Continuous fiber 3D printing high-bearing deformation self-monitoring ceramic matrix composite truss as well as preparation method and application of continuous fiber 3D printing high-bearing deformation self-monitoring ceramic matrix composite truss

Abstract

The invention discloses a continuous fiber 3D printing high-bearing deformation self-monitoring ceramic matrix composite truss and a preparation method and application thereof, and relates to the technical field of additive manufacturing. The truss comprises an upper chord member, a lower chord member and a built-in unit arranged between the upper chord member and the lower chord member; the built-in units comprise units in one or more shapes of a triangle, a trapezoid, a circle and a diamond; the truss structurally comprises a single-layer truss or a plurality of layers of trusses; the truss is composed of continuous conductive fibers, a pyrolytic carbon interface and a precursor ceramic matrix. The conductive layer is deposited on the fiber surface of the composite material and the matrix crack, so that a conductive network is formed in the ceramic-based composite material with poor conductivity, the conductivity is improved, the ceramic-based composite material is endowed with piezoresistive performance, and integration of bearing and monitoring is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of additive manufacturing, and in particular to a continuous fiber 3D printed high-load bearing self-monitoring deformation ceramic-based composite material truss and a preparation method and application thereof. Background Art

[0002] Truss structures have excellent physical and mechanical properties such as light weight, high specific stiffness, sound insulation, heat insulation, and impact resistance. When the volume is constant, the load-bearing capacity of the truss structure is significantly higher than that of the solid layered structure, which is an effective way to achieve ultra-light structure / function integration. At present, high-temperature resistant load-bearing / monitoring integrated trusses have broad application needs in the fields of aviation, aerospace, navigation, and national defense construction. However, the actual service of the truss structure is relatively harsh, and it may be subjected to coupling effects such as heat, force, and corrosion to produce microcracks. It is difficult to monitor the existence of microcracks in a short period of time. As the service time increases, the microcracks will be transformed into crack sources, which seriously threatens the normal load-bearing of the truss structure. Therefore, the health status monitoring of the truss structure is very important. Currently, commonly used monitoring methods include acoustic emission, ultrasonic method, CT scanning, infrared thermal imaging, embedded sensor elements, etc., but these methods require the help of external detection equipment, and embedded sensor elements will affect the strength of the structure. Therefore, it is of great significance to develop self-monitoring / high-load-bearing integrated structural materials.

[0003] The prior art discloses a continuous fiber reinforced polymer-based composite material capable of self-monitoring and self-healing. However, due to the poor conductivity of the polymer matrix, the detection of components requires reserving part of the continuous fibers for connection with electrodes, which is not convenient for monitoring components in service. The composite of continuous fibers and polymer materials is not conducive to improving environmental tolerance, limiting its application in extreme environments. A pure SiOC ceramic piezoresistive sensor with good accuracy and repeatability and high sensitivity prepared by technicians in this field using digital light processing (DLP) technology, but this type of sensor has a small monitoring strain range and is only suitable for small deformation monitoring of precision instruments. It is not sufficient for structural bearing and fails to achieve integrated high-load monitoring. The above methods cannot take into account the characteristics of high load-bearing, high temperature resistance, and self-monitoring at the same time, and it is difficult to achieve real-time monitoring of truss structures during service.

[0004] Continuous fiber ceramic matrix composites have excellent high temperature stability, high temperature creep resistance and oxidation resistance, and can be used for load bearing in extreme environments. The prior art also discloses a ceramic composite forming method using fiber-reinforced ceramic precursor 3D printing technology, which prints and forms a composite wire mixed with reinforced fibers and heated and molten ceramic precursors, enabling rapid manufacturing of composite parts with complex structures, greatly reducing manufacturing costs and production cycles. However, due to the poor electrical conductivity of the precursor ceramics, the material cannot be used in sensor elements. Summary of the invention

[0005] In view of the deficiencies in the above-mentioned background technology, the present invention provides a continuous fiber 3D printed high-load self-monitoring deformation ceramic-based composite truss and its preparation method and application. On the one hand, the method strengthens the body fiber with 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 ceramic matrix surface, the overall electrical conductivity of the truss is improved, and the resistance value of the truss changes rapidly and accurately with the occurrence of deformation and fracture. The present invention does not require pre-embedded sensor devices, and does not require reserved fiber connection electrodes. It is expected to be used for force monitoring in extreme environments such as high temperature and high load, as well as in various stress and strain environments.

