A method for monitoring damage of a silicon carbide matrix composite based on resistance change

Abstract

The present application relates to a kind of silicon carbide matrix composite damage monitoring methods based on resistance change, belong to composite damage monitoring technical field, the probability model of fiber failure in the resistance model composite is coupled to obtain composite damage monitoring model, the damage state of composite is monitored and evaluated in real time based on the composite damage monitoring model, ensure the service safety and reliability of composite, effectively predict the remaining useful life of composite, prevent the occurrence of catastrophic failure.

Description

Technical Field

[0001] This invention relates to the field of composite material damage monitoring technology, and specifically to a method for monitoring damage in silicon carbide matrix composite materials based on resistance changes. Background Technology

[0002] Two-dimensional carbon fiber reinforced silicon carbide matrix composites (2D-C / SiCs) have attracted much attention due to their low density and excellent high-temperature mechanical properties, showing broad application prospects in hot-end components of aero-engines. When subjected to external forces, 2D-C / SiC composites exhibit energy dissipation mechanisms such as matrix cracking, fiber pull-out, interfacial debonding, and slippage, resulting in pseudo-plastic fracture characteristics. This effectively improves the damage tolerance of the composite material and prevents catastrophic failure. In practical engineering applications, to ensure the service safety and reliability of materials, it is essential to monitor and assess the damage state of the materials in real time, thereby effectively predicting the remaining service life of component materials and preventing catastrophic failures.

[0003] Currently used damage monitoring methods include traditional non-destructive testing technologies such as ultrasonic C-scanning, X-ray, and thermal imaging. These methods typically require the structural components to be taken out of service for a considerable period of time for inspection and evaluation. Some of these technologies are more suitable for detecting larger interlayer defects, but are not sensitive enough to small defects perpendicular to the material surface caused by conditions such as tensile creep. Summary of the Invention

[0004] In view of the above problems, the present invention provides a damage monitoring method for silicon carbide matrix composites based on resistance change. The present invention couples the probability model of fiber failure in the composite material with the resistance model to obtain a composite material damage monitoring model. Based on the composite material damage monitoring model, the damage state of the composite material is monitored and evaluated in real time, which ensures the service safety and reliability of the composite material, effectively predicts the remaining service life of the composite material, and prevents the occurrence of catastrophic failures.

[0005] This invention provides a method for damage monitoring of silicon carbide matrix composites based on resistance changes, comprising:

[0006] S1. Establish a probabilistic model of matrix cracks leading to carbon fiber failure based on the global load sharing GLS model;

[0007] It is understood that the carbon fibers are present in the composite material; the composite material is a silicon carbide matrix composite material, including carbon fibers, a matrix, and a pyrolytic carbon interface;

[0008] Preferably, the composite material is a single-layer carbon fiber reinforced silicon carbide matrix composite material;

[0009] For example, the composite material is a two-dimensional carbon fiber reinforced silicon carbide matrix composite material 2D-C / SiCs;

[0010] Preferably, the specific steps for establishing the probabilistic model of carbon fiber failure in step S1 include:

[0011] S11. Defect distribution of carbon fiber is obtained based on the global load sharing GLS model;

[0012] S12. Based on the defect distribution of carbon fibers in the composite material, obtain the probability of carbon fiber failure;

[0013] S13. Introduce parameter one into the failure probability of the carbon fiber to obtain the probability model of matrix cracks causing carbon fiber failure.

[0014] It is understood that parameter one represents a factor influencing the matrix crack effect;

[0015] Furthermore, the expression for the defect distribution of the composite carbon fiber in step S11 is as follows:

[0016]

[0017] Wherein, Φ(·) represents the defect distribution of carbon fibers in the composite material, L represents the total length of the carbon fibers, and the carbon fibers are composed of several carbon fiber segments of length δ; σ represents the stress intensity, n represents the shape parameter of the carbon fibers in the Weibull parameters, σ0 represents the initial stress of the carbon fibers in the Weibull parameters, and L0 represents the original length of the carbon fibers in the Weibull parameters.

[0018] Furthermore, the expression for the probability of carbon fiber failure in step S12 is:

[0019]

[0020] Among them, P f (·) is a function of the probability of carbon fiber failure; exp(·) is the natural exponential function.

[0021] Furthermore, step S13 describes the probability model for matrix cracks leading to carbon fiber failure.

[0022]

[0023] Among them, P f ′(·) is the probability function of matrix cracks affecting carbon fiber failure, and k is the influence factor of matrix cracks.

