Method and system for monitoring parameters in composite material preparation process based on piezoelectric sensing

Abstract

The invention provides a parameter monitoring method and system in a composite material preparation process based on piezoelectric sensing, and belongs to the field of composite material detection, and the parameter monitoring method comprises the following steps: when resin flows in a fiber preform of a composite material, continuously collecting resin diversion ultrasonic guided wave signals of the composite material through a piezoelectric sensing network, the piezoelectric sensing network is embedded in the fiber preform in advance, and is constructed by integrating a plurality of piezoelectric sensors on a flexible carrying layer; and determining a transmitting-receiving mode differential signal according to the transmitting-receiving mode signal and a predetermined resin diversion baseline data signal, determining the position and time of the resin in the fiber preform according to the amplitude and the phase, and determining a two-dimensional resin flow front according to the position and the time. The method overcomes the defect that a traditional on-line monitoring method can only realize point, line and local three-dimensional resin flow front monitoring, realizes visualization of an internal flow field of the fiber preform, and improves monitoring robustness in a composite material preparation process.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of composite material detection, and particularly relates to a parameter monitoring method and system for composite material preparation based on piezoelectric sensing. BACKGROUND

[0002] The liquid molding process of composite materials is one of the most commonly used methods for preparing fiber-reinforced resin-based composite materials. With the advantages of strong adaptability to complex structures, low cost and near-net shaping, it has become the core process for manufacturing high-performance components in the fields of aerospace, high-end equipment and the like. However, in the liquid molding process of composite materials, the flow and infiltration behavior of resin in the fiber preform directly determines the density, mechanical properties and service reliability of the composite material, so the real-time monitoring of multiple parameters in the whole process of the liquid molding of composite materials is the core requirement to ensure product quality.

[0003] In view of the above requirements, the existing point-type sensing technologies such as resistance sensors and dielectric sensors can only realize monitoring at a single point or in a linear region. The resistance sensor judges the resin infiltration through resistance mutation, but is limited by electrode arrangement and can only monitor a local area, and has poor adaptability to complex curvature components. The dielectric sensor monitors the degree of curing through the change of dielectric constant, but cannot reflect the position of the resin flow front. In summary, the existing monitoring technologies cannot accurately reflect the state of the resin flow front when facing complex curvature components, and have poor robustness. SUMMARY

[0004] In order to solve the problems of single measurement parameter, small sensing range and poor robustness when facing complex curvature components existing in the existing monitoring technologies, the application provides a parameter monitoring method and system for composite material preparation based on piezoelectric sensing.

[0005] In order to achieve the above purpose, the application provides the following technical scheme: The parameter monitoring for composite material preparation based on piezoelectric sensing comprises: When the resin flows in the fiber preform of the composite material, the piezoelectric sensing network continuously collects the resin flow ultrasonic guided wave signal of the composite material, wherein the piezoelectric sensing network is pre-embedded in the fiber preform and is constructed by integrating a plurality of piezoelectric sensors on a flexible carrier layer, the piezoelectric sensing network comprises a plurality of groups of piezoelectric sensors serving as ultrasonic exciters and receivers, and the piezoelectric sensors serving as receivers are used to receive the resin flow ultrasonic guided wave signal emitted and returned by the piezoelectric sensors serving as ultrasonic exciters; The difference signal is determined according to the resin flow ultrasonic guided wave signal and the resin flow baseline data signal pre-determined by the piezoelectric sensing network, the two-dimensional plane position and time of the resin in the fiber preform are determined according to the amplitude and phase of the difference signal, and the two-dimensional resin flow front of the composite material is determined according to the two-dimensional plane position and time.

[0006] Optionally, the parameter monitoring method for composite material preparation based on piezoelectric sensing provided by the present invention further includes: Multiple piezoelectric sensors are mounted on a flexible mounting layer to obtain a piezoelectric sensing network; When a fiber preform is prepared by stacking multiple layers of dry carbon fiber cloth, a piezoelectric sensing network is embedded in the fiber preform to obtain a piezoelectric sensing network pre-embedded in the fiber preform.

[0007] Optionally, the composite material is placed in a mold, and the piezoelectric sensing network also includes a piezoelectric sensor fixed to the back of the mold for acquiring spontaneous and spontaneously received mode signals in the resin-conducting ultrasonic guided wave signal. The parameter monitoring method for composite material preparation based on piezoelectric sensing provided by the present invention further includes: The spontaneous recovery mode differential signal is determined based on the spontaneous recovery mode signal and the resin flow baseline data signal; Calculate the pulse echo signal energy amplitude of the differential signal in the self-transmitting and self-receiving mode, and determine the position of the resin in the thickness direction within the fiber preform based on the pulse echo signal energy amplitude. The three-dimensional resin flow front of the composite material is determined by the two-dimensional resin flow front and the position in the thickness direction.

