Method for estimating thermal expansion molding process parameters of foam sandwich composite material, foam sandwich composite material and preparation method of foam sandwich composite material

Abstract

The invention provides a method for estimating thermal expansion molding process parameters of a foam sandwich composite material, the foam sandwich composite material and a preparation method of the foam sandwich composite material. The estimation method comprises the following steps: testing an expansion pressure-time relation curve of the expandable foam rubber under the conditions of different temperatures and different expansion rates, and when the maximum value of the expansion pressure exceeds 100 kPa, recording a corresponding expansion rate range and a temperature range; testing a viscosity-curing time relation curve of resin in the prepreg at different temperatures, and recording a corresponding temperature range when the curing time does not exceed 10 minutes and the viscosity is not lower than 100 Pa.s; and taking the overlapped part of the recorded temperature range of the expandable foam rubber and the recorded temperature range of the resin as an estimated temperature range of thermal expansion mold pressing, and taking the recorded expansion rate range as an estimated expansion rate range of a thermal expansion mold pressing process. According to the estimation method, the production process stability of the sandwich composite material is improved.

Description

Technical Field

[0001] This invention relates to the field of foam technology, and more specifically, to a method for predicting the thermal expansion molding process parameters of a foam sandwich composite material, a foam sandwich composite material, and a method for preparing the same. Background Technology

[0002] The presence of a foam core in lightweight foam sandwich composites enhances the structural designability and functionality of components. Among these, complex reinforced and hybrid sandwich composites significantly improve the interfacial mechanical properties and Z-axis strength of traditional foam sandwich composites. From the perspective of energy conservation and improved material utilization efficiency, foam sandwich composites hold promise for further applications in aerospace, automotive, sports, and marine industries.

[0003] Traditional foam sandwich composite molding processes mainly include autoclave molding, prepreg-vacuum bag (VBO), and vacuum-assisted resin injection molding (VARI). Among these, the autoclave process has high equipment investment costs and high energy consumption, making it unsuitable for most civilian products. The VBO process uses prepreg as raw material and vacuum pressure molding to prepare sandwich composite parts. The VBO process for preparing grid-reinforced foam sandwich composite structures requires designing complex molds to form the reinforcing grid core, embedding the foam, and finally connecting the skin to the core. This multi-step process is inefficient, and the interface performance between the web and foam after molding is poor, limiting the large-scale production of the product. The VARI process uses vacuum pressure to inject resin into a fabric preform to form parts. For complex reinforced structures, the resin cannot fully impregnate the fabric in the web, resulting in numerous defects in the web of the composite material after molding. Although the VARI process is less expensive, the molding quality and efficiency of the web structure make it unsuitable for large-scale production. Therefore, traditional sandwich composite material molding processes suffer from problems such as high cost, high energy consumption, low efficiency, and poor molding quality of complex web structures, which seriously limit the development of sandwich composite materials.

[0004] A novel thermal expansion molding process (TEMP) originates from silicone or pressure bags as internal expansion sources. Within a closed mold, thermal expansion or pressurization generates internal expansion pressure, molding the composite material. Expanded foam, as part of a lightweight core, simultaneously acts as an expansion source, generating internal expansion pressure to integrally mold a sandwich composite material. The inside-out pressure application more easily solves the defects caused by traditional processes molding products with internal radius corners. Furthermore, the variability of the foam expansion ratio gives it high shaping efficiency and allows for directional control of molding pressure, achieving molding pressures higher than VBO and VARI processes (>100 kPa). Therefore, TEMP technology holds promise for enhancing the application potential of complex reinforced and hybrid sandwich composite materials.

[0005] However, the stability of the TEMP process is affected by the combined effects of the foaming and resin curing reactions. Currently, there are no studies or reports addressing the stability issues, thus preventing the large-scale application of the TEMP process. Summary of the Invention

[0006] The main objective of this invention is to provide a method for predicting the thermal expansion molding process parameters of foam sandwich composite materials, foam sandwich composite materials and their preparation methods, so as to solve the problem of poor process stability in the preparation of sandwich composite materials using thermal expansion molding process in the prior art.

