Accurate and efficient design strategy for composite material forming process

Abstract

The invention discloses a precise and efficient design strategy of a composite material forming process, which comprises the following steps: (1) based on a resin matrix curing physicochemical characteristic ex-situ test, obtaining a high-precision phase transformation curing graph, and formulating a single-temperature step forming process; (2) arranging an optical fiber sensor by adopting a high characteristic response sensor, monitoring the whole molding process of the composite material in situ with high precision, and carrying out characteristic response analysis on a sensing signal; (3) in combination with a phase transformation curing graph and sensing signal analysis, a curing behavior induction mechanism is explored, and a curing behavior process adjustable interval is accurately divided; and (4) carrying out multi-parameter comparison screening of the forming process. The method has the advantages that in-situ / ex-situ testing means are adopted for high-precision collaborative analysis of the curing behavior of the composite material, based on theoretical analysis, monitoring verification and multi-parameter comparison and screening, the design precision and regulation and control efficiency of process parameters are improved, and a precise and efficient design strategy is provided for formulation of a high-dimensional-precision and high-performance composite material forming process.

Description

Technical Field

[0001] The present invention relates to a precise and efficient design strategy for a composite material forming process, belonging to the field of composite material forming process design, and specifically relates to a precise and efficient process design and regulation strategy based on in-situ / non-in-situ hybrid monitoring means for the high forming precision and high-performance forming manufacturing requirements of fiber-reinforced resin matrix composites. Background Art

[0002] Composite materials have the advantages of flexible forming processes, high designability of structure / performance, etc., and are widely used in fields such as aerospace and new energy. However, the forming process of composite materials is a process strongly coupled by multiple physical fields such as heat-chemical reaction-mechanical stress / strain. Physical and chemical properties such as crosslink density, degree of curing reaction, and glass transition temperature gradually develop as the curing reaction of the resin matrix proceeds. At the structural level, curing behaviors such as interlayer slip, resin seepage, phase transition, curing shrinkage, thermal strain, and warping deformation will also occur. It can be said that the rationality of the design of forming process parameters is an important influencing factor restricting the improvement of the forming precision and mechanical properties of composite materials.

[0003] Currently, there are mainly two types of ideas for the forming process design of composite materials. The first type is to use a differential scanning calorimeter, and design the forming process with reference to the onset temperature, peak temperature, and post-curing temperature of the curing exothermic peak of the resin matrix, combined with the characteristics of the composite material, such as viscosity, reactivity, etc. This non-in-situ forming process design method has a simple and labor-saving process, but there are problems such as the amplification effect of curing exotherm and poor correspondence between material characteristics and process parameter regulation in the implementation process. It highly depends on the experience of designers, requires performance analysis and verification by combining multiple batches of specimens, has a high R & D cost, and at the same time, targeted regulation design cannot be carried out for the structural dimension accuracy. The second type is to use in-situ monitoring technologies such as flexible sensors and digital image correlation to monitor the deformation state and internal defects of composite materials during the forming process in real time, and adjust the forming process based on intuitive digital and image information. This type of method fits the forming conditions, but it needs to stop the vehicle for detection multiple times during the forming process of composite materials, and has problems such as single test and poor operability. For closed forming processes such as compression molding, hot pressing, and vacuum resin transfer molding, due to multiple stop monitoring and interruption of the process implementation, it will instead have a negative impact on the performance and dimensional accuracy of composite materials.

[0004] The in-situ monitoring technology based on Fiber Bragg Grating (FBG) sensing is widely used in the monitoring of the curing behavior of composite materials and the process control of their properties. Yixin_Qi et al. used FBG sensors to compare and monitor the curing processes of rapidly cured and conventionally cured CFRP laminates, and found that there was an obvious self-exothermic behavior during the curing of rapidly cured CFRP laminates, resulting in an increase in the curing peak temperature and residual strain by 27.4 °C and 2207.4 με, respectively (see QI Y, JIANG D, JU S, et al. Investigation of strain history in fast and conventional curing epoxy-matrix composites by FBGs[J]. Composites Science and Technology, 2018, 159: 18-24.). Hak-Sung Kim et al. used FBG sensors to monitor the process-induced strain of CFRP laminates. By adjusting the curing cycle, the residual stress was reduced by about 50%, and the static strength and fatigue life were increased by 16% and 614%, respectively (see Hak-Sung Kim, Seong-Hwan Yoo, Seung-Hwan Chang. In situ monitoring of the strain evolution and curing reaction of composite laminates to reduce the thermal residual stress using FBG sensor and dielectrometry[J]. Composites Part B, 2013, 44(1): 446-452.). However, the above studies did not conduct a detailed analysis of the FBG sensing signals, and the correlation mechanism between the FBG sensing signals and the CFRP curing behavior and process parameters was not clear, which greatly affected the forming quality and performance control efficiency of CFRP.

