Fiber-reinforced resin molded body

Abstract

This invention relates to a fiber-reinforced resin molded article used in mobility products such as automobiles. [Solution] A fiber-reinforced resin molded article having a box-like shape with one open side, wherein each side is composed of at least three or more fiber-reinforced resin layers and adhesive layers bonding each layer, characterized in that a dynamic load is applied to at least one side from the outer surface of the box-like object, a static load is applied to at least one side constituting the box-like object from the inner surface of the box-like object, and in a region of the side to which the dynamic load is applied that does not come into contact with an adjacent surface, there is at least one unbonded region where there is no adhesive layer between the layers of the fiber-reinforced resin on the side to which the dynamic load is applied (first side), with the central surface between one surface and the other surface in the thickness direction of each surface as the boundary, and there is no unbonded region on the side to which the static load is applied (second side).

Description

[Technical Field]

[0001] The present invention relates to a fiber-reinforced resin molded article. [Background Art]

[0002] In recent years, in the automotive market, development of environmentally friendly vehicles has been progressing in order to achieve future carbon neutrality by reducing CO₂ emissions, and the market expansion of electric vehicles (hereinafter referred to as EVs) and hybrid vehicles is advancing.

[0003] An EV is a vehicle that uses internal power of a battery as its power source, and it is necessary to mount a large heavy-weight battery to ensure a cruising distance per charge. Generally, an EV battery is housed in a battery case to minimize the influence of disturbances such as external force and external environment. Therefore, the battery case desirably has a structure excellent in strength and rigidity to prevent deformation and breakage when the heavy-weight battery is housed therein.

[0004] Furthermore, weight reduction of the vehicle is effective for increasing the cruising distance per charge of an EV. Therefore, weight reduction is demanded for various components of automobiles, and it is also desirable to reduce the weight of the battery case as well.

[0005] In order to realize a battery case that is lightweight and excellent in strength and rigidity, application of fiber-reinforced resin base materials having excellent mechanical properties to battery cases has been increasing in recent years. In Patent Document 1, a fiber-reinforced resin base material is applied to a battery case, thereby realizing a battery case that is lightweight and excellent in strength and rigidity.

[0006] In addition to being lightweight and possessing excellent strength and rigidity, the battery case also requires high energy absorption performance during collisions. If the impact load acting on the battery during a collision is too large, the battery may be damaged and there is a risk of explosion, so it is desirable to ensure sufficient energy absorption in the battery case and reduce the impact load acting on the battery. Patent document 2 describes arranging structural members that absorb energy during a collision in the battery case in order to reduce the impact load on the battery during a collision. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2013-201112 [Patent Document 2] Japanese Patent Publication No. 2023-178084 [Overview of the project] [Problems that the invention aims to solve]

[0008] As mentioned above, applying fiber-reinforced resin substrates to battery cases is effective in achieving a lightweight structure with excellent strength and rigidity.

[0009] On the other hand, in order to obtain a structure with excellent energy absorption performance, it is ideal to suppress the rapid increase in load during a collision, maintain a constant load, and increase the displacement to ensure sufficient energy absorption. For this reason, fiber-reinforced resin substrates, especially continuous fiber-reinforced resin substrates which are high-rigidity materials, are unsuitable for battery cases in terms of energy absorption performance. Therefore, it is common to arrange impact-absorbing structural members made of resins (plastics) that are low-rigidity and highly flexible to ensure energy absorption. However, adding impact-absorbing members to a battery case presents challenges in securing space for these structural members and increasing the amount of joining work.

[0010] To achieve a battery case that is lightweight, has excellent strength and rigidity, and possesses high energy absorption performance, it is effective to combine multiple components and materials with different properties, but this leads to an increase in manufacturing processes and weight. Therefore, there is a need to achieve both a lightweight, strong, and rigid structure and high energy absorption performance using only fiber-reinforced resin substrates. However, it is difficult to achieve high energy absorption performance while suppressing a rapid increase in load with fiber-reinforced resin substrates, which are high-rigidity materials.

