Testing method for ultrahigh-cycle fatigue strength of interface between particle and matrix and fatigue sample

Abstract

The invention relates to the technical field of material mechanical property testing, in particular to a testing method for ultrahigh-cycle fatigue strength of a particle and matrix interface and a fatigue sample. The fatigue test sample comprises a to-be-tested particle and a matrix combined with the to-be-tested particle, and the matrix comprises two test ends which are separated and independently combined on the opposite sides of the to-be-tested particle, so that a first combination interface and a second combination interface which are used for testing the interface fatigue strength of the particle and the matrix are respectively formed between the two test ends and the to-be-tested particle. According to the method, the matrix only covers the side walls of the spherical microparticles, so that the interference of the matrix is effectively isolated, and the quantitative test of the ultrahigh-cycle fatigue strength of the interface can be realized. Compared with the prior art, the method solves the problems of high cost, long period, difficult separation interface effect and the like, breaks through the precision bottleneck in the composite material interface fatigue test, and provides key technical support for interface structure optimization and life prediction.

Description

Technical Field

[0001] The invention relates to the technical field of material mechanical property testing, and in particular to a testing method for ultra-high cycle fatigue strength of an interface between particles and a matrix and a fatigue specimen. Background Art

[0002] In recent years, with the increasing requirements for thermal management performance in the fields of new energy, electronic equipment, and aerospace, particle-reinforced composite materials with both functional and mechanical properties have become a research hotspot. Among them, by introducing different types of functional particles (such as phase change microcapsules, thermal conductive particles, reinforced particles, etc.) into the matrix material, the multifunctional synergy of the material can be achieved. In composite materials, particle-reinforced structures often achieve load transfer and stress dispersion through the interface between particles and the matrix, and their interface properties have a decisive influence on the overall mechanical behavior of the material. In practical applications, especially in dynamic service environments, the interface fatigue strength between particles and the matrix directly determines the long-term reliability and service life of the material.

[0003] At present, the performance evaluation of particle-reinforced composites mainly relies on macroscopic mechanical tests, such as tensile, compression and bending tests. These methods usually regard the material as a macroscopic homogeneous material and characterize the material properties through stress-strain curves or fracture modes. As described in the article "A New Method for Predicting the Interface Mechanical Properties of Particle-Reinforced Composites" published in the 53(5) issue of the Journal of Mechanics in 2021, a single-particle-filled PDMS composite sample was provided. It can be found that the particle to be tested is completely coated by the composite material, so that its measurement data will be affected by the composite material adhered around the particle. Therefore, it is difficult for such methods to accurately evaluate the local mechanical properties of the interface between the particle and the matrix, and it is impossible to clearly distinguish the effects of the particles, the matrix and the bonding interface on the mechanical properties of the composite material. Especially under fatigue loading conditions, the initiation, propagation and final failure process of local cracks at the interface are difficult to explore. Therefore, it is urgent to develop more sophisticated local characterization methods for the interface area between particles and the matrix. Summary of the invention

[0004] The present invention aims to overcome the defect in the prior art that it is difficult to accurately measure the ultra-high cycle fatigue strength of the interface area between particles and matrix under high-frequency and low-amplitude loading conditions, and provides a test method for the ultra-high cycle fatigue strength of the interface between particles and matrix and a fatigue specimen to overcome the above defect.

[0005] In order to achieve the above-mentioned invention object, the present invention adopts the following technical solutions: In a first aspect, the present invention discloses a fatigue specimen for testing the interfacial fatigue strength between a particle and a matrix, which includes a particle to be tested and a matrix combined with the particle to be tested. The matrix includes two separated and independently combined test ends on opposite sides of the particle to be tested, so that a first bonding interface and a second bonding interface for testing the interfacial fatigue strength between the particle and the matrix are respectively formed between the two test ends and the particle to be tested.

