JP7536593B2 - Stress measurement method and stress measurement device - Google Patents

Description

The present invention relates to a stress measurement method and a stress measurement device for measuring the existing stress of a structure.

The existing stress of concrete and steel structures is measured for various purposes, such as considering earthquake reinforcement, examining safety after an earthquake, or as an indicator for deciding the order of renewal. In addition, the tension of PC structures that deteriorates with age is confirmed by measuring the stress of the concrete.

Conventionally, known methods for measuring the stress of structures include the stress relief method and the magnetostriction method using a magnetostrictive sensor. In the stress relief method, a strain gauge is installed in a concrete structure and a core is removed, the change in strain before and after the core is removed is measured, and the existing stress is estimated based on this change. In the magnetostriction method, the axial force of steel materials such as reinforcing bars and PC steel bars is measured using a magnetostrictive sensor (EM sensor) by utilizing the property of magnetostriction that generates strain when magnetized. Note that when measuring the stress of reinforcing bars in reinforced concrete structures using the magnetostriction method, large-scale chipping work is required. For this reason, the magnetostriction method is effective when steel materials are exposed by anchors, etc.

For example, in the method for measuring existing stress described in Patent Document 1, a certain area of a concrete structure at a position to be subjected to stress measurement is taken as a core, the change in strain in the core before and after taking is detected, and the stress is evaluated based on the change in strain.

The system for measuring the existing stress of rebars in reinforced concrete structures described in Patent Document 2 has a stress measurement sensor that includes a hollow member into which the rebar to be measured is inserted, a secondary coil wound around the inside of the hollow member, a primary coil wound around the outside of the hollow member, and a thermometer that measures the temperature of the rebar. This system has a conversion equation calculation means that inserts a calibration rebar into the stress measurement sensor and applies a pulse current to the primary coil to obtain a conversion equation using the induced current value obtained through the secondary coil and the temperature detected by the thermometer, a detection means that uses a stress measurement sensor installed in the rebar to be measured to detect the induced current value through the secondary coil by the pulse current of the primary coil and detects the temperature with a thermometer, and a stress calculation means that calculates the induced current value and temperature using the conversion equation to obtain the existing stress of the rebar.

The tension management system described in Patent Document 3 is composed of a low thermal conductivity temperature measuring sheet installed on the inner surface of the sheath at a predetermined location of the PC steel, a thermocouple attached to the temperature measuring sheet to detect changes in the temperature difference between the outer and inner surfaces of the temperature measuring sheet that occur during the tensioning process in which tension is applied to the PC steel, and a temperature data logger that displays the change in temperature difference between the outer and inner surfaces of the temperature measuring sheet during the tensioning process detected by the thermocouple, and calculates the actual tension of the PC steel at the predetermined location from the change in temperature difference between the outer and inner surfaces of the temperature measuring sheet detected by the thermocouple based on the relationship between the change in temperature difference between the outer and inner surfaces of the temperature measuring sheet and the assumed tension of the PC steel.

JP 2001-289717 A JP 2003-270059 A JP 2017-179861 A

However, with conventional stress measurement methods, structures must be destroyed to remove the cores or to install stress measurement sensors such as magnetostrictive sensors, which may reduce the durability of the structure. With the magnetostrictive method, there is no need to destroy the structure if the steel material is exposed beforehand, but structures in which stress can be measured are limited to those with exposed steel material. In addition, the magnetostrictive method requires dedicated measuring equipment, which creates the problem of high costs.

Furthermore, in conventional stress measurement methods such as those described in Patent Document 3, it is necessary to attach measuring devices such as a temperature sheet, a thermocouple, and a temperature data logger to the inside of the structure beforehand. This means that there is a risk that the durability of the structure will decrease due to the attachment of the measuring devices, and the structures that can measure stress are limited to those that have measuring devices inside.

Furthermore, with conventional stress measurement methods, it was sometimes difficult to measure the stress of a structure without specialized knowledge, making the measurement process difficult.

To solve the above problems, the present invention provides a stress measurement method and a stress measurement device that can easily measure the stress of various structures without requiring specialized knowledge and without destroying the structures.

