Eccentric tension test method, eccentric tension of CMC using this method, and damage identification

Abstract

The present invention discloses an eccentric tensile test method, eccentric tensile test on CMC and damage identification using this method. A CMC-ES model and a CMC-DTI model are loaded on a traditional electronic universal testing machine, and an adjustable fixture (40) is installed on the chucks (10, 20). The eccentric tensile test method can complete the eccentric tensile test on CMC material specimens at different eccentric angles. By using the mechanical property parameters at different eccentric angles and applying multi-scale wavelet time-frequency and finite element analysis, a CMC eccentric tensile mechanics database is constructed. In the CMC-DTI model, a method combining fracture morphology and acoustic emission peak frequency is used. The EUMTT system of the present invention realizes the identification of damage types of CMC material specimens.

Description

Technical Field

[0001] The present invention relates to an eccentric testing method using an electronic universal testing machine, and more particularly, to a method for implementing an eccentric tensile test on a ceramic matrix composite (CMC) on an electronic universal testing machine, and a method for identifying the damage type of the CMC material through eccentric tensile parameters. Background Art

[0002] An electronic universal testing machine is an instrument used to test specimens for mechanical properties such as tension, compression, bending, shear, and peeling. The loading method is the same as that of a mechanical universal testing machine, both utilizing mechanical transmission. However, electronic universal testing machines utilize electronic technology to measure force, displacement, and deformation, unlike the pendulum, pointer, and dial methods used in mechanical universal testing machines. Loading speed control also utilizes an electronic speed control unit, replacing the speed control handwheel of a mechanical universal testing machine. When connected to a computer, control, testing, and data processing can be automated. In short, the electronic universal testing machine is a new type of testing machine that combines electronic technology with mechanical transmission.

[0003] "Engineering Materials Mechanics Test" published by Guangdong Science and Technology Press in July 2005, by Zhan Sheng and Mu Cuiling. Pages 18-20 disclose an electronic universal testing machine, which is divided into two parts: the main unit and the computer control. The main unit is used to clamp, fix, load, and transform the force of the test sample. The upper and lower chucks clamp the upper and lower ends of the test sample. The computer control mainly provides the power source, realizes the transmission of force and transmission mode, and collects and analyzes data. Please refer to the electronic universal testing machine. Figure 1 shown.

[0004] Acoustic emission technology (AE) has been widely used for damage detection in structures and components due to its advantages of dynamic and real-time detection. Practice has shown that different tissue materials experience varying degrees of damage when subjected to loads, and the characteristics of the AE waveform signals emitted by these different damage states vary. For example, elastoplastic damage and yield damage occurring under static tensile loads will each exhibit distinct AE waveform parameters such as amplitude, phase, and frequency. Furthermore, CMC material specimens with unique structural properties also possess unique AE waveform characteristics under various deformation damage states. Therefore, AE technology can be used as a tool to monitor the deformation damage state of CMC material specimens.

[0005] Ceramic matrix composites (CMC) have high-temperature mechanical stability and great application potential. However, the fracture mechanism of CMC materials is very complex and the toughness is insufficient, which severely limits the engineering application of CMC materials. When CMC materials are fabricated into various complex-shaped components, due to the combined effects of aerodynamics, thermal loads, and mechanical loads, the complex-shaped components are not only often subjected to tensile loads but also the coupling action of shear forces. Currently, most of the electronic universal testing machines can only conduct tensile mechanical tests for simple stress states in the longitudinal direction and cannot simulate the tests under complex stress states in the application scenarios. Summary of the Invention

[0006] In order to perform eccentric tensile tests on CMC material specimens using a traditional electronic universal testing machine, a CMC-ES model, a CMC-DTI model are loaded on the traditional electronic universal testing machine, and an adjustable fixture (40) designed by the present invention is installed on the chucks (10, 20), which is called an electronic universal testing machine for eccentric tensile testing (EUMTT), that is, the EUMTT system. In the EUMTT system of the present invention, the installation method of the adjustable fixture (40) includes: installing the adjustable fixture (40) designed by the present invention on the upper chuck (10) of the traditional electronic universal testing machine, or installing the adjustable fixture (40) designed by the present invention on the lower chuck (20) of the traditional electronic universal testing machine, or installing the adjustable fixture (40) designed by the present invention on both the upper chuck (10) and the lower chuck (20) of the traditional electronic universal testing machine.

[0007] Another object of the present invention is to propose an eccentric tensile testing method for an electronic universal testing machine, which can perform eccentric tensile tests on CMC material specimens at different eccentric angles. The material mechanical property parameters obtained by the eccentric tensile testing method are used to construct a CMC eccentric tensile mechanics database. The CMC eccentric tensile mechanics database includes mechanical property parameters such as tensile, compression, bending, shear, and peel.

[0008] The third object of the present invention is to identify the type of damage of CMC material specimens under the EUMTT system based on the CMC eccentric tensile mechanics database.

[0009] An eccentric tensile and damage identification method for CMC includes a traditional electronic universal testing machine; characterized in that: it further includes a CMC-ES model, a CMC-DTI model, and an adjustable fixture (40) installed on the chucks (10, 20);

[0010] The CMC-ES model is used to extract the characteristics of the acoustic emission waveform signal of the CMC material under the eccentric tensile test; the acoustic emission waveform information collected by the acoustic emission probe is pre-amplified to form the acoustic emission waveform amplification information stored in the CMC-ES model;

[0011] The CMC-DTI model is used, on the one hand, to record the mechanical performance parameters of CMC material samples (30) with different eccentric angles θ under eccentric tensile testing, and the mechanical performance parameters are used to construct a CMC eccentric tensile mechanical database; on the other hand, the damage type of the CMC material under eccentric tensile testing is identified based on the CMC eccentric tensile mechanical database and the real-time collected acoustic emission waveform amplification information;

[0012] The adjustable clamp (40) consists of a clamp body (41), a position-adjustable lock core (42) and a lock column (43); the position-adjustable lock core (42) is placed in a lock cavity (41A) of the clamp body (41); a lock pin (43B) of the lock column (43) passes through an array upper lock hole (41C) of the clamp body (41) and is inserted into an array lower lock hole (42B) of the position-adjustable lock core (42).

