Continuous fiber-reinforced three-dimensional lattice foam sandwich structure and method of making

Abstract

The application discloses a kind of continuous fiber reinforced three-dimensional lattice foam sandwich structure, belong to composite material structure technical field.The sandwich structure includes foam core layer, the continuous long fiber rope in the oblique through hole distributed in three-dimensional lattice in core layer inside, and the fiber reinforced panel that is compounded in the surface of core layer.The application also discloses corresponding preparation method, and foam raw material is foamed and solidified into plate material and is cut into core layer blank;Directional drilling mold is used to drill out the oblique through hole distributed in three-dimensional lattice on core layer blank;Whole continuous long fiber rope is threaded into through hole and pre-tightening is fixed;Laying fiber reinforced panel and compounding solidification molding.The application uses continuous long fiber rope to replace traditional segmented short fiber column, whole fiber rope is naturally continuous, pre-tightening force is consistent, significantly improves the overall load capacity and mechanical property stability of sandwich structure, while greatly simplifying process flow, reduces preparation working hours and material cost.

Description

Technical Field

[0001] This invention belongs to the field of composite material structure technology, specifically relating to a foam sandwich structure and its preparation method, and more particularly to a sandwich structure with a continuous fiber-reinforced three-dimensional lattice skeleton implanted inside the foam core layer and its preparation method. Background Technology

[0002] Foam sandwich structures are composite material structures composed of upper and lower panels and a middle foam core layer. They possess excellent properties such as high specific strength, high specific stiffness, sound insulation, and heat insulation, and are widely used in aerospace, shipbuilding, rail transportation, and construction. To further improve the mechanical properties of foam sandwich structures, researchers have proposed a technical solution of embedding a fiber-reinforced three-dimensional lattice structure inside the foam core layer.

[0003] Currently, the fabrication of three-dimensional lattice-reinforced foam sandwich structures mainly employs the following two technical approaches: The first method involves pre-arranging pre-fabricated fiber pillars or prepreg pillars in specific positions within a mold before foaming the raw material, followed by foaming and curing. The drawbacks of this method are that positioning the fiber pillars is difficult, displacement easily occurs during foaming, the interfacial bonding between the fiber pillars and the foam matrix is ​​unstable, and the foaming quality is difficult to guarantee.

[0004] The second method involves using CNC machining to mill three-dimensional lattice grooves point by point and layer by layer on the cured foam core layer, and then inserting segmented short fiber pillars one by one into each groove. This method has the problems of long processing cycle and high economic cost, and the lack of connection between the segmented short fiber pillars results in poor overall integrity and large dispersion of the mechanical properties of each pillar.

[0005] The two technical approaches mentioned above share a common drawback: each reinforcing member in the three-dimensional lattice is manufactured or inserted independently in segments, making it difficult to ensure the consistency of the preload and mechanical properties of each member. The overall process is complex and costly, which is not conducive to industrial mass production.

[0006] Therefore, there is an urgent need to develop a foam sandwich structure and its preparation method that is simple to manufacture, low in cost, has good consistency in mechanical properties of the reinforcing body, and is suitable for automated production. Summary of the Invention

[0007] In view of one or more of the above-mentioned defects or improvement needs of the prior art, the present invention provides a continuous fiber reinforced three-dimensional lattice foam sandwich structure and its preparation method, aiming to solve the technical problems of complex preparation process, high cost and poor mechanical property consistency of the existing three-dimensional lattice reinforced foam sandwich structure.

[0008] To achieve the above objectives, according to a first aspect of the present invention, a continuous fiber-reinforced three-dimensional lattice foam sandwich structure is provided, comprising: A foam core layer, wherein oblique through holes distributed in a three-dimensional lattice are formed on the foam core layer, and the oblique through holes converge and connect within the foam core layer; Continuous long fiber ropes are threaded through the oblique through holes and are in a taut state to form a three-dimensional lattice reinforcement skeleton inside the foam core layer; A fiber-reinforced panel is laminated to at least one surface of the foam core layer.

[0009] As a further improvement of the present invention, the three-dimensional dot matrix is ​​composed of several basic units repeatedly arranged in the planar direction of the foam core layer, each basic unit containing four oblique through holes, and the axes of the four oblique through holes intersect at the same point on one side of the foam core layer in the thickness direction. The oblique through holes of adjacent basic units are connected at the junction edge of the bottom and side surfaces of the foam core layer, forming a continuous threading path that is interconnected; the continuous long fiber rope is sequentially threaded through each oblique through hole along the continuous threading path.

[0010] As a further improvement of the present invention, the spacing between the oblique through holes on the bottom surface of the foam core layer satisfies the following: the ratio of the spacing between adjacent holes in the width direction to the spacing between adjacent holes in the length direction is 1:0.5 to 1:1.5.