[0005] To solve the above problems, the present invention provides a precise and efficient design strategy for the composite material forming process, which is based on the high-precision collaborative analysis of the curing behavior of composite materials by in-situ / non-in-situ hybrid monitoring means, and the multi-parameter comparison and optimization of the composite material structure quality index and performance index under the process parameter control index, so as to improve the design accuracy and control efficiency of the composite material forming process parameters, and provide theoretical guidance and technical support for the high-precision and efficient forming of high-dimensional precision and high-performance composite materials. Summary of the Invention

[0006] A precise and efficient design strategy for a composite material forming process, characterized by comprising the following steps:

[0007] (1) Analysis of curing physical and chemical properties: Conduct analysis on the curing reaction characteristics, gelation transition, and glass transition of the resin matrix to form a high-precision temperature-time-phase transition curing diagram. Based on the time distribution of each phase state, formulate a single-temperature-step forming process, and verify and analyze the curing effect of the resin matrix under the single-temperature-step forming process in combination with the glass transition temperature to ensure the theoretical guidance accuracy of the temperature-time-phase transition curing diagram for the evolution law of the physical and chemical properties during the curing process of the resin matrix;

[0008] (2) In-situ monitoring of the entire forming process: Based on the fiber optic sensor with high characteristic response settings, in-situ monitor the entire forming process of the composite material, conduct analysis on the characteristic response of the sensing signal, and verify the sensitivity and accuracy of the in-situ monitoring in combination with the fitting of the monitoring sensitivity coefficient and the analysis of the disturbance strain to ensure the analysis accuracy of the characteristic response of the sensing signal to each curing behavior;

[0009] (3) Division of the process adjustable range of curing behavior: Combine the temperature-time-phase transition curing diagram of the resin matrix and the analysis of the characteristic response of the sensing signal, comprehensively analyze the induction mechanism of the curing behavior of the composite material in each phase state interval, and accurately divide the process adjustable range of various curing behaviors;

[0010] (4) Comparative optimization of multiple process parameters for forming: Based on the process adjustable range of curing behavior, design process parameter control indicators, prepare composite material specimens, design structural quality and performance indicators, conduct comparative optimization of multiple parameters, screen out forming process parameters with high dimensional accuracy and high performance, and improve the control efficiency of high dimensional accuracy and high performance process parameters based on the screening and optimization of multiple parameters at the design end and the application end.

[0011] The analysis of the curing reaction characteristics includes, but is not limited to, the evolution law of the isothermal curing reaction degree, the analysis of the maximum reaction degree, the analysis of the reaction autocatalytic effect, and the competition law between the polymerization and diffusion effects. Based on the analysis of the curing reaction characteristics, the determination accuracy of the gelation transition and the glass transition can be improved. The curing of the resin matrix is a process of multi-phase state evolution from liquid to rubber to solid. In different phase states, the evolution law of the curing reaction characteristics with process parameters is the primary factor for efficiently controlling the void content, mechanical properties, and dimensional accuracy of the composite material structure.

[0012] The specific steps of the gelation transition analysis are as follows:

[0013] (1) Conduct a variance significance statistic on the isothermal curing reaction enthalpy values under multiple sample tests, use 0.05 as the difference significance threshold, and screen the isothermal test temperature and time conditions based on the same variance significance letters or asterisks;

[0014] (2) Based on the above isothermal test temperature and time conditions, perform isothermal curing rheological tests. Combining with the evolution law of rheological parameters, taking the balance of the competition between polymerization and diffusion effects in the curing reaction as the verification standard, screen the best gelation transition criterion, and determine the gelation transition time and the degree of curing reaction at gelation transition;

[0015] (3) Conduct fitting analysis on the isothermal test temperature and gelation transition time to obtain the gelation transition curve of the resin matrix for drawing the temperature-time phase transition curing diagram;

[0016] (4) The gelation transition criterion includes but is not limited to the time or degree of curing when the shear storage modulus is equal to the loss modulus, the time or degree of curing at the minimum value of the complex viscosity, the time or degree of curing at the maximum value of the second derivative of the complex viscosity, and the time or degree of curing at the maximum value of the first derivative of the shear storage modulus.

[0017] The specific steps of the glass transition analysis are as follows:

[0018] (1) Perform non-isothermal tests on the resin matrix in the completely uncured and completely cured states, and obtain the glass transition temperature (T g0 ) in the completely uncured state and the glass transition temperature (T g∞ ) in the completely cured state by extrapolation or the average value method;

[0019] (2) Perform glass transition temperature (T g ) tests on the resin matrix with different degrees of curing reaction (α) at each isothermal temperature, and conduct fitting analysis based on the empirical formula of the glass transition temperature. The calculation of the empirical formula of the glass transition temperature is as follows:

[0020]

[0021] α is the degree of curing reaction, T g is the glass transition temperature, T g0 is the glass transition temperature in the completely uncured state, T g∞ is the glass transition temperature in the completely cured state, and λ is the structural parameter, with a value between 0 and 1;

[0022] (3) Combining the isothermal and non-isothermal curing reaction degree analysis, taking the glass transition occurring within the time interval dominated by the reaction diffusion effect as the verification standard, screen the glass transition criterion, and determine the glass transition time and the degree of curing reaction at glass transition;

[0023] (4) Conduct fitting analysis on the isothermal test temperature and the glass transition time to obtain the glass transition curve of the resin matrix for drawing the temperature-time phase transition curing diagram;

[0024] (5) The vitrification transition criteria include, but are not limited to, the time or degree of cure when the vitrification transition temperature is equal to the isothermal test temperature, the time or degree of cure when the evolution trend of the curing reaction degree tends to be stable, and the time or degree of cure when the evolution trend of the shear storage modulus in the rheological test tends to be stable.