[0024] This invention utilizes the assumption in the GLS model that the load lost due to fiber fracture and slippage during axial loading is uniformly transferred to all unbroken fibers in the transverse direction. Simultaneously, it introduces a matrix crack influence factor k to obtain a probabilistic model of carbon fiber failure in composite materials. For CMC composites, the first damage occurring during loading is matrix cracking, leading to nonlinear deformation of the composite. Stress concentration occurs at the matrix crack location, significantly increasing the probability of carbon fiber fracture. An influence factor k is introduced to characterize matrix cracking. k is related to the stress distribution in the matrix and fibers during loading; in other words, k is a parameter related to material properties, determining the impact of matrix cracking on the fiber failure probability in the composite material.

[0025] S2. Introduce a pyrolytic carbon interface into the carbon fiber to obtain carbon fiber one; obtain the piezoelectric factor of carbon fiber one; modify the piezoelectric factor of carbon fiber one to obtain an updated piezoelectric factor of carbon fiber one.

[0026] A composite material is obtained based on carbon fiber 1; the resistivity and number of carbon fibers of the composite material are obtained when there is no damage; the resistivity and number of carbon fiber fractures of the composite material are obtained when there is damage based on the updated piezoelectric factor of carbon fiber 1.

[0027] Resistance 1 is obtained based on the resistivity of the composite material in the undamaged state and the number of carbon fibers; Resistance 2 is obtained based on the resistivity of the composite material in the damaged state and the number of broken carbon fibers.

[0028] The resistance model is obtained using resistor one and resistor two.

[0029] Preferably, the specific steps for obtaining the resistance model in step S2 include:

[0030] S21. Obtain the carbon fiber resistance, and obtain the carbon fiber piezoelectric factor based on the carbon fiber resistance;

[0031] Preferably, the pyrolytic carbon interface is a PyC interface;

[0032] The expression for the piezoelectric factor of the carbon fiber is:

[0033]

[0034] Where α is the piezoelectric factor of carbon fiber, R is the resistance of carbon fiber, L represents the total length of carbon fiber, and v f denoted by ρ, where ρ is the Poisson's ratio of the carbon fiber, and r represents the radius of the carbon fiber.

[0035] S22. A pyrolytic carbon interface is introduced into the carbon fiber to obtain carbon fiber one.

[0036] S23. Obtain the carbon fiber resistance, and obtain the carbon fiber piezoelectric factor based on the carbon fiber resistance and the carbon fiber piezoelectric factor.

[0037] A second parameter is introduced into the carbon fiber piezoelectric factor for correction, resulting in an updated carbon fiber piezoelectric factor.

[0038] Preferably, the second parameter is the interface dynamic damage influence factor, which is used to characterize the relationship between the electrical conductivity and strain of carbon fiber one.

[0039] Furthermore, the expression for the carbon fiber piezoelectric factor in step S23 is as follows:

[0040]

[0041] Where, α ε R is the piezoelectric factor of carbon fiber under strain ε. total For a carbon fiber resistor, L is the total length of the carbon fiber, and v total For carbon fiber 1, Poisson's ratio, ρ total Let ν be the electrical conductivity of carbon fiber 1. f is the Poisson's ratio for carbon fiber.

[0042] The expression for parameter two is:

[0043]

[0044] Where b is parameter two, φ f φ is the resistivity of carbon fiber. i The resistivity of the pyrolytic carbon interface, v f v is the Poisson's ratio for carbon fiber. i ε is the Poisson's ratio at the pyrolytic carbon interface, and ε is the strain intensity.

[0045] The expression for updating the carbon fiber piezoelectric factor in step S23 is:

[0046]

[0047] Where, α′ ε To update the piezoelectric factor of carbon fiber under strain ε, φ f φ is the resistivity of carbon fiber. i The resistivity of the pyrolytic carbon interface, v f v is the Poisson's ratio for carbon fiber. i α is the Poisson's ratio of the pyrolytic carbon interface, and α is the piezoelectric factor of the carbon fiber.

[0048] S24. Carbon fiber and silicon carbide matrix are synthesized to obtain a composite material;

[0049] Obtain the resistivity of the composite material without damage; it is understood that the damage is caused by deformation under load.

[0050] The resistivity of the composite material under damage is obtained based on the resistivity of the composite material without damage and the piezoelectric factor of the updated carbon fiber.

[0051] Furthermore, the resistivity expression of the composite material under damage described in step S24 is as follows:

[0052] φ c ′=(1+α′ ε ε)φ c

[0053] Where, φ c φ' represents the resistivity of the composite material under damage. c The resistivity of the composite material when undamaged.

[0054] S25. The number of carbon fiber fractures in the composite material is obtained by using a probability model of carbon fiber failure caused by matrix cracks.

