Method for determining critical load of ceramic matrix composite material

Abstract

The invention discloses a method for determining the critical load of a ceramic matrix composite material, and belongs to the technical field of damage mechanics of composite materials. The determination method comprises the following steps: preparing a sample containing a carbon fiber reinforced phase and a ceramic matrix phase; acquiring mechanical property data at different depths by adopting a continuous rigidity measurement technology; controlling a nano-scratch load gradient based on an indentation result, and acquiring a mechanical signal in situ to identify a critical load threshold value; microcosmic damage characteristics under different loads are analyzed through SEM; and finally, in combination with mechanical properties, mechanical signals and microscopic damage characteristics, establishing microscopic-macroscopic quantitative correlation so as to determine fracture critical conditions of the fibers under different scales. According to the determination method, the microscopic fracture mechanism can be deeply analyzed, the cross-scale critical condition can be accurately judged, and important support is provided for optimization design and safety application of the ceramic matrix composite material.

Description

Technical Field

[0001] This application belongs to the field of composite material damage mechanics technology, specifically relating to a method for determining the critical load of ceramic matrix composite materials. Background Technology

[0002] Ceramic matrix composites, with their excellent comprehensive properties such as high strength, high temperature resistance, and wear resistance, have become core materials for critical structural components in extreme environment fields such as aerospace and high-end energy, and their service reliability is directly related to the safe operation of equipment. However, these materials are composed of fiber-reinforced phases and ceramic matrix phases, with complex interfacial interactions and fracture behavior exhibiting significant multi-scale characteristics—at the microscale, the fiber-matrix interface debonding and microcrack initiation gradually evolve and affect the macroscopic fracture mode.

[0003] Therefore, accurately determining the critical fracture conditions of fibers at different scales is a core prerequisite for achieving optimized material design and ensuring their safe application under complex working conditions. Summary of the Invention

[0004] The purpose of this application is to provide a method for determining the critical load of ceramic matrix composites. This method can systematically, accurately, and with broad applicability determine the critical fracture conditions of ceramic matrix composite fibers by establishing a quantitative correlation model of micro-macro damage evolution.

[0005] To achieve the above objectives, this application provides a method for determining the critical load of ceramic matrix composite materials, comprising the following steps: Samples of ceramic matrix composites were prepared; wherein the ceramic matrix composites include a carbon fiber reinforcing phase and a ceramic matrix phase; By employing continuous stiffness measurement technology, mechanical property data of samples at different depths are measured to obtain nanoindentation test results; Based on the nanoindentation test results, the nano-scratching load gradient was controlled to perform nano-scratching tests on the sample surface, and mechanical signals were collected in situ to obtain the nano-scratching test results; among them, the mechanical signals were used to identify the critical load thresholds of different fracture modes. The surface morphology of the sample after nano-scratch test was analyzed, the micro-damage characteristics generated under different loads were observed and recorded, and the SEM analysis results were obtained. Based on mechanical property data, mechanical signals, and microscopic damage characteristics, a quantitative correlation between microscopic damage and macroscopic mechanical response is established to determine the critical fracture conditions of ceramic matrix composite fibers at different scales.

[0006] Furthermore, samples of ceramic matrix composites were prepared, including: The ceramic matrix composite material is cut to the preset size using a diamond cutting machine; The cut sample was ground and polished using a precision grinding / polishing machine to achieve a sample roughness Ra < 2 μm; The ceramic matrix composite sample was obtained by ion beam polishing under an argon atmosphere and a specific voltage using an ion thinner instrument; the surface roughness of the ceramic matrix composite sample was less than 80 nm.

[0007] Furthermore, nanoindentation tests were performed at the longitudinal interface and cross-section of the carbon fiber reinforced phase and the ceramic matrix phase, respectively, to evaluate the mechanical property data of different regions.

[0008] Furthermore, the mechanical property data includes hardness and elastic modulus.

[0009] Furthermore, the nano-scratch test was performed using the Nano Indenter G200 system, equipped with a conical diamond indenter with a radius of 5 μm, under a constant normal load mode.

[0010] Furthermore, the ceramic matrix composite material is C f When using / SiC, the load gradient includes constant normal loads of 20mN, 30mN, 40mN, 50mN, 80mN, 110mN, 140mN, 170mN and 200mN, the scratching speed is 15μm / s, and the scratching direction is aligned with the longitudinal section of the carbon fiber reinforcing phase.

