KR100915789B1 - Stress-strain measuring control method using bellows structure - Google Patents

Abstract

Disclosed is a load-strain measurement control method using a bellows structure. According to the present invention, in the load-strain measurement control method using a bellows structure for controlling a deformation according to a load by adding a uniform load to a test piece for a set time, a first step of inputting a set time and a target load (S110) ); Opening the inlet gas solenoid valve which allows the gas to flow into the bellows structure elastically stretched so that the load applied to the test piece T reaches the target load and the thrust is generated by the gas pressure; Closing the inlet gas solenoid valve and comparing a minute difference between a target load and an actual load measured from the load cell; If the actual load does not reach the target load, opening the inlet gas control valve in proportion to the error amount; Opening the outflow gas control valve in proportion to the amount of error if the actual load exceeds the target load; Maintaining a constant load by repeating in real time when the set time has not elapsed; And recovering the added load by opening the effluent gas solenoid valve which allows the gas to flow out of the bellows structure 100 when the set time has elapsed.

The present invention provides a control method of a load-strain measuring device using a metal bellows pipe 110 without employing a hydraulic pump and a hydraulic cylinder, and precisely controls the gas pressure inside the bellows pipe to impose various modes of load on the test piece. There is a measurable effect.

Description

Stress-strain measuring control method using bellows structure

The present invention relates to a load-strain measurement control method using a bellows structure, and in particular, employs a metal bellows tube that elastically expands and contracts by gas pressure without using an electrically operated hydraulic pump and a hydraulic cylinder. The present invention relates to a measurement control method capable of imposing and measuring various modes of load on a test piece by precisely controlling the gas pressure inside the bellows pipe.

Conventional load-strain gauges are equipped with an electric motor or a hydraulic pump and a hydraulic cylinder to apply a load to a test piece, and are designed to obtain a large load by the pressure of the fluid acting on the piston of the hydraulic cylinder. However, the conventional measuring device configured as described above must be equipped with an electric motor, a hydraulic pump, a cylinder, a piston, and a hydraulic transmission structure to generate power, so that the complexity and enlargement of the device are inevitable.

In order to evaluate the integrity of materials used in nuclear reactors, it is essential to inspect the nuclear reactor structural materials (in-service system) and simulated irradiation tests in the irradiation test hole of the research reactor during operation of the reactor. In-service inspection and investigation of research reactors The testing of material properties in test holes is usually carried out in long, narrow spaces and in harsh environments where neutrons are irradiated. There must be features that can be controlled. In addition, the load application system using the conventional liquid fluid has a high risk of liquid fluid leakage at the core of the reactor and there is a problem of sealing leakage between the piston and the inner wall of the cylinder. In order to safely perform material testing in a nuclear reactor environment, a device is required to ensure the high temperature sealability of the load-bearing fluid on the specimen.

In addition, there is a need for an apparatus capable of applying a load of various modes to a specimen and measuring the same, and a method for controlling the measurement to accurately measure the same.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and does not use electrically driven electric motors, hydraulic pumps and hydraulic cylinders and liquid fluids, and can maintain elasticity at high temperatures and elastically expandable metal bellows. It is an object of the present invention to provide a load-strain measurement control method using a bellows structure in which various and precise loads are applied to a material under test by using a tube to measure strain accordingly.

In the present invention for achieving the above object, in the load-strain measurement control method using a bellows structure to control the deformation according to the load by adding a uniform load to the test piece during the set time, the set time and the target load A first step of inputting (S110); The inlet gas solenoid valve 331 which elastically expands and contracts so that the load applied to the test piece T reaches the target load and induces gas into the bellows structure 100 in which thrust is generated by the gas pressure is opened. Second step (S120); Closing the inlet gas solenoid valve 331 and comparing a minute difference between a target load and an actual load measured from the load cell 410 (S130); A fourth step (S140) of opening the inflow gas control valve 321 for adjusting the amount of gas introduced into the bellows structure 100 in proportion to an error amount when the actual load does not reach the target load in the third step; A fifth step (S150) of opening the outflow gas control valve (322) for controlling the amount of gas flowing out of the bellows structure (100) in proportion to the amount of error when the actual load exceeds the target load in the third step; A sixth step (S160) of maintaining a constant load by repeating the third to fifth steps in real time when a set time has not elapsed; And a seventh step S170 of recovering the added load by opening the outflow gas solenoid valve 332 to allow gas to flow out from the bellows structure 100 when the set time has elapsed.

