Continuous fiber 3D printing high bearing self-monitoring deformation ceramic matrix composite truss and preparation method and application thereof

Abstract

The application discloses a continuous fiber 3D printing high-bearing self-monitoring deformation ceramic matrix composite truss and a preparation method and application thereof, and relates to the technical field of additive manufacturing. The truss comprises top chords, bottom chords and built-in units arranged between the top chords and the bottom chords; the built-in units comprise one or more shapes of units selected from a triangle, a trapezoid, a circle and a rhombus; the structure of the truss comprises single-layer or multi-layer trusses; and the constituent material of the truss comprises continuous conductive fibers, pyrolytic carbon interfaces and precursor ceramic matrices. The application deposits a conductive layer on the fiber surface and the matrix crack of the composite material, so that an electrically poor ceramic matrix composite forms an electrically conductive network in the interior, the electrical conductivity of the ceramic matrix composite is improved, the ceramic matrix composite is endowed with piezoresistive performance, and bearing monitoring integration is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of additive manufacturing technology, in particular to a continuous fiber 3D printed high bearing self-monitoring deformation ceramic matrix composite truss and its preparation method and application. BACKGROUND

[0002] The truss structure has excellent physical and mechanical properties such as light weight, high specific stiffness, sound and heat insulation, and impact resistance. When the volume is constant, the bearing capacity of the truss structure is significantly higher than that of the solid layered structure several times, which is an effective way to realize the integration of ultra-light structure / function. At present, the bearing / monitoring integrated truss with high temperature resistance has broad application demand in the fields of aviation, aerospace, navigation, national defense construction, etc. The truss structure is actually served in a harsh environment, and may be subjected to thermal, force, corrosion and other coupling to produce micro-cracks. It is difficult to monitor the existence of micro-cracks in a short period of time, and micro-cracks will be converted into crack sources as the service time increases, which seriously threatens the normal bearing of the truss structure. Therefore, the health state monitoring of the truss structure is very important. The current commonly used monitoring methods include acoustic emission method, ultrasonic method, CT scanning, infrared thermal imaging, and pre-embedded sensing elements, but these methods need to use external detection equipment, and the pre-embedded sensing elements will affect the structural strength, so it is of great significance to develop self-monitoring / high bearing integrated structural materials.

[0003] The prior art discloses a continuous fiber reinforced polymer matrix composite capable of self-monitoring and self-healing, but due to the poor conductivity of the polymer matrix, the detection of the component requires that part of the continuous fibers be connected with the electrode to realize the detection. It is not convenient to monitor the components in service. The composite of continuous fibers and polymer materials is not conducive to improving environmental tolerance, which limits its application in extreme environments. The skilled person in the art uses digital light processing (DLP) technology to prepare a pure SiOC ceramic piezoresistive sensor with good precision and repeatability, and high sensitivity, but the strain monitoring range of this sensor is small, and it is only suitable for small deformation monitoring of precision instruments, and is not sufficient for structural bearing, and cannot realize high bearing monitoring integration. The above methods cannot simultaneously consider high bearing, high temperature resistance, self-monitoring and other characteristics, and it is difficult to realize real-time monitoring of the truss structure during service.

[0004] Continuous fiber ceramic matrix composites have excellent high temperature stability, high temperature creep resistance and oxidation resistance, and can be applied to bearing in extreme environments. The prior art also discloses a ceramic composite forming method of fiber reinforced ceramic precursor 3D printing technology. The composite wire material mixed by the reinforcing fibers and the heated and molten ceramic precursor is printed and formed, which can realize the rapid manufacturing of composite parts with complex structure, greatly reducing the manufacturing cost and production cycle. However, due to the poor conductivity of the precursor ceramic, the application of the material on the sensing element cannot be realized. SUMMARY

[0005] In view of the deficiencies in the background art, the present application provides a continuous fiber 3D printed high load self-monitoring deformation ceramic matrix composite truss and its preparation method and application. On the one hand, the reinforcing fiber has excellent electrical conductivity and mechanical properties, and the ceramic matrix gives the composite truss high temperature resistance; on the other hand, the conductive interface phase network connects the fiber and the surface of the ceramic matrix, the overall electrical conductivity of the truss is improved, and the resistance value of the truss changes quickly and accurately with the occurrence of deformation and fracture. The present application does not need to pre-embed sensor devices and pre-reserve fiber connection electrodes, and is expected to be applied to stress monitoring in extreme environments such as high temperature and high load and various stress and strain environments.

