Forming method for realizing continuous fibers around holes of carbon fiber reinforced composite material

Abstract

The invention provides a forming method for realizing continuous fibers around holes of a carbon fiber reinforced composite material, and relates to the technical field of carbon fiber reinforced composite material processing. According to the method, mechanical drilling of the perforated CFRP is omitted, the needle pin is utilized to form the hole, the fiber around the hole is not broken or only a small part of the fiber is broken, the stress concentration around the hole is reduced, and compared with a common perforated CFRP test piece with consistent drilling aperture, the perforated tensile strength of the test piece containing the continuous fiber around the hole can be improved by 30% or above, and the tensile strength of the test piece containing the continuous fiber around the hole can be improved by 30% or above. And the opening compression strength is improved by more than 40%.

Description

Technical Field

[0001] The invention relates to the technical field of carbon fiber reinforced composite material processing, and in particular to a method for realizing continuous forming of fibers around holes of a carbon fiber reinforced composite material. Background Art

[0002] CFRP (carbon fiber reinforced composite material) is made of multiple layers of prepreg stacked at a certain design angle. It has excellent specific strength and specific modulus. In actual use, holes will be opened for component assembly.

[0003] At present, the most widely used CFRP hole-opening technology is still drilling, that is, using a drill bit to achieve mechanical removal, which will result in a large number of broken fibers at the drilled CFRP holes, reducing the number of load-bearing fibers. Relevant reports point out that the tensile strength of the hole-opening test piece after mechanical drilling is about 35% lower than that of the non-hole-opening test piece, and the compressive strength of the hole-opening is about 56% lower than that of the non-hole-opening test piece. Summary of the invention

[0004] The purpose of the present invention is to provide a method for forming carbon fiber reinforced composite materials with continuous fibers around the holes. The present invention achieves continuous or small breakage of fibers around the holes during the CFRP forming process, which can effectively improve the open hole tensile strength and open hole compression strength of CFRP.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for realizing continuous forming of fibers around holes of a carbon fiber reinforced composite material, comprising the following steps:

[0007] The prepreg of the carbon fiber reinforced composite material is split according to the designed ply thickness and ply sequence to obtain a plurality of prepregs;

[0008] According to the target structure, the first prepreg is laid in a lower mold, wherein the lower mold is provided with a circular hole; the first prepreg is first heated, and then a needle pin is passed through the heated first prepreg along the circular hole of the lower mold, and the needle pin is pulled out to form a first hole in the first prepreg;

[0009] Laying a second prepreg on the surface of the first prepreg with the first hole, performing a second heating on the second prepreg, and passing a needle pin through the first hole and the second prepreg in sequence along the circular hole of the lower mold to form a second hole in the second prepreg; repeating this process until the last prepreg is laid in the lower mold, and forming a last hole in the last prepreg with a needle pin, thereby obtaining a laminated prepreg with holes;

[0010] Insert a cylindrical pin into the hole of the laminated prepreg, cover the upper mold, the upper mold is a non-porous plate, the upper end of the cylindrical pin is in contact with the upper mold, the surrounding is in contact with the laminated prepreg, and the lower end extends into the circular hole of the lower mold, an elastic pad is placed at the lower end of the cylindrical pin, and solidification is performed. After the cylindrical pin is pulled out, an open-pored carbon fiber reinforced composite material is formed.

[0011] Preferably, the needle pin comprises a cylindrical section and a needle head, and the inclination of the needle head is less than 40°.

[0012] Preferably, the needle pin and the circular hole of the lower mold are clearance-matched, and the clearance is within 0.05 mm.

[0013] Preferably, the length of the cylindrical pin satisfies: the thickness of the laminated prepreg < the length of the cylindrical pin < the thickness of the lower mold + the thickness of the laminated prepreg.

[0014] Preferably, the cylindrical pin and the circular hole of the lower mold are clearance-fitted, and the clearance is within 0.05 mm.

[0015] Preferably, the lower end of the cylindrical pin is chamfered.

[0016] Preferably, the thickness of each prepreg is independently 0.125 to 0.5 mm.

[0017] Preferably, before laying the first portion of prepreg into the lower mold, the lower mold is also preheated.

[0018] Preferably, each time the needle pin passes through the prepreg, the needle pin is left in the prepreg for a certain period of time, so that the profile of the hole formed after the needle pin is pulled out is fixed.

[0019] Preferably, the temperature at which each prepreg is heated is sufficient to soften the resin in the hole forming region of the prepreg.

