KR20210125665A - Fatigue Test System of Materials Using Vibration Tester - Google Patents

Abstract

The present invention relates to a fatigue test system of a material measuring fatigue life of a material by applying vibration after mounting a sample in a vibration tester. The purpose of the present invention is to provide the fatigue test system enabling a sample to be vibrated by generating vibration after mounting the plurality of samples in the vibration tester. Provided is the fatigue test system deriving a portion where a neck of the sample is formed for applying larger external force to the sample only by the vibration through finite-element analysis (FEA). Moreover, the present invention can provide the fatigue test data of the material which can be reflected on a product design by converting G-N data into stress-life (S-N) data based on the G-N data generated by the reciprocating repeating number of the sample and vibration acceleration computed from an amplitude applied by the vibration tester.

Description

Fatigue Test System of Materials Using Vibration Tester

The present invention relates to a fatigue test system for a material, and more particularly, to a fatigue test system for a material that measures the fatigue life of a material by applying vibration after mounting a specimen in a vibration tester.

Fatigue properties of materials are essential information for predicting fatigue life of products. In the modern industrial environment where new materials are constantly being developed, in order to check the applicability of new materials in advance, it is necessary to know the fatigue properties of the materials. A study on the lifespan must be carried out, and in order to check the fatigue life of the material, a test that predicts the fatigue life by repeatedly stretching and compressing a specimen made of the material is used.

The above-described conventional fatigue test is prepared by mounting a dog bone-shaped specimen in an apparatus for performing a fatigue test, repeatedly applying a tensile-compressive load to the specimen, and measuring the number of repetitions until the specimen is destroyed. It is represented by one SN diagram. In the conventional fatigue test, one specimen is mounted in a device for performing the fatigue test, and repeated tensile-compression loads are applied until the specimen is destroyed according to the test conditions. At this time, since the number of repetitions is as low as 1000 times and as high as 100,000 times, it takes a lot of time and money to perform a fatigue test on one specimen. In addition, in order to create a meaningful SN diagram that can be reflected in the design of a machine or structure, tests must be conducted under various test conditions, and multiple tests must be performed under the same test conditions to increase the reliability of test results. There is a problem that it takes a lot of time to draw the SN diagram of .

In order to solve the above problem, a tensile-compressive load can be applied after a plurality of specimens are mounted in a fatigue test performing apparatus. There is a problem that the SN diagram cannot be obtained.

1. Republic of Korea Patent Publication No. 10-2015-0118606 ("Cavitation / Fatigue / Erosion Experimental Apparatus for Test Specimens Using Ultrasonic Vibration", October 23, 2015)

The present invention has been devised to solve the above problems, and an object of the present invention is to provide a fatigue test system in which a plurality of specimens are mounted in a vibration test apparatus and then vibration is generated to cause the specimen to vibrate, and only by vibration To provide a fatigue test system that derives the part where the neck of the specimen will be formed through the finite element analysis method so that a large external force can be applied to the specimen.

In addition, based on the vibration acceleration calculated from the amplitude applied by the vibration tester and the GN data generated by the number of round trip repetitions of the specimen, it can be converted into stress life (SN) data to provide fatigue test data of materials that can be reflected in product design. The purpose of this is to provide a fatigue test system with

The fatigue test system of the material of the present invention is formed in the form of a plate extending along the height direction, the specimen array including the first to n specimens in which the neck is narrower than the peripheral area at a specific height; a coupling portion rigidly coupled to the upper ends of the first to n specimens so that the first to n specimens are perpendicular to the ground; a vibrating unit for applying vibration of a predetermined vibration frequency and a predetermined amplitude to the coupling unit; control the operation of the vibrating unit, detect whether each of the first to n specimens is broken , a control unit that calculates stress life (SN) data based on the applied vibration frequency and amplitude information, wherein n>1.