[0011] As a further improvement of the present invention, the material of the continuous long fiber rope includes one or more of glass fiber, carbon fiber, aramid fiber, and nylon fiber, and the continuous long fiber rope is woven or bundled from multiple bundles of fibers. The continuous long fiber rope is impregnated with thermosetting resin or thermoplastic resin.

[0012] As a further improvement of the present invention, the fiber-reinforced panel is made of fiber-reinforced resin-based composite material, wherein the reinforcing fibers include one or more of glass fibers, carbon fibers, and aramid fibers.

[0013] According to a second aspect of the present invention, a method for preparing a continuous fiber-reinforced three-dimensional lattice foam sandwich structure is provided, comprising the following steps: S1 foams and solidifies the foam raw material into a foam board, and then cuts the foam board into core layer blanks; S2 uses a directional drilling die to drill oblique through holes in the core layer blank in a three-dimensional dot matrix distribution. The oblique through holes intersect and connect within the core layer blank. S3 inserts the continuous long fiber rope into each of the oblique through holes in sequence and pre-tightens and fixes it, so that the continuous long fiber rope forms a three-dimensional lattice reinforcement skeleton inside the core layer blank. S4. A fiber-reinforced panel blank is laid on at least one side surface of the core layer blank through which the continuous long fiber rope is threaded. S5 combines and solidifies the fiber-reinforced panel blank with the core layer blank to form a continuous fiber-reinforced three-dimensional lattice foam sandwich structure.

[0014] As a further improvement of the present invention, in S2, a directional drilling die is used to drill oblique through holes with a three-dimensional dot matrix distribution on the core layer blank, including: The core layer blank is inserted into the positioning slot of the directional drilling mold and fixed. A through-hole is formed in the core blank by drilling along the oblique guide groove on the directional drilling mold using a drill bit. The length and width of the positioning slot are adapted to the length and width of the core blank, respectively. The axes of each of the inclined guide slots intersect at a point in space. This intersection point corresponds to a spatial node formed by the intersection of each inclined through hole on one end face of the core blank in the thickness direction.

[0015] As a further improvement of the present invention, in S3, the continuous long fiber rope is sequentially threaded into each of the oblique through holes and pre-tightened and fixed, including: A continuous long fiber rope is inserted from one end of the core layer blank, passes through each oblique through hole in sequence, and then passes back in the opposite direction after reaching the other end, forming a reciprocating winding path that runs through all the oblique through holes. A pre-tension force is applied to the continuous long fiber rope to keep it taut in each of the oblique through holes; and the two ends of the taut continuous long fiber rope are fixed.

[0016] As a further improvement of the present invention In step S3, before threading the continuous long fiber rope through the oblique through hole, the method further includes: impregnating the continuous long fiber rope with a thermosetting resin or a thermoplastic resin; and / or, In S5, the composite curing and molding process employs vacuum-assisted molding, autoclave curing, or compression molding; and / or, In S5, after the composite curing and molding, the following steps are also included: cutting and trimming the cured sandwich structure along the projection contour of the three-dimensional lattice reinforcing skeleton on the bottom surface of the foam core layer.

[0017] According to a third aspect of the present invention, a directional drilling mold is provided for a method of preparing the continuous fiber reinforced three-dimensional lattice foam sandwich structure, comprising: The base is provided with a positioning slot for accommodating the core blank, the length and width of which are adapted to the length and width of the core blank, respectively. Multiple oblique guide slots are arranged in a three-dimensional dot matrix on the base. The axes of each oblique guide slot intersect at a point in space. This intersection point corresponds to a spatial node formed by the intersection of the oblique through holes on one end face of the core blank in the thickness direction. It is used to guide the drill bit to drill oblique through holes in the core blank with the same oblique guide slot distribution structure.

[0018] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art: (1) This invention creates interconnected oblique through holes in the foam core layer, allowing a single continuous long fiber rope to repeatedly wind and uniformly pre-tighten within the foam core layer, forming an integrated three-dimensional lattice reinforcement skeleton. The entire fiber rope is naturally continuous, avoiding weak mechanical zones between segmented reinforcements; at the same time, uniform pre-tightening ensures that the pre-tightening force of each reinforcement branch is basically consistent, avoiding the problem of mechanical property dispersion caused by differences in the manufacturing of segmented short fiber columns, and significantly improving the overall load-bearing capacity and mechanical property stability of the sandwich structure.

[0019] (2) The foam core layer of this invention adopts the method of integral foaming and curing first, followed by cutting and drilling, which ensures the foaming quality and avoids the interference of pre-embedded reinforcing parts on the foaming process. In addition, the use of directional drilling mold to guide the drill bit can accurately control the position and direction of the oblique through hole, ensure the geometric accuracy of the three-dimensional lattice, and effectively avoid the cracking and collapse of the foam material during the drilling process.