[0006] The first object of the present application is to provide a continuous fiber 3D printed high load self-monitoring deformation ceramic matrix composite truss, which comprises a top chord, a bottom chord, and a built-in unit arranged between the top chord and the bottom chord.

[0007] The built-in unit comprises one or more shapes of triangle, trapezoid, circle and rhombus.

[0008] The structure of the truss comprises a single-layer or multi-layer truss.

[0009] The constituent material of the truss comprises continuous conductive fibers, pyrolytic carbon interface and precursor ceramic matrix.

[0010] Preferably, the continuous conductive fiber comprises carbon fiber and / or carbon nanotube fiber.

[0011] The precursor ceramic matrix is one or more of SiOC, SiC and SiCN.

[0012] The second object of the present application is to provide a preparation method of a continuous fiber 3D printed high load self-monitoring deformation ceramic matrix composite truss, comprising the following steps:

[0013] Designing the truss structure and generating a 3D printing path file;

[0014] Importing the 3D printing path file into a continuous fiber printer, using continuous conductive fibers and ceramic precursor resin as raw materials to print a fiber reinforced ceramic precursor resin, and then crosslinking, curing and pyrolyzing to obtain a ceramic composite preform truss; wherein cracks are generated during pyrolysis, which connect the fiber and the surface of the matrix;

[0015] Depositing a layer of conductive interface on the fiber and the surface of the matrix through the cracks, and then densifying to obtain a continuous fiber 3D printed high load self-monitoring deformation ceramic matrix composite truss.

[0016] Preferably, the deposition adopts chemical vapor infiltration, electrophoretic deposition or solution impregnation.

[0017] Preferably, the densification adopts chemical vapor infiltration or precursor pyrolysis impregnation.

[0018] Preferably, the ceramic precursor resin is one or more of polysiloxane, polymethylsilsesquioxane, polycarbosilane and polysilazane.

[0019] Preferably, the cross-linking and curing adopts ultraviolet curing or thermal curing.

[0020] The thermal curing is soaking the fiber-reinforced ceramic precursor resin in a reaction kettle containing an alkaline solution, heating to 60-90 DEG C, and keeping warm for 1-5 h; the ultraviolet curing is curing under ultraviolet light for 1-10 h.

[0021] Preferably, the pyrolysis is sintering the cross-linked and cured product in a tube furnace in an inert atmosphere, first heating from room temperature to 200-300 DEG C at a rate of 1-5 DEG C / min, keeping warm for 1-2 h, then heating to 900-1400 DEG C, keeping warm for 1-3 h, and finally naturally cooling to room temperature to obtain a preform truss of the ceramic composite material.

[0022] Preferably, the truss structure is designed, including:

[0023] According to different application requirements, a suitable truss structure is designed, a three-dimensional model of the bearing structure is obtained through a three-dimensional modeling software, a suitable amount and manner of fiber laying are designed by simulating and analyzing the bearing stress of the structure by using finite elements, and finally a 3D printing path file is generated.

[0024] The three-dimensional modeling software is Solidworks, CAD or CINEMA 4D.

[0025] The third object of the present application is to provide an application of the continuous fiber 3D printed high bearing self-monitoring deformation ceramic matrix composite truss in piezoresistive sensing.

