A method for predicting the fatigue life of a unidirectional plate of a ceramic matrix composite in different fiber layup directions

Abstract

The application discloses a kind of ceramic matrix composite different fiber lay-up direction unidirectional plate fatigue life prediction method.The method first obtains the tensile strength of fiber lay-up direction 0 °,90 ° unidirectional plate, critical angle, and the static strength and fatigue strength-life function curve of different fiber lay-up angle unidirectional plate;The fiber, matrix damage contribution ratio corresponding to each angle is calculated, the fatigue strength-life function curve of 90 ° unidirectional plate is inferred through the curve of the critical angle two sides skew angle, to determine the fiber, matrix dominant basic fatigue curve;Subsequently, the weighted combination model with contribution ratio as weight is constructed;Finally, according to the size relationship between fiber lay-up angle and critical angle, the contribution ratio is corrected by selecting correction function, to realize fatigue life prediction.The prediction method of the application is in line with the failure characteristics of ceramic matrix composite, improves the accuracy and applicability of fatigue life prediction of different lay-up direction unidirectional plate, and provides technical support for related laminated structure design.

Description

Technical Field

[0001] This invention relates to the field of fatigue life prediction of composite materials, and in particular to a method for predicting the fatigue life of unidirectional plates with different fiber layup directions of ceramic matrix composite materials. Background Technology

[0002] Ceramic matrix composites possess excellent high-temperature resistance, low density, high specific strength, and good oxidation resistance, demonstrating great potential in high-temperature components for aerospace applications. C / SiC composites, as an important type of fiber-reinforced ceramic matrix composite, are characterized by short preparation cycles, high cost-effectiveness, and excellent mechanical properties. These materials have wide applications in critical areas such as thermal protection systems and braking devices. In everyday use, the most common form of fiber-reinforced composites is laminates, which are composed of unidirectional plates with various layup angles. The performance of a laminate is determined by the combined performance of each unidirectional plate. Therefore, predicting the life and strength of fiber-reinforced composite unidirectional plates is crucial and forms the basis for laminate performance prediction.

[0003] For unidirectional laminates, relatively mature methods exist for predicting their fatigue life at room temperature. However, these methods primarily target polymer-based composites such as GFRP (glass fiber reinforced polymer) and CFRP (carbon fiber reinforced polymer), while research on fatigue life prediction for ceramic matrix composites (CMC) is relatively scarce. Because CMC involves failure mechanisms significantly different from polymer-based materials during service, such as high-temperature oxidation and interfacial debonding, its fatigue behavior is more complex, necessitating the development of targeted models that reflect its unique damage evolution. On the other hand, in engineering practice, the most commonly used structural form of fiber-reinforced composites is laminated plates, which are composed of stacked unidirectional laminates with different layup angles. The macroscopic mechanical properties and fatigue behavior of laminates are essentially determined by the combined properties of each unidirectional laminate. Therefore, accurately predicting the fatigue life and strength degradation of unidirectional laminates under fatigue loads is the foundation and prerequisite for further analysis and design of laminated plate structures.

[0004] In summary, there is an urgent need to establish a fatigue life prediction method applicable to unidirectional plates, especially ceramic matrix composite unidirectional plates. This is not only of theoretical significance for understanding the damage mechanism of materials under cyclic loading, but also of important engineering value for realizing the safe design and life assessment of laminated structures. Summary of the Invention

[0005] The purpose of this invention is to provide a method for predicting the fatigue life of unidirectional ceramic matrix composite plates with different fiber layup directions, addressing the aforementioned shortcomings. Specifically, it refers to a method for predicting the fatigue life of unidirectional ceramic matrix composite plates based on laminates with different fiber layup sequences, applicable to unidirectional plates with different fiber angles.

