WO2014204032A1

WO2014204032A1 - Indentation fatigue test module

Info

Publication number: WO2014204032A1
Application number: PCT/KR2013/005560
Authority: WO
Inventors: 권동일; 전승원; 장희광; 지정현
Original assignee: 서울대학교산학협력단
Priority date: 2013-06-17
Filing date: 2013-06-24
Publication date: 2014-12-24
Also published as: KR101455112B1

Abstract

The present invention relates to an indentation fatigue test module mounted on an indentation tester applied to an indentation fatigue evaluation system. According to an embodiment of the present invention, an indentation fatigue test module mounted on an indentation tester applied to an indentation fatigue evaluation system has an actuator which is a piezoelectric-type actuator, the actuator moving an indenter and applying an indentation load, thereby advantageously applying loads repeatedly at a frequency of up to 100Hz and, at the same time, implementing 50mN-grade load resolution and 10nm-grade displacement resolution.

Description

Indentation Fatigue Test Module

The present invention relates to an indentation fatigue test module, and more particularly, to an indentation fatigue test module mounted to an indentation tester applied to an indentation fatigue evaluation system.

In general, the method of evaluating the physical properties of materials using indentation testers is currently receiving considerable attention. The biggest advantage of using the indentation tester is that the preparation of specimens is very simple and local properties can be evaluated. It is possible to test in real time in the field.

In the case of standard test methods for measuring the physical properties of materials, such as the tensile test method, the processing of specimens is more complicated than the indentation test method, it is more difficult to evaluate the physical properties in the local area, and it is impossible to evaluate the properties in real time. Have.

On the other hand, indentation tester is a method of evaluating the material properties by precisely measuring the indentation load and displacement while infiltrating the indenter into the material, and is often used for material property evaluation because it can supplement the limitations of the conventional method of measuring material properties. have.

On the other hand, the physical property evaluation method of the material using the conventional indentation tester has been used to limit the static test as a test evaluation method for infiltrating the indenter at the test rate of about 1mm / min.

Currently, the property evaluation method through the indentation tester is generally used based on the test speed of less than once per second, and there is no system that repeatedly performs the test at the dynamic test speed of more than once per second.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned background, and comprises a piezoelectric actuator having a piezoelectric actuator configured to move an indenter and apply an indentation load in an indentation fatigue test module mounted on an indentation test system applied to an indentation fatigue characteristic evaluation system. The purpose of the present invention is to provide a press-fit fatigue test module that realizes a load resolution of 50mN and a displacement resolution of 100nm while simultaneously applying a load.

The object of the present invention is not limited thereto, and other objects not mentioned will be clearly understood by those skilled in the art from the following description.

According to one embodiment of the invention, the indentation to apply an indentation load to the specimen; A piezoelectric actuator having a sensor unit connected to the lower part and applying a indentation load generated by polarization of the piezoceramic provided therein to the indenter, and measuring a displacement of the piezoceramic to convert into a voltage signal; A load cell connected to the piezoelectric actuator and measuring the indentation load to convert into an electrical signal; And a controller unit configured to receive and process an electrical signal with respect to the indentation load and a voltage signal with respect to the movement displacement, and to control a voltage applied to the piezoceramic.

According to one embodiment of the present invention, the piezoelectric actuator is a piezoelectric actuator by moving the indenter and applying a load in the indentation fatigue test module mounted on the indentation fatigue test system applied to the indentation fatigue characteristics evaluation system, repeatedly at a frequency of up to 100 Hz At the same time, load resolution of 50mN and displacement resolution of 100nm are realized.

1 is a graph showing the frequency characteristics according to the voltage in the piezoelectric actuator of the indentation fatigue test module according to an embodiment of the present invention.

Figure 2 is a perspective view of the indentation fatigue test module according to an embodiment of the present invention.

3 is an exploded perspective view of the indentation fatigue test module of FIG. 2.

Figure 4 is a perspective view of the indentation fatigue test module according to another embodiment of the present invention.

5 is an exploded perspective view of FIG. 4.

6 is a block diagram of the indentation fatigue test module of FIG. 2.

7 is a graph showing the indentation fatigue behavior of the S45C evaluated by the indentation fatigue characteristics evaluation system using the indentation fatigue test module according to an embodiment of the present invention.