[0026] Compared with the prior art, the present application has the beneficial effects that:

[0027] The application provides a continuous fiber 3D printing high-bearing self-monitoring deformation ceramic matrix composite truss and a preparation method and application thereof, and is based on ceramic matrix composite interface regulation, and a pyrolytic carbon interface is deposited on a fiber surface and a base crack surface to deposit a coating, that is, modification of the fiber surface and the base surface after 3D printing. The application ingeniously utilizes cracks generated by pyrolysis and shrinkage of a ceramic precursor, so that the pyrolytic carbon can be deposited on the fiber, and the fiber and the base surface are connected. The technical problem to be solved by the application is to deposit a conductive layer on the fiber surface and the base crack of the composite material, so that an electrically poor ceramic matrix composite material forms an electrically conductive network in the interior, the electrical conductivity of the ceramic matrix composite material is improved, the ceramic matrix composite material is endowed with piezoresistive performance, and bearing and monitoring integration is realized.

[0028] The technical scheme adopted by the application breaks through the application of the ceramic matrix composite material in the piezoresistive sensing field, and combines a truss structure with 3D printing manufacturing of the ceramic matrix composite material, so that low-cost and integrated rapid forming of the continuous fiber ceramic matrix composite truss structure is realized, a feasible solution is provided for bearing structure health monitoring in an extreme environment. The truss structure is designed to be various, fast-responding, hysteresis-free and high-sensitivity, and has excellent mechanical-resistance response characteristics.

[0029] The application can be applied to fine measurement under a small load, can be applied to measurement under high bearing, can meet measurement under various stress and strain environments, shows timeliness and accuracy in self-perception response characteristics of the load, and can effectively predict and distinguish possible damage of the structure by monitoring resistance of the structure.

[0030] The application is also applicable to alternating incremental loading and constant load cycle conditions with different load amplitudes, and shows stability and repeatability in self-perception response characteristics of the load, and in actual engineering application, the loaded state of the structure can be inversely deduced by resistance change value.

[0031] The application is a simultaneous modification of the fiber and the ceramic matrix surface, the deposited pyrolytic carbon interface not only weakens the interface bonding between the fiber and the ceramic matrix, promotes fiber pullout, but also connects the fiber surface and the ceramic matrix surface, improves the electrical conductivity of the ceramic matrix composite material itself, and thus plays the bearing / monitoring integration performance. The technical scheme adopted by the application breaks through the application of the ceramic matrix composite material in the piezoresistive sensing field, and combined with 3D printing technology, low-cost and integrated rapid forming of the ceramic matrix composite material can be realized. The truss structure is designed to be various, fast-responding, hysteresis-free and high-sensitivity, has excellent mechanical-resistance response characteristics, and the high-temperature resistance of the ceramic matrix also enables the ceramic matrix composite material to be applied in a high-temperature environment, thereby providing a feasible solution for bearing structure health monitoring in an extreme environment. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a process flow schematic diagram in the implementation process of the application.

[0033] Figure 2 is the schematic diagram of mechanical-resistance response characteristics test in the application.

[0034] Figure 3 is the schematic diagram of sensing mechanism of ceramic matrix composite material and pyrolytic carbon interface prepared by chemical vapor infiltration method.

[0035] Figure 4 is the 3D printed CCFs / SiOC / SiC composite material single-layer trapezoidal corrugated truss provided in Example 1, which is internally provided with four trapezoidal units, and the size of the truss is 60*10*6 mm 3 .

[0036] Figure 5 is the mechanical-resistance response characteristic characterization of the single-layer trapezoidal truss piezoresistive sensor provided in Example 1: (a, b) response sensitivity; (c) reaction time.

[0037] Figure 6 is the self-sensing response performance of the single-layer trapezoidal truss piezoresistive sensor under different loads in Example 2: (a) load spectrum; (b) 100-1000 N; (c) 300, 600, 900 N; (d) 1000 N.

[0038] Figure 7 is the 3D printed CCFs / SiOC composite material double-layer trapezoidal corrugated truss provided in Example 2, which is internally provided with four trapezoidal units in each layer, and the size of the truss is 60*18*6 mm 3 : (a) series trapezoidal double-layer truss; (b) parallel trapezoidal double-layer truss.