The stress measurement method of the present invention involves heating a structure to be measured at a predetermined heating position, estimating the amount of change in the state of the structure due to heating, and measuring the current stress of the structure based on the amount of change in the state of the structure.

The stress measuring device of the present invention also includes a heating unit that heats the structure to be measured at a predetermined heating position, and a stress measuring unit that estimates the amount of change in the state of the structure caused by the heating and measures the current stress of the structure based on the amount of change in the state of the structure.

In the above-mentioned stress measurement method or stress measurement device, the temperature of the structure is detected at two or more detection positions spaced apart from the heating position in the stress direction applied to the structure, and the current stress of the structure is measured based on the temperature detection result of the structure as the amount of change in the state of the structure, based on the correspondence between the thermal conductivity of the structure and the current stress of the structure.

In the above-mentioned stress measurement method or stress measurement device, the existing stress of the structure may be measured based on the correspondence between the time gradient of the temperature difference between the two or more detection positions as the thermal conductivity of the structure and the existing stress of the structure.

In the above-mentioned stress measurement method or stress measurement device, the correspondence relationship may be preset to indicate the relationship between the first time gradient of the temperature difference in a predetermined first temperature range and the second time gradient of the temperature difference in a predetermined second temperature range, and the existing stress.

Furthermore, in the above-mentioned stress measurement method or stress measurement device, the correspondence relationship may be preset to indicate the relationship between the ratio of the first time gradient and the second time gradient and the strain of the structure corresponding to the existing stress.

The present invention makes it possible to easily measure the stress of various structures without requiring specialized knowledge and without destroying the structures.

1 is a block diagram showing a stress measuring device according to an embodiment of the present invention. 1 is a front perspective view of a stress measuring device according to an embodiment of the present invention; FIG. 2 is a perspective view showing a stress measuring device according to an embodiment of the present invention, viewed from behind. 1 is a graph showing the time gradient of the temperature difference between two points on a structure. 1 is a graph showing the relationship between the ratio of the temperature difference between two points over different temperature ranges versus time gradient and strain for structures under various conditions. 5 is a flowchart showing an example of a stress measurement operation performed by the stress measurement device according to the embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. Note that, although terms indicating directions and positions are used in this specification, these terms are used for convenience of explanation and do not limit the technical scope of the present invention.

The stress measurement method for measuring the stress acting on a structure in the present invention will be described with reference to Figs. 1 to 3, taking the stress measurement device 1 of this embodiment as an example. Fig. 1 is a block diagram showing the stress measurement device 1. Fig. 2 is a perspective view showing the stress measurement device 1 from the front. Fig. 3 is a perspective view showing the stress measurement device 1 from the back.

The stress measuring device 1 is used to measure the stress acting on a structure, such as a concrete structure (e.g., an RC column or RC beam) or a steel structure (e.g., a steel column). The stress measuring device 1 is configured with a control unit 3, a memory unit 4, a heating unit 5, a temperature detection unit 6, an operation unit 7, a display unit 8, and a power supply unit 9 housed in a housing 2.

One side (e.g., the lower side) of the housing 2 in a predetermined reference direction (e.g., the up-down direction) along the back surface is the heating side, and the other side (e.g., the upper side) opposite the heating side is the temperature detection side. When measuring the stress of a structure, the stress measuring device 1 is attached or positioned so that the back surface of the housing 2 is aligned with the surface of the structure so that the reference direction of the housing 2 is along the direction of stress applied to the structure. In addition, the housing 2 is preferably configured to have at least one of various heat-shielding functions, such as a heat-shielding material, a heat-shielding coating, or the attachment of a heat-shielding sheet, in order to reduce the effects of environmental temperature.

The control unit 3 is configured with a computer such as a CPU (Central Processing Unit) and controls the stress measuring device 1. The memory unit 4 is configured with storage media such as a ROM (Read Only Memory) and a RAM (Random Access Memory) as internal memory. The control unit 3 and the memory unit 4 are provided inside the housing 2. The control unit 3 is connected to each part of the stress measuring device 1 and controls each part.