[0007] To achieve the above objectives, according to one aspect of the present invention, a method for estimating the thermal expansion molding process parameters of a foam sandwich composite material is provided. The method includes: step S11, testing the expansion pressure-time relationship curves of the expandable foam adhesive under different temperatures and expansion ratios; when the maximum expansion pressure exceeds 100 kPa, recording the corresponding expansion ratio range and temperature range; step S12, testing the viscosity-curing time relationship curves of the resin in the prepreg at different temperatures; when the curing time is no more than 10 min and the viscosity is not less than 100 Pa·s, recording the corresponding temperature range; and step S13, taking the portion of the temperature range recorded in step S11 that overlaps with the temperature range recorded in step S12 as the estimated temperature range for thermal expansion molding, and taking the expansion ratio range recorded in step S11 as the estimated expansion ratio range for the thermal expansion molding process.

[0008] Furthermore, the different temperatures in step S11 and step S12 are each set independently within a temperature range of 90 to 180°C; and / or, the different expansion ratios are set within a range of 2 to 10 expansion ratios.

[0009] Furthermore, in step S11 above, a high and low temperature test chamber and a universal testing machine are used together to test the expansion pressure-time relationship curve of the expandable foam adhesive under different temperatures and different expansion ratios.

[0010] According to another aspect of the present invention, a method for preparing a foam sandwich composite material is provided, the method comprising: step S21, sequentially attaching expandable foam adhesive and prepreg onto polyethylene terephthalate foam to obtain a preform; step S22, placing the preform into a mold for thermal expansion molding to obtain a foam sandwich composite material, wherein the temperature and expansion ratio of the thermal expansion molding are the estimated temperature and estimated expansion ratio obtained by the aforementioned estimation method.

[0011] Furthermore, in step S22 above, the mold is a mold with degassing holes.

[0012] Furthermore, the above-mentioned expandable foam adhesive is prepared by mixing raw materials including epoxy resin, curing agent, accelerator, foaming agent, foam stabilizer and diluent; the mass ratio of epoxy resin, curing agent, accelerator, foaming agent, foam stabilizer and diluent is 100:1~20:0.5~2:2~30:0.1~1:0.1~1.

[0013] Furthermore, the epoxy resin is selected from any one or more of E-51, E-44, E-20, E-14, E-12, F-44, and F-51; and / or, the curing agent is selected from any one or more of dicyandiamide, hexamethylenetetramine, triethylenetetramine, and phthalic anhydride; and / or, the accelerator is selected from any one or more of o-cresol, resorcinol, and triethanolamine; and / or, the foaming agent is selected from any one or more of 4,4'-oxobisbenzenesulfonylhydrazine, sodium formate, ammonium bicarbonate, and polyesteramide; and / or, the foam stabilizer is selected from any one or more of silicone oil, polyol compounds, silicone compounds, sulfonated fatty alcohols, and sulfonated fatty acids; and / or, the diluent is selected from any one or more of organic solvents such as toluene, acetone, and ethanol.

[0014] Furthermore, the prepreg includes resin and fiber, and the difference between the curing temperature of the resin and the decomposition temperature of the foaming agent in the expandable foam adhesive is 0 to 50°C.

[0015] Furthermore, the aforementioned fibers are selected from any one or more of glass fibers, carbon fibers, aramid fibers, and basalt fibers.

[0016] According to another aspect of the present invention, a foam sandwich composite material is provided, which is prepared by the aforementioned preparation method.