[0039] Figure 8 is the self-sensing response performance of the series / parallel trapezoidal truss under different loads in Example 2: (a, b) sensitivity of the series / parallel trapezoidal truss; (c) 100, 400, 700 N; (d) 1000 N. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the technical solutions of the present application and to implement them, the present application will be further described below in conjunction with specific embodiments and drawings, but the embodiments are not limiting on the present application.

[0041] The first aspect of the present application provides a continuous fiber 3D printed high-load self-monitoring deformation ceramic matrix composite truss, which comprises a top chord, a bottom chord, and an internal unit arranged between the top chord and the bottom chord;

[0042] The internal unit comprises one or more shapes of triangular, trapezoidal, circular, and diamond-shaped units;

[0043] The structure of the truss comprises a single-layer or multi-layer truss.

[0044] The constituent material of the truss comprises continuous conductive fibers, pyrolytic carbon interfaces and precursor ceramic matrices.

[0045] The continuous conductive fibers comprise carbon fibers and / or carbon nanotube fibers.

[0046] The precursor ceramic matrix is one or more of SiOC, SiC and SiCN.

[0047] In an embodiment, a continuous fiber 3D-printed high-load self-monitoring deformation ceramic matrix composite truss comprises built-in units and upper and lower chords, and the constituent material comprises continuous conductive fibers, pyrolytic carbon interfaces and precursor ceramic matrices, and the ceramic composite truss has high load-bearing performance. The truss structure is not limited to a single-layer or multi-layer truss, the built-in units are not limited to triangular, trapezoidal, circular and rhombic basic patterns, and the number of built-in units is not limited. The built-in units and the upper and lower chords are all composed of three materials, i.e., fibers, interfaces and matrices. The continuous conductive fibers are not limited to carbon fibers and carbon nanotube fibers with high temperature resistance. The precursor ceramic matrix is not limited to one or more of SiOC, SiC and SiCN.

[0048] The second aspect of the present application provides a preparation method of a continuous fiber 3D-printed high-load self-monitoring deformation ceramic matrix composite truss, comprising the following steps:

[0049] Designing a truss structure and generating a 3D printing path file;

[0050] Importing the 3D printing path file into a continuous fiber printer, using continuous conductive fibers and ceramic precursor resin as raw materials to print a fiber-reinforced ceramic precursor resin, and then cross-linking, curing and pyrolyzing to obtain a ceramic composite preform truss. Cracks are generated during pyrolysis, and the cracks connect the fiber and the matrix surface.

[0051] Depositing a layer of pyrolytic carbon interface on the fiber and the matrix surface through the cracks as a channel, and then performing densification treatment to obtain the continuous fiber 3D-printed high-load self-monitoring deformation ceramic matrix composite truss.

[0052] The ceramic precursor resin is one or more of polysiloxane, polymethylsilsesquioxane, polycarbosilane and polysilazane.

[0053] The cross-linking and curing are performed by ultraviolet light curing or thermal curing.

[0054] The heat curing is soaking the fiber-reinforced ceramic precursor resin in a reaction kettle containing an alkaline solution, heating to 60-90℃, and keeping for 1-5h; the ultraviolet light curing is curing for 1-10h under ultraviolet light; wherein the alkaline solution is ammonia solution, sodium hydroxide solution, etc.

[0055] The cracking is sintering the cross-linked and cured product in a tubular furnace in an inert atmosphere, first heating from room temperature to 200-300℃ at a rate of 1-5℃ / min, keeping for 1-2h, then heating to 900-1400℃, keeping for 1-3h, and finally naturally cooling to room temperature to obtain a truss of a ceramic composite preform.