[0011] This invention provides a fiber-reinforced resin molded article that achieves both lightweight, high strength and rigidity, and high energy absorption performance. [Means for solving the problem]

[0012] To solve the above problems, the present invention employs the following methods 1 to 9. [1] A fiber-reinforced resin molded article that is a box-shaped object with one side open, and each side is composed of at least three or more fiber-reinforced resin layers and adhesive layers that bond the layers together, wherein a dynamic load is applied to at least one side from the outer surface of the box-shaped object, and a static load is applied to at least one surface constituting the box-shaped object from the inner surface of the box-shaped object, and in a region that does not come into contact with adjacent surfaces of the side to which the dynamic load is applied, there is at least one unbonded area between the layers of the fiber-reinforced resin on the first side to which the dynamic load is applied, with the central surface between one surface and the other surface in the thickness direction of each surface as the boundary, and there is no unbonded area on the second side to which the static load is applied. [2] The fiber-reinforced resin molded article according to [1], wherein the maximum length L1 [mm] of the straight line S1 connecting two points on the periphery of one of the unadhered regions is 10% or more and 80% or less of the length [mm] of the longest side forming the surface having the unadhered region. [3] The fiber-reinforced resin molded article according to [1], wherein the length L2 [mm] of the straight line S2 connecting the midpoint of S1 in one of the unadhered regions and two points on the periphery extending diagonally is 10% or more and less than 100% of the maximum length L1 [mm] of the straight line S1 connecting two points on the periphery in one of the unadhered regions. [4] The fiber-reinforced resin molded article according to [1], wherein the maximum length L1 [mm] of the straight line S1 connecting two points on the periphery of one of the unadhered regions is 10% or more and 80% or less of the length [mm] of the longest side forming the surface having the unadhered region, the length L2 [mm] of the straight line S2 connecting the midpoint of L1 and two points on the periphery extending diagonally is 10% or more and less than 100% of the maximum length L1 [mm] of the straight line S1 connecting two points on the periphery of one of the unadhered regions, and the proportion of unadhered regions present on one surface having an unadhered region is 1% or more and 50% or less. [5] The fiber-reinforced resin molded article according to [1], wherein at least one of the unbonded regions is located at a position where a dynamic load is applied to the first surface side. [6] The fiber-reinforced resin molded article according to [1], wherein the fiber-reinforced resin layer is a continuous fiber-reinforced resin layer in which resin is impregnated into continuous fibers. [7] The fiber-reinforced resin layer is a continuous fiber-reinforced resin layer in which resin is impregnated into continuous fibers, and when the extension direction of L1 is set to 0°, there exists a parallel fiber-reinforced resin layer in which the orientation direction θ of the continuous fibers is in the range of -30° < θ < 30°, and the proportion of the parallel fiber-reinforced resin layer among the fiber-reinforced resin layers constituting the side surface having an unadhered area is 25% or more and 100% or less, as described in [1]. [8] The fiber-reinforced resin molded article according to [1], wherein the unadhered area exists only on the side surface. [9] The fiber-reinforced resin molded body according to [1], wherein the bottom shape of the box-shaped object is rectangular. [Effects of the Invention]

[0013] According to the present invention, when used in automotive components such as battery cases, it is possible to obtain a fiber-reinforced resin molded article that is lightweight, has excellent strength and rigidity, and can achieve both high energy absorption performance. [Brief explanation of the drawing]

[0014] [Figure 1] It is a schematic diagram showing a fiber-reinforced resin molded product according to an embodiment of the present invention, where (a) is a perspective view of the fiber-reinforced resin molded product, (b) is a plan view seen from the opening of the box-shaped member of the fiber-reinforced resin molded product, and (c) is a vertical cross-sectional view taken along line A-A' shown in (b). [Figure 2] It is a schematic diagram showing an input load acting on the fiber-reinforced resin molded product 1 according to an embodiment of the present invention due to an external factor, where (a) is a plan view seen from the opening of the box-shaped member of the fiber-reinforced resin molded product, and (b) is a vertical cross-sectional view taken along line B-B' shown in (a). [Figure 3] It is a schematic diagram showing a cross-section of a fiber-reinforced resin molded product according to an embodiment of the present invention, where (a) is a cross-sectional view of a portion where no unbonded region exists, and (b) is a cross-sectional view of a portion where an unbonded region exists. [Figure 4] It is a schematic diagram showing a fiber-reinforced resin molded product according to an embodiment of the present invention. [Figure 5] It is a schematic diagram showing a fiber-reinforced resin molded product according to embodiments of Example 1 and Comparative Example 1, where (a) is a perspective view of the fiber-reinforced resin molded product, and (b) is a schematic diagram of a cross-section in the thickness direction. [Figure 6] It is a schematic diagram showing impact test conditions according to the present invention. [Figure 7] It is a schematic diagram showing static bending test conditions according to the present invention. [Figure 8] It is a schematic diagram showing the fiber-reinforced resin molded product according to the embodiment of Example 1, where (a) is a perspective view of the fiber-reinforced resin molded product, and (b) is a schematic diagram of a cross-section in the thickness direction. [Figure 9] It is a load-displacement diagram obtained from impact test simulations in Comparative Example 1 and Example 1. [Figure 10] It is a load-displacement diagram obtained from static bending test simulations in Comparative Example 1 and Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described below with reference to the drawings as appropriate to facilitate understanding, but the present invention is not limited in any way by these drawings. Furthermore, the description of specific embodiments shown in the drawings can also be understood as a description of the present invention as a broader concept.