[0020] (3) The present invention uses a whole continuous long fiber rope to replace the traditional multiple segmented short fiber columns or prepreg columns, which greatly reduces the number of components and operation procedures, significantly reduces material costs and labor costs, and the perforation and pre-tightening operation of the continuous long fiber rope is easy to be mechanized or even automated.

[0021] (4) By adjusting the material, weaving method, resin type and hole spacing ratio of the continuous long fiber rope, the mechanical properties and anisotropy of the three-dimensional lattice skeleton can be flexibly controlled to meet the different lightweight load-bearing requirements of aerospace, shipbuilding, rail transportation, construction and other fields. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of the continuous fiber reinforced three-dimensional lattice foam sandwich structure according to an embodiment of the present invention; Figure 2 This is a partial perspective structural diagram of the foam core layer according to an embodiment of the present invention; Figure 3 This is a flowchart illustrating the preparation method of the continuous fiber reinforced three-dimensional lattice foam sandwich structure according to an embodiment of the present invention. Figure 4 This is a schematic diagram of the directional drilling mold structure according to an embodiment of the present invention; Figure 5 This is a schematic diagram of the continuous long fiber rope winding path according to an embodiment of the present invention; Figure 6 The figures show the quasi-static compression test results of Embodiment 1 and Comparative Example 1 of the present invention; Figure 7 The figures show the axial compression stability test results of Embodiment 1 and Comparative Example 1 of the present invention; Figure 8 The diagram shows the results of the three-point bending test of Embodiment 1 and Comparative Example 1 of the present invention.

[0023] In all the accompanying drawings, the same reference numerals denote the same technical features, specifically: 1. Foam core layer; 2. Angled through hole; 3. Continuous long fiber rope; 4. Fiber reinforced panel; 5. Base; 6. Positioning slot; 7. Angled guide hole slot. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0025] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0026] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0027] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0028] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0029] See Figure 1 and Figure 2 The continuous fiber-reinforced three-dimensional lattice foam sandwich structure of this invention includes a foam core layer 1, continuous long fiber ropes 3, and a fiber-reinforced panel 4. The foam core layer 1 has obliquely oriented through-holes 2 arranged in a three-dimensional lattice, which converge and connect within the foam core layer 1. The continuous long fiber ropes 3 are threaded through the obliquely oriented through-holes 2 and are in a tensioned state to form a three-dimensional lattice reinforcement skeleton inside the foam core layer 1. The fiber-reinforced panel 4 is laminated to at least one surface of the foam core layer 1.

[0030] In a preferred embodiment, the three-dimensional dot matrix is ​​a pyramid-shaped dot matrix, meaning that the three-dimensional dot matrix is ​​composed of several basic units repeatedly arranged in the planar direction of the foam core layer 1. Each basic unit contains four oblique through holes 2, and the axes of the four oblique through holes 2 intersect at the same point on one side of the foam core layer 1 in the thickness direction. The oblique through holes 2 of adjacent basic units connect at the intersection edge of the bottom and side surfaces of the foam core layer 1, forming a continuous threading path that allows for the uninterrupted threading of the continuous long fiber rope 3. The continuous long fiber rope 3 is sequentially threaded through the oblique through holes 2 of each basic unit along the continuous threading path, and its two ends are fixed to the ends of the foam core layer 1 or inside the fiber-reinforced panel 4.

[0031] It should be noted that the planar direction of the foam core layer 1 in this invention refers to the direction defined by a plane perpendicular to the thickness direction of the foam core layer, including the length direction of the foam core layer and the width direction which can be selected as needed. That is, when the sandwich structure is beam-shaped, the basic units can be arranged repeatedly mainly along the length direction; when the sandwich structure is plate-shaped, the basic units can be arranged in an array-like repeating pattern along both the length and width directions.

[0032] In a preferred embodiment, the spacing between the oblique through holes 2 on the bottom surface of the foam core layer 1 satisfies the following condition: the ratio of the spacing between adjacent holes in the width direction to the spacing between adjacent holes in the length direction is 1:0.5 to 1:1.5. By adjusting the ratio of the spacing between holes in the width direction to the length direction, the spatial configuration and mechanical properties of the three-dimensional lattice are controlled, achieving periodic close arrangement of the lattice structure in both the length and width directions; at the same time, it ensures that the foam hole walls between adjacent oblique through holes have sufficient thickness, avoiding excessively thin hole walls due to overly dense hole spacing, which could lead to cracking or breakage during drilling, thus ensuring processability and core layer integrity.

