A strain-controlled method and system for testing the fatigue life of an impact

Abstract

The application discloses a strain-controlled impact fatigue life test method and system, comprising the following steps: S1: arbitrarily selecting a bullet of a specific length, performing test shooting with the bullet of the specific length, determining experimental parameters of required strain rate loading and an impact fatigue strain amplitude generated by the bullet of the specific length; and repeatedly performing impact fatigue test under corresponding experimental parameters until a sample is fractured, and the total number of impacts is an impact fatigue life of the corresponding strain amplitude under the required strain rate; S2: replacing the bullet, adjusting the experimental parameters through test shooting, determining that the replaced bullet generates the same strain rate under the experimental parameters in S1, and performing impact fatigue life test under the corresponding experimental parameters; and S3: replacing the bullet, repeating S2, and realizing impact fatigue life test of other bullet lengths under the corresponding strain rate. The application has important significance for formulating future impact fatigue test standards and developing an impact test machine.

Description

Technical Field

[0001] This invention belongs to the research fields of impact fatigue life testing and impact fatigue failure, and can be used to test the strain-controlled impact fatigue life of materials, especially metallic materials. Specifically, it relates to a strain-controlled impact fatigue life testing method and system. Background Technology

[0002] In aerospace, weaponry, and marine engineering, many structural components are subjected to repeated impact (impact fatigue) loads during their service life. Unlike conventional fatigue, impact fatigue is characterized by rapid loading rates, high strain rates, and the strain rate effect of materials. Furthermore, due to the stress wave effect, impact fatigue can cause structural components to fail suddenly without the formation of obvious cracks. Therefore, impact fatigue life testing of materials is essential before they are used in impact fatigue-resistant design. However, due to the complexity of impact fatigue loads and the influence of the material's own strain rate effect, there are currently no mature and systematic testing standards and methods for impact fatigue testing. Given the current limitations of impact fatigue research and the urgent need to study the impact fatigue life and failure mechanisms of materials, developing mature and standardized impact fatigue testing methods is particularly important.

[0003] In conventional fatigue research, strain control is commonly used to test the fatigue life of materials, with strain measurement under fatigue load typically achieved using a contact extensometer. However, current impact fatigue research mostly focuses on controlling impact energy to test the impact fatigue life of materials under different impact energies. For example, adjusting the height of the drop hammer can be used to test the impact fatigue life under different impact energies. However, according to the formula... (1) The formula for calculating the impact velocity of the falling hammer shows that the change in the height of the falling hammer will inevitably cause a change in the impact velocity. As a result, the impact fatigue life measured under different impact energies will be affected by the material strain rate effect. In particular, for materials that are sensitive to strain rate, this test method cannot accurately reflect the impact fatigue failure behavior of the material. Summary of the Invention

[0004] This invention aims to address the shortcomings of existing technologies by proposing a strain-controlled impact fatigue life testing method and system. This will help establish standardized and systematic impact fatigue life testing standards, and further promote the development of the field of impact fatigue research, particularly in the areas of impact fatigue failure mechanisms and impact fatigue-resistant design.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] A strain-controlled impact fatigue life testing method includes the following steps:

[0007] S1: Randomly select a bullet of a specific length, test it with the bullet of the specific length, determine the experimental parameters of the required strain rate loading and the impact fatigue strain amplitude generated by the bullet of the specific length; and perform repeated impact fatigue tests under the corresponding experimental parameters until the sample breaks. The total number of impacts is the impact fatigue life of the corresponding strain amplitude under the required strain rate.

[0008] S2: Replace the bullet, test fire, adjust the experimental parameters, determine the experimental parameters of the replaced bullet under the same strain rate as in S1, and conduct impact fatigue life test under the corresponding experimental parameters.

[0009] S3: Replace the bullet and repeat S2 to achieve impact fatigue life test of other bullet lengths at the corresponding strain rates.

[0010] Preferably, the method further includes: according to actual needs, replacing bullets of arbitrary length to conduct impact fatigue life tests under multiple impact fatigue strain amplitudes.