[0025] The criteria for formulating the single-temperature step forming process should comprehensively consider whether the resin matrix reaches complete cure, whether the fiber optic sensor can effectively monitor the curing behavior, and whether the curing behavior has sufficient responsiveness to process parameters; the specific steps are as follows:

[0026] (1) The resin matrix reaches the maximum reaction degree at the isothermal time.

[0027] (2) The resin matrix reaches the maximum vitrification transition temperature at the isothermal time.

[0028] (3) The optimal time for the resin matrix to be in the liquid state, sol / gel rubber state, sol / gel glass state, and gel glass state is 5 min to 180 min.

[0029] The criteria for formulating the high-characteristic response sensing setting should consider whether the fiber optic sensor can produce an obvious signal response to the curing behavior for subsequent high-precision identification, including but not limited to the sensor fixing method, pigtail processing technology, and sensor encapsulation technology; the specific steps are as follows:

[0030] (1) The sensor fixing method includes, but is not limited to, the embedded type, surface-mounted type, and bridging type.

[0031] (2) The pigtail processing technology includes, but is not limited to, not applying tensile strain to the sensor, freely placing the pigtail, applying 0 - 500 tensile microstrain to the sensor, freely placing the pigtail, applying 0 - 500 tensile microstrain to the sensor, fixing the pigtail with hot melt adhesive, not applying tensile strain to the sensor, and fixing the pigtail.

[0032] (3) The sensor encapsulation technology includes, but is not limited to, no coating, using a 0 - 50 μm thick polypropylene coating, using a 0 - 50 μm thick polyimide coating, and using a 0 - 50 μm thick metal coating.

[0033] The analysis of the characteristic response of the sensing signal is as follows:

[0034] (1) The selection of characteristic response points includes the sudden increase points, sudden decrease points, platforms, and inflection points generated by the sensing signal with the implementation of the process, the evolution of the curing reaction degree, and the phase transition.

[0035] (2) Screening of characteristic response points, including screening sudden increase points, sudden decrease points, platforms, and inflection points generated with the implementation of the process, the evolution of the degree of curing reaction, and phase transition, with the disturbance strain range as the signal noise range. The disturbance strain refers to the offset of the sensing signal of the fiber optic sensor due to uncontrollable external forces;

[0036] (3) Comparative evaluation of characteristic responsiveness, including the characteristic response amplitude comparison method, where the signal values of characteristic response points a and b are subtracted to evaluate the characteristic responsiveness of the corresponding curing behavior in this stage;

[0037] (4) Comparative evaluation of characteristic responsiveness, including the rate comparison method, where the signal values between characteristic response points a and b are linearly fitted to evaluate the characteristic responsiveness of the corresponding curing behavior in this stage;

[0038] (5) Error evaluation of characteristic responsiveness, including fitting R 2 or as a reference, with the disturbance strain range as a reference, where R 2 is the fitting determination coefficient, is the adjusted determination coefficient after fitting;

[0039] (6) The curing behaviors include but are not limited to pressure extrusion seepage, vacuum extrusion seepage, gelation transition, vitrification transition, complete curing transition, resin flow, resin volume expansion, consolidation strain, chemical shrinkage, thermal strain, and unstable strain caused by the mismatch of the thermal expansion coefficients of the resin and fibers.

[0040] The comparison of multiple process parameters of the forming process is as follows:

[0041] (1) The process parameter control indicators include but are not limited to pressure, constant temperature, and constant temperature time;

[0042] (2) The structural quality indicators include but are not limited to porosity, consolidation strain, curing shrinkage, thermal strain, and residual strain;

[0043] (3) The performance indicators include but are not limited to flexural strength and interlaminar shear strength.

[0044] The resin matrix includes but is not limited to epoxy resin, phenolic resin, unsaturated polyester, bismaleimide resin, melamine resin, and cyanate resin.

[0045] The fiber components of the composite material include but are not limited to carbon fiber, glass fiber, basalt fiber, polyamide fiber, silicon carbide fiber, polyester fiber, acrylic fiber, polytetrafluoroethylene fiber, and polyphenylene sulfide fiber.

[0046] Advantages of the Invention

[0047] The present invention provides a precise and efficient design strategy for a composite material forming process, with the following effects:

[0048] (1) Based on a variety of ex-situ testing methods, accurately analyze the curing reaction characteristics and phase transition laws of the resin matrix. Starting from the design end, provide sufficient theoretical guidance for the design, regulation, and optimization of process parameters, and ensure the in-situ monitoring of subsequent curing behavior and the accuracy requirements of process parameter regulation.

[0049] (2) Based on fiber optic sensors with high characteristic responses, in-situ and real-time monitor the composite material forming process, establish a characteristic response analysis method for sensing signals, clarify the process adjustable range of various curing behaviors, and meet the high-precision analysis of the evolution and induction mechanisms of various curing behaviors under the strong thermo-chemical-mechanical coupling effect of composite materials. Provide theoretical guidance for the regulation and design of process parameters from the component level.

