JP2025095565A - Propeller blade and manufacturing method thereof - Google Patents

Abstract

To provide a propeller blade which can achieve both productivity and high strength reliability.SOLUTION: A propeller blade has a member shaped in a propeller shape in which fiber-reinforced composite materials where reinforcement fibers are uniaxially or multiaxially oriented are stacked, wherein the member has at least one layer of the fiber-reinforced composite materials in which the reinforcement fibers are uniaxially oriented, and in a layer in which the reinforcement fibers are oriented at an angle of 60° or more with respect to a bottom direction (wing length direction) from a wing end of the propeller blade, among the layers of the fiber-reinforced composite materials in which the reinforcement fibers are uniaxially oriented, a sheet-like prepreg as a raw material is molded by applying a notch thereto, and in at least the bottom part of the propeller blade, the reinforcement fibers are disconnected at a fiber length of 10 to 100 mm.SELECTED DRAWING: None

Description

The present invention relates to a propeller blade.

The propeller blades have a wing shape and rotate around the drive shaft to push the air backwards, generating thrust. To push the air backwards efficiently, the propeller blades have a complex shape in which the angle of attack and chord length change from the base to the tip.

Because reducing the weight of propeller blades contributes to increasing the payload and range of an aircraft, high-strength, high-rigidity fiber-reinforced materials are used as structural materials. However, as propeller blades have complex shapes as mentioned above, molding them is difficult, and high-build production is difficult.

On the other hand, in recent years, there has been active development of aircraft with many propeller blades, such as Urban Air Mobility (UAM) and drones, and in the future, it will be necessary to produce propeller blades at a higher build rate than ever before.

JP 2023-97542 A JP 2007-261141 A International Publication No. 2017/159567

In recent years, UAM and drones have been developed that have many propeller blades. To increase the flight range and time of these aircraft, there is a high need to reduce their weight, especially for the propeller blades that are installed in large numbers per aircraft. To meet this need for weight reduction, fiber-reinforced composite materials with high specific strength and high specific rigidity are used for the propeller blades.

When manufacturing propeller blades made of fiber-reinforced composite materials, using prepregs, which are made by impregnating a reinforced fiber base material with resin, can suppress fiber twisting during molding and also reduce weight variation in the molded product, allowing for the production of high-quality propeller blades.

The process of molding propeller blades using prepregs involves cutting out the base material, shaping, and curing under heat and pressure, in that order. Of these processes, the shaping process is particularly difficult in propeller blade molding and is likely to become a bottleneck in production rate. It is extremely difficult to arrange prepregs made of continuous fibers without wrinkles for molded products in which the chordwise length of the propeller blade, the angle of attack, and the curvature of the airfoil shape change continuously in the blade span direction. Since the size of a propeller blade is at most a few meters, shaping is often performed by hand. When shaping is performed by hand, the work takes time and there is variation in the work due to the manual work.

In light of this, there is a high demand for automating the forming process. One method for automating forming is the automatic forming method using hot forming. In hot forming, the temperature of the prepreg laminate is raised to the desired temperature, and the resin viscosity is reduced to control the hardness of the laminate, improving formability and performing automatic forming.

It is possible to shape the prepreg laminate to a certain degree by using hot forming, but for molded products such as propeller blades, where the chord length, angle of attack, and curvature of the airfoil shape change continuously in the span direction, it is extremely difficult to arrange the prepregs without wrinkles because the continuous fibers are stretched.

Patent Document 1 shows molding using a prepreg substrate laminate, which is characterized by being composed of a prepreg substrate laminate formed by laminating multiple layers of prepreg substrates with finite length slits and a prepreg substrate that uses continuous unslit carbon fibers as reinforcing fibers and is arranged on at least one side of the outermost layer of the prepreg substrate laminate. However, sufficient strength reliability cannot be obtained for propeller blades, which require high strength reliability to ensure bird strike resistance.

As shown in Patent Document 2, a molding material using a unidirectional carbon fiber sheet and randomly oriented short fiber bundles is shown, but the randomly oriented material has fibers that tend to orient in the out-of-plane direction, making it inferior to continuous fiber materials in terms of strength and rigidity. In addition, as with Patent Document 1, it does not provide sufficient strength reliability for propeller blades, which require high strength reliability to ensure bird strike resistance.