[0056] The deposition uses chemical vapor infiltration (CVI), electrophoretic deposition or solution immersion; when using chemical vapor infiltration, C3H6 and Ar are used as the precursor system, CVI is used to deposit a pyrolytic carbon interface layer on the truss of the ceramic composite preform, and the deposition time is 48-240h;

[0057] The densification uses chemical vapor infiltration or precursor cracking immersion; when using chemical vapor infiltration, CH3SiCl3, H2 and Ar are used as the precursor system, CVI is used to densify the truss of the preform with a pyrolytic carbon interface, and the deposition time is 48-240h; when using precursor cracking immersion, the truss of the preform with a pyrolytic carbon interface is immersed in a ceramic precursor resin solution under vacuum pressure for 2-5h, and after curing, it is cracked in an inert atmosphere, and the process is repeated 6-10 times; wherein the ceramic precursor resin solution is one or more of polysiloxane, polymethylsilsesquioxane, polycarbosilane, polysilazane solution.

[0058] Designing the truss structure includes: designing a suitable truss structure according to different application requirements, obtaining a three-dimensional model of the bearing structure through a three-dimensional modeling software, designing a suitable amount of fiber laying and laying method by simulating and analyzing the bearing stress of the structure using finite elements, and finally generating a 3D printing path file; wherein the three-dimensional modeling software is Solidworks, CAD or CINEMA 4D.

[0059] In an embodiment, referring to Figure 1 Fig. 1 shows a preparation process of a continuous fiber 3D printed high bearing self-monitoring deformation ceramic matrix composite truss, which includes the following steps:

[0060] 1) Design a suitable truss structure according to different application requirements, obtain a three-dimensional model of the bearing structure through a three-dimensional modeling software, design a suitable amount of fiber laying and laying method by simulating and analyzing the bearing stress of the structure using finite elements, and finally generate a G-Code file of the printing path;

[0061] The three-dimensional modeling software in step 1) is not limited to Solidworks, CAD or CINEMA 4D, etc.

[0062] 2) The G-Code file of the three-dimensional model obtained in step 1) is imported into a continuous fiber printer to print a fiber-reinforced ceramic precursor resin by taking conductive fibers and ceramic precursor resin as raw materials, and then the fiber-reinforced ceramic precursor resin is cross-linked, solidified and cracked to obtain a truss of a ceramic composite preform.

[0063] The ceramic precursor resin in step 2) is not limited to polysiloxane, polymethylsilsesquioxane, polycarbosilane, polysilazane, etc.

[0064] 3) The volume shrinkage of the precursor ceramic after cracking in step 2) produces cracks, and the cracks connect the fiber and the surface of the matrix to obtain a truss of a preform with poor overall continuous conductivity and load-bearing capacity. A layer of pyrolytic carbon interface is deposited on the cracks as a channel to form a continuous conductive interface network in the truss of the preform, thereby improving the overall conductivity. At the same time, the existence of the fiber surface interface can weaken the interface bonding between the fiber and the ceramic matrix, promote the fiber pull-out and improve the mechanical properties of the ceramic composite. Then, the surface cracks of the truss of the preform are filled and densified to improve the load-bearing capacity, and a truss of a ceramic matrix composite with high load-bearing and self-monitoring deformation integration is obtained. It should be noted that the pyrolytic carbon interface is a conductive interface layer.

[0065] The interface layer deposition in step 3) is not limited to vapor deposition, liquid deposition; and the densification treatment is not limited to chemical vapor infiltration (CVI), precursor pyrolysis impregnation (PIP), etc.

[0066] The third aspect of the present application provides an application of a continuous fiber 3D printed high load-bearing self-monitoring deformation ceramic matrix composite truss in piezoresistive sensing.

[0067] It should be noted that the experimental methods used in the present application are conventional methods unless otherwise specified; and the reagents and materials used are commercially available unless otherwise specified.

[0068] Referring to Figure 2 The mechanical-resistance response characteristic test schematic diagram in the present application is shown. As can be seen from Figure 2 , the truss is placed on a universal testing machine after the two ends are bonded with copper sheets by silver paste, the two ends of the copper sheet are connected with a multimeter through wires, the resistance value R0 under the condition of no pressure is read, the multimeter will monitor the resistance value Ri of the sample under load in time, and the mechanical-resistance response characteristic of the sample can be obtained by calculating ΔR / R0 and combining the loading curve.