[0006] This invention provides a method for predicting the fatigue life of unidirectional plates with different fiber layup directions in ceramic matrix composites. The ceramic matrix composites are composed of unidirectional plates with different fiber layup directions. The method includes: S101. Obtain the axial tensile strength of a one-way sheet with a fiber layup direction angle of 0°, the longitudinal tensile strength and critical angle of a one-way sheet with a fiber layup direction angle of 90°; and obtain the static strength of a one-way sheet under a specific fiber layup direction angle and the fatigue strength-life function curve corresponding to the specific fiber layup direction angle. S102. Based on the static strength of one-way sheet under a specific fiber layup direction angle, the axial tensile strength of one-way sheet with a fiber layup direction angle of 0°, and the longitudinal tensile strength of one-way sheet with a fiber layup direction angle of 90°, calculate the fiber damage contribution ratio and matrix damage contribution ratio corresponding to the specific fiber layup direction angle. S103. Select a first off-axis angle where the fiber layup direction angle is less than the critical angle and a second off-axis angle where the fiber layup direction angle is greater than the critical angle. Based on the fatigue strength-life function curves corresponding to the first and second off-axis angles, predict the fatigue strength-life function curves of a one-way plate with a fiber layup direction angle of 90° using fiber-dominated and matrix-dominated prediction methods, respectively. Use the fatigue strength-life function curve of a one-way plate with a fiber layup direction angle of 0° as the fiber-dominated basic fatigue curve and the fatigue strength-life function curve of a one-way plate with a fiber layup direction angle of 90° as the matrix-dominated basic fatigue curve. S104. Construct a fatigue strength and fatigue life function curve model for an off-axis unidirectional plate. The model is a weighted combination of the fiber-dominated basic fatigue curve and the matrix-dominated basic fatigue curve, wherein the weights are the fiber damage contribution ratio and the matrix damage contribution ratio. S105. Select the corresponding correction function based on the relationship between the fiber layup direction angle and the critical angle, and introduce the correction function to correct the fiber damage contribution ratio and matrix damage contribution ratio used in the model, and predict the fatigue life of unidirectional plates with different fiber layup directions of ceramic matrix composites.

[0007] According to one embodiment of the present invention, the critical angle is calculated based on the axial tensile strength of a one-way plate with a fiber layup direction angle of 0° and the longitudinal tensile strength of a one-way plate with a fiber layup direction angle of 90°. The formula for calculating the critical angle is:

[0008] In the formula X is the critical angle, where X is the axial tensile strength of a one-way sheet with a fiber layup angle of 0°, and Y is the longitudinal tensile strength of a one-way sheet with a fiber layup angle of 90°.

[0009] According to an embodiment of the present invention, the formula for calculating the fiber damage contribution ratio and matrix damage contribution ratio corresponding to the specific fiber layup direction angle is as follows: Based on the static strength of the one-way sheet at a specific fiber layup direction angle, the axial tensile strength of the one-way sheet with a fiber layup direction angle of 0°, and the longitudinal tensile strength of the one-way sheet with a fiber layup direction angle of 90°.

[0010] In the formula Contribution to fiber damage Contribution ratio to matrix damage The angle of the fiber layup direction in a unidirectional fiberboard. Angle of fiber layup direction The static strength of a one-way slab.

[0011] According to one embodiment of the present invention, the static strength of a one-way sheet at a specific fiber layup direction angle is obtained by a static tensile test of the one-way sheet at room temperature; and the fatigue strength-life function curve corresponding to the specific fiber layup direction angle is obtained by a fatigue test of the one-way sheet at room temperature.

[0012] According to one embodiment of the present invention, the shear static strength is measured by the ±45° laminate monotonic tensile method, and the shear damage contribution ratio is calculated based on the shear static strength and the static strength of the unidirectional plate at a specific fiber layup direction angle.

[0013] According to one embodiment of the present invention, the shear damage contribution ratio is calculated by the following formula:

[0014] In the formula, The contribution ratio to shear damage is given by S, where S is the static shear strength. The angle of the fiber layup direction in a one-way sheet; Angle of fiber layup direction The static strength of a one-way slab.

[0015] According to one embodiment of the present invention, the fatigue strength versus fatigue life function curve model of an off-axis unidirectional plate is as follows:

[0016] Among them, calculation , The formula is:

[0017] In the formula It is the angle of deviation. The fatigue strength of a one-way plate with a lifespan of N. Y(N) represents the fiber-dominated basic fatigue curve, and Y(N) represents the matrix-dominated basic fatigue curve. Contribution to fiber damage Contribution ratio to matrix damage This is a correction function.

[0018] According to one embodiment of the present invention, the correction function includes a correction function for a one-way sheet with a fiber layup direction angle less than a critical angle and a correction function for a one-way sheet with a fiber layup direction angle greater than a critical angle. For a one-way board with a fiber layup direction angle less than a critical angle, the model is corrected using a correction function for one-way boards with a fiber layup direction angle less than a critical angle. For a one-way board with a fiber layup direction angle greater than the critical angle, the model is corrected using a correction function for one-way boards with a fiber layup direction angle greater than the critical angle.