The memory unit 4 stores programs and data for controlling each part and each function of the stress measuring device 1, and the control unit 3 controls each part and each function by executing arithmetic processing based on the programs and data stored in the memory unit 4. For example, the control unit 3 operates as the stress measuring unit 10 by executing the programs stored in the memory unit 4.

The storage unit 4 is also configured to be connectable to an external memory such as an SD card or USB memory, allowing data to be read from and written to the external memory. The external memory is connected to the storage unit 4 by being inserted into a slot 2a provided on the top, front, or back of the housing 2.

The heating unit 5 heats the structure at a predetermined heating position. The heating unit 5 is, for example, a planar heating element such as a rubber heater or a belt heater controlled by the control unit 3, or other heater, configured so as not to damage the structure, and heats the surface of the structure by contacting it. For example, the heating unit 5 is composed of a planar rubber heater in which both sides of a special heating element are bonded with a heat-resistant insulating layer. The heating unit 5 of such a rubber heater can be formed thinner to increase the temperature rise rate, and can be formed lighter and more flexible to be easily attached to the stress measuring device 1 and to increase the contact with the structure. The heating unit 5 also includes a temperature controller controlled by the control unit 3, and controls heating to a predetermined heating temperature (for example, 80°C). The heating unit 5 has a heating surface on the back of the housing 2 and is provided on the heating side of the housing 2 in the reference direction, and may be formed to extend in a direction perpendicular to the reference direction. In other words, the heating unit 5 is provided on one side of the stress direction of the structure.

The temperature detection unit 6 detects the temperature of the structure at two predetermined detection positions spaced apart from the heating position in the direction of stress applied to the structure. The temperature detection unit 6 is composed of, for example, a thermocouple or other temperature sensor controlled by the control unit 3, and detects the temperature of the structure by contacting the surface of the structure and outputs the detection result to the control unit 3. The temperature detection unit 6 has a temperature detection surface on the back surface of the housing 2 and is provided on the temperature detection side of the housing 2 in the reference direction.

The temperature detection unit 6 includes a first temperature sensor 11 and a second temperature sensor 12. The first temperature sensor 11 is provided on the temperature detection side at a predetermined first distance from the heating unit 5 in the reference direction of the housing 2. The second temperature sensor 12 is provided on the temperature detection side at a further predetermined second distance from the first temperature sensor 11 in the reference direction of the housing 2. The first temperature sensor 11 and the second temperature sensor 12 may be formed to extend in a direction perpendicular to the reference direction.

The stress measuring device 1 may be configured to include a suction cup that is attached to the structure, a belt that is wrapped around the structure, or the like, so that the heating unit 5 and the temperature detection unit 6 can maintain close contact with the structure.

The operation unit 7 has various operation buttons for instructing the stress measuring device 1 to start or end stress measurement. Each operation button of the operation unit 7 is provided on the front side of the housing 2 so that it can be operated by an operator. The operation unit 7 outputs operation input by the operator to the control unit 3.

The display unit 8 is configured with a display device such as a liquid crystal display, and is controlled by the control unit 3 to display a screen related to stress measurement by the stress measuring device 1, for example, a stress measurement result screen. The operation unit 7 and the display unit 8 may be configured with a touch panel.

The power supply unit 9 is composed of a battery or the like, and supplies the power required for stress measurement by the stress measurement device 1 to each part of the stress measurement device 1. Note that it is preferable for the power supply unit 9 to supply DC power so as not to affect the measurement, thereby preventing AC waves from affecting the measurement. The power supply unit 9 may be supplied with power converted from an external AC power source into DC.

The stress measurement unit 10 estimates the amount of change in the state of the structure caused by heating, for example, the thermal conductivity of the structure, based on the temperature detection result of the temperature detection unit 6 when the heating unit 5 heats the structure, and measures the current stress of the structure based on this amount of change in the state of the structure.