In addition, the eighth step (S180) for recovering the added load by opening the outflow gas solenoid valve 332 when the test piece (T) is broken.

In the load-strain measurement control method using a bellows structure that adds a load that increases according to a pattern set for a set time to measure the deformation according to the load, inputting the set time and the slope of the first function (increase pattern) First step (S210) to; A second step (S220) of comparing a minute difference between the target load over time and the actual load measured from the load cell 410; In the second step, when the actual load does not reach the target load, the inlet gas control valve 321 elastically stretches and adjusts the amount of gas flowing into the bellows structure 100 in which thrust is generated by the gas pressure. A third step (S230) of opening in proportion to the error amount; A fourth step (S240) of opening the outflow gas control valve (322) for adjusting the amount of gas flowing out of the bellows structure (100) in proportion to the amount of error when the actual load exceeds the target load in the second step; A fifth step (S250) of applying a load which is continuously increased by repeating the second to fourth steps in real time when the set time has not elapsed; And a sixth step (S260) of recovering the added load by opening the outflow gas solenoid valve allowing the gas to flow out of the bellows structure 100 when the set time has elapsed.

In addition, when the test piece (T) is broken, the seventh step (S270) of recovering the added load by opening the outflow gas solenoid valve 332, characterized in that it further comprises.

In the load-strain measurement control method using a bellows structure which repeatedly increases or decreases a load according to a set pattern during a set time and measures deformation according to the load, the set time, maximum load, minimum load, A first step (S310) of inputting a repetition period; A second step S320 of determining a repetition period s; A third step of comparing the difference between the target load over time and the actual load measured from the load cell 410 when it is determined that the repetition period s is smaller than 60 seconds (s) in the second step (= period is fast). Step S330; A fourth step (S340) of opening the inflow gas solenoid valve (331) in proportion to an error amount to allow gas to flow into the bellows structure (100) when the actual load does not reach the target load in the third step; A fifth step (S350) of opening the outflow gas solenoid valve (332) in proportion to an error amount so that the gas flows out of the bellows structure (100) when the actual load exceeds the target load in the third step; A sixth step (S360) of repeatedly applying a load which increases and decreases in real time by repeating the third to fifth steps when the set time has not elapsed; A seventh step of comparing the difference between the target load over time and the actual load measured from the load cell 410 when it is determined that the repetition period s is greater than 60 seconds (s) in the second step. Step S370; An eighth step S380 of opening the inflow gas control valve 321 for controlling the amount of gas introduced from the bellows structure 100 in proportion to an error amount when the actual load does not reach the target load in the seventh step; A ninth step (S390) of opening the outflow gas control valve (322) for adjusting the amount of gas flowing out of the bellows structure (100) in proportion to the error amount when the actual load exceeds the target load in the seventh step; And a tenth step (S400) of repeatedly applying a load which increases and decreases in real time by repeating the seventh to ninth steps when the set time has not elapsed.

In addition, when the test piece (T) is broken, the eleventh step (S410) of recovering the added load by opening the outflow gas solenoid valve 332; characterized in that it further comprises.

Due to the present invention as described above, by adopting a flexible metal bellows pipe, instead of an electric motor, a hydraulic pump and a hydraulic cylinder, and a gas pressure control means for precisely adjusting the internal pressure of the bellows pipe, a load applying means for mechanical testing of materials To control the gas pressure inside the bellows pipe using a load-strain gauge that allows the material test to be carried out in a narrow and narrow space, such as a research reactor for research reactors. There is an effect that can be precisely controlled to measure the deformation of the specimen according to.