[0011] Furthermore, the mechanical signals include tangential force signals, acoustic emission signals, and displacement signals; among them, Mechanical signals are used to identify critical load thresholds for different fracture modes, including identifying critical points for damage initiation or propagation through abrupt changes in tangential force or peak values ​​of acoustic emission signals.

[0012] Furthermore, the microscopic damage characteristics include interface debonding characteristics, matrix crack characteristics, and fiber fracture characteristics.

[0013] Furthermore, micro-damage characteristics also include interface slip characteristics, local plastic deformation characteristics, microcrack initiation characteristics, and microcrack propagation characteristics.

[0014] Furthermore, a quantitative correlation between microscopic damage and macroscopic mechanical response is established, including: correlating the loads corresponding to the abrupt change points of the mechanical signals monitored in the nano-scratch test with the microscopic damage mode to determine the precise critical load for the occurrence of the microscopic damage mode.

[0015] In summary, this application has the following advantages: The method for determining the critical load of ceramic matrix composites provided in this application firstly uses nanoindentation technology and continuous stiffness measurement to accurately measure the mechanical properties of the material at different depths, revealing the variation of hardness and elastic modulus of the fiber and matrix with depth at the microscale, thereby achieving differentiated characterization of their microscopic mechanical responses. Based on this, a gradient nano-scratching load scheme is designed, combined with in-situ mechanical signal acquisition (such as tangential force and acoustic emission signals) and surface morphology analysis using high-resolution scanning electron microscopy (SEM), to capture the microscopic damage characteristics of the fiber under different loads in real time (such as interface debonding, microcrack initiation and propagation, fiber fracture, etc.). Finally, by integrating microscopic mechanical property data, in-situ damage signals, and macroscopic fracture characteristics, a quantitative correlation model of fiber micro-macroscopic damage evolution is constructed, thereby systematically and accurately determining the critical conditions for cross-scale fracture of ceramic matrix composite fibers, providing key theoretical basis and experimental support for the optimized design of materials and safe applications under extreme conditions. Attached Figure Description

[0016] Figure 1 C after the scratch test involved in the embodiments of this application f / SiC composite material sample image.

[0017] Figure 2 This refers to the sample preparation and surface treatment process involved in the embodiments of this application, wherein, Figure 2 (a) The diamond wire cutting machine used. Figure 2 (b) is an untreated unidirectional silicon carbide / carbon fiber composite material. Figure 2 (c) The precision grinding and polishing machine used is EM TXP. Figure 2 (d) shows the EM RES102 ion thinning system used. Figure 2 (e) is a surface-polished unidirectional silicon carbide / carbon fiber composite material. Figure 2 (f) is the three-dimensional optical profilometer used.

[0018] Figure 3 This indicates the roughness measurement under a 10x objective lens.

[0019] Figure 4 This indicates the roughness measurement under a 50x objective lens.

[0020] Figure 5 This is a schematic diagram of the nanoindentation testing process and sample microstructure involved in the embodiments of this application, wherein, Figure 5 (a) represents the microstructure of the longitudinal fibers of the composite material. Figure 5 (b) represents the microstructure of the fiber cross-section of the composite material. Figure 5 (c) indicates the use of the G200 nanoindenter. Figure 5 (d) shows a schematic diagram of LSF. Figure 5 (e) shows a schematic diagram of CSF. Figure 5 (f) shows a schematic diagram of the substrate.

[0021] Figure 6 The mechanical property curves of the silicon carbide matrix obtained during the experiments involved in the embodiments of this application are shown below. Figure 6 (a) represents the intensity curve. Figure 6 (b) represents the elastic modulus curve. Figure 6 (c) represents the load curve.

[0022] Figure 7 The mechanical property curves of the carbon fiber reinforced phase obtained during the experiments involved in the embodiments of this application are shown below. Figure 7 (a) represents the intensity curve. Figure 7 (b) represents the elastic modulus curve. Figure 7 (c) represents the load curve.

[0023] Figure 8 The mechanical property curves of the carbon fiber reinforced phase end face obtained during the experiment involved in the embodiments of this application are shown below. Figure 8 (a) represents the intensity curve. Figure 8 (b) represents the elastic modulus curve. Figure 8 (c) represents the load curve.