[0019] According to one embodiment of the present invention, a correction function is used to calculate a unidirectional plate with a fiber layup direction angle less than a critical angle. The formula is: ; Correction function for calculating unidirectional plates with fiber layup direction angles greater than the critical angle. The formula is:

[0020] in, ; In the formula, Let X represent the shear damage contribution ratio, X be the axial tensile strength of a one-way sheet with a fiber layup angle of 0°, and Y be the longitudinal tensile strength of a one-way sheet with a fiber layup angle of 90°. The angle of the fiber layup direction in a unidirectional fiberboard. θ is the static strength of the one-way sheet when the fiber layup angle is θ; N is the predicted life.

[0021] According to an embodiment of the present invention, the fatigue strength versus fatigue life function curve model of an off-axis unidirectional plate includes: For unidirectional boards with fiber layup direction angles less than the critical angle, the following formula is used for lifetime prediction:

[0022] For one-way boards with fiber layup direction angles greater than the critical angle, the following formula is used for life prediction;

[0023] in, ; In the formula, Let X represent the shear damage contribution ratio, X be the axial tensile strength of a one-way sheet with a fiber layup angle of 0°, and Y be the longitudinal tensile strength of a one-way sheet with a fiber layup angle of 90°. The angle of the fiber layup direction in a unidirectional fiberboard. θ represents the static strength of the one-way sheet when the fiber layup angle is θ; N represents the predicted life. It is the angle of deviation. The fatigue strength of a one-way plate with a lifespan of N; This is the critical angle.

[0024] By adopting the above technical solution, the present invention has at least the following beneficial effects: The fatigue life prediction method for unidirectional plates with different fiber layup directions of ceramic matrix composites of the present invention is based on the development of fatigue life prediction of composite materials. It considers the influence of fiber and matrix failure on fatigue strength of unidirectional plates. For off-axis unidirectional plates, their fatigue characteristics depend on the synergistic effect of fibers and matrix, and the contribution ratio of the two is different at different off-axis angles. Combining the contribution ratio and shear contribution ratio, the fatigue life of unidirectional plates with different fiber layup directions is predicted. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 The shape and dimensions of the one-way plate specimen used in the experiment according to the embodiments of the present invention; Figure 2 This is a graph showing the relationship between the longitudinal, transverse, and shear contribution ratios of a one-way plate according to an embodiment of the present invention and the angle. Figure 3 The image shows the fatigue test SN curves of unidirectional plates with different fiber layup direction angles according to an embodiment of the present invention. Figure 4 This is a flowchart of a method for predicting the fatigue life of unidirectional plates with different fiber layup directions according to an embodiment of the present invention; Figure 5 This is a comparison chart of the experimental life and the predicted life of the fatigue life prediction method according to an embodiment of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0028] It should be noted that the specific structure, features, and advantages of the present invention will be illustrated by examples below. However, all descriptions are for illustrative purposes only and should not be construed as limiting the present invention in any way. Furthermore, any single technical feature described or implied in the embodiments mentioned herein, or any single technical feature shown or implied in the accompanying drawings, can still be arbitrarily combined or deleted among these technical features (or their equivalents) to obtain more other embodiments of the present invention that may not be directly mentioned herein.

[0029] This invention addresses the development of fatigue life prediction for composite materials by considering the impact of fiber and matrix failure on fatigue strength in unidirectional composite plates. For off-axis unidirectional plates, their fatigue characteristics depend on the synergistic effect of fibers and matrix, and the contribution ratios of the two differ at different off-axis angles. Combining the contribution ratio and shear contribution ratio, a life prediction model is proposed, which achieves the effect of predicting the fatigue life of unidirectional plates with different fiber layups.

[0030] To achieve the above objectives, according to one aspect of the present invention, a method for predicting the fatigue life of unidirectional plates with different fiber layup directions in ceramic matrix composites is provided, wherein the ceramic matrix composites are composed of unidirectional plates with different fiber layup directions.