In this embodiment, the stress measurement unit 10 estimates the thermal conductivity of the structure as the amount of change in the state of the heated structure, and measures the current stress of the structure based on the thermal conductivity of the structure. However, the present invention is not limited to this example. For example, in another embodiment, the stress measurement unit 10 may estimate one or more of various amount of change in state of the structure that changes due to heating, not limited to thermal conductivity, and measure the current stress of the structure based on the one or more amount of change in state. For example, the stress measurement device 1 is configured to detect the temperature, moisture content, and deformation of the appearance of the heated structure, and to detect the degree of heat diffusion and transmission temperature at multiple detection points around the heated structure. The stress measurement unit 10 may estimate the amount of change in state of the structure based on the detection results, and may also estimate the amount of change in state of the structure based on the detection results and the time elapsed since the generation of the structure.

Next, an experiment is described in which the temperature of a structure is detected when the structure is heated, together with the measurement of the existing stress of the structure. In this experiment, grout is used as the structure to be tested. In this experiment, a rubber heater is used to heat the structure, which is formed into a rectangular sheet shape with a thickness of 1 mm, a length of 30 mm, and a width of 300 mm, and operates at a voltage of 100 V, a capacity of 90 W, and a watt density of 1.0 W/ ^cm2 .

In this experiment, the strain of the structure was measured with a strain gauge to measure the existing stress of the structure, and the structure was heated with a rubber heater at a predetermined heating position, and the temperature of the structure was detected with thermocouples at two predetermined detection positions of the structure. Here, the distance between the first thermocouple on the side closer to the rubber heater and the rubber heater was set to 35 mm, and the distance between the second thermocouple on the side farther from the rubber heater and the first thermocouple was set to 25 mm. In addition, in order to subtract the influence of the initial temperature of the structure before heating and to measure the degree of heat transfer between the two detection positions in the structure, the temperature difference between the two detection positions was calculated and the time gradient (slope) of the temperature difference was monitored. The two detection positions of the structure were set apart in the direction in which the load is applied to the structure, i.e., the stress direction.

As a result of this experiment, the temperature difference between the two detection points on the structure steadily increased over time, as shown in Figure 4. Figure 4 is a graph showing the time gradient of the temperature difference between two points on the structure.

In this experiment, the temperature difference was detected when no load was applied to the structure, i.e., when no stress was generated in the structure, and when a load was applied to the structure with a jack or the like, i.e., when stress was generated in the structure. Figure 4 shows a graph of the temperature difference Da when no load was applied to the structure, and a graph of the temperature difference Db when a load was applied to the structure. At this time, it was measured by the strain gauge that no strain was generated in the structure when no load was applied to the structure, but strain was generated in the structure when a load was applied to the structure.

According to this experiment, when no load is applied to the structure, the time gradient (slope) of the temperature difference Da is nearly linear in a predetermined first temperature range T1 (e.g., 0.5 to 3.0°C) from the start of heating until the temperature difference becomes large enough, and the temperature difference Da increases at a predetermined gradient. However, when a load is applied to the structure, the time gradient (slope) of the temperature difference Db is nearly linear in a predetermined second temperature range T2 (e.g., 0.5 to 2.0°C) immediately after the start of heating, but becomes gentler after the second temperature range T2 is exceeded. In other words, the temperature difference Db increases at different gradients in the first temperature range T1 and the second temperature range T2.

In this way, this experiment verified that when a load is applied to a structure, a temperature difference between the two detection positions is less likely to occur compared to when no load is applied to the structure, and therefore heat is more easily transferred. For example, since there are tiny gaps inside the structure, it can be assumed that applying a load (stress) to the structure narrows or fills the gaps, making it easier for heat to transfer.

In this experiment, the time gradient of the temperature difference and the strain were measured for structures under various initial temperature and load conditions. When no load (stress) was applied, the ratio (I1/I2) of the first time gradient I1 in the first temperature range T1 to the second time gradient I2 in the second temperature range T2 was approximately 1. On the other hand, when a load (stress) was applied, the time gradient of the temperature difference became gentler after the second temperature range T2 had elapsed, so the ratio (I1/I2) of the first time gradient I1 in the first temperature range T1 to the second time gradient I2 in the second temperature range T2 was smaller than 1. The relationship between the ratio (I1/I2) of the temperature difference between two points in different temperature ranges with different time gradients and strain for structures under various conditions is shown in the graph in Figure 5.