In addition, the control unit calculates an applied vibration acceleration (G) that is a vibration acceleration applied to the corresponding specimen array based on the amplitude, and based on the relational expression between the vibration acceleration and the stress, an application corresponding to the applied vibration acceleration Estimating the stress, calculating the stress life (SN) data based on N1 to Nn, which is the number of reciprocating motions of each of the first to n specimens, and the estimated applied stress until the specimen is broken with respect to the vibration of the amplitude characterized in that

In addition, the vibration frequency is characterized in that the resonance frequency of at least one of the first to n specimens.

In addition, the vibration frequency is characterized in that the first to n specimens vibrated at the vibration frequency are not twisted, but are reciprocating frequencies in a vertical direction with respect to the surface of the specimen.

In addition, the control unit, characterized in that for variably controlling at least one of the vibration frequency and the amplitude.

In addition, the control unit repeatedly performs a fatigue test while changing at least one of the vibration frequency and amplitude of the applied vibration, and N1 to Nn, which is the number of reciprocating motions at the break of each of the first to n specimens of each test, It is characterized in that the stress life (SN) data is calculated based on the accumulated data of the applied vibration frequency and amplitude information.

In addition, the fatigue test system of the material further comprises a strain gauge coupled to the neck of each of the first to n specimens, and the control unit, the first to n specimens vibrating from the strain gauge The strain of the neck of each of the specimens receiving, and multiplying the strain of the neck of the first to n specimens and the elastic modulus of the first to n specimens input in advance, respectively, to estimate the stresses S1 to Sn acting on the first to n specimens, and the stresses S1 to Sn and stress life (SN) data is calculated based on the N1 to Nn.

In addition, the control unit receives the fatigue test results previously performed on at least one specimen having the same shape and material as at least one of the first to n specimens, and the input fatigue test results, the N1 to Nn and Stress life (SN) data is calculated by estimating the stress applied to the first to n specimens based on the amplitude applied to the specimen array.

In addition, the controller compares the number of repetitions for a predetermined stress of the input fatigue test result with the N1 to Nn, and calculates the vibration acceleration and stress corresponding to the amplitude.

In addition, the control unit repeatedly performs a fatigue test while changing at least one of the vibration frequency and amplitude of the applied vibration, and N1 to Nn, which is the number of reciprocating motions at the break of each of the first to n specimens of each test, Stores the applied vibration frequency and amplitude information, and compares the number of repetitions for a predetermined stress of the input fatigue test result with N1 to Nn, which is the number of reciprocating motions of the test target specimen array, and the vibration acceleration corresponding to the applied amplitude and Generate stress life (SN) data by calculating the stress, but supplement the stress life (SN) data through interpolation (interpolation or extrapolation) between the applied amplitude or vibration acceleration and stress based on the input fatigue test result characterized in that

The fatigue test system of the present invention generates vibration after fixing a plurality of specimens to a vibration test apparatus, and it is possible to simultaneously test a plurality of specimens, thereby shortening the test time. In addition, the reliability of the test can be improved because the specimen is manufactured after the part where the neck of the specimen will be formed is derived through the finite element analysis method so that a large external force can be applied to the specimen only with vibration. In addition, based on the vibration acceleration calculated from the amplitude applied by the vibration tester and the GN data generated by the number of round trip repetitions of the specimen, it is converted into stress life (SN) data to provide fatigue test data of materials that can be reflected in product design. It is possible to provide a fatigue test system that can do this.

1 is a schematic diagram of a material fatigue test system according to an embodiment of the present invention;
2 is an enlarged side view of a material fatigue test system according to an embodiment of the present invention;
3 is a perspective view of a modeled specimen according to a plurality of vibration modes of a material fatigue test system according to an embodiment of the present invention;
4 is a front view of a modeled specimen of a material fatigue test system according to an embodiment of the present invention;
5 is a control block diagram of a material fatigue test system according to an embodiment of the present invention;
6 is a front view of a specimen of a material fatigue test system according to a first embodiment of the present invention;
7 is a flowchart of SN data generation of a fatigue test system for a material according to a first embodiment of the present invention;
8 is a flowchart of SN data generation of a material fatigue test system according to a second embodiment of the present invention;

Hereinafter, an embodiment of the present invention as described above will be described in detail with reference to the drawings.