[0006] In the fatigue specimen of the present invention, the matrix only covers the side wall of the particle, forming a clear single interfacial loading path, effectively isolating the interference of the matrix, ensuring that the test load acts precisely on the interfacial area, realizing independent and quantitative characterization of the interfacial fatigue strength, and avoiding the influence of the matrix and particle monomers in the traditional method. In practice, the particle to be tested is preferably a spherical microparticle. In addition, the matrix used to form the two test ends here can be either the same material or different materials. When the materials of the test ends are the same, the fatigue strength between a single material and the particle can be tested: by changing the area of the bonding interfaces on both sides of the particle to be tested, tensile tests are performed on both sides of the fatigue specimen with the same matrix. As the load increases, the fatigue specimen will first break at the bonding interface with a smaller area, thus limiting the fatigue failure to a single interface, facilitating subsequent calculations and making the test results more accurate.

[0007] Furthermore, the area of the first bonding interface is equal to the area of the second bonding interface, and the two test ends are made of different matrices. In practice, it is often necessary to compare the bonding strengths between a variety of materials and the particle to be tested. At this time, if single interfacial fatigue strength tests are performed separately, the experimental efficiency is relatively low. Therefore, the present invention can fix test ends made of different materials on opposite sides of the particle to be tested, while ensuring that the areas of the first bonding interface and the second bonding interface are the same. After multiple loadings, fatigue failure will occur at the interface between the material with a weaker bond and the particle, so that the fatigue strengths of the interfaces between two materials and the same particle can be visually compared, and at the same time, the fatigue strength of the interface between the material on the side with a weak bond and the particle can be measured.

[0008] In a second aspect, the present invention discloses a preparation method for a fatigue specimen for testing the interfacial fatigue strength between a particle and a matrix, including the following steps: S1. Fix the particle to be tested with a test end mold filled with a liquid matrix, so that the liquid matrix is restricted on opposite sides of the particle to be tested; S2. Cure the liquid matrix, and then remove the test end mold, so that the cured matrix respectively forms a first bonding interface and a second bonding interface on opposite sides of the particle to be tested, thereby obtaining the fatigue specimen of the present invention.

[0009] Further, in step S1, the test end mold is a microtube with a slit inside, and the gap of the slit is smaller than the particle size of the to-be-tested particles. After the microtube sucks in the mixture of the to-be-tested particles and the liquid matrix, individual particles will naturally be stuck at the slit, separating the matrix on both sides. At this time, the contact surface between the matrix at the slit and the to-be-tested particles is smaller, while the contact surface on the other side is larger, forming bonding interfaces with different areas.

[0010] Further, in step S1, the test end mold is two glass tubes with the same inner diameter, and the inner diameter of the glass tubes is smaller than the particle size of the to-be-tested particles. When it is necessary to compare the bonding strengths between two materials and the to-be-tested particles, the two glass tubes are respectively filled with the two materials, and then fixed on the opposite sides of the to-be-tested particles. After the two materials solidify, two bonding interfaces with the same area are formed on the surface of the to-be-tested particles.

[0011] Further, in step S1, the liquid matrix is a thermosetting resin, preferably one or two of epoxy resin, polyurethane, and phenolic resin.

[0012] In a third aspect, the present invention also discloses a test method for the ultra-high cycle fatigue strength of the interface between particles and a matrix, including the following steps: S1. Prepare the fatigue specimen as described above; S2. Input a static voltage signal that increases step by step to the motor of the material testing machine, record the output load, and fit the voltage-load data to obtain the voltage-load conversion coefficient of the loading system; S3. Fix the test end of the fatigue specimen on the material testing machine through a fixture and perform pre-tightening; set the stress peak value, stress ratio, and loading frequency to obtain the target stress of this experiment; convert the target stress into a sine excitation signal through the voltage-load conversion coefficient, and drive the motor to apply a cyclic tensile load to the fatigue specimen.

[0013] S4. During the loading process, measure the actual stress, dynamically compare the deviation between the measured stress amplitude and the target stress amplitude by the system, and dynamically adjust the voltage excitation signal to keep the stress constant and the response stable; when the system detects a sudden change in the response, automatically terminate the loading, and the fatigue strength of the interface between the particles and the matrix can be evaluated through the number of cycles at this time.

