrate is heated while being pressed against the inner surface of the mold by heat and pressure from the bag containing the superheated steam.

7. The method for manufacturing a cylindrical body according to claim 6, wherein, Further includes: Water is heated in a heating device to generate superheated steam; and While the molding substrate is pressed against the inner surface of the mold and heated, the superheated steam is circulated between the heating device and the bag.

Images