[0017] Applying the technical solution of this invention, excessively low expansion pressure is detrimental to improving the structural stability of foam sandwich composite materials, and excessively long curing time of the resin in the prepreg is detrimental to improving the production efficiency of foam sandwich composite materials. Therefore, this application estimates a reasonable operating temperature and expansion ratio before implementing suitable thermal expansion molding of the foam sandwich composite material, providing an effective basis for actual production. Specifically: In step S11, this application records the expansion ratio range and temperature range corresponding to the maximum expansion pressure exceeding 100 kPa, which helps to prepare foam sandwich composite materials with higher tensile and compressive strength. Excessively long curing time of the resin in the prepreg is detrimental to improving the production efficiency of the foam sandwich composite material. In step S12, the temperature range corresponding to a curing time not exceeding 10 minutes and a viscosity not lower than 100 Pa·s is recorded, ensuring that the resin completes curing within 10 minutes, which helps to improve the production efficiency of the foam sandwich composite material. In step S13, the portion of the temperature range overlapping with the temperature range recorded in step S11 and step S12 is used as the estimated temperature range for thermal expansion molding, which helps to balance the temperature required for the expansion of the expandable foam adhesive and the temperature required for resin curing. In actual thermal expansion molding, the operating parameters can be set according to the estimated temperature and estimated expansion ratio obtained in the above steps, which can effectively improve the stability of the production process of sandwich composite materials. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0019] Figure 1 The expansion pressure versus time curves of the expandable foam adhesive of Example 1 of this application at different expansion ratios at 110°C and the viscosity versus time curve of the resin at 110°C are shown.

[0020] Figure 2 The expansion pressure versus time curves of the expandable foam adhesive of Example 1 of this application at different expansion ratios at 120°C and the viscosity versus time curve of the resin at 120°C are shown.

[0021] Figure 3 The expansion pressure versus time curves of the expandable foam adhesive of Example 1 of this application at different expansion ratios at 130°C and the viscosity versus time curve of the resin at 130°C are shown.

[0022] Figure 4 The expansion pressure versus time curves of the expandable foam adhesive of Example 1 of this application at different expansion ratios at 140°C and the viscosity versus time curve of the resin at 140°C are shown.

[0023] Figure 5 The expansion pressure versus time curves of the expandable foam adhesive of Example 1 of this application at different expansion ratios at 150°C and the viscosity versus time curve of the resin at 150°C are shown.

[0024] Figure 6 The foam sandwich composite material prepared in Example 2 of this application is shown. Detailed Implementation

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0026] As analyzed in the background section of this application, the existing technology uses thermal expansion molding to prepare sandwich composite materials, which has poor process stability. In order to solve the above problems, this application provides a method for predicting the thermal expansion molding process parameters of foam sandwich composite materials, foam sandwich composite materials and their preparation methods.

[0027] It should be noted that the expansion ratio refers to the degree of expansion of the expandable foam adhesive relative to its original state.

[0028] In a typical embodiment of this application, a method for estimating the thermal expansion molding process parameters of a foam sandwich composite material is provided. The estimation method includes: step S11, testing the expansion pressure-time relationship curve of the expandable foam adhesive under different temperatures and expansion ratios, and recording the corresponding expansion ratio range and temperature range when the maximum expansion pressure exceeds 100 kPa; step S12, testing the viscosity-curing time relationship curve of the resin in the prepreg at different temperatures, and recording the corresponding temperature range when the curing time is no more than 10 min and the viscosity is not less than 100 Pa·s; step S13, taking the portion of the temperature range recorded in step S11 that overlaps with the temperature range recorded in step S12 as the estimated temperature range for thermal expansion molding, and taking the expansion ratio range recorded in step S11 as the estimated expansion ratio range for the thermal expansion molding process.

