Forming Method for Uniform Resin Distribution and Low Porosity in Thick Layers of Carbon Fiber Composite Materials

Abstract

The present invention discloses a forming method for uniform resin distribution and low porosity in thick layers of carbon fiber composite materials, which specifically includes the following steps: Step 1, partitioning the thick composite laminate structure in the thickness direction; Step 2, according to the partitioning result obtained in Step 1, pasting a film on the surface layer of the laid layers after partitioning, and performing heating and pressurization for pre-compaction; Step 3, encapsulating all the pre-compacted partitioned laminates and curing them according to the curing process curve provided by the material supplier; Step 4, demolding the thick composite laminate. The present invention does not require replacing new materials and equipment, nor a large amount of flow compaction simulation and experimental data. Only by partitioning the laminate and performing heating and pressurization for pre-compaction can it ensure uniform resin distribution inside the thick composite laminate and reduce the internal porosity.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite material forming, and relates to a forming method for uniform resin distribution and low porosity of thick layers of carbon fiber composite materials. Background Art

[0002] Currently, the forming process of thick carbon fiber composite laminates is usually as follows: using prepreg, manually laying or automatically laying to the required thickness or number of layers, then encapsulating with materials such as release film and vacuum bag, and then putting it into an autoclave for curing and forming under a certain temperature or pressure.

[0003] When the laminate structure is thick and there is resin flow during the curing process of the prepreg system used, the resin flow rate of the layers close to the forming mold is too small, while the resin flow rate of the layers close to the outer resin absorption layer is too large, resulting in uneven resin distribution in the thickness direction of the laminate. At the same time, due to the large thickness of the thick laminate, the curing pressure cannot be effectively transmitted to the layers close to the mold, resulting in insufficient pressure in these layers and defects such as pores, thus greatly reducing the service mechanical properties of the laminate structure.

[0004] For controlling the gradient distribution of resin and porosity of thick composite laminates, the current technology controls from the curing process or the material system. Among them, for the control of the curing process, a large number of experiments or finite element simulation methods are required to find a sufficiently large curing pressure or a suitable heating curve, but there is currently no suitable coordination method. And from the control of the material system, once the laminate is designed, the material is fixed and cannot be changed. Therefore, how to solve the problem of regulating the resin uniformity and porosity of existing thick composite laminates urgently needs to be solved. Summary of the Invention

[0005] The purpose of the present invention is to provide a forming method for uniform resin distribution and low porosity of carbon fiber composite material structures, which solves the problems of uneven resin distribution and high porosity existing in the current forming method of thick laminates.

[0006] The technical solution adopted by the present invention is a forming method for uniform resin distribution and low porosity of thick layers of carbon fiber composite materials, which specifically includes the following steps:

[0007] Step 1, partitioning the thick composite laminate structure in the thickness direction;

[0008] Step 2, according to the partitioning result obtained in Step 1, lay a glue film on the surface layer of the partitioned layers, and perform heating and pressurization for pre-compaction;

[0009] Step 3, perform curing and forming on the thick laminate processed in Step 2;

[0010] Step 4: Demold the thick laminate formed in Step 3.

[0011] The features of the present invention also lie in:

[0012] The specific process of Step 1 is as follows: The thick carbon fiber composite laminate is successively divided into N partition layers along the thickness direction, and the first partition layer is the side close to the mold.

[0013] The specific process of Step 2 is as follows:

[0014] Step 2.1: Lay the first partition layer of the carbon fiber composite material on the mold, lay a resin-made film on the upper surface of the first partition layer to form the first partition ply, and after pre-pressing the first partition ply, encapsulate the first partition ply with an encapsulating material to obtain the first partition encapsulation body;

[0015] Step 2.2: Place the first partition encapsulation body obtained in Step 2.1 into an autoclave, heat it at a heating rate of 0.100 °C / min to 400 - 100 °C, while applying a pressure of 0.4 - 0.8 MPa, keep it warm for 100 - 300 min, then cool it down to room temperature, and then take out the first partition encapsulation body from the autoclave and remove the encapsulating material to obtain the first partition compacted layer;

[0016] Step 2.3: Lay the second partition layer of the carbon fiber composite material on the upper surface of the first partition compacted layer obtained in Step 2.2, and lay a resin-made film on the upper surface of the second partition layer to form the second partition ply;

[0017] Step 2.4: After overall encapsulating the first partition compacted layer obtained in Step 2.2 and the second partition ply obtained in Step 2.3, obtain the second partition encapsulation body;