As shown in Figure 5, this experiment verified that there is an almost linear relationship between the ratio of the time gradients of the temperature difference (I1/I2) and the strain. Note that the greater the strain in the structure, the smaller the time gradient ratio becomes from 1. This makes it possible to estimate the strain (existing stress) occurring in the structure by measuring the temperature difference between two detection positions on the structure.

In this way, when the structure is heated, the temperature difference between the two detection positions, i.e., the thermal conductivity of the structure, changes depending on the existing stress of the structure. In other words, it can be estimated that there is a predetermined relationship between the existing stress of the structure and the thermal conductivity of the structure. Therefore, the stress measuring device 1 of this embodiment is configured to measure the existing stress of the structure based on the correspondence between the thermal conductivity of the structure estimated based on the temperature detection result of the structure and the existing stress of the structure. Specifically, in the stress measuring device 1, the correspondence between the ratio (I1/I2) of the first time gradient I1 in the first temperature range T1 and the second time gradient I2 in the second temperature range T2 and the strain (existing stress) is preset for the temperature difference at the two detection positions of the structure when the structure is heated at the heating position, and the correspondence data is stored in the memory unit 4.

In particular, when the heating unit 5 heats the structure, the stress measuring unit 10 calculates the ratio of the first time gradient I1 of the first temperature range T1 of the temperature difference to the second time gradient I2 of the second temperature range T2 based on the temperatures detected at two predetermined detection positions by the two first and second temperature sensors 11 and 12 of the temperature detecting unit 6. Then, the stress measuring unit 10 refers to the correspondence stored in the memory unit 4 as described above, and estimates and measures the existing stress of the structure based on the ratio of the time gradients of the temperature difference (I1/I2).

Next, the stress measurement operation (stress measurement method) performed by the stress measurement device 1 of this embodiment will be described with reference to the flowchart in FIG. 6.

First, the worker assumes the direction of stress acting on the structure to be measured based on the state in which the structure is installed, and positions the stress measuring device 1 so that the reference direction of the housing 2 is aligned with the direction of stress acting on the structure. At this time, the worker positions the stress measuring device 1 so that the heating unit 5 and temperature detection unit 6 are in contact with the surface of the structure.

Next, the operator operates the operation unit 7 to input the start of the stress measurement operation (step S1). The operation unit 7 instructs the control unit 3 to start the stress measurement operation.

The control unit 3 controls the heating unit 5 to heat the structure at a predetermined heating position (step S2), and controls the temperature detection unit 6 to detect the temperature at two predetermined detection positions of the structure (step S3). The control unit 3 inputs the temperature detection results at the two detection positions by the temperature detection unit 6.

The control unit 3 also operates as a stress measurement unit 10 to estimate the amount of change in the state of the structure due to heating based on the temperature detection results at the two detection positions of the structure, and to measure the existing stress of the structure based on the amount of change in the state of the structure. For example, the stress measurement unit 10 calculates the temperature difference based on the temperature detection results at the two detection positions of the structure (step S4). The stress measurement unit 10 monitors the time gradient of the temperature difference, and calculates the ratio of the first time gradient I1 of the first temperature range T1 of the temperature difference to the second time gradient I2 of the second temperature range T2 (step S5). Then, the stress measurement unit 10 refers to the correspondence stored in the memory unit 4, and estimates and measures the existing stress of the structure based on the ratio of the time gradients of the temperature difference (I1/I2) (step S6).

Then, the control unit 3 displays the measurement results of the stress of the structure by the stress measurement unit 10 on the display unit 8, or stores them in the internal memory or external memory of the storage unit 4 (step S7).