[0050] (3) Based on the multi-parameter comparison of the process regulation parameter indicators, structural quality indicators, and performance indicators of the composite material forming process, explore the influence laws of the forming process suitable for high dimensional accuracy and high performance composite materials. Combine in-situ / ex-situ testing methods for high-precision collaborative analysis of curing behaviors, improve the design accuracy and regulation efficiency of process parameters, and provide precise and efficient design and regulation strategies for the formulation of the forming process of high dimensional accuracy and high performance composite materials. Description of the Drawings

[0051] Figure 1 It is a flowchart of the composite material forming process design strategy according to the embodiment of the present invention;

[0052] Figure 2 It is an analysis diagram of the curing reaction characteristics of the resin matrix according to the embodiment of the present invention;

[0053] Figure 3 It is an analysis diagram of the gelation transition of the resin matrix according to the embodiment of the present invention;

[0054] Figure 4 It is an analysis diagram of the glass transition of the resin matrix according to the embodiment of the present invention;

[0055] Figure 5 It is a temperature-time-phase transition curing diagram of the resin matrix according to the embodiment of the present invention;

[0056] Figure 6 It is an analysis diagram of the characteristic response of the sensing signal according to the embodiment of the present invention; Detailed Embodiments

[0057] Such as Figure 1As shown in the figure, it is a flow chart of the composite material forming process design strategy. The first step of the implementation of the present invention is to analyze the physical and chemical evolution characteristics of the resin matrix curing process by non-in-situ testing means, and based on the verification analysis of the phase transition criterion, form a high-precision temperature-time-phase transition curing diagram for the subsequent high-precision analysis of the curing behavior. In addition, based on the phase time distribution, a single temperature step curing forming process is selected for the subsequent regulation design of the forming process regulation parameters; the second step is to monitor the whole process of composite material forming by fiber optic sensors with different settings, conduct characteristic response analysis on the curing behavior, screen the fiber optic sensors with high characteristic response sensing settings, and verify the monitoring sensitivity and accuracy by combining the sensitivity coefficient fitting analysis and disturbance strain analysis of temperature and strain monitoring; the third step is to deeply analyze the change law and induction mechanism of the curing behavior of the composite material in each phase interval based on the temperature-time-phase transition curing diagram and characteristic response analysis, and accurately divide the process adjustable interval of the curing behavior to ensure the accuracy and effectiveness of the process regulation parameter settings; the fourth step is to design process parameter regulation indicators based on the process adjustable interval of the curing behavior, prepare composite material specimens, conduct structural quality and performance evaluation, determine the forming and performance status of the composite material from the design end and application end, clarify the influence law of the forming process parameters and the curing behavior, and improve the design efficiency of the forming process with high dimensional accuracy and high performance adaptation.

[0058] The present invention will be further described below with reference to the accompanying drawings. It should be noted that the following description is only for explaining the present invention and does not limit its content.

[0059] Example 1

[0060] The resin matrix uses epoxy resin and the fiber component uses carbon fiber.

[0061] Step 1: Physical and chemical characteristics of the resin matrix curing process

[0062] As Figure 2 , the analysis diagram of the resin matrix curing reaction characteristics. Under the isothermal test of the differential scanning calorimeter, the balance of polymerization and diffusion effects occurs after the maximum reaction rate and before the obvious decline, and the corresponding curing reaction interval is 0.17 - 0.54;

[0063] Perform variance significance statistics on the enthalpy values under multi-sample tests, set 0.05 as the difference significance threshold, and select 85°C, 90°C, and 95°C as the isothermal test processes with the same variance significance letter markings as the standard. As Figure 3 , the analysis diagram of the resin matrix gelation transition. Taking the balance of the competition between polymerization and diffusion effects as the standard, screen the curing degree at the minimum complex viscosity as the best gelation transition criterion, with the corresponding curing reaction degree of 0.49. Non-linearly fit the gelation transition time and temperature to obtain the gelation transition curve for the drawing of the temperature-time-phase transition curing diagram.

[0064] The fully uncured glass transition temperature T of the resin matrix g0 = -38.6 °C, and the fully cured glass transition temperature T g∞ = 103 °C. The fitting empirical formula for the glass transition temperature (T g ) is shown in the following formula (4):

[0065]

[0066] α is the degree of curing reaction, and T g is the glass transition temperature.

[0067] As Figure 4 , in the glass transition analysis diagram of the resin matrix, taking the time interval in which the glass transition occurs in the time interval dominated by the reaction diffusion effect (α > 0.54) as the standard, screening the best glass transition criterion with the glass transition temperature equal to the isothermal test temperature, corresponding to the curing reaction degree α = 0.96, performing a non-linear fitting analysis on the glass transition time and temperature, and obtaining the glass transition curve for the drawing of the temperature-time-phase transition curing diagram.