Patent Document 3 shows an example in which, when molding a flat lightweight component such as a propeller blade, reinforcing fibers are raised from a prepreg (cut prepreg) having cuts in the skin of the propeller blade to improve the adhesive strength with the core layer. However, although the adhesive strength between the skin and the core layer is improved, as with Patent Document 1, sufficient strength reliability cannot be obtained for propeller blades, which require high strength reliability to ensure bird strike resistance.

As described above, conventional technology has demonstrated methods for improving formability using cut prepregs and short fiber reinforced materials, but has not demonstrated a method for achieving both high build rate and strength reliability.

Therefore, the objective of the present invention is to provide a propeller blade that can achieve both productivity and high strength reliability.

In order to solve the above problems, the present invention provides the following means.
[1] A propeller blade having a member formed into a propeller shape by laminating fiber-reinforced composite material in which the reinforcing fibers are oriented uniaxially or multiaxially, said member having at least one layer of fiber-reinforced composite material in which the reinforcing fibers are uniaxially oriented, and characterized in that, among the layers of fiber-reinforced composite material in which the reinforcing fibers are oriented at an angle of 60° or more relative to the direction from the tip to the root (blade length direction) of the propeller blade, the reinforcing fibers are interrupted at a fiber length of 10 to 100 mm at least in the root portion of the propeller blade.
[2] A propeller blade as described in [1], wherein the ratio of the maximum value to the minimum value of the vertical cross-sectional outer periphery is 1.2 or more in a region within 30% of the blade length from the blade root.
[3] A method for producing a propeller blade, comprising the steps of laminating a plurality of sheet-like prepregs in which reinforcing fibers are uniaxially or multiaxially oriented to obtain a laminated prepreg (first step), shaping the laminated prepreg into a propeller shape (second step), and heat-curing the laminated prepreg in a propeller blade molding die (third step), wherein, among the sheet-like prepregs in which the reinforcing fibers are uniaxially oriented, the prepregs contain reinforcing fibers oriented at an angle of 60° or more relative to the direction from the blade tip to the root (blade length direction) of the propeller blade, at least in a portion corresponding to the root of the propeller blade, the reinforcing fibers contained in the prepregs are interrupted at a fiber length of 10 to 100 mm.
[4] The method for manufacturing a propeller blade according to [3] above, characterized in that in the second step, pressure is applied to the surface of the laminated prepreg while tension is applied to the laminated prepreg, thereby shaping it into the shape of an outer layer surface or an inner layer surface of a propeller blade skin.
[5] The method for manufacturing a propeller blade according to the above [3] or [4], characterized in that in the second step, the laminated prepreg is preheated and shaped into a propeller shape.
[6] The method for manufacturing a propeller blade according to any one of [3] to [5] above, wherein the second step is a step of placing a laminated prepreg between a mold having a shape of an outer layer side surface of a propeller blade skin and a mold having a shape of an inner layer side surface, and sandwiching and pressing the laminated prepreg between the two molds to form it into a propeller shape, and wherein before pressing the laminated prepreg between the two molds, a part of the laminated prepreg is brought into contact only with the mold having the shape of the inner layer side surface, and then pressing is performed.

The present invention provides a propeller blade that is both highly manufacturable and highly reliable in strength. The propeller blade of the present invention is particularly suitable for aircraft that use a large number of propeller blades, such as UAMs and drones.

Schematic diagram of an example of a prepreg with cuts

The propeller blade according to the present invention is a propeller blade having a member formed into a propeller shape by laminating fiber-reinforced composite material in which the reinforcing fibers are oriented uniaxially or multiaxially, and the member has at least one layer of fiber-reinforced composite material in which the reinforcing fibers are oriented uniaxially, and is characterized in that, among the layers of fiber-reinforced composite material in which the reinforcing fibers are oriented uniaxially, the reinforcing fibers are oriented at an angle of 60° or more from the tip to the root direction (span direction) of the propeller blade, at least in the root portion of the propeller blade, the reinforcing fibers are interrupted at a fiber length of 10 to 100 mm.