[0024] Figure 9 The results are from a nano-scratch test under a load of 20 mN. Figure 9 (a) shows the curve of surface displacement versus surface scratch distance. Figure 9 (b) shows the curve of the lateral force on the sample versus the distance to the surface scratch. Figure 9 (c) represents a scanning electron microscope (SEM) image of the surface morphology.

[0025] Figure 10 The results are from a nano-scratch test under a 30mN load. Figure 10 (a) shows the curve of surface displacement versus surface scratch distance. Figure 10 (b) shows the curve of the lateral force on the sample versus the distance to the surface scratch. Figure 10 (c) represents a scanning electron microscope (SEM) image of the surface morphology.

[0026] Figure 11 These are the results of a nano-scratch test under a load of 40 mN. Figure 11 (a) shows the curve of surface displacement versus surface scratch distance. Figure 11 (b) shows the curve of the lateral force on the sample versus the distance to the surface scratch. Figure 11 (c) represents a scanning electron microscope (SEM) image of the surface morphology.

[0027] Figure 12 These are the results of a nano-scratch test under a 50mN load. Figure 12 (a) shows the curve of surface displacement versus surface scratch distance. Figure 12 (b) shows the curve of the lateral force on the sample versus the distance to the surface scratch. Figure 12 (c) represents a scanning electron microscope (SEM) image of the surface morphology.

[0028] Figure 13 The results are from a nano-scratch test under an 80mN load. Figure 13 (a) shows the curve of surface displacement versus surface scratch distance. Figure 13 (b) shows the curve of the lateral force on the sample versus the distance to the surface scratch. Figure 13 (c) represents a scanning electron microscope (SEM) image of the surface morphology.

[0029] Figure 14 The results are from a nano-scratch test under a load of 110 mN. Figure 14 (a) shows the curve of surface displacement versus surface scratch distance. Figure 14 (b) shows the curve of the lateral force on the sample versus the distance to the surface scratch. Figure 14 (c) represents a scanning electron microscope (SEM) image of the surface morphology.

[0030] Figure 15 The results are from a nano-scratch test under a load of 140 mN. Figure 15 (a) shows the curve of surface displacement versus surface scratch distance. Figure 15 (b) shows the curve of the lateral force on the sample versus the distance to the surface scratch. Figure 15 (c) represents a scanning electron microscope (SEM) image of the surface morphology.

[0031] Figure 16 The results are from a nano-scratch test under a load of 170 mN. Figure 16 (a) shows the curve of surface displacement versus surface scratch distance. Figure 16 (b) shows the curve of the lateral force on the sample versus the distance to the surface scratch. Figure 16 (c) represents a scanning electron microscope (SEM) image of the surface morphology.

[0032] Figure 17 The results are from a nano-scratch test under a load of 200 mN. Figure 17 (a) shows the curve of surface displacement versus surface scratch distance. Figure 17 (b) shows the curve of the lateral force on the sample versus the distance to the surface scratch. Figure 17 (c) represents a scanning electron microscope (SEM) image of the surface morphology. Detailed Implementation

[0033] The principles and features of this application are described below with reference to embodiments. The examples are for illustrative purposes only and are not intended to limit the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0034] Currently, research on the fracture behavior of ceramic matrix composites is mostly focused on the macroscopic level, primarily analyzing failure mechanisms through overall mechanical property testing and macroscopic fracture morphology observation. However, in-depth analysis of the microscopic mechanisms of fiber fracture (such as the initiation threshold of fiber damage, the critical slip condition at the fiber-matrix interface, and the critical load for microcrack propagation into fibers) is lacking. This limitation at the macroscopic level prevents the establishment of a quantitative correlation between microscopic damage evolution and macroscopic fracture behavior, making it difficult to accurately define the critical fracture conditions of fibers at both the microscopic and macroscopic scales. This severely restricts our understanding of material fracture mechanisms and the design and application of high-performance ceramic matrix composites.

[0035] Based on this, this application provides a method for determining the critical load of ceramic matrix composites, which combines nanoindentation testing and nanoscratch testing. This method can not only analyze the macroscopic fracture behavior of composite materials, but also explore the damage mechanism at the microscopic level. Furthermore, it can be used to guide the selection and application of materials to ensure their reliability and safety under complex working conditions.

[0036] Specifically, it includes the following steps: S1. Prepare a sample of ceramic matrix composite material; wherein the ceramic matrix composite material includes a carbon fiber reinforced phase and a ceramic matrix phase.