1 is a view schematically showing a load-strain measurement control method using a bellows structure according to an embodiment of the present invention,

2 is an enlarged view of the bellows pipe 110 of FIG. 1;

3 is a view showing the flow of the gas pressure control means 300 for controlling the bellows pipe 110 of FIG.

4A is a diagram showing a load mode of a test in which a uniform load is applied to a test piece;

4b is a diagram showing a load mode of a test in which a constantly increasing load is added to a test piece;

4c shows the load mode of the test of repeatedly adding increasing and decreasing loads to the test piece;

5 is a flowchart illustrating a method of controlling a load-strain measurement control method using a bellows structure when the load of FIG. 4A is added;

FIG. 6 is a flowchart illustrating a method of controlling a load-strain measurement control method using a bellows structure when the load of FIG. 4B is added, and

7 is a flowchart illustrating a method of controlling a load-strain measurement control method using a bellows structure when the load of FIG. 4C is added.

<Description of Symbols for Main Parts of the Present Invention>

100; Bellows structure 110; Bellows tube

120; Connection flange 121; volt

130; Sealing plate 200; Load-bearing means

210; Moving frame 211; Upper plate

212; Load transfer shaft 213; Lower transfer plate

220; Fixed frame 221; Upper fixing plate

222; Intermediate fixation plate 223; Bottom fixing plate

224; Consolidation 225; bushing

230; Coupling 231; Upper fixed shaft

232; Lower fixed shaft 240; stopper

300; Gas pressure control means 310; Gas buffer

311; Pressure transducer 320; Micro Gas Controller

321; Inlet gas control valve 322; Outflow Gas Control Valve

330; Solenoid controller 331; Inlet Gas Solenoid Valve

332; Outflow gas solenoid valve 333; Solenoid Switch Controller

340; Selector 350; Manual Valve

360; Helium gas cylinder 370; A / D converter

400; Measuring means 410; Load cell

420; Micrometa 430; Displacement Transducer (LVDT)

431; Measuring core T; Test piece

The above objects and other features of the present invention will become more apparent by describing the preferred embodiments of the present invention in detail with reference to the accompanying drawings. For reference, in the following description of the present invention, if it is determined that a detailed description of related known functions or configurations may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

1 is a view schematically showing a load-strain measuring device according to an embodiment of the present invention, Figure 2 is an enlarged view showing the bellows pipe 110 of Figure 1, Figure 3 1 is a view showing the flow of the gas pressure control means 300 for controlling the bellows pipe 110 of Figure 1, Figure 4a is a view showing the load mode of the test to apply a uniform load, 4b is a constant increasing load Figure 4c is a view showing the load mode of the test to add the, Figure 4c is a view showing the load mode of the test to add increasing and decreasing load repeatedly, Figure 5 controls the load-strain measurement when adding the load of Figure 4a 6 is a flowchart illustrating a method of controlling a load-strain measurement when the load of FIG. 4B is added, and FIG. 7 is a method of controlling a load-strain measurement when the load of FIG. 4C is added. Indicate It is a flow chart.

Referring to Figures 1 to 3, the present invention is elastically stretched while the bellows structure 100 is generated thrust (推力), the load for transmitting the thrust generated by the bellows structure 100 to the test piece (T) Imposing means 200 Measuring means 400 for continuously measuring the load and deformation imposed on the gas pressure control means 300 and the test piece (T) to adjust the pressure of the gas flowing into the bellows structure 100, outflow It includes.