[0029] Excessively low expansion pressure is detrimental to improving the structural stability of foam sandwich composites, and excessively long curing time of the resin in the prepreg is detrimental to improving the production efficiency of foam sandwich composites. Therefore, this application estimates a reasonable operating temperature and expansion ratio before implementing suitable thermal expansion molding of the foam sandwich composite, providing a valid basis for actual production. Specifically: In step S11, this application records the expansion ratio range and temperature range corresponding to the maximum expansion pressure exceeding 100 kPa, which helps to prepare foam sandwich composites with higher tensile and compressive strength. Excessively long curing time of the resin in the prepreg is detrimental to improving the production efficiency of the foam sandwich composite. In step S12, the temperature range corresponding to a curing time not exceeding 10 minutes and a viscosity not lower than 100 Pa·s is recorded, ensuring that the resin completes curing within 10 minutes, which helps to improve the production efficiency of the foam sandwich composite. In step S13, the overlapping portion of the temperature range recorded in step S11 and step S12 is used as the estimated temperature range for thermal expansion molding, which helps to balance the temperature required for the expansion of the expandable foam adhesive and the temperature required for resin curing. In actual thermal expansion molding, the operating parameters can be set according to the estimated temperature and estimated expansion ratio obtained in the above steps, which can effectively improve the stability of the production process of sandwich composite materials.

[0030] In addition, the viscosity of the resin in the prepreg was tested by selecting the same resin as the prepreg system and using a rheometer to obtain the isothermal rheological properties of the resin, thereby fitting the viscosity-curing time relationship curve of the resin at different temperatures.

[0031] In one embodiment of this application, the different temperatures in step S11 and step S12 are each set independently within a temperature range of 90 to 180°C; and / or, the different expansion ratios are set within a range of 2 to 10 expansion ratios.

[0032] Typically, the temperatures required for the foaming of expandable foam adhesives and the curing temperatures required for the resin in prepregs are in the range of 90–180°C. Therefore, the different temperatures in step S11 and step S12 are each independently set within the temperature range of 90–180°C, or they can be determined according to the range of the optimal decomposition temperature of the foaming agent in the expandable foam adhesive, thereby helping to obtain a suitable range of estimated temperatures using the estimation method of this application. The typical expansion ratio range of expandable foam adhesives is 2–10. Therefore, different expansion ratios are set within the expansion ratio range of 2–10, thereby helping to obtain a suitable range of estimated expansion ratios using the estimation method of this application.

[0033] In addition, the expansion pressure monitoring time depends on the curing time of the selected resin. The resin shrinks in the later stage of curing, and the expansion pressure will tend to decrease. Generally, the medium-temperature curing prepreg system needs to be monitored for more than 120 minutes.

[0034] To improve the accuracy of the prediction method, in one embodiment of this application, it is preferable to use a high and low temperature test chamber and a universal testing machine in step S11 to test the expansion pressure-time relationship curve of expandable foam adhesive under different temperatures and different expansion ratios.

[0035] The specific steps are as follows: Place the mold in a high and low temperature test chamber at the set temperature, then quickly place the expandable foam adhesive into the mold, and lock the mold using a press. Set the universal testing machine to a fixed position to obtain the load-time curve. Calculate the expansion pressure of the expandable foam adhesive based on the mold size and load, and obtain the expansion pressure-time curve.

[0036] In another typical embodiment of this application, a method for preparing a foam sandwich composite material is provided. The method includes: step S21, sequentially attaching expandable foam adhesive and prepreg onto polyethylene terephthalate foam to obtain a preform; step S22, placing the preform into a mold for thermal expansion molding to obtain a foam sandwich composite material, wherein the temperature and expansion ratio of the thermal expansion molding are the estimated temperature and estimated expansion ratio obtained by the aforementioned estimation method.

[0037] Step S21: The polyethylene terephthalate foam is sculpted into the designed shape, and then expandable foam adhesive and prepreg are sequentially applied to the foam to obtain a preform. When cutting the prepreg, care should be taken to control the radius of curvature (R-angle) to within two. To improve efficiency, the expandable foam adhesive should be designed as a monolithic structure whenever possible. Step S22: The preform is placed in a mold for thermal expansion molding. A small gap is required between the preform and the mold to facilitate easy placement of the preform into the mold. Since the thermal expansion molding temperature and expansion ratio in the above-mentioned method for preparing foam sandwich composite materials are estimated using the estimation method of this application, this preparation method has high process stability.

[0038] In addition, the above-mentioned thermal expansion molding process can be carried out by locking the mold with bolts and using an oven as the heating source, or by using a press as the heating source and locking the mold with the pressure of the press. Generally speaking, the temperature gradient of the press is more stable.