[0014] Further, in step S3, the target stress is calculated by the following formula: where, is the target stress, is the stress ratio, is the stress peak value, is the loading frequency; The sine excitation signal is calculated by the following formula: Among them, is the equivalent contact area of the interface between the particle and the matrix, is the system voltage-load conversion coefficient. The equivalent contact area of the interface between the particle and the matrix is the area of the projection plane of the first bonding interface or the second bonding interface on the particle to be measured.

[0015] Furthermore, in step S4, the actual stress is calculated by the following formula: Among them, is the measured driving force.

[0016] In practice, the present invention can construct a loading system with a voice coil motor as the core. The controller outputs a high-frequency and low-amplitude sinusoidal voltage signal to drive the motor to generate a controllable load, and at the same time, a high-sensitivity load sensor is integrated in the loading path to monitor the response force in real time.

[0017] Furthermore, in step S4, a lock-in amplifier is used to assist the load sensor to measure the actual stress. The present invention uses a lock-in amplifier to extract and filter the amplitude and phase of the weak load signal. Ultra-high cycle fatigue tests usually require the material to withstand more than 10 7 times, and even up to 10 9 times and above of cyclic load actions. To reduce the test time, a high-frequency and low-stress amplitude loading method is usually adopted. However, under this loading condition, the response signal of the specimen is extremely weak and is easily interfered by noise and difficult to be accurately captured, resulting in problems such as insufficient accuracy of the test results, seriously limiting the test efficiency and the credibility of the results. Therefore, the present invention uses a lock-in amplifier combined with low-amplitude sinusoidal excitation and a high-sensitivity load sensor to accurately capture the weak response signal of the specimen interface area under high-frequency and low-amplitude cyclic loading, and solves the problem that the load signal is difficult to be accurately captured under noise interference.

[0018] Therefore, the present invention has the following beneficial effects: (1) The present invention uses a fatigue specimen with the matrix only covering the side wall of the particle. Through the preferred scheme, a clear single interface loading path can be formed, effectively isolating the matrix interference, and enabling the quantitative test of the ultra-high cycle fatigue strength of the interface.

[0019] (2) The present invention prepares the fatigue specimen through a microtube with a slit in the preferred scheme, and significantly improves the experimental efficiency on the premise of ensuring the accurate formation of the first and second bonding interfaces between the matrix and the fatigue specimen.

[0020] (3) The present invention can form test ends with different materials on both sides of the particle to be measured, and while comparing the bonding forces of the two materials with the particle to be measured, complete the test of the interface fatigue strength between the weakly bonded material and the particle to be measured.

[0021] (4)The present invention realizes real-time capture of the interface dynamic response at the microscale and high-frequency, low-amplitude, stable and controllable fatigue loading through the high-frequency drive and lock-in amplifier of the voice coil motor in the preferred scheme. Compared with the existing methods, the present invention solves the problems of high cost, long cycle, and difficulty in separating the interface effect, breaks through the accuracy bottleneck in the fatigue test of the composite material interface, and provides key technical support for interface structure optimization and life prediction. Description of the Drawings

[0022] Figure 1 It is a flowchart of a test method for the ultra-high cycle fatigue strength of the interface between particles and the matrix of the present invention.

[0023] Figure 2 It is a schematic diagram of the principle of a test method for the ultra-high cycle fatigue strength of the interface between particles and the matrix of the present invention.

[0024] Figure 3 It is a flowchart of the preparation of a fatigue specimen for testing the fatigue strength of the interface between particles and the matrix in Example 1 of the present invention.

[0025] Figure 4 It is a schematic diagram of the structure of a fatigue specimen for testing the fatigue strength of the interface between particles and the matrix in Example 1 of the present invention.

[0026] Figure 5 It is a schematic diagram of the test of a fatigue specimen for testing the fatigue strength of the interface between particles and the matrix in Example 1 of the present invention.

[0027] Figure 6 It is a flowchart of the preparation of a fatigue specimen for testing the fatigue strength of the interface between particles and the matrix in Example 2 of the present invention.

[0028] Figure 7 It is a schematic diagram of the structure of a fatigue specimen for testing the fatigue strength of the interface between particles and the matrix in Example 2 of the present invention.