[0011] Preferably, the specific method of S1 includes:

[0012] S11: Select any bullet sample and fire it several times to obtain the incident wave, reflected wave and transmitted wave collected by the data acquisition system.

[0013] S12: Based on the incident wave, the reflected wave and the transmitted wave, the data is processed using the three-wave method to determine the impact strain amplitude and experimental parameters of repeated impacts of the bullet sample at the required strain rate.

[0014] S13: Repeatedly impact the bullet sample according to the experimental parameters determined in S12 until the bullet sample breaks. The total number of impacts is the impact fatigue life corresponding to the impact strain amplitude in S12.

[0015] Preferably, the specific method of S2 includes:

[0016] By replacing the bullet specimens with other lengths, and by adjusting the experimental parameters, repeat steps S11 and S12 to determine the experimental parameters that produce the same strain rate as in step S12 and the impact fatigue strain amplitude corresponding to the bullet specimens of other lengths.

[0017] Preferably, the specific method of S3 includes:

[0018] Repeated impact loading is performed based on the experimental parameters determined in S2 to obtain the impact fatigue life under the impact fatigue strain amplitude determined in S2.

[0019] Preferably, the method for determining the impact strain amplitude and experimental parameters of repeated impacts of the bullet specimen at the desired strain rate in step S12 includes:

[0020]

[0021]

[0022]

[0023] in The variable represents the strain rate, t represents time, and c represents the strain rate. B The wave velocity in the rod, l s ε represents the gauge length of the specimen. r E represents reflected strain, ε(t) represents strain, σ(t) represents stress, and E B A represents the elastic modulus of the rod. B A represents the cross-sectional area of ​​the rod. s ε represents the cross-sectional area of ​​the gauge length of the specimen. t This represents transmission strain.

[0024] The present invention also provides a strain-controlled impact fatigue life testing system for implementing the strain-controlled impact fatigue life testing method, comprising: a first fatigue life testing module, a second fatigue life testing module and a third fatigue life testing module.

[0025] The first fatigue life test module is used to arbitrarily select a bullet of a specific length, test it with the bullet of the specific length, determine the experimental parameters of the required strain rate loading and the impact fatigue strain amplitude generated by the bullet of the specific length; and perform repeated impact fatigue tests under the corresponding experimental parameters until the sample breaks, the total number of impacts being the impact fatigue life of the corresponding strain amplitude under the required strain rate.

[0026] The second fatigue life test module is used to replace the bullet, and through test firing, adjust the experimental parameters to determine the experimental parameters under the impact of the replaced bullet that produce the same strain rate as in the first fatigue life test module, and conduct impact fatigue life test under the corresponding experimental parameters.

[0027] The third fatigue life test module is used to replace the bullet and repeat the second fatigue life test module to achieve impact fatigue life test of other bullet lengths under corresponding strain rates.

[0028] Preferably, the system further includes: according to actual needs, replacing bullets of arbitrary length to conduct impact fatigue life tests under multiple impact fatigue strain amplitudes.

[0029] Compared with existing technologies, the advantages of this invention are as follows: Based on the conventional split-type Hopkinson bar test system, this invention designs a strain-controlled impact fatigue life testing method and system. Since materials themselves exhibit varying degrees of strain rate effects, the strain rate should be kept consistent during strain-controlled impact fatigue life testing to avoid the influence of the material's own strain rate effect on impact fatigue life. By changing the length of the projectile in the split-type Hopkinson bar system and maintaining a consistent peak velocity for each projectile during impact fatigue loading, the influence of the strain rate effect can be ignored, thus achieving strain-controlled impact fatigue life testing. This invention is of great significance for the future formulation of impact fatigue testing standards and the development of impact testing machines. Attached Figure Description

[0030] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of a strain-controlled impact fatigue life testing method according to an embodiment of the present invention.

[0032] Figure 2 Schematic diagram of bullets of different lengths equipped with the split Hopkinson lever according to Embodiment 1 of the present invention;

[0033] Figure 3 The stress wave incident waveforms of different bullets under the same amplitude (and the same strain rate) in Embodiment 1 of the present invention are shown.