[0039] In one embodiment of this application, in step S22 above, the mold is a mold provided with degassing holes.

[0040] This application uses a mold with degassing holes, which helps to reduce the amount of resin seeping out from the gaps in the mold.

[0041] In one embodiment of this application, the expandable foam adhesive is prepared by mixing raw materials including epoxy resin, curing agent, accelerator, foaming agent, foam stabilizer and diluent; the mass ratio of epoxy resin, curing agent, accelerator, foaming agent, foam stabilizer and diluent is 100:1~20:0.5~2:2~30:0.1~1:0.1~1.

[0042] Preferably controlling the mass ratio of epoxy resin, curing agent, accelerator, foaming agent, foam stabilizer and diluent within the above range helps to improve the tensile strength and compressive strength of foam sandwich composite materials.

[0043] To enhance the synergistic effect among the components and further improve the tensile and compressive strength of the foam sandwich composite material, in one embodiment of this application, the epoxy resin is preferably selected from any one or more of E-51, E-44, E-20, E-14, E-12, F-44, and F-51; and / or, the curing agent is selected from any one or more of dicyandiamide, hexamethylenetetramine, triethylenetetramine, and phthalic anhydride; and / or, the accelerator is selected from any one or more of o-cresol, resorcinol, and triethanolamine; and / or, the foaming agent is selected from any one or more of 4,4'-oxobis(phenylenesulfonyl)hydrazine, sodium formate, ammonium bicarbonate, and polyesteramide; and / or, the foam stabilizer is selected from any one or more of silicone oil, polyol compounds, silicone compounds, sulfonated fatty alcohols, and sulfonated fatty acids; and / or, the diluent is selected from any one or more of organic solvents such as toluene, acetone, and ethanol.

[0044] Epoxy resins include high-temperature resistant epoxy resins, solid epoxy resins, and liquid epoxy resins. The high-temperature resistant epoxy resins are designated as F-44 and / or F-51. The solid epoxy resins are selected from any one or more of E-20, E-14, and E12. The liquid epoxy resins are selected from any one or more of E-51, E-44, and E-55. The addition of liquid epoxy resin helps to ensure thorough and uniform mixing of the epoxy resin with other reagents. Solid epoxy resin is used to control the viscosity of the expandable foam adhesive, and the addition of high-temperature resistant epoxy resin helps to improve the temperature resistance of the expandable foam adhesive. The formulation of expandable foam adhesive involves three components: A, B, and C. Component A is a mixture of high-temperature resistant epoxy resin and solid epoxy resin. Component B is a mixture of liquid epoxy resin, curing agent, and accelerator. A three-roll mill is used to thoroughly mix the solid powders within the system. Component C is a mixture of foaming agent, foam stabilizer, and diluent. After thorough mixing, it is combined with components A and B and stirred at high speed for about 15-20 minutes until all components are evenly mixed, thus preparing an expandable foam adhesive. During the mixing process, it is important to ensure that the temperature of component A is reduced to 80-100℃ before mixing with components B and C. Temperatures that are too high or too low are not conducive to controlling the prepolymerization degree of the epoxy resin.

[0045] In one embodiment of this application, the prepreg comprises resin and fiber, and the difference between the curing temperature of the resin and the decomposition temperature of the foaming agent in the expandable foam adhesive is 0 to 50°C.

[0046] In the prepreg, the resin is uniformly attached to the fiber. It is preferable to control the difference between the curing temperature of the resin and the decomposition temperature of the foaming agent in the expandable foam adhesive within the above-mentioned range. This helps to broaden the range of the estimated temperature, thereby helping to further improve the process stability of the preparation method.

[0047] The aforementioned prepreg is a fiber-reinforced polymer-based prepreg, including but not limited to, the type of the aforementioned prepreg being BAC-449.

[0048] In order to reduce production costs, in one embodiment of this application, the fibers are preferably selected from any one or more of glass fibers, carbon fibers, aramid fibers and basalt fibers.