[0029] Figure 8 It is a schematic diagram of the test of a fatigue specimen for testing the fatigue strength of the interface between particles and the matrix in Example 2 of the present invention.

[0030] In the figure: the particle to be tested 1; the test end 2; the slit 3; the fixture 4; the first bonding interface 10; the second bonding interface 20; the test end mold 30. Detailed Embodiments

[0031] The technical solution of the present invention is further clearly and completely described below through specific embodiments and in combination with the accompanying drawings. It should be noted that the embodiments described in the present invention are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating processes are given, but they are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. The experimental methods used in the following embodiments are conventional methods unless otherwise specified, and the materials, reagents, etc. used in the embodiments, unless otherwise specified, can be obtained from commercial channels. In the present invention, unless otherwise specified, the required structural components are all structural components well known to those skilled in the art or disclosed in the prior art.

[0032] Embodiment 1: In the first step, fatigue specimens are prepared. Microcapsules are selected as the particles to be tested 1, epoxy resin is used as the matrix, and the test end mold 30 is a glass tube with a diameter of 300 µm. The midpoint of the glass tube shrinks inward to form a circular slit with a diameter of 100 µm. Figure 3 As shown, microcapsules with diameters between 100 µm and 300 µm are prepared (the size of the microcapsules is measured by laser confocal electron microscopy), the microcapsules and the resin are mixed, and a curing agent (tetraethylenepentamine, the addition amount is 12.5% of the resin mass) is added. The mixture of microcapsules and resin is sucked in through the above-mentioned glass tube, and a single microcapsule is clamped at the slit so that the resins on both sides of the microcapsule are separated, and the resin in the slit can only contact the surface of the microcapsule. After the resin in the tube is cured, the glass tube is corroded with hydrofluoric acid to obtain a single microcapsule resin interface fatigue specimen. The structure of the fatigue specimen is shown in FIG. Figure 4 As shown, the contact surface between the test end 2 at the slit and the particle 1 to be tested is a first bonding interface 10 , and the contact surface between the test end 2 on the side opposite to the slit and the particle 1 to be tested is a second bonding interface 20 .

[0033] In the second step, the standard sample is installed in the fixture 4 for pre-tightening, and the DC voltage signal ( U = 0.1 V, 0.2 V, 0.3 V…), drive the loading system to apply static loads of different amplitudes, record the corresponding load changes through high-precision load sensors, plot the obtained voltage-load data into a curve, and take its slope through linear fitting to obtain the system voltage-load conversion coefficient. The standard sample is a metal rod with known stiffness. The principle of the test system is as follows Figure 2 As shown, the system voltage-load conversion factor is measured to be 0.6 N / V.

[0034] The third step is Figure 5As shown, the test end 2 of the fatigue specimen is clamped and fixed by the fixture 4 of the material testing machine, a pre-tightening force is applied, and the target stress peak value is set. = 2 MPa, stress ratio r = 0.1 and loading frequency f = 300 Hz. The target stress is calculated by the following formula: The target stress is converted into a sinusoidal excitation signal by the following formula : where A is the area of the projection plane of the first bonding interface 10 on the test particle, which is equal to the cross-sectional area of the circular slit. In the formula, R is 50 µm.

[0035] In the fourth step, the control system inputs the above sinusoidal excitation voltage signal to drive the motor to perform high-frequency and low-amplitude fatigue loading on the specimen until the number of cycles reaches 10 7 times or more. The load response during the specimen loading process is obtained by the load sensor as the input signal of the lock-in amplifier.

[0036] In the fifth step, the controller records the actual stress and the number of cycles in real time. The actual stress is calculated by the following formula: The system dynamically compares the deviation between the actual stress amplitude and the target stress amplitude, and dynamically adjusts the voltage excitation signal to keep the stress constant and the response stable. As the load is applied to the fatigue specimen, since the area of the first bonding interface 10 is smaller than that of the second bonding interface 20, the resin here is more likely to debond from the test particle 1. When the system detects a sudden change in the response, it indicates that the separation of the particle and the resin occurs at the first bonding interface 10, and the system automatically terminates the loading. At this time, the recorded number of cycles is 1.47×10 8 , and the fatigue strength of the interface between the particle and the matrix can be evaluated through this number of cycles.