[0016] The present invention relates to a fiber-reinforced resin molded article that is a box-shaped object with one open side, and each side is composed of at least three or more fiber-reinforced resin layers and adhesive layers that bond each layer, wherein a dynamic load is applied to at least one side of the box-shaped object from the external surface, and a static load is applied to at least one side of the box-shaped object from the internal surface, and in a region that does not come into contact with adjacent surfaces of the side to which the dynamic load is applied, there is at least one unbonded region where there is no adhesive layer between the layers of the fiber-reinforced resin on the side to which the dynamic load is applied (first side), with the central plane between one surface and the other surface in the thickness direction of each surface as the boundary, and there is no unbonded region on the side to which the static load is applied (second side).

[0017] Figure 1 is a schematic diagram showing a fiber-reinforced resin molded body according to one embodiment of the present invention, where Figure 1(a) is a perspective view of the fiber-reinforced resin molded body, (b) is a plan view of the fiber-reinforced resin molded body seen from the opening of the box-shaped object, and (c) is a longitudinal cross-sectional view along the line A-A' shown in (b).

[0018] The fiber-reinforced resin molded body 1 of the present invention is a box-shaped object with one side open. A box-shaped object with one side open is a shape in which the top surface is open and the bottom surface 2 is open, and the bottom surface 2 is open and the sides 3 rise up to surround the periphery of the bottom surface 2, as shown in Figures 1(a) to (c).

[0019] The bottom surface of the box-shaped object, which has one open side, is a polygonal shape with three or more sides, and each side has multiple sides that rise perpendicular to the surface.

[0020] Each surface forming the open-sided box-shaped object of the present invention is composed of at least three or more fiber-reinforced resin layers and adhesive layers that bond the layers together.

[0021] In this specification, the term "layer" in a fiber-reinforced resin layer refers to a portion derived from each individual substrate in a molded article obtained by molding a preform made by laminating multiple fiber-reinforced resin substrates. A fiber-reinforced resin molded article is formed when, during the molding process, the interlayers of each fiber-reinforced resin layer in the molded article are bonded to adjacent layers at least at one location. In this specification, the term "bonding layer" refers to the boundary between layers when, during the process of molding a preform made by laminating multiple fiber-reinforced resin substrates, the laminated and adjacent fiber-reinforced resin substrates are bonded together by the resin contained in each fiber-reinforced resin substrate.

[0022] In the present invention, the type of reinforcing fiber contained in the fiber-reinforced resin substrate is not particularly limited, but carbon fiber, glass fiber, aramid fiber, poly(p-phenylene)-benzobis-oxazole (PBO) fiber, etc. can be used, and two or more of these may be used in combination.

[0023] Furthermore, there are no specific restrictions on the types of resins included in the fiber-reinforced resin substrate, other than the inclusion of thermosetting resins. Examples of thermosetting resins include epoxy resins, unsaturated polyester resins, vinyl ester resins, phenolic resins, and polyimide resins. Considering adhesion to fibers and moldability, epoxy resins and vinyl ester resins are preferred. In addition to thermosetting resins, thermoplastic resins may also be used. Examples of thermoplastic resins include ABS resins, nylon resins, polyetheretherketone resins, and polyolefin resins. Note that two or more of these listed resin types may be used in combination.

[0024] In this invention, it is important that each surface forming the box-shaped object is composed of at least three fiber-reinforced resin layers. Having three or more layers allows for the creation of unbonded areas between the substrates, as described later, asymmetrically with the neutral plane in the thickness direction of the surface as the boundary, making it possible to control the deformation under dynamic loads and static loads, as described later. Furthermore, having three or more layers increases the design freedom for strength and rigidity.