[0006] The first object of the present invention is to provide a continuous fiber 3D printed high-load bearing self-monitoring deformation ceramic matrix composite truss, the truss comprising an upper chord, a lower chord, and a built-in unit arranged between the upper chord and the lower chord; The built-in units include units of one or more shapes of triangle, trapezoid, circle, rhombus; The structure of the truss includes a single-layer or multi-layer truss; The truss is made of materials including continuous conductive fibers, a pyrolytic carbon interface, and a precursor ceramic matrix.

[0007] Preferably, the continuous conductive fibers include carbon fibers and / or carbon nanotube fibers; The precursor ceramic matrix is ​​one or more of SiOC, SiC and SiCN.

[0008] The second object of the present invention is to provide a method for preparing a continuous fiber 3D printed high-load bearing self-monitoring deformation ceramic-based composite truss, comprising the following steps: Design truss structure and generate 3D printing path file; The 3D printing path file is imported into a continuous fiber printer, and a fiber-reinforced ceramic precursor resin is printed using continuous conductive fibers and ceramic precursor resin as raw materials, followed by cross-linking, curing, and cracking to obtain a preform truss of a ceramic composite material; cracks are generated during the cracking, and the cracks connect the fiber and the matrix surface; A conductive interface layer is deposited on the surface of the fiber and the matrix using the crack as a channel, and then after densification treatment, a continuous fiber 3D printed high-load-bearing self-monitoring deformation ceramic-based composite truss is obtained.

[0009] Preferably, the deposition is carried out by chemical vapor infiltration, electrophoretic deposition or solution impregnation.

[0010] Preferably, the densification is carried out by chemical vapor infiltration or precursor cracking impregnation.

[0011] Preferably, the ceramic precursor resin is one or more of polysiloxane, polymethylsilsesquioxane, polycarbosilane and polysilazane.

[0012] Preferably, the cross-linking curing adopts ultraviolet curing or thermal curing; The thermal curing is to immerse the fiber-reinforced ceramic precursor resin in a reaction kettle containing an alkaline solution, heat it to 60-90° C., and keep it warm for 1-5 hours; the ultraviolet light curing is to cure it under an ultraviolet light for 1-10 hours.

[0013] Preferably, the cracking is to sinter the cross-linked and cured product in a tubular furnace in an inert atmosphere, first heating from room temperature to 200-300°C at a rate of 1-5°C / min, keeping warm for 1-2 h, then heating to 900-1400°C, keeping warm for 1-3 h, and finally naturally cooling to room temperature to obtain a preform truss of a ceramic composite material.

[0014] Preferably, the truss structure is designed, including: Design a suitable truss structure according to different application requirements, then use 3D modeling software to obtain a 3D model of the load-bearing structure, and use finite element simulation to analyze the load-bearing conditions of the structure to design the appropriate fiber laying amount and laying method, and finally generate a 3D printing path file; Among them, the 3D modeling software is Solidworks, CAD or CINEMA 4D.

