High-frequency cyclic load experimental device and method for generating type II crack propagation of composite material

Abstract

The invention discloses a high-frequency cyclic load experimental device and a high-frequency cyclic load experimental method for generating type II crack propagation of a composite material, and relates to the field of crack propagation test of the composite material. The cam is used for realizing controllable loading of a load by changing the rotating speed of the cam and providing a high-frequency displacement load through high-speed rotating motion of the cam, so that the test frequency is accurate and controllable, and the difficulty in high-frequency loading of the load of a traditional fatigue testing machine is overcome; the distance between the camshaft center and the contour is designed according to the required loading condition, millimeter-level displacement loading can be achieved, and the difficulty that the displacement amplitude is too low when ultrasonic fatigue equipment is adopted for high-frequency loading is overcome; the maximum energy release rate is calculated by introducing a dynamic factor determined by mechanical simulation, the change trend of the dynamic effect of the structure along with the test frequency can be accurately captured, and the defect that the high-frequency oscillation load is not accurately measured by a traditional method is overcome; and finally, carrying out regression on the accurately obtained maximum energy release rate and crack propagation rate to obtain fatigue crack propagation parameters of the composite material under the high-frequency load.

Description

Technical Field

[0001] The present invention relates to the field of composite material crack propagation testing, and in particular to a high-frequency cyclic loading test device and method for generating composite material mode II crack propagation. Background Art

[0002] Mode II crack growth in composite materials occurs when the crack surface is subjected to reciprocating shear stresses parallel to the surface and perpendicular to the crack front, causing the cracks to slide apart. The study of Mode II crack growth requires measuring the crack growth rate under cyclic loading. , and using Paris's law Maximum energy release rate for crack driving force Perform regression to determine fatigue crack growth parameters for composite materials and The commonly used experimental method is to use a fatigue testing machine to generate cyclic displacement, test the size of the cyclic load during the loading process and calculate the maximum energy release rate. The disadvantages of this method are: (1) The load loading frequency of the fatigue testing machine is low, generally 1~10 Hz, and high-frequency load loading is difficult; (2) The dynamic effect of the structure increases with the increase of the load loading frequency. The load measurement equipment is difficult to capture the high-frequency oscillation load, the test accuracy is not high, and the maximum energy release rate cannot be accurately calculated. In addition, ultrasonic fatigue equipment can be used for high-frequency loading tests, but its loading displacement amplitude is only about tens of microns, which cannot achieve millimeter-level amplitude loading. Summary of the Invention

[0003] In view of the above-mentioned deficiencies in the prior art, the present invention provides a high-frequency cyclic loading experimental device and method for generating type II crack propagation in composite materials, which can realize sinusoidal displacement loading with controllable frequency, high-frequency loading and displacement loading with millimeter amplitude, while avoiding the measurement of high-frequency oscillating loads. By introducing dynamic factors The maximum energy release rate can be accurately calculated Finally, the material parameters are accurately obtained through regression and , and can quantitatively reflect the frequency effect of material crack propagation.

[0004] The technical solution of the present invention is: A first aspect of the present invention provides a high-frequency cyclic load test device for generating Type II crack extension in a composite material, the device comprising a positioning fixture for fixing the uncracked end of a Type II crack extension delaminated specimen; the end of the delaminated end of the Type II crack extension delaminated specimen contacts a cam; the cam is connected to the output shaft of a gearbox; the input shaft of the gearbox is connected to the output shaft of a motor; a microscope is provided on one side of the Type II crack extension delaminated specimen for observing the length of crack extension.