[0068] As Figure 5 , in the temperature-time-phase transition curing diagram of the resin matrix, aiming at the complete curing of the resin system, the durations of the resin matrix in the liquid state, sol / gel rubber state, and sol / gel glass state at 90 °C are 15 min, 40 min, and 10 min respectively, and the time required for the curing reaction degree to reach the maximum is at least 65 min. Therefore, a single-temperature step forming process of 90 °C / 80 min is designed.

[0069] As Figure 4 , in the glass transition analysis diagram of the resin matrix, the differential scanning calorimetry is used to measure the glass transition temperature of the cured resin matrix. Under the forming process of 90 °C / 80 min, the resin matrix reaches complete curing, and the glass transition temperature reaches the maximum of 103 °C, which is consistent with the glass transition temperature (T g∞ ) in the completely cured state.

[0070] Step 2: In-situ monitoring of the whole process of composite material forming

[0071] The fixing method of the fiber optic sensor is embedded. The commercial coating of fiber optic sensor 1 is removed, a 50 tensile microstrain is applied to the sensor, and the pigtail is in a free state; the commercial coating of fiber optic sensor 2 is removed, a 50 tensile microstrain is applied to the sensor, and the pigtail is in a state fixed by hot melt adhesive; the commercial coating of fiber optic sensor 3 is retained, a 50 tensile microstrain is applied to the sensor, and the pigtail is in a free state; the commercial coating of fiber optic sensor 4 is retained, a 50 tensile microstrain is applied to the sensor, and the pigtail is in a state fixed by hot melt adhesive.

[0072] The composite material is formed by a hot pressing process, and the process parameters are set as follows:

[0073] (1) Pretreatment stage: Constant pressure treatment at 250 psi for 10 min and heating at 10 °C / min;

[0074] (2) Constant temperature stage: Constant temperature curing at 90 °C for 80 min;

[0075] (3) Cooling stage: Natural cooling.

[0076] As Figure 6 shown, in the analysis diagram of the characteristic response of the sensing signal, the sudden increase points, sudden decrease points, platforms, and inflection points generated by the sensing signal with the evolution of the process implementation, the degree of curing reaction, and the phase transition are selected as the characteristic response points. The disturbance strain is ±0.5 με. The characteristic response points are screened, and the characteristic response amplitude method is used to compare the characteristic responses of the fiber optic sensor to extrusion seepage, resin volume expansion and flow, consolidation strain, chemical shrinkage, gelation transition, glass transition, complete curing transition, thermal strain, and residual strain. The characteristic response error is ±0.5 με with the disturbance strain as the reference.

[0077] As shown in Table 1 below for the analysis of the characteristic response of the sensing signal, during the whole process of composite material forming, the sensing signal of fiber optic sensor 1 has obvious characteristic responses to various curing behaviors, and the monitored residual strain is 80 με. The characteristic responses of fiber optic sensors 2 - 4 to curing shrinkage, thermal strain, and residual strain are weak. Therefore, fiber optic sensor 1 is selected as the fiber optic sensor for high characteristic response sensing settings, which can accurately, comprehensively, and effectively guide the division of the process adjustable range of various curing behaviors.

[0078] Step 3: Division of the process adjustable range

[0079] As shown in Table 2 below, the process adjustable range of each curing behavior, combined with the temperature-time-phase transformation curing diagram and the characteristic response analysis of the sensing signal, during the whole process of composite material forming, the extrusion and seepage of resin are accompanied by the implementation of the pressure process, which can be adjusted by regulating the magnitude of the compressive stress; the volume expansion and resin flow are accompanied by the implementation of the heating process, which can be adjusted by setting the heating rate; the gelation transformation, glass transition and curing are only affected by the curing reaction process of the resin matrix, that is, only related to the isothermal temperature setting, and the control purpose can be achieved by setting the isothermal temperature and multi-temperature step curing system; the consolidation strain is formed before the gelation transformation and is affected by the comprehensive influence of the pressurization process, temperature and resin flow; the chemical shrinkage is formed after the gelation transformation and before the end of cooling and is only related to the increase in the degree of curing reaction, and the control purpose can be achieved by adjusting the isothermal temperature; the thermal strain is affected by temperature, the volume fraction of component materials and the coefficient of thermal expansion, and the control purpose can be achieved by adjusting the pressure process and the isothermal temperature; the residual strain is the sum of the consolidation strain, curing shrinkage and thermal strain. Therefore, the residual strain can be controlled throughout the forming stage.

[0080] Step 4: Multi-parameter comparison and optimization of the forming process

[0081] As shown in Table 3 below, the multi-parameter comparison of the forming process, based on the process adjustable range of the curing behavior, designs pressure, isothermal temperature, and isothermal time as the process parameter control indicators. The optical fiber sensor 1 is used, and the fixing method is embedded. The commercial coating is stripped off, the sensor is applied with 50 tensile microstrains, and the pigtail is in a free placement state to monitor the whole process of composite material forming in real time as a high-characteristic response sensing setting. The porosity, consolidation strain, curing shrinkage, thermal strain, and residual strain are set as the structural quality indicators. Composite material specimens under different forming processes are prepared, and the flexural strength and interlaminar shear strength are set as the performance indicators.