[0008] Optionally, in the parameter monitoring method for composite material preparation based on piezoelectric sensing provided by the present invention, each pair of piezoelectric sensors, which serve as ultrasonic exciters and receivers, constitutes a generator and receiver for pulse echo signals. Each piezoelectric sensor, used to collect the spontaneously generated and received mode signals in the ultrasonic guided wave signals of resin flow, simultaneously serves as an exciter and receiver for ultrasonic guided wave signals.

[0009] Optionally, the parameter monitoring method for composite material preparation based on piezoelectric sensing provided by the present invention further includes: When the composite material is cured and molded, the cross-linking curing ultrasonic guided wave signal of the composite material is continuously collected through a piezoelectric sensing network; The degree of curing of the composite material is determined based on the amplitude of the cross-linking curing ultrasonic guided wave signal and the curing baseline data signal, wherein the curing baseline data is the resin guiding ultrasonic guided wave signal collected at the end of resin guiding. The loss modulus of the composite material was determined based on the energy of the cross-linking curing ultrasonic guided wave signal and the curing baseline data.

[0010] Optionally, the parameter monitoring method for composite material preparation based on piezoelectric sensing provided by the present invention further includes: The cross-linking curing differential signal is determined based on the cross-linking curing ultrasonic guided wave signal and the curing baseline data signal; The amplitude integral curve of the ultrasonic guided wave signal is obtained by integrating the amplitude of the cross-linked curing differential signal. The degree of curing of the composite material is determined based on the amplitude integral curve of the ultrasonic guided wave signal.

[0011] Optionally, the parameter monitoring method for composite material preparation based on piezoelectric sensing provided by the present invention further includes: The energy change index is calculated based on the energy characteristic value of the cross-linking curing differential signal; The loss modulus of the composite material is determined based on the energy change index.

[0012] Optionally, in the parameter monitoring method for composite material preparation based on piezoelectric sensing provided by the present invention, the piezoelectric sensor is a ceramic piezoelectric sensor with a radius of 2-4 mm and a thickness of 0.2-0.33 mm.

[0013] Optionally, in the parameter monitoring method for composite material preparation based on piezoelectric sensing provided by the present invention, the flexible mounting layer is an insulating carrier film layer, and the thickness of the insulating carrier film layer is less than or equal to 100 μm.

[0014] This invention also provides a parameter monitoring system for the composite material preparation process based on piezoelectric sensing, comprising: The signal acquisition module is used to continuously acquire the resin-conducting ultrasonic wave signal of the composite material through a piezoelectric sensing network when the resin flows in the fiber preform of the composite material. The piezoelectric sensing network is pre-embedded in the fiber preform and is constructed by integrating multiple piezoelectric sensors on a flexible mounting layer. The piezoelectric sensing network includes multiple sets of piezoelectric sensors that serve as ultrasonic exciters and receivers. The piezoelectric sensors that serve as receivers are used to receive the resin-conducting ultrasonic wave signal emitted and returned by the piezoelectric sensors that serve as ultrasonic exciters. The flow front construction module is used to determine the differential signal based on the resin guiding ultrasonic wave signal and the resin guiding baseline data signal pre-determined by the piezoelectric sensing network, determine the two-dimensional planar position and time of the resin in the fiber preform based on the amplitude and phase of the differential signal, and determine the two-dimensional resin flow front of the composite material based on the two-dimensional planar position and time.

[0015] The parameter monitoring method, system, computer equipment, and medium based on piezoelectric sensing provided by this invention have the following beneficial effects: The composite material performance monitoring method provided by this invention utilizes the advantages of ultrasonic guided waves, such as long propagation distance and sensitivity to structural discontinuities. Multiple piezoelectric sensors actively emit ultrasonic guided waves and combine them with baseline data to determine differential signals. Based on the amplitude and phase of the differential signals, the specific position of the resin in the two-dimensional plane within the fiber preform is determined, thereby identifying the two-dimensional resin flow front. A pre-embedded flexible piezoelectric sensing network forms a sensing unit array covering the key monitoring area. The ultrasonic guided wave signal acquired by each excitation-reception path contains overall information about the medium state along its propagation path. The spatial distribution of the resin's wetting state in the two-dimensional plane can be inverted through the amplitude and phase changes of the differential signals along multiple paths. This enables quantitative and visual monitoring of the flow front morphology, position, and propagation velocity, avoiding the shortcomings of existing technologies where isolated, discrete point sensor interpolation is insufficient to capture complete flow field information of the resin within the fiber preform plane. Furthermore, since the present invention pre-embeds the flexible piezoelectric sensing network into the fiber preform of the composite material, it ensures the fit between the piezoelectric sensing network and the component. Even when dealing with complex curved components, it can still visualize the internal flow field of the fiber preform, ensuring the accuracy and robustness of parameter monitoring.