[0015] The third object of the present invention is to provide a continuous fiber 3D printed high-load-bearing self-monitoring deformation ceramic-based composite truss for use in piezoresistive sensing.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a continuous fiber 3D printed high-load-bearing self-monitoring deformation ceramic-based composite truss and its preparation method and application. The present invention is based on the interface regulation of ceramic-based composite materials, and deposits a coating on the fiber surface and the surface of matrix cracks through pyrolytic carbon interface deposition, that is, the modification of the fiber surface and the matrix surface after 3D printing. The present invention cleverly uses the cracks generated by the decomposition and shrinkage of the ceramic precursor to allow pyrolytic carbon to be deposited on the fiber and connect the fiber with the matrix surface. The technical problem to be solved by the present invention is to deposit a conductive layer on the fiber surface and matrix cracks of the composite material, so that a conductive network is formed inside the ceramic-based composite material with poor conductivity, thereby improving its conductivity, giving the ceramic-based composite material piezoresistive properties, and realizing integrated load-bearing monitoring.

[0017] The technical solution adopted by the present invention breaks through the application of ceramic-based composite materials in the field of piezoresistive sensing, and combines the truss structure with the 3D printing manufacturing of ceramic-based composite materials, realizing low-cost, integrated rapid prototyping of continuous fiber ceramic-based composite truss structures, and providing a feasible solution for the health monitoring of load-bearing structures in extreme environments. The truss structure has a variety of designs, fast response, no hysteresis, high sensitivity, and excellent mechanical-resistance response characteristics.

[0018] The present invention can be applied to both fine measurements under tiny loads and measurements under high loads, and can also meet the measurement requirements under a variety of stress and strain environments. The self-sensing response characteristics to the loads show timeliness and accuracy, and by monitoring the resistance of the structure, it can effectively predict and identify possible damage to the structure.

[0019] The present invention is also applicable to alternating progressive load increases and constant load cycle conditions with different load amplitudes. The self-sensing response characteristics of the load show stability and repeatability. In actual engineering applications, the loading state of the structure can be inferred by the resistance change value.

[0020] The present invention is a simultaneous modification of the fiber and ceramic matrix surfaces. The deposited pyrolytic carbon interface not only weakens the interfacial bonding between the fiber and the ceramic matrix and promotes fiber extraction, but also connects the fiber surface with the ceramic matrix surface, thereby improving the electrical conductivity of the ceramic matrix composite material itself, thereby giving full play to its load-bearing / monitoring integrated performance. The technical solution adopted by the present invention has made a breakthrough in the application of ceramic matrix composite materials in the field of piezoresistive sensing, and combined with 3D printing technology, it can achieve low-cost, integrated rapid prototyping of ceramic matrix composite materials. The truss structure has a variety of designs, fast response, no hysteresis, and high sensitivity, and has excellent mechanical-resistance response characteristics. The high temperature resistance of the ceramic matrix also allows the ceramic matrix composite material to be used in high temperature environments, providing a feasible solution for the health monitoring of load-bearing structures in extreme environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the implementation process of the present invention.

[0022] Figure 2 It is a schematic diagram of the mechanical-resistance response characteristic test in the present invention.

[0023] Figure 3 It is a schematic diagram of the sensing mechanism of the ceramic-based composite material of the present invention and a pyrolytic carbon interface prepared by chemical vapor infiltration.

[0024] Figure 4 The 3D printed CCFs / SiOC / SiC composite single-layer trapezoidal corrugated truss provided in Example 1 has four built-in trapezoidal units and the size of the truss is 60 × 10 × 6 mm 3 .

[0025] Figure 5 The mechanical-resistance response characteristics of the single-layer trapezoidal truss piezoresistive sensor of Example 1 are characterized as follows: (a, b) response sensitivity; (c) response time.

[0026] Figure 6 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.

[0027] Figure 7 The 3D printed CCFs / SiOC composite double-layer trapezoidal corrugated truss provided in Example 2 has 4 built-in 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.

[0028] Figure 8 The self-sensing response performance of the series / parallel ladder trusses of Example 2 under different loads: (a, b) sensitivity of the series / parallel ladder trusses; (c) 100, 400, 700 N; (d) 1000 N. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention.