Hereinafter, some embodiments of the present invention will be described in detail through exemplary drawings. In adding reference numerals to the components of each drawing, it should be noted that the same reference numerals are assigned to the same components as much as possible even though they are shown in different drawings. In addition, in describing the present invention, when it is determined that the detailed description of the related well-known configuration or function may obscure the gist of the present invention, the detailed description thereof will be omitted.

In addition, in describing the component of this invention, terms, such as 1st, 2nd, A, B, (a), (b), can be used. These terms are only for distinguishing the components from other components, and the nature, order or order of the components are not limited by the terms. If a component is described as being "connected", "coupled" or "connected" to another component, that component may be directly connected to or connected to that other component, but there may be another configuration between each component. It is to be understood that the elements may be "connected", "coupled" or "connected".

1. Background of Selection of Actuator for Applying Indentation Load Repeatedly to Specimen in Indentation Fatigue System

As described above, in the conventional fatigue tester, a linear motor method and a hydraulic pump method are largely used as an actuator capable of applying a fatigue load, but in one embodiment of the present invention, piezoelectric ( piezo electric) was applied.

In order to adopt a method suitable for the indentation fatigue characteristics evaluation system among these three types of actuators, the indentation fatigue load range and the frequency range were set, and the repetitive load and frequency range and the pros and cons of the actuator method were compared.

Table 1 shows the test materials, cyclic loads and frequency ranges of the indentation fatigue study.

Table 1

As shown in Table 1 above, the indentation fatigue load and the frequency band were applied to a cyclic load up to 1000 N according to the elasto-plastic and fracture behavior of the material, and the frequency range was 20 Hz or less. Based on this evidence, an actuator suitable for building an indentation fatigue characteristic evaluation system was selected.

The load, frequency range and advantages and disadvantages of the actuators are listed in Table 2 below.

TABLE 2

As described above, the linear motor type and the hydraulic pump type actuators have a large maximum repeat load range and guarantee a frequency range of about 200 Hz, while the 100N to 2000N range set as the main repeat load range in the indentation fatigue characteristic evaluation system. There was a difficulty in controlling the load.

On the other hand, the piezoelectric actuator applied to an embodiment of the present invention was able to satisfy the cyclic load range of the indentation fatigue characteristic evaluation system and at the same time can realize a load resolution of 50mN class and displacement resolution of 10nm class.

In addition, compared to the linear motor method and the hydraulic pump method, there is less equipment to be constructed, and since it is compatible with the existing continuous indentation equipment in constructing the entire indentation fatigue equipment, it is the most suitable actuator method for the indentation fatigue characteristic evaluation system. Was chosen.

2. Real-time feedback system implementation and controller selection

In constructing the indentation fatigue characteristic evaluation system, it is important to control the indentation load and displacement desired by the actual user by controlling the input value and the output value of the signal in real time.

Therefore, the closed loop control method is adopted so that the indentation load and displacement can be controlled in real time even in the high frequency region of the whole system.

The piezoelectric actuator basically applies a repetitive load in the axial direction in proportion to the input voltage value. The control of the voltage value is responsible for the controller according to the experimental conditions, the typical characteristics are as shown in FIG.

It is important to determine the optimal indentation load range and frequency range to achieve the best dynamic characteristic for indentation fatigue testing. In uniaxial tensile fatigue testing, the main difference between high and low cycle fatigue is the difference in the applied load ranges.

Uniaxial tensile fatigue tester generally applies dynamic load by hydraulic pump type or mechanical linear motor type. To perform high cycle fatigue test, the cyclic load range should be set low. On the other hand, in the low cycle fatigue test, a higher cyclic load can be applied than the high cycle fatigue test. This is because the indentation load range and the signal range that can be processed are determined according to the frequency range for stable fatigue tester operation and accurate test data calculation.

In other words, the frequency range and the load range are inversely related in the dynamic characteristics, and the relationship is the same in the indentation fatigue system using a piezoelectric actuator. The range of signals that can be processed by the controller section of the piezoelectric actuator is determined according to the frequency and the load range. Therefore, in order to secure the optimum dynamic characteristics, it is inevitable to select the controller unit best suited to the set indentation fatigue test conditions.

As shown in FIG. 1, the indentation load is applied in proportion to the input voltage value, which is inversely related to the frequency. The frequency range that can be applied at the maximum input voltage is fixed. When the frequency range is exceeded, the input value of the voltage that can be applied decreases according to the capacity of a capacitor.

That is, the load range that can be applied is reduced. At this time, the capacity of the capacitor depends on the type of piezoelectric actuator.