[0013] The CMC-ES model is used to record the peak frequency, amplitude distribution, and energy parameter distribution of the stretching process under different eccentric displacements. The specific execution steps are as follows:

[0014] Step (A), initially there is no eccentric displacement;

[0015] Step (B) inputs an eccentric displacement, converts it into digital information using the analog-to-digital method of the acoustic emission instrument, extracts the digital information using a multi-scale wavelet time-frequency analysis method, and removes non-intrinsic signals to obtain the intrinsic signal characteristics of each damage behavior;

[0016] Step (C), using fast Fourier transform to obtain the main frequency of the waveform of each damage behavior;

[0017] In step (D), the acoustic emission band distributions of four damage behaviors were obtained, which, from low to high, represent matrix cracking, interface debonding, fiber bundle breakage, and fiber breakage, respectively;

[0018] Step (E): clustering the acoustic emission peak frequencies using the k-means method to obtain the proportions of the four types of damage signals, and obtaining the influence of eccentric displacement on the acoustic emission of damage behavior, which is stored in the CMC-ES model;

[0019] Step (F), accumulating the acoustic emission energy of the four damage signals respectively, obtaining the influence of different eccentric displacements on the energy release of the four damages, and storing it in the CMC-ES model;

[0020] Step (G): Establish a strength-life relationship through Weibull analysis in the CMC-ES model, and then use it to estimate the life and reliability of CMC materials; fracture toughness is regarded as a strength parameter, and acoustic emission energy is regarded as a life parameter, and then the influence law of fracture toughness on eccentric displacement is obtained.

[0021] Under different eccentric displacements, use the CMC-ES model to monitor the damage behavior of CMC material specimens, and combine the CMC-DTI model to distinguish four types of damage; the specific identification steps are as follows:

[0022] Identification step A: Tensile tests corresponding to different eccentric angles;

[0023] Identification step B: Noise reduction of acoustic emission parameters;

[0024] Identification step C: Peak frequency as a pattern recognition parameter;

[0025] Identification step D: Cluster analysis of acoustic emission peak frequencies;

[0026] Identification step E: Eliminate the non-intrinsic signal band;

[0027] Identification step F: Fracture toughness correction based on finite element;

[0028] Identification step G: Identification of damage types;

[0029] Compared with traditional electronic universal testing machines, the EUMTT system of the present invention has the following advantages:

[0030] ① Traditional electronic mechanical testing machines are not sufficient to detect complex stress states. In order to approach the actual application environment of CMC materials, the EUMTT system of the present invention realizes the mechanical property detection of CMC materials under a tensile-bending coupled stress state.

[0031] ② The mechanical property parameters of CMC materials obtained by the eccentric tensile testing method of the present invention have obtained the damage characteristic analysis information of toughness and strength under different eccentric conditions, and obtained the service conditions for optimizing the toughness of ceramic matrix composites, which is beneficial to expanding the application range of ceramic matrix composites.

[0032] ③ The eccentric tensile testing method of the present invention can be combined with different models of material mechanical testing machines, and the testing operation is convenient.

[0033] ④ The present invention constructs a CMC eccentric tensile mechanics database, and uses multi-scale wavelet time-frequency and finite element analysis to extract the characteristics of mechanical property parameters under different eccentric angles. The eccentric tensile test combines the acoustic emission peak information, so that the characteristic information of strength-toughness-acoustic emission can be combined.

[0034] ⑤ In the CMC-DTI model, the fracture morphology is combined with the acoustic emission peak frequency to fully realize the detection of fracture behavior by acoustic emission.

[0035] ⑥ The eccentric tensile testing method of the present invention is applicable to a wide range of material systems, including unidirectionally reinforced ceramic matrix composites, 2.5D and 3D woven ceramic matrix composites, etc.

[0036] ⑦ The eccentric tensile test method of the present invention establishes a performance analysis library, which is beneficial for key components to fully exert their toughness in different environments, different shapes, and different parts while meeting strength requirements, thereby expanding the scope of use of ceramic-based composites and improving material utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is the structural diagram of a traditional electronic universal testing machine.

[0038] Figure 2 It is a structural block diagram of the electronic universal testing machine for eccentric tensile testing of the present invention.

[0039] Figure 2A The present invention is a test block diagram of an electronic universal testing machine for eccentric tensile testing.

[0040] Figure 3 It is a structural block diagram of the adjustable clamp of the present invention.

[0041] Figure 3A It is an exploded view of the adjustable clamp of the present invention.

[0042] Figure 3B This is a structural block diagram of the adjustable clamp from another perspective of the present invention.

[0043] Figure 4 It is an assembly diagram of the adjustable clamp and the upper and lower clamps of the present invention.

[0044] Figure 4A yes Figure 4 Remove the assembly drawing of the upper and lower chucks.

[0045] Figure 4B yes Figure 4 Structural diagram of the assembly of four adjustable clamps.

[0046] Figure 5 It is a schematic diagram of the working distance calibration of the offset size of the present invention.

[0047] Figure 5A It is a schematic diagram of calibrating the eccentric distance of the offset dimension of the present invention.

[0048] Figure 5B Schematic diagram of the offset during the eccentric tensile test of the present invention.

[0049] Figure 5C It is a schematic diagram of the calibration of the eccentric angle of the present invention.

[0050] Figure 5D It is the preferred eccentric angle determined by the eccentric tensile test of the present invention.

[0051] Figure 6 This is a tensile performance diagram of the CMC material after the eccentric tensile test of the present invention.