[0034] Figure 4 This is a flowchart of the impact fatigue life test of Embodiment 1 of the present invention, which achieves strain control by changing the bullet length. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Example 1

[0038] like Figure 1 As shown, this invention discloses a strain-controlled impact fatigue life testing method, comprising the following steps:

[0039] S1: Arbitrarily select a specific bullet length, test-fire with that bullet, determine the experimental parameters for the required strain rate loading and the impact fatigue strain amplitude generated by the bullet. Then, perform repeated impact fatigue tests under these parameters until the specimen fractures. The total number of impacts is the impact fatigue life of the corresponding bullet (i.e., the corresponding strain amplitude) at that strain rate.

[0040] S2: Replace the bullet, test fire, adjust the experimental parameters, determine the experimental parameters under the same strain rate as in S1 when the bullet is impacted, and conduct impact fatigue life test under these parameters.

[0041] S3: Replace the bullet and repeat step S2 to perform impact fatigue life tests on other bullet lengths at corresponding strain rates. Depending on actual needs, bullets of any length can be used to perform impact fatigue life tests at multiple impact fatigue strain amplitudes.

[0042] In this embodiment, the specific method of S1 includes:

[0043] S11: Select any bullet and fire it several times to obtain the incident wave, reflected wave and transmitted wave collected by the data acquisition system;

[0044] S12: By processing the data using the three-wave method, the impact strain amplitude and experimental parameters of repeated impacts of the bullet at the required strain rate can be determined.

[0045] S13: Repeatedly impact the specimen according to the experimental parameters determined in the second step until the specimen breaks. The total number of impacts is the impact fatigue life corresponding to the impact strain amplitude in the second step.

[0046] In this embodiment, the specific method of S2 includes:

[0047] By changing to bullets of different lengths, S11 and S12 were repeated by adjusting the experimental parameters to determine the experimental parameters that produce the same strain rate as in S12 and the corresponding impact fatigue strain amplitude of the bullet.

[0048] In this embodiment, the specific method of S3 includes:

[0049] By repeatedly applying impact loading based on the experimental parameters determined in S2, the impact fatigue life at the impact fatigue strain amplitude can be obtained.

[0050] A typical split Hopkinson rod uses high-pressure nitrogen gas in a cylinder to accelerate the bullet, achieving impact loading. This embodiment uses pure titanium as an example to provide a more complete and detailed explanation of the technical solution and advantages of the present invention, such as... Figure 2 The image shows bullets of different lengths that are equipped with the split Hopkinson lever system. Figure 2 The diagram shows bullets of 100mm, 150mm and 210mm. At a strain rate of 1000m / s, the resulting impact fatigue strain amplitudes are 0.045, 0.053 and 0.070, respectively. Figure 3 for Figure 2 The image shows the incident wave waveforms generated by three bullets at a peak strain rate of 1000 / s. This embodiment is only a part of the embodiments of the present invention and does not represent all embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without inventive effort, such as the present invention's ability to achieve wide strain rate impact fatigue life testing by adjusting air pressure and bullet acceleration distance, are all within the scope of protection of the present invention.

[0051] The technical solution provided by the present invention will be described in detail below with reference to examples and accompanying drawings.

[0052] An embodiment of the present invention provides a strain-controlled impact fatigue life testing method, referencing... Figure 2 , Figure 3 and Figure 4 This includes the following steps:

[0053] Step 1: Using a 100mm long bullet, adjust the experimental parameters and conduct several test shots. Based on the incident wave, reflected wave, and transmitted wave collected by the data acquisition system, calculate the strain rate and stress-strain curve according to equations (2)-(4) to obtain the experimental parameters (such as air pressure, bullet acceleration distance, etc.) corresponding to a strain rate of 1000 / s generated by the 100mm bullet and the impact fatigue strain amplitude ε generated by the 100mm bullet. 100 ;

[0054]

[0055]

[0056]

[0057] in The variable represents the strain rate, t represents time, and c represents the strain rate. B The wave velocity in the rod, l s ε represents the gauge length of the specimen. r E represents reflected strain, ε(t) represents strain, σ(t) represents stress, and E B A represents the elastic modulus of the rod. BA represents the cross-sectional area of ​​the rod. s ε represents the cross-sectional area of ​​the gauge length of the specimen. t This represents transmission strain.

