A method of reducing internal defects in a composite material wound article

Abstract

The present application relates to a kind of methods for reducing the internal defects of composite winding products, the present application can realize the accurate control of winding product size by outer mold, control winding tension before injecting glue, so as to provide driving force for inner resin and inhibit its defect generation;During the injection process, the resin matched with winding resin is injected into the winding product by driving pressure, the driving force of injection cooperates with winding tension, drives away bubble from inside and outside at the same time, balances the distribution of resin, solves the problems of high porosity of fiber winding product, uneven resin distribution and low interlaminar performance, improves the integrity, density and uniformity of winding product.The present application effectively reduces the crack initiation source of product, improves the stress transfer ability of product interior, improves the load-carrying capacity of such components, avoids the sharp reduction of effective stiffness caused by the invasion of pressure medium due to the mutual penetration of internal pores, improves the reliability of such products.

Description

Technical Field

[0001] This invention relates to a method for reducing internal defects in composite material wound products. Background Technology

[0002] Composite materials using fibers such as carbon fiber, aramid fiber, and glass fiber as reinforcement and resins such as epoxy resin, vinyl ester resin, and polyester resin as the matrix are favored in aerospace, transportation, medical, and chemical industries due to their lightweight, high strength, corrosion resistance, fatigue resistance, and designability. These composite materials possess a unique "material-structure integration" characteristic, meaning that the material preparation process is also the process of realizing its structure. Therefore, to fully utilize the advantages of composite materials, it is necessary to strictly control internal defects such as voids, fiber wrinkles, and the number, size, and distribution of resin-rich and resin-poor regions to avoid a decrease in the fatigue life and load-bearing capacity of the components.

[0003] Products such as gas cylinders, flywheels, pipes, and supports, characterized by rotational symmetry, are well-suited for rapid fabrication using automated winding processes to enhance product competitiveness. However, when fabricating composite materials with rotating structures using winding processes, the continuously wound fibers may experience gaps near the pore areas and fiber intersections due to fiber accumulation. During the curing stage, resin flow can easily lead to voids and uneven resin distribution. When the product is subjected to loads other than internal pressure, the inability to effectively transfer stress can cause these defects to become crack initiation sources, accelerating delamination, resin cracking, and fiber breakage, ultimately leading to product failure. Especially for products subjected to external pressure loads, the interconnectedness of numerous micropores allows pressure media to penetrate, causing a rapid decrease in the effective stiffness of the component and resulting in failure.

[0004] To address the aforementioned issues, Chinese invention patent application CN113665095A, entitled "A Molding Mold and Method for Reducing Internal Defects in Composite Material Wound Products," discloses a solution. The molding mold includes a rotating core mold and an outer female mold that encloses the rotating core mold. The rotating core mold includes an inner core and mandrels located at both ends of the inner core. The outer female mold includes an upper shell and a lower shell that match the inner core. The upper and lower shells are fitted together to enclose the inner core and are sealed together by a sealing connector. A filling gap is provided between the inner walls of the upper and lower shells and the outer wall of the inner core. The lower shell has a glue inlet, and the upper shell has a glue outlet. This solution avoids voids near the polar hole area and fiber intersections by using automated continuous fiber winding, thus solving problems such as voids and uneven resin distribution caused by resin flow during the curing stage.

[0005] However, the above solution only has a good driving effect on the flow of the outer resin, while it is difficult to effectively drive the flow of the inner resin. As a result, the inner resin is still prone to voids, which affects the overall density and uniformity of the product.

[0006] Therefore, the current molding methods for composite material winding products need further improvement. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for reducing internal defects in composite material wound products, which addresses the current state of the technology. This method injects resin that matches the winding resin into the wound product by driving pressure and combines the control of winding tension to solve the problems of multiple pores and uneven resin content in the product, thereby improving the density and uniformity of the product.

[0008] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0009] A method for reducing internal defects in composite material wound articles includes the following steps:

[0010] (1) The resin-impregnated winding fibers are wound onto the mandrel with a tension of 1.8% to 2.2% of the fiber strength, decreasing by 4.5% to 5.5% per layer; when the winding layer thickness reaches 3 mm, the fiber yarn is wound at 90° on the outer surface of the product with an initial tension of 85% to 95% and the number of winding layers is not less than 2; the winding tension is used to provide driving force to the inner resin to suppress the formation of its defects;

[0011] (2) Then place the wound rotary product on the tooling frame and cover its surface with release cloth, continuous felt or flow guide net in sequence; so that the resin can quickly cover the wound product.