[0016] Furthermore, the multiple piezoelectric sensors integrated on the flexible mounting layer in this invention form a flexible piezoelectric sensing network. During the compaction of the fiber preform, this network can deform in tandem with the preform without significantly affecting resin flow and cross-linking molding. Simultaneously, it eliminates the influence of sensor leads on the composite material's structural properties, thereby reducing the impact of sensor embedding on the composite material structure. Moreover, because the flexible mounting layer is thin and flexible, it can deform with the structure without causing breakage or failure, significantly improving the stability of the sensing network and extending the sensor's lifespan. Attached Figure Description

[0017] To more clearly illustrate the embodiments and design schemes of the present invention, the accompanying drawings required for this embodiment will be briefly described below. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A schematic diagram of a parameter monitoring method for composite material preparation based on piezoelectric sensing provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the piezoelectric sensing network interlayer provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the connection of the composite material structure liquid forming piezoelectric sensing monitoring system provided in an embodiment of the present invention; Figure 4A schematic diagram of the arrangement of a piezoelectric sensor based on pulse echo provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the piezoelectric sensor network-based monitoring of the liquid forming process of composite materials, provided in an embodiment of the present invention. Figure 6 This is a schematic diagram of the piezoelectric sensing network and composite material structure after co-curing, as provided in an embodiment of the present invention. Detailed Implementation

[0019] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0020] Existing resistive sensors and dielectric sensors are difficult to effectively reflect the position of the resin flow front, while infrared thermal imagers can capture the temperature field changes of resin flow, but they are difficult to quantify the kinetic parameters of the curing reaction such as gel time and degree of curing.

[0021] To address the shortcomings of existing sensing and monitoring technologies in real-time monitoring of multiple parameters throughout the entire liquid molding process of composite materials—namely, limited measurement parameters, small sensing range, and poor adaptability to complex curved components—this invention proposes a full-field, multi-parameter online monitoring technology for the liquid molding process of composite materials. Based on the propagation characteristics of ultrasonic guided waves and the distributed arrangement of a flexible sensor network, a multi-parameter monitoring of the composite material structure is achieved through an array of sensors. Based on the amplitude, phase, and energy characteristics of ultrasonic signals, the technology simultaneously reflects the changing trends of resin flow front, degree of cure, and loss modulus parameters, overcoming the limitations of traditional single-parameter, small-range monitoring. Using a polyimide film as the piezoelectric sensor mounting layer significantly reduces interference to the liquid molding process of the composite material. The sensors can operate stably at 250°C, making them suitable for high-temperature resin systems and complex curved surface components. After co-curing with the composite material, they enable full life-cycle monitoring from manufacturing to service.

[0022] Example 1 Taking the vacuum-assisted resin infusion process of fiber-reinforced resin matrix composites as an example, this invention provides a parameter monitoring method based on piezoelectric sensing during the composite material preparation process, specifically as follows: Figure 1 As shown, it includes the following steps: Step 11: Mount multiple piezoelectric sensors on a flexible mounting layer to obtain a piezoelectric sensing network. The piezoelectric sensors are ceramic piezoelectric sensors with a radius of 2-4 mm and a thickness of 0.2-0.33 mm; the flexible mounting layer is an insulating carrier film with a thickness of less than or equal to 100 μm.

[0023] Specifically, firstly, based on the location and size of the piezoelectric sensor, a flexible mounting layer is designed using micro-nano electronic integrated circuit technology. The piezoelectric sensor is then mounted on this flexible layer to form a multifunctional intelligent piezoelectric sensing network, serving as a sandwich layer within the fiber preform. For example, the piezoelectric sensing network might look like this... Figure 2 As shown, the device includes piezoelectric sensors 5, printed circuits 6, and a flexible mounting layer 7. The nine piezoelectric sensors 5 are arranged in a rectangular grid layout. Each sensor can be used as both an exciter and a receiver. The longitudinal spacing is 90 mm and the lateral spacing is 150 mm. Preferably, the piezoelectric sensors 5 are lead zirconate titanate piezoelectric sensors with a radius of 3 mm and a thickness of 0.2 mm.