[0005] A second aspect of the present invention provides a high-frequency cyclic loading test method for generating mode II crack growth in a composite material, the method comprising the following steps: S1: According to the sinusoidal displacement required for the type II crack extension delamination specimen to be tested, the cam push stroke is set to the maximum loading displacement, the cam return stroke is set to the minimum loading displacement, and the distance between the cam shaft center and the outer contour is designed accordingly. ; S2: Fix the Type II crack extension delamination specimen to be tested on the positioning fixture, contact the cam with the end of one end of the delamination of the specimen, connect the cam to the output shaft of the gearbox and the input shaft of the gearbox to the motor; set a microscope on one side of the Type II crack extension delamination specimen to be tested, observe the position of the crack tip through the microscope, and record the current crack length ; S3: Loading frequency according to required load Set the speed of the gearbox and start the motor to conduct the experiment; S4: Elapsed time After that, stop the motor and set the cam to the maximum loading displacement. Observe the position of the crack tip through a microscope and record the crack length at this time. ; S5: Calculate the number of loading cycles , and calculate the crack growth rate ; S6: Introducing dynamic factors to calculate cracks Expand to The maximum energy release rate between ; S7: The crack growth rate obtained in S5 and the maximum energy release rate obtained by S6 and plotted in a logarithmic form on the coordinate system, i.e., the logarithm of the crack growth rate The vertical axis is the logarithm of the maximum energy release rate is the horizontal coordinate, and the points are plotted in this coordinate system; S8: Start the motor to continue the cyclic loading of the load, and repeat the contents of S4 to S7 until the crack stops expanding. Based on all the plotted points in the coordinate system, perform regression according to the Paris law to determine the fatigue crack growth parameters of the composite material under high frequency loading. and .

[0006] Furthermore, according to the high-frequency cyclic load test method, the distance between the cam shaft center and the outer contour is Determine according to the following formula:

[0007] in, represents the maximum loading displacement; represents the minimum loading displacement; Represents the angle between the line connecting the outer contour of the camshaft and the horizontal line. ,in is the loading frequency, is the loading time within a cycle.

[0008] Furthermore, according to the high-frequency cyclic loading test method, the actual maximum energy release rate ,in is the dynamic factor; is the maximum energy release rate applied.

[0009] Furthermore, according to the high-frequency cyclic load test method, the maximum energy release rate applied is ,in is the average crack length, is the longitudinal elastic modulus of the composite material, is the total thickness of the delaminated specimen with mode II crack growth, is the length of the uncracked portion of the delamination specimen with mode II crack growth, It is the ratio of crack length to total length of the specimen.

[0010] Furthermore, according to the high-frequency cyclic load test method, the dynamic factor The method for determining is: using the finite element numerical simulation method to build a simulation model of the II type crack extension delamination specimen, given the ratio of the crack length to the total length of the specimen In the case of Perform simulation calculations and determine the maximum energy release rate of the simulation using virtual crack closure technology , and calculate the maximum energy release rate under this load condition , at this time the dynamic factor adopts Obtained by calculation.

[0011] Furthermore, according to the high-frequency cyclic load test method, the expression of Paris's law described in S8 is: .

[0012] Compared with the prior art, the present invention has the following beneficial effects: The device of the present invention uses a cam to achieve controllable load loading by changing its rotation speed and can provide high-frequency displacement load through its high-speed rotation motion, making the test frequency precisely controllable and overcoming the difficulty of high-frequency load loading in traditional fatigue testing machines. By designing the distance between the cam shaft center and the profile according to the required loading conditions, millimeter-level displacement loading can be achieved, overcoming the difficulty of too low displacement amplitude in high-frequency loading using ultrasonic fatigue equipment. The maximum energy release rate is calculated by introducing dynamic factors determined by mechanical simulation. , can accurately capture the changing trend of structural dynamic effects with test frequency, overcoming the shortcomings of traditional methods of measuring high-frequency oscillation loads; finally, by accurately obtaining the maximum energy release rate and crack growth rate By performing regression, the fatigue crack growth parameters of composite materials under high frequency loading can be obtained. and . BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic structural diagram of a high-frequency cyclic loading test apparatus for generating mode II crack growth in composite materials according to this embodiment; Figure 2 Schematic diagram of the process of a high-frequency cyclic loading test method for generating mode II crack growth in a composite material according to this embodiment; Figure 3 Schematic diagram of the cam shape designed based on sinusoidal loading conditions, where (a) is a schematic diagram of the loading displacement; (b) is a schematic diagram of the distance between the cam shaft center and the outer contour designed based on (a); Figure 4 Dynamic factor Schematic diagram of the relationship with load loading frequency; Figure 5 Schematic diagram of the fitting straight line between crack growth rate and maximum energy release rate;

[0014] The accompanying drawings illustrate: 1—Positioning fixture; 2—Cam; 3—Gearbox; 4—Motor; 5—Microscope; 6—Type II crack growth delamination specimen. DETAILED DESCRIPTION