[0031] The method includes the following steps: S101. Obtain the axial tensile strength of a one-way sheet with a fiber layup direction angle of 0°, the longitudinal tensile strength and critical angle of a one-way sheet with a fiber layup direction angle of 90°; and obtain the static strength of a one-way sheet under a specific fiber layup direction angle and the fatigue strength-life function curve corresponding to the specific fiber layup direction angle. S102. Based on the static strength of one-way sheet under a specific fiber layup direction angle, the axial tensile strength of one-way sheet with a fiber layup direction angle of 0°, and the longitudinal tensile strength of one-way sheet with a fiber layup direction angle of 90°, calculate the fiber damage contribution ratio and matrix damage contribution ratio corresponding to the specific fiber layup direction angle. S103. Select a first off-axis angle where the fiber layup direction angle is less than the critical angle and a second off-axis angle where the fiber layup direction angle is greater than the critical angle. Based on the fatigue strength-life function curves corresponding to the first and second off-axis angles, predict the fatigue strength-life function curves of a one-way plate with a fiber layup direction angle of 90° using fiber-dominated and matrix-dominated prediction methods, respectively. Use the fatigue strength-life function curve of a one-way plate with a fiber layup direction angle of 0° as the fiber-dominated basic fatigue curve and the fatigue strength-life function curve of a one-way plate with a fiber layup direction angle of 90° as the matrix-dominated basic fatigue curve. S104. Construct a fatigue strength and fatigue life function curve model for an off-axis unidirectional plate. The model is a weighted combination of the fiber-dominated basic fatigue curve and the matrix-dominated basic fatigue curve, wherein the weights are the fiber damage contribution ratio and the matrix damage contribution ratio. S105. Select the corresponding correction function based on the relationship between the fiber layup direction angle and the critical angle, and introduce the correction function to correct the fiber damage contribution ratio and matrix damage contribution ratio used in the model, and predict the fatigue life of unidirectional plates with different fiber layup directions of ceramic matrix composites.

[0032] According to one embodiment of the present invention, the critical angle is calculated based on the axial tensile strength of a one-way plate with a fiber layup direction angle of 0° and the longitudinal tensile strength of a one-way plate with a fiber layup direction angle of 90°. The formula for calculating the critical angle is:

[0033] In the formula X is the critical angle, where X is the axial tensile strength of a one-way sheet with a fiber layup angle of 0°, and Y is the longitudinal tensile strength of a one-way sheet with a fiber layup angle of 90°.

[0034] According to an embodiment of the present invention, the formula for calculating the fiber damage contribution ratio and matrix damage contribution ratio corresponding to the specific fiber layup direction angle is as follows: Based on the static strength of the one-way sheet at a specific fiber layup direction angle, the axial tensile strength of the one-way sheet with a fiber layup direction angle of 0°, and the longitudinal tensile strength of the one-way sheet with a fiber layup direction angle of 90°.

[0035] In the formula Contribution to fiber damage Contribution ratio to matrix damage The angle of the fiber layup direction in a unidirectional fiberboard. Angle of fiber layup direction The static strength of a one-way slab.

[0036] According to one embodiment of the present invention, the static strength of a one-way sheet at a specific fiber layup direction angle is obtained by a static tensile test of the one-way sheet at room temperature; and the fatigue strength-life function curve corresponding to the specific fiber layup direction angle is obtained by a fatigue test of the one-way sheet at room temperature.

[0037] According to one embodiment of the present invention, the shear static strength is measured by the ±45° laminate monotonic tensile method, and the shear damage contribution ratio is calculated based on the shear static strength and the static strength of the unidirectional plate at a specific fiber layup direction angle.

[0038] According to one embodiment of the present invention, the shear damage contribution ratio is calculated by the following formula:

[0039] In the formula, The contribution ratio to shear damage is given by S, where S is the static shear strength. The angle of the fiber layup direction in a one-way sheet; Angle of fiber layup direction The static strength of a one-way slab.

[0040] According to one embodiment of the present invention, the fatigue strength versus fatigue life function curve model of an off-axis unidirectional plate is as follows:

[0041] Among them, calculation , The formula is:

[0042] In the formula It is the angle of deviation. The fatigue strength of a one-way plate with a lifespan of N. Y(N) represents the fiber-dominated basic fatigue curve, and Y(N) represents the matrix-dominated basic fatigue curve. Contribution to fiber damage Contribution ratio to matrix damage This is a correction function.

[0043] According to one embodiment of the present invention, the correction function includes a correction function for a one-way sheet with a fiber layup direction angle less than a critical angle and a correction function for a one-way sheet with a fiber layup direction angle greater than a critical angle. For a one-way board with a fiber layup direction angle less than a critical angle, the model is corrected using a correction function for one-way boards with a fiber layup direction angle less than a critical angle. For a one-way board with a fiber layup direction angle greater than the critical angle, the model is corrected using a correction function for one-way boards with a fiber layup direction angle greater than the critical angle.