[0037] Example 2 In the first step, the fatigue specimen is prepared. Microcapsules are selected as the test particles 1, epoxy resin and polyurethane are used as the matrix materials for the two test ends 2 respectively, and a glass tube with an inner diameter of 100 µm is used as the test end mold 30. As Figure 6As shown, microcapsules with a diameter slightly larger than 100 µm were prepared (the microcapsule size was measured by a laser confocal electron microscope). First, the microcapsules were mixed in alcohol. A glass tube was used to fix the microcapsules by continuously applying suction. Then, it was connected to a glass tube filled with epoxy resin on the opposite side. After the epoxy resin was cured, the glass tube filled with alcohol was directly separated. Then, the glass tube filled with polyurethane was connected to the test particle 1 at the opposite position of the glass tube filled with epoxy resin. After the polyurethane was cured, the glass tubes on both sides were etched away with hydrofluoric acid to obtain the fatigue specimen as shown in Figure 7 . At this time, the contact interface between the epoxy resin and the test particle 1 is the first bonding interface 10, and the contact interface between the polyurethane and the test particle 2 is the second bonding interface 20.

[0038] In the second step, the standard sample was installed in the fixture 4 for preloading. By controlling the output of a DC voltage signal that increased step by step ( U = 0.1 V, 0.2 V, 0.3 V...), the loading system was driven to apply static loads of different amplitudes. The corresponding load changes were recorded by a high-precision load sensor. The obtained voltage-load data was plotted as a curve, and the slope was obtained by linear fitting to obtain the system voltage-load conversion coefficient. The standard sample was a calibrated spring. The principle of the test system is as shown in Figure 2 . The system voltage-load conversion coefficient was measured to be 0.6 N / V.

[0039] In the third step, as shown in Figure 8 , the test end 2 of the fatigue specimen was clamped and fixed by the fixture 4, and a preloading force was applied. The target stress peak = 2 MPa, the stress ratio r = 0.1, and the loading frequency f = 300 Hz were set. The target stress was calculated by the following formula: The target stress was converted into a sinusoidal excitation voltage signal by the following formula : where A is the area of the projection plane of the glass tube on the test particle, which is equal to the cross-sectional area of the glass tube. The R in the formula is 50 µm.

[0040] In the fourth step, the control system input the above sinusoidal excitation signal to drive the motor to perform high-frequency and low-amplitude fatigue loading on the specimen until the number of cycles reached more than 10 7 times. The load response during the specimen loading process was obtained by the load sensor as the input signal of the lock-in amplifier.

[0041] In the fifth step, the controller records the actual stress and the number of cycles in real time. The actual stress is calculated by the following formula: The system dynamically compares the deviation between the actual stress amplitude and the target stress amplitude, and dynamically adjusts the voltage excitation signal to keep the stress constant and the response stable. As the load is applied to the fatigue specimen, when the system detects a sudden change in the response, it is found that debonding occurs at the second bonding interface 20, indicating that the bonding ability between the polyurethane and the microcapsules is poor. At this time, the recorded number of cycles is 7.41×10 7 That is, the fatigue strength of the interface between the polyurethane and the microcapsules can be evaluated.

[0042] Using the test method for the fatigue strength of the interface between particle matrices of the present invention, the control accuracy of the stress amplitude at the particle-matrix interface in a micro-specimen can be better than ±5%. The system loading response can be extracted by a lock-in amplifier, and combined with the conversion formula, the real-time maintenance of the stress amplitude and the stress ratio control can be achieved. Compared with the traditional fatigue test method, this method can realize the quantitative test of the ultra-high cycle fatigue strength of the interface and perform high-frequency loading, significantly reducing the test time, having good efficiency advantages, and being applicable to the evaluation of the interface fatigue performance of various typical particle-reinforced composite material systems.