The bellows structure 100, the bellows pipe 110 is elastically stretched and the thrust generated by the gas pressure (110); Connecting flanges 120 which extend to upper and lower ends of the bellows pipe 110 and are connected to the load-bearing means 200 through fastening means; And a sealing plate interposed between the connection flange 120 and the load applying means 200 to seal the bellows pipe 110 and transmitting a thrust generated by gas pressure to the load applying means 200. 130; characterized in that it comprises a. Wherein the fastening means is shown as a bolt (121). In addition, since the material of the bellows pipe 110 is made of stainless steel, it has a high durability.

The load applying means 200, the upper fixing plate 221 is fixed to the upper end of the bellows structure 100, the lower fixing plate 223 is provided to be spaced apart below the upper fixing plate 221 and the upper movement An intermediate fixing plate 222 fixed between the plate 211 and the lower movable plate 213 and a connecting shaft 224 connecting the upper fixing plate 221 and the intermediate fixing plate 222 and the lower fixing plate 223. The fixed frame 220 is configured.

In addition, the load-carrying means 200 is fixed to the lower end of the bellows structure 100 and the upper movable plate 211 is lowered in accordance with the thrust generated in the bellows structure 100 and the intermediate fixing plate 222 A lower portion of the movable plate 213 spaced apart from the upper movable plate 211 and interlocked with the upper movable plate 211, and a load transfer shaft 212 connecting the upper movable plate 211 and the lower movable plate 213; The upper fixing shaft 231 is fixed to the middle fixing plate 222 and installed below the middle fixing plate 222, and is fixed to the lower moving plate 213 and installed to the upper portion of the lower moving plate 213. It is installed at the end of the lower movable shaft 232 and the upper fixed shaft 231 and the lower movable shaft 232 to support both ends of the test piece (T) and includes a coupling 230 that can be attached and detached of the test piece (T) The moving frame 210 is configured.

In addition, the upper portion of the lower fixing plate 223 is provided with a stopper 240 to mitigate the impact of the moving frame 210 when the test piece (T) is broken, the intermediate fixing plate 222 is the load transfer shaft 212 Is coupled to the bushing 225 for guiding the load transfer shaft 212.

The gas pressure control means 300 may include: a gas buffer 310 supplying or recovering gas to the bellows structure 100 to prevent the internal gas pressure of the bellows structure 100 from being rapidly changed; A pressure transducer 311 measuring the pressure of the gas buffer 310 and converting the pressure into an electrical signal; The amount of gas flowing into or out of the inlet gas control valve 321 and the outflow gas control valve 322 and the gas buffer 310 to precisely control the amount of the gas flowing into or out of the gas buffer 310. An inlet gas solenoid valve 331 and an outlet gas solenoid valve 332 which are rapidly adjusted; A micro gas controller 320 for controlling the inflow gas control valve 321 and the outflow gas control valve 322; A solenoid controller 330 for controlling the inflow gas solenoid valve 331 and the outflow gas solenoid valve 332 and a solenoid opening and closing controller 333 for controlling the opening / closing time thereof; And a selector 340 that selects a controller to perform control by receiving an electrical signal from the pressure transducer 311 or the measuring means 400. Reference numeral 350, which is not described, denotes a manual valve 350 provided with a plurality of required positions and configured to manually operate the flow rate, where 360 is a helium gas cylinder 360 in which gas is first stored and supplied, and 370 is a load cell 410. Or A / D converter 370 converts the value measured by the displacement transducer 430 to a voltage signal and sends it to the display device of the computer.

The measuring means 400 is installed on the upper fixed shaft 231 to measure the load applied to the test piece (T) and converts it into an electrical signal to the A / D converter 370 of the gas pressure control means 300 A load cell 410 which is transmitted to the display device of the personal computer or transmitted to each controller for controlling the load; A micrometer 420 disposed at a lower end of the intermediate fixing plate 222 to measure an absolute amount of a moving distance of the moving frame 210; And measuring a change amount of the test piece T through the measuring core 431 fixedly installed on the intermediate fixing plate 222 and the lower movable plate 213 to be deformed in the same manner as the test piece T, and converting the converted amount into an electrical signal. Displacement transducer 430 (LVDT); characterized in that it comprises a.