[0049] In another typical embodiment of this application, a foam sandwich composite material is provided, which is prepared by the aforementioned preparation method.

[0050] The aforementioned foam sandwich composite material has high structural stability. The foam sandwich composite material can be a complex reinforced sandwich composite material product. The product usually includes complex radius corners and internal web structure designs, such as complex reinforced sandwich composite material lifting lugs. This type of lifting lug structure can be used in connection structural components in the fields of automobiles, construction, aerospace, and rail transportation.

[0051] The beneficial effects of this application will be further illustrated below with reference to the embodiments.

[0052] Example 1

[0053] (1) Formulation of expandable foam adhesive: It involves three components, A, B and C. Component A is a high-temperature resistant epoxy resin (F-44) and a solid epoxy resin (E-20). Component B is a mixture of liquid epoxy resin (E-51), curing agent (dicyandiamide) and accelerator (o-cresol). The solid powder in the system is fully mixed using a three-roll mill. Component C is a mixture of foaming agent (4,4'-oxobisbenzenesulfonylhydrazine), foam stabilizer (silicone oil), and diluent (toluene). After thorough mixing, it is combined with component B and component A (temperature reduced to 80°C) and stirred at high speed for about 15 minutes until all components are uniformly mixed. This yields an expandable foam adhesive. The mass ratio of epoxy resin, curing agent, accelerator, foaming agent, foam stabilizer, and diluent is 100:15:1.5:15:0.5:0.5, and the mass ratio of high-temperature resistant epoxy resin, solid epoxy resin, and liquid epoxy resin is 20:20:60.

[0054] (2) Test of expansion pressure-time relationship curve of expandable foam under different temperatures and expansion ratios: Expandable foam was coated onto fiberglass mat using an impregnation device, and release paper was then attached to the top and bottom to make a test sample with a thickness of 1 mm. A high and low temperature test chamber and a universal testing machine were used. The high and low temperature test chamber mainly controlled the test temperature, while the universal testing machine could control the displacement to remain constant through a program and record the load-time curve to calculate the change of expansion pressure generated during the expansion of the expandable foam over time. The test used a mold with pores for venting gas. The mold had an inner diameter of 200 mm and different thicknesses of aluminum alloy rings. The upper and lower molds used aluminum alloy plates with a thickness of 5 mm. When the mold was preheated to the test temperature in the high and low temperature test chamber, the test sample was placed in it, and the compression clamp of the universal testing machine applied an initial preload of about 10 N. The experiment included five temperature points (110℃, 120℃, 130℃, 140℃, and 150℃) and five expansion ratios (2, 4, 6, 8, and 10 times expansion), totaling 25 experiments. Since most medium-temperature curing epoxy resin systems have a curing time of approximately 120 minutes, the internal pressure generated by the expanding foam was recorded within 120 minutes for each experiment, resulting in expansion pressure-time curves for the expandable foam adhesive under different temperatures and expansion ratios.

[0055] (3) Viscosity-time relationship curve test of resin in prepreg at different temperatures: The prepreg model is BAC-449. The same resin as the resin in the prepreg is used for testing. A rheometer is used. Five temperature points of 110℃, 120℃, 130℃, 140℃ and 150℃ are designed for the test. The viscosity of the resin changes with time and the viscosity-time relationship curve of the resin at different temperature points is obtained.