[0052] Figure 7 It is the acoustic emission amplitude-count distribution diagram collected by the acoustic emission probe.

[0053] Figure 8 It is the distribution diagram of acoustic emission amplitude, count, energy and peak value collected by the acoustic emission probe.

[0054] Figure 9 It is a tensile curve and peak frequency distribution diagram of the CMC-ES model after the eccentric tensile test of the present invention.

[0055] Figure 10 This is a wavelet time-frequency analysis diagram of the CMC-ES model after the eccentric stretching test of the present invention.

[0056] Figure 11 It is a fast Fourier transform analysis diagram of the CMC-ES model after the eccentric tensile test of the present invention.

[0057] Figure 12 This is a distribution diagram of tensile damage sites at different eccentric angles using the CMC-DTI model of the present invention.

[0058] Figure 13 It is a diagram of the advance acquisition of the time when the acoustic emission signal appears as the eccentric angle increases in the CMC-ES model of the present invention, in which the amplified waveform information is obtained.

[0059] Figure 14 This is an analysis diagram of acoustic emission waveform characteristics corresponding to four types of damage behaviors using the CMC-ES model of the present invention.

[0060] 1. Upper left adjustable fixture 1A. Upper left fixture body 1B. Upper left position adjustable lock core 1C. Upper left lock post 2. Upper right adjustable fixture 2A. Upper right fixture body 2B. Upper right position adjustable lock core 2C. Upper right lock post 3. Lower left adjustable fixture 3A. Lower left fixture body 3B. Lower left position adjustable lock core 3C. Lower left lock post 4. Lower right adjustable fixture 4A. Lower right fixture body 4B. Lower right position adjustable lock core 4C. Lower right lock post 5A. Upper left stop 5B. Upper right stop 5C. Lower left stop 5D. Lower right stop 10. Upper chuck 20. Lower chuck 30. CMC material specimen 40. Adjustable fixture 41. Fixture body 41A. Lock cavity 41B. Vertical limit block 41C. Array upper lock hole 41D. Lock opening panel 41E. Outer chute 41F. Scale board 42. Position adjustable lock core 42A. Upper panel 42B. Array lower lock hole 43. Lock post 43A. Horizontal baffle 43B. Lock pin DETAILED DESCRIPTION

[0061] The present invention will be described in further detail below with reference to the accompanying drawings.

[0062] See also Figure 2 、 Figure 2A As shown, in order to be able to identify the damage type of CMC under eccentric tensile test of ceramic matrix composite (CMC), the present invention uses a traditional electronic universal testing machine (see Figure 1), and added a CMC material acoustic emission subsystem (referred to as the CMC-ES model) and a CMC material damage type identification subsystem (referred to as the CMC-DTI model) to its computer system. When performing an eccentric tensile test, the adjustable fixture 40 designed in the present invention is installed on the chuck of a conventional electronic universal testing machine. This forms an electronic universal testing machine for eccentric tensile testing (EUMTT), or EUMTT system. The EUMTT system of the present invention implements eccentric tensile testing of CMC material specimens through software modeling without disassembling or assembling the conventional electronic universal testing machine.

[0063] In the EUMTT system of the present invention, the CMC-ES model is used to extract the characteristics of the acoustic emission waveform signal from CMC materials during eccentric tensile testing. An acoustic emission probe is positioned on the CMC material specimen 30. The acoustic emission waveform information collected by the acoustic emission probe is pre-amplified and stored in the CMC-ES model as amplified acoustic emission waveform information.

[0064] In the EUMTT system of the present invention, the CMC-DTI model is used to record the mechanical performance parameters of CMC material specimens 30 under eccentric tensile testing at different eccentric angles θ. These mechanical performance parameters form a CMC eccentric tensile mechanical database. Furthermore, the damage type of the CMC material under eccentric tensile testing is identified based on the CMC eccentric tensile mechanical database and real-time amplified acoustic emission waveform information (stored in the CMC-ES model). In the present invention, the CMC eccentric tensile mechanical database is a table with multiple rows and five columns recording various mechanical indicators.

[0065] Specimen shape Eccentric angle Test environment External load Mechanical characteristics

[0066] The eccentricity angle accuracy range is 0.5 degrees to 2.5 degrees.

[0067] The test environment includes temperature, medium, humidity, etc.

[0068] External loads include tension, compression, bending, torsion, impact, alternating stress, etc.

[0069] Mechanical characteristics include brittleness, strength, plasticity, hardness, toughness, fatigue strength, elasticity, ductility, rigidity, yield point or yield stress, etc.

[0070] Damage types include matrix cracking, interfacial debonding, fiber bundle fracture, and fiber fracture.

[0071] Adjustable clamp 40

[0072] To achieve both eccentric tensile testing on an electronic mechanical testing machine and rapid disassembly, the present invention designs the fixture for holding the CMC material specimen 30 as a detachable, adjustable, split structure. This allows for eccentric tensile testing on an electronic mechanical testing machine without requiring structural modifications to existing electronic mechanical testing machines.

[0073] See also Figure 3 、 Figure 3A As shown, the adjustable clamp 40 designed in the present invention is composed of a clamp body 41, a position-adjustable lock core 42, and a lock column 43. The position-adjustable lock core 42 is placed in a lock cavity 41A of the clamp body 41, and a lock pin 43B of the lock column 43 is inserted into a lower lock hole 42B of the position-adjustable lock core 42.

[0074] The clamp body 41 is provided with a lock cavity 41A, an unlocking panel 41D and a scale plate 41F.

[0075] A vertical limit block 41B is provided in the lock cavity 41A; the vertical limit block 41B is used to limit the maximum depth of the position-adjustable lock core 42 in the lock cavity 41A.