[0020] The present invention provides a method for forming continuous fibers around holes of a carbon fiber reinforced composite material, comprising the following steps: splitting a prepreg of a carbon fiber reinforced composite material according to a designed ply thickness and ply sequence to obtain a plurality of prepregs; laying a first prepreg in a lower mold according to a target structure, wherein the lower mold is provided with a circular hole; performing a first heating on the first prepreg, and then passing a needle pin through the heated first prepreg along the circular hole of the lower mold, and pulling out the needle pin to form a first hole in the first prepreg; laying a second prepreg on the surface of the first prepreg with the first hole, and performing a second heating on the second prepreg , pass the needle pin through the first hole and the second prepreg in sequence along the circular hole of the lower mold, and form a second hole in the second prepreg; repeat this process until the last prepreg is laid in the lower mold, and the last hole is formed in the last prepreg by the needle pin, so as to obtain a laminated prepreg with holes; insert a cylindrical pin into the hole of the laminated prepreg, cover the upper mold, the upper end of the cylindrical pin contacts the upper mold, the surrounding area contacts the laminated prepreg, and the lower end extends into the circular hole of the lower mold, an elastic pad is placed at the lower end of the cylindrical pin, and solidification is performed. After the cylindrical pin is pulled out, an open-pored carbon fiber reinforced composite material is formed.

[0021] The present invention eliminates the need for mechanical drilling of the perforated CFRP and utilizes a needle pin to form a hole, thereby achieving no breakage or only partial breakage of fibers around the hole, thereby reducing stress concentration around the hole. Compared with a perforated CFRP specimen with a uniform hole diameter drilled conventionally, the perforated tensile strength of the specimen with continuous fibers around the hole obtained by the present invention can be increased by more than 30%, and the perforated compressive strength can be increased by more than 40%. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a simplified schematic diagram of CFRP forming in an embodiment of the present invention, wherein 1-laminated prepreg to be hot-pressed, 2-prepreg after splitting, 3-lower mold, 4-heating table, 5-support, 6-needle pin, 7-cylindrical pin with chamfer, 8-elastic pad, 9-blocking strip, 10-upper mold;

[0023] Figure 2 This is a photo of the needle pin passing through the prepreg in Example 1;

[0024] Figure 3 This is a photo of the open-pore carbon fiber reinforced composite material that has been hot-pressed and cured in Example 1;

[0025] Figure 4 The curing and forming working system of Example 1 and Comparative Example 1;

[0026] Figure 5 This is a drilling photo of Comparative Example 1;

[0027] Figure 61 is the displacement load curve of the open hole compression of Example 1 and Comparative Example 1;

[0028] Figure 7 The displacement load curves of the open hole compression of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0029] The present invention provides a method for realizing continuous forming of fibers around holes of a carbon fiber reinforced composite material, comprising the following steps:

[0030] The prepreg of the carbon fiber reinforced composite material is split according to the designed ply thickness and ply sequence to obtain a plurality of prepregs;

[0031] According to the target structure, the first prepreg is laid in a lower mold, wherein the lower mold is provided with a circular hole; the first prepreg is first heated, and then a needle pin is passed through the heated first prepreg along the circular hole of the lower mold, and the needle pin is pulled out to form a first hole in the first prepreg;

[0032] Laying a second prepreg on the surface of the first prepreg with the first hole, performing a second heating on the second prepreg, and passing a needle pin through the first hole and the second prepreg in sequence along the circular hole of the lower mold to form a second hole in the second prepreg; repeating this process until the last prepreg is laid in the lower mold, and forming a last hole in the last prepreg with a needle pin, thereby obtaining a laminated prepreg with holes;

[0033] Insert a cylindrical pin into the hole of the laminated prepreg, cover the upper mold, the upper mold is a non-porous plate, the upper end of the cylindrical pin is in contact with the upper mold, the surrounding is in contact with the laminated prepreg, and the lower end extends into the circular hole of the lower mold, an elastic pad is placed at the lower end of the cylindrical pin, and solidification is performed. After the cylindrical pin is pulled out, an open-pored carbon fiber reinforced composite material is formed.

[0034] In the present invention, unless otherwise specified, the raw materials and equipment used are commercially available products well known in the art.

[0035] The present invention splits the prepreg of the carbon fiber reinforced composite material according to the designed layer thickness and layer sequence to obtain a plurality of prepregs.