[0056] (4) Parameter determination: From Figure 1 It can be seen that at 110℃, the resin curing time is 33 minutes, and the maximum expansion pressure exceeds 100 kPa when the expansion ratio is 2 and 4 times; from Figure 2 It can be seen that at 120℃, the resin curing time is 17 minutes, and the maximum expansion pressure exceeds 100 kPa when the expansion ratio is 2 and 4 times; from Figure 3 It can be seen that at 130℃, the resin curing time is 9 minutes, and the maximum expansion pressure exceeds 100 kPa when the expansion ratio is 2, 4, and 6 times; from Figure 4 It can be seen that at 140℃, the resin curing time is 4.6 minutes, and the maximum expansion pressure exceeds 100 kPa when the expansion ratio is 2, 4, and 6 times; from Figure 5 It can be seen that at 150℃, the resin curing time is 2.4 minutes, and the maximum expansion pressure exceeds 100 kPa when the expansion ratio is 2, 4, and 6 times. Since the foam scorches at 150℃, this temperature is unsuitable. At 110℃ and 120℃, the resin curing time is too long, affecting production efficiency, so these temperatures are also unsuitable. Therefore, the final suitable temperature range for thermal expansion molding of composite materials is 130–140℃, with a foam expansion ratio of 2–6 times. It should be noted that… Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 In the equation, E2-1, E4-1, E6-1, E8-1, and E10-1 each independently represent expansion ratios of 2, 4, 6, 8, and 10 times, respectively.

[0057] Example 2

[0058] Using the thermal expansion molding process obtained in Example 1, a complex sandwich composite lifting lug structure was prepared with a molding temperature of 135°C and an expansion ratio of 4. The expandable foam adhesive and prepreg materials were the same as in Example 1. Specifically, polyethylene terephthalate (PET) foam was first sculpted into the designed shape. Then, the prepreg and expandable foam adhesive were cut according to the designed structure. The thermally expandable epoxy foam prepreg was laid onto the PET foam core, followed by the prepreg. The press was preheated to 135°C, and then the lifting lug preform was placed in the mold with an expansion ratio of 4. The mold was then locked using the press. The mold gradually heated to 135°C, and simultaneously, the resin curing reaction and the foam prepreg foaming reaction occurred, resulting in the composite material as shown in Example 1. Figure 6 The foam sandwich composite material shown.

[0059] Example 3

[0060] The difference from Example 2 is that the temperature of the composite material obtained by the thermal expansion molding process in Example 1 is 130°C and the expansion ratio is 2 times to prepare the complex sandwich composite material lifting lug structure, and finally obtain the foam sandwich composite material.

[0061] Example 4

[0062] The difference from Example 2 is that the temperature of the composite material obtained by the thermal expansion molding process in Example 1 is 140°C and the expansion ratio is 6 times to prepare the complex sandwich composite material lifting lug structure, and finally obtain the foam sandwich composite material.

[0063] Comparative Example 1

[0064] The difference from Example 2 is that the temperature of the thermal expansion molding process for the composite material is 120°C, and the expansion ratio is 8 times to prepare the complex sandwich composite material lifting lug structure, and finally obtain the foam sandwich composite material.

[0065] Performance testing

[0066] The compressive strength of the foam sandwich composite materials prepared in the examples and comparative examples was tested according to the ASTM D1621-2016 test standard. The test results are shown in Table 1.

[0067] Table 1

[0068] Implementation / Comparative Example Compressive strength / MPa Example 2 2.3 Example 3 3.5 Example 4 1.7 Comparative Example 1 0.8

[0069] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0070] Excessively low expansion pressure is detrimental to improving the structural stability of foam sandwich composites, and excessively long curing time of the resin in the prepreg is detrimental to improving the production efficiency of foam sandwich composites. Therefore, this application estimates a reasonable operating temperature and expansion ratio before implementing suitable thermal expansion molding of the foam sandwich composite, providing a valid basis for actual production. Specifically: In step S11, this application records the expansion ratio range and temperature range corresponding to the maximum expansion pressure exceeding 100 kPa, which helps to prepare foam sandwich composites with higher tensile and compressive strength. Excessively long curing time of the resin in the prepreg is detrimental to improving the production efficiency of the foam sandwich composite. In step S12, the temperature range corresponding to a curing time not exceeding 10 minutes and a viscosity not lower than 100 Pa·s is recorded, ensuring that the resin completes curing within 10 minutes, which helps to improve the production efficiency of the foam sandwich composite. In step S13, the overlapping portion of the temperature range recorded in step S11 and step S12 is used as the estimated temperature range for thermal expansion molding, which helps to balance the temperature required for the expansion of the expandable foam adhesive and the temperature required for resin curing. In actual thermal expansion molding, the operating parameters can be set according to the estimated temperature and estimated expansion ratio obtained in the above steps, which can effectively improve the stability of the production process of sandwich composite materials.