[0025] In the present invention, it is important that a dynamic load is applied to at least one surface constituting the box-shaped object from the outer surface of the box-shaped object, and a static load is applied from the inner surface of the box-shaped object.

[0026] Figure 2 is a schematic diagram showing the input load acting on a fiber-reinforced resin molded body 1 according to one embodiment of the present invention due to external factors. Figure 2(a) is a plan view of the fiber-reinforced resin molded body as seen from the opening of the box-shaped object, and (b) is a longitudinal cross-sectional view along the line B-B' shown in (a).

[0027] As shown in Figures 2(a) and 2(b), the dynamic load 6 applied from the external surface acts on at least one side surface 3. The static load 5 applied from the internal surface acts on at least one side surface 3 and the bottom surface 2. It is important that both the dynamic load from the external surface and the static load from the internal surface act on at least one side surface. An example of a situation where both the dynamic load from the external surface and the static load from the internal surface act is when a box-shaped object is installed inside a car, where there is a load from the outside of the box-shaped object due to collisions, etc., and a pressing force from the inside of the box-shaped object due to internal components.

[0028] In this specification, a static load is defined as a state in which a constant load is always acting, and an example of this is the load from the weight of the items placed inside a box-shaped object. The input location, number of inputs, and magnitude of the input load are not specifically defined.

[0029] In this specification, a dynamic load refers to a state in which a load that changes over time is applied, such as an impact load from an external collision or a fall. The number of input dynamic loads and the magnitude of the input loads are not specifically defined.

[0030] In this invention, it is important that in the region of the side surface to which a dynamic load is applied that does not come into contact with adjacent surfaces, there is at least one unadhered region where no adhesive layer exists between the layers of the fiber-reinforced resin layer on the side to which the dynamic load is applied (first surface), with the central plane between one surface and the other surface in the thickness direction of each surface as the boundary, and there is no unadhered region on the side to which a static load is applied (second surface).

[0031] In this specification, an unbonded area refers to a region in a molded article where the interlayers of each fiber-reinforced resin layer are not bonded. The process by which unbonded areas are formed is not particularly limited, but they are formed by the failure to apply adhesive, the insertion of release film, etc. Interlayer delamination that occurs during the deformation process after molding, or interlayer voids due to molding defects, are not defined as unbonded areas.

[0032] As shown in Figure 1(a), one side surface 3 having an unbonded area 4 has an unbonded area in a region that does not come into contact with the other side surface. If the location of the unbonded area is at a corner of a box-shaped structure (where two surfaces are adjacent) where stress concentration is expected to occur during deformation, there is a possibility of a significant decrease in strength and rigidity. Therefore, it is preferable from the viewpoint of strength and rigidity performance for the unbonded area to be in a region that does not come into contact with the other side surface.

[0033] Figure 3 is a schematic diagram showing a cross-section of a fiber-reinforced resin molded article according to one embodiment of the present invention, where Figure 3(a) is a cross-sectional view of a portion without an unbonded area, and (b) is a cross-sectional view of a portion with an unbonded area.

[0034] In areas without unglued regions, as shown in Figure 3(a), the structure consists of a fiber-reinforced resin layer 7 and an adhesive layer 8, with each fiber-reinforced resin layer being integrally connected in the thickness direction with the adhesive layer 8 in between.

[0035] In areas with unbonded regions, as shown in Figure 3(b), the structure consists of a fiber-reinforced resin layer 7, an adhesive layer 8, and an unbonded region 4. It is important that the unbonded region 4 exists on the side 10 where the dynamic load 6 is applied (first surface), with the boundary being the central surface 9 between one surface and the other in the thickness direction of the side, and that there is no unbonded region on the side 11 where the static load is applied (second surface).

[0036] By providing an unadhesive region 4 on the side where the dynamic load is applied (the first surface), the layer on the outer surface side where the dynamic load 6 is applied in the area 10 of the box-shaped structure becomes fragmented, resulting in a thin group of fragmented layers on the outer surface side 10 of the box-shaped structure. The stress state of this thin group of fragmented layers during deformation differs significantly between the application of a dynamic load and a static load. When a dynamic load is applied, the side 10 where the dynamic load 6 is applied (the first surface) and which has the unadhesive region 4 becomes concave, and the thin group of fragmented layers enters a compressive stress state. Under compressive stress, the unadhesive region 4 absorbs the deformation and buckles locally, efficiently absorbing energy while suppressing a rapid increase in load, resulting in a structure with excellent energy absorption performance.