[0030] A first aspect of the present invention provides a continuous fiber 3D printed high-load bearing self-monitoring deformation ceramic matrix composite truss, the truss comprising an upper chord, a lower chord, and a built-in unit arranged between the upper chord and the lower chord; The built-in units include units of one or more shapes of triangle, trapezoid, circle, rhombus; The structure of the truss includes a single-layer or multi-layer truss; The truss is made of materials including continuous conductive fibers, a pyrolytic carbon interface, and a precursor ceramic matrix.

[0031] Wherein, the continuous conductive fibers include carbon fibers and / or carbon nanotube fibers; The precursor ceramic matrix is ​​one or more of SiOC, SiC and SiCN.

[0032] In one embodiment, a continuous fiber 3D printed high-load self-monitoring deformation ceramic-based composite truss includes built-in units and upper and lower chords, and the constituent materials are 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 single-layer or multi-layer trusses, and the built-in units are not limited to basic shapes such as triangles, trapezoids, circular rhombuses, and the number of built-in units is not limited; the built-in units and the upper and lower chords are composed of three materials: fibers, interfaces, and matrices; the continuous conductive fibers are not limited to high-temperature resistant carbon fibers, carbon nanotube fibers, etc.; the precursor ceramic matrix is ​​not limited to one or more of SiOC, SiC, SiCN, etc.

[0033] A second aspect of the present invention provides a method for preparing a continuous fiber 3D printed high-load bearing self-monitoring deformation ceramic-based composite truss, comprising the following steps: Design truss structure and generate 3D printing path file; The 3D printing path file is imported into a continuous fiber printer, and a fiber-reinforced ceramic precursor resin is printed using continuous conductive fibers and ceramic precursor resin as raw materials, followed by cross-linking, curing, and cracking to obtain a preform truss of a ceramic composite material; cracks are generated during the cracking, and the cracks connect the fiber and the matrix surface; A layer of pyrolytic carbon interface is deposited on the surface of the fiber and the matrix using the crack as a channel, and then subjected to densification treatment to obtain a continuous fiber 3D printed high-load-bearing self-monitoring deformation ceramic-based composite truss.

[0034] The ceramic precursor resin is one or more of polysiloxane, polymethylsilsesquioxane, polycarbosilane and polysilazane.

[0035] The cross-linking curing adopts ultraviolet curing or thermal curing; Wherein, the heat curing is to immerse the fiber reinforced ceramic precursor resin in a reaction kettle containing an alkaline solution, heat it to 60-90°C, and keep it warm for 1-5 hours; the ultraviolet light curing is to cure it under an ultraviolet light for 1-10 hours; wherein the alkaline solution is an ammonia solution, a sodium hydroxide solution, etc.; The cracking is to place the cross-linked and solidified product in a tubular furnace in an inert atmosphere for sintering, first heating from room temperature to 200-300°C at a rate of 1-5°C / min, keeping warm for 1-2 hours, then heating to 900-1400°C, keeping warm for 1-3 hours, and finally naturally cooling to room temperature to obtain a preform truss of a ceramic composite material.

[0036] The deposition adopts chemical vapor infiltration (CVI), electrophoretic deposition or solution impregnation; wherein, when chemical vapor infiltration is adopted, it includes: using C3H6 and Ar as a precursor system, using CVI to deposit a pyrolytic carbon interface layer on the preform truss of the ceramic composite material, and the deposition time is 48-240 hours; The densification adopts chemical vapor infiltration or precursor cracking and impregnation; when chemical vapor infiltration is adopted, CH3SiCl3, H2 and Ar are used as the precursor system, and CVI is used to densify the preform truss with deposited pyrolytic carbon interface, and the deposition time is 48-240h; when precursor cracking and impregnation is adopted, it includes: vacuum pressure impregnating the preform truss with deposited pyrolytic carbon interface in a ceramic precursor resin solution for 2-5h, cracking in an inert atmosphere after curing, and repeating 6-10 times; wherein the ceramic precursor resin solution is one or more solutions of polysiloxane, polymethylsilsesquioxane, polycarbosilane, and polysilazane.