[0055] The expression for the number of fractures in the carbon fiber is:

[0056] N b =NP′ f (σ,L)

[0057] Where, N b P represents the number of carbon fibers that broke in the composite material, where N is the number of carbon fibers in the composite material. f ′(·) is the probability function of matrix cracks causing carbon fiber failure.

[0058] The number of carbon fibers in the composite material is obtained, and the resistance is obtained based on the resistivity of the composite material under undamaged conditions and the number of carbon fibers.

[0059] The resistance is obtained based on the resistivity of the composite material under damage and the number of carbon fiber fractures.

[0060] Furthermore, the expression for resistor one in step S25 is:

[0061]

[0062] Where R0 is resistance 1, i.e., the resistance of the composite material when undamaged; φ c denoted as the resistivity of the composite material when undamaged, L represents the total length of the carbon fiber, which is composed of several carbon fiber segments of length δ; A is the cross-sectional area of ​​the composite material in the direction of current conduction.

[0063] Furthermore, the expression for resistor two in step S25 is:

[0064]

[0065] Where R is resistance 2, i.e., the resistance of the composite material when damaged, φ e φ' represents the resistivity at the crack in the composite material. c ′ represents the resistivity of the composite material under damage, l c This represents the relative sliding distance between the carbon fiber and the matrix at the crack when the composite material is damaged.

[0066] S26. Obtain the resistance model using resistor one and resistor two.

[0067] Furthermore, the expression for the resistance model described in step S26 is:

[0068]

[0069] Wherein, ΔR is the resistive coupling value, δ is the length of the carbon fiber segment, and the carbon fiber is composed of several carbon fiber segments of length δ.

[0070] The C / SiC composite material of this invention is composed of a SiC matrix, carbon fibers, and a pyrolytic carbon interface. When damage occurs in the composite material, the electrical resistance at the damaged site changes, such as... Figure 1 As shown, with the introduction of a matrix crack Δ, the carbon fiber and the matrix slide relative to each other at the crack. The matrix crack leads to stress concentration, and the carbon fiber will preferentially fracture in the slip zone of the matrix crack. That is, after fracture, the resistance Re of the entire slip zone is ∞. Figure 2 As shown; based on the carbon fiber fracture number N b Thus, the resistance is obtained as R.

[0071] The resistivity of the matrix of the composite material of the present invention is much greater than that of carbon fiber, and it does not participate in the current conduction in the loading direction. Even if there are cracks in the slip zone after the composite material is damaged, the conductive medium is still the same as that of the intact composite material.

[0072] The C / SiC composite material of this invention includes a pyrolytic carbon PyC interface with excellent conductivity and carbon fibers. Therefore, an updated carbon fiber piezoelectric factor is introduced. That is, the dynamic carbon fiber piezoelectric factor includes, on the one hand, the resistivity change caused by simple deformation, and on the other hand, the overall structure formed by the pyrolytic carbon interface and carbon fibers changes after damage, which further leads to a change in resistivity.

[0073] S3. Replace the carbon fiber length in the resistance model with the electrically ineffective length to obtain the updated resistance model;

[0074] The probability model of matrix crack failure to carbon fiber described in step S1 is coupled with the updated resistance model to obtain a composite material damage monitoring model.

[0075] Preferably, the expression for the composite material damage monitoring model in step S3 is:

[0076]

[0077] in, δ represents the damage value of the composite material. ec E is the electrically ineffective length. f This represents the Young's modulus of carbon fiber.

[0078] The composite material damage monitoring model constructed in this invention introduces an electrically ineffective length δ. ec It is applicable to all carbon fiber reinforced silicon carbide matrix composite specimens, extending from single layer to multilayer to obtain models of other different specimens.

[0079] S4. Use the composite material damage monitoring model to monitor the damage of the composite material.

[0080] This invention provides a damage detection model suitable for real-time detection of internal damage in ceramic matrix composites (CMCs). CMCs are highly sensitive to changes in electrical resistance (ER) when the matrix cracks. ER indirectly measures the cracking and crack propagation in the matrix. Damage accumulation is monitored using ER technology under high-temperature tensile conditions. This model can accurately detect minute cracks and damage in materials without damaging the material structure, providing real-time data to help in the timely detection and assessment of damage.

[0081] Compared with the prior art, the present invention has at least the following beneficial effects:

[0082] (1) This invention introduces the interface dynamic damage influence factor b, proposes the influence of interface materials on conductivity, and deepens the understanding of the conductivity mechanism in composite materials;

[0083] (2) The composite material damage monitoring model of the present invention takes into account the factors of matrix cracks, interface damage and fiber breakage at the same time, and its results show good consistency with experimental results.