[0033] In a preferred embodiment, the continuous long fiber rope 3 is made of one or more of glass fiber, carbon fiber, aramid fiber, and nylon fiber, and the continuous long fiber rope 3 is woven or bundled from multiple bundles of fibers. More preferably, the continuous long fiber rope 3 is impregnated with thermosetting resin or thermoplastic resin, and after curing, it forms a reliable anchor with the foam core layer 1 and the fiber-reinforced panel 4, improving the interfacial bonding strength and synergistic load-bearing capacity.

[0034] In a preferred embodiment, the fiber-reinforced panel 4 is made of a fiber-reinforced resin-based composite material, wherein the reinforcing fibers include one or more of glass fibers, carbon fibers, and aramid fibers. During the composite curing process, the fiber-reinforced panel 4 and the continuous long fiber ropes in the foam core layer 1 are integrally connected through the resin matrix. The panel not only bears out-of-plane loads but also transfers the loads to the three-dimensional lattice skeleton inside the core layer through the continuous long fiber ropes, fully utilizing the tensile strength of the fiber-reinforced material and the lightweight advantages of the foam core layer to achieve high specific strength and high specific stiffness of the structure.

[0035] In a preferred embodiment, the foam core layer 1 is made of a drillable lightweight foam material, including but not limited to polyurethane foam (PU), polymethacrylamide foam (PMI), and polyvinyl chloride foam (PVC). This type of material possesses sufficient structural strength and toughness, allowing for mechanical drilling with conventional drill bits. It is less prone to cracking or fragmentation during drilling, maintaining the geometric integrity of the oblique through-holes. Simultaneously, this type of material has a low density (typically 30~200 kg / m³), ensuring the lightweight characteristics of the sandwich structure.

[0036] Furthermore, such as Figure 3As shown, this embodiment of the invention also provides a method for preparing a continuous fiber reinforced three-dimensional lattice foam sandwich structure, comprising the following steps: S1 foams and solidifies the foam raw material into foam board, and then cuts the foam board into core layer blanks; S2 uses a directional drilling mold to drill oblique through holes in the core layer blank in a three-dimensional dot matrix distribution. The oblique through holes intersect and connect within the core layer blank. S3 inserts the continuous long fiber rope into each oblique through hole in sequence and pre-tightens and fixes it, so that the continuous long fiber rope forms a three-dimensional lattice reinforcement skeleton inside the core layer blank. S4 A fiber-reinforced panel blank is laid on at least one side surface of a core blank with a continuous long fiber rope; S5 combines and solidifies fiber-reinforced panel blanks with core layer blanks to form fiber-reinforced panels.

[0037] In a preferred embodiment, step S2 employs Figure 4 The directional drilling mold shown drills oblique through holes with a three-dimensional dot matrix distribution on the core blank.

[0038] Specifically, the directional drilling mold includes a base 5 and multiple oblique guide slots 7. The base 5 is provided with positioning slots 6 for accommodating the core blank. The length and width of the positioning slots 6 are adapted to the length and width of the core blank, respectively (the width of the positioning slots 6 is preferably adapted to the width of the core blank to clamp the core blank; the length of the positioning slots 6 is preferably not less than the length of the core blank). Multiple oblique guide slots 7 are arranged in a three-dimensional lattice on the base 5. The axes of each oblique guide slot 7 intersect at a point in space. This intersection point corresponds to a spatial node formed by the intersection of the oblique through holes on one end face of the core blank in the thickness direction. This node is used to guide the drill bit to drill oblique through holes in the core blank with the same distribution structure as the oblique guide slots.

[0039] In use, the core layer blank is inserted into the positioning slot 6 for fixation, and a drill bit is used to drill along the oblique guide slot 7 to form a through oblique through hole in the core layer blank. Due to the precise positioning and guidance of the oblique guide slot 7, the positional and directional accuracy of each oblique through hole can be guaranteed, and the cracking and collapse of the foam material during the drilling process can be effectively avoided.

[0040] It should be noted that the oblique guide slots on the directional drilling die do not correspond to only one basic unit, but are arranged in an array along the length and / or width of the base according to the periodic arrangement of the three-dimensional lattice, covering the entire planar area of ​​the core blank. This allows for the drilling of all oblique through holes on the core blank in a single positioning operation. Each basic unit corresponds to a set of four oblique guide slots. Adjacent basic units share the same hole position at the edge of the bottom surface, and the guide slot corresponding to that hole position serves two basic units simultaneously.

[0041] In a preferred embodiment, step S3, before threading the continuous long fiber rope into the oblique through hole, further includes: impregnating the continuous long fiber rope with thermosetting resin or thermoplastic resin. The resin-impregnated fiber rope has a certain rigidity, facilitating threading, and during the subsequent curing process, the resin anchors the fiber rope to the inner wall of the through hole and the panel, forming a reliable interfacial bond.