Due to the structure as described above, the internal pressure due to the gas is applied to the bellows pipe 110, the thrust is generated, the upper transfer plate 211 is moved downward by the generated thrust, and thus the load transfer shaft 212 bushing The lower movable plate 213 is pushed through 225. The force acting on the lower movable plate 213 is transmitted to the test piece T by the coupling 230 to act as a tensile force. Here, the thrust generated in the bellows pipe 110 is calculated by the formula (bellows cross-sectional area) x (bellows internal pressure)-(bellows spring constant) x (bellows deformation amount).

Hereinafter, the control method of the present invention will be described in detail with reference to FIGS. 4 to 7. The load acting on the test piece T can be imposed in three modes as shown in Fig. 4, respectively. First, when a static load is applied to the specimen (T) for a certain time, second, when the load is gradually increased, third, the magnitude of the load can be imposed a fatigue load repeating the increase and repetition.

In the load-strain measurement control method using a bellows structure in which a uniform load is added to the test piece for setting time to control the deformation according to the load, in the first step S110, the setting time and the target load are input to the computer. . In the second step (S120), the helium gas cylinder 360 is opened and the inflow gas solenoid valve 331 is opened so that the load applied to the test piece T reaches the target load, thereby allowing the gas to flow into the gas buffer 310 and the bellows pipe 110. To be injected into. At this time, since the pressure inside the bellows pipe 110 and the pressure of the gas buffer 310 reach an equilibrium pressure at about the same time, the pressure inside the bellows pipe 110 is controlled by controlling the pressure of the gas buffer 310 and finally, the test piece ( The load on T) is adjusted. In the third step S130, the inlet gas solenoid valve 331 is closed at the moment when the load applied to the test piece T reaches the target load. At this time, due to the instantaneous difference between the control signal input time and the operating time of the inlet gas solenoid valve 331, the actual load on the test piece (T) is slightly different from the target load. Therefore, in this step, a minute difference between the target load and the actual load measured from the load cell 410 is compared. In the fourth step S140, when the actual load does not reach the target load in the third step, the inlet gas control valve 321 for adjusting the amount of gas introduced into the bellows pipe 110 is opened in proportion to the error amount. The amount of gas introduced into the gas buffer 310 is adjusted, so that the internal pressure of the bellows pipe 110 has a pressure corresponding to the target load. If the actual load exceeds the target load in the third step, the fifth step (S150) of opening the outflow gas control valve 322 for adjusting the amount of gas flowing out from the bellows pipe 110 in proportion to the error amount Is done. The inflow gas control valve 321 and the outflow gas control valve 322 are controlled using the micro gas controller 320. In the sixth step S160, when the set time has not elapsed, the third to fifth steps are repeated in real time to maintain a constant load. When the set time has elapsed, a seventh step S170 of recovering the added load by opening the outflow gas solenoid valve 332 to allow gas to flow out from the bellows pipe 110 is performed and the second to sixth steps are performed. When the test piece T breaks during the execution, the eighth step S180 of recovering the added load by opening the outflow gas solenoid valve 332 is performed.

The ability to continuously adjust micro loads to a constant value is extremely important when testing materials in neutron irradiation environments such as research reactors. In the neutron irradiation environment, the internal gas temperature of the bellows tube 110 continuously changes due to the increase and decrease of the reactor output. Therefore, in order to maintain a constant load on the test piece T, it is necessary to precisely control the minute change of the load continuously. .