[0084] (3) The present invention constructs a composite material damage monitoring model, which provides a powerful tool for studying the damage mechanism of complex braided C / SiC composite materials and predicting damage using resistance technology;

[0085] (4) This invention uses the relative change rate of resistance to predict the strain of composite materials, and maintains good accuracy in variable service environments as the failure probability of composite materials increases.

[0086] The predicted strain of the composite material damage monitoring model gradually exceeds the actual strain experienced by the composite material, ensuring that the predicted strain before the composite material fails is greater than the actual strain. This enhances the warning effect and safety of the composite material damage model in engineering applications. Attached Figure Description

[0087] The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of the invention.

[0088] Figure 1 This is a schematic diagram of the resistance change when the matrix cracks in an embodiment of the present invention;

[0089] Figure 2 This is a schematic diagram of the resistance network when the composite material fibers break in an embodiment of the present invention;

[0090] Figure 3 This is a schematic diagram of the interface damage after deflecting the matrix crack in an embodiment of the present invention;

[0091] Figure 4(a) is a schematic diagram of the relative rate of change of resistance with strain in the cyclic loading and unloading experiment in the embodiment of the present invention;

[0092] Figure 4(b) is a schematic diagram of the model fitting results of the cyclic loading and unloading experiment in the embodiment of the present invention;

[0093] Figure 5(a) is a schematic diagram of the model fitting results of the uniaxial tensile test in the embodiment of the present invention;

[0094] Figure 5(b) is a schematic diagram of damage prediction in a uniaxial tensile test in an embodiment of the present invention;

[0095] Figure 5(c) is a schematic diagram of the model fitting error of the uniaxial tensile test in the embodiment of the present invention;

[0096] Figure 5(d) is a schematic diagram of the damage prediction error of the uniaxial tensile test in the embodiment of the present invention;

[0097] Figure 6 This is a schematic diagram of the damage prediction diagram of a uniaxial tensile test recorded at a certain moment in an embodiment of the present invention. Detailed Implementation

[0098] To better understand the above-described objectives, features, and advantages of the present invention, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other. Furthermore, the present invention can be implemented in other ways different from those described herein; therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0099] A specific embodiment of the present invention, such as Figure 1-6 This invention discloses a method for damage monitoring of silicon carbide matrix composites based on resistance changes. To illustrate the effectiveness of the proposed method, a specific embodiment is provided below for detailed explanation of the above technical solution. The specific implementation steps are as follows:

[0100] This invention provides a method for damage monitoring of silicon carbide matrix composites based on resistance changes, comprising:

[0101] S1. Establish a probabilistic model of matrix cracks leading to carbon fiber failure based on the global load sharing GLS model;

[0102] It is understood that the carbon fibers are present in the composite material; the composite material is a silicon carbide matrix composite material, including carbon fibers, a matrix, and a pyrolytic carbon interface;

[0103] Preferably, the composite material is a single-layer carbon fiber reinforced silicon carbide matrix composite material;

[0104] For example, the composite material is a two-dimensional carbon fiber reinforced silicon carbide matrix composite material 2D-C / SiCs;

[0105] Preferably, the specific steps for establishing the probabilistic model of carbon fiber failure in step S1 include:

[0106] S11. Defect distribution of carbon fiber is obtained based on the global load sharing GLS model;

[0107] S12. Based on the defect distribution of carbon fibers in the composite material, obtain the probability of carbon fiber failure;

[0108] S13. Introduce parameter one into the failure probability of the carbon fiber to obtain the probability model of matrix cracks causing carbon fiber failure.

[0109] It is understood that parameter one represents a factor influencing the matrix crack effect;

[0110] Furthermore, the expression for the defect distribution of the composite carbon fiber in step S11 is as follows:

[0111]

[0112] Wherein, Φ(·) represents the defect distribution of carbon fibers in the composite material, L represents the total length of the carbon fibers, and the carbon fibers are composed of several carbon fiber segments of length δ; σ represents the stress intensity, m represents the shape parameter of the carbon fibers in the Weibull parameters, σ0 represents the initial stress of the carbon fibers in the Weibull parameters, and L0 represents the original length of the carbon fibers in the Weibull parameters.

[0113] Furthermore, the expression for the probability of carbon fiber failure in step S12 is:

[0114]

[0115] Among them, P f (·) is a function of the probability of carbon fiber failure; exp(·) is the natural exponential function.

[0116] Furthermore, step S13 describes the probability model for matrix cracks leading to carbon fiber failure.

[0117]

[0118] Among them, P f ′(·) is the probability function of matrix cracks affecting carbon fiber failure, and k is the influence factor of matrix cracks.