1 is a schematic diagram showing the configuration of a fatigue test system for a material according to an embodiment of the present invention. As shown in FIG. 1, in the fatigue test system of the material of the present invention, a plurality of specimens 100 formed of a material for testing fatigue properties are coupled to the coupling portion 200 at a predetermined interval to form a specimen array, Each specimen 100 is formed to extend in the height direction, and a neck 110 having a narrower width than the peripheral area at a specific height is formed. The coupling part 200 is coupled to the upper end of the specimen 100 , and a separate fixing device may be provided to prevent the specimen 100 from being separated from the coupling part 200 during the fatigue test. The coupling unit 200 to which the plurality of specimens 100 are coupled is placed on the vibrating unit 300 , and the vibrating unit 300 applies a predetermined vibration frequency and a predetermined amplitude to the coupling unit 200 . The combined plurality of specimens 100 vibrates. The vibrator 300 is electrically connected to the control unit 400 that controls the operation of the vibrator 300 . In addition to the function of controlling the operation of the vibrating unit 300 , the control unit 400 detects whether each of the first to nth specimens constituting the specimen array is broken. At this time, as a method for detecting whether each specimen 100 is broken, it may be detected through a difference in vibration frequency or amplitude applied by the vibrating unit 300 , or may be detected through a photographing device, and strain on the specimen 100 . When the gauge is attached, whether the specimen 100 is broken can be detected from the output signal of the strain gauge. Stores N1 to Nn, which is the number of reciprocating motions (N) that each specimen 100 vibrates until it breaks, and stress life data (hereinafter, SN data) based on the vibration frequency and amplitude information applied by the vibrating unit 300 ) is calculated. The calculated S-N data may be transmitted to the operator's PC or portable terminal.

2 is an enlarged side view of a material fatigue test system according to an embodiment of the present invention. As shown in FIG. 2 , the specimen 100 coupled to the coupling unit 200 vibrates by vibration applied from the vibrating unit 300 at a predetermined frequency and a predetermined amplitude. At this time, it is preferable that the specimen 100 vibrates in a direction perpendicular to the surface of the specimen 100 . That is, when the specimen 100 moves forward by vibration, the front surface of the specimen 100 is compressed, and when the specimen 100 moves backward by vibration, the front surface of the specimen 100 is tensioned. As the specimen 100 is repeatedly moved forward and backward by vibration, the specimen 100 is compressed and tensioned, and compressive and tensile forces are repeatedly applied to the specimen 100 to break the specimen 100 . At this time, the control unit 400 stores the number of reciprocating motions (N) in which the specimen 100 vibrates and reciprocates until it is fractured.

When planning a fatigue test, it must be possible to predict the load applied to the specimen. In the traditional tensile-compression fatigue test method, the load applied to the specimen can be calculated by dividing the load condition by the cross-sectional area of the specimen. However, in the case of a fatigue test using a vibration tester, it is necessary to know the relationship and influence between the specimen shape and the vibration frequency because the load applied to the specimen varies depending on the shape of the specimen and the condition of the vibration frequency of the test. If the test is planned and performed without prior analysis of the relationship between the specimen shape and the vibration frequency, meaningless test results may appear or other parts (e.g., joints) other than the area of the specimen (the neck of the specimen) in which the fracture was expected to occur. In case the maximum load is applied to the area combined with Therefore, in the present invention, in order to solve the above problem, the relationship between the shape of the specimen and the vibration frequency is analyzed through finite element analysis, and based on this, the optimal specimen shape used for the fatigue test is suggested to increase the reliability of the fatigue test. characterized. This will be described in detail with reference to FIGS. 3 and 4 .