[0037] Designing a truss structure includes: designing a suitable truss structure according to different application requirements, obtaining a three-dimensional model of the load-bearing structure through three-dimensional modeling software, and using finite element simulation to analyze the load-bearing conditions of the structure to design a suitable fiber laying amount and laying method, and finally generating a 3D printing path file; wherein the three-dimensional modeling software is Solidworks, CAD or CINEMA 4D.

[0038] In one embodiment, see Figure 1 As shown, a preparation process of a continuous fiber 3D printed high-load bearing self-monitoring deformation ceramic matrix composite truss includes the following steps: 1) Design a suitable truss structure according to different application requirements, then use 3D modeling software to obtain a 3D model of the load-bearing structure, and use finite element simulation to analyze the load-bearing conditions of the structure to design the appropriate fiber laying amount and laying method, and finally generate a G-Code file for the printing path; The 3D modeling software in step 1) is not limited to Solidworks, CAD or CINEMA 4D, etc.; 2) importing the G-Code file of the three-dimensional model obtained in step 1) into a continuous fiber printer, using conductive fibers and ceramic precursor resin as raw materials, printing to obtain fiber-reinforced ceramic precursor resin, and then cross-linking, curing, and cracking to obtain a preform truss of a ceramic composite material; The ceramic precursor resin in step 2) is not limited to polysiloxane, polymethylsilsesquioxane, polycarbosilane, polysilazane, etc.; 3) The precursor ceramic in step 2) shrinks in volume after pyrolysis and produces cracks. The cracks connect the fiber and the matrix surface, and the overall continuous conductivity and load-bearing capacity of the obtained preform truss are poor. Using the cracks as a channel, a layer of pyrolytic carbon interface is deposited on the surface of the fiber and the matrix, so that a continuous conductive interface network is formed inside the preform truss, which improves the overall conductivity. At the same time, the presence of the fiber surface interface can weaken the interface bonding between the fiber and the ceramic matrix, promote fiber pull-out, and improve the mechanical properties of the ceramic composite. Subsequently, the surface cracks of the preform truss are filled and densified to improve the load-bearing performance, and a high-load-bearing / self-monitoring deformation integrated ceramic-based composite truss is obtained; it should be noted that the pyrolytic carbon interface is the conductive interface layer.

[0039] The interface layer deposition in step 3) is not limited to vapor phase deposition and liquid phase deposition; the densification treatment is not limited to chemical vapor infiltration (CVI), precursor pyrolysis impregnation (PIP), etc.; A third aspect of the present invention provides an application of a continuous fiber 3D printed high-load-bearing self-monitoring deformation ceramic-based composite truss in piezoresistive sensing.

[0040] It should be noted that the experimental methods used in the present invention are all conventional methods unless otherwise specified; the reagents and materials used are all commercially available unless otherwise specified.

[0041] See also Figure 2 As shown in FIG. 1 , a schematic diagram of the mechanical-resistance response characteristic test in the present invention is shown. Figure 2 It can be seen that the copper sheets at both ends of the frame under pressure are bonded with silver paste and then placed on the universal testing machine. The two ends of the copper sheet are connected to the multimeter through wires to read the resistance value R0 when not under pressure. The multimeter will timely monitor the resistance value Ri of the sample when it is loaded, calculate ΔR / R0, and combine it with the loading curve to know the mechanical-resistance response characteristics of the sample.

[0042] See also Figure 3 As shown, the sensing mechanism schematic diagram of the ceramic matrix composite material of the present invention (a) and the pyrolytic carbon interface prepared by chemical vapor infiltration (b); Figure 3 It can be seen that the reinforced carbon fiber in the truss structure prepared by continuous carbon fiber 3D printing has excellent conductivity and mechanical properties. Within the elastic range, its resistance will show a certain regular reversible change with the action of external force. Within the inelastic range, its resistance will change irreversibly and may even increase suddenly. In addition, when the truss structure is under load, the pyrolytic carbon interface network inside the ceramic matrix deforms and the resistance changes. Therefore, the truss structure exhibits a self-sensing effect on the load.