[0037] When a static load is applied, the side 10 on which the dynamic load 6 is applied, which has an unbonded region 4, becomes convex, and the thin fault group enters a tensile stress state. Under tensile stress, local buckling does not occur, so the reduction in stiffness and strength is small.

[0038] In this specification, buckling is defined as the phenomenon in which a sudden and large deformation occurs when a compressive load is applied to a slender or thin structural member, and the load exceeds a level lower than the compressive strength. The load at which buckling occurs varies depending on the shape of the structural member; in the case of a long, slender or thin shape, the load at which buckling occurs is small.

[0039] In this specification, energy absorption performance is determined by the amount of energy absorbed during a collision, and the greater the amount of energy absorbed, the higher the energy absorption performance. Furthermore, if the load on the object being hit increases rapidly during a collision, the safety of the object being hit is a concern. Therefore, from a safety standpoint, it is desirable to suppress the rapid increase in load, maintain a load close to a constant load, increase the displacement, and then ensure sufficient energy absorption.

[0040] In this specification, energy absorption is the amount of energy converted from the kinetic energy of the colliding objects during a collision into energy used for deformation of the structural object being collided with. In this specification, energy absorption is calculated as the area of ​​the load-displacement diagram, which consists of the displacement from the start of deformation to a certain load when a dynamic load is applied to the side, and the reaction force associated with the deformation. The constant load is arbitrarily set based on the required performance, specifications, etc., for each product. If the product fractures during the collision, the energy absorption may be calculated from the displacement until the final fracture of the product and the reaction force associated with the deformation.

[0041] The surfaces constituting the box-shaped object have a mixture of areas with and without unadhesive areas. The sides constituting the box-shaped object only need to have an unadhesive area on at least one surface; if there is a configuration as shown in Figure 3(b) with an unadhesive area on at least one side, the remaining sides may be configured as shown in Figure 3(a).

[0042] Unbonded areas may exist in multiple locations in a single thickness-direction cross-section, as long as they are located on the side where the dynamic load is applied (the first surface), and may also exist in multiple locations on a single surface.

[0043] Figure 4 is a schematic diagram showing a fiber-reinforced resin molded article according to one embodiment of the present invention, in which straight lines S1 and S2 are defined as shape factors of the unbonded region 4.

[0044] A straight line S1 is a straight line connecting the longest distance between any two points on the periphery 12 of a single unadhered region 4, and the length of the straight line S1 is defined as L1.

[0045] The straight line S2 is a straight line connecting two points on the periphery 12 that extends perpendicularly to the midpoint of S1 within one unglued region 4, and the length of the straight line S2 is defined as L2.

[0046] A single unadhered region refers to a single area where unadhered regions exist continuously within the plane. If there are multiple unadhered regions, S1 and S2 are defined for each of them.

[0047] While there are no specific regulations regarding the measurement method around the unadhered area, examples include X-ray CT measurement and ultrasonic testing.

[0048] In the present invention, it is preferable that the length L1 [mm] of the straight line S1 connecting the longest distance between any two points on the periphery of one unadhesive region is 10% or more and 80% or less of the length [mm] of the longest side forming the surface having the unadhesive region.

[0049] When the length L1 [mm] of the straight line S1 connecting any two points on the periphery of the unbonded area is 80% or more of the length [mm] of the longest side forming the surface with the unbonded area, buckling is more likely to occur when subjected to impact load, which is effective in improving energy absorption performance. On the other hand, if the unbonded area is too large, it leads to a decrease in the strength and rigidity of the fiber-reinforced resin molded body. Taking the above into consideration, it is preferable that L1 be between 10% and 80% of the length [mm] of the longest side forming the surface with the unbonded area.

[0050] Furthermore, for the same reasons as described above for S1, it is preferable that the length L2 [mm] of the straight line S2 connecting two points on the periphery that intersects the midpoint of S1 at a right angle within one unadhered region is 10% or more and less than 100% of the length L1 [mm] of the straight line S1 connecting the longest distance between any two points on the periphery of one unadhered region.