[0076] The unlocking panel 41D is provided with an array of upper lock holes 41C. Each of the upper lock holes 41C is used to receive a lock pin 43B of a lock column 43. The number of lock holes in the array 41C can be designed based on the requirements of the eccentric tensile test. Generally, there are no fewer than four lock holes.

[0077] The scale plate 41F is used to measure the test distance of the position-adjustable lock cylinder 42 during the eccentric tensile test.

[0078] A slide groove 41E for placing a stop block is provided on the outer panel of the fixture body 41. The fixture body 41 is installed on the chuck of the electronic mechanical testing machine through the cooperation of the stop block, the slide groove 41E and the limit groove of the chuck on the electronic mechanical testing machine.

[0079] The upper panel 42A of the position-adjustable lock cylinder 42 is provided with an array of lower lock holes 42B. Each of these arrays is used to receive a lock pin 43B of a lock cylinder 43. The number of these arrays can be designed based on the requirements of the eccentric tensile test. Generally, there are no fewer than four lock holes.

[0080] A cross baffle 43A and a locking pin 43B are provided on a locking column 43. After the locking pin 43B is inserted into an array of upper locking holes 41C and an array of lower locking holes 42B, the cross baffle 43A contacts an unlocking panel 41D of a fixture body 41. After passing through the array of upper locking holes 41C, the locking pin 43B of the locking column 43 is inserted into the array of lower locking holes 42B, realizing the installation of the fixture body 41 and an axially adjustable lock core 42.

[0081] In the present invention, in order to further elaborate in detail how the adjustable fixture 40 adjusts the eccentric position during an eccentric tension test on a traditional electro-mechanical testing machine, it is completed through the cooperation of the locking column 43 with the array of upper locking holes 41C and the array of lower locking holes 42B. As Figure 3A shown, the array of upper locking holes 41C is provided with an upper A locking hole, an upper B locking hole, an upper C locking hole, and an upper D locking hole from the inside to the outside; the array of lower locking holes 42B is provided with a lower A locking hole, a lower B locking hole, a lower C locking hole, and a lower D locking hole from the inside to the outside. When the locking pin 43B of the locking column 43 passes through the upper D locking hole and is inserted into the lower D locking hole (as Figure 3 shown), the axially adjustable lock core 42 is closer to a scale plate 41F, which is called a near-field eccentric tension test. When the locking pin 43B of the locking column 43 passes through the upper D locking hole and is inserted into the lower A locking hole (as Figure 3B shown), the axially adjustable lock core 42 is farther from the scale plate 41F, which is called a far-field eccentric tension test. The distance between the end face plate of the scale plate 41F and the outer vertical face plate of the axially adjustable lock core 42 is denoted as D 偏心 , simply referred to as the fixture eccentric distance.

[0082] Installation of the adjustable fixture on an electro-mechanical testing machine

[0083] A CMC material specimen 30 needs to be installed on an electro-mechanical testing machine through a certain fixture and then the mechanical properties of the material are tested. Referring to Figure 1 、 Figure 4 、 Figure 4A 、 Figure 4B 、 Figure 5 、 Figure 5A 、 Figure 5B 、 Figure 5C shown, the designed adjustable fixture 40 of the present invention is installed on the chuck of a traditional electro-mechanical testing machine.

[0084] Referring to Figure 5 shown, the vertical distance between an upper chuck 10 and a lower chuck 20 of an electro-mechanical testing machine is denoted as the working distance H; the structures of the upper chuck 10 and the lower chuck 20 are the same, and the minimum lateral distance of the upper chuck 10 is denoted as the clamping distance D.

[0085] Referring to Figure 5A shown, the lateral width of the upper left adjustable fixture 1 is denoted as D1C The horizontal width of the upper right adjustable clamp 2 is denoted as D 2C The maximum distance between the outer panel of the upper left position adjustable lock cylinder 1B of the upper left adjustable fixture 1 and the outer panel of the upper right position adjustable lock cylinder 2B of the upper right adjustable fixture 2 is recorded as D max . The D max It is also the maximum thickness of the end of the clamped CMC material sample 30. The size of the adjustable fixture installed on the chuck of the traditional electronic mechanical testing machine satisfies D=D max +D 1C +D 2C .

[0086] See also Figure 5C As shown in the figure, the angle between the center line of the chuck of the electronic mechanical testing machine and the offset line of the specimen is recorded as the eccentric angle θ. The mechanical properties of the CMC material sample 30 at different eccentric angles θ are recorded by a CMC material damage type identification subsystem (referred to as CMC-DTI model) stored in a computer of the electronic mechanical testing machine.

[0087] See also Figure 5D As shown in FIG. , the eccentric angle θ of the present invention, obtained through finite element analysis, ranges from 0 to 2.5 degrees. 0 degrees refers to the initial angle when the test specimen is mounted on the electronic mechanical testing machine. Preferred eccentric angles are 0.72, 1.43, and 2.15 degrees, respectively.

[0088] The dimensions of the CMC material sample 30 include length, width, thickness, and curvature radius (non-standard). Generally, the thickness of the upper and lower ends of the CMC material sample 30 is the same.

[0089] The adjustable clamp 40 of the present invention is designed to adjust the extension or retraction of the position-adjustable lock core 42 by assembling the position-adjustable lock core 42 and the lock post 43. The assembly methods of the adjustable clamp and the clamp are:

[0090] Assembly method A

[0091] In the present invention, assembly method A refers to an eccentric tensile mechanical property test performed by installing adjustable clamps on both the upper chuck 10 and the lower chuck 20 of the electronic mechanical testing machine.

[0092] See also Figure 4 As shown, the upper left adjustable fixture 1 is installed on one end of the upper chuck 10 of the electronic mechanical testing machine through the upper left stopper 5A; the upper right adjustable fixture 2 is installed on the other end of the upper chuck 10 of the electronic mechanical testing machine through the upper right stopper 5B.

