A method for predicting the fatigue life of a composite material

Abstract

The application discloses a kind of composite fatigue life prediction method, comprising the following steps: acquisition prediction data;Prediction data processing;Building prediction metamodel;Building fatigue life prediction model.The application is carried out quasi-static mechanical property test and fatigue mechanical property test by multiple points, obtains different types of data, increases the data amount in prediction process, can improve the accuracy of prediction;By building the fatigue life prediction model of carbon fiber composite material, the parameter of the carbon fiber composite material to be predicted is input into the fatigue life prediction model, and then fatigue life prediction is carried out by different prediction methods, which can improve the accuracy of the fatigue life prediction model of carbon fiber composite material.

Description

Technical Field

[0001] This invention relates to the field of performance prediction technology, and in particular to a method for predicting the fatigue life of composite materials. Background Technology

[0002] Carbon fiber reinforced composites are composite materials formed using carbon fibers or carbon fiber fabrics as reinforcement and resins, ceramics, metals, cement, carbonaceous materials, or rubber as the matrix. Among many lightweight materials, they have high specific strength and specific stiffness, resulting in significant weight reduction effects, and are widely used in aerospace and military products.

[0003] Existing invention patent 201910046021.X proposes a method for predicting the fatigue life of composite materials. This method uses readily available vibration acquisition equipment to collect frequencies and then predicts fatigue life, offering simplicity, ease of implementation, and good accuracy. However, existing technologies for predicting the fatigue life of carbon fiber reinforced composite materials still require repeated testing. Predictions for different material types also require repeated testing. Furthermore, the fatigue behavior of composite materials under multiple stress levels is complex, and impact damage can significantly reduce the residual strength and fatigue performance of composite materials. Accurate prediction of the fatigue life of composite materials under impact damage, high-frequency, low-amplitude vibration fatigue loads is difficult. Therefore, a method for predicting the fatigue life of composite materials is urgently needed to address these issues. Summary of the Invention

[0004] The purpose of this invention is to provide a method for predicting the fatigue life of composite materials. By acquiring different types of data and increasing the amount of data in the prediction process, the accuracy of the prediction can be improved.

[0005] To solve the above technical problems, the technical solution of the present invention is: a method for predicting the fatigue life of composite materials, comprising the following steps: S1: Collect prediction data The composite material is prepared into test specimens, and the mechanical properties of the test specimens are tested. The test data is recorded and used as prediction data. S2: Predictive Data Processing Based on the predicted data, the stress ratio, cyclic average stress, cyclic stress, and tensile angle are obtained to construct a constant amplitude life diagram; S3: Constructing a predictive meta-model Data from the constant amplitude lifetime map is extracted, and three-dimensional model data of the composite material is obtained using modeling software. A predictive meta-model of the composite material is then constructed based on the three-dimensional model data. S4: Construct a fatigue life prediction model The fatigue life prediction method is imported into the prediction meta-model of composite materials. The fatigue life prediction method calls the data in the prediction meta-model to predict the fatigue life of composite materials, thus completing the construction of the composite material fatigue life prediction model, which is used to predict the fatigue life of different composite materials.

[0006] Preferably, in step S1, the composite material is carbon fiber fabric, including carbon fiber nonwoven fabric, carbon fiber prepreg, carbon fiber woven fabric, and carbon fiber knitted fabric; the test sample can be prepared from one or more of the carbon fiber fabrics.

[0007] Preferably, in step S1, the composite material is prepared into a test sample using a vacuum induction process, the specific steps of which are as follows: S101: Set a vacuum bag on the mold and place the composite material inside the vacuum bag; S102: Insert an injection pipe into the top of the vacuum bag and seal it. First, remove the air from the vacuum bag, and then inject resin into the vacuum bag through the injection pipe. Use the vacuum to guide the resin to penetrate into the fibers of the composite material for impregnation. S103: After the resin solidifies, the composite material is taken out of the vacuum bag of the mold and placed in an oven at 80°C for 6 hours to harden, thus preparing the test sample.

[0008] Preferably, in step S1, the mechanical property test includes quasi-static mechanical property test, fatigue mechanical property test, and mechanical property test including impact damage.

[0009] Preferably, the quasi-static mechanical property test is performed using a hydraulic mechanical testing machine, a mechanical extensometer, and a laser extensometer, with the specific steps as follows: Step 1: Prepare three identical test specimens for each test group, and set the loading direction and loading rate of the hydraulic mechanics testing machine load; Step 2: Under the loading rate, the test specimens are subjected to compression tests along the loading direction of the load until the load is applied to all three test specimens and they fail. Step 3: Collect test data using a mechanical extensometer and a laser extensometer, and use the average of the test data as the test result.

[0010] Preferably, step S2 includes the following steps: S201: The critical value of the stress ratio is used as the boundary line of the fatigue behavior region of the composite material. The SN curve of the stress ratio R is obtained from the boundary rays of each fatigue behavior region starting from the origin, where S is the stress amplitude and N is the number of cycles. S202: Connect the same lifetime points on the SN curves under different stress ratios to obtain an equal lifetime curve diagram; S203: Use the rainflow calculation method to correct the variable amplitude load and obtain the constant amplitude load spectrum; S204: Construct a constant amplitude lifetime diagram based on the constant amplitude load spectrum.