3 is a perspective view illustrating a modeled specimen according to a plurality of vibration modes of a material fatigue test system according to an embodiment of the present invention. At this time, the modeled specimen is a vibration test, the modeling specimen 100M shown in FIG. is the second vibration mode to which the second vibration frequency value is input.

As shown in (a) of FIG. 3 , it can be seen that the modeling specimen 100M vibrates in a direction perpendicular to the surface in the first vibration mode. This transmits an appropriate vibration frequency value to the control unit 400 so that the vibration unit 300 applies vibration of the first vibration frequency. However, as shown in FIG. 3(b), in the second vibration mode, the modeling specimen 100M did not vibrate in a direction perpendicular to the surface and torsion was generated, so the second vibration frequency value was not suitable for the fatigue test. It can be seen that this is a frequency value. Therefore, it is effective because the frequency value at which the specimen 100 will vibrate before the fatigue test can be derived through the finite element analysis method in advance.

4 shows a front view of a modeled specimen of a material fatigue test system according to an embodiment of the present invention. 4A is a third vibration mode to which a third vibration frequency value is input, and FIG. 4B is a fourth vibration mode to which a fourth vibration frequency value is input. In this case, the third and fourth vibration frequencies are frequencies at which the modeling specimens 100Ma and 100Mb vibrate in a direction perpendicular to the surface.

The modeling specimen 100Ma of the third vibration mode may receive the greatest external force when the neck 110Ma is formed at a position separated by L1 from the region coupled to the coupling part 200, and the modeling specimen 100Ma of the fourth vibration mode ( 100Mb) may receive the greatest external force when the neck 110Mb is formed at a position separated by L2 from the region coupled to the coupling unit 200 . Even with the vibration frequency that moves the specimen 100 perpendicular to the surface, the external force acting on the neck 110 of the specimen 100 varies according to the height at which the neck 110 is formed. Therefore, after drawing a plurality of modeling specimens each having different neck positions at a predetermined frequency that vibrates the specimen in the vertical direction of the specimen, simulation through finite element analysis, the modeling specimen having the position of the neck where the external force acts the greatest A fatigue test is performed with the specimen 100 manufactured in the shape of (100), and it is preferable that the vibration frequency at which the external force acts the greatest on the neck 110 of the specimen 100 is the resonance frequency.

5 is a block diagram of a control unit of a material fatigue test system according to an embodiment of the present invention. As shown in FIG. 5 , the controller 400 includes a receiver 410 , a transmitter 420 , a vibration acceleration calculator 430 , and an S-N data generator 440 . The receiver 410 receives the vibration frequency value calculated through the finite element analysis method described with reference to FIG. 3 , and the strain gauge 120 for measuring the strain of the specimen 100 is placed on the neck 110 of the specimen 100 . When attached, it receives strain from the strain gauge 120 . The vibration acceleration calculation unit 430 calculates the vibration acceleration G at which the specimen 100 reciprocates based on the magnitude of a predetermined amplitude applied by the vibration unit 300, and the SN data generation unit 440 is SN data is generated based on the accumulated data of the number of reciprocating motions N1 to Nn of each of the 1st to nth specimens, and the vibration frequency and amplitude information applied to the vibrating unit 300 . The S-N data generated by the S-N data generating unit 440 is preferably transmitted to the worker's PC or portable terminal by the transmitting unit 420 or stored in a separate storage device.

Two embodiments in which the fatigue test system of the present invention generates S-N data will be described with reference to FIGS. 6 to 8 . First, a first embodiment will be described with reference to FIGS. 6 and 7 .

6 is a front view showing a specimen of a fatigue test system for a material according to a first embodiment of the present invention. As shown in FIG. 6 , the strain gauge 120 is coupled to the neck 110 of each specimen 100 . The strain gauge 120 is respectively installed on the neck 110 of the first to n-th specimens to measure the strain, and transmits it to the control unit 400 , and the control unit 400 receives the strain transmitted from the strain gauge 120 . Received stress is calculated, and the SN data generation unit 440 calculates the SN data. It will be described in more detail with reference to the flowchart shown in FIG. 7 .