[0093] The left - lower adjustable fixture 3 is installed at one end of the lower chuck 20 of the electro - mechanical testing machine through the left - lower stopper 5C; the right - lower adjustable fixture 4 is installed at the other end of the lower chuck 20 of the electro - mechanical testing machine through the right - lower stopper 5D.

[0094] See Figure 5B 、 Figure 5C As shown, adjust the upper - left adjustable fixture 1 so that the CMC material specimen 30 has an eccentric angle and set the eccentric distance D of the upper - left adjustable fixture 1 移 ; the upper - right adjustable fixture 2, the left - lower adjustable fixture 3 and the right - lower adjustable fixture 4 remain in the initial state, and the eccentric tensile test of the CMC material specimen 30 is carried out, and various mechanical property parameters of the CMC material specimen 30 are recorded.

[0095] Assembly method B

[0096] In the present invention, the assembly method B refers to the eccentric tensile mechanical property test carried out by installing an adjustable fixture on the upper chuck 10 of the electro - mechanical testing machine.

[0097] Assembly method C

[0098] In the present invention, the assembly method C refers to the eccentric tensile mechanical property test carried out by installing an adjustable fixture on the lower chuck 20 of the electro - mechanical testing machine.

[0099] The present invention uses a mechanically adjustable adjustable fixture 40 to change the inclination of the specimen to be tested on the electro - mechanical testing machine, thereby providing a quantifiable eccentric angle. At the same time, the pressure sensing system records the lateral pressure, and the acoustic emission system is used to record the eccentric tensile damage parameters to form a damage analysis table. The traditional tensile testing machine does not require special treatment, and the adjustable fixture 40 supports all mechanically fixed universal mechanical tensile testing machines. Regardless of the model, the CMC - ES model and the CMC - DTI model have no conflict with the own system of the universal mechanical testing machine and can achieve data sharing.

[0100] CMC - ES model

[0101] See Figure 2 As shown, in the present invention, a plurality of acoustic emission probes are arranged on the CMC material specimen, and a pre - amplifier is connected between the output ends of the plurality of acoustic emission probes and the acoustic emission instrument. The pre - amplifier is used to perform a 40dB amplification process on the received multiplexed sensing information and then output it to the CMC - ES model.

[0102] The wavelet time-frequency analysis method used in this paper is based on the article "Basics of Wavelet Analysis," edited by Cao Huaixin and Guo Zhihua, Science Press, April 2016, pages 148-150. Because CMC material damage processes involve multiple damage scales, multiple wavelet basis functions are used to collaboratively process damage behavior and optimize wavelet time-frequency analysis for CMC materials. This method, referred to in this paper as a multiscale wavelet time-frequency analysis method, is referred to as "multiscale wavelet time-frequency analysis."

[0103] The CMC-ES model of the present invention is used to record the peak frequency, amplitude distribution, and energy parameter distribution of the stretching process under different eccentric displacements. The specific execution steps are:

[0104] In step (A), there is no eccentric displacement initially.

[0105] In step (B), an eccentric displacement is input, and the analog-to-digital signal is converted into digital information using the acoustic emission instrument. After the digital information is extracted using the multi-scale wavelet time-frequency analysis method, the non-intrinsic signals are eliminated to obtain the intrinsic signal characteristics of each damage behavior (matrix cracking, interface debonding, fiber bundle breakage, and fiber breakage).

[0106] Step (C): using fast Fourier transform (FFT) to obtain the main frequency of the waveform of each damage behavior.

[0107] In step (D), the acoustic emission band distributions of four damage behaviors were obtained, which, from low to high, represent matrix cracking, interface debonding, fiber bundle breakage, and fiber breakage, respectively.

[0108] Step (E) clusters the acoustic emission peak frequencies using the k-means method to obtain the proportions of the four types of damage signals, obtains the influence of eccentric displacement on the acoustic emission of damage behavior, and stores it in the CMC-ES model.

[0109] Step (F) accumulates the acoustic emission energy of the four damage signals respectively, obtains the influence of different eccentric displacements on the energy release of the four damages, and stores it in the CMC-ES model.

[0110] In step (G), a strength-life relationship is established in the CMC-ES model through Weibull analysis, which is then used to estimate the life and reliability of the CMC material. Fracture toughness is considered as a strength parameter, while acoustic emission energy is considered as a life parameter, and the influence of fracture toughness on eccentric displacement is obtained.

[0111] Based on this, the distribution of the influence of eccentric angle on damage behavior was obtained, and a standard database for CMC eccentric tensile mechanics was established, which is helpful in judging whether the toughness of ceramic matrix composites and each component (matrix, interface and fiber) meet the standard usage requirements.

[0112] The parameter analysis adopted by the CMC-ES model of the present invention is respectively energy, count, amplitude and peak frequency. In the acoustic emission parameters, the amplitude threshold is 35 dB and the energy threshold is set to 5 kV·microsec. Before the eccentric tension test, the acoustic emission instrument needs to perform a lead break test to ensure good reception of acoustic emission signals. If the amplitude of the lead break signal reaches more than 90 dB for three consecutive times, it can ensure the normal operation of the acoustic emission instrument.

[0113] The content recorded by the CMC-ES model of the present invention includes: eccentric preset angle, working distance, pressure value, each acoustic emission parameter, and the parameters of the specimen to be tested.