[0043] Example 1 The single-layer trapezoidal corrugated truss piezoresistive sensing structure was designed using Solidworks software, and the single-layer trapezoidal corrugated truss structure was formed using continuous fiber 3D printing. Continuous carbon fibers (CCFs) and polymethylsilsesquioxane were used as printing materials and stacked layer by layer. The fiber-reinforced ceramic precursor resin truss was then immersed in a reactor containing an alkaline solution, heated to 90°C, and kept warm for 3 hours. The cross-linked and cured truss was sintered in a tubular furnace in an argon atmosphere, first heated from room temperature to 200°C at a rate of 2°C / min, kept warm for 2 hours, then heated to 900°C, kept warm for 2 hours, and finally naturally cooled to room temperature to obtain a prefabricated truss of a ceramic composite material.

[0044] Using C3H6-Ar as the precursor system, CVI was used to deposit a pyrolytic carbon interface layer of about 300 nm on the preform truss of the ceramic composite material for 144 h, thereby obtaining a preform truss with a deposited pyrolytic carbon interface. Finally, using CH3SiCl3-H2-Ar as the precursor system, CVI was used to deposit SiC ceramics inside the preform truss at the pyrolytic carbon interface to make it dense. The deposition time was 480 h, and the CCFs / SiOC / SiC single-layer corrugated trapezoidal truss was obtained, as shown in Figure 4 .

[0045] It should be noted that in the low load range, the sensitivity is relatively large, and in the high load range, the sensitivity begins to decrease. As the load increases, the resistance change rate ΔR / R0 decreases, and the decline curve of ΔR / R0 presents a nonlinear process. The decline curve is approximately divided into three linear stages. It can be found that the initial decline is relatively fast, then tends to stabilize, and finally in the high load range, there is a slowing decline trend. After the truss matrix is ​​subjected to force, the internal conductive interface phase spacing becomes smaller and the concentration increases. In the low load stage, the more dispersed conductive interface phases in the structure rapidly gather under the action of the load, the resistance value decreases rapidly, and the resistance change rate ΔR / R0 is large; in the high load stage, the concentration of the conductive interface phase is getting closer and closer to the threshold, causing the resistance change rate ΔR / R0 to begin to slow down, as shown in Figure 5-a. The resistance of the truss has a certain sensitivity to the response of the load. Define the sensitivity coefficient (S) of the material, P is the load, and the relationship between sensitivity and material can be defined by the following formula:

[0046] The relationship between the sensitivity coefficient and the applied load is shown in Figure 5-b. The sensitivity coefficient strongly depends on the applied load. In the load range of 1500 N, the sensitivity coefficient increases from 6.4 N to -1 Reduced to 0.94 N -1The finger pressing method was used to measure the response time of the truss to the force. As shown in Figure 5-c, the truss was repeatedly pressed and lifted. Even under small pressure, the truss can respond in time. The resistance decreases rapidly when it is pressed, and the resistance value returns to the initial level synchronously when it is lifted. The average reaction time of the resistance calculated over multiple cycles is 0.12 s.

[0047] The self-sensing accuracy, stability and repeatability of the continuous fiber 3D printed CCFs / SiOC / SiC trapezoidal truss were verified in depth. An alternating load of 100~1000 N was applied to the truss to verify the accuracy of its self-sensing performance. The load spectrum and response spectrum are shown in Figure 2. Figure 6 -a, b. As the load increases and decreases alternately, ΔR / R0 responds synchronously, showing a good correspondence and accuracy. Starting from the load spectrum, the self-sensing response characteristics of the truss under 300, 600 and 900 N loads 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 maintain good consistency in 10 cycles, indicating that the truss has good precision and accuracy in the load sensing process. The repeatability and stability of the truss self-sensing characteristics were further evaluated under 1000 N constant load cycles for 50 times. The results are shown in Figure 6 -d, in each cycle, ΔR / R0 still changes instantaneously with the load without any hysteresis. Overall, the trapezoidal truss has good sensitivity, high accuracy and repeatability in its load sensing response, showing good potential in the field of structural sensing.