[0058] Step 2: Using the experimental parameters determined in Step 1, repeatedly apply impact loading to the specimen until it fractures. The total number of impacts is the impact fatigue strain amplitude ε at a strain rate of 1000 / s. 100 The corresponding impact fatigue life N 100 ;

[0059] Step 3: Replace with a 150mm bullet and repeat Step 1 to determine the experimental parameters corresponding to a strain rate of 1000 / s for the 150mm bullet and the impact fatigue strain amplitude ε corresponding to a strain rate of 1000 / s for the 150mm bullet. 150 ;

[0060] Step 4: Using the experimental parameters determined in Step 3, repeatedly impact the specimen until it fractures. The total number of impacts is the impact fatigue life N corresponding to the impact fatigue strain amplitude ε2 at a strain rate of 1000 / s. 150 ;

[0061] Step 5: Replace with 210mm and repeat steps 3 and 4 to obtain the impact fatigue strain amplitude ε when the strain rate is 1000 / s. 210 The corresponding impact fatigue life N 210 .

[0062] like Figure 3 The figure shows the incident loading waves generated by 100mm, 150mm, and 210mm bullets at a strain rate of approximately 1000 / s. Since the peak strain rate is the same, this test does not address the influence of material strain rate on impact fatigue life. It should be noted that in actual testing, a wider range of impact fatigue strains can be achieved by simply adjusting the bullet length and experimental parameters. Figure 4 This is a schematic diagram of the impact fatigue life test process in this embodiment, which achieves strain control by changing the bullet length.

[0063] Example 2

[0064] The present invention also provides a strain-controlled impact fatigue life testing system, comprising: a first fatigue life testing module, a second fatigue life testing module and a third fatigue life testing module;

[0065] The first fatigue life test module is used to arbitrarily select a bullet of a specific length, test it with the bullet of a specific length, determine the experimental parameters of the required strain rate loading and the impact fatigue strain amplitude generated by the bullet of a specific length; and perform repeated impact fatigue tests under the corresponding experimental parameters until the sample breaks. The total number of impacts is the impact fatigue life of the corresponding strain amplitude under the required strain rate.

[0066] The second fatigue life test module is used to replace the bullet. Through test firing, the experimental parameters are adjusted to determine the experimental parameters under the impact of the replaced bullet at the same strain rate as in the first fatigue life test module, and then the impact fatigue life test is carried out under the corresponding experimental parameters.

[0067] The third fatigue life test module is used to replace the bullet and repeat the second fatigue life test module to achieve impact fatigue life test of other bullet lengths under corresponding strain rates.

[0068] In this embodiment, the system further includes: according to actual needs, replacing bullets of arbitrary length to conduct impact fatigue life tests under multiple impact fatigue strain amplitudes.

[0069] In this embodiment, the specific working process of the first fatigue life test module includes:

[0070] Step 1: Select any bullet and fire it several times to obtain the incident wave, reflected wave, and transmitted wave collected by the data acquisition system.

[0071] Step 2: By processing the data using the three-wave method, the impact strain amplitude and experimental parameters of repeated impacts of the bullet at the required strain rate can be determined.

[0072] Step 3: Repeatedly impact the sample according to the experimental parameters determined in step 2 until the sample breaks. The total number of impacts is the impact fatigue life corresponding to the impact strain amplitude in step 2.

[0073] In this embodiment, the specific working process of the second fatigue life testing module includes:

[0074] By replacing the bullet with a different length, and by adjusting the experimental parameters, repeat steps 1 and 2 of the specific working process of the first fatigue life test module to determine the experimental parameters that produce the same strain rate as in step 2 and the corresponding impact fatigue strain amplitude of the bullet.

[0075] In this embodiment, the specific working process of the second fatigue life testing module includes:

[0076] By repeatedly applying impact loads based on the experimental parameters determined by the specific working process of the second fatigue life test module, the impact fatigue life under the impact fatigue strain amplitude can be obtained.