[0037] In a specific embodiment, the preparation of a ceramic matrix composite sample includes: S101, cutting the ceramic matrix composite to a preset size, such as 6mm × 10mm × 3mm, using a diamond wire cutter; S102, grinding and polishing the cut sample using a precision grinding / polishing machine to achieve a sample roughness Ra < 2μm; S103, performing ion beam polishing under an argon atmosphere with a specific voltage using an ion thinner to obtain the ceramic matrix composite sample; the surface roughness of the ceramic matrix composite sample is less than 80nm. In this application, the diamond wire cutter has high hardness and high cutting precision, which can reduce the damage to the internal structure of the sample (such as the fiber-matrix interface and the original morphology of the fiber) by mechanical stress during the cutting process, avoid introducing additional cracks or deformation, and preserve the intrinsic microstructure of the material. Furthermore, through a step-by-step process of mechanical grinding and polishing followed by ion beam polishing, the roughness is gradually reduced from the micrometer level (Ra < 2μm) to the nanometer level (Ra < 80nm), achieving precise control of surface roughness while balancing efficiency and precision. The subsequent ion thinning instrument operates in an argon (inert gas) atmosphere, which can prevent the sample from reacting with oxygen, water vapor, etc. in the air during high-energy processing, prevent surface oxidation or chemical contamination, and ensure the intrinsic nature of the surface chemical state.

[0038] The surface treatment of the samples described above serves three purposes: First, it ensures the accuracy of nanoindentation testing: Nanoindentation testing requires calculating hardness and elastic modulus through the contact behavior between the indenter and the sample surface. If the surface is rough (Ra is too high), it will lead to deviations in the measurement of the actual contact area of ​​the indenter, thus distorting the mechanical property data. An ultra-smooth surface (Ra < 80 nm) ensures that data such as indentation depth and load-displacement curves accurately reflect the intrinsic mechanical response of the fiber and the matrix. Second, it ensures the effectiveness of nanoscratch testing: Nanoscratch testing identifies the critical fracture load through scratch behavior under gradient loads. Excessive surface roughness introduces additional frictional fluctuations, interfering with the interpretation of in-situ mechanical signals such as tangential force and acoustic emission signals. A smooth surface ensures the uniqueness of the "load-damage" correlation during the scratching process, accurately capturing the critical load threshold for fiber fracture. Third, it improves the clarity of SEM microscopic analysis: Scanning electron microscopy (SEM) needs to observe the microscopic damage characteristics after nanoscratch (such as interface debonding, microcracks, and fiber breakage). The unevenness of a rough surface will mask or misjudge these microscopic features. Ultra-smooth surfaces make damage details (such as nanoscale cracks and interface slip marks) clearly visible, providing reliable morphological evidence for establishing the correlation between "microscopic damage and macroscopic fracture".

[0039] S2. Using continuous stiffness measurement technology (CSM), the mechanical property data of the sample at different depths are measured to obtain nanoindentation test results.

[0040] The core principle of Continuous Stiffness Measurement (CSM) technology is to superimpose a small-amplitude dynamic sinusoidal load onto a static load, monitor the displacement response of the indenter during the material indentation process in real time, and calculate the contact stiffness of the material at different indentation depths using dynamic mechanical analysis methods. This allows for the derivation of hardness (the material's ability to resist localized plastic deformation) and elastic modulus (the material's ability to resist elastic deformation). This application focuses on ceramic matrix composites (containing carbon fiber reinforcement, ceramic matrix, and interface phases), testing both at the longitudinal interface (axial contact area between the fiber and the matrix) and the cross-section (radial contact area between the fiber cross-section and the matrix). This is because composite materials exhibit significant anisotropy: the mechanical properties of the fibers (such as strength and elastic modulus) differ along the axial (longitudinal) and radial (transverse) directions, and the interfacial bonding strength between the fiber and the matrix also varies with direction. CSM technology, by continuously recording the relationship between indentation depth and mechanical parameters, can accurately capture the differences in mechanical properties of different phases (fiber, matrix, and interface) at the microscale.

[0041] In a specific implementation, nanoindentation tests are performed at the longitudinal interface and cross-section of the carbon fiber reinforcing phase and the ceramic matrix phase, respectively, to evaluate the mechanical property data of different regions. By testing the longitudinal and cross-sections of the fiber, matrix, and interface separately, the differences in hardness and elastic modulus between the reinforcing phase (carbon fiber), matrix phase (ceramic), and interface phase can be clearly distinguished, avoiding the averaging effect in macroscopic testing from masking the performance differences of the microscopic phases.