[0015] To facilitate understanding of the present application, a more comprehensive description of the present application will be provided below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present application. However, the present application may be implemented in many different forms and is not limited to the forms described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0016] Figure 1 FIG. 1 is a schematic structural diagram of a high-frequency cyclic load test apparatus for producing a composite material type II crack extension according to the present embodiment. Figure 1 As shown, the high frequency cyclic load test device includes a positioning fixture 1, a cam 2, a gearbox 3, a motor 4 and a microscope 5. Figure 1 As shown, the uncracked end of the Type II crack propagation delamination specimen 6 is fixed by a positioning fixture 1; the cam 2 is in contact with the end of the delamination end of the Type II crack propagation delamination specimen 6; the central axis of the cam 2 is fixed by the positioning fixture 1 and connected to the output shaft of the gearbox 3; the input shaft of the gearbox 3 is connected to the output shaft of the motor 4 through a coupling; the microscope 5 is located on one side of the Type II crack propagation delamination specimen, focusing on the crack tip to be cracked, and is used to observe the length of the crack propagation. Figure 1 middle is the crack length of the delaminated specimen 6 with mode II crack growth, is the length of the uncracked portion of the delamination specimen 6 with mode II crack growth, is the total thickness of the delaminated specimen 6 with mode II crack growth.

[0017] Figure 2 FIG. 1 is a flow chart of a method for producing a high-frequency cyclic loading test of a composite material mode II crack propagation according to the present embodiment. Figure 2 As shown, the high-frequency cyclic loading test method for mode II crack growth of composite materials includes the following steps: Step 1: Design the loading cam according to the sinusoidal displacement required to load the delamination specimen for mode II crack propagation.

[0018] In this embodiment, the cam stroke is set to the maximum loading displacement. , the return stroke is set to the minimum loading displacement To achieve the cyclic loading amplitude. Figure 3 (b) Based on Figure 3 (a) Schematic diagram of the distance between the cam shaft center and the outer contour designed for the required loading displacement conditions. Determine according to the following formula:

[0019] In the formula is the angle between the line connecting the outer contour of the camshaft and the horizontal line, ,in is the loading frequency, is the loading time within a cycle.

[0020] Step 2: Fix the Type II crack extension delamination specimen to be tested on the positioning fixture, contact the cam with the end of one end of the delamination of the specimen, and connect the cam to the output shaft of the gearbox and the input shaft of the gearbox to the motor; set the microscope on one side of the Type II crack extension delamination specimen to be tested, and observe the position of the crack tip through the microscope, and record the current crack length ; Step 3: Load frequency according to the required load Set the transmission speed , where the loading frequency (Hz) and the speed of the gearbox The relationship between (rpm) is , turn on the motor and conduct the experiment.

[0021] Step 4: Elapsed Time After that, stop the motor and set the cam to the maximum loading displacement. , the number of cyclic loads at this time ; Then observe the position of the crack tip through a microscope and record the crack length at this time The crack growth rate is Perform calculations.

[0022] Step 5: Introduce the dynamic factors determined by mechanical simulation to calculate the crack Expand to The maximum energy release rate between .

[0023] True maximum energy release rate Different from the maximum energy release rate applied , considering the forced vibration response of the structure generated by the delamination specimen of type II crack extension due to high frequency loading, the relationship between the two is , where the maximum energy release rate applied is , is a dynamic factor.

[0024] Where, is the average crack length, is the longitudinal elastic modulus of the composite material, is the total thickness of the delaminated specimen with mode II crack growth, is the length of the uncracked portion of the delamination specimen with mode II crack growth, is the ratio of the crack length to the total length of the specimen, such as Figure 1 shown.

[0025] is a dynamic factor, which is the loading frequency , the ratio of crack length to total length of the specimen function of the maximum loading displacement It is irrelevant and only reflects the vibration response of forced vibration as the loading frequency increases. The determination method is: using the finite element numerical simulation method to construct a simulation model of the II type crack extension delamination specimen, at a given ratio of crack length to total specimen length In the case of Perform simulations and determine the maximum energy release rate using Virtual Crack Closure Technique (VCCT) , and calculate the maximum energy release rate under this load condition , at this time the dynamic factor adopts Calculated, dynamic factor and loading frequency The relationship between Figure 4 shown.

[0026] Step 6: The crack growth rate obtained in step 4 and the maximum energy release rate obtained in step 5 are associated and plotted logarithmically into the coordinate system, such as Figure 5 As shown, the logarithm of the crack growth rate The vertical axis is the logarithm of the maximum energy release rate Use y as the horizontal axis to plot points.