[0051] Furthermore, in the present invention, it is most preferable that, among the unadhesive areas, the maximum length L1 [mm] of the straight line S1 connecting any two points on the periphery of one unadhesive area is 10% or more and 80% or less of the length [mm] of the longest side forming the surface having the unadhesive area, the length L2 [mm] of the straight line S2 connecting two points on the periphery that intersects perpendicularly with the midpoint of S1 is 10% or more and less than 100% of the length L1 [mm] of the straight line S1 connecting the longest distance between any two points on the periphery of one unadhesive area, and the proportion of unadhesive areas present on one surface having an unadhesive area is 1% or more and 50% or less.

[0052] If a surface has an unbonded area, a large proportion of that area will result in a greater decrease in the strength and rigidity of the molded article. Therefore, it is preferable that the proportion of the unbonded area on a single surface is between 1% and 50%.

[0053] Furthermore, from the viewpoint of improving energy absorption performance, it is preferable that the present invention has at least one unadhered area at a position where the dynamic load on the first surface is applied.

[0054] Furthermore, in the present invention, it is preferable that the fiber-reinforced resin layer is a continuous fiber-reinforced resin layer in which resin is impregnated into continuous fibers.

[0055] In the case of discontinuous fibers, load transmission becomes inefficient due to the interruption of the fibers, resulting in a decrease in the mechanical properties of the molded body. Therefore, for fiber-reinforced resin layers applied to molded bodies, continuous fiber layers are often more effective in improving the mechanical properties such as strength and rigidity of the molded body.

[0056] Furthermore, in the present invention, the fiber-reinforced resin layer is a continuous fiber-reinforced resin layer in which resin is impregnated into continuous fibers, and when the extension direction of S1 is set to 0°, there exists a parallel fiber-reinforced resin layer in which the orientation direction θ of the continuous fibers is in the range of -30° < θ < 30°, and it is preferable that the proportion of the parallel fiber-reinforced resin layer among the fiber-reinforced resin layers constituting the side surface having an unadhered area is 25% or more and 100% or less.

[0057] It is preferable that the continuous fiber-reinforced resin layer applied to the surface having an unadhered area is a parallel fiber-reinforced resin layer in which the orientation direction of the fibers of the continuous fiber layer is oriented in the range of -30° < θ < 30°, when the extension direction of S1 is 0°, in order to mitigate the reduction in stiffness after buckling caused by the presence of an unadhered area. More preferably, the layer oriented in the range of -30° < θ < 30° accounts for 25% to 100% of the fiber-reinforced resin layer constituting the surface having an unadhered area.

[0058] Furthermore, in this invention, it is preferable that the unadhesive areas exist only on the sides. The unadhesive areas are provided to improve energy absorption performance when an impact load is applied to the sides during a car collision. On the other hand, providing unadhesive areas raises concerns about a decrease in strength and rigidity. Therefore, it is preferable that the bottom surface, which is less likely to be directly subjected to an impact load during a car collision, does not have unadhesive areas, and that they exist only on the sides.

[0059] Furthermore, in the present invention, it is preferable that the bottom shape of the box-shaped object is rectangular. As mentioned above, the shape of the bottom is not particularly limited as long as it is polygonal, but since it is applied to an EV battery case, it is assumed to be rectangular. [Examples]

[0060] To confirm the effectiveness of the fiber-reinforced resin molded body, which combines a lightweight structure with excellent strength and rigidity with high energy absorption performance, the mechanical properties of the fiber-reinforced resin molded body were investigated. As part of the investigation of mechanical properties, simulations simulating impact test conditions and static bending test conditions were performed on a box-shaped fiber-reinforced resin molded body using the finite element method. The simulation software LS-DYNA (R12.1.0) from ANSYS, which is widely used in academia and industry, was used. The impact test confirmed the effect of energy absorption performance, while the static bending test confirmed the effect on strength and rigidity.

[0061] (Fiber-reinforced resin molded product) To verify the mechanical properties, the effects of the present invention were confirmed based on a box-shaped fiber-reinforced resin molded body 1 shown in Figure 5. The fiber-reinforced resin molded body was a box shape as shown in Figure 5(a), with a longitudinal length L of 800 [mm], a width length W of 400 [mm], and a side height H of 100 [mm]. The fiber-reinforced resin molded body was constructed with the fiber orientation direction 13 on each surface in Figure 5(a) as the 0° direction, and consisted of a 0° layer 14, a 90° layer 15, a 45° layer 16, a -45° layer 17, and an adhesive layer 8 as components, as shown in Figure 5(b). The lamination structure consisted of preforms in which the fiber orientation direction of each fiber-reinforced resin layer was (0° / 90° / 45° / -45°)², which were laminated symmetrically with the central surface 9 in the thickness direction of the surface as the boundary. All fiber-reinforced resin substrates were continuous fiber-reinforced resin substrates having the same mechanical properties, and the density of the fiber-reinforced resin substrate was 1.6 [g / cm³]. 3 The tensile modulus of the fibers contained in the fiber-reinforced resin substrate was set to 230 [GPa].