The propeller blade according to the present invention has a wing shape, and rotates around the drive shaft to push air backward and obtain thrust. In general, when a fiber-reinforced composite material is applied to a propeller blade to obtain a lightweight, highly rigid, and strong propeller blade, a preferred embodiment is that the outer shape is molded from the fiber-reinforced composite material, and a member that supports the fiber-reinforced composite material forming the outer shape is arranged inside the molded propeller blade. Here, examples of the member that supports the shape of the propeller blade include a solid embodiment such as expanded foam, and an embodiment in which the fiber-reinforced composite material is partially stiffened from the inside, such as a rib. In the propeller blade according to the present invention, the outer shape of the propeller blade is formed from a fiber-reinforced composite material (hereinafter, the member of the fiber-reinforced composite material formed into the propeller shape may be referred to as a "skin" for convenience). The skin is formed by laminating fiber-reinforced composite materials in which the reinforcing fibers are oriented uniaxially or multiaxially.

Examples of reinforcing fibers used in the skin include organic fibers such as aramid fibers, polyethylene fibers, and polyparaphenylene benzoxazole (PBO) fibers; inorganic fibers such as glass fibers, carbon fibers, silicon carbide fibers, alumina fibers, Tyranno fibers, basalt fibers, and ceramic fibers; metal fibers such as stainless steel fibers and steel fibers; boron fibers; natural fibers; and modified natural fibers. Among these, the present invention preferably uses carbon fibers, which are the lightest of these reinforcing fibers and have particularly excellent properties in terms of specific strength and specific elastic modulus, as well as excellent heat resistance and chemical resistance. Furthermore, PAN-based carbon fibers are more preferable because they are easier to obtain high-strength carbon fibers.

The reinforcing fibers are oriented uniaxially, which means that the reinforcing fibers are oriented in one direction, as in unidirectional prepregs and uniaxial woven substrates. The reinforcing fibers are oriented multiaxially, which means that reinforcing fibers oriented in multiple directions exist in one layer, as in woven fiber substrates. In general, the material properties of fiber-reinforced composite materials change significantly depending on the fiber orientation direction. For example, when a tensile load is applied in the fiber orientation direction, and when a tensile load is applied in a direction perpendicular to the fiber orientation direction, the strength and rigidity are generally both higher when a tensile load is applied in the fiber orientation direction. On the other hand, propeller blades are subjected to various loads during operation. For this reason, the reinforcing fibers that make up the skin of a propeller blade are not all oriented in the same direction, and the propeller blade contains reinforcing fibers oriented in multiple directions. In the present invention, the orientation direction of a uniaxially or multiaxially oriented fiber-reinforced composite material can be controlled for each layer to control the mechanical properties of the propeller blade skin.

The fiber-reinforced composite material in the present invention is a material in which the reinforcing fibers are impregnated with a resin. The type of resin is not particularly limited, but examples thereof include thermosetting resins such as epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, epoxy acrylate resins, urethane acrylate resins, phenoxy resins, alkyd resins, urethane resins, maleimide resins, and cyanate resins, polyethylene terephthalate (PET) resins, polybutylene terephthalate (PBT) resins, polytrimethylene terephthalate (PTT) resins, polyethylene (PE) resins, polypropylene (PP) resins, styrene-based resins, polyoxymethylene (POM) resins, polyamide (PA) resins, polycarbonate (PC) resins, polymethylene methacrylate (PMMA) resins, polyvinyl chloride (PVC) resins, polyphenylene sulfide (PPS) resins, and polyphenylene The resin may be a fluorine-based resin such as ether (PPE) resin, modified PPE resin, polyimide (PI) resin, polyamideimide (PAI) resin, polyetherimide (PEI) resin, polysulfone (PSU) resin, modified PSU resin, polyethersulfone resin, polyketone (PK) resin, polyarylene ether ketone resin (PAEK), polyarylate (PAR) resin, polyethernitrile (PEN) resin, phenolic resin, phenoxy resin, or polytetrafluoroethylene resin; or a thermoplastic elastomer such as polystyrene resin, polyolefin resin, polyurethane resin, polyester resin, polyamide resin, polybutadiene resin, polyisoprene resin, or a fluorine-based resin; or a copolymer or modified product thereof; or a mixture thereof. Further, examples of the polyarylene ether ketone resin (PAEK) include polyether ketone (PEK), polyether ether ketone (PEEK), polyether ether ketone ketone (PEEKK), polyether ketone ketone (PEKK), polyether ketone ether ketone ketone (PEKEKK), polyether ether ketone ether ketone (PEEKEK), polyether ether ether ketone (PEEEK), and polyether diphenyl ether ketone (PEDEK).