[0027] Step 7: Turn on the motor to continue the load cycle and repeat the contents of steps 4 to 6 until the crack stops expanding. Obtain all the plot points of the correlation between the maximum energy release rate and the crack growth rate in the logarithmic form in the coordinate system and calculate the value according to Paris's law. Perform regression, such as Figure 5 As shown, the fatigue crack growth parameters of composite materials under high frequency loading are determined and .

[0028] It should be understood that, inspired by the technical concept of the present invention, those skilled in the art may make various improvements or changes based on the above content without departing from the content of the present invention, which still fall within the scope of protection of the present invention.

Claims

1. A high-frequency cyclic loading test device for generating mode II crack growth in composite materials, characterized in that: The device includes a positioning tool for fixing the uncracked end of a Type II crack extension delamination specimen; the end of the delamination end of the Type II crack extension delamination specimen contacts a cam; the cam is connected to the output shaft of a gearbox; the input shaft of the gearbox is connected to the output shaft of a motor; and a microscope is provided on one side of the Type II crack extension delamination specimen for observing the length of crack extension.

2. A high-frequency cyclic loading test method for producing mode II crack growth in composite materials, characterized in that: The method comprises the following steps: S1: According to the sinusoidal displacement required for the type II crack extension delamination specimen to be tested, the cam push stroke is set to the maximum loading displacement, the cam return stroke is set to the minimum loading displacement, and the distance between the cam shaft center and the outer contour is designed accordingly. ; S2: Fix the Type II crack extension delamination specimen to be tested on the positioning fixture, contact the cam with the end of one end of the delamination of the specimen, connect the cam to the output shaft of the gearbox and the input shaft of the gearbox to the motor; set a microscope on one side of the Type II crack extension delamination specimen to be tested, observe the position of the crack tip through the microscope, and record the current crack length ; S3: Loading frequency according to required load Set the speed of the gearbox and start the motor to conduct the experiment; S4: Elapsed time After that, stop the motor and set the cam to the maximum loading displacement. Observe the position of the crack tip through a microscope and record the crack length at this time. ; S5: Calculate the number of loading cycles , and calculate the crack growth rate ; S6: Introducing dynamic factors to calculate cracks Expand to The maximum energy release rate between ; S7: The crack growth rate obtained in S5 and the maximum energy release rate obtained by S6 and plotted in a logarithmic form on the coordinate system, i.e., the logarithm of the crack growth rate The vertical axis is the logarithm of the maximum energy release rate is the horizontal coordinate, and the points are plotted in this coordinate system; S8: Start the motor to continue the cyclic loading of the load, and repeat the contents of S4 to S7 until the crack stops expanding. Based on all the plotted points in the coordinate system, perform regression according to the Paris law to determine the fatigue crack growth parameters of the composite material under high frequency loading. and .

3. The high-frequency cyclic load test method according to claim 2, characterized in that: The distance between the cam shaft center and the outer contour Determine according to the following formula: in, represents the maximum loading displacement; represents the minimum loading displacement; Represents the angle between the line connecting the outer contour of the camshaft and the horizontal line. ,in is the loading frequency, is the loading time within a cycle.

4. The high-frequency cyclic load test method according to claim 3, characterized in that: True maximum energy release rate ,in is the dynamic factor; is the maximum energy release rate applied.

5. The high-frequency cyclic load test method according to claim 4, characterized in that: The maximum energy release rate applied ,in is the average crack length, is the longitudinal elastic modulus of the composite material, is the total thickness of the delaminated specimen with mode II crack growth, is the length of the uncracked portion of the delamination specimen with mode II crack growth, It is the ratio of crack length to total length of the specimen.

6. The high-frequency cyclic loading test method according to claim 5, characterized in that: The dynamic factor The method for determining is: using the finite element numerical simulation method to construct a simulation model of the II type crack extension delamination specimen, given the ratio of the crack length to the total length of the specimen In the case of Perform simulation calculations and determine the maximum energy release rate of the simulation using virtual crack closure technology , and calculate the maximum energy release rate applied under this load condition , at this time the dynamic factor adopts Obtained by calculation.

7. The high-frequency cyclic loading test method according to claim 6, characterized in that: The expression of Paris's law described in S8 is .

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