[0024] The material of the flexible mounting layer 7 is preferably a polyimide Kapton film with a thickness of less than or equal to 0.1 mm. Its ability to operate normally at a temperature of 473 K and its insulation voltage of 200 V ensure the normal operation of the piezoelectric sensor network under high temperature, high pressure and high load conditions.

[0025] And, as Figure 3 As shown, the piezoelectric sensor 5 can be embedded in different positions of different fiber layers in the fiber preform 4 to monitor the state information of the composite material structure. For example, during the liquid molding process of the composite material, the piezoelectric sensor 5 mounted on the flexible mounting layer 7 passes through the reserved circular hole 8 in the high-temperature chamber 1 and is embedded in different positions of different fiber layups in the fiber preform 4, and then the reserved circular hole 8 is sealed with high-temperature sealant 3.

[0026] The excitation and receiving ends of the piezoelectric sensor 5 are connected to the monitoring system of the ultrasonic guided wave basic experimental platform. The monitoring system of the ultrasonic guided wave basic experimental platform includes an ultrasonic guided wave excitation-receiver 9 and a host computer software 10. The guided wave excitation and receiving system in the ultrasonic guided wave excitation-receiver 9 excites and receives ultrasonic guided waves through a one-to-one transmission and reception working mode. The signal power amplification system amplifies the collected ultrasonic guided wave signal, and the host computer software 10 displays the amplified ultrasonic guided wave signal, thereby realizing the acquisition, storage and display of ultrasonic guided wave signals throughout the entire process of composite material liquid molding, so as to monitor the three-dimensional resin flow front, dry spot defects, degree of curing and loss modulus in the whole field.

[0027] Step 12: When multilayer dry carbon fiber cloth is stacked layer by layer to prepare fiber preform, a piezoelectric sensing network is embedded in the fiber preform to obtain a piezoelectric sensing network pre-embedded in the fiber preform.

[0028] Specifically, after the piezoelectric sensing network is constructed, a release agent is applied to an aluminum mold, and then several layers of dry carbon fiber cloth of specific dimensions are stacked and laid. The flexible, multifunctional piezoelectric sensing network is embedded in specific layers of the fiber preform and adhered to the bottom of the aluminum mold. Interface leads are then used to connect to the ultrasonic guided wave and pulse echo signal excitation and reception system. The mold can be a 6061 aluminum mold with dimensions of 600mm × 600mm × 2mm and a thickness of 2mm to facilitate ultrasonic guided wave propagation.

[0029] For example, such as Figure 3 As shown, high-temperature sealing tape 3 is pasted around the mold 2. Release cloth 16, flow guide net 17, and vacuum bag 15 are then laid sequentially on the fiber preform 4. The suction pipe is then connected to the vacuum pump 11 via the resin collector 12 to prevent resin 14 from being drawn into the vacuum pump 11 and damaging it. Uniform pressure is applied using the vacuum pump 11 to ensure the preform and piezoelectric sensing network are tightly compacted. The piezoelectric sensing network is firmly adhered to the back of the mold using Loctite EA9394 adhesive. Afterwards, the mold 2, fiber preform 4, etc., are placed in the high-temperature chamber 1. The piezoelectric sensor 5 is connected to the ultrasonic guided wave exciter-receiver 9 through the pre-drilled circular hole 8 in the high-temperature chamber 1.

[0030] Among them, the piezoelectric sensor based on pulse echo is arranged as follows: Figure 4 As shown, 18 piezoelectric sensors were firmly attached to the back of an aluminum mold using Loctite EA9394 adhesive. Each pair of sensors formed a generator and receiver for pulse echo signals, with a center-to-center distance of 9 mm.

[0031] Step 13: When the resin flows in the fiber preform of the composite material, the resin-conducting ultrasonic wave signal of the composite material is continuously collected by the piezoelectric sensing network. The piezoelectric sensing network is pre-embedded in the fiber preform and is constructed by integrating multiple piezoelectric sensors on a flexible mounting layer. The piezoelectric sensing network includes multiple sets of piezoelectric sensors that serve as ultrasonic exciters and receivers. The piezoelectric sensors that serve as receivers are used to receive the resin-conducting ultrasonic wave signals emitted and returned by the piezoelectric sensors that serve as ultrasonic exciters.