In conclusion, the optimal combination of actuator and controller was determined based on the indentation fatigue test conditions, and the accurate data was calculated by setting the feedback in real time.

3. Structure of indentation fatigue test module mounted on indentation tester applied to indentation fatigue characteristic evaluation system

Figure 2 is a perspective view of the indentation fatigue test module according to an embodiment of the present invention. 3 is an exploded perspective view of the indentation fatigue test module of FIG. 2. Figure 4 is a perspective view of the indentation fatigue test module according to another embodiment of the present invention. 5 is an exploded perspective view of FIG. 4. 6 is a block diagram of the indentation fatigue test module of FIG. 2.

As shown in these figures, the indentation fatigue test module according to an embodiment of the present invention, the indentation 210 for applying an indentation load to the specimen; The indenter 210 is connected to the lower part, the indentation load generated by the polarization of the piezoceramic 633 provided therein is applied to the indenter 210, and the displacement of the piezoceramic 633 is measured. A piezoelectric actuator 230 having a sensor part 631 converting the voltage signal into a voltage signal; A load cell 250 connected to the piezoelectric actuator 230 and measuring an indentation load to convert into an electrical signal; And a controller unit 270 that receives and processes the electrical signal for the indentation load and the voltage signal for the movement displacement, and controls the voltage applied to the piezoceramic 633.

The indenter 210 applies an indentation load to the specimen. The indenter 210 is, for example, pyramidal, conical, cylindrical, square pillar, spherical, vickers, snoop, etc. ) Can be achieved.

On the other hand, the indenter 210 may be connected to the lower portion of the piezoelectric actuator 230 via the connecting jig 220, for this purpose, the upper end of the indenter 210 is inserted into the lower portion of the connecting jig 220 A coupling groove (not shown) is formed to be coupled, and a protrusion coupling portion 321 is formed at an upper portion of the connecting jig 220, so that the connecting jig 220 is formed at a lower portion of the piezoelectric actuator 230. 235 may be inserted and coupled.

In addition, the coupling jig 220 has a coupling hole 323 to which the fixing member 221 is coupled to fix the upper end of the indenter 210 inserted through the coupling groove (not shown).

That is, the fixing member 221 is coupled to the connecting jig 220 through the coupling hole 323, by pressing the upper end of the indenter 210, the indenter 210 is coupled to the connecting jig 220 and fixed. To be possible.

In this way, by fixing the indenter 210 to the connecting jig 220 with the fixing member 221, when the indenter 210 needs to be replaced, the fixing member 221 is loosened and the indenter 210 is easily replaced. You can do it.

Subsequently, in the piezoelectric actuator 230, the piezoelectric particles 210 are connected to the lower portion, and the indentation load generated by the polarization phenomenon of the piezoceramic 633 provided therein is applied to the piezoelectric particles 210.

That is, the piezoceramic 633 provided in the piezoelectric actuator 230 is formed in a laminated structure, and a polarization phenomenon occurs when a voltage is applied, and the force generated at this time is the indentation load on the indenter 210. Will be delivered.

On the other hand, the piezoelectric actuator 230 is provided with a sensor unit 631 that measures the displacement of the piezoceramic 633 and converts it into a voltage signal, which is measured by the sensor unit 631 and converted into a voltage signal. The movement displacement of 633 corresponds to the indentation depth of the indenter 210 for injecting the specimen, and the voltage signal is transmitted to the controller unit 270 which will be described later.

The sensor part 631 may be provided as, for example, a strain gauge sensor or a capacitive sensor, and the piezoelectric actuator 230 includes a sensor part adapter 231 to provide a controller. The unit 270 and the sensor unit 631 are electrically connected to each other.

Subsequently, the load cell 250 is connected to the piezoelectric actuator 230. The load cell 250 measures the indentation load, converts it into an electrical signal, and transmits it to the controller unit 270.

The load cell 250 may be coupled to the upper portion of the piezoelectric actuator 230 via the coupling jig 240, for this purpose, the upper end of the coupling jig 240 protrudes from the lower portion of the load cell 250. 351 is inserted into the coupling groove 341 is formed, the upper portion of the piezoelectric actuator 230 is inserted into the protrusion coupling portion 343 formed in the lower portion of the coupling jig 240 is inserted into the coupling groove. 331 is formed.