[0011] Preferably, in step S2, the prediction data collected in step S1 is screened and the names of the prediction data are labeled before constructing the constant amplitude lifetime map.

[0012] Preferably, in step S4, the fatigue life prediction method includes the nominal stress method, the local stress-strain method, the fracture mechanics method, the probabilistic fracture mechanics method, the field strength method, and the energy method.

[0013] Compared with the prior art, the beneficial effects of the present invention are: (1) By conducting quasi-static mechanical property tests and fatigue mechanical property tests at multiple points, different types of data are obtained, increasing the amount of data in the prediction process and improving the accuracy of the prediction; (2) By constructing a fatigue life prediction model for carbon fiber composite materials, inputting the parameters of the carbon fiber composite material to be predicted into the fatigue life prediction model, and then using different prediction methods to predict the fatigue life, the accuracy of the fatigue life prediction model for carbon fiber composite materials can be improved. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention 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.

[0015] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0016] The present invention will now be described in further detail with reference to the accompanying drawings. The terminal technical solutions of the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0017] like Figure 1 As shown, the present invention provides a method for predicting the fatigue life of composite materials, comprising the following steps: S1: Collect prediction data The composite material is prepared into test specimens, and quasi-static mechanical properties and fatigue mechanical properties are tested at multiple points on the test specimens. The test data are recorded and used as prediction data.

[0018] The composite material is a carbon fiber fabric, including carbon fiber nonwoven fabric, carbon fiber prepreg, carbon fiber woven fabric, and carbon fiber knitted fabric. The test sample can be prepared from one or more of the carbon fiber fabrics.

[0019] In this embodiment, the composite material is prepared into test samples using a vacuum induction process, and the specific steps are as follows: S101: Set a vacuum bag on the mold and place the composite material inside the vacuum bag; S102: Insert an injection pipe into the top of the vacuum bag and seal it. First, remove the air from the vacuum bag, and then inject resin into the vacuum bag through the injection pipe. Use the vacuum to guide the resin to penetrate into the fibers of the composite material for impregnation. S103: After the resin solidifies, the composite material is taken out of the vacuum bag of the mold and placed in an oven at 80°C for 6 hours to harden, thus preparing the test sample.

[0020] In this embodiment, the quasi-static mechanical property test is conducted using a hydraulic mechanical testing machine, a mechanical extensometer, and a laser extensometer. The specific steps of the quasi-static mechanical property test are as follows: Step 1: Prepare three identical test samples for each test group, and set the loading direction and loading rate of the hydraulic mechanical testing machine; the loading direction is the 0° direction, that is, the axial direction of the test sample; the loading rate is 0.4 mm / min.

[0021] Step 2: Under the loading rate, the test specimens are subjected to compression tests along the loading direction of the load until the load is applied to all three test specimens and they fail.

[0022] Step 3: Collect test data using a mechanical extensometer and a laser extensometer, and use the average value of the test data as the test result. The test results are shown in Table 1.

[0023] Table 1 Compression Test Results Sample number Failure load KN Compressive strength (MPa) Failure strain % Elastic modulus GPa 1 5.342 211.36 0.99 21.418 2 5.368 214.85 1.02 21.421 3 5.471 218.83 1.03 21.408 mean 5.394 215.01 1.01 21.416 In this embodiment, the conditions set for the fatigue mechanical property test are as follows: (1) The loading frequencies are 1Hz, 5Hz and 15Hz respectively; (2) The load loading directions for the tensile fatigue test are 0° and 45° respectively; (3) The load direction for the compression fatigue test is the 0° direction; (4) The test environment was set according to ASTM D3479 standard, specifically the temperature was set to 20±5℃ and the humidity was set to 45±5%RH.

[0024] Fatigue mechanical properties were tested at a stress level with a stress ratio R=0.1, and the test results are shown in Table 2.

[0025] Table 2 Fatigue mechanical property test results Stress amplitude MPa Lifespan 1 Lifespan 2 Lifespan 3 297 625 846 1001 281 1932 3270 8880 275 29540 45211 69342 248 155860 190848 211543 231 905610 1319912 1486316 S2: Predictive Data Processing The prediction data collected in step S1 is filtered, and the names of the prediction data are labeled.

[0026] Based on the selected prediction data, the stress ratio, cyclic average stress, cyclic stress and tensile angle are obtained to construct a constant amplitude life diagram. The specific steps are as follows: S201: The critical value of the stress ratio is used as the boundary line of the fatigue behavior region of the composite material. The SN curve of the stress ratio R is obtained from the boundary rays of each fatigue behavior region starting from the origin, where S is the stress amplitude and N is the number of cycles. S202: Connect the same lifetime points on the SN curves under different stress ratios to obtain an equal lifetime curve diagram; S203: Use the rainflow calculation method to correct the variable amplitude load and obtain the constant amplitude load spectrum; S204: Construct a constant amplitude lifetime diagram based on the constant amplitude load spectrum.