[0036] The present invention has no special requirements for the prepreg, and any prepreg known in the art for preparing carbon fiber reinforced composite materials can be used. In an embodiment of the present invention, the prepreg model is USN12500 unidirectional prepreg of Guangwei Composites. The present invention does not specifically limit the splitting process. In the present invention, after splitting, the thickness of each prepreg is independently preferably 0.125-0.5 mm, and in an embodiment of the present invention, it can be specifically 0.2 mm, 0.25 mm, 0.3 mm, 0.4 mm or 0.5 mm, which will not be exhaustively listed here. In the present invention, each prepreg is preferably a unidirectional prepreg. The present invention controls the thickness of each prepreg within the above range. On the one hand, it is convenient for the needle pin to enter and reduce the number of fiber breaks around the hole. On the other hand, it is easy to place when stacking the prepreg. If the thickness is too thin, wrinkles are easily generated during the stacking process.

[0037] After the splitting, the present invention lays the first portion of prepreg into the lower mold according to the target structure.

[0038] Before the laying, the present invention preferably preheats the lower mold first; the preheating temperature is preferably determined according to the optimal fluidity temperature of the resin contained in the prepreg, generally 60-80°C.

[0039] In the present invention, the target carbon fiber reinforced composite material can be a flat piece, a curved piece, a specimen of equal thickness, a specimen of variable thickness, a specimen of large thickness, etc. The present invention does not make any special limitation on this, and the corresponding mold can be selected according to the target specimen.

[0040] In the present invention, the lower mold is provided with circular holes; the present invention does not specifically limit the number and position of the circular holes, and requires matching the position and number of the target openings in the carbon fiber reinforced composite material. In the present invention, the aperture of the circular holes is preferably larger than the aperture of the target opening in the carbon fiber reinforced composite material. The aperture of the circular hole of the lower mold is d, and the aperture of the target opening is D, preferably satisfying 0<dD≤0.05mm.

[0041] After laying the first prepreg into the lower mold, the present invention performs a first heating on the first prepreg, then passes a needle pin through the heated first prepreg along the circular hole of the lower mold, pulls out the needle pin, and forms a first hole in the first prepreg.

[0042] In the present invention, the first heating may be heating the first prepreg as a whole or locally; the temperature of the first heating is preferably sufficient to soften the resin in the hole forming area of ​​the first prepreg. For prepregs commonly used in the art, such as the USN12500 unidirectional prepreg of Guangwei Composites, the general heating temperature is preferably 60 to 80°C. The present invention facilitates the pin to pass through the prepreg and reduces fiber breakage by heating.

[0043] In the present invention, the needle pin preferably includes a cylindrical section and a needle head, and the inclination of the needle head is preferably less than 40°. In an embodiment of the present invention, the inclination of the needle head can specifically be 10°, 20°, 30° or 35°, which will not be enumerated here. In the present invention, the diameter of the cylindrical section of the needle pin is the same as the aperture of the target opening in the carbon fiber reinforced composite material, and the diameter size of the needle pin can be selected according to the target opening size. In the present invention, the needle pin and the circular hole of the lower mold are clearance fit, and the clearance is preferably within 0.05mm. In the present invention, the material of the needle pin is preferably stainless steel.

[0044] In the present invention, the surface of the needle pin and the surface of the circular hole of the lower mold are preferably coated with demoulding wax. The present invention facilitates the insertion and extraction of the needle pin by coating the demoulding wax agent on the surface of the needle pin and the surface of the circular hole.

[0045] In the present invention, after the needle pin passes through the first prepreg, the present invention preferably allows the needle pin to stay in the first prepreg for a certain period of time, so as to fix the contour of the first hole formed after the needle pin is pulled out. The present invention does not require a specific time of stay, as long as the hole contour can be relatively fixed. In the embodiment of the present invention, the stay is specifically 1 minute. The present invention forms a hole with a fixed contour, which is conducive to avoiding damage to the fibers around the already formed hole during subsequent piercing.

[0046] After forming the first hole, the present invention lays a second prepreg on the surface of the first prepreg with the first hole, performs a second heating on the second prepreg, and passes a needle pin through the first hole and the second prepreg in sequence along the circular hole of the lower mold to form a second hole in the second prepreg; this is repeated until the last prepreg is laid in the lower mold, and a last hole is formed in the last prepreg by using a needle pin, thereby obtaining a laminated prepreg with holes.

[0047] In the present invention, the temperature at which each prepreg is heated is preferably sufficient to soften the resin in the hole forming region of the prepreg, which will not be elaborated herein.

[0048] Each time the pin passes through the prepreg, it is preferred that the pin stays in the prepreg for a certain period of time to ensure that the contour of the hole formed after the pin is pulled out is fixed.

[0049] After obtaining the laminated prepreg with holes, the present invention inserts a cylindrical pin into the hole of the laminated prepreg, covers the upper mold, puts an elastic pad at the lower end of the cylindrical pin, performs curing and forming, and after pulling out the cylindrical pin, forms an open-pored carbon fiber reinforced composite material.