On the other hand, unlike the above, the load cell 250 may be coupled to the lower portion of the piezoelectric actuator 230 via the first connector 410, for this purpose, the first connector 410 is a piezoelectric actuator (top) Protruding support 511 is inserted into and coupled to the coupling portion 235 formed at the lower portion of the 230.

In addition, at least one fastening hole 551 is formed in the load cell 250 in the axial direction, and at least one through hole 411 is formed in the first connector 410 to correspond to the fastening hole 551. The coupling member 450 is inserted into and fastened to the 551 and the through hole 411 to couple the load cell 250 and the first connector 410.

In addition, the second connector 430 connects the load cell 250 and the connecting jig 220, and the second connector 430 may be provided in a cylindrical shape, and the load cell 250 is disposed on the second connector 430. Fastening groove 531 is formed is inserted into the lower end of the projecting end 351 is inserted into the coupling groove, the lower connection connecting groove 321 is formed in the upper part of the connecting jig 220 is inserted into the coupling groove. (Not shown) is formed.

Subsequently, the controller unit 270 receives and processes the electrical signal for the indentation load and the voltage signal for the movement displacement, and controls the voltage applied to the piezoceramic 633. The controller unit 270 includes the sensor unit 631. It may be made by including a monitoring unit 671 for monitoring the voltage signal transmitted from).

That is, the monitoring unit 671 monitors the voltage signal transmitted from the sensor unit 631 (which is a voltage signal corresponding to the movement displacement of the piezoceramic 633) to monitor the movement displacement of the piezoceramic 633. do.

In addition, the controller unit 270 may further include a servo controller unit 673 that processes the voltage signal transmitted from the sensor unit 631 and converts the voltage signal into displacement data.

That is, the servo controller 667 processes a voltage signal transmitted from the sensor unit 631 (this is a voltage signal corresponding to the displacement of the piezoceramic 633), and converts it into movement displacement data of the piezoceramic 633. The displacement data of the piezoceramic 633 becomes data corresponding to the indentation depth of the indenter 210.

In addition, the controller unit 270 may further include a power supply control unit 675 for applying a voltage to the piezoceramic 633.

That is, the power supply control unit 675 controls the voltage applied to the piezoceramic 633 provided in the piezoelectric actuator 230, and the piezoelectric actuator 230 is pressed into the piezoelectric particle 210 by the piezoelectric actuator 230. FIG. To control the load.

On the other hand, the piezoelectric actuator 230 is provided with a piezoceramic adapter 233 to electrically connect the power supply control unit 675 and the piezoceramic 633 of the controller unit 270.

An example of the specification of the indentation fatigue test module having such a configuration is summarized in Table 3 below.

TABLE 3

As shown in Table 3 above, the maximum indentation load range of the indentation fatigue test module according to an embodiment of the present invention is 4500N, the maximum frequency range is 200Hz, the maximum indentation depth is 180μm. The maximum frequency value at a maximum indentation load of 4500N is about 20 Hz and the maximum frequency value at a minimum indentation load of 1N is about 200 Hz.

4. Experimental Verification of Indentation Fatigue Characterization System

In order to experimentally verify the indentation fatigue characteristics evaluation system using the indentation fatigue test module according to an embodiment of the present invention, the indentation fatigue test was performed on S45C, which is a general structural steel material. The test conditions were set to 20N minimum indentation load and 200N maximum indentation load under load control, and the load load was set as sine wave type. The frequency was 1 Hz and the test time was set to 1 hour and a total of 5 experiments were repeated.

What we wanted to verify experimentally was the accuracy and reproducibility of the data. In order to verify the accuracy of the data, the scattering degree of the data in the indentation load and displacement was examined.

The scattering range of the maximum indentation load and the minimum indentation load was less than about 1 N when the cyclic load was applied, and the scattering ranges of the maximum displacement and the minimum displacement were within 0.5μm and accurately measured within the error range of 1%.

In order to verify the reproducibility of the data, the superposition of the displacement versus cycle curve derived from five indentation fatigue tests was examined. In the displacement versus cycle curve, the error range was found to overlap within 5%.

As shown in FIG. 7, the increase patterns of the maximum indentation depth and the minimum indentation depth were similar, and as the number of cycles increased, the increase rate of the indentation depth decreased.

According to one embodiment of the present invention as described above, in the indentation fatigue test module mounted on the indentation fatigue test system applied to the indentation fatigue characteristics evaluation system by moving the indenter and applying the indentation load to the piezoelectric actuator, The load is repeatedly applied at a frequency of 100 Hz, and at the same time, the load resolution of 50 mN and the displacement resolution of 100 nm are realized.