[0027] S3: Constructing a predictive meta-model Data from the constant amplitude lifetime map is extracted, and three-dimensional model data of the composite material is obtained using Catia modeling software. A predictive meta-model of the composite material is then constructed based on the three-dimensional model data. S4: Construct a fatigue life prediction model The fatigue life prediction method is imported into the prediction meta-model of composite materials. The fatigue life prediction method calls the data in the prediction meta-model to predict the fatigue life of composite materials, thus completing the construction of the composite material fatigue life prediction model, which is used to predict the fatigue life of different composite materials.

[0028] In this embodiment, the fatigue life prediction method includes the nominal stress method, the local stress-strain method, the fracture mechanics method, the probabilistic fracture mechanics method, the field strength method, and the energy method. The above prediction methods are used to predict the fatigue life of different carbon fiber composite materials.

[0029] All parts not covered in this invention are the same as or implemented using existing technologies.

[0030] The above description, in conjunction with specific embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for predicting the fatigue life of composite materials, characterized in that: Includes the following steps: S1: Collect prediction data The composite material is prepared into test specimens, and the mechanical properties of the test specimens are tested. The test data is recorded and used as prediction data. S2: Predictive Data Processing Based on the predicted data, the stress ratio, cyclic average stress, cyclic stress, and tensile angle are obtained to construct a constant amplitude life diagram; S3: Constructing a predictive meta-model Data from the constant amplitude lifetime map is extracted, and three-dimensional model data of the composite material is obtained using modeling software. A predictive meta-model of the composite material is then constructed based on the three-dimensional model data. S4: Construct a fatigue life prediction model The fatigue life prediction method is imported into the prediction meta-model of composite materials. The fatigue life prediction method calls the data in the prediction meta-model to predict the fatigue life of composite materials, thus completing the construction of the composite material fatigue life prediction model, which is used to predict the fatigue life of different composite materials.

2. The method for predicting the fatigue life of a composite material according to claim 1, characterized in that: In step S1, the composite material is carbon fiber fabric, including carbon fiber nonwoven fabric, carbon fiber prepreg, carbon fiber woven fabric and carbon fiber knitted fabric; the test sample can be prepared from one or more of the carbon fiber fabrics.

3. The method for predicting the fatigue life of a composite material according to claim 1, characterized in that: In step S1, the composite material is prepared into a test sample using a vacuum induction process. The specific steps are as follows: S101: Set a vacuum bag on the mold and place the composite material inside the vacuum bag; S102: Insert an injection pipe into the top of the vacuum bag and seal it. First, remove the air from the vacuum bag, and then inject resin into the vacuum bag through the injection pipe. Use the vacuum to guide the resin to penetrate into the fibers of the composite material for impregnation. S103: After the resin solidifies, the composite material is taken out of the vacuum bag of the mold and placed in an oven at 80°C for 6 hours to harden, thus preparing the test sample.

4. The method for predicting the fatigue life of a composite material according to claim 1, characterized in that: In step S1, the mechanical property test includes quasi-static mechanical property test, fatigue mechanical property test and mechanical property test including impact damage.

5. The method for predicting the fatigue life of a composite material according to claim 4, characterized in that: The quasi-static mechanical properties were tested using a hydraulic mechanical testing machine, a mechanical extensometer, and a laser extensometer. The specific steps are as follows: Step 1: Prepare three identical test specimens for each test group, and set the loading direction and loading rate of the hydraulic mechanics testing machine load; Step 2: Under the loading rate, the test specimens are subjected to compression tests along the loading direction of the load until the load is applied to all three test specimens and they fail. Step 3: Collect test data using a mechanical extensometer and a laser extensometer, and use the average of the test data as the test result.

6. The method for predicting the fatigue life of a composite material according to claim 1, characterized in that: Step S2 includes the following steps: S201: The critical value of the stress ratio is used as the boundary line of the fatigue behavior region of the composite material. The SN curve of the stress ratio R is obtained from the boundary rays of each fatigue behavior region starting from the origin, where S is the stress amplitude and N is the number of cycles. S202: Connect the same lifetime points on the SN curves under different stress ratios to obtain an equal lifetime curve diagram; S203: Use the rainflow calculation method to correct the variable amplitude load and obtain the constant amplitude load spectrum; S204: Construct a constant amplitude lifetime diagram based on the constant amplitude load spectrum.

7. The method for predicting the fatigue life of a composite material according to claim 1, characterized in that: In step S2, before constructing the constant amplitude lifetime map, the prediction data collected in step S1 needs to be filtered and the names of the prediction data need to be labeled.

8. The method for predicting the fatigue life of a composite material according to claim 1, characterized in that: In step S4, the fatigue life prediction method includes the nominal stress method, the local stress-strain method, the fracture mechanics method, the probabilistic fracture mechanics method, the field strength method, and the energy method.

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