[0042] In a preferred embodiment, the winding path of the continuous long fiber rope in step S3 is as follows: the continuous long fiber rope 3 enters from the opening at the bottom of a basic unit, ascends along the oblique through-hole to the spatial node, turns, descends along another oblique through-hole to the common opening at the bottom of the adjacent basic unit, exits, and continues to ascend from the common opening into the adjacent basic unit. Using the above winding method, after reaching the other end, it reverses and winds back, forming a reciprocating winding path. The entire continuous long fiber rope 3 can pass through all the oblique through-holes 2 without interruption or splicing during the winding process, forming a continuous and integral three-dimensional lattice reinforcement skeleton inside the foam core layer 1.

[0043] More preferably, the winding path adopts Figure 5 The illustrated cross-threading method allows continuous long fiber ropes to advance in a crisscross pattern between basic units, sequentially passing through each oblique through-hole, and then returning in the opposite direction after reaching the other end, forming a reciprocating cross-threading path. This method allows the fiber ropes to be distributed in a mesh-like pattern within the core layer plane, resulting in balanced stress in all directions and superior shear resistance. It is understandable that the specific threading path can be adjusted according to the lattice arrangement and equipment conditions, as long as the entire fiber rope continuously passes through all oblique through-holes.

[0044] More preferably, in step S3, after the continuous long fiber rope 3 is wound, it is pre-tightened and fixed, specifically including the following steps: First, tension is applied to one or both ends of the continuous long fiber rope 3 to keep it taut in each of the oblique through holes 2.

[0045] The magnitude of the preload should be determined based on factors such as the material and density of the foam core layer 1, and the diameter and strength of the fiber rope. If the preload is too small, the fiber rope will be loose and unable to effectively bear the load; if the preload is too large, it may cause localized crushing of the foam core layer at the pore walls. Generally, the preload is controlled within a range that just tensions the fiber rope without causing significant deformation of the foam.

[0046] Next, the two ends of the tensioned continuous long fiber rope 3 are fixed to the ends of the core layer blank. Preferably, the fixing method can be knotting, temporary tape application, hot melting to form a ball head, or adhesive bonding, etc., to maintain the tension of the fiber rope during the subsequent panel laying and composite curing process.

[0047] It should be noted that in the subsequent composite curing step S5, the resin impregnated on the surface of the continuous long fiber rope 3 is cured by heat, bonding the continuous long fiber rope 3 to the inner wall of the through-hole of the foam core layer, forming a permanent anchor. At this point, the temporary fixation at both ends of the continuous long fiber rope 3 can be removed or retained.

[0048] This invention employs a single, continuous long fiber rope that is repeatedly wound around the thread, combined with an arrangement of interconnected oblique through-holes at the bottom edge, creating an uninterrupted, continuous threading path and providing a structural foundation for automated threading. Unlike existing technologies that require inserting segmented short fiber posts one by one, the structure of this invention allows the entire fiber rope to be pulled through all the oblique through-holes in one go, and can automatically apply pre-tension, significantly improving threading efficiency and pre-tension control accuracy.

[0049] In a preferred embodiment, in S5, the composite curing molding adopts a vacuum-assisted molding process, an autoclave curing process, or a compression molding process.

[0050] In a preferred embodiment, step S5, after composite curing and molding, further includes a step of cutting and trimming the cured sandwich structure. Specifically, the cutting and trimming is performed along the projection contour of the three-dimensional lattice reinforcement skeleton on the bottom surface of the foam core layer. This step ensures that the cut edge is aligned with the fiber reinforcement skeleton, avoiding weak areas of unreinforced foam at the edges, while removing excess material to ensure dimensional accuracy and appearance quality. Waterjet cutting is further preferred, as it has advantages such as no heat-affected zone, narrow kerf, and good edge quality.

[0051] To better illustrate the technical solutions and effects of the embodiments of the present invention, the following embodiments and comparative examples are provided: Example 1 This embodiment provides a continuous fiber-reinforced three-dimensional lattice foam sandwich beam, including a foam core layer 1, a continuous long fiber rope 3 passing through the interior of the foam core layer 1, and fiber-reinforced panels 4 composited on the upper and lower surfaces of the foam core layer 1.