[0050] The present invention preferably inserts the cylindrical pin from above the laminated prepreg. In the present invention, the lower end of the cylindrical pin is preferably chamfered to facilitate insertion into the laminated prepreg.

[0051] In the present invention, the upper mold is a plate without holes.

[0052] After the cylindrical pin is inserted, the upper end of the cylindrical pin contacts the upper mold, the periphery contacts the laminated prepreg, and the lower end extends into the circular hole of the lower mold. In the present invention, the surface of the cylindrical pin is coated with release wax.

[0053] In the present invention, the diameter of the cylindrical pin is the same as the size of the target opening in the carbon fiber reinforced composite material; the cylindrical pin is preferably clearance-matched with the circular hole of the lower mold, and the clearance is preferably within 0.05 mm.

[0054] In the present invention, the length of the cylindrical pin preferably satisfies: the thickness of the laminated prepreg < the length of the cylindrical pin < the thickness of the lower mold + the thickness of the laminated prepreg; and the length of the cylindrical pin + the thickness of the elastic pad after compaction = the thickness of the lower mold + the thickness of the laminated prepreg. In the present invention, the curing process will compress the elastic pad, and the thickness after curing is the thickness of the elastic pad after compaction.

[0055] In the present invention, the material of the cylindrical pin is preferably stainless steel.

[0056] In the present invention, the elastic pad and the circular hole of the lower mold are preferably interference fit. Placing the elastic pad in the present invention can seal the hole of the lower mold to prevent resin from overflowing, while ensuring that the prepreg is fully compacted.

[0057] Before covering the mold, the present invention preferably places rubber strips around the laminated prepreg to prevent resin from overflowing during subsequent curing and forming.

[0058] The present invention has no special requirements for the curing conditions. Suitable curing conditions can be selected according to the composition of the prepreg, which is common knowledge in the art.

[0059] The present invention opens holes during the CFRP forming process to achieve continuous or small-scale breakage of fibers around the holes, which can effectively improve the hole-opening tensile strength and hole-opening compressive strength of CFRP.

[0060] The method for realizing continuous forming of fibers around the holes of a carbon fiber reinforced composite material provided by the present invention is described in detail below in conjunction with the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0061] Figure 1 It is a simplified schematic diagram of CFRP forming according to an embodiment of the present invention, wherein: 1-laminated prepreg to be hot pressed, 2-prepreg after splitting, 3-lower mold, 4-heating table, 5-support, 6-needle pin, 7-cylindrical pin with chamfer, 8-elastic pad, 9-rubber strip, 10-upper mold.

[0062] Example 1

[0063] (1) The prepreg model is USN12500 unidirectional prepreg produced by Guangwei Composites, and the working thickness of the prepreg is 0.125 mm (i.e., the thickness of each unidirectional prepreg); the layering of the laminated prepreg 1 to be hot-pressed is [45 / 0 / -45 / 90] 3S , 24 unidirectional prepregs are divided into 6 parts to form prepreg 2 after division, which is equivalent to a thickness of 0.5 mm for each prepreg, wherein the plies are [45 / 0 / -45 / 90] for 3 parts and [90 / -45 / 0 / 45] for 3 parts;

[0064] (2) placing the lower mold 3 on a heating table 4 and heating it to 70° C.

[0065] (3) Place the prepreg with a layer of [45 / 0 / -45 / 90] on the specified position of the lower mold 3, and use the heating table 4 to heat the first prepreg to 80° C. 80° C. is the optimal fluidity temperature of the resin used. The lower mold 3 is supported by the support 5;

[0066] (4) Use a special needle pin to pierce the hole in the lower mold (see Figure 2 ), the surface of the needle pin and the circular hole surface of the lower mold are coated with demoulding wax, the nominal size of the cylindrical section of the needle pin is 6mm, the tolerance is -0.05mm, the inclination of the needle pin head is 20°, the needle pin and the lower mold are clearance fit, and the maximum clearance is controlled within 0.05mm. After piercing the hole, the needle pin is left in the first prepreg for 1min to form the hole, and a hole is formed in the first prepreg;

[0067] (5) Repeat steps (3) and (4) until all prepregs are completely stacked, all holes are pierced, and the pins are pulled out to obtain laminated prepregs;

[0068] (6) Insert a chamfered cylindrical pin 7 into the hole formed by the laminated prepreg. The surface of the cylindrical pin 7 is coated with demoulding wax. The nominal size of the cylindrical pin 7 is 6 mm. The cylindrical section of the cylindrical pin is clearance-matched with the lower mold hole. The clearance is controlled within 0.05 mm. Put an elastic pad 8 at the lower end of the cylindrical pin 7, place a rubber strip 9 around the laminated prepreg, and finally cover the upper mold 10. Figure 4 After curing, the mold is removed and the cylindrical pin is pulled out to form an open-pored carbon fiber reinforced composite material (see Figure 3 ), the nominal diameter of the aperture is 6mm.