[0012] (3) Assemble the combined external mold or vacuum bag film coated with release agent with the winding product. The external mold or vacuum bag film will be combined with the core mold containing the winding product to form a closed mold cavity, the specific dimensions of which must meet the product requirements.

[0013] (4) Connect the glue inlet and the glue outlet, wherein the line connecting the glue inlet and the glue outlet intersects the winding center axis and is located at the lowest point and the highest point of the wound product, respectively.

[0014] (5) Use pressure equipment (glue dispensing machine or vacuum pump) to introduce resin that has been degassed under vacuum for no less than 5 minutes and has a viscosity of no more than 5 Pa·s into the mold cavity. If the resin viscosity is high, the flow rate of the resin inside the product can be increased by appropriately raising the temperature of the oven.

[0015] (6) Stop injecting resin when the resin flows out continuously without bubbles from the nozzle, close the valve, and cure and demold according to the corresponding requirements.

[0016] Preferably, in step (1), the winding fiber is spread out to a single layer thickness of no more than 0.3 mm.

[0017] Preferably, in step (1), the resin-impregnated winding fibers are wound onto the mandrel with a tension decreasing by 5% per layer, based on a tension of 2% of the fiber strength. In step (1), after the winding layer thickness reaches 3 mm, the fiber yarn is wound at 90° on the outer surface of the product with an initial tension of 90% and the number of layers is not less than 4. By adopting the above scheme, the winding tension is used to provide a driving force to the inner resin to suppress the formation of defects.

[0018] Preferably, in step (4), before connecting the inlet and outlet, the assembled mold is subjected to an airtightness test, and the pressure change is less than 1% within 5 minutes.

[0019] Preferably, in step (6), after stopping the glue injection, the glue inlet valve is closed but the glue outlet valve is kept connected to the vacuum system to avoid voids caused by changes in solubility.

[0020] Preferably, after step (6) is completed, if the winding thickness of the product has reached the designed thickness, the product and the outer sealing system are put into the oven to complete the curing and demolding process; if the designed thickness has not been reached, the outer sealing system is removed after the resin viscosity is greater than 100 Pa·s and the subsequent winding, curing and demolding process is started.

[0021] Compared with the prior art, the advantages of the present invention are as follows: The present invention can achieve accurate control of the size of the wound product through the external mold. Before injection, the winding tension is controlled, thereby providing driving force to the inner resin to suppress the generation of defects. During the injection process, the resin matching the winding resin is injected into the inside of the wound product through driving pressure. The driving force of injection and the winding tension work together to eliminate air bubbles from the inside and outside while balancing the distribution of resin. This solves the problems of high porosity, uneven resin distribution and low interlayer performance of fiber wound products, improves the integrity, density and uniformity of the wound product, and helps to enhance the ability of the wound product to resist external loads and fatigue life.

[0022] This invention significantly reduces the sources of crack initiation in products, improves the stress transmission capacity within the product, and enhances the load-bearing capacity of such components. In particular, for components subjected to external pressure loads, it avoids the sharp reduction in effective stiffness caused by the intrusion of pressure media due to the interconnection of internal pores, thereby improving the reliability of such products. Attached Figure Description

[0023] Figure 1 This is a diagram illustrating the winding process of the winding fibers on the mandrel in an embodiment of the present invention;

[0024] Figure 2This is a cross-sectional view of the mold during the winding process in an embodiment of the present invention. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0026] like Figure 1 , 2 As shown, the method for reducing internal defects in composite material wound products in this embodiment includes the following steps:

[0027] (1) The winding yarn is wound on the core mold 2 with a fiber tension of 2% and a decreasing order of 5%, and the fiber bundle is spread out to a single layer thickness of no more than 0.3mm; when the thickness of the winding layer 6 reaches 3mm, the fiber yarn is wound on the surface of the product at 90° with an initial winding tension of 90%, and the number of winding layers is 4, which generates a driving force for the flow of the inner resin to suppress the generation of defects.

[0028] (2) Place the wound rotary product in the tooling frame and cover it with release cloth, continuous felt or flow guide net in sequence to facilitate the resin to quickly cover the wound product.

[0029] (3) Assemble the combined external mold or vacuum bag film coated with release agent with the wound product. The external mold or vacuum bag film will be combined with the core mold of the rotating product to form a closed mold cavity 4, the specific dimensions of which must meet the product requirements.

[0030] (4) Perform an airtightness test on the assembled mold. The pressure change is less than 1% within 5 minutes. Connect the inlet 1 and the outlet 5. The line connecting the inlet 1 and the outlet 5 intersects the winding center axis and is located at the lowest and highest points of the wound product, respectively.