There are no particular limitations on the shape of the skin, and it may be a structure divided into an upper skin having the shape of an upper blade of the propeller blade and a lower skin having the shape of a lower blade of the propeller blade, or a configuration in which laminated reinforced fiber composite material is wound in a spiral shape to form a propeller shape. In addition, a sandwich structure may be formed by providing a porous body or honeycomb core inside the skin.

The structure of the inside of the skin of the propeller blade of the present invention is not particularly limited, and as mentioned above, for example, a porous body may be arranged and used as a core material, or a hollow structure may be formed and interposed between the skins in the thickness direction of the blade, with a reinforcing structure such as a shear web extending in the blade span direction.

The present invention is also characterized by having at least one layer of fiber-reinforced composite material in which the reinforcing fibers are uniaxially oriented. Uniaxially oriented fiber-reinforced composite material has no fiber orientation in the layer thickness direction, making it easy to obtain high mechanical properties. It is also preferable because it can strongly bring out the anisotropy of the fiber-reinforced composite material.

In addition, in the present invention, among the layers of fiber-reinforced composite material in which the reinforcing fibers are oriented in a uniaxial orientation, the layer in which the reinforcing fibers are oriented at an angle of 60° or more with respect to the direction from the tip to the base of the propeller blade (span direction) is characterized in that the reinforcing fibers are interrupted at a fiber length of 10 to 100 mm at least in the base part of the propeller blade (for convenience, this layer may be referred to as a "chord-direction interrupted fiber layer"). Here, the direction from the tip to the base of the propeller blade (span direction) refers to the long side direction of the rectangle (for convenience, referred to as the "circumscribed rectangle") that has the smallest area among the rectangles circumscribing the image obtained by projecting parallel light such as natural light perpendicular to the plane of rotation of the propeller blade. In addition, "intermittent" means that the fibers in the layer that were continuous are present in the layer in a cut state, and a discontinuity is observed when the fibers are traced in the longitudinal direction. As shown in Figure 1, this discontinuity can be formed by cutting the fibers by making a cut 102 in a fiber-reinforced composite material in which reinforcing fibers 103 are uniaxially oriented. The root portion refers to the region from the base of the blade to within 30% of the blade length. When straight lines intersect, two pairs of opposite angles can be recognized at the intersection, but in this invention, the angle between the blade length direction and the orientation direction of the reinforcing fibers is determined as the smaller angle.

The cuts in the chordwise intermittent fiber layer may be made over the entire area of the propeller blade, or may be made only at the root of the propeller blade. By providing the chordwise intermittent fiber layer, the change in circumferential length in the chordwise direction that occurs when forming the shape of the propeller blade, and the change in circumferential length of the inner layer and the outer layer of the skin can be absorbed, and there is an advantage that the formability is significantly improved while not causing a decrease in the strength of the propeller blade. This effect is easily obtained because the change in the blade shape is particularly large at the root of the propeller blade. On the other hand, among the layers of fiber-reinforced composite material in which the reinforcing fibers are oriented in a uniaxial orientation, for layers in which the reinforcing fibers are oriented at an angle of less than 60° from the tip to the root direction (blade length direction) of the propeller blade, the fibers contained in such a fiber-reinforced composite material layer are preferably continuous fibers. Layers oriented at an angle of less than 60° to the blade length direction are less susceptible to changes in circumference when forming into the shape of a propeller blade, and to changes in circumference between the inner and outer layers of the skin, and have little adverse effect on formability, but they largely govern the strength of the propeller blade, so it is preferable to use continuous fibers.