In the load-strain measurement control method using a bellows structure for controlling the deformation according to the load by adding a load that increases according to the pattern set during the set time, the first step (S210) is the set time and the micro gas controller In operation 320, a slope (increase pattern) of the linear function is input. In the second step (S220) of comparing the minute difference between the target load continuously changing to the primary function value with time and the actual load measured from the load cell 410, when the actual load does not reach the target load in the second step The third step (S230) of opening the inlet gas control valve 321 in proportion to the error amount, if the actual load exceeds the target load in the second step, opening the outflow gas control valve 322 in proportion to the error amount The fourth step (S240) is performed sequentially so that the load added to the test piece (T) is gradually increased. Next, when the set time has not elapsed, a fifth step (S250) of applying a continuously increasing load by repeating the second to fourth steps in real time, and the outflow gas solenoid valve 332 when the set time has elapsed. When the test piece (T) is broken during the sixth step (S260) and the second to fifth steps to recover the added load by opening the outlet gas solenoid valve 332 to recover the added load A seventh step S270 is performed. Due to this control, the load applied to the test piece T increases linearly.

In the load-strain measurement control method using a bellows structure for controlling the deformation according to the load by repeatedly adding a decreasing load to the test piece repeatedly according to the set pattern during the set time, the first step (S310) Enter the maximum load, minimum load, and repetition cycle. Next, in the second step (S320) of determining the repetition period (s), if the repetition period (s) in the second step is determined to be less than 60 seconds (s) (= period is faster) the target load over time And comparing the difference between the actual load measured from the load cell 410 and the third step (S330), when the actual load does not reach the target load in the third step, the inlet gas solenoid valve 331 is opened in proportion to the error amount. In the fourth step (S340), the fifth step (S350) for opening the outflow gas solenoid valve 332 in proportion to the error amount when the actual load exceeds the target load in the third step, the set time has not elapsed In this case, a sixth step S360 of repeatedly applying the increasing and decreasing loads is sequentially performed by repeating the third to fifth steps in real time.

If it is determined in the second step that the repetition period (s) is greater than 60 seconds (s) (= period is late), the difference between the target load over time and the actual load measured from the load cell 410 is compared. In the seventh step (S370), when the actual load does not reach the target load in the seventh step, the eighth step (S380) to open the inflow gas control valve 321 in proportion to the error amount, the actual load in the seventh step When the target load is exceeded, the ninth step S390 of opening the outflow gas control valve 322 in proportion to the error amount is increased, and if the set time has not elapsed, the seventh to ninth steps are repeatedly increased in real time. When the test piece T is broken during the tenth step S400 and the third to tenth steps of repeatedly applying a decreasing load, the outlet gas solenoid valve 332 is opened to recover the added load. The eleventh step S410 is performed in sequence.

Through the control method as described above, when the thrust due to the internal pressure of the bellows pipe 110 is transmitted and the tensile force is applied to the test piece (T), the material is stretched according to its inherent characteristics. When the material is stretched, the length of the measurement core of the displacement transducer 430 that holds the micrometer 420 attached to the lower surface of the intermediate fixing plate 222 is changed. Since the amount of extension of the test piece T is equal to the change in the position of the measuring core, the change in the position of the measuring core is measured by the displacement transducer 430, and the load applied to the test piece T is placed on the lower surface of the intermediate fixing plate 222. It is measured by the load cell 410 attached. The amount of stretching measured by the displacement transducer 430 and the load measured by the load cell 410 are converted into voltage signals and sent to the display device of the computer through the A / D converter 370.

The present invention has been described in an exemplary manner. The terminology used herein is for the purpose of description and should not be regarded as limiting. Many modifications and variations of the present invention are possible in light of the above teachings. Accordingly, the invention may be freely practiced within the scope of the claims unless otherwise stated.

Claims (6)