[0044] According to one embodiment of the present invention, a correction function is used to calculate a unidirectional plate with a fiber layup direction angle less than a critical angle. The formula is: ; Correction function for calculating unidirectional plates with fiber layup direction angles greater than the critical angle. The formula is:

[0045] in, ; In the formula, Let X represent the shear damage contribution ratio, X be the axial tensile strength of a one-way sheet with a fiber layup angle of 0°, and Y be the longitudinal tensile strength of a one-way sheet with a fiber layup angle of 90°. The angle of the fiber layup direction in a unidirectional fiberboard. θ is the static strength of the one-way sheet when the fiber layup angle is θ; N is the predicted life.

[0046] According to an embodiment of the present invention, the fatigue strength versus fatigue life function curve model of an off-axis unidirectional plate includes: For unidirectional boards with fiber layup direction angles less than the critical angle, the following formula is used for lifetime prediction:

[0047] For one-way boards with fiber layup direction angles greater than the critical angle, the following formula is used for life prediction;

[0048] in, ; In the formula, Let X represent the shear damage contribution ratio, X be the axial tensile strength of a one-way sheet with a fiber layup angle of 0°, and Y be the longitudinal tensile strength of a one-way sheet with a fiber layup angle of 90°. The angle of the fiber layup direction in a unidirectional fiberboard. θ represents the static strength of the one-way sheet when the fiber layup angle is θ; N represents the predicted life. It is the angle of deviation. The fatigue strength of a one-way plate with a lifespan of N; This is the critical angle.

[0049] This invention presents a prediction method for unidirectional needle-punched C / SiC composite off-axis single-layer plates, a key candidate material in the aerospace field. It systematically investigates the mechanical response under cyclic loading, aiming to solve the challenge of accurately predicting the fatigue life of materials under complex stress conditions. The study innovatively integrates the fatigue strength evolution mechanism of 0° and 90° single-layer plates, extracts key parameters, and constructs characteristic functions, forming an optimized fatigue life prediction model applicable to different layup angles. Multiple comparative experiments verify that the model accurately captures the fatigue behavior characteristics of materials under different load conditions, with high agreement between theoretical predictions and measured data, effectively overcoming the prediction bias of traditional models under non-0° / 90° layup angles. Further analysis shows that the fiber arrangement direction plays a decisive role in the fatigue resistance of the material by affecting the internal stress transmission path and damage evolution rate. This research improves the fatigue performance evaluation system of C / SiC composite materials, providing important theoretical basis and technical support for the structural design, performance optimization, and safety assessment of this type of material under complex stress conditions in aerospace.

[0050] Specifically, the present invention verifies the proposed model through systematic fatigue tests and static tensile tests on unidirectional plates with different fiber orientations.

[0051] The specific experimental scheme is as follows: Two types of mechanical property tests were conducted on unidirectional needle-punched carbon fiber reinforced silicon carbide (UN-C / SiC) composite materials at room temperature: static tensile tests and stress-controlled fatigue tests. All fatigue tests used a loading frequency of 3Hz, a stress ratio R=0.1, and a sine wave as the load waveform. The unidirectional plate specimens were... Figure 1 The specific geometric dimensions shown ensure the comparability and consistency of the experimental results. This experimental design not only provides crucial foundational data for model validation, but also lays a reliable foundation for accurately evaluating the applicability and accuracy of the prediction method by controlling key experimental parameters.

[0052] Figure 4 The following is a detailed flowchart of the method in an embodiment.

[0053] Step 1: All specimens used in the experiment were plate-shaped. The corresponding stress loading and fatigue load levels were set according to the structural design requirements, and the static strength and fatigue life of the one-way plates were tested at room temperature. Based on the Hashin failure criterion, the calculation formula for the critical angle can be derived as follows:

[0054] In the formula, X is the critical angle, where X is the axial tensile strength of a one-way sheet with a fiber layup angle of 0°, and Y is the longitudinal tensile strength of a one-way sheet with a fiber layup angle of 90°.

[0055] Step 2: Obtain the static strength of the one-way sheet at different fiber angles through static tensile tests at room temperature. Based on the static strength of the 0° and 90° one-way sheets, the damage contribution ratio of the fiber and matrix at different fiber angles can be calculated. The formula for the contribution ratio is as follows:

[0056] In the formula, , These represent the contribution ratios of fiber damage and matrix damage, respectively. The angle of the fiber layup direction in a unidirectional fiberboard. Angle of fiber layup direction The static strength of a one-way slab.