[0042] In specific implementations, the mechanical property data include hardness and elastic modulus. The measured hardness and elastic modulus of the carbon fiber, ceramic matrix, and interface are core parameters describing the microscopic mechanical behavior of the material. These parameters directly determine the material's response mode to load in subsequent nano-scratch tests (e.g., whether the matrix cracks before the fiber, and whether the interface is prone to debonding).

[0043] S3. Based on the nanoindentation test results, control the nano-scratch load gradient, perform nano-scratch tests on the sample surface, and collect mechanical signals in situ to obtain nano-scratch test results; among them, the mechanical signals are used to identify the critical load thresholds of different fracture modes.

[0044] The nano-scratch test in this application simulates the damage process of materials under contact stress by applying a controllable normal load to the sample surface with a diamond indenter and sliding it along a preset direction. Its core principle is that the interaction between the indenter and the material surface will gradually transition from elastic deformation to plastic deformation, microcrack initiation, interface debonding, and finally fiber breakage as the load increases, and different damage modes correspond to specific mechanical response characteristics.

[0045] In this specific implementation, the nano-scratch test uses the Nano Indenter G200 system, equipped with a conical diamond indenter with a radius of 5 μm, and is performed under a constant normal load mode. By controlling the normal force of the indenter on the sample to remain stable, the scratching process under the same load is ensured to be consistent, facilitating the comparison of damage differences under different loads.

[0046] In a specific embodiment, the ceramic matrix composite material is C f When using / SiC, the load gradient includes constant normal loads of 20mN, 30mN, 40mN, 50mN, 80mN, 110mN, 140mN, 170mN, and 200mN. The scratching speed is 15μm / s, and the scratching direction is aligned with the longitudinal section of the carbon fiber reinforcing phase. This can match the main stress direction of the fiber in actual service (axial stress is the main force) to ensure the correlation between the test results and the actual service state of the material.

[0047] In a specific implementation, the mechanical signals include tangential force signals, acoustic emission signals, and displacement signals. These mechanical signals are used to identify the critical load thresholds for different fracture modes, including identifying the critical points of damage initiation or propagation through abrupt changes in tangential force or peak values ​​in the acoustic emission signals. Specifically, the tangential force reflects the frictional resistance of the material to the sliding of the indenter; when interfacial debonding or microcracks occur, the material's resistance to sliding abruptly changes, leading to a sudden increase or decrease in tangential force. The acoustic emission signal is the stress wave released when internal cracks initiate or propagate, or when fibers break; its peak value corresponds to the occurrence of the damage event. The discontinuity of the displacement signal reflects the sudden deformation of the material caused by fracture. By analyzing the characteristic changes of these signals, the critical load thresholds for different fracture modes can be accurately located.

[0048] S4. Analyze the surface morphology of the sample after the nano-scratch test, observe and record the micro-damage characteristics generated under different loads, and obtain the SEM analysis results.

[0049] Nanoscale scratch testing induces characteristic microscopic damage (such as interfacial debonding, matrix cracking, and fiber breakage) in ceramic matrix composites (fibers, matrix, and interface phases) under different loads. Scanning electron microscopy (SEM), with its nanoscale resolution, allows direct observation of the surface morphology and damage details of the scratched area. This enables precise correlation between damage morphology and corresponding load conditions, achieving a visual correspondence between microscopic damage characteristics and load gradients. Direct observation of damage morphology via SEM, compared to relying solely on mechanical signals (such as sudden changes in tangential force or acoustic emission peaks), provides a more intuitive way to identify damage types (e.g., distinguishing between interfacial failure, matrix cracking, or fiber breakage), avoiding ambiguity in mechanical signal interpretation and improving the accuracy of damage assessment. Furthermore, it allows for direct binding of microscopic damage characteristics to specific load values ​​(e.g., interfacial debonding at 20 mN, matrix crack propagation at 50 mN, and fiber breakage at 110 mN), providing a direct basis for establishing the load-damage-critical condition correspondence.

[0050] In a specific implementation, the micro-damage characteristics include interface debonding characteristics, matrix crack characteristics, and fiber fracture characteristics.

[0051] In specific implementations, the micro-damage characteristics also include interface slip characteristics, local plastic deformation characteristics, microcrack initiation characteristics, and microcrack propagation characteristics.