delete In the load-strain measurement control method using a bellows structure for controlling the deformation according to the load by adding a uniform load to the test piece for a set time, A first step (S110) of inputting a set time and a target load; The inlet gas solenoid valve 331 which elastically expands and contracts so that the load applied to the test piece T reaches the target load and induces gas into the bellows structure 100 in which thrust is generated by the gas pressure is opened. Second step (S120); Closing the inlet gas solenoid valve 331 and comparing a minute difference between a target load and an actual load measured from the load cell 410 (S130); A fourth step (S140) of opening the inflow gas control valve 321 for adjusting the amount of gas introduced into the bellows structure 100 in proportion to an error amount when the actual load does not reach the target load in the third step; A fifth step (S150) of opening the outflow gas control valve (322) for controlling the amount of gas flowing out of the bellows structure (100) in proportion to the amount of error when the actual load exceeds the target load in the third step; A sixth step (S160) of maintaining a constant load by repeating the third to fifth steps in real time when a set time has not elapsed; And A seventh step (S170) of recovering the added load by opening the outflow gas solenoid valve 332 for allowing the gas to flow out of the bellows structure 100 when the set time has elapsed; And A bellows structure comprising: an eighth step (S180) of recovering the added load by opening the outflow gas solenoid valve 332 when the test piece T breaks during the second to sixth steps. Load-strain measurement control method using In the load-strain measurement control method using a bellows structure for controlling the deformation according to the load by adding a load that increases according to the pattern set during the set time, A first step (S210) of inputting a set time and a slope (increase pattern) of the first-order function; A second step (S220) of comparing a minute difference between the target load over time and the actual load measured from the load cell 410; In the second step, when the actual load does not reach the target load, the inlet gas control valve 321 elastically stretches and adjusts the amount of gas flowing into the bellows structure 100 in which thrust is generated by the gas pressure. A third step (S230) of opening in proportion to the error amount;  A fourth step (S240) of opening the outflow gas control valve (322) for adjusting the amount of gas flowing out of the bellows structure (100) in proportion to the amount of error when the actual load exceeds the target load in the second step; A fifth step (S250) of applying a load which is continuously increased by repeating the second to fourth steps in real time when the set time has not elapsed; And When the set time has elapsed, the sixth step (S260) for recovering the added load by opening the outflow gas solenoid valve to allow the gas to flow out from the bellows structure 100; Load-strain measurement control method. The method of claim 3, wherein And a seventh step S270 of recovering the added load by opening the effluent gas solenoid valve 332 when the test piece T is broken during the second to fifth steps. Load-strain measurement control method using structure. In the load-strain measurement control method using the bellows structure to control to measure the deformation according to the load by repeatedly adding to the test piece increases and decreases according to the set pattern during the set time, A first step (S310) of inputting a set time, a maximum load, a minimum load, and a repetition period; A second step S320 of determining a repetition period s; A third step of comparing the difference between the target load over time and the actual load measured from the load cell 410 when it is determined that the repetition period s is smaller than 60 seconds (s) in the second step (= period is fast). Step S330; A fourth step (S340) of opening the inflow gas solenoid valve (331) in proportion to an error amount to allow gas to flow into the bellows structure (100) when the actual load does not reach the target load in the third step;  A fifth step (S350) of opening the outflow gas solenoid valve (332) in proportion to an error amount so that the gas flows out of the bellows structure (100) when the actual load exceeds the target load in the third step; A sixth step (S360) of repeatedly applying a load which increases and decreases in real time by repeating the third to fifth steps when the set time has not elapsed; A seventh step of comparing the difference between the target load over time and the actual load measured from the load cell 410 when it is determined that the repetition period s is greater than 60 seconds (s) in the second step. Step S370; An eighth step S380 of opening the inflow gas control valve 321 for controlling the amount of gas introduced from the bellows structure 100 in proportion to an error amount when the actual load does not reach the target load in the seventh step;  A ninth step (S390) of opening the outflow gas control valve (322) for adjusting the amount of gas flowing out of the bellows structure (100) in proportion to the error amount when the actual load exceeds the target load in the seventh step; And If the set time has not elapsed, the tenth step (S400) to repeatedly give a load that increases and decreases in real time repeating the seventh to the ninth step (S400); Strain measurement control method. The method of claim 5, wherein If the test piece (T) is broken during the third step to the tenth step, the eleventh step (S410) of recovering the added load by opening the outflow gas solenoid valve 332; bellows further comprising a Load-strain measurement control method using structure.