[0018] Step 2.5: Place the second partition encapsulation body obtained in Step 2.4 into an autoclave, heat it at a heating rate of 0.100 °C / min to 400 - 100 °C, while applying a pressure of 0.4 - 0.8 MPa, keep it warm for 100 - 300 min, then cool it down to room temperature, and then take out the encapsulation body from the autoclave and remove the encapsulating material to obtain the second partition compacted layer;

[0019] Step 2.6: Repeat Steps 2.2 - 2.5, and continue to lay the third partition layer, the fourth partition layer,..., the (N - 1)th partition layer on the second partition compacted layer in sequence to obtain the (N - 1)th partition compacted layer;

[0020] Step 2.7: Lay the carbon fiber composite material's Nth partition layer on the upper surface of the N - 1 partition compacted layer obtained in Step 2.6. Lay a resin - made film on the upper surface of the Nth partition layer to form the Nth partition ply, and uniformly encapsulate the N partition layers to obtain the entire encapsulated body of the thick carbon fiber composite laminate.

[0021] In Step 2.2 and Step 2.0, the heating rate, heating temperature, and pressing pressure are determined according to the resin flow model shown in the following formula (1) to ensure that the resin content is uniformly distributed in the thickness direction of the thick carbon fiber composite laminate, and the resin flow time when it no longer changes with time is the shortest holding time:

[0022]

[0023] In the formula, k x 、k y 、k z are the permeabilities of the composite material in the x, y, and z directions respectively; m v is the volume change coefficient; P r is the resin pressure; η is the resin viscosity.

[0024] The beneficial effects of the present invention are as follows: The forming method provided by the present invention only needs to adjust the partitions of the thick composite laminate, lay a resin layer on the surface of the partitions, and then pre - compact the plies of the partitions to achieve the purpose of adjusting the resin content and porosity inside the thick composite laminate. Compared with the prior art, the present invention does not require replacing additional materials and equipment, is easy to operate, and does not require a large amount of flow compaction simulation data. At the same time, the setting of the forming parameters does not need to be changed, effectively solving the problems of uneven internal resin distribution and too high porosity in the thick composite laminate after forming in the existing forming methods, and ensuring that the mechanical properties of the thick composite laminate meet the design requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic diagram of the structural partition of the thick laminate in the method for forming a thick carbon fiber composite laminate with uniform resin distribution and low porosity of the present invention;

[0026] Figure 2 is the curing process curve of the method for forming a thick carbon fiber composite laminate with uniform resin distribution and low porosity of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention will be described in detail below in conjunction with the drawings and specific embodiments.

[0028] The method for forming a thick carbon fiber composite laminate with uniform resin distribution and low porosity of the present invention specifically includes the following steps:

[0029] Step 1, Plan the ply partition of the thick laminate: According to the thickness characteristics of the thick composite laminate, divide the thick composite laminate into partitions along the thickness direction (from bottom to top, the bottommost is the first layer, close to the mold side, and are successively divided into the first partition, the second partition to the Nth partition), which serves as the basis for subsequent batch pre-compaction; the thickness of each partition is 001000.

[0030] Step 2, Laying, encapsulation and pre-compaction of partitioned plies:

[0031] First, for the plies of the first partition, according to the designed ply requirements, lay the prepreg layer by layer on the mold, and on the topmost layer of the first partition, lay a resin-made film, and after pre-pressing, encapsulate it with encapsulating material; place the encapsulated plies of the first partition into the autoclave, heat it up to 400100°C at a heating rate of 0.100°C0000, and at the same time apply a pressure of 0.400.8 MPa, keep it warm for 10030000 and then cool it down to room temperature. Then take out the encapsulated body from the autoclave, remove the encapsulating material, and continue to lay the second partition on the topmost layer of the first partition according to the ply design angle requirements. After laying, also lay a resin layer on the topmost layer of the second partition. After integrally encapsulating the first and second partitions, place them into the autoclave, heat it up to 400100°C at a heating rate of 0.100°C0000, and at the same time apply a pressure of 0.400.8 MPa, keep it warm for 10030000 and then cool it down to room temperature. Then take out the encapsulated body from the autoclave, remove the encapsulating material, and continue to lay the third partition and the resin layer on the topmost layer of the second partition according to the ply design angle requirements, and repeat the above process until the last partition is laid.

[0032] In Step 2, for the heating temperature, the target prepreg can be experimentally measured using dynamic differential scanning calorimetry to obtain its viscosity-temperature curve. In this viscosity-temperature curve, the temperature corresponding to the minimum viscosity is the optimal heating temperature.

[0033] The applied pressure, according to the maximum pressure value that the autoclave equipment used can reach, is preferably 0.8 MPa.