In the above description, all elements constituting the embodiments of the present invention are described as being combined or operating in combination, but the present invention is not necessarily limited to the embodiments. In other words, within the scope of the present invention, all of the components may be selectively operated in combination with one or more.

In addition, the terms "comprise", "comprise" or "having" described above mean that the corresponding component may be included, unless otherwise stated, and thus excludes other components. It should be construed that it may further include other components instead. All terms, including technical and scientific terms, have the same meanings as commonly understood by one of ordinary skill in the art unless otherwise defined. Terms commonly used, such as terms defined in a dictionary, should be interpreted to coincide with the contextual meaning of the related art, and shall not be construed in an ideal or excessively formal sense unless explicitly defined in the present invention.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may make various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited by these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

[Description of the code]

210: indenter

230: piezoelectric actuator

250: load cell

270 controller

631: sensor unit

633: Piezoceramic

CROSS-REFERENCE TO RELATED APPLICATIONCROSS-REFERENCE TO RELATED APPLICATION

This patent application claims priority under No. 119 (a) (35 USC § 119 (a)) of the Patent Application No. 10-2013-0068994 filed to Korea on June 17, 2013. All content is incorporated by reference in this patent application. In addition, if this patent application claims priority for the same reason for countries other than the United States, all its contents are incorporated into this patent application by reference.

Claims

Indenter for applying an indentation load to the specimen;

The piezoelectric element is connected to the lower part, the piezoelectric piezoelectric sensor is provided with a sensor unit for applying the indentation load generated by the polarization phenomenon of the piezoceramic provided therein to the piezoelectric, measuring the displacement of the piezoceramic to convert into a voltage signal Anticorrosive actuators;

A load cell connected to the piezoelectric actuator and measuring the indentation load to convert into an electrical signal; And

A controller unit for receiving and processing the electrical signal for the indentation load and the voltage signal for the displacement, and controlling a voltage applied to the piezoceramic;

Indentation fatigue test module comprising a.
The method of claim 1,

The indentation fatigue test module, characterized in that the piezoelectric is connected to the lower portion of the piezoelectric actuator via a connecting jig.
The method of claim 2,

The connecting jig has a protruding fastening portion inserted into a coupling portion formed at a lower portion of the piezoelectric actuator, and a coupling groove having an upper end portion of the piezoelectric particle inserted therein is formed therein. Test module.
The method of claim 3, wherein

The load cell, the indentation fatigue test module, characterized in that coupled to the upper portion of the piezoelectric actuator via a coupling jig.
The method of claim 4, wherein

The coupling jig, the coupling groove is formed to be coupled to the protrusion is inserted into the protrusion formed in the lower portion of the load cell in the upper portion, and the protrusion coupling portion is inserted into the insertion groove formed in the upper portion of the piezoelectric actuator in the lower portion is formed. Indentation fatigue test module, characterized in that.
The method of claim 2,

The load cell, the indentation fatigue test module, characterized in that coupled to the lower portion of the piezoelectric actuator via a first connector.
The method of claim 6,

The first connector, the indentation fatigue test module, characterized in that the projecting support is inserted into the coupling portion formed in the lower portion of the piezoelectric actuator is formed in the upper portion.
The method of claim 7, wherein

At least one fastening hole is formed in the load cell in the axial direction,

Indentation fatigue test module, characterized in that the first connector is formed with one or more through-holes to which the coupling member penetrating the fastening hole is inserted.
The method of claim 6,

Further comprising a second connector for connecting the load cell and the connection jig,

The upper part of the second connector is formed with a fastening groove for inserting and engaging the protruding end portion formed in the lower portion of the load cell, the lower end is formed with a connecting groove for inserting and engaging the protruding fastening portion formed in the upper portion of the connecting jig. Indentation fatigue test module, characterized in that.
The method of claim 1,

The controller unit,

Indentation fatigue test module further comprises a monitoring unit for monitoring the voltage signal transmitted from the sensor unit.
The method of claim 10,

The controller unit,

And a servo controller unit for processing the voltage signal transmitted from the sensor unit and converting the voltage signal into displacement data.
The method of claim 11,

The controller unit,

Indentation fatigue test module further comprises a power supply control unit for applying a voltage to the piezoceramic.