[0062] (Impact test simulation) As shown in Figure 6, the test conditions for the impact test involved fixing a central fixing position 18 on the bottom surface of a box-shaped fiber-reinforced resin molded body 1 along the widthwise length W, applying a dynamic load to the side surface 3 of the box-shaped body from the outside, and evaluating the amount of energy absorbed. The dynamic load conditions applied to the side surface 3 were set as follows: a spherical impact object 19 with dynamic energy collided with the side surface at the center of the longitudinal length L and side surface height H.

[0063] (Static bending simulation) As shown in Figure 7, the static bending test conditions involved fixing a central fixing position 18 on the bottom surface of a box-shaped fiber-reinforced resin molded body 1 along a widthwise length W, and applying a static load 20 to the side surface 3 of the box-shaped body from the inside of the box. The strength and stiffness at that time were evaluated. The static load applied to the side surface 3 was applied at the center of the longitudinal length L and height H of the side surface. Strength was evaluated based on the load until the initial failure of the fiber-reinforced resin molded body, and stiffness was evaluated based on the initial slope of the displacement-load curve.

[0064] (Example 1) As the fiber-reinforced resin molded body for Example 1, the structure of the fiber-reinforced resin molded body 1 shown in Figure 8 was adopted.

[0065] As shown in Figure 8(a), an unadhesive area 4 was provided on the side surface of the fiber-reinforced resin molded body 1 at the position where the dynamic load 6 is applied (the position where the spherical object 19 collides) on the side surface 3 where the spherical impactor collides in the impact test simulation. As shown in Figure 6(b), when repeatedly laminating (0° / 90° / 45° / -45°), an unadhesive area 4 was provided at the boundary between the -45° layer 17 and the 0° layer 14 in the region where the dynamic load 6 is applied, with the central surface 9 as the boundary. Furthermore, the length L1 of S1, which connects any two points on the periphery of the unadhesive area, was set to 200 mm, and the length L2 of S2, which connects the midpoint of S1 and two points on the periphery of the unadhesive area that intersect S1 at a right angle, was set to 80 mm, and S1 was oriented in the same direction as the orientation direction 13 of the fibers contained in the fiber-reinforced resin layer laminated in the 0° direction of the surface having the unadhesive area. The side surfaces other than the unadhesive area 4 had the lamination configuration shown in Figure 5(b).

[0066] The impact test simulation results, as shown by the solid line 21 in the displacement-load diagram of Figure 9, demonstrated that the load increase was suppressed by a decrease in load during the test, and that the displacement up to a certain load could be secured. Furthermore, the inclusion of an unbonded area made structural buckling more likely to occur near the unbonded area, ensuring sufficient displacement up to a certain load, resulting in an energy absorption performance approximately 30% better than that of Comparative Example 1, which will be described later.

[0067] Furthermore, the static bending simulation results were obtained as solid line 23 in the displacement-load diagram of Figure 10. Compared with the dotted line 24, which represents the static bending test results of Comparative Example 1 described later, the static bending test result 23 of Example 1 showed a smaller initial inclination, approximately 4% lower than that of Comparative Example 1. On the other hand, the load at the time of initial failure was equivalent.

[0068] (Comparative Example 1) As the fiber-reinforced resin molded article for Comparative Example 1, the structure of the fiber-reinforced resin molded article shown in Figure 5 was adopted.

[0069] Specifically, no unbonded areas 4 were provided on any of the sides, resulting in the laminated configuration shown in Figure 5(b).

[0070] The impact test simulation results, as shown by the dotted line 22 in the displacement-load diagram of Figure 9, indicated that the load did not decrease significantly before reaching a constant load, and the constant load was reached earlier compared to Example 1.

[0071] Furthermore, the results of the static bending simulation were found to be the dotted line 24 in the displacement-load diagram of Figure 10.