[0082] Under different process parameter control indicators, the structural quality indicators and performance indicators are as shown in Table 3, the multi-parameter comparison of the forming process (Example 1).

[0083] Comparative Example 2

[0084] Step 1: The criterion for gelation transformation in the physical and chemical characteristics of the resin matrix curing process is selected as the curing degree when the shear storage modulus is equal to the loss modulus, and the others are the same as in Example 1. After testing, the degree of curing reaction of the gelation transformation is 0.68, which does not meet the standard of the balance of the competition between polymerization and diffusion effects.

[0085] Comparative Example 3

[0086] Step 1: In the physical and chemical properties during the curing process of the resin matrix, the gelation transition criterion is selected as the degree of cure at the maximum value of the second derivative of the complex viscosity, and the others are the same as in Example 1. After testing, the degree of cure at the gelation transition is 0.86, which does not meet the standard of the competition between polymerization and diffusion effects reaching equilibrium.

[0087] Comparative Example 4

[0088] Step 1: In the physical and chemical properties during the curing process of the resin matrix, the gelation transition criterion is selected as the degree of cure at the maximum value of the first derivative of the shear storage modulus, and the others are the same as in Example 1. After testing, the degree of cure at the gelation transition is 0.65, which does not meet the standard of the competition between polymerization and diffusion effects reaching equilibrium.

[0089] Example 5

[0090] The resin matrix uses cyanate resin, and the fiber component uses carbon fiber.

[0091] Step 1: Physical and chemical properties during the curing process of the resin matrix

[0092] Under the isothermal test of a differential scanning calorimeter, the equilibrium between polymerization and diffusion effects occurs after the maximum reaction rate and before the obvious decline, and the corresponding curing reaction interval is 0.42 - 0.60.

[0093] Perform a variance significance statistic on the enthalpy values under multi-sample tests, set 0.05 as the difference significance threshold, and select 90°C, 120°C, and 150°C as the isothermal test processes based on the same variance significance letter marking. Taking the competition between polymerization and diffusion effects reaching equilibrium as the standard, screen the degree of cure at which the shear storage modulus and loss modulus are equal as the best gelation transition criterion, corresponding to a curing reaction degree of 0.55, and fit the gelation transition curve.

[0094] The fully uncured glass transition temperature T of the resin matrix g0 =-46°C, and the fully cured glass transition temperature T g∞ =160°C. The fitting empirical formula for the glass transition temperature (T g ) is shown in the following formula (4):

[0095]

[0096] α is the degree of cure, and T g is the glass transition temperature.

[0097] Taking the glass transition occurring in the time interval dominated by the reaction diffusion effect (α > 0.60) as the standard, screen the degree of cure at which the evolution trend of the shear storage modulus in the rheological test tends to be stable as the best glass transition criterion, corresponding to a curing reaction degree α = 0.92, and fit the glass transition curve.

[0098] Aiming at the complete curing of the resin system, the durations of the resin matrix in the liquid state, sol / gel rubber state, and sol / gel glass state at 150 °C are 20 min, 45 min, and 10 min respectively, and the time required for the curing reaction degree to reach the maximum is at least 75 min. Therefore, 150 °C / 120 min is designed as the single-temperature step forming process.

[0099] The differential scanning calorimetry is used to test the glass transition temperature of the cured resin matrix. After the glass transition temperature verification, under the 150 °C / 120 min forming process, the resin matrix reaches complete curing, and the glass transition temperature reaches the maximum of 160 °C, which is consistent with the glass transition temperature (T g∞ ) in the completely cured state.

[0100] Step 2: In-situ monitoring of the whole process of composite material forming

[0101] The fixing method of the fiber optic sensor is embedded. The commercial coating of the fiber optic sensor 1 is stripped, a 100 tensile microstrain is applied to the sensor, and the pigtail is in a free placement state; the commercial coating of the fiber optic sensor 2 is stripped, a 100 tensile microstrain is applied to the sensor, and the pigtail is in a state of being fixed by hot melt adhesive.

[0102] The hot pressing process is used for the forming of the composite material, and the process parameters are set as follows:

[0103] (1) Pretreatment stage: Constant pressure treatment at 500 psi / 30 min and heating at 10 °C / min;

[0104] (2) Constant temperature stage: Constant temperature curing at 150 °C / 120 min;

[0105] (3) Cooling stage: Natural cooling.

[0106] The sudden increase points, sudden decrease points, platforms, and inflection points of the sensing signal generated with the implementation of the process, the degree of curing reaction evolution, and the phase transition are selected as the characteristic response points. The disturbance strain is ±1.5 με, the characteristic response points are screened, and the characteristic response amplitudes method is used to compare the characteristic responses of the fiber optic sensor to extrusion seepage, resin volume expansion and flow, consolidation strain, chemical shrinkage, gelation transition, glass transition, complete curing transition, thermal strain, and residual strain. The characteristic response error takes the disturbance strain as the reference of ±1.5 με.

[0107] During the entire process of composite material forming, the sensing signals of the fiber optic sensor 1 produce obvious characteristic responses to each curing behavior, and the monitored residual strain is 186 με. The fiber optic sensor 2 has a weak characteristic response to consolidation strain and glass transition. Therefore, selecting the fiber optic sensor 1 as the fiber optic sensor with high characteristic response sensing settings can accurately, comprehensively and effectively guide the division of the process adjustable range of various curing behaviors.