[0119] This invention utilizes the assumption in the GLS model that the load lost due to fiber fracture and slippage during axial loading is uniformly transferred to all unbroken fibers in the transverse direction. Simultaneously, it introduces a matrix crack influence factor k to obtain a probabilistic model of carbon fiber failure in composite materials. For CMC composites, the first damage occurring during loading is matrix cracking, leading to nonlinear deformation of the composite. Stress concentration occurs at the matrix crack location, significantly increasing the probability of carbon fiber fracture. An influence factor k is introduced to characterize matrix cracking. k is related to the stress distribution in the matrix and fibers during loading; in other words, k is a parameter related to material properties, determining the impact of matrix cracking on the fiber failure probability in the composite material.

[0120] S2. Introduce a pyrolytic carbon interface into the carbon fiber to obtain carbon fiber one; obtain the piezoelectric factor of carbon fiber one; modify the piezoelectric factor of carbon fiber one to obtain an updated piezoelectric factor of carbon fiber one.

[0121] A composite material is obtained based on carbon fiber 1; the resistivity and number of carbon fibers of the composite material are obtained when there is no damage; the resistivity and number of carbon fiber fractures of the composite material are obtained when there is damage based on the updated piezoelectric factor of carbon fiber 1.

[0122] Resistance 1 is obtained based on the resistivity of the composite material in the undamaged state and the number of carbon fibers; Resistance 2 is obtained based on the resistivity of the composite material in the damaged state and the number of broken carbon fibers.

[0123] The resistance model is obtained using resistor one and resistor two.

[0124] Preferably, the specific steps for obtaining the resistance model in step S2 include:

[0125] S21. Obtain the carbon fiber resistance, and obtain the carbon fiber piezoelectric factor based on the carbon fiber resistance;

[0126] Preferably, the pyrolytic carbon interface is a PyC interface;

[0127] The expression for the piezoelectric factor of the carbon fiber is:

[0128]

[0129] Where α is the piezoelectric factor of carbon fiber, R is the resistance of carbon fiber, L represents the total length of carbon fiber, and v f denoted by ρ, where ρ is the Poisson's ratio of the carbon fiber, and r represents the radius of the carbon fiber.

[0130] S22. A pyrolytic carbon interface is introduced into the carbon fiber to obtain carbon fiber one.

[0131] S23. Obtain the carbon fiber resistance, and obtain the carbon fiber piezoelectric factor based on the carbon fiber resistance and the carbon fiber piezoelectric factor.

[0132] A second parameter is introduced into the carbon fiber piezoelectric factor for correction, resulting in an updated carbon fiber piezoelectric factor.

[0133] Preferably, the second parameter is the interface dynamic damage influence factor, which is used to characterize the relationship between the electrical conductivity and strain of carbon fiber one.

[0134] Furthermore, the expression for the carbon fiber piezoelectric factor in step S23 is as follows:

[0135]

[0136] Where, α ε R is the piezoelectric factor of carbon fiber under strain ε. total For a carbon fiber resistor, L is the total length of the carbon fiber, and v total For carbon fiber 1, Poisson's ratio, ρ total V represents the electrical conductivity of carbon fiber 1. f is the Poisson's ratio for carbon fiber.

[0137] The expression for parameter two is:

[0138]

[0139] Where b is parameter two, φ f φ is the resistivity of carbon fiber. i The resistivity of the pyrolytic carbon interface, ν f ν is the Poisson's ratio of carbon fiber. i ε is the Poisson's ratio at the pyrolytic carbon interface, and ε is the strain intensity.

[0140] The expression for updating the carbon fiber piezoelectric factor in step S23 is:

[0141]

[0142] Where, α′ ε To update the piezoelectric factor of carbon fiber under strain ε, φ f φ is the resistivity of carbon fiber. i The resistivity of the pyrolytic carbon interface, ν f ν is the Poisson's ratio of carbon fiber.i α is the Poisson's ratio of the pyrolytic carbon interface, and α is the piezoelectric factor of the carbon fiber.

[0143] S24. Carbon fiber and silicon carbide matrix are synthesized to obtain a composite material;

[0144] Obtain the resistivity of the composite material without damage; it is understood that the damage is caused by deformation under load.

[0145] The resistivity of the composite material under damage is obtained based on the resistivity of the composite material without damage and the piezoelectric factor of the updated carbon fiber.

[0146] Furthermore, the resistivity expression of the composite material under damage described in step S24 is as follows:

[0147] φ c ′=(1+α′ ε ε)φ c

[0148] Where, φ c φ' represents the resistivity of the composite material under damage. c The resistivity of the composite material when undamaged.

[0149] S25. The number of carbon fiber fractures in the composite material is obtained by using a probability model of carbon fiber failure caused by matrix cracks.