[0114] CMC-DTI model

[0115] Since continuous fiber-reinforced silicon carbide composites have high-temperature mechanical stability and great application potential; however, their fracture mechanisms are very complex and their toughness is insufficient, which severely limits their applications. Herein, the present invention constructs a CMC material damage type identification subsystem (abbreviated as CMC-DTI model), and the CMC-DTI model is used to realize the damage identification of 2.5D woven silicon carbide / silicon carbide composites (2.5D SiCf / SiC), so as to realize the judgment of the weak links with insufficient toughness of the CMC material specimens and lay a foundation for their toughening research. Under different eccentric displacements, the CMC-ES model is used to monitor the damage behavior of CMC material specimens, and combined with the CMC-DTI model to distinguish four damage types (matrix cracking, interlayer cracking, fiber bundle fracture and fiber fracture). The specific identification steps are as follows:

[0116] Identification step A, tensile tests corresponding to different eccentric angles;

[0117] In the present invention, the tensile displacements corresponding to eccentric angles of 0.7 and 2.1 degrees respectively are selected, and the CMC material specimens are tested under eccentric tension, and the results with different microstructures and acoustic emission signals are obtained. Figure 6 (a) and Figure 6 (d), corresponding Figure 6 (a)'s microstructure is as Figure 6 (b), Figure 6 (c), corresponding Figure 6 (d)'s microstructure is as Figure 6 (e), Figure 6 (f) shown. Figure 6 (a)'s fracture type shows a relatively smooth fracture surface with less fiber pull-out, while in Figure 6 (d)'s fracture type, the fiber pull-out behavior caused by interfacial debonding is significant; Figure 6 (a) and Figure 6 (d)'s fiber pull-out lengths are asFigure 6 As shown in (h), the maximum ranges of the extraction lengths are 20 - 25 μm and 95 - 100 μm respectively; and the increase in the eccentric displacement results in Figure 6 an increase in the number of fiber fractures in (d). Figure 6 (a) and Figure 6 the number of Type 2 acoustic emission signals in (d) increases by 13.9% (as shown in Figure 6 (g)), which corresponds to the morphological differences in Figure 6 (b), Figure 6 (e), indicating that interfacial debonding corresponds to Type 2 acoustic emission signals; Figure 6 (a) and Figure 6 the number of Type 4 acoustic emission signals in (d) increases by 8.2%, which corresponds to the morphology of the number of fiber fractures in Figure 6 (b), Figure 6 (e), indicating that fiber fracture corresponds to Type 4 acoustic emission signals. Figure 6 (a) and Figure 6 the axial fracture strength of (d) is as shown in Figure 6 (i).

[0118] Recognition step B, noise reduction of acoustic emission parameters;

[0119] In the present invention, the CMC - DTI model receives the amplified acoustic emission waveform information output by the CMC - ES model, namely the acoustic emission amplitude, count, energy, and peak frequency parameters. Since the acoustic emission signals have a high correlation in terms of amplitude and count, in order to reduce secondary noise, the acoustic emission waveform amplification information deviating from consistency is eliminated, and the result after elimination is as shown in Figure 7 .

[0120] Recognition step C, peak frequency as the pattern recognition parameter;

[0121] In the present invention, after comparing the distributions of the acoustic emission amplitude, count, energy, and peak frequency in Figure 8 , the peak frequency is adopted as the parameter for pattern recognition.

[0122] Recognition step D, clustering analysis of acoustic emission peak frequency;

[0123] In the present invention, K - means clustering is performed on the acoustic emission peak frequency parameter in the amplified acoustic emission waveform information. The peak frequency can be divided into four types, which are successively represented as Type 1 - Type 4 from bottom to top in Figure 9 .

[0124] The K-means clustering method described above refers to the content on pages 322-324 of *Fundamentals of Statistical Natural Language Processing*, published by Publishing House of Electronics Industry in January 2005, authored by (US) Christopher D. Manning and (Germany) Hinrich Schütze, and translated by Yuan Chunfa, Li Qingzhong, Wang Yun, Li Wei, Cao Defang, etc.

[0125] Recognition step E, removing the non-intrinsic signal band;

[0126] In the present invention, the amplified information of the acoustic emission waveform collected during the operation of the CMC-ES model is easily affected by other non-dominant feature bands. The wavelet time-frequency analysis obtained as a function of frequency and time in the CMC-DTI model helps to discover and filter non-feature frequency bands. The same Type 1-Type 4 acoustic emission signals are selected for denoising during different eccentric loading processes. The results show that from the beginning to the end of the acquisition process, the characteristic frequency band remains unchanged ( Figure 10 ), while the non-dominant frequency band has no fixed distribution, indicating that it contains other signal features. After removing these non-dominant frequency bands, the basic features of each damage behavior are characterized by FFT ( Figure 11 ), which is beneficial for subsequent recognition.

[0127] Recognition step F, finite element-based fracture toughness correction;

[0128] In the CMC-DTI model of the present invention, the finite element analysis method is used to simulate and record the maximum surface stress σ f , and the fracture energy is corrected to judge the toughness of the CMC material specimen The tensile test results for different eccentric angles (here 0.7 and 2.1 degrees are selected) show that as the eccentric angle increases, more positions of the matrix are damaged, and at the same time, the fibers are more likely to be stressed and fractured, as Figure 12 shown.

[0129] ε0 is the fracture strain.

[0130] σ a is the axial stress, and σ a is used to correct σ f , and this parameter is the test result of the eccentric tensile test conducted on the EUMTT system of the present invention.

[0131] E is the elastic modulus.

[0132] y max is the distance from the neutral layer of the specimen to the outer surface, here it is half of the thickness, and ρ(β) is the radius of curvature.

[0133] ρ(β) is the radius of curvature.

[0134] Recognition step G, damage type recognition;

[0135] In the present invention, by analyzing the acoustic emission peak frequency parameter in the amplified information of the acoustic emission waveform, as the eccentric angle increases, Figure 13 the appearance time of the Type 3 acoustic emission signal of (a, b, c) in Figure 12 gradually advances. At the same time, the finite element simulation results of

[0136] also show that as the eccentric angle increases, the position where the fiber bundle breaks will increase. Finally, it is shown that the fiber bundle breakage is the Type 3 acoustic emission signal obtained by the CMC-ES model. Figure 14 As shown Figure 14 (a) is the waveform feature of Type 1, corresponding to the damage behavior of matrix cracking; Figure 14 (b) is the waveform feature of Type 2, corresponding to the damage behavior of interface debonding; Figure 14 (c) is the waveform feature of Type 3, corresponding to the damage behavior of fiber bundle breakage; Figure 14 (d) is the waveform feature of Type 4, corresponding to the damage behavior of fiber breakage.