[0072] Table 1 shows the simulation results for Example 1 and Comparative Example 1. The energy absorption amount for Example 1 obtained from the impact test simulation was approximately 30% greater than that for Comparative Example 1. In addition, the initial slope of the load-displacement diagram for Example 1 obtained from the static bending simulation was approximately 4% smaller than that for Comparative Example 1. Furthermore, the fracture load for Example 1 obtained from the static bending simulation was approximately 2% smaller than that for Comparative Example 1.

[0073] From the above, the fiber-reinforced resin molded body of Example 1 was able to improve energy absorption while maintaining the strength and rigidity of conventional fiber-reinforced resin molded bodies.

[0074] [Table 1] [Explanation of Symbols]

[0075] 1. Fiber-reinforced resin molded body 2. Base 3 Sides 4 Unbonded area 5 Static load 6 Dynamic loads 7 Fiber-reinforced resin layer 8 Adhesive layer 9 Central plane 10. The side on which the dynamic load is applied (the first side) 11. The side on which the static load is applied (the second side) 12 Periphery of the unadhered area 13. Fiber orientation direction 14 0° layer 15 90° layer 16 45° layer 17 -45° layer 18 Central fixed position 19 Spherical impact object 20 Static load 21. Impact test simulation results for Example 1 22. Impact test simulation results for Comparative Example 1 23 Static bending simulation results for Example 1 24. Static bending simulation results for Comparative Example 1

Claims

1. A fiber-reinforced resin molded article having one open side, wherein each side is composed of at least three or more fiber-reinforced resin layers and adhesive layers bonding the layers together, wherein a dynamic load is applied to at least one side from the outer surface of the box-shaped object, and a static load is applied to at least one side constituting the box-shaped object from the inner surface of the box-shaped object, and in a region of the side to which the dynamic load is applied that does not come into contact with an adjacent surface, there is at least one unbonded region where there is no adhesive layer between the layers of the fiber-reinforced resin on the side to which the dynamic load is applied (first side), with the central plane between one surface and the other surface in the thickness direction of each surface as the boundary, and there is no unbonded region on the side to which the static load is applied (second side).

2. The fiber-reinforced resin molded article according to claim 1, wherein the length L1 [mm] of the straight line S1 connecting the longest distance between any two points on the periphery of one of the unadhered regions is 10% or more and 80% or less of the length [mm] of the longest side forming the surface having the unadhered region.

3. The fiber-reinforced resin molded article according to claim 1, wherein the length L2 [mm] of the straight line S2 connecting two points on the periphery that intersects perpendicularly with the midpoint of S1 in one of the unadhered regions is 10% or more and less than 100% of the length L1 [mm] of the straight line S1 connecting the longest distance between any two points on the periphery of one of the unadhered regions.

4. The fiber-reinforced resin molded article according to claim 1, wherein the maximum length L1 [mm] of the straight line 1 connecting any two points on the periphery of one of the unadhered areas is 10% or more and 80% or less of the length [mm] of the longest side forming the surface having the unadhered area, the length L [mm]2 of the straight line S2 connecting two points on the periphery that intersects perpendicularly with the midpoint of S1 is 10% or more and less than 100% of the length L1 [mm] of the straight line S1 connecting the longest distance between any two points on the periphery of one of the unadhered areas, and the proportion of unadhered areas present on one surface having an unadhered area is 1% or more and 50% or less.

5. The fiber-reinforced resin molded article according to claim 1, wherein at least one of the unadhered regions is located at a position where a dynamic load is applied to the first surface side.

6. The fiber-reinforced resin molded article according to claim 1, wherein the fiber-reinforced resin layer is a continuous fiber-reinforced resin layer in which resin is impregnated into continuous fibers.

7. The fiber-reinforced resin layer is a continuous fiber-reinforced resin layer in which resin is impregnated into continuous fibers, and when the extension direction of S1 is set to 0°, there exists a parallel fiber-reinforced resin layer in which the orientation direction θ (°) of the continuous fibers is in the range of -30° < θ < 30°, and the proportion of the parallel fiber-reinforced resin layer among the fiber-reinforced resin layers constituting the side surface having an unadhered area is 25% or more and 100% or less, as described in claim 1.

8. The fiber-reinforced resin molded article according to claim 1, wherein the unadhered area exists only on the side surface.

9. The fiber-reinforced resin molded body according to claim 1, wherein the bottom shape of the box-shaped object is rectangular.

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