[0108] Step 3: Division of process adjustable range

[0109] Keep consistent with Example 1.

[0110] Step 4: Multi-parameter comparison and optimization of forming process

[0111] Based on the process adjustable range of the curing behavior, the constant temperature and the constant temperature time are designed as the process parameter control indicators. Using the fiber optic sensor 1, the fixing method is embedded, the commercial coating is removed, the sensor is applied with 100 tensile microstrains, and the pigtail is in a free placement state to monitor the entire process of composite material forming in real time as a high characteristic response sensing setting. The porosity and residual strain are set as the structural quality indicators, and the interlaminar shear strength is set as the performance indicator.

[0112] Under different process parameter control indicators, the structural quality indicators and performance indicators are as shown in Table 4, the multi-parameter comparison of the forming process (Example 5).

[0113] The multi-parameter comparison of the forming process of each example is shown in Tables 3 and 4 below. From the process control parameters, structural quality and performance indicator data in Tables 3 and 4, it can be seen that the in-situ / non-in-situ testing methods and process parameter design described in this example have the advantages of high accuracy and high efficiency, and are universal for the design of composite material forming processes under different types of resin systems. In addition, the correlation mechanism and influence mechanism between the curing behavior and process parameters under each process adjustable range are verified, which greatly shortens the optimization cycle of the forming process of high dimensional accuracy and high performance composites and improves the R & D efficiency of composite material forming processes.

[0114] Table 1 Analysis of characteristic response of sensing signals

[0115]

[0116] Table 2 Process adjustable range of each curing behavior

[0117]

[0118] Table 3 Multi-parameter comparison of forming process (Example 1)

[0119]

[0120] Table 4 Multi-parameter comparison of forming process (Example 5)

[0121]

Claims

1. A precise and efficient design strategy for a composite material forming process, characterized in that, It includes the following steps: (1) Curing physical and chemical property analysis: Conduct the analysis of the curing reaction characteristics, gelation transition analysis, and glass transition analysis of the resin matrix to form a high-precision temperature-time-phase transition curing diagram. Based on the time distribution of each phase state, formulate a single-temperature step forming process, and verify the curing effect of the resin matrix under the single-temperature step forming process by combining with the glass transition temperature analysis; (2) In-situ monitoring of the entire forming process: Based on the fiber optic sensors with high characteristic response settings, in-situ monitor the entire forming process of the composite material, conduct the characteristic response analysis of the sensing signals, and verify the sensitivity and accuracy of the in-situ monitoring by combining with the fitting of the monitoring sensitivity coefficient and the disturbance strain analysis; (3) Division of the process adjustable range of the curing behavior: Combine the temperature-time-phase transition curing diagram of the resin matrix and the characteristic response analysis of the sensing signals, comprehensively analyze the induction mechanism of the curing behavior of the composite material in each phase state interval, and accurately divide the process adjustable range of various curing behaviors; (4) Comparison and optimization of multiple forming process parameters: Based on the process adjustable range of the curing behavior, design the process parameter control indexes, prepare the composite material specimens, design the structure quality and performance indexes, conduct the comparison and optimization of multiple parameters, and screen the forming process parameters with high dimensional accuracy and high performance.

2. The precise and efficient design strategy of a composite material forming process according to claim 1, characterized in that The curing reaction characteristic analysis includes, but is not limited to, the evolution law of the isothermal curing reaction degree, the analysis of the maximum reaction degree, the analysis of the reaction autocatalytic effect, and the competition law between the polymerization and diffusion effects.

3. The precise and efficient design strategy for a composite material forming process according to claim 1, characterized in that, The gelation transition analysis is carried out as follows: (1) Conduct a variance significance statistic on the isothermal curing reaction enthalpy values under multiple sample tests. Taking 0.05 as the difference significance threshold, screen the isothermal test temperature and time conditions based on the standard that the same variance significance letters or asterisks are marked; (2) Conduct an isothermal curing rheological test. Taking the balance of the competition between the polymerization and diffusion effects of the curing reaction as the verification standard, screen the best gelation transition criterion, and determine the gelation transition time or the gelation transition curing reaction degree; (3) Conduct a fitting analysis on the isothermal test temperature and the gelation transition time to obtain the gelation transition curve of the resin matrix; (4) The gelation transition criteria include, but are not limited to, the time or curing degree when the shear storage modulus is equal to the loss modulus, the time or curing degree at the minimum value of the complex viscosity, the time or curing degree at the maximum value of the second derivative of the complex viscosity, and the time or curing degree at the maximum value of the first derivative of the shear storage modulus.