[0057] Step 3: The shear strength of the ceramic matrix composite at room temperature was measured using the ±45° laminate monotonic tensile method. The shear strength performance trend was fitted by the shear damage contribution ratio. The formula for the shear damage contribution ratio is as follows:

[0058] In the formula, S is the static shear strength. Contribution ratio to shear damage The angle of the fiber layup direction in a one-way sheet; Angle of fiber layup direction The static strength of a one-way slab. For example... Figure 2 The figure shows the contribution ratio of the fiber and matrix, as well as the contribution ratio under shear conditions, as a function of angle. It can be seen that the contribution ratio of the fiber and matrix changes most significantly when the shear contribution ratio is at its maximum. Therefore, it is considered that the shear contribution ratio has a moderately prolonging effect on fatigue.

[0059] Step 4: Obtain the fatigue strength-life function curves (hereinafter referred to as fatigue life SN curves) of unidirectional plates with different fiber layups through fatigue tests at room temperature. The form is as follows:

[0060] In the formula, Let be the maximum cyclic fatigue stress, a and b be fitting constants, and N be the fatigue life. The SN curve of the 0° one-way plate is denoted as X(N).

[0061] like Figure 3 The image shows the SN curves for different fiber layup orientation angles. From... Figure 3 As can be seen, the SN curves for fiber layup direction angles of 0, 15, 45, and 60° can be directly measured.

[0062] Step 5: The 90° fatigue curve can be obtained by... The fatigue life curves of the two sides with skew angles are used to predict the fatigue life, and the prediction formula is as follows; This formula is a prediction formula for fiber-dominated failure:

[0063] This formula is a prediction formula for matrix-dominated failure:

[0064] in, For the angle of deviation The fatigue strength of a one-way plate with a lifespan of N. The fatigue strength of a 0° one-way sheet with a lifespan of N. Let N be the shear fatigue strength under shear conditions with a lifespan of N. The fatigue strength of a 90° one-way plate with a life of N.

[0065] like Figure 3 As shown, based on the known fatigue SN curves of 60° and 15° unidirectional plates, since 15° is smaller than the critical angle of ceramic matrix composites, while 60° is larger than the critical angle of ceramic matrix composites.

[0066] The fatigue load-life curves from these two angles can be used to obtain the fatigue SN curve of a 90° unidirectional plate of ceramic matrix composite material using the following formula ( ), among which, such as Figure 3 As shown, the fatigue strength of a 0° one-way plate at a lifetime of N. It can be measured directly. The fatigue strength of the one-way plate with a life of N at skew angles of 15° and 60° can be directly measured. , Therefore, the fatigue SN curve of a 90° one-way plate can be calculated. ).

[0067] .

[0068] Step 6: For an off-axis unidirectional plate, its fatigue characteristics depend on the synergistic effect of the fiber and the matrix, and the contribution ratio of the two differs at different off-axis angles. Therefore, the SN curve of the off-axis unidirectional plate can be regarded as a weighted combination of the fatigue load-life curves at 0° and 90°, and the relationship can be expressed by the following formula:

[0069] In the formula, It is the fatigue strength function with a lifespan of N for a one-way plate when the off-axis angle is θ. and These represent the contribution ratios of the fiber and the matrix during fatigue failure, respectively.

[0070] Step 7: Since shear strength promotes fatigue propagation, from Figure 2 As can be seen, shear contributes to fatigue propagation. However, since the damage contribution ratio is only the value under static strength, the effect of load on fatigue propagation must be considered. Therefore: For one-way plates with fiber skew angles less than the critical angle, the damage contribution ratio is corrected using the following formula: That is, when... When this happens, the correction function used is:

[0071] For correction functions, .

[0072] For one-way plates with fiber skew angles greater than the critical angle, the damage contribution ratio is corrected using the following formula: That is, when... When this happens, the correction function used is:

[0073] For correction functions, ...

[0074] Substituting the correction function into the formula, we can obtain the final result. and contribution ratio .

[0075] Step 8: Substitute the final contribution ratio formula into the proposed lifetime prediction method. For unidirectional plates with fiber skew angles less than the critical angle, i.e., when... At that time, the following formula is used for lifetime prediction:

[0076] For one-way sheets with fiber skew angles greater than the critical angle, i.e. when At that time, the following formula is used for lifetime prediction:

[0077] In the formula, N represents fatigue life.

[0078] It is the angle of fiber layup direction in fatigue testing. The fatigue strength of a one-way sheet with a lifespan of N can be calculated by taking the maximum known stress applied to the one-way sheet.