[0043] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any person skilled in the art, without departing from the scope of the technical solution of the present invention, based on the technical essence of the present invention, any simple modification, equivalent replacement, and improvement made to the above embodiments still fall within the protection scope of the technical solution of the present invention.

Claims

1. A fatigue specimen for testing the interfacial fatigue strength between particles and a matrix, characterized in that: It includes the particle to be tested (1) and a matrix combined with the particle to be tested (1). The matrix includes two testing ends (2) that are separated and independently combined on the opposite sides of the particle to be tested (1), such that a first bonding interface (10) and a second bonding interface (20) for testing the interfacial fatigue strength between the particle and the matrix are respectively formed between the two testing ends (2) and the particle to be tested (1).

2. The fatigue specimen for testing the interfacial fatigue strength between particles and a matrix according to claim 1, characterized in that: The area of the first bonding interface (10) is equal to the area of the second bonding interface (20), and the two testing ends (2) are made of different matrices.

3. A method for preparing a fatigue specimen for testing the interfacial fatigue strength between particles and a matrix, characterized in that, It includes the following steps: S1. Fix the particle to be tested (1) to the testing end mold (30) filled with the liquid matrix, such that the liquid matrix is restricted on the opposite sides of the particle to be tested (1); S2. Cure the liquid matrix, and then remove the testing end mold (30), such that the cured matrix respectively forms the first bonding interface (10) and the second bonding interface (20) on the opposite sides of the particle to be tested (1), thereby obtaining the fatigue specimen as described in claim 1.

4. The preparation method of a fatigue specimen for testing the interfacial fatigue strength between particles and a matrix according to claim 3, wherein: In step S1, the testing end mold (30) is a microtube with a slit (3) provided inside the tube, and the gap of the slit (3) is smaller than the particle size of the particle to be tested (1).

5. The preparation method of a fatigue specimen for testing the interfacial fatigue strength between particles and a matrix according to claim 3, characterized in that: In step S1, the testing end mold (30) is two glass tubes with the same inner diameter, and the inner diameter of the glass tubes is smaller than the particle size of the particle to be tested (1).

6. The preparation method of a fatigue specimen for testing the interfacial fatigue strength between particles and a matrix according to claim 3, characterized in that: The liquid matrix in step S1 is a thermosetting resin.

7. A test method for the ultra-high cycle fatigue strength of the interface between particles and the matrix, characterized in that, It includes the following steps: S1. Prepare the fatigue specimen as described in claim 1 or 2; S2. Input a static voltage signal with a gradually increasing level to the motor of the material testing machine, record the output load, and fit the voltage-load data to obtain the voltage-load conversion coefficient of the loading system; S3. Fix the testing ends (2) of the fatigue specimen to the material testing machine through a fixture (4) and pre-tighten it; set the stress peak value, stress ratio, and loading frequency to obtain the target stress of this experiment; convert the target stress into a sinusoidal excitation signal through the voltage-load conversion coefficient, and drive the motor to apply a periodic tensile load to the fatigue specimen; S4. During the loading process, measure the actual stress, dynamically compare the deviation between the measured stress amplitude and the target stress amplitude by the system, and dynamically adjust the voltage excitation signal to keep the stress constant and the response stable; When the system detects a sudden change in the response, automatically terminate the loading, and the fatigue strength of the particle-matrix interface can be evaluated through the number of cycles at this time.

8. The testing method for the ultra-high cycle fatigue strength of the interface between particles and a matrix according to claim 7, characterized in that: In step S3, the target stress is calculated by the following formula: Among them, is the target stress, is the stress ratio, is the stress peak value, is the loading frequency; The target stress is converted into a sinusoidal excitation signal by the following formula: Among them, is the equivalent contact area of the particle-matrix interface.

9. The test method for the ultra-high cycle fatigue strength of the interface between particles and the matrix according to claim 8, wherein: In step S4, the actual stress is calculated by the following formula: Among them, is the measured driving force.

10. The test method for ultra-high cycle fatigue strength of the interface between particles and matrix according to claim 7, wherein: In step S4, a lock-in amplifier is used to assist the load sensor to measure the actual stress.

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