[0048] Example 2 Solidworks software was used to design two types of double-layer trapezoidal corrugated truss piezoresistive sensing structures in series and in parallel, and continuous fiber 3D printing was used to form the double-layer trapezoidal corrugated truss structure. Continuous carbon fiber and polymethylsilsesquioxane were used as printing materials and stacked layer by layer. The fiber-reinforced ceramic precursor resin truss was placed under ultraviolet light for curing for 5 hours, and then the cross-linked and cured truss was placed in an argon atmosphere tube furnace for sintering. It was first heated from room temperature to 200℃ at a rate of 2℃ / min, kept warm for 2 hours, and then heated to 900℃, kept warm for 2 hours, and finally cooled naturally to room temperature to obtain a ceramic composite material (CCFs / SiOC) truss preform.

[0049] A liquid phase method was then used to deposit a PyC conductive interface layer of about 300 nm on the CCFs / SiOC truss preform. A 50% by mass phenolic resin / ethanol solution was used as the impregnation liquid. The CCFs / SiOC truss preform was vacuum pressure impregnated in the impregnation liquid for 2 h. After drying, it was cracked at 900°C in an argon atmosphere to obtain a truss preform with a pyrolytic carbon interface.

[0050] Finally, the SiOC ceramics were deposited inside the CCFs / SiOC truss preform to make it dense by using the precursor pyrolysis impregnation method: the preform truss with the pyrolytic carbon interface deposited was placed in a polysiloxane ceramic precursor solution for vacuum pressure impregnation for 2 h, and then cracked in an argon atmosphere at 900 °C. The cracked truss was then placed in a polysiloxane ceramic precursor solution for vacuum pressure impregnation, cured and cracked, and the process was repeated 8 times to obtain a CCFs / SiOC double-layer corrugated trapezoidal truss, as shown in FIG. Figure 7 .

[0051] like Figure 8 -a,b show that the variation trend of ΔR / R0 of the two structures with load shows that as the load increases, ΔR / R0 decreases nonlinearly. The sensitivity of the series structure and the parallel structure are 26.7 N -1 and 8.5 N -1 . The series structure has a high bearing capacity, and its anti-deformation ability is better than that of the parallel structure. The resistance value has a larger range of variation, so it is more sensitive to the load. The accuracy and stability of the self-sensing response of the series trapezoidal truss were further verified, and the self-sensing response characteristics of the structure under 10 cycles of 100, 400 and 700 N constant loads were tested. The results are shown in Figure 8-c. ΔR / R0 is -11.5%, -21.4% and -25.9%, respectively. The change trend and sensitivity are consistent. As the load increases, the increase in the ΔR / R0 value begins to decrease. Based on the relationship between ΔR / R0 and load within the elastic range, the loading state of the structure can still be accurately inferred. Under the three load conditions, the resistance response of the structure remains basically stable, and the peak and trough values ​​fluctuate slightly. It can be proved that the self-sensing performance of the series trapezoidal truss is also stable and accurate. The structure was further loaded with a load of 1000 N for 50 cycles, and the result curve Figure 8 -d shows that while the series-connected trapezoidal trusses maintain stable load-bearing, ΔR / R0 also changes uniformly and is repeatable. It can be inferred that during this process, the series-connected trapezoidal trusses did not produce obvious cumulative damage that led to a sudden change in resistance, and the structure was still within the range of elastic deformation.

[0052] In summary, the series-connected trapezoidal trusses have good mechanical-resistance self-sensing response characteristics, can accurately identify different loads, and have stable sensing performance after repeated deformation. They can also respond promptly to minor damage caused by pressure on the structure through changes in resistance. Although the load-bearing performance and sensitivity of the parallel structure are lower than those of the series structure, resistance monitoring can accurately reflect the load-bearing conditions of the structure, and even show responses to delayed fracture behavior, which provides a very valuable reference for the engineering application of actual parallel structures.