The state in which the reinforcing fibers are interrupted at fiber lengths of 10 to 100 mm refers to, for example, a state obtained by inserting incisions 102 into a prepreg in which reinforcing fibers 103 are oriented in one direction 101 as continuous fibers, as shown in FIG. 1, for a prepreg containing continuous fibers oriented in one direction (note that the outer edge of FIG. 1 is a notation for convenience of illustration, and in this figure the actual reinforcing fibers 103 are continuous with the fiber orientation 101), or a state in which short fibers with fiber lengths of 10 to 100 mm are oriented uniaxially. In particular, when using an incised prepreg in which incisions are inserted into a prepreg containing continuous fibers, there are no particular restrictions on the incision insertion pattern.

In addition, the propeller blade of the present invention preferably has a ratio of the maximum value to the minimum value of the vertical cross-sectional periphery of 1.2 or more in a region within 30% of the blade length from the blade root. The region within 30% of the blade length from the blade root is a portion corresponding to a region that is included in 30% of the length from the rotation center to the short side of the circumscribing rectangle, which passes through the rotation center of the propeller blade, is parallel to the short side of the circumscribing rectangle, and is perpendicular to the rotation plane, from a plane that passes through the rotation center of the propeller blade, is parallel to the short side of the circumscribing rectangle, and is 30% of the length from the rotation center to the short side of each rectangle, if there are short sides of the rectangle equidistant from the rotation center. In addition, the vertical cross-sectional periphery is the periphery length of a cross section perpendicular to the rotation plane obtained by cutting the propeller blade parallel to the short side of the circumscribing rectangle. The present invention is particularly notable for the improvement in formability of a propeller blade in which the ratio of the maximum value to the minimum value of the vertical cross-sectional periphery is 1.2 or more in a region within 30% of the blade length from the blade root.

The method for manufacturing a propeller blade of the present invention includes a step of laminating a plurality of sheet-shaped prepregs in which the reinforcing fibers are oriented uniaxially or multiaxially to obtain a laminated prepreg (first step), a step of forming the laminated prepreg into a propeller shape (second step), and a step of heat-curing the laminated prepreg in a mold for forming a propeller blade (third step). In the prepregs in the form of sheets, i.e., flat plates, in which the reinforcing fibers are oriented at an angle of 60° or more from the tip to the root direction (span direction) of the propeller blade, the reinforcing fibers contained in the prepreg are interrupted at a fiber length of 10 to 100 mm at least in the portion corresponding to the root of the propeller blade. The portion corresponding to the root is the portion that will become the root portion after molding into a propeller blade.

When making the skin of a propeller blade from a fiber-reinforced composite material, it is preferable to use a prepreg in which a fiber-reinforced base material is impregnated with resin and left in a semi-cured state, and then molded into a propeller shape, as this can be easily molded into the desired shape and can be made into a high-strength component by curing. In this case, a prepreg in which the reinforcing fibers are oriented uniaxially or multiaxially can be used, but on the other hand, since the skin of a propeller blade has a complex shape as mentioned above, the uniaxially or multiaxially oriented reinforcing fibers are pushed out, making it difficult to mold into a blade shape. This difficulty is particularly high when attempting to automate the molding process.

In the method for producing a propeller blade of the present invention, in order to obtain a propeller blade having high mechanical properties while improving formability, particularly automatic formability, a prepreg containing reinforcing fibers oriented at an angle of 60° or more from the tip of the propeller blade to the root direction (blade length direction) is used in which the reinforcing fibers contained in the prepreg are interrupted at a fiber length of 10 to 100 mm. In this case, in the prepreg, the cut is made at least in the part corresponding to the root, and the cut may be made over the entire prepreg. Such a prepreg can be easily obtained by cutting the continuous reinforcing fibers so that the fiber length is 10 to 100 mm. In the first step, such a prepreg and other prepregs are laminated to form a laminated prepreg. In addition, the laminated prepreg can be trimmed in advance of the parts that will not be needed when it is molded into the skin of the propeller blade in preparation for the second step. Adding such a step is advantageous in terms of automating the process. In addition, among layers of fiber-reinforced composite material in which the reinforcing fibers are uniaxially oriented, in layers in which the reinforcing fibers are oriented at an angle of less than 60° from the tip to the root direction (span direction) of the propeller blade, it is preferable that the fibers contained in such layers of fiber-reinforced composite material are continuous fibers.