[0032] Specifically, after the fiber preform is constructed, the ultrasonic guided waves are excited and received using two working modes of piezoelectric sensors: one-to-one transmission and one-to-reception and self-transmission and self-reception. A sensing path that can cover the entire preform is set, and the optimal frequency of each sensing path is determined by frequency scanning. The ultrasonic guided wave data recorded at the optimal frequency at the initial moment is used as the resin guiding baseline data signal.

[0033] After that, as Figure 5As shown, the door of the high-temperature chamber 1 is kept open, and the vacuum pump 11 and the resin control valve are turned on, so that the liquid resin 14 passes through the injection seat 13 at a uniform speed at room temperature to fill the compacted fiber preform. When the fiber preform is completely impregnated by the resin 14, the resin control valve is turned off. During the resin filling process, ultrasonic guided wave signals and pulse echo signals are collected at fixed time intervals.

[0034] Step 14: Determine the differential signal based on the resin guiding ultrasonic wave signal and the resin guiding baseline data signal predetermined by the piezoelectric sensing network. Determine the two-dimensional planar position and time of the resin in the fiber preform based on the amplitude and phase of the differential signal. Determine the two-dimensional resin flow front of the composite material based on the two-dimensional planar position and time.

[0035] The composite material is placed in the mold, and the piezoelectric sensing network also includes a piezoelectric sensor fixed to the back of the mold for acquiring the spontaneous and spontaneous mode signals in the resin-guided ultrasonic wave signal. Step 14 also includes: Step 141: Calculate the pulse echo signal energy amplitude of the self-generated and self-received differential signal, and determine the position of the resin in the thickness direction within the fiber preform based on the pulse echo signal energy amplitude. Step 142: Determine the three-dimensional resin flow front of the composite material based on the two-dimensional resin flow front and the position in the thickness direction. In this process, each pair of piezoelectric sensors, serving as both ultrasonic exciters and receivers, constitutes a pulse echo signal generator and receiver. Each piezoelectric sensor, used to acquire the spontaneously generated and received mode signals in the ultrasonic guided wave signal of the resin flow, simultaneously acts as both an exciter and receiver for the ultrasonic guided wave signal.

[0036] Specifically, based on the leakage Lamb wave theory, when the resin impregnates the fiber preform and covers the sensing path—that is, when the resin flows through the ultrasonic guided wave sensing range—the ultrasonic guided wave signal leaks into the resin through the adjacent solid-liquid interface, causing changes in the ultrasonic guided wave signal. For example, the amplitude of the ultrasonic guided wave will decrease, and the phase will shift. Since ultrasonic guided wave signals have characteristics such as long propagation distance and sensitivity to structural discontinuities, they can be used to sense the resin flow front over a large area. Therefore, ultrasonic guided waves generated by the piezoelectric sensor in a transmit-receive mode can monitor the resin wetting in a two-dimensional plane; pulse echoes generated by the piezoelectric sensor in a self-transmit and self-receive mode can monitor the resin flow front in the thickness direction; combining the transmit-receive and self-receive modes of the piezoelectric sensor can achieve full-field monitoring of the three-dimensional resin flow front in both the two-dimensional plane and the thickness direction.

[0037] Specifically, for the ultrasonic guided wave signal collected by the piezoelectric sensor in the fiber preform interlayer, Hilbert transform is performed to extract the amplitude and phase characteristics of the ultrasonic guided wave signal, and a quantitative relationship between the amplitude and phase and the resin flow front is constructed to achieve precise two-dimensional planar positioning of the resin flow front; for the pulse echo signal collected by the piezoelectric sensor bonded to the back of the mold, the relevant energy amplitude at time i is calculated. As shown in formula (1): (1) in, Let be the total signal energy of a certain path at time i. and These are the lower and upper limits of the signal energy value space, respectively. Let k be the signal amplitude corresponding to the kth sampling point. It is the cross-correlation coefficient between time i and the baseline signal. For discrete baseline signals, Let i be the discrete baseline signal value at the k-th sampling point at time i. To discrete the current signal, Let i be the discrete current signal value at the k-th sampling point at time i. and They represent and The mean.