[0069] Referring to Figure 3The ceramic matrix composite sensing mechanism schematic diagram (a) and the pyrolytic carbon interface (b) prepared by the chemical vapor infiltration method are shown. Figure 3 As can be seen from the above, the reinforcing carbon fibers in the truss structure prepared by continuous carbon fiber 3D printing have excellent electrical conductivity and mechanical properties. Within the elastic range, the resistance of the truss structure will change reversibly in a certain rule under the action of external force, and within the non-elastic range, the resistance will change irreversibly, and even may increase suddenly. In addition, when the truss structure bears a load, the pyrolytic carbon interface network in the ceramic matrix deforms, and the resistance changes. Therefore, the truss structure exhibits a self-sensing effect on the load.

[0070] Example 1

[0071] A single-layer trapezoidal corrugated truss pressure resistance sensing structure was designed using Solidworks software, and a single-layer trapezoidal corrugated truss structure was formed by continuous fiber 3D printing. Continuous carbon fibers (CCFs) and polymethylsilsesquioxane were used as printing raw materials to form a layer-by-layer stack, and then the fiber-reinforced ceramic precursor resin truss was soaked in a reaction kettle containing an alkaline solution, heated to 90℃, and kept for 3h. The cross-linked and cured truss was placed in an argon atmosphere tube furnace, heated from room temperature to 200℃ at a rate of 2℃ / min, kept for 2h, then heated to 900℃, kept for 2h, and finally naturally cooled to room temperature to obtain a ceramic composite preform truss.

[0072] A pyrolytic carbon interface layer of about 300nm was deposited on the ceramic composite preform truss by CVI using C3H6-Ar as the precursor system, and the deposition time was 144h to obtain a preform truss with a deposited pyrolytic carbon interface.

[0073] Finally, CH3SiCl3-H2-Ar was used as the precursor system, and SiC ceramic was deposited inside the preform truss with a deposited pyrolytic carbon interface by CVI to densify it, and the deposition time was 480h to obtain a CCF / SiOC / SiC single-layer corrugated trapezoidal truss. Figure 4 .

[0074] It should be noted that in the low load range, the sensitivity is larger, and in the high load range, the sensitivity starts to decrease. With the increase of load, the resistance change rate ΔR / R0 decreases, and the decline curve of ΔR / R0 presents a nonlinear process. By approximately dividing the decline curve into three linear stages, it can be found that the initial decline is faster, then it tends to be stable, and finally in the high load range, there is a slowing down trend. The internal conductive interface spacing of the truss matrix decreases and the concentration increases under stress. In the low load stage, the relatively dispersed conductive interface in the structure rapidly gathers under the action of load, the resistance value rapidly decreases, and the resistance change rate ΔR / R0 is large; in the high load stage, the concentration of the conductive interface phase is closer and closer to the threshold value, so that the resistance change rate ΔR / R0 starts to show a slowing down trend, as shown in Figure 5-a. The resistance of the truss has a certain sensitivity to the load. Define the sensitivity coefficient (S) of the material, P is the load, and the relationship between the sensitivity and the material can be defined by the following formula:

[0075]

[0076] The relationship between the sensitivity coefficient and the applied load is shown in Figure 5-b, and the sensitivity coefficient is strongly dependent on the applied load. In the load range of 1500 N, the sensitivity coefficient decreases from 6.4 N -1 to 0.94 N -1 . The response time of the truss to stress is measured by finger pressing method, as shown in Figure 5-c, and the truss is subjected to repeated pressing-lifting cycles. Even under small pressure, the truss can respond in time, the resistance decreases rapidly under pressure, and the resistance returns to the initial level synchronously when lifted, and the average response time of the resistance is 0.12 s after multiple cycles.