Next, the laminated prepreg is shaped into a propeller shape. When shaping into a propeller shape, it is preferable to press the laminated prepreg into a mold having the shape of the outer layer side surface of the propeller blade skin or the shape of the inner layer side surface to perform shaping. Examples of a mold having the shape of the outer layer side surface of the propeller blade skin or the shape of the inner layer side surface include a propeller blade molding mold, a propeller blade core, and a preform mold. The propeller blade molding mold is a mold that forms the blade shape of the propeller blade when the prepreg is heated and cured in the subsequent process. The propeller blade core may be, for example, a porous body that remains in the final molded product, or it may be a core that is removed after the prepreg is heated and cured to form a hollow part inside the propeller blade. The preform mold is a mold that is used only to shape the laminated prepreg into a propeller shape. The laminated prepreg that has been shaped into a propeller shape in the second process is made into the final shape of the propeller blade through the third process. For example, from the viewpoint of preventing the prepreg from getting caught in the propeller blade mold and for reasons such as the fact that it is heated, pressurized, cured and compressed to form a molded product, it is not necessary to shape the prepreg to the point of matching the final shape of the propeller blade after the second process. By pressing the laminated prepreg prepared as described above against something having the outer layer surface shape or inner layer surface shape of the propeller blade skin, such as a propeller blade mold, a propeller blade core or a preform mold, shaping can be completed satisfactorily without tension on the fibers. Furthermore, shaping into a propeller shape in this way makes it possible to automate the process.

In the third step, the laminated prepreg formed into the propeller shape obtained in the second step is heat cured. Heat curing is performed by placing the laminated prepreg formed into the propeller shape in a propeller blade mold in order to fix it into the blade shape of the propeller blade.

In the present invention, it is preferable that in the second step, the laminated prepreg is pressed against a propeller blade core, a preform mold, or a propeller blade molding mold while tension is applied to the laminated prepreg to form the shape. When forming the propeller shape while tension is applied, by using a chordwise interrupted fiber layer, the stretching effect can be effectively utilized to form the shape well without wrinkles. There are no particular restrictions on the direction in which tension is applied, but when applying tension to a part of the propeller blade surface that has a curvature in the chordwise direction or a part where the blade circumference in the chordwise direction changes significantly, applying tension in the chordwise direction is preferable because it allows for good shaping.

In addition, in the present invention, when forming the laminated prepreg into a propeller shape, the laminated prepreg is placed between a mold having the shape of the outer layer surface of the propeller blade skin and a mold having the shape of the inner layer surface, and the laminated prepreg is sandwiched and pressed between the two molds to form the propeller shape. Furthermore, it is preferable that before pressing the laminated prepreg between the two molds, only a part of the laminated prepreg is brought into contact with the mold having the shape of the inner layer surface, and then the pressing is performed.

By placing a laminated prepreg between a mold having the shape of the outer layer surface of the propeller blade skin and a mold having the shape of the inner layer surface, and sandwiching and pressing the laminated prepreg between the two molds, it is easy to shape it into a propeller shape, and it is also advantageous in automation. In addition, if a part of the laminated prepreg is brought into contact only with the mold having the shape of the inner layer surface at a stage before pressing the laminated prepreg with the two molds, and then pressing is performed, the movement of the laminated prepreg that is in contact with the mold having the shape of the inner layer surface is fixed, and the outer layer surface side of the laminated prepreg is stretched. When pressing is performed while applying tension, it is preferable to change the direction of applying tension and increase the pressing force as the contact area between the laminated prepreg and the mold having the shape of the inner layer surface increases. When a propeller blade is manufactured using the manufacturing method of the present invention, the improvement of formability by providing a chord-direction interrupted fiber layer can be effectively performed, and the blade can be well shaped without wrinkles.

In the manufacturing method of the present invention, when forming the laminated prepreg into a propeller shape, it is preferable to preheat the laminated prepreg. Preheating the laminated prepreg makes it easier to obtain the elongation effect of the incised prepreg, reducing the forming force required when forming into a propeller shape and improving the formability. As described above, the present invention is particularly suitable for automatically obtaining three-dimensional preforms to improve the production rate of propeller blades, and for reducing operational variability during production to maintain high quality propeller blades.