[0038] In summary, by analyzing the amplitude and phase characteristics of ultrasonic guided waves, an "amplitude / phase-resin flow front" curve can be constructed, enabling large-area two-dimensional monitoring of the resin flow front. Similarly, by analyzing the correlation energy amplitude (CEA) of the pulse echo signal, an "amplitude-energy-resin flow front" curve can be constructed, enabling monitoring of resin penetration in the thickness direction. Furthermore, the three-dimensional resin flow front of the composite material can be determined by combining the two-dimensional resin flow front with the analysis of the two-dimensional resin flow front. When the amplitude, phase, and CEA of the ultrasonic guided wave and the pulse echo signal all tend to stabilize, it is considered that the resin has completely impregnated the fiber preform.

[0039] Step 15: When the composite material is cured and formed, the cross-linking curing ultrasonic guided wave signal of the composite material is continuously collected through the piezoelectric sensing network.

[0040] Step 16: Determine the degree of curing of the composite material based on the amplitude of the cross-linking curing ultrasonic guided wave signal and the curing baseline data signal, wherein the curing baseline data is the resin guiding ultrasonic guided wave signal collected at the end of resin guiding.

[0041] The degree of curing of the composite material can be determined through the following steps: Step 161: Determine the cross-linking curing differential signal based on the cross-linking curing ultrasonic guided wave signal and the curing baseline data signal.

[0042] Step 162: Integrate the amplitude of the cross-linked curing differential signal to obtain the amplitude integral curve of the ultrasonic guided wave signal.

[0043] Step 163: Determine the degree of curing of the composite material based on the amplitude integral curve of the ultrasonic guided wave signal.

[0044] Specifically, after the resin filling process is completed, the door of the high-temperature chamber 1 is closed and a heat preservation temperature of 50°C is set. Under this condition, the chamber is kept warm and cured for 6 hours. While waiting for the resin to cure, an ultrasonic guided wave signal is collected every 2 minutes. Since the ultrasonic guided wave signal is closely related to the elastic modulus of the material, the elastic modulus of the composite material structure will change as the curing process proceeds, causing the amplitude of the ultrasonic guided wave signal to change accordingly. The ultrasonic guided wave differential signal is obtained by subtracting the corresponding baseline signal from the current ultrasonic guided wave signal. The amplitude characteristics of the ultrasonic guided wave differential signal are extracted and integrated to form an "amplitude-time" integral curve, which can track the change in curing degree in real time, such as identifying the resin gel point and glass transition point. The integration process is shown in formula (2):

[0045] (2) Where X is the amplitude of the ultrasonic guided wave, and t represents time. This is the starting point of the curing process. Let i be the time point corresponding to time i. Let (i+1) be the time point corresponding to time i, and n be the total number of time points. This is the end point of the curing process. This represents the amplitude of the ultrasonic guided wave at time i. This represents the amplitude of the ultrasonic guided wave at time (i+1). This represents the amplitude of the ultrasonic guided wave at time (i+2). When using ultrasonic guided waves to monitor the resin crosslinking and curing process, the piezoelectric sensor is connected to the signal generator and the acquisition card, serving as both an excitation and a receiver.

[0046] Step 17: Determine the loss modulus of the composite material based on the energy of the cross-linking curing ultrasonic guided wave signal and the curing baseline data.

[0047] The loss modulus of the composite material can be determined through the following steps: Step 171: Calculate the energy change index based on the energy characteristic value of the cross-linking curing differential signal.

[0048] Step 172: Determine the loss modulus of the composite material based on the energy change index.

[0049] Specifically, the loss modulus EVI of the resin can also be characterized and tracked by the energy change index of the ultrasonic guided wave signal, as shown in formula (3): (3) in, and These are the initial and final times of signal truncation, respectively. It is the baseline signal of the i-th sensing path at the initial moment. yes The Hilbert transform result, This is the current signal. Subtract baseline signal The resulting scattered signal yes The result after Hilbert transformation.

[0050] After curing, the composite material structure is removed from the high-temperature chamber 1, the vacuum bag is removed, and the surface of the co-cured product consisting of the piezoelectric sensing network and the composite material is simply processed. At this point, the flexible piezoelectric sensing network has been permanently integrated with the composite material structure, such as... Figure 6 As shown, it can be used for both active and passive monitoring based on ultrasonic guided waves. From resin filling to structural health monitoring, data acquisition and analysis can be completed in a single platform.