[0034] Based on the resin flow model and the viscosity-temperature curve, use numerical analysis software to analyze the resin flow behavior under the combined action of the heating temperature, heating rate, and applied pressure adopted, to ensure that the resin content is evenly distributed in the thickness direction of the laminate, and the resin flow time when it no longer changes with time is the shortest holding time.

[0035] The above resin flow model can be expressed as:

[0036]

[0037] In the formula, k x 、ky , k z are the permeabilities of the composite material in the x, y, and z directions respectively; m v is the volume change coefficient, which describes the stress-strain behavior of an object under constrained compression; P r is the resin pressure; η is the resin viscosity.

[0038] The above calculation process is as follows: Given the resin viscosity-temperature curve, fiber permeability, heating temperature, and pressurization pressure, the holding time is solved. The fiber permeability is input into the simulation model, and based on the heating temperature and viscosity-temperature curve, the resin viscosity at that moment is calculated. Then, the pressurization pressure is applied to the outer surface of the composite material, and the resin content distribution at different holding times can be solved.

[0039] Step 3, curing and forming: Place the thick composite laminate after laying the last partition into the autoclave for heating and pressurization, and the curing and forming process is as Figure 2 shown.

[0040] Step 4, demolding: After the forming in the autoclave is completed, take out the mold and the preform from the autoclave, then remove the sealing tape and encapsulation material outside the thick composite laminate, and then take out the composite laminate structure from the mold.

Claims

1. A method for forming a thick layer of carbon fiber composite material with uniform resin distribution and low porosity, characterized in that: Specifically, it includes the following steps: Step 1: Divide the thick composite laminate structure in the thickness direction; the specific process of Step 1 is as follows: The thick carbon fiber composite laminate is sequentially divided into N partition layers along the thickness direction, and the first partition layer is the side close to the mold; in Step 1, the thickness of each partition layer is 5 - 10 mm; Step 2: According to the partition result obtained in Step 1, paste a film on the surface layer of the laid layers after partitioning, and perform heating and pressurizing for pre-compaction; The specific process of Step 2 is as follows: Step 2.1: Paste the first partition layer of the carbon fiber composite material on the mold, lay a film made of resin on the upper surface of the first partition layer to form the first partition laid layer, perform pre-pressing on the first partition laid layer, and then use encapsulation material to encapsulate the first partition laid layer to obtain the first partition encapsulated body; Step 2.2: Place the first partition encapsulated body obtained in Step 2.1 into an autoclave, heat it at a heating rate of 0.1 - 5 °C / min to 40 - 100 °C, simultaneously apply a pressure of 0.4 - 0.8 MPa, keep it warm for 15 - 30 min and then cool it down to room temperature, then take out the first partition encapsulated body from the autoclave, remove the encapsulation material, and obtain the first partition compacted layer; Step 2.3: Lay the second partition layer of the carbon fiber composite material on the upper surface of the first partition compacted layer obtained in Step 2.2, and lay a film made of resin on the upper surface of the second partition layer to form the second partition laid layer; Step 2.4: After integrally encapsulating the first partition compacted layer obtained in Step 2.2 and the second partition laid layer obtained in Step 2.3, obtain the second partition encapsulated body; Step 2.5: Place the second partition encapsulated body obtained in Step 2.4 into an autoclave, heat it at a heating rate of 0.1 - 5 °C / min to 40 - 100 °C, simultaneously apply a pressure of 0.4 - 0.8 MPa, keep it warm for 15 - 30 min and then cool it down to room temperature, then take out the encapsulated body from the autoclave, remove the encapsulation material, and obtain the second partition compacted layer; Step 2.6: Repeat Steps 2.2 - 2.5, and continue to paste the third partition layer, the fourth partition layer,..., the (N - 1)th partition layer on the second partition compacted layer in sequence to obtain the (N - 1)th partition compacted layer; Step 2.7: Lay the Nth partition layer of the carbon fiber composite material on the upper surface of the (N - 1)th partition compacted layer obtained in Step 2.6, lay a film made of resin on the upper surface of the Nth partition layer to form the Nth partition laid layer, and integrally encapsulate the N partition layers to obtain the entire encapsulated body of the thick carbon fiber composite laminate; In Step 2.2 and Step 2.5, the heating rate, heating temperature, and applied pressure are determined according to the resin flow model shown in the following formula (1) to ensure that the resin content is evenly distributed in the thickness direction of the thick carbon fiber composite laminate, and the resin flow time when it no longer changes with time is the shortest holding time: （1）； Wherein, k x , k y , k z are respectively the permeabilities of the composite material along x , y and z in three directions; m v is the volume change coefficient; P r is the resin pressure; η is the resin viscosity; Step 3: Cure and mold the thick laminate processed in Step 2; Step 4: Demold the thick laminate molded in Step 3.

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