[0052] The foam core layer 1 is a polyurethane foam core layer with dimensions of 330mm in length, 50mm in width, and 30mm in thickness. Inclined through-holes 2 arranged in a pyramidal three-dimensional lattice pattern are formed on the foam core layer 1. The inclined through-holes 2 intersect and connect at the nodes of the pyramidal lattice within the foam core layer 1. Specifically, on the bottom surface of the foam core layer 1, the distance between the axes of adjacent inclined through-holes 2 in the width direction is 30mm, and the distance in the length direction is 20mm. The angle between the inclined through-holes 2 and the bottom surface of the foam core layer 1 is determined according to the geometric parameters of the pyramidal lattice, such that the axes of each inclined through-hole 2 intersect at one end face in the thickness direction of the foam core layer, and this intersection point is located in the middle of the width direction, making the inclined through-holes on the left and right sides symmetrically distributed about the centerline of the core layer's width direction, forming a symmetrical pyramidal lattice structure.

[0053] The continuous long fiber rope 3 is a nylon fiber rope impregnated with epoxy resin, composed of 10 bundles of nylon thread. The continuous long fiber rope 3 is threaded through each of the oblique through holes 2 and is in a taut state, thereby forming a pyramid-shaped three-dimensional lattice reinforcement skeleton inside the foam core layer 1. The two ends of the continuous long fiber rope 3 are fixed to the ends of the foam core layer 1.

[0054] The fiber-reinforced panel 4 is a glass fiber reinforced epoxy resin-based composite material panel, which is laminated to the upper and lower surfaces of the foam core layer 1 through a vacuum-assisted molding process.

[0055] The method for preparing a continuous fiber-reinforced three-dimensional lattice foam sandwich beam according to an embodiment of the present invention includes the following steps: (1) Preparation of foam core layer blank Polyurethane foam raw material is injected into a flat mold for foaming and curing to obtain a foam board. After the foam board has completely cured, it is cut into beam-shaped core layer blanks with a width of 50mm, a thickness of 30mm, and a length of 330mm according to the design dimensions.

[0056] (2) Machining oblique through holes use Figure 4 The directional drilling mold shown drills oblique through holes 2 in a pyramid-shaped three-dimensional lattice distribution on the core blank.

[0057] The length of the base 5 is the same as the length of the core blank, which is 330mm. The inner width of the positioning groove 6 is 50mm, which matches the width of the core blank, and the depth of the positioning groove 6 matches the thickness of the core blank.

[0058] The oblique guide slots 7 are formed on the base 5. The axes of each oblique guide slot 7 intersect at the apex of the pyramid-shaped three-dimensional lattice, that is, the spatial node formed by the intersection of each oblique through hole on one end face of the core layer blank in the thickness direction. On the bottom surface of the base 5, the spacing of the axes of the oblique guide slots 7 in the width direction is 30mm and the spacing in the length direction is 20mm, which is consistent with the design dimensions of the pyramid-shaped lattice.

[0059] The core blank is fixed in the positioning slot 6, and a fine drill bit is used to drill along the oblique guide slots 7 to drill oblique through holes 2 through the core blank. The diameter of the oblique through hole 2 is slightly larger than the diameter of the continuous long fiber rope 3. In this embodiment, the drill bit diameter is φ2mm and the diameter of the continuous long fiber rope 3 is φ1.8mm.

[0060] (3) Insert the continuous long fiber rope like Figure 5As shown, a single continuous long fiber rope 3 is threaded into the oblique through-hole 2 processed in step S2. Specifically, the continuous long fiber rope 3 is threaded through the first oblique through-hole 2 at one end of the core layer blank, then through each oblique through-hole 2 in sequence, reaching the other end and then returning through the last oblique through-hole 2, forming a reciprocating crisscrossing winding path. After winding, a pre-tension force is applied to the continuous long fiber rope 3 to maintain it in a taut state within each oblique through-hole 2 without significant crushing of the foam pore walls. Then, the two ends of the continuous long fiber rope 3 are knotted and fixed to the ends of the core layer blank.

[0061] (4) Laying fiber-reinforced panel blanks Glass fiber prepreg is laid on the upper and lower surfaces of the core prepreg containing continuous long fiber ropes 3, serving as the prepreg for the fiber-reinforced panel 4. Two layers of glass fiber prepreg are laid, each with a thickness of approximately 0.2 mm, a resin content of approximately 35%, and a fiber surface density of 220 g / m².

[0062] (5) Composite curing molding A vacuum-assisted molding process is employed, in which the core layer blank, after the panel blank has been laid out, is placed in a vacuum bag. After vacuuming, epoxy resin is injected, allowing the resin to impregnate the panel fibers and the ends of the continuous long fiber ropes on the surface of the core layer. Subsequently, the entire assembly is placed in an autoclave, heated to 120°C at a rate of 2°C / min, held at that temperature for 2 hours, and then heated to 180°C at a rate of 1°C / min, held at that temperature for 4 hours, to cure and solidify.

[0063] (6) Cutting and trimming After curing, the sandwich beam is cut and trimmed in the width direction according to the design size requirements, along the projection outline of the three-dimensional lattice reinforced skeleton on the bottom surface of the foam core layer using water jet cutting, and finally a pyramid-shaped continuous fiber reinforced three-dimensional lattice foam sandwich beam with a width of 30mm is obtained.