[0051] Because this invention directly mounts multiple piezoelectric sensors onto a flexible circuit-printed thin film to form a flexible sensing network, it is easy to operate and possesses characteristics such as corrosion resistance, high temperature resistance, and few leads. It can be directly adhered to the surface of composite material structures or embedded in specific internal layers. Furthermore, since the piezoelectric sensors can actively emit ultrasonic guided waves to monitor the resin flow front, degree of cure, and loss modulus across the entire field, leveraging the advantages of ultrasonic guided waves such as long propagation distance and sensitivity to structural discontinuities, it can be used for three-dimensional resin flow front and degree of cure monitoring across the entire field. This overcomes the limitations of traditional online monitoring methods, which can only achieve point, line, and local three-dimensional resin flow front and degree of cure monitoring, realizing multi-parameter online sensing and global monitoring of the flow front and degree of cure. In addition, the sensor is integrally molded with the composite material and is suitable for high-temperature resin molding such as epoxy resin and bismaleimide resin, ensuring the simplicity and compatibility of parameter monitoring during the preparation of composite materials based on piezoelectric sensing.

[0052] In summary, this invention solves the key problem that single sensing technologies cannot simultaneously acquire multiple parameters, enabling visualization of the internal flow field and curing degree distribution of fiber preforms. The multifunctional piezoelectric sensing network embedded within the composite material transforms it into a smart structure, suitable for full lifecycle health monitoring of composite structure manufacturing, service, and maintenance. By analyzing monitoring data and combining it with models, it provides profound guidance for composite material design and manufacturing processes, improving the safety and reliability of composite structures during their service life. The full-field multi-parameter online monitoring system and method for the liquid molding process of this invention can be extended to full-field monitoring of other composite material molding processes.

[0053] Example 2 This invention also provides a parameter monitoring system for the composite material preparation process based on piezoelectric sensing, comprising: The signal acquisition module is used to continuously acquire the resin-conducting ultrasonic wave signal of the composite material through a piezoelectric sensing network when the resin flows in the fiber preform of the composite material. The piezoelectric sensing network is pre-embedded in the fiber preform and is constructed by integrating multiple piezoelectric sensors on a flexible mounting layer. The piezoelectric sensing network includes multiple sets of piezoelectric sensors that serve as ultrasonic exciters and receivers. The piezoelectric sensors that serve as receivers are used to receive the resin-conducting ultrasonic wave signal emitted and returned by the piezoelectric sensors that serve as ultrasonic exciters. The flow front construction module is used to determine the differential signal based on the resin guiding ultrasonic wave signal and the resin guiding baseline data signal pre-determined by the piezoelectric sensing network, determine the two-dimensional planar position and time of the resin in the fiber preform based on the amplitude and phase of the differential signal, and determine the two-dimensional resin flow front of the composite material based on the two-dimensional planar position and time.

[0054] It should be noted that the above specific embodiments enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. Therefore, although the present invention has been described in detail in this specification and embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention; and all technical solutions and improvements that do not depart from the spirit and scope of the present invention are covered within the protection scope of the present invention patent. No reference numerals in the claims should be construed as limiting the scope of the claims. Any simple variations or equivalent substitutions of technical solutions that can be readily obtained by those skilled in the art within the scope of the technology disclosed in the present invention are within the protection scope of the present invention.

Claims

1. A parameter monitoring method based on piezoelectric sensing during the preparation of composite materials, characterized in that, include: When the resin flows within the fiber preform of the composite material, the resin-conducting ultrasonic guided wave signal of the composite material is continuously acquired through a piezoelectric sensing network. The piezoelectric sensing network is pre-embedded in the fiber preform and is constructed by integrating multiple piezoelectric sensors on a flexible mounting layer. The piezoelectric sensing network includes multiple sets of piezoelectric sensors that serve as ultrasonic exciters and receivers. The piezoelectric sensors that serve as receivers are used to receive the resin-conducting ultrasonic guided wave signal emitted and returned by the piezoelectric sensors that serve as ultrasonic exciters. A differential signal is determined based on the resin-guided ultrasonic wave signal and the resin-guided baseline data signal predetermined by the piezoelectric sensing network. The two-dimensional planar position and time of the resin in the fiber preform are determined based on the amplitude and phase of the differential signal. The two-dimensional resin flow front of the composite material is determined based on the two-dimensional planar position and time.

2. The parameter monitoring method for composite material preparation based on piezoelectric sensing according to claim 1, characterized in that, Before continuously acquiring the resin-conducting ultrasonic guided wave signal of the composite material through the piezoelectric sensing network, the method further includes: Multiple piezoelectric sensors are mounted on the flexible mounting layer to obtain the piezoelectric sensing network; When the fiber preform is prepared by stacking multiple layers of dry carbon fiber cloth, the piezoelectric sensing network is embedded in the fiber preform to obtain the piezoelectric sensing network pre-embedded in the fiber preform.