[0071] The above are merely embodiments of the present invention and are not intended to limit the invention. Those skilled in the art will recognize that the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., 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 method for predicting the thermal expansion molding process parameters of a foam sandwich composite material, characterized in that, The estimation method includes: Step S11: Test the expansion pressure-time relationship curve of expandable foam adhesive under different temperatures and expansion ratios. When the maximum expansion pressure exceeds 100 kPa, record the corresponding expansion ratio range and temperature range. Step S12: Test the viscosity-curing time relationship curve of the resin in the prepreg at different temperatures. When the curing time is no more than 10 min and the viscosity is not less than 100 Pa·s, record the corresponding temperature range. Step S13: The portion of the temperature range that overlaps with the temperature range recorded in step S11 and step S12 is taken as the range of the estimated temperature for thermal expansion molding, and the range of expansion ratio recorded in step S11 is taken as the range of the estimated expansion ratio for the thermal expansion molding process.

2. The prediction method according to claim 1, characterized in that, The different temperatures in step S11 and the different temperatures in step S12 are each set independently within a temperature range of 90 to 180°C; and / or, the different expansion ratios are set within a range of 2 to 10 expansion ratios.

3. The estimation method according to claim 1 or 2, characterized in that, In step S11, a high and low temperature test chamber and a universal testing machine are used to test the expansion pressure-time relationship curve of the expandable foam adhesive under different temperatures and different expansion ratios.

4. A method for preparing a foam sandwich composite material, characterized in that, The preparation method includes: Step S21: Expandable foam adhesive and prepreg are sequentially applied to polyethylene terephthalate foam to obtain a preform; Step S22: The preform is placed into a mold for thermal expansion molding to obtain the foam sandwich composite material, wherein the temperature and expansion ratio of the thermal expansion molding are the estimated temperature and estimated expansion ratio obtained by the estimation method according to any one of claims 1 to 3.

5. The preparation method according to claim 4, characterized in that, In step S22, the mold is a mold with degassing holes.

6. The preparation method according to claim 4 or 5, characterized in that, The expandable foam adhesive is prepared by mixing raw materials including epoxy resin, curing agent, accelerator, foaming agent, foam stabilizer and diluent; the mass ratio of epoxy resin, curing agent, accelerator, foaming agent, foam stabilizer and diluent is 100:1~20:0.5~2:2~30:0.1~1:0.1~1.

7. The preparation method according to claim 6, characterized in that, The epoxy resin is selected from any one or more of E-51, E-44, E-20, E-14, E-12, F-44 and F-51; And / or, the curing agent is selected from any one or more of dicyandiamide, hexamethylenetetramine, triethylenetetramine, and phthalic anhydride; And / or, the accelerator is selected from any one or more of o-cresol, resorcinol and triethanolamine; And / or, the foaming agent is selected from any one or more of 4,4'-oxobisbenzenesulfonyl hydrazine, sodium formate, ammonium bicarbonate and polyesteramide; And / or, the foam stabilizer is selected from any one or more of silicone oil, polyol compounds, silicone compounds, sulfonated fatty alcohols, and sulfonated fatty acids; And / or, the diluent is selected from any one or more organic solvents such as toluene, acetone, and ethanol.

8. The preparation method according to any one of claims 4 to 7, characterized in that, The prepreg comprises resin and fiber, and the difference between the curing temperature of the resin and the decomposition temperature of the foaming agent in the expandable foam adhesive is 0 to 50°C.

9. The preparation method according to claim 8, characterized in that, The fiber is selected from any one or more of glass fiber, carbon fiber, aramid fiber and basalt fiber.

10. A foam sandwich composite material, characterized in that, The foam sandwich composite material is prepared by the preparation method according to any one of claims 4 to 9.

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