[0137] Accordingly, on the one hand, the CMC-DTI model records the mechanical property parameters of the CMC material specimen 30 at different eccentric angles under the eccentric tension test, and the mechanical property parameters are used to construct the CMC eccentric tension mechanical database; on the other hand, based on the CMC eccentric tension mechanical database and the amplified acoustic emission waveform information collected in real time (stored in the CMC-ES model), the identification of the damage type of the CMC material under the eccentric tension test is completed.

[0138] Perform the eccentric tension test of the CMC material on the EUMTT system

[0139] Eccentric tension test step one, adjustable fixture;

[0140] In the present invention, the adjustable fixture is installed according to the test requirements.

[0141] The upper and lower chucks of the traditional electronic mechanical testing machine are both installed with the adjustable fixture of the present invention.

[0142] If it is set to the mechanical property test with an eccentric angle at the upper part, two adjustable fixtures designed by the present invention are installed at the upper chuck 10 of the EUMTT system, such as Figure 4 the left upper adjustable fixture 1 and the right upper adjustable fixture 2 installed at the upper end of

[0143] If it is set to perform a mechanical property test with an eccentric angle at the lower part, two adjustable fixtures designed by the present invention are installed at the lower chuck 20 of the EUMTT system, such as Figure 4 The left-lower adjustable fixture 3 and the right-lower adjustable fixture 4 installed at the lower end of

[0144] Step two of the eccentric tension test: Initialize the EUMTT system;

[0145] Power on the EUMTT system and initialize the CMC-ES model and the CMC-DTI model in the computer.

[0146] Step three of the eccentric tension test: Set the dimensions of the CMC material specimen;

[0147] Input the workpiece dimensions of the CMC material specimen 30, namely length, width, and thickness.

[0148] If the CMC material specimen 30 is a standard workpiece, only the length, width, and thickness need to be set.

[0149] If the CMC material specimen 30 is a non-standard workpiece, the length, width, thickness, radius of curvature, etc. need to be set.

[0150] Step four of the eccentric tension test: Set the mechanical property test parameters under eccentric tension;

[0151] Set the parameters required for the eccentric tension test, including working distance, eccentric distance, load, tensile rate, etc.

[0152] Step five of the eccentric tension test: Start the CMC-ES model;

[0153] Start the CMC-ES model, record the ambient noise signal, set the threshold of the acoustic emission amplitude parameter to achieve initial ambient filtering, and store the acoustic emission fracture test results in real time; collect the acoustic emission lead-breaking test results. If the lead breaks continuously three times and the amplitude reaches above 90 dB each time, the acoustic emission acquisition requirement is met.

[0154] Step six of the eccentric tension test: Start the CMC-DTI model;

[0155] Perform real-time data acquisition, identify the damage type through the CMC-DTI model, and output the mechanical property parameters of the CMC material specimen 30, such as strength, elastic modulus, fracture toughness, etc.

[0156] Step seven of the eccentric tension test: Shut down the EUMTT system;

[0157] Sequentially shut down the CMC-DTI model, the CMC-ES model, the material mechanics test control unit, and the main power supply of the EUMTT system.

[0158] The test values listed above are only for illustrating the technical concept and features of the present invention, aiming to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and shall not be used to limit the protection scope of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention shall be covered within the protection scope of the present invention.