3. The parameter monitoring method for composite material preparation based on piezoelectric sensing according to claim 1, characterized in that, The composite material is placed in a mold. The piezoelectric sensing network also includes a piezoelectric sensor fixed to the back of the mold for acquiring the spontaneous emission and reception mode signal in the resin-guided ultrasonic wave signal. After determining the two-dimensional resin flow front of the composite material based on the two-dimensional planar position, it further includes: The spontaneous self-collection mode differential signal is determined based on the spontaneous self-collection mode signal and the resin flow baseline data signal; Calculate the pulse echo signal energy amplitude of the self-echo mode differential signal, and determine the position of the resin in the thickness direction within the fiber preform based on the pulse echo signal energy amplitude. The three-dimensional resin flow front of the composite material is determined by the two-dimensional resin flow front and the position in the thickness direction.

4. The parameter monitoring method for composite material preparation based on piezoelectric sensing according to claim 3, characterized in that, In the multiple sets of piezoelectric sensors that serve as ultrasonic exciters and receivers, each pair of sensors constitutes a generator and receiver for pulse echo signals. In the piezoelectric sensors used to acquire the spontaneously generated and received mode signals in the resin-guided ultrasonic wave signals, each sensor simultaneously serves as an exciter and receiver for the ultrasonic wave signals.

5. The parameter monitoring method for composite material preparation based on piezoelectric sensing according to claim 1, characterized in that, After determining the two-dimensional resin flow front of the composite material based on the two-dimensional planar position, the method further includes: When the composite material is cured and molded, the cross-linking curing ultrasonic guided wave signal of the composite material is continuously collected through a piezoelectric sensing network; The degree of curing of the composite material is determined based on the amplitude of the cross-linking curing ultrasonic guided wave signal and the curing baseline data signal, wherein the curing baseline data is the resin guiding ultrasonic guided wave signal collected at the end of resin guiding; The loss modulus of the composite material is determined based on the energy of the cross-linking cured ultrasonic guided wave signal and the curing baseline data.

6. The parameter monitoring method for composite material preparation based on piezoelectric sensing according to claim 5, characterized in that, Determining the degree of curing of the composite material based on the amplitude of the cross-linking curing ultrasonic guided wave signal and the curing baseline data includes: The cross-linking curing differential signal is determined based on the cross-linking curing ultrasonic guided wave signal and the curing baseline data signal; The amplitude integral curve of the ultrasonic guided wave signal is obtained by integrating the amplitude of the cross-linked cured differential signal. The degree of curing of the composite material is determined based on the amplitude integral curve of the ultrasonic guided wave signal.

7. The parameter monitoring method for composite material preparation based on piezoelectric sensing according to claim 6, characterized in that, The loss modulus of the composite material is determined based on the energy of the cross-linked curing ultrasonic guided wave signal and the curing baseline data, including: The energy change index is calculated based on the energy characteristic value of the cross-linking curing differential signal; The loss modulus of the composite material is determined based on the energy change index.

8. The parameter monitoring method for composite material preparation based on piezoelectric sensing according to claim 1, characterized in that, The piezoelectric sensor is a ceramic piezoelectric sensor with a radius of 2-4 mm and a thickness of 0.2-0.33 mm.

9. The parameter monitoring method for composite material preparation based on piezoelectric sensing according to claim 1, characterized in that, The flexible mounting layer is an insulating carrier film layer, and the thickness of the insulating carrier film layer is less than or equal to 100 μm.

10. A parameter monitoring system for composite material preparation based on piezoelectric sensing, characterized in that, include: A signal acquisition module is used to continuously acquire the resin-conducting ultrasonic wave signal of the composite material through a piezoelectric sensing network when the resin flows in the fiber preform of the composite material. The piezoelectric sensing network is pre-embedded in the fiber preform and is constructed by integrating multiple piezoelectric sensors on a flexible mounting layer. The piezoelectric sensing network includes multiple sets of piezoelectric sensors that serve as ultrasonic exciters and receivers. The piezoelectric sensors that serve as receivers are used to receive the resin-conducting ultrasonic wave signal emitted and returned by the piezoelectric sensors that serve as ultrasonic exciters. The flow front construction module is used to determine a differential signal based on the resin-guiding ultrasonic wave signal and the resin-guiding baseline data signal predetermined by the piezoelectric sensing network, determine the two-dimensional planar position and time of the resin in the fiber preform based on the amplitude and phase of the differential signal, and determine the two-dimensional resin flow front of the composite material based on the two-dimensional planar position and time.

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