[0064] Example 2 This embodiment provides a continuous fiber-reinforced three-dimensional lattice foam laminate. Compared with Embodiment 1, the only difference is that the fiber-reinforced panel 4 is only laid on one side of the foam core layer 1, while the other side is not covered with a panel and is either directly exposed or only covered with a release film. It is suitable for applications that only require single-sided load-bearing or have extreme weight requirements, such as drone wing skin and satellite structural panels.

[0065] The difference between the preparation method of this embodiment and that of embodiment 1 is that in step (4), glass fiber prepreg is laid only on the upper surface of the core blank, and release film is laid on the lower surface or directly in contact with the mold; the remaining steps are the same as those of embodiment 1.

[0066] Example 3 This embodiment provides a continuous fiber-reinforced three-dimensional lattice foam sandwich panel. Compared with Embodiment 1, the difference is that the foam core layer 1 is plate-shaped (500mm in length, 500mm in width, and 30mm in thickness). The oblique guide slots on the directional drilling mold are arrayed in both the length and width directions, covering the entire planar area of ​​the core layer blank. The size of the fiber-reinforced panel 4 is consistent with the size of the core layer blank. During threading, the continuous long fiber rope 3 is a single continuous fiber rope, starting from one end of the plate-shaped core layer, sequentially threaded through the first column of oblique through holes to the other end, passing through the through hole at the bottom edge, moving to the adjacent column, and then reversing back. This serpentine process is repeated until a single continuous rope passes through all the oblique through holes. The remaining material selection, drilling, curing, and cutting and trimming steps are the same as in Embodiment 1, finally obtaining a 500mm×500mm sandwich panel product.

[0067] Example 4 This embodiment provides a continuous fiber-reinforced three-dimensional lattice foam sandwich panel, which differs from Embodiment 1 in that: the core layer is composed of multiple core layer blanks with pre-threaded ropes arranged along the width direction, with each blank tightly abutting against the others, and fiber-reinforced panels are integrally laid on the upper and lower surfaces. Composite curing connects the blanks into a complete sandwich panel. This method is suitable for scenarios where large-format panels are prepared by assembling narrow blanks.

[0068] Comparative Example 1 This comparative example provides a traditional segmented short fiber column reinforced three-dimensional lattice foam sandwich beam. Compared with Example 1, in step (3), multiple discontinuous hard short fiber columns that have been heated and cured are inserted into the oblique through holes 2 processed in step S2. The length of the short fiber column is the same as the axial length of the oblique through hole, and one short fiber column is inserted into each oblique through hole.

[0069] Test case The mechanical properties of the continuous fiber-reinforced three-dimensional lattice foam sandwich beam prepared in Example 1 and Comparative Example 1 (traditional segmented short prepreg fiber column reinforced foam sandwich beam) were systematically tested. The test methods and results are as follows: Quasi-static compression test: The test was conducted in accordance with GB / T 1453-2022 "Test Method for Flat Compression Performance of Sandwich Structures or Cores", with a loading rate of 2 mm / min. The compressive strength, compressive modulus and failure mode were recorded.

[0070] Axial compression stability test: The test was conducted in accordance with GB / T 1454-2021 "Test Method for Lateral Compression Performance of Sandwich Structures" to test the stability and load-bearing capacity of the sandwich structure under lateral compressive load.

[0071] Three-point bending test: The test was conducted in accordance with GB / T 1456-2005 "Test Method for Bending Performance of Sandwich Structures", with a span of 200 mm and a loading rate of 5 mm / min. The bending strength, bending stiffness and failure mode were recorded.

[0072] The test results are as follows Figures 6 to 8 As shown, the results indicate that, under the same fiber volume fraction, the compressive strength of the specimens of this invention is increased by approximately 5%-10%, the axial compressive stability is increased by approximately 3%-5%, and the bending stiffness is increased by approximately 5%-8%. These results demonstrate that the integrated three-dimensional lattice-reinforced skeleton formed by a single continuous long fiber rope in this invention possesses superior load-bearing capacity and structural stability. More importantly, the coefficient of variation (coefficient of variation) of the mechanical properties of the specimens of this invention is reduced from 15.3% for the comparative specimens to 6.7%, indicating a significant improvement in the consistency of the mechanical properties of each member and a marked improvement in the overall stability and reliability of the sandwich structure.

[0073] Furthermore, the preparation time of the specimens of the present invention is reduced by about 40%, and the material cost is reduced by about 35%, which fully verifies the advantages of the present invention in terms of process simplification and cost control.