In this embodiment, as described above, the stress measuring device 1 includes at least the heating unit 5 and the stress measuring unit 10 of the control unit 3. The heating unit 5 heats the structure to be measured at a predetermined heating position. The stress measuring unit 10 estimates the amount of change in the state of the structure caused by heating, and measures the current stress of the structure based on the amount of change in the state of the structure. For example, the stress measuring device 1 includes a temperature detecting unit 6 that detects the temperature of the structure at two or more detection positions spaced apart from the heating position in the stress direction applied to the structure, and the stress measuring unit 10 measures the current stress of the structure based on the temperature detection result of the structure, based on the correspondence between the thermal conductivity of the structure and the current stress of the structure as the amount of change in the state of the structure. Specifically, the stress measuring unit 10 measures the current stress of the structure based on the correspondence between the time gradient of the temperature difference at two or more detection positions as the thermal conductivity of the structure and the current stress of the structure.

The stress measurement method of the present invention is not limited to the configuration of the stress measurement device 1 described above, and heats the structure to be measured at a predetermined heating position, estimates the amount of change in the state of the structure due to heating, and measures the current stress of the structure based on the amount of change in the state of the structure. For example, the stress measurement method detects the temperature of the structure at two or more detection positions spaced from the heating position in the stress direction applied to the structure, and measures the current stress of the structure based on the temperature detection result of the structure and the correspondence between the thermal conductivity of the structure and the current stress of the structure as the amount of change in the state of the structure. Specifically, the stress measurement method measures the current stress of the structure based on the correspondence between the time gradient of the temperature difference at two or more detection positions as the thermal conductivity of the structure and the current stress of the structure.

The above-mentioned configuration allows an operator to measure the existing stress of a structure through simple operations without requiring specialized knowledge, without destroying the structure, and without having to install measuring equipment inside the structure in advance. In addition, since there is no need to destroy the structure or prepare measuring equipment inside the structure, the method can be applied to stress measurements of various types of structures, whether they are new or existing.

In addition, in this embodiment, the correspondence between the time gradient of the temperature difference and the stress of the structure is set in advance to show the relationship between the first time gradient I1 of the temperature difference in a predetermined first temperature range T1 and the second time gradient I2 of the temperature difference in a predetermined second temperature range T2, and the existing stress. This allows the time gradient to be identified in detail, so that the existing stress to be obtained can be more accurately estimated and measured.

Furthermore, in this embodiment, the correspondence between the time gradient of the temperature difference and the stress of the structure is preset to indicate the relationship between the ratio I1/I2 of the first time gradient I1 and the second time gradient I2 described above and the strain of the structure corresponding to the existing stress. This allows the time gradient to be identified in more detail, so that the existing stress to be determined can be estimated and measured more accurately.

In the above embodiment, in order to set the correspondence between the time gradient of the temperature difference and the stress of the structure, an example was described in which the temperature range in which there is a sufficient temperature difference from the start of heating is set as the first temperature range T1 (e.g., 0.5 to 3.0°C) and the temperature range immediately after the start of heating is set as the second temperature range T2 (e.g., 0.5 to 2.0°C), but the present invention is not limited to this example. For example, the temperature range immediately after the start of heating may be set as the second temperature range T2 (e.g., 0.5 to 2.0°C), while the temperature range in which there is a sufficient temperature difference after the second temperature range T2 has elapsed may be set as the first temperature range T1 (e.g., 2.0 to 3.0°C).

In the above embodiment, an example in which the heating unit 5 is provided on the back surface of the housing 2 has been described, but the present invention is not limited to this example. For example, in other embodiments, the heating unit 5 may be independent of the housing 2 and connected to the housing 2 via wiring.

In the above embodiment, an example was described in which the temperature detection unit 6 is provided on the back surface of the housing 2, but the present invention is not limited to this example. For example, in other embodiments, the temperature detection unit 6 may be independent of the housing 2 and connected to the housing 2 via a wire.

In addition, in the above embodiment, an example was described in which the temperature detection unit 6 is equipped with two temperature sensors, a first temperature sensor 11 and a second temperature sensor 12, and detects temperature at two detection positions, but the present invention is not limited to this example.

For example, in another embodiment, the temperature detection unit 6 may be equipped