The present invention will be explained in more detail below with reference to examples. However, the present invention should not be interpreted as being limited to the description in the Examples section. The orientation direction of the reinforcing fibers is defined as 0° in the direction from the base of the blade to the tip of the blade (span direction), and 90° in the direction from the leading edge of the blade to the trailing edge of the blade (chord direction).

Example 1
Toray Composite Materials America, Inc. P707AG-15 carbon fiber unidirectional prepreg was prepared and cut out to match the shapes of the upper and lower propeller blade skins. By adjusting the cutout, a prepreg (prepreg 1) in which the carbon fibers were oriented in the 0° direction and a prepreg (prepreg 2) in which the carbon fibers were oriented in the 90° direction were obtained.

When cutting out the prepreg 2, linear cuts were periodically inserted at 10° to the orientation direction of the carbon fibers, so that all the carbon fibers were interrupted by the cuts, and the fiber length after the cuts was 30 mm. At this time, the length of the cuts in the direction perpendicular to the carbon fibers was 10 mm.

Next, we prepared F6273C-07M carbon fiber woven prepreg manufactured by Toray Composite Materials America, Inc., in which orthogonal biaxial woven carbon fiber fabric was impregnated with resin, and cut it out to match the shapes corresponding to the upper and lower propeller blade skins. We obtained a prepreg (prepreg 3) in which the carbon fibers in the fabric were oriented in the -45° and +45° directions.

Prepreg 1, prepreg 2 and prepreg 3 were laminated in the following order from the outer surface of the blade: [prepreg 3/prepreg 1/prepreg 1/prepreg 1/prepreg 2/prepreg 1/prepreg 2/prepreg 1/prepreg 2/prepreg 3] corresponding to the upper and lower skins of the propeller blade, respectively, to obtain laminated prepregs that would become the upper and lower skins of the propeller blade.

The obtained laminated prepreg was pressed against the surface of a preform mold having a cavity in the shape of a propeller skin, which would become the inner layer when made into a skin, while applying tension in the chord direction, resulting in a state in which a part of the surface that would become the inner layer surface when made into a skin of the laminated prepreg was shaped on the surface of the preform mold. The preform mold was then closed to obtain a laminated prepreg shaped into the shape of the upper skin of a propeller blade. Next, a laminated prepreg shaped into the shape of the lower skin was obtained in the same manner as for the upper skin. Neither the laminated prepreg that would become the upper skin when made into a skin, nor the laminated prepreg that would become the lower skin when made into a skin, experienced wrinkles or fiber tension during shaping.

Polypla Evonik Co., Ltd.'s polymethacrylimide rigid foam ROHACELL (registered trademark) 110 IG-F was cut into the core shape of a propeller blade to obtain a porous core member. The porous core member was then sandwiched between a laminated prepreg shaped into the shape of the upper skin and a laminated prepreg shaped into the shape of the lower skin, and then placed in a propeller blade mold and clamped, after which it was heated and cured in an oven.

The surface of the molded product was visually confirmed to be smooth. In addition, the cross section of the molded product was polished until the fiber-reinforced composite material layer could be seen, and then examined under a microscope, which confirmed that there were no voids or disturbances in the layer structure due to wrinkles.

Example 2
A porous core member obtained by the same method as that described in Example 1 and a mold (mold 1A) that gives the shape of the outer surface of the upper skin of the propeller blade when made into a skin were prepared. Next, the laminated prepreg obtained by the same method as that described in Example 1 was preheated to 60°C, and pressed against the porous core member while applying tension in the chord direction, so that a part of the surface that should become the inner layer side surface when made into a skin of the laminated prepreg was shaped on the outer surface of the porous core member. Next, the mold 1A was placed on the laminated prepreg, and the laminated prepreg was sandwiched between the porous core member and the mold 1A and pressure was applied to complete the shaping of the laminated prepreg. Thereafter, the mold 1A was removed, and a composite (composite A) was obtained in which the laminated prepreg that becomes the upper skin of the propeller blade when made into a skin was covered on the porous core member.