[0053] The present invention describes preferred embodiments and their effects. However, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0054] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A continuous fiber 3D printed high-load bearing self-monitoring deformation ceramic matrix composite truss, characterized in that: The truss comprises an upper chord, a lower chord, and a built-in unit arranged between the upper chord and the lower chord; The built-in units include units of one or more shapes of triangle, trapezoid, circle, rhombus; The structure of the truss includes a single-layer or multi-layer truss; The constituent materials of the truss include continuous conductive fibers, a pyrolytic carbon interface and a precursor ceramic matrix.

2. The continuous fiber 3D printed high-load bearing self-monitoring deformation ceramic matrix composite truss according to claim 1, characterized in that: The continuous conductive fibers include carbon fibers and / or carbon nanotube fibers; The precursor ceramic matrix is ​​one or more of SiOC, SiC and SiCN.

3. A method for preparing a continuous fiber 3D printed high-load bearing self-monitoring deformation ceramic matrix composite truss according to claim 1 or 2, characterized in that: The following steps are involved: Design truss structure and generate 3D printing path file; The 3D printing path file is imported into a continuous fiber printer, and a fiber-reinforced ceramic precursor resin is printed using continuous conductive fibers and ceramic precursor resin as raw materials, followed by cross-linking, curing, and cracking to obtain a preform truss of a ceramic composite material; cracks are generated during the cracking, and the cracks connect the fiber and the matrix surface; A layer of pyrolytic carbon interface is deposited on the surface of the fiber and the matrix using the crack as a channel, and then subjected to densification treatment to obtain a continuous fiber 3D printed high-load-bearing self-monitoring deformation ceramic-based composite truss.

4. The method for preparing a continuous fiber 3D printed high-load bearing self-monitoring deformation ceramic matrix composite truss according to claim 3, characterized in that: The deposition is carried out by chemical vapor infiltration, electrophoretic deposition or solution impregnation.

5. The method for preparing a continuous fiber 3D printed high-load bearing self-monitoring deformation ceramic matrix composite truss according to claim 3, characterized in that: The densification is carried out by chemical vapor infiltration or precursor cracking and impregnation.

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

7. The method for preparing a continuous fiber 3D printed high-load bearing self-monitoring deformation ceramic matrix composite truss according to claim 3, characterized in that: The cross-linking curing adopts ultraviolet curing or thermal curing; The thermal curing is to immerse the fiber-reinforced ceramic precursor resin in a reaction kettle containing an alkaline solution, heat it to 60-90° C., and keep it warm for 1-5 hours; the ultraviolet light curing is to cure it under an ultraviolet light for 1-10 hours.

8. The method for preparing a continuous fiber 3D printed high-load bearing self-monitoring deformation ceramic matrix composite truss according to claim 3, characterized in that: The cracking is to place the cross-linked and solidified product in a tubular furnace in an inert atmosphere for sintering, first heating from room temperature to 200-300°C at a rate of 1-5°C / min, keeping warm for 1-2 hours, then heating to 900-1400°C, keeping warm for 1-3 hours, and finally naturally cooling to room temperature to obtain a preform truss of a ceramic composite material.

9. The method for preparing a continuous fiber 3D printed high-load bearing self-monitoring deformation ceramic matrix composite truss according to claim 3, characterized in that: Design of truss structures, including: Design a suitable truss structure according to different application requirements, then use 3D modeling software to obtain a 3D model of the load-bearing structure, and use finite element simulation to analyze the load-bearing conditions of the structure to design the appropriate fiber laying amount and laying method, and finally generate a 3D printing path file; Among them, the 3D modeling software is Solidworks, CAD or CINEMA 4D.

10. Application of the continuous fiber 3D printed high-load bearing self-monitoring deformation ceramic-based composite truss according to claim 1 or 2 in piezoresistive sensing.

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