Claims

1. An EUMTT system for eccentric tension and damage identification of CMC, comprising a traditional electronic universal testing machine; characterized in that: It also includes a CMC-ES model, a CMC-DTI model, and an adjustable fixture (40) installed on the chucks (10, 20); the CMC-ES model refers to the acoustic emission subsystem of ceramic matrix composite materials; the CMC-DTI model refers to the damage type identification subsystem of ceramic matrix composite materials; the EUMTT system refers to the electronic universal testing machine for eccentric tension testing; the EUMTT system does not disassemble and assemble the traditional electronic universal testing machine, but realizes the eccentric tension testing of CMC material specimens through software program modeling; The CMC-ES model is used to extract the acoustic emission waveform signal characteristics of CMC materials under eccentric tension testing; the acoustic emission waveform information collected by the acoustic emission probe forms the amplified acoustic emission waveform information after pre-amplification processing and is stored in the CMC-ES model; The CMC-DTI model is used on the one hand to record the mechanical property parameters of the CMC material specimen (30) at different eccentric angles under eccentric tensile tests, and the mechanical property parameters are used to construct a CMC eccentric tensile mechanics database; on the other hand, based on the CMC eccentric tensile mechanics database and the amplified information of the acoustic emission waveform collected in real time, it is used to complete the identification of the damage type of the CMC material under eccentric tensile tests; ​ The adjustable fixture (40) consists of a fixture body (41), a position-adjustable lock core (42), and a lock post (43); The position-adjustable lock core (42) is placed in the lock cavity (41A) of the fixture body (41), and the lock pin (43B) of the lock post (43) sequentially passes through the array of upper lock holes (41C) of the fixture body (41) and then inserts into the array of lower lock holes (42B) of the position-adjustable lock core (42); Under different eccentric displacements, the CMC-ES model is used to monitor the damage behavior of CMC material specimens, and the CMC-DTI model is combined to distinguish four damage types; the specific identification steps are as follows: Identification step A, tensile tests corresponding to different eccentric angles; Select the tensile displacement corresponding to the eccentric angle, and conduct tests on the CMC material specimen under eccentric tension to obtain results with different microstructures and acoustic emission signals; Identification step B, noise reduction of acoustic emission parameters; Since the acoustic emission signals have a high correlation in terms of amplitude and count, in order to reduce secondary noise, the waveform information deviating from consistency is eliminated; Identification step C, peak frequency as the pattern recognition parameter; Use the peak frequency as the parameter for pattern recognition to process the distributions of acoustic emission amplitude, count, energy, and peak frequency; Identification step D, clustering analysis of acoustic emission peak frequency; Perform K-means clustering on the acoustic emission peak frequency parameters in the amplified acoustic emission waveform information; Identification step E, removing the non-intrinsic signal band; Select the same type of acoustic emission signal for denoising during different eccentric loading processes. After removing the non-dominant frequency band, the basic characteristics of each damage behavior are characterized by FFT; Identification step F, fracture toughness correction based on finite element; The finite element analysis method is used to simulate and record the maximum surface stress and the fracture energy is corrected to judge the toughness of the CMC material specimen ; is the fracture strain; is the axial stress; is the elastic modulus; is the distance from the neutral layer of the specimen to the outer surface; is the radius of curvature; Identification step G, damage type identification; The fracture damage type realizes the identification of the damage behavior corresponding to fiber fracture in waveform characteristics through acoustic emission peak frequency, morphology analysis, and finite element analysis; 2. The EUMTT system for eccentric stretching and damage identification of CMC according to claim 1, characterized in that: The CMC-ES model is used to record the peak frequency, amplitude distribution, and energy parameter distribution of the tensile process under different eccentric displacements; the specific implementation steps are as follows: Step (A), initially there is no eccentric displacement; Step (B): Input an eccentric displacement, convert it into digital information by the analog-to-digital conversion of the acoustic emission instrument, extract the digital information using the multi-scale wavelet time-frequency analysis method, and eliminate the non-intrinsic signals to obtain the intrinsic signal characteristics of each damage behavior. Step (C): Obtain the waveform main frequency of each damage behavior using the fast Fourier transform. Step (D): Obtain the acoustic emission frequency band distributions of the four damage behaviors, which represent matrix cracking, interface debonding, fiber bundle fracture, and fiber fracture from low to high respectively. Step (E): Use the k-means method to cluster the acoustic emission peak frequencies, obtain the proportions of the four damage signals, obtain the influence law of the eccentric displacement on the acoustic emission of the damage behavior, and store it in the CMC-ES model. Step (F): Accumulate the acoustic emission energy of the four damage signals respectively, obtain the influence law of different eccentric displacements on the energy release of the four damages, and store it in the CMC-ES model. Step (G): Establish a strength-life relationship through Weibull analysis in the CMC-ES model, and then use it to estimate the life and reliability of the CMC material; the fracture toughness is regarded as a strength parameter, and the acoustic emission energy is regarded as a life parameter, and then the influence law of the fracture toughness on the eccentric displacement is obtained.

3. The EUMTT system for eccentric tension and damage identification of CMC according to claim 1, characterized in that: The CMC eccentric tension mechanics database is a table recording various mechanical indexes with multiple rows and five columns.

4. An eccentric tensile test method applied to CMC materials, characterized in that: It is to add the CMC-ES model and the CMC-DTI model to the computer of the traditional electronic universal testing machine, and install adjustable fixtures (40) on the chucks (10, 20). The CMC-ES model described above is used to complete the extraction of the acoustic emission waveform signal characteristics of the CMC material under eccentric tension testing; the acoustic emission waveform information collected by the acoustic emission probe is pre-amplified and processed to form the amplified acoustic emission waveform information stored in the CMC-ES model. The CMC-DTI model is used to record the different eccentric angles under eccentric tensile test. The mechanical performance parameters of the CMC material sample (30) are used to construct a CMC eccentric tensile mechanical database. On the other hand, the damage type of the CMC material under the eccentric tensile test is identified based on the CMC eccentric tensile mechanical database and the real-time acquired acoustic emission waveform amplification information. The eccentric tension testing of the CMC material in the EUMTT system includes the following steps: Eccentric tension testing step one: Adjustable fixture. Install an adjustable fixture on the chuck of the traditional electronic mechanics testing machine according to the test requirements. Eccentric tension testing step two: Initialize the EUMTT system. Power on the EUMTT system and initialize the CMC-ES model and the CMC-DTI model in the computer. The EUMTT system refers to the electronic universal testing machine for eccentric tension testing; the EUMTT system does not disassemble and assemble the traditional electronic universal testing machine, but realizes the eccentric tension testing of the CMC material specimen through software program modeling. Eccentric tension testing step three: Set the dimensions of the CMC material specimen. Input the workpiece dimensions of the CMC material specimen (30), length, width, and thickness. If the CMC material specimen (30) is a standard workpiece, only the length, width, and thickness need to be set. If the CMC material specimen (30) is a special-shaped workpiece, the length, width, thickness, and radius of curvature need to be set. Eccentric tension testing step four: Set the mechanical property test parameters under eccentric tension. Set the parameters required for eccentric tension testing, including working distance, eccentric distance, load, and tensile rate. Eccentric tension testing step five: Start the CMC-ES model. Turn on the CMC-ES model, record the environmental noise signal, set the acoustic emission amplitude parameter threshold to achieve initial environmental filtering, and store the acoustic emission fracture test results in real time; collect the acoustic emission lead breakage test results. If the lead breaks continuously three times and the amplitude reaches above 90 dB each time, then the acoustic emission acquisition requirements are met. Step six of the eccentric tension test, start the CMC-DTI model. Perform real-time data acquisition, identify the damage type through the CMC-DTI model, and output the mechanical property parameters of the CMC material specimen (30), including strength, elastic modulus, and fracture toughness. Step seven of the eccentric tension test, turn off the EUMTT system. Sequentially turn off the CMC-DTI model, CMC-ES model, material mechanics test control unit, and the main power supply of the EUMTT system.

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