[0077] The self-sensing accuracy, stability and repeatability of the continuous fiber 3D printed CCFs / SiOC / SiC ladder truss are further verified. The alternating load of 100-1000 N is applied to the truss to verify the accuracy of its self-sensing performance, and the load spectrum and response spectrum are shown in Figure 6 -a, b. With the alternating increase and decrease of the load, ΔR / R0 responds synchronously, showing good correspondence and accuracy. Starting from the load spectrum, the self-sensing response characteristics of the truss under 300, 600 and 900 N load for 10 cycles are verified Figure 6 -c), under different loads, the response curves show different resistance change rates, with maximum values of-3.16%, -7.34% and-10.61% respectively, and good consistency is maintained in 10 cycles, indicating that the truss has good precision and accuracy in sensing load. The repeatability and stability of the self-sensing characteristics of the truss are further evaluated under the condition of 1000 N constant load for 50 times, and the results are shown in Figure 6As shown in -d, within each cycle, ΔR / R0 still changes instantaneously with the load, without any hysteresis. Overall, the trapezoidal truss exhibits good sensitivity, high accuracy, and repeatability in its load sensing response, demonstrating great potential in the field of structural sensing.

[0078] Example 2

[0079] Two types of double-layer trapezoidal corrugated truss piezoresistive sensing structures, one in series and one in parallel, were designed using Solidworks software. The double-layer trapezoidal corrugated truss structures were then formed using continuous fiber 3D printing. Continuous carbon fibers and polymethylsilsesquioxane were used as printing materials and stacked layer by layer. The fiber-reinforced ceramic precursor resin truss was cured under ultraviolet light for 5 hours, and then the cross-linked and cured truss was sintered in a tube furnace under an argon atmosphere. The temperature was first raised from room temperature to 200°C at a rate of 2°C / min and held for 2 hours, then raised to 900°C and held for 2 hours. Finally, it was naturally cooled to room temperature to obtain a ceramic composite material (CCFs / SiOC) truss preform.

[0080] A PyC conductive interface layer of approximately 300 nm was deposited on the CCFs / SiOC truss preform using a liquid phase method. The CCFs / SiOC truss preform was then impregnated in a 50% phenolic resin / ethanol solution under vacuum pressure for 2 hours. After drying, it was pyrolyzed at 900℃ in an argon atmosphere to obtain a truss preform with a pyrolytic carbon interface.

[0081] Finally, a precursor pyrolysis impregnation method was used to deposit SiOC ceramics inside the CCFs / SiOC truss preform to achieve density: the preform truss with deposited pyrolytic carbon interfaces was placed in a polysiloxane ceramic precursor solution for vacuum pressure impregnation for 2 hours, cured, and then pyrolyzed in an argon atmosphere at 900℃. Subsequently, the pyrolyzed truss was again placed in a polysiloxane ceramic precursor solution for vacuum pressure impregnation, cured, and pyrolyzed. This process was repeated 8 times to obtain a CCFs / SiOC double-layer corrugated trapezoidal truss, as shown below. Figure 7 .

[0082] like Figure 8 As shown in -a and -b, the overall trend of ΔR / R0 variation with load for both structures shows that ΔR / R0 decreases nonlinearly with increasing load. The sensitivities of the series structure and the parallel structure are 26.7 N, respectively. -1 and 8.5 N -1The load-carrying capacity of the series structure is high, the anti-deformation capacity of the structure is better than that of the parallel structure, and the resistance value change range is larger, so the load is more sensitive. The self-sensing response accuracy and stability of the series trapezoidal truss are further verified, and the self-sensing response characteristics of the structure under 100, 400 and 700 N constant load 10 cycles are tested, and the results are shown in Fig. 8-c, ΔR / R0 is-11.5%, -21.4% and-25.9% respectively, the change trend and sensitivity remain unchanged, and the increase amplitude of ΔR / R0 value starts to decrease with the increase of load. According to the relationship between ΔR / R0 and load in the elastic range, the load state of the structure can still be accurately inferred, and the resistance response of the structure under three load conditions remains basically stable, and the peak-to-valley value fluctuation is small, which can prove that the self-sensing performance of the series trapezoidal truss also has stability and accuracy. Further 1000 N load 50 cycles are carried out on the structure, and the result curve Figure 8 -d shows that the series trapezoidal truss changes uniformly with the change of ΔR / R0 while maintaining stable bearing, and has repeatability, it can be inferred that during this process, the series trapezoidal truss does not produce obvious cumulative damage to cause the resistance to change suddenly, and the structure is still in the elastic deformation range.