[0052] S5. Based on mechanical property data, mechanical signals and micro-damage characteristics, establish a quantitative correlation between micro-damage and macro-mechanical response in order to determine the critical fracture conditions of ceramic matrix composite fibers at different scales.

[0053] The macroscopic mechanical response (such as strength and fracture toughness) of ceramic matrix composites is essentially the cumulative result of damage evolution in the microstructure (fibers, matrix, interfaces). For example, microscopic interface debonding leads to a decrease in macroscopic load transfer efficiency, and microscopic fiber fracture directly causes macroscopic material failure. This application establishes a mapping relationship between microscopic damage characteristics (such as interface debonding and fiber fracture, obtained by SEM observation) and macroscopic mechanical signals (such as shear force abrupt changes and acoustic emission peaks, collected in situ by nano-scratch testing) and corresponding load values ​​by quantitatively binding them together. This enables cross-scale analysis from microscopic damage mechanisms to macroscopic mechanical behavior.

[0054] In a specific implementation, a quantitative correlation is established between microscopic damage and macroscopic mechanical response. This includes correlating the loads corresponding to abrupt changes in mechanical signals detected during nano-scratch testing with microscopic damage modes to determine the precise critical loads at which these modes occur. By correlating the critical loads of different damage modes (e.g., 50 mN for interface debonding → 80 mN for matrix crack propagation → 110 mN for fiber fracture), the evolution path and priority of damage can be clearly revealed, clarifying whether fiber fracture is a subsequent or initiating damage, thus providing a logical chain for analyzing the fracture mechanism.

[0055] The quantitative critical conditions (such as the critical load / stress for fiber fracture) in this application can be directly used to guide the design of ceramic matrix composites (such as adjusting the interfacial bonding strength to increase the critical load for fiber fracture), and also provide a safety threshold basis for their application in high-performance fields (such as high-temperature structural components), thus realizing the bridging role from basic research to engineering application.

[0056] The technical solutions described above in this application will be explained in detail below with reference to specific embodiments.

[0057] Example 1 This embodiment provides a method for determining the critical load of a ceramic matrix composite material, selecting a 50mm×50mm×3mm carbon fiber reinforced silicon carbide ceramic matrix composite material (C... f / SiC, such as Figure 2 (b) As the research object, it has excellent high-temperature stability and mechanical properties, and has wide applications in aerospace and nuclear engineering. The carbon fiber volume fraction of the composite material is 42%-47%, and the fiber diameter is 5μm-7μm. The sample is prepared by chemical vapor infiltration (CVI) combined with polymer infiltration pyrolysis (PIP) process, and has low porosity and high flexural strength.

[0058] The method for determining the critical load of ceramic matrix composites includes the following steps: (1) Sample preparation Cutting: using, for example Figure 2 (a) shows a diamond wire cutter that cuts the composite material into untreated samples with dimensions of 6mm × 10mm × 3mm, minimizing mechanical damage during the cutting process.

[0059] Grinding and polishing: using methods such as... Figure 2 (c) shows the precision grinding / polishing machine EM TXP, which uses diamond sandpaper of different grit sizes (240 mesh, 1200 mesh, 2400 mesh, 2μm) to grind the sample in sequence.

[0060] Ion beam polishing: To obtain an ultra-smooth surface suitable for nano-scratches, ion beam polishing is used... Figure 2(d) shows an ion thinning instrument, EM RES 102, used an argon atmosphere to perform ion beam polishing on the sample for 30 minutes at a voltage of 6 keV, ultimately obtaining a sample with a surface roughness (Ra) of less than 80 nm. The sample was then processed using... Figure 2 (f) is observed using a three-dimensional optical profilometer, and its surface is as shown. Figure 2 As shown in (e). Figure 3 and Figure 4 These are schematic diagrams showing roughness measured under objective lenses of different magnifications.

[0061] (2) Nanoindentation experiment Experimental equipment: such as Figure 5 (c) shows the Nano Indenter G200 nanoindenter used in the experiment. This device is equipped with advanced sensors for precise control and acquisition of load and displacement data. A triangular pyramidal Berkovich indenter, suitable for C... f The hardness and elastic modulus of the ceramic and fiber phases of the SiC composite material were measured. The microstructure of the longitudinal fibers and the microstructure of the fiber cross-sections of the composite material are shown below. Figure 5 (a) and Figure 5 As shown in (b).