[0069] Comparative Example 1

[0070] Refer to Example 1, drill holes, lay up in the same layering order, and cure and mold under the same conditions. Figure 4 , the hole diameter is 6mm, the actual drilling photos are as follows Figure 5As shown, the drill bit is a carbide twist drill with a coating, the nominal diameter of the twist drill is 6 mm, the drilling speed is 1500 rpm, and the feed speed is 30 mm / min.

[0071] The open-hole tensile strength and open-hole compressive strength tests were performed on the carbon fiber reinforced composite materials after opening in Example 1 and Comparative Example 1. The open-hole tensile strength test was performed according to ASTM D 5766, and the open-hole compressive strength test was performed according to ASTM D6484. The test results are shown in Table 1. Figure 6 and Figure 7 . Figure 6 and Figure 7 In the examples, drilling holes refers to Comparative Example 1, and punching holes refers to Example 1. Figure 6 It can be seen that the open hole tensile strength of Example 1 is 658.13 MPa, while the open hole tensile strength of Comparative Example 1 is only 419.09 MPa; Figure 7 It can be seen that the open hole compression strength of Example 1 is 445.3 MPa, while the open hole compression strength of Comparative Example 1 is only 297.40 MPa, which shows that the forming method of the present invention achieves no or less breakage of fibers around the hole, greatly improving the open hole tensile strength and open hole compression strength.

[0072] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for forming continuous fibers around holes of a carbon fiber reinforced composite material, characterized in that: The following steps are involved: The prepreg of the carbon fiber reinforced composite material is split according to the designed ply thickness and ply sequence to obtain a plurality of prepregs; According to the target structure, the first prepreg is laid in a lower mold, wherein the lower mold is provided with a circular hole; the first prepreg is first heated, and then a needle pin is passed through the heated first prepreg along the circular hole of the lower mold, and the needle pin is pulled out to form a first hole in the first prepreg; Laying a second prepreg on the surface of the first prepreg with the first hole, performing a second heating on the second prepreg, and passing a needle pin through the first hole and the second prepreg in sequence along the circular hole of the lower mold to form a second hole in the second prepreg; repeating this process until the last prepreg is laid in the lower mold, and forming a last hole in the last prepreg with a needle pin, thereby obtaining a laminated prepreg with holes; Insert a cylindrical pin into the hole of the laminated prepreg, cover the upper mold, the upper mold is a non-porous plate, the upper end of the cylindrical pin is in contact with the upper mold, the surrounding is in contact with the laminated prepreg, and the lower end extends into the circular hole of the lower mold, an elastic pad is placed at the lower end of the cylindrical pin, and solidification is performed. After the cylindrical pin is pulled out, an open-pored carbon fiber reinforced composite material is formed.

2. The forming method according to claim 1, characterized in that: The needle pin comprises a cylindrical section and a needle head, and the inclination of the needle head is less than 40°.

3. The forming method according to claim 1 or 2, characterized in that: The needle pin and the circular hole of the lower mold are clearance matched, and the clearance is within 0.05mm.

4. The forming method according to claim 1, characterized in that: The length of the cylindrical pin satisfies: the thickness of the laminated prepreg < the length of the cylindrical pin < the thickness of the lower mold + the thickness of the laminated prepreg.

5. The forming method according to claim 1, characterized in that: The cylindrical pin and the circular hole of the lower mold are clearance-matched, and the clearance is within 0.05 mm.

6. The forming method according to claim 1, 4 or 5, characterized in that: The lower end of the cylindrical pin is chamfered.

7. The forming method according to claim 1, characterized in that: The thickness of each prepreg is independently 0.125 to 0.5 mm.

8. The forming method according to claim 1, characterized in that: Before laying the first prepreg into the lower mold, the method further includes preheating the lower mold.

9. The forming method according to claim 1, characterized in that: Each time the needle pin passes through the prepreg, the needle pin is left in the prepreg for a certain period of time to fix the profile of the hole formed after the needle pin is pulled out.

10. The forming method according to claim 1, characterized in that: Each prepreg is heated to a temperature sufficient to soften the resin in the hole forming regions of the prepreg.

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