[0150] The expression for the number of fractures in the carbon fiber is:

[0151] N b =NP′ f (σ,L)

[0152] Where, N b P represents the number of carbon fibers that broke in the composite material, where N is the number of carbon fibers in the composite material. f ′(·) is the probability function of matrix cracks causing carbon fiber failure.

[0153] The number of carbon fibers in the composite material is obtained, and the resistance is obtained based on the resistivity of the composite material under undamaged conditions and the number of carbon fibers.

[0154] The resistance is obtained based on the resistivity of the composite material under damage and the number of carbon fiber fractures.

[0155] Furthermore, the expression for resistor one in step S25 is:

[0156]

[0157] Where R0 is resistance 1, i.e., the resistance of the composite material when undamaged; φ cdenoted as the resistivity of the composite material when undamaged, L represents the total length of the carbon fiber, which is composed of several carbon fiber segments of length δ; A is the cross-sectional area of ​​the composite material in the direction of current conduction.

[0158] Furthermore, the expression for resistor two in step S25 is:

[0159]

[0160] Where R is resistance 2, i.e., the resistance of the composite material when damaged, φ e φ' represents the resistivity at the crack in the composite material. c ′ represents the resistivity of the composite material under damage, l c This represents the relative sliding distance between the carbon fiber and the matrix at the crack when the composite material is damaged.

[0161] S26. Obtain the resistance model using resistor one and resistor two.

[0162] Furthermore, the expression for the resistance model described in step S26 is:

[0163]

[0164] Wherein, ΔR is the resistive coupling value, δ is the length of the carbon fiber segment, and the carbon fiber is composed of several carbon fiber segments of length δ.

[0165] The C / SiC composite material of this invention is composed of a SiC matrix, carbon fibers, and a pyrolytic carbon interface. When damage occurs in the composite material, the electrical resistance at the damaged site changes, such as... Figure 1 As shown, with the introduction of a matrix crack Δ, the carbon fiber and the matrix slide relative to each other at the crack. The matrix crack leads to stress concentration, and the carbon fiber will preferentially fracture in the slip zone of the matrix crack. That is, after fracture, the resistance Re of the entire slip zone is ∞. Figure 2 As shown; based on the carbon fiber fracture number N b Thus, the resistance is obtained as R.

[0166] The resistivity of the matrix of the composite material of the present invention is much greater than that of carbon fiber, and it does not participate in the current conduction in the loading direction. Even if there are cracks in the slip zone after the composite material is damaged, the conductive medium is still the same as that of the intact composite material.

[0167] The C / SiC composite material of this invention includes a pyrolytic carbon PyC interface with excellent conductivity and carbon fibers. Therefore, an updated carbon fiber piezoelectric factor is introduced. That is, the dynamic carbon fiber piezoelectric factor includes, on the one hand, the resistivity change caused by simple deformation, and on the other hand, the overall structure formed by the pyrolytic carbon interface and carbon fibers changes after damage, which further leads to a change in resistivity.

[0168] S3. Replace the carbon fiber length in the resistance model with the electrically ineffective length to obtain the updated resistance model;

[0169] The probability model of matrix crack failure to carbon fiber described in step S1 is coupled with the updated resistance model to obtain a composite material damage monitoring model.

[0170] Preferably, the expression for the composite material damage monitoring model in step S3 is:

[0171]

[0172] in, δ represents the damage value of the composite material. ec E is the electrically ineffective length. f This represents the Young's modulus of carbon fiber.

[0173] The composite material damage monitoring model constructed in this invention introduces an electrically ineffective length δ. ec It is applicable to all carbon fiber reinforced silicon carbide matrix composite specimens, extending from single layer to multilayer to obtain models of other different specimens.

[0174] S4. Use the composite material damage monitoring model to monitor the damage of the composite material.

[0175] This invention provides a damage detection model suitable for real-time detection of internal damage in ceramic matrix composites (CMCs). CMCs are highly sensitive to changes in electrical resistance (ER) when the matrix cracks. ER indirectly measures the cracking and crack propagation in the matrix. Damage accumulation is monitored using ER technology under high-temperature tensile conditions. This model can accurately detect minute cracks and damage in materials without damaging the material structure, providing real-time data to help in the timely detection and assessment of damage.

[0176] Example 1

[0177] (1) Select a 2D single-layer plain weave carbon fiber reinforced silicon carbide matrix composite material of 130mm×10mm×0.5mm and first conduct a cyclic loading and unloading test on it. The loading and unloading are carried out at a speed of 0.05mm / min to simulate the actual service environment of the composite material.

[0178] (2) The resistance of the composite material was measured using the four-probe method. The two outer probes measured the current and the two inner probes measured the voltage. The outer probes were 90 mm apart and the inner probes were 80 mm apart. Acoustic emission was also installed outside the resistance probes as an auxiliary monitoring method. The experiment monitored the sample throughout the entire cycle and plotted the relative change rate of resistance and strain at the same time as the experimental results.