[0062] Experimental methods: 1) Indentation in different regions: Indentation experiments are performed in different regions of the composite material to capture its anisotropic behavior. For example... Figure 5 (f) For the ceramic phase (matrix), indentation is performed on the silicon carbide matrix to evaluate its mechanical properties; such as Figure 5 (e) and Figure 5 (d) For the fibrous phase, indentations were made on the longitudinal section (LSF) and cross section (CSF) of the fiber to analyze the interaction and anisotropy between the fiber and the matrix.

[0063] 2) Depth-dependent analysis: Using the continuous stiffness measurement (CSM) method, a small oscillation is applied during the indentation process to monitor the stiffness change of the material at different indentation depths in real time, thereby obtaining the curves of hardness and elastic modulus as a function of indentation depth. Figures 6-8 ).

[0064] (3) Nanoscale scratch test Experimental equipment and parameters: The Nano Indenter G200 system was used for nano-scraping experiments, equipped with a conical diamond tip (radius: 5 μm) to ensure precise load control and scratch repeatability. A continuous loading method was used, applying constant normal loads of 20 mN, 30 mN, 40 mN, 50 mN, 80 mN, 110 mN, 140 mN, 170 mN, and 200 mN, with a scratching speed of 15 μm / s, aligned with the fiber longitudinal section (LSF).

[0065] Experimental procedure: 1) Scratch test: C under different normal loads f Nano-scratching experiments were conducted on SiC composite materials, and real-time data during the scratching process were recorded, including tangential force, acoustic emission signals, and displacement discontinuities (the surface displacement versus surface scratch distance curves of samples under different loads are shown in Figure 1). Figure 9-17 As shown in (a) above, the curves of lateral force versus surface scratch distance for samples under different loads are as follows: Figures 9-17 (as shown in (b)).

[0066] 2) Surface damage analysis: The surface damage mechanism after scratching was characterized using scanning electron microscopy (SEM) (results for different loads are shown below). Figures 9-17 As shown in (c) above, observe and record damage phenomena such as interface delamination, matrix spalling, and fiber breakage to determine the microstructural failure modes under different load thresholds. Figure 1 As shown, it is a schematic diagram of a composite material sample after a scratch test.

[0067] (4) Experimental data integration and analysis 1) Characterization results of nanoindentation experiments: Silicon carbide ceramic matrix phase: within the indentation depth range of 300nm-500nm, such as Figure 6 (a) Figure 6 As shown in (b), the hardness (H) and elastic modulus (E) of the silicon carbide matrix are stable at 38.74±0.89GPa and 418.15±9.35GPa, respectively, indicating that the matrix has uniformity at the submicron scale. Its high hardness to elastic modulus ratio (H / E=0.092) reflects the brittleness of the matrix. Limited plastic deformation leads to easy generation of radial cracks under local stress.

[0068] Carbon fiber reinforcing phase: The mechanical properties of carbon fibers exhibit significant anisotropy. For example... Figure 7 (a) Figure 7As shown in (b), when the indentation depth is 1000nm-1400nm on the fiber side surface (cross section), the hardness (Hside) and elastic modulus (Eside) are 3.00±0.10GPa and 29.15±1.35GPa, respectively.

[0069] On the fiber end surface (longitudinal section), such as Figure 7 (a) Figure 7 As shown in (b), when the indentation depth is 1500 nm-1800 nm, the hardness (Hend) and elastic modulus (Eend) are 6.20 ± 0.08 GPa and 123.9 ± 2.6 GPa, respectively. This indicates that the graphite layers arranged along the fiber axis play an important role in resisting deformation, and the longitudinal load-bearing capacity of the fibers is stronger.

[0070] 2) Characterization results of nano-scratch experiments Critical load threshold: C was determined by real-time monitoring of tangential force, acoustic emission signal, and displacement discontinuity during the scratching process. f Critical load thresholds for fracture mode transition of SiC composites under different loads. Figures 9-17 It can be seen that: 20mN-40mN is the ductile domain, 50mN-80mN is the micro-brittle fracture domain, 80mN-140mN is the micro-to-macro-brittle fracture transition domain, and greater than 140mN is the macro-brittle fracture domain.