Next, a mold (Mold 1B) that would give the shape of the outer surface of the lower skin of the propeller blade when made into a skin and a laminated prepreg obtained by the same method as that described in Example 1 were prepared, and the remaining half of the composite A that was not covered with the laminated prepreg was covered with the laminated prepreg that would become the upper skin of the propeller blade when made into a skin by carrying out the same operation as above. Neither the laminated prepreg that would become the upper skin when made into a skin nor the laminated prepreg that would become the lower skin when made into a skin had any wrinkles or fiber tension during shaping.

The composite covered with the laminated prepreg obtained by the above procedure was then placed in a propeller blade mold, and after the mold was closed, it was heated and cured in an oven for molding.

The surface of the resulting molded product was visually confirmed to be smooth. Furthermore, the cross section of the molded product was polished until the fiber-reinforced composite material layer could be seen, and then examined under a microscope, where it was confirmed that there were no voids or disturbances in the layer structure due to wrinkles.

(Comparative Example 1)
A molded product (propeller blade) was obtained in the same manner as in Example 1, except that no cuts were made in prepreg 2. During the process of obtaining a laminated prepreg shaped into the shape of the upper skin of the propeller blade, the carbon fibers were stretched in the layer corresponding to prepreg 2, and the shaped laminated prepreg was wrinkled.

The surface of the molded product was confirmed to be smooth by visual inspection, but after polishing the cross section of the molded product until the fiber-reinforced composite material layer could be seen, it was confirmed under a microscope that wrinkles had caused a disturbance in the layer structure, and that voids existed in those areas. Due to the disturbance in the layer structure and the presence of voids, it is clear that the reliability of the molded product is inferior to that of the molded product in the examples.

The propeller blade of the present invention is particularly excellent in formability during molding, allows for automated manufacturing, and has high mechanical properties, making it suitable for use in propellers for UAMs, drones, etc.

101: fiber orientation direction 102: incision 103: reinforcing fiber

Claims (6)

A propeller blade having a member formed into a propeller shape by laminating fiber-reinforced composite material in which reinforcing fibers are oriented uniaxially or multiaxially, the member having at least one layer of fiber-reinforced composite material in which reinforcing fibers are oriented uniaxially, and, among the layers of fiber-reinforced composite material in which reinforcing fibers are oriented at an angle of 60° or more from the tip to the root direction (span direction) of the propeller blade, the reinforcing fibers are interrupted at least at the root portion of the propeller blade at a fiber length of 10 to 100 mm. The propeller blade of claim 1, in which the ratio of the maximum to minimum values of the vertical cross-sectional circumference is 1.2 or more in a region within 30% of the blade length from the blade root. A method for manufacturing a propeller blade, comprising the steps of laminating a plurality of sheet-shaped prepregs in which the reinforcing fibers are oriented uniaxially or multiaxially to obtain a laminated prepreg (first step), forming the laminated prepreg into a propeller shape (second step), and heat-curing the laminated prepreg in a propeller blade mold (third step), characterized in that, among the sheet-shaped prepregs in which the reinforcing fibers are oriented uniaxially, the reinforcing fibers are oriented at an angle of 60° or more from the tip to the base direction (blade length direction) of the propeller blade, at least in the portion corresponding to the base of the propeller blade, the reinforcing fibers contained in the prepreg are interrupted at a fiber length of 10 to 100 mm. The method for manufacturing a propeller blade according to claim 3, characterized in that in the second step, pressure is applied to the surface of the laminated prepreg while tension is applied to the laminated prepreg, to shape it into the shape of the outer layer surface or the shape of the inner layer surface of the propeller blade skin. The method for manufacturing a propeller blade according to claim 3 or 4, characterized in that in the second step, the laminated prepreg is preheated and shaped into a propeller shape. The method for manufacturing a propeller blade according to claim 3 or 4, characterized in that the second step is a step of placing a laminated prepreg between a mold having the shape of the outer layer surface of the propeller blade skin and a mold having the shape of the inner layer surface, and sandwiching and pressing the laminated prepreg between the two molds to form it into a propeller shape, and that before pressing the laminated prepreg between the two molds, a part of the laminated prepreg is brought into contact only with the mold having the shape of the inner layer surface, and then pressing is performed.

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