[0083] In summary, the series trapezoidal truss has good mechanical-resistance self-sensing response characteristics, can accurately identify different loads, and the sensing performance is stable after repeated deformation. The small damage caused by the structure under pressure can also be responded in time through the resistance change. Although the bearing capacity and sensitivity of the parallel structure are smaller than those of the series structure, the resistance monitoring can also accurately reflect the bearing condition of the structure, and even exhibit the response to the delayed fracture behavior, which provides a very valuable reference for the engineering application of the actual parallel structure.

[0084] The preferred embodiments and their effects are described. However, those skilled in the art can make further changes and modifications to the embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0085] Although the embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for fabricating a high-load-bearing, self-monitoring deformation ceramic matrix composite truss using continuous fiber 3D printing, characterized in that, Includes the following steps: Design the truss structure and generate the 3D printing path file; The 3D printing path file is imported into a continuous fiber printer. Using continuous conductive fibers and ceramic precursor resin as raw materials, fiber-reinforced ceramic precursor resin is printed. Subsequently, it is cross-linked, cured, and pyrolyzed to obtain a preform truss of ceramic composite material. During pyrolysis, cracks are generated, which connect the fiber and the matrix surface. A layer of pyrolytic carbon interface is deposited on the surface of the fiber and the matrix through cracks, followed by densification treatment, to obtain a continuous fiber 3D printed high load-bearing ceramic matrix composite truss with self-monitoring deformation. The truss structure includes an upper chord, a lower chord, and an internal unit between the upper and lower chords; The built-in unit includes units of one or more shapes selected from triangle, trapezoid, circle, and rhombus; The truss structure includes single-layer or multi-layer trusses; The truss is composed of continuous conductive fibers, pyrolytic carbon interfaces, and precursor ceramic matrix. The continuous conductive fiber includes carbon fiber and / or carbon nanotube fiber. The precursor ceramic matrix is ​​one or more of SiOC, SiC, and SiCN; The deposition is performed using chemical vapor infiltration, electrophoretic deposition, or solution impregnation. The densification is achieved by chemical vapor infiltration or precursor pyrolysis impregnation. The cross-linking curing is performed using ultraviolet light curing or thermal curing; Thermocuring involves immersing the fiber-reinforced ceramic precursor resin in a reaction vessel containing an alkaline solution, heating it to 60-90°C, and holding it at that temperature for 1-5 hours; UV curing involves curing it under a UV lamp for 1-10 hours. The pyrolysis involves placing the cross-linked and cured product in a tube furnace under an inert atmosphere for sintering. The product is first heated from room temperature to 200-300°C at a rate of 1-5°C / min and held for 1-2 hours. Then, the temperature is raised to 900-1400°C and held for 1-3 hours. Finally, the product is allowed to cool naturally to room temperature to obtain a precast truss of ceramic composite material.

2. The method for preparing a high-load-bearing, self-monitoring deformation ceramic matrix composite truss using continuous fiber 3D printing according to claim 1, characterized in that, The ceramic precursor resin is one or more of polysiloxane, polymethylsilsesquioxane, polycarbosilane, and polysilazane.

3. The method for preparing a high-load-bearing, self-monitoring deformation ceramic matrix composite truss using continuous fiber 3D printing according to claim 1, characterized in that, Design the truss structure, including: Design appropriate truss structures according to different application requirements, obtain three-dimensional models of load-bearing structures through three-dimensional modeling software, and use finite element simulation to analyze the load-bearing stress of the structure to design appropriate fiber laying amount and laying method, and finally generate 3D printing path files. The 3D modeling software used is Solidworks, CAD, or CINEMA 4D.

4. The application of a continuous fiber 3D printed high load-bearing self-monitoring deformation ceramic matrix composite truss prepared by the method of any one of claims 1 to 3 in piezoresistive sensing.

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