[0071] Fracture Mechanism Analysis: SEM was used to observe the surface morphology after scratching, revealing the fracture mechanism of the composite material under different loads. In the ductile domain, the main characteristics were interfacial shear slip and limited plastic deformation, with smooth interfacial gaps. In the micro-brittle fracture domain, transverse microcracks and partial fiber debonding appeared. In the micro-to-macro-brittle fracture transition domain, crack bridging and partial fiber fracture were observed. In the macro-brittle fracture domain, catastrophic fiber fracture and matrix spalling occurred, with severe interfacial debonding.

[0072] While specific embodiments of this application have been described in detail, this should not be construed as limiting the scope of protection of this application. Various modifications and variations that can be made by those skilled in the art without inventive effort within the scope described in the claims still fall within the scope of protection of this application.

Claims

1. A method for determining the critical load of a ceramic matrix composite material, characterized in that, Includes the following steps: A sample of a ceramic matrix composite material is prepared; wherein the ceramic matrix composite material comprises a carbon fiber reinforcing phase and a ceramic matrix phase; The mechanical properties of the sample at different depths were measured using continuous stiffness measurement technology to obtain nanoindentation test results. Based on the nanoindentation test results, the nano-scratch load gradient is controlled, and a nano-scratch test is performed on the sample surface, and mechanical signals are collected in situ; wherein, the mechanical signals are used to identify the critical load thresholds for different fracture modes. Analyze the surface morphology of the samples after nano-scratch testing, and observe and record the micro-damage characteristics generated under different loads; Based on the mechanical property data, mechanical signals, and microscopic damage characteristics, a quantitative correlation between microscopic damage and macroscopic mechanical response is established to determine the critical fracture conditions of the ceramic matrix composite fiber at different scales.

2. The method for determining the critical load of ceramic matrix composite materials according to claim 1, characterized in that, The sample for preparing the ceramic matrix composite material includes: The ceramic matrix composite material is cut to the preset size using a diamond cutting machine; The cut sample was ground and polished using a precision grinding / polishing machine to achieve a sample roughness Ra < 2 μm; A ceramic matrix composite sample was obtained by ion beam polishing under an argon atmosphere and a specific voltage using an ion thinner. The surface roughness of the ceramic matrix composite sample was less than 80 nm.

3. The method for determining the critical load of ceramic matrix composite materials according to claim 1, characterized in that, The nanoindentation tests were performed at the longitudinal interface and cross-section of the carbon fiber reinforced phase and the ceramic matrix phase, respectively, to evaluate the mechanical property data of different regions.

4. The method for determining the critical load of ceramic matrix composite materials according to claim 3, characterized in that, The mechanical property data include hardness and elastic modulus.

5. The method for determining the critical load of ceramic matrix composite materials according to claim 1, characterized in that, The nano-scratch test was performed using the Nano Indenter G200 system, equipped with a conical diamond indenter with a radius of 5 μm, under a constant normal load mode.

6. The method for determining the critical load of ceramic matrix composite materials according to claim 1, characterized in that, The ceramic matrix composite material is C. f When using / SiC, the load gradient includes constant normal loads of 20mN, 30mN, 40mN, 50mN, 80mN, 110mN, 140mN, 170mN, and 200mN, the scratching speed is 15μm / s, and the scratching direction is aligned with the longitudinal section of the carbon fiber reinforcing phase.

7. The method for determining the critical load of ceramic matrix composite materials according to claim 1, characterized in that, The mechanical signals include tangential force signals, acoustic emission signals, and displacement signals; wherein... The mechanical signal is used to identify critical load thresholds for different fracture modes, including: identifying critical points for damage initiation or propagation by abrupt changes in the tangential force or peak values ​​of the acoustic emission signal.

8. The method for determining the critical load of ceramic matrix composite materials according to claim 1, characterized in that, The microscopic damage characteristics include interface debonding characteristics, matrix crack characteristics, and fiber fracture characteristics.

9. The method for determining the critical load of ceramic matrix composite materials according to claim 1 or 8, characterized in that, The micro-damage characteristics also include interface slip characteristics, local plastic deformation characteristics, microcrack initiation characteristics, and microcrack propagation characteristics.

10. The method for determining the critical load of ceramic matrix composite materials according to claim 1, characterized in that, The establishment of a quantitative correlation between microscopic damage and macroscopic mechanical response includes: correlating the load corresponding to the abrupt change point of the mechanical signal monitored in the nano-scratch test with the microscopic damage mode to determine the precise critical load at which the microscopic damage mode occurs.

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