[0074] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A continuous fiber-reinforced three-dimensional lattice foam sandwich structure, characterized in that, include: A foam core layer, wherein oblique through holes distributed in a three-dimensional lattice are formed on the foam core layer, and the oblique through holes converge and connect within the foam core layer; Continuous long fiber ropes are threaded through the oblique through holes and are in a taut state to form a three-dimensional lattice reinforcement skeleton inside the foam core layer; A fiber-reinforced panel is laminated to at least one surface of the foam core layer; The three-dimensional lattice is composed of several basic units arranged repeatedly in the planar direction of the foam core layer. Each basic unit contains four oblique through holes, and the axes of the four oblique through holes intersect at the same point on one side of the foam core layer in the thickness direction. The oblique through holes of adjacent basic units are connected at the junction edge of the bottom and side surfaces of the foam core layer, forming a continuous threading path that is interconnected; the continuous long fiber rope is sequentially threaded through each oblique through hole along the continuous threading path.

2. The continuous fiber-reinforced three-dimensional lattice foam sandwich structure according to claim 1, characterized in that, The spacing between the oblique through holes on the bottom surface of the foam core layer satisfies the following: the ratio of the spacing between adjacent holes in the width direction to the spacing between adjacent holes in the length direction is 1:0.5 to 1:1.

5.

3. The continuous fiber-reinforced three-dimensional lattice foam sandwich structure according to claim 1, characterized in that, The continuous long fiber rope is made of one or more of glass fiber, carbon fiber, aramid fiber, and nylon fiber, and the continuous long fiber rope is woven or bundled from multiple bundles of fibers. The continuous long fiber rope is impregnated with thermosetting resin or thermoplastic resin.

4. The continuous fiber-reinforced three-dimensional lattice foam sandwich structure according to claim 1, characterized in that, The fiber-reinforced panel is made of fiber-reinforced resin-based composite material, wherein the reinforcing fibers include one or more of glass fibers, carbon fibers, and aramid fibers.

5. A method for preparing the continuous fiber-reinforced three-dimensional lattice foam sandwich structure according to any one of claims 1-4, characterized in that, Includes the following steps: S1 foams and solidifies the foam raw material into a foam board, and then cuts the foam board into core layer blanks; S2 uses a directional drilling die to drill oblique through holes in the core layer blank in a three-dimensional dot matrix distribution. The oblique through holes intersect and connect within the core layer blank. S3 inserts the continuous long fiber rope into each of the oblique through holes in sequence and pre-tightens and fixes it, so that the continuous long fiber rope forms a three-dimensional lattice reinforcement skeleton inside the core layer blank. S4. A fiber-reinforced panel blank is laid on at least one side surface of the core layer blank through which the continuous long fiber rope is threaded. S5 combines and solidifies the fiber-reinforced panel blank with the core layer blank to form a continuous fiber-reinforced three-dimensional lattice foam sandwich structure.

6. The method for preparing a continuous fiber-reinforced three-dimensional lattice foam sandwich structure according to claim 5, characterized in that, In S2, a directional drilling die is used to drill oblique through holes with a three-dimensional lattice distribution on the core layer blank, including: The core layer blank is inserted into the positioning slot of the directional drilling mold and fixed. A through-hole is formed in the core blank by drilling along the oblique guide groove on the directional drilling mold using a drill bit. The length and width of the positioning slot are adapted to the length and width of the core blank, respectively. The axes of each of the inclined guide slots intersect at a point in space. This intersection point corresponds to a spatial node formed by the intersection of each inclined through hole on one end face of the core blank in the thickness direction.

7. The method for preparing a continuous fiber-reinforced three-dimensional lattice foam sandwich structure according to claim 5, characterized in that, In S3, the continuous long fiber rope is sequentially threaded into each of the oblique through holes and pre-tightened and fixed, including: A continuous long fiber rope is inserted from one end of the core layer blank, passes through each oblique through hole in sequence, and then passes back in the opposite direction after reaching the other end, forming a reciprocating winding path that runs through all the oblique through holes. A pre-tension force is applied to the continuous long fiber rope to keep it taut in each of the oblique through holes; and the two ends of the taut continuous long fiber rope are fixed.

8. The method for preparing a continuous fiber-reinforced three-dimensional lattice foam sandwich structure according to claim 5, characterized in that, In step S3, before threading the continuous long fiber rope through the oblique through hole, the method further includes: impregnating the continuous long fiber rope with a thermosetting resin or a thermoplastic resin; and / or, In S5, the composite curing and molding process employs vacuum-assisted molding, autoclave curing, or compression molding; and / or, In S5, after the composite curing and molding, the following steps are also included: cutting and trimming the cured sandwich structure along the projection contour of the three-dimensional lattice reinforcing skeleton on the bottom surface of the foam core layer.

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