As shown in FIG. 7, first, the strain gauge 120 coupled to the neck 110 of the specimen 100 measures the strain of the neck 110 when the specimen 100 vibrates at a predetermined vibration frequency and a predetermined amplitude. A strain measurement step (S100) to be measured is performed. The strain measured by the strain gauge 120 is transmitted to the control unit 400, and a strain reception step (S110) in which the control unit 400 receives the strain is performed, and the control unit 400 receives the strain received in the strain reception step (S110). A stress calculation step (S120) of multiplying the strain by the elastic modulus of the material input in advance to calculate the stresses S1 to Sn acting on the first to nth specimens is performed. At this time, the vibration acceleration Ga is calculated by the vibration acceleration calculator 430 based on the predetermined amplitude information, and based on the values of S1 to Sn that are stresses acting on the first to n specimens calculated when the vibration acceleration Ga is used. Thus, the SN data calculation step (S130) in which the SN data is calculated is performed. Even if the magnitude of the amplitude applied by the vibrating unit 300 is adjusted on the basis of the S1 to Sn values, which are the stresses acting on the first to n specimens calculated when the vibration acceleration (Ga), the relation between the vibration acceleration and the stress (vibration acceleration ( G) = k Ⅷ stress (S), k = constant), it is possible to estimate the stress applied to the neck 110 of the specimen 100.

8 is a flowchart illustrating S-N data generation of a material fatigue test system according to a second embodiment of the present invention. As shown in FIG. 8 , a fatigue test is first performed on a specimen formed of the same shape and material as the specimen 100 of the present invention using a conventional fatigue test apparatus, and a pre-fatigue test result is obtained. In this case, the conventional fatigue test apparatus is a fatigue test apparatus that is coupled to both ends of one specimen and repeatedly applies stress including predetermined tensile and compressive forces to one specimen.

The control unit 400 receives the result of the pre-fatigue test performed on one specimen with the conventional fatigue test apparatus through the pre-fatigue test result receiving step (S200), and the first to n-th according to the fatigue test result of the present invention. The fatigue test result reception step (S210) of the present invention in which N1 to Nn, which is the number of reciprocating motions of the specimen, and amplitude information applied by the vibrator 300 are received. At this time, the amplitude information applied by the vibrator 300 is calculated as a vibration acceleration by the vibration acceleration calculator 430 . The vibration acceleration calculation step S220 of calculating the vibration acceleration Gb by comparing the number of repetitions for a predetermined stress of the pre-fatigue test result with N1 to Nn, which is the number of reciprocating motions of the specimen 100 of the present invention, is performed. In this case, the number of reciprocating motions N compared with the number of repetitions may be one of an average value of N1 to Nn or an average value of intermediate values excluding a maximum value and a minimum value among N1 to Nn values. Thereafter, the S-N data calculation step S230 in which S-N data is generated by calculating the vibration acceleration Gb and stress corresponding to the amplitude information applied by the vibrating unit 300 is performed.

At this time, even if the amplitude level applied by the vibrating unit 300 is adjusted, the neck 110 of the specimen 100 according to the relational expression between vibration acceleration and stress (vibration acceleration (G) = k Ⅷ stress (S), k = constant). The applied stress can be estimated, and the SN data can be supplemented through interpolation or extrapolation between vibration acceleration and stress.

The technical idea should not be construed as being limited to the above-described embodiment of the present invention. Various modifications can be made at the level of those skilled in the art without departing from the gist of the present invention as claimed in the claims. Accordingly, such improvements and modifications fall within the protection scope of the present invention as long as it is apparent to those skilled in the art.