[0179] (3) Input the strain corresponding to the resistance at the same time into the composite material damage monitoring model to obtain the prediction result.

[0180] As shown in Figures 4(a) and 4(b), the experimental results and model results fit well in the early stages of loading. Deviations begin to appear around 70% of the maximum strain, but the overall trend remains consistent. Furthermore, under the same resistance change, the model-predicted strain is greater than the actual strain. Combined with the acoustic emission results, it can be concluded that the "pseudo-failure" caused by defects in the preparation of the single-layer material during the 70% to 90% maximum strain stage is an influence of the preparation process and is a phenomenon difficult to control artificially. This is somewhat improved in multilayer materials.

[0181] Example 2

[0182] (1) The test specimen was still selected as a 2D single-layer plain weave carbon fiber reinforced silicon carbide matrix composite material of 130mm×10mm×0.5mm. Uniaxial tensile test was performed on it. The loading rate was ten times that of cyclic loading and unloading, 0.5mm / min.

[0183] (2) The resistance of the composite material was measured using a four-probe method. The two outer probes measured the current, and the two inner probes measured the voltage. The outer probes were 90 mm apart, and the inner probes were 80 mm apart. The entire process of the sample was monitored, and the relative change rate of resistance and strain at the same time were plotted as curves as experimental results.

[0184] (3) Input the relative rate of change of resistance and strain at the same time into the composite material damage monitoring model to obtain the prediction results;

[0185] As shown in Figure 5, the model prediction results are still good. The time taken for the specimen to fail under uniaxial tension with a higher rate is short. The effective data collected during the experiment are evenly distributed on both sides of the model fitting curve. The maximum absolute error of the fitting does not exceed 1%. From the perspective of engineering strain prediction, in the strain range near the sample failure, the strain predicted by the model is greater than the actual strain. The maximum absolute error of the prediction throughout the process does not exceed 0.2%, and the maximum error is within the strain range of the specimen's safe service life. Therefore, the prediction effect of this model has practical application potential.

[0186] Example 3

[0187] (1) Test samples of the same specifications under low loading rate uniaxial tensile test, with a loading rate of 0.05 mm / min. Measure their resistance using the four-probe method.

[0188] (2) The difference between Example 1 and Example 2 is that this example only records the initial resistance value from the beginning, and selects a certain moment to start the multimeter to start measuring the resistance until the sample completely fails. In order to simulate the situation in actual application where the damage of the object is monitored from a certain moment, rather than continuously monitored from the moment the sample is used, it is suitable for situations where the degree of damage to the object needs to be evaluated from a certain moment, such as when the service life of the sample is too long and real-time monitoring is required to ensure safety.

[0189] Assuming the resistance at the start of recording satisfies the model, the relative rates of change of all resistances during the recording period can be calculated, as shown in the following figures. Figure 6 As shown, the actual strain of the specimen and the predicted strain obtained by the model are compared. Overall, the model prediction effect is better. Even under high strain near failure, the strain predicted by the model is greater than the actual strain. Under this low loading rate, the data acquisition is more accurate, and the maximum absolute error does not even exceed 0.1%, which has practical significance for predicting damage in engineering.

[0190] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for damage monitoring of silicon carbide matrix composites based on resistance changes, characterized in that, include: S1. Establish a probabilistic model of matrix cracks leading to carbon fiber failure based on the global load sharing GLS model; S2. Introduce a pyrolytic carbon interface into the carbon fiber to obtain carbon fiber 1; obtain the piezoelectric factor of carbon fiber 1. The carbon fiber piezoelectric factor is corrected to obtain an updated carbon fiber piezoelectric factor. Composite materials were obtained based on carbon fiber; Obtain the resistivity and number of carbon fibers of the composite material without damage; Based on the updated carbon fiber piezoelectric factor, the resistivity of the composite material under damage and the number of carbon fiber fractures were obtained. Resistance 1 is obtained based on the resistivity of the composite material in the undamaged state and the number of carbon fibers; Resistance 2 is obtained based on the resistivity of the composite material in the damaged state and the number of broken carbon fibers. The resistance model is obtained using resistor one and resistor two. S3. Replace the carbon fiber length in the resistance model with the electrically ineffective length to obtain the updated resistance model; The probability model of matrix crack failure to carbon fiber described in step S1 is coupled with the updated resistance model to obtain a composite material damage monitoring model. The expression for the composite material damage monitoring model described in step S3 is: in, This represents the damage value of the composite material. For electrically ineffective length, This represents the Young's modulus of carbon fiber. To update carbon fiber in strain The piezoelectric factor below, The influencing factor of matrix cracks. These are the shape parameters of the carbon fiber in the Weibull parameters. This represents the initial stress of the carbon fiber in the Weibull parameters. L 0 represents the original length of the carbon fiber in the Weibull parameters. exp (•) is the natural exponential function; S4. Use the composite material damage monitoring model to monitor the damage of the composite material.