[0077] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A strain-controlled, impact fatigue life testing method, characterized by, The method comprises the following steps: S1: arbitrarily selecting a bullet of a specific length, performing a test shot with the bullet, determining experimental parameters of a required strain rate loading and an impact fatigue strain amplitude generated by the bullet of the specific length, and performing repeated impact fatigue tests under the corresponding experimental parameters until the sample is broken, and the total number of impacts is the impact fatigue life under the corresponding strain amplitude at the required strain rate; S2: replacing the bullet, adjusting the experimental parameters through a test shot, and determining that the replaced bullet generates the same experimental parameters as in S1 under the same strain rate, and performing impact fatigue life tests under the corresponding experimental parameters; S3: replacing the bullet, repeating S2, and achieving impact fatigue life tests of other bullet lengths under the corresponding strain rate.

2. The strain-controlled impact fatigue life test method according to claim 1, wherein the method further comprises replacing a bullet of any length to perform impact fatigue life tests under a plurality of impact fatigue strain amplitudes according to actual needs. The specific method of S1 comprises:

3. The strain-controlled, impact fatigue life test method of claim 1, wherein, S11: optionally selecting a bullet sample and performing a plurality of test shots on the bullet sample to obtain incident waves, reflected waves and transmitted waves collected by a data collection system; S12: processing data by using a three-wave method based on the incident waves, the reflected waves and the transmitted waves to determine an impact strain amplitude of the bullet sample under a required strain rate and experimental parameters of repeated impacts; S13: performing repeated impact loading on the bullet sample according to the experimental parameters determined in S12 until the bullet sample is broken, and the total number of impacts is the impact fatigue life corresponding to the impact strain amplitude in S12. The specific method of S2 comprises:

4. The strain-controlled, impact fatigue life test method of claim 3, wherein, replacing a bullet sample of another length, repeating S11 and S12 by adjusting experimental parameters, and determining that the bullet sample of the other length generates the same experimental parameters as in S12 under the same strain rate and the corresponding impact fatigue strain amplitude of the bullet sample of the other length. The specific method of S3 comprises:

5. The strain-controlled, impact fatigue life test method of claim 4, wherein, performing repeated impact loading according to the experimental parameters determined in S2 to obtain the impact fatigue life under the impact fatigue strain amplitude determined in S2.

6. The strain-controlled impact fatigue life test method according to claim 3, wherein the method of determining the impact strain amplitude of the bullet sample under the required strain rate and the experimental parameters of repeated impacts in S12 comprises: including: a first fatigue life test module, a second fatigue life test module and a third fatigue life test module; wherein represents the strain rate, t represents time, c B represents the wave speed in the rod, l s represents the sample gauge length, ε ｒ represents the reflected strain, ε(t) represents the strain, σ(t) represents the stress, E B represents the elastic modulus of the rod, A B represents the cross-sectional area of the rod, A S represents the sample gauge cross-sectional area, ε t represents the transmitted strain.

7. A strain-controlled, impact fatigue life testing system for implementing a strain-controlled, impact fatigue life testing method according to any one of claims 1 to 6, characterized by the first fatigue life test module is configured to arbitrarily select a bullet of a specific length, perform a test shot with the bullet, determine experimental parameters of a required strain rate loading and an impact fatigue strain amplitude generated by the bullet of the specific length, and perform repeated impact fatigue tests under the corresponding experimental parameters until the sample is broken, and the total number of impacts is the impact fatigue life under the corresponding strain amplitude at the required strain rate; ​ ​ The second fatigue life test module is used for replacing the bullet, adjusting the experimental parameters through trial shooting, determining the experimental parameters of the replaced bullet under the same strain rate as in the first fatigue life test module, and performing impact fatigue life test under the corresponding experimental parameters. The third fatigue life test module is used for replacing the bullet, repeating the second fatigue life test module, and achieving impact fatigue life test of other bullet lengths under the corresponding strain rate.

8. The strain-controlled impact fatigue life test system according to claim 7, wherein the system further comprises replacing the bullet of any length to perform impact fatigue life test under multiple impact fatigue strain amplitudes according to actual needs. ​

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