[0031] (5) The resin that has undergone vacuum degassing for no less than 5 minutes and has a viscosity of no more than 5 Pa·s is introduced into the mold cavity 4 through a pressure device (glue injection machine or vacuum pump). If the resin viscosity is high, the flow rate of the resin in the product can be increased by appropriately raising the temperature of the oven.

[0032] (6) To ensure that the mold cavity 4 is filled with resin, the wound product can be placed at an angle so that the inlet 1 is at the lowest point and the outlet 5 is at the highest point; stop the injection when the outlet 5 flows out a continuous and bubble-free resin, close the inlet valve but keep the outlet valve connected to the vacuum system to avoid gaps caused by changes in solubility.

[0033] (7) If the winding thickness of the product has reached the design thickness, the product and the outer sealing system will be put into the oven to complete the curing, demolding and other processes. If the design thickness has not been reached, the outer sealing system will be removed after the resin viscosity is greater than 100 Pa·s, and the subsequent winding, curing and demolding processes will begin.

[0034] This embodiment achieves accurate control of the dimensions of the wound product through an external mold. Before injection, the winding tension is controlled to provide driving force to the inner resin and suppress its defect formation. During the injection process, the resin matching the winding resin is injected into the wound product through driving pressure. The injection driving force and winding tension work together to expel air bubbles from the inside and outside while balancing the resin distribution. This solves the problems of high porosity, uneven resin distribution, and low interlayer performance in fiber wound products, improves the integrity, density, and uniformity of the wound product, and helps to enhance the wound product's ability to resist external loads and fatigue life.

[0035] This embodiment effectively reduces the sources of crack initiation in the product, improves the stress transmission capacity inside the product, and enhances the load-bearing capacity of such components. In particular, for components subjected to external pressure loads, it avoids the sharp reduction in effective stiffness caused by the intrusion of pressure medium due to the interconnection of internal pores, thereby improving the reliability of such products.

[0036] The specification and claims of this invention use terms indicating direction, such as "front," "rear," "upper," "lower," "left," "right," "side," "top," and "bottom," to describe various exemplary structural parts and elements of the invention. However, these terms are used herein merely for ease of explanation and are determined based on the exemplary orientations shown in the accompanying drawings. Since the embodiments disclosed in this invention can be arranged in different orientations, these terms indicating direction are for illustrative purposes only and should not be considered as limitations. For example, "upper" and "lower" are not necessarily limited to directions opposite to or consistent with the direction of gravity.

Claims

1. A method for reducing internal defects in composite material wound products, characterized in that... Includes the following steps: (1) The resin-impregnated winding fibers are wound onto the mandrel according to the tension of 2% of the fiber strength and the decreasing order of 5% per layer; when the winding layer thickness reaches 3mm, the fiber yarn is wound onto the outer surface of the product at 90° with 90% initial tension and the number of winding layers is not less than 4. Wherein, the winding fiber is spread out to a single layer thickness of no more than 0.3 mm; (2) Then place the wound rotary product on the tooling frame and cover it with release cloth, continuous felt or flow guide net in sequence; (3) Assemble the combined external mold or vacuum bag film coated with release agent with the winding product. The external mold or vacuum bag film will be combined with the core mold containing the winding product to form a closed mold cavity. (4) Connect the glue inlet and the glue outlet, wherein the line connecting the glue inlet and the glue outlet intersects the winding center axis and is located at the lowest point and the highest point of the wound product, respectively; (5) The resin with a vacuum degassing time of not less than 5 minutes and a viscosity of not more than 5 Pa·s is introduced into the mold cavity through a pressure device; (6) Stop injecting resin when a continuous stream of resin without bubbles flows out of the nozzle, close the valve, and cure and demold according to the corresponding requirements.

2. The method for reducing internal defects in composite material wound articles according to claim 1, characterized in that: In step (4), before connecting the inlet and outlet, the assembled mold is tested for air tightness, and the pressure change is less than 1% within 5 minutes.

3. The method for reducing internal defects in composite material wound articles according to claim 1 or 2, characterized in that: In step (6), after stopping the glue injection, close the glue inlet valve but keep the glue outlet valve connected to the vacuum system to avoid voids caused by changes in solubility.

4. The method for reducing internal defects in composite material wound articles according to claim 1 or 2, characterized in that: In step (6), if the winding thickness of the product has reached the design thickness, the product and the outer sealing system are put into the oven to complete the curing and demolding process; if the design thickness has not been reached, the outer sealing system is removed after the resin viscosity is greater than 100 Pa·s to start the subsequent winding, curing and demolding process.

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