2. The method for damage monitoring of silicon carbide matrix composite materials according to claim 1, characterized in that, The carbon fibers are present in the composite material; the composite material is a silicon carbide matrix composite material, including carbon fibers, a matrix and a pyrolytic carbon interface.

3. The method for damage monitoring of silicon carbide matrix composite materials according to claim 1, characterized in that, The specific steps for establishing the probabilistic model of carbon fiber failure as described in step S1 include: S11. Defect distribution of carbon fiber is obtained based on the global load sharing GLS model; S12. Based on the defect distribution of carbon fibers in the composite material, obtain the probability of carbon fiber failure; S13. Introduce parameter one into the failure probability of the carbon fiber to obtain the probability model of matrix cracks causing carbon fiber failure.

4. The method for damage monitoring of silicon carbide matrix composite materials according to claim 3, characterized in that, The expression for the defect distribution of the composite carbon fiber in step S11 is: in, This represents the defect distribution of carbon fibers in the composite material. L The total length of the carbon fiber is δ, and the carbon fiber is composed of several carbon fiber segments of length δ. Stress intensity These are the shape parameters of the carbon fiber in the Weibull parameters. This represents the initial stress of the carbon fiber in the Weibull parameters. L 0 represents the original length of the carbon fiber in the Weibull parameter.

5. The method for damage monitoring of silicon carbide matrix composite materials according to claim 4, characterized in that, The probability model of matrix cracks leading to carbon fiber failure described in step S13; in, (•) Let be the probability function of matrix cracks causing carbon fiber failure. The influencing factor of matrix cracks. exp (•) is the natural exponential function.

6. The method for damage monitoring of silicon carbide matrix composite materials according to claim 4, characterized in that, The specific steps for obtaining the resistance model in step S2 include: S21. Obtain the carbon fiber resistance, and obtain the carbon fiber piezoelectric factor based on the carbon fiber resistance; S22. A pyrolytic carbon interface is introduced into the carbon fiber to obtain carbon fiber one. S23. Obtain the carbon fiber resistance, and obtain the carbon fiber piezoelectric factor based on the carbon fiber resistance and the carbon fiber piezoelectric factor. A second parameter is introduced into the carbon fiber piezoelectric factor for correction, resulting in an updated carbon fiber piezoelectric factor. S24. Carbon fiber and silicon carbide matrix are synthesized to obtain a composite material; Obtain the resistivity of the composite material without damage; The resistivity of the composite material under damage is obtained based on the resistivity of the composite material without damage and the piezoelectric factor of the updated carbon fiber. S25. The number of carbon fiber fractures in the composite material is obtained by using a probability model of carbon fiber failure caused by matrix cracks. The number of carbon fibers in the composite material is obtained, and the resistance is obtained based on the resistivity of the composite material under undamaged conditions and the number of carbon fibers. The resistance is obtained based on the resistivity of the composite material under damage and the number of carbon fiber fractures. S26. Obtain the resistance model using resistor one and resistor two.

7. The method for damage monitoring of silicon carbide matrix composite materials according to claim 6, characterized in that, The expression for parameter two is: in, b For parameter two, The resistivity of carbon fiber is denoted as . The resistivity of the pyrolytic carbon interface. The Poisson's ratio of carbon fiber. The Poisson's ratio at the pyrolysis carbon interface. The value is the strain intensity.

8. The method for damage monitoring of silicon carbide matrix composite materials according to claim 7, characterized in that, The expression for updating the carbon fiber piezoelectric factor in step S23 is: in, To update carbon fiber in strain The piezoelectric factor below, The resistivity of carbon fiber is denoted as . The resistivity of the pyrolytic carbon interface. The Poisson's ratio of carbon fiber. The Poisson's ratio at the pyrolysis carbon interface. This refers to the piezoelectric factor of carbon fiber.

9. The method for damage monitoring of silicon carbide matrix composite materials according to claim 6, characterized in that, The expression for the resistance model described in step S26 is: in, ΔR This is the resistive coupling value. For resistor one, For resistor two, The length of the carbon fiber segment. The resistivity of the composite material under damage. The resistivity of the composite material when undamaged. The number of carbon fibers that break in the composite material. This represents the number of carbon fibers in the composite material. This represents the cross-sectional area of ​​the composite material in the direction of current conduction.

Images