4. The precise and efficient design strategy for a composite material forming process according to claim 1, characterized in that, The glass transition analysis is carried out as follows: (1) Perform non-isothermal tests on the resin matrix in a completely uncured and cured state, and obtain the glass transition temperature (T g0 ) in the completely uncured state and the glass transition temperature (T g∞ ) in the completely cured state by extrapolation or the average value method; (2) Test the glass transition temperature (T g ) of the resin matrix with different degrees of curing reaction (α) at each isothermal temperature, and perform fitting analysis based on the empirical formula of the glass transition temperature. The empirical formula for calculating the glass transition temperature is as follows: α is the degree of curing reaction, T g is the glass transition temperature, T g0 is the glass transition temperature in the completely uncured state, T g∞ is the glass transition temperature in the completely cured state, λ is the structure parameter, and the value is between 0 and 1; (3) Combine the isothermal and non-isothermal curing reaction degree analysis. Taking the glass transition occurring in the time interval dominated by the reaction diffusion effect as the verification standard, screen the glass transition criterion, and determine the glass transition time or the glass transition curing reaction degree; (4) Conduct a fitting analysis on the isothermal test temperature and the glass transition time to obtain the glass transition curve of the resin matrix; (5) The glass transition criteria include, but are not limited to, the time or curing degree when the glass transition temperature is equal to the isothermal test temperature, the time or curing degree when the evolution trend of the curing reaction degree tends to be stable, and the time or curing degree when the evolution trend of the shear storage modulus in the rheological test tends to be stable.

5. According to the precise and efficient design strategy of a composite material forming process described in claim 1, the formulation features of the single temperature gradient forming process are as follows: (1) The resin matrix reaches the maximum reaction degree at the constant temperature time; (2) The resin matrix reaches the maximum glass transition temperature at the constant temperature time; (3) The optimal times for the resin matrix to be in the liquid state, sol / gel rubber state, sol / gel glass state, and gel glass state are within 5 min to 180 min.

6. The precise and efficient design strategy for a composite material forming process according to claim 1, characterized in that, The high-characteristic response sensing setup includes, but is not limited to, sensor fixing methods, pigtail processing techniques, and sensor encapsulation processes; the specific steps are as follows: (1) Sensor fixing methods, including but not limited to embedded, surface-mounted, and bridging types; (2) Pigtail processing techniques, including but not limited to not applying tensile strain to the sensor, leaving the pigtail freely placed, applying 0 - 500 tensile microstrains to the sensor, leaving the pigtail freely placed, applying 0 - 500 tensile microstrains to the sensor, fixing the pigtail using hot melt adhesive, not applying tensile strain to the sensor, and fixing the pigtail using hot melt adhesive; (3) Sensor encapsulation processes, including but not limited to no coating, using a polypropylene coating with a thickness of 0 - 50 μm, using a polyimide coating with a thickness of 0 - 50 μm, and using a metal coating with a thickness of 0 - 50 μm.

7. The precise and efficient design strategy for a composite material forming process according to claim 1, characterized in that, The analysis of the characteristic response of the sensing signal is as follows: (1) Selection of characteristic response points, including sudden increase points, sudden decrease points, plateaus, and inflection points generated by the sensing signal with the implementation of the process, the evolution of the curing reaction degree, and the phase transition; (2) Screening of characteristic response points, including screening the sudden increase points, sudden decrease points, plateaus, and inflection points generated by the implementation of the process, the evolution of the curing reaction degree, and the phase transition with the disturbance strain range as the signal noise range; (3) Comparative evaluation of characteristic response, including the characteristic response amplitude comparison method, where the signal values of characteristic response points a and b are subtracted to evaluate the characteristic response of the curing behavior in this stage; (4) Comparative evaluation of characteristic response, including the rate comparison method, where the signal values between characteristic response points a and b are linearly fitted to evaluate the characteristic response of the curing behavior in this stage; (5) Feature response error evaluation, including fitting R with the sensitivity coefficients monitored by temperature and strain 2 or as a reference, with the disturbance strain range as a reference, where R 2 is the fitting coefficient of determination, is the adjusted coefficient of determination after fitting; (6) The curing behavior includes, but is not limited to, pressure extrusion seepage, vacuum extrusion seepage, gelation transition, glass transition, complete curing transition, resin flow, resin volume expansion, consolidation strain, chemical shrinkage, thermal strain, and unstable strain caused by the mismatch of the thermal expansion coefficients of the resin and fibers.

8. The precise and efficient design strategy for a composite material forming process according to claim 1, characterized in that The comparison of multiple parameters of the forming process is as follows: (1) Process parameter control indicators include, but are not limited to, pressure, constant temperature, and constant temperature time; (2) Structural quality indicators include, but are not limited to, porosity, consolidation strain, curing shrinkage, thermal strain, and residual strain; (3) Performance indicators include, but are not limited to, flexural strength and interlaminar shear strength.

9. The precise and efficient design strategy of a composite material forming process according to claim 1, characterized in that, The resin matrix includes, but is not limited to, epoxy resin, phenolic resin, unsaturated polyester, bismaleimide resin, melamine resin, and cyanate resin.

10. The precise and efficient design strategy of a composite material forming process according to claim 1, characterized in that, The fiber components of the composite material include, but are not limited to, carbon fiber, glass fiber, basalt fiber, polyamide fiber, silicon carbide fiber, polyester fiber, acrylic fiber, polytetrafluoroethylene fiber, and polyphenylene sulfide fiber.

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