[0079] Steps 2 and 3 introduce the contribution ratio of fibers and matrix at failure; Step 5 adopts a special 90° transverse fatigue SN curve calculation method; Step 7, combined with Step 6, proposes a fatigue life prediction model for unidirectional plates with different fiber layup sequences, which can convert unidirectional plates with other fiber angles into a method dominated by both transverse and longitudinal fatigue when the transverse and longitudinal master fatigue curves are known.

[0080] To fully verify the accuracy and reliability of the fatigue life prediction method proposed in this invention, the model-predicted life is compared with experimental test results, specifically for example... Figure 5 As shown in the figure. Analysis results demonstrate that this method exhibits good applicability in predicting the fatigue life of unidirectional plates with different fiber orientation angles. By establishing a quantitative relationship between fiber angle and fatigue life, the model can effectively evaluate the fatigue characteristics of ceramic matrix composites under different layup directions. From Figure 5 Further observation reveals that the data points comparing the predicted and experimental lifetimes are mainly distributed within a 3x error band. Considering the inherent discrete properties of composite materials, this error level is within an acceptable range for engineering applications, fully demonstrating the feasibility and robustness of this method in practical applications. The prediction model established in this invention provides a reliable theoretical basis for the strength design and lifetime assessment of composite material structures under complex stress states, and has strong engineering application value.

[0081] The fatigue life prediction formula proposed in this invention has the following outstanding advantages: First, the calculation process is simple and efficient, requiring only a small amount of basic experimental data, including fatigue tests and static strength tests under room temperature conditions, to construct a complete prediction model. This significantly reduces the large number of test samples and complex procedures required by traditional fatigue testing, effectively reducing time and economic costs, and possessing good engineering practicality and promotional value. Second, this method can accurately predict the fatigue life of ceramic matrix composite unidirectional plates under different fiber layup angles. Multiple sets of experiments have verified that the predicted results and measured data show a high degree of agreement, fully demonstrating the model's adaptability and prediction accuracy under complex stress states, proving its reliability and applicability in practical engineering applications. In summary, this model can accurately assess the fatigue life of ceramic matrix composite unidirectional plates based on only limited experimental data, providing important technical support for related structural design and life management, and possessing significant engineering application value.

[0082] The above are exemplary embodiments disclosed in this invention. The order of the disclosed embodiments is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. However, it should be noted that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the disclosed embodiments of this invention (including the claims) is limited to these examples. Various changes and modifications can be made without departing from the scope defined by the claims. The functions, steps, and / or actions of the methods according to the disclosed embodiments described herein do not need to be performed in any particular order. Furthermore, although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular.

[0083] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for predicting the fatigue life of unidirectional plates with different fiber layup directions in ceramic matrix composites, characterized in that, The ceramic matrix composite material consists of unidirectional plates with different fiber layup directions; the method includes: S101. Obtain the axial tensile strength of a one-way sheet with a fiber layup direction angle of 0°, the longitudinal tensile strength and critical angle of a one-way sheet with a fiber layup direction angle of 90°; and obtain the static strength of a one-way sheet under a specific fiber layup direction angle and the fatigue strength-life function curve corresponding to the specific fiber layup direction angle. S102. Based on the static strength of one-way sheet under a specific fiber layup direction angle, the axial tensile strength of one-way sheet with a fiber layup direction angle of 0°, and the longitudinal tensile strength of one-way sheet with a fiber layup direction angle of 90°, calculate the fiber damage contribution ratio and matrix damage contribution ratio corresponding to the specific fiber layup direction angle. S103. Select a first off-axis angle where the fiber layup direction angle is less than the critical angle and a second off-axis angle where the fiber layup direction angle is greater than the critical angle. Based on the fatigue strength-life function curves corresponding to the first and second off-axis angles, predict the fatigue strength-life function curves of a one-way plate with a fiber layup direction angle of 90° using fiber-dominated and matrix-dominated prediction methods, respectively. Use the fatigue strength-life function curve of a one-way plate with a fiber layup direction angle of 0° as the fiber-dominated basic fatigue curve and the fatigue strength-life function curve of a one-way plate with a fiber layup direction angle of 90° as the matrix-dominated basic fatigue curve. S104. Construct a fatigue strength and fatigue life function curve model for an off-axis unidirectional plate. The model is a weighted combination of the fiber-dominated basic fatigue curve and the matrix-dominated basic fatigue curve, wherein the weights are the fiber damage contribution ratio and the matrix damage contribution ratio. S105. Select the corresponding correction function based on the relationship between the fiber layup direction angle and the critical angle, and introduce the correction function to correct the fiber damage contribution ratio and matrix damage contribution ratio used in the model, and predict the fatigue life of unidirectional plates with different fiber layup directions of ceramic matrix composites.