100 Psalms
110 neck
120 strain gauge
200 joint
300 vibrator
400 control
410 receiver
420 transmitter
430 Vibration Acceleration Calculator
440 SN generator

Claims (10)

a specimen array including first to n specimens formed in the form of a plate extending along the height direction and having a neck narrower than the peripheral region at a specific height;
a coupling portion rigidly coupled to the upper ends of the first to n specimens so that the first to n specimens are perpendicular to the ground;
a vibrating unit for applying vibration of a predetermined vibration frequency and a predetermined amplitude to the coupling unit;
Controls the operation of the vibrating unit, detects whether each of the first to n specimens is broken, and N1 to Nn, which is the number of reciprocating motions of each of the first to n specimens, until each of the first to n specimens is broken , a control unit for calculating stress life (SN) data based on the applied vibration frequency and amplitude information;
A fatigue test system for a material, characterized in that n>1.
According to claim 1,
The control unit is
Calculating an applied vibration acceleration (G), which is a vibration acceleration applied to the corresponding specimen array based on the amplitude,
Based on the relational expression between the vibration acceleration and the stress, the applied stress corresponding to the applied vibration acceleration is estimated,
Material characterized in that the stress life (SN) data is calculated based on N1 to Nn, which is the number of reciprocating motions of each of the first to n specimens, and the estimated applied stress until the specimen is broken with respect to the vibration of the amplitude of the fatigue test system.
According to claim 1,
The vibration frequency is a fatigue test system for a material, characterized in that the resonance frequency of at least one of the first to n specimens.
According to claim 1,
The vibration frequency is
Fatigue testing system for a material, characterized in that the first to n specimens vibrated at the vibration frequency are not twisted and have a frequency at which they reciprocate in a vertical direction with respect to the surface of the specimen.
According to claim 1,
The control unit is
Fatigue test system for a material, characterized in that at least one of the vibration frequency and the amplitude is variably controlled.
According to claim 1,
The control unit is
Repeatedly performing a fatigue test while changing at least one of the vibration frequency and amplitude of the applied vibration,
Material characterized in that the stress life (SN) data is calculated based on the accumulated data of N1 to Nn, the number of reciprocating motions at break of each of the first to n specimens of each test, and the applied vibration frequency and amplitude information Fatigue test system.
According to claim 1,
The fatigue test system of the material further comprises a strain gauge coupled to the neck of each of the first to n specimens,
The control unit is
receiving the strain of the neck of each of the vibrating first to n specimens from the strain gauge,
Multiplying the strain of the neck of the 1st to nth specimens and the elastic modulus of the 1st to nth specimens input in advance, respectively, to estimate S1 to Sn, which are stresses acting on the 1st to nth specimens,
The fatigue test system for a material, characterized in that the stress life (SN) data is calculated based on the stresses S1 to Sn and the N1 to Nn.
According to claim 1,
The control unit is
receiving a fatigue test result previously performed on at least one specimen having the same shape and material as at least one of the first to n specimens,
As a result of the input fatigue test, stress life (SN) data is calculated by estimating the stress applied to the first to n specimens based on the amplitudes applied to the N1 to Nn and the specimen array. Fatigue test system.
9. The method of claim 8,
The control unit is
A fatigue test system for a material, characterized in that by comparing the number of repetitions for a predetermined stress of the input fatigue test result with the N1 to Nn, the vibration acceleration and stress corresponding to the amplitude are calculated.
10. The method of claim 9,
The control unit is
Repeatedly performing a fatigue test while changing at least one of the vibration frequency and amplitude of the applied vibration,
Storing N1 to Nn, which is the number of reciprocating motions at break of each of the first to n specimens of each test, applied vibration frequency and amplitude information,
By comparing the number of repetitions for a predetermined stress of the input fatigue test result and N1 to Nn, which is the number of reciprocating motions of the test target specimen array, the vibration acceleration and stress corresponding to the applied amplitude are calculated to obtain the stress life (SN) data. create, but
A fatigue test system for a material, characterized in that it supplements the stress life (SN) data through an interpolation method (interpolation or extrapolation) between the applied amplitude or vibration acceleration and stress based on the input fatigue test result.

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