2. The fatigue life prediction method according to claim 1, characterized in that, The critical angle is calculated based on the axial tensile strength of a one-way sheet with a fiber layup direction angle of 0° and the longitudinal tensile strength of a one-way sheet with a fiber layup direction angle of 90°. The formula for calculating the critical angle is: In the formula X is the critical angle, where X is the axial tensile strength of a one-way sheet with a fiber layup angle of 0°, and Y is the longitudinal tensile strength of a one-way sheet with a fiber layup angle of 90°.

3. The fatigue life prediction method according to claim 1, characterized in that, The formulas for calculating the fiber damage contribution ratio and matrix damage contribution ratio corresponding to specific fiber layup direction angles are as follows: (Based on the static strength of one-way sheets with a fiber layup direction angle of 0° and the axial tensile strength of one-way sheets with a fiber layup direction angle of 90°). In the formula Contribution to fiber damage Contribution ratio to matrix damage The angle of the fiber layup direction in a unidirectional fiberboard. Angle of fiber layup direction The static strength of a one-way slab.

4. The fatigue life prediction method according to claim 1, characterized in that, The static strength of one-way sheets at a specific fiber layup angle was obtained by static tensile testing at room temperature; and the fatigue strength-life function curve corresponding to a specific fiber layup angle was obtained by fatigue testing at room temperature.

5. The fatigue life prediction method according to claim 1, characterized in that, The static shear strength of the laminate was measured by the monotonic tensile method at ±45°. The shear damage contribution ratio was calculated based on the static shear strength and the static strength of the unidirectional plate at a specific fiber layup angle.

6. The fatigue life prediction method according to claim 5, characterized in that, The shear damage contribution ratio is calculated using the following formula: In the formula, The contribution ratio to shear damage is given by S, where S is the static shear strength. The angle of the fiber layup direction in a one-way sheet; Angle of fiber layup direction The static strength of a one-way slab.

7. The fatigue life prediction method according to claim 1, characterized in that, The fatigue strength versus fatigue life function curve model for an off-axis unidirectional plate is as follows: Among them, calculation , The formula is: In the formula It is the angle of deviation. The fatigue strength of a one-way plate with a lifespan of N. Y(N) represents the fiber-dominated basic fatigue curve, and Y(N) represents the matrix-dominated basic fatigue curve. Contribution to fiber damage Contribution ratio to matrix damage This is a correction function.

8. The fatigue life prediction method according to claim 5, characterized in that, The correction functions include correction functions for one-way sheets with fiber layup direction angles less than the critical angle and correction functions for one-way sheets with fiber layup direction angles greater than the critical angle. For a one-way board with a fiber layup direction angle less than a critical angle, the model is corrected using a correction function for one-way boards with a fiber layup direction angle less than a critical angle. For a one-way board with a fiber layup direction angle greater than the critical angle, the model is corrected using a correction function for one-way boards with a fiber layup direction angle greater than the critical angle.

9. The fatigue life prediction method according to claim 5, characterized in that, Correction function for calculating unidirectional plates with fiber layup direction angles less than the critical angle. The formula is: ； Correction function for calculating unidirectional plates with fiber layup direction angles greater than the critical angle. The formula is: in, ; In the formula, Let X represent the shear damage contribution ratio, X be the axial tensile strength of a one-way sheet with a fiber layup angle of 0°, and Y be the longitudinal tensile strength of a one-way sheet with a fiber layup angle of 90°. The angle of the fiber layup direction in a unidirectional fiberboard. θ is the static strength of the one-way sheet when the fiber layup angle is θ; N is the predicted life.

10. The fatigue life prediction method according to claim 9, characterized in that, The fatigue strength versus fatigue life function curve model for an off-axis unidirectional plate includes: For unidirectional boards with fiber layup direction angles less than the critical angle, the following formula is used for lifetime prediction: For one-way boards with fiber layup direction angles greater than the critical angle, the following formula is used for life prediction; in, ; In the formula, Let X represent the shear damage contribution ratio, X be the axial tensile strength of a one-way sheet with a fiber layup angle of 0°, and Y be the longitudinal tensile strength of a one-way sheet with a fiber layup angle of 90°. The angle of the fiber layup direction in a unidirectional fiberboard. θ represents the static strength of the one-way sheet when the fiber layup angle is θ; N represents the predicted life. It is the angle of deviation. The fatigue strength of a one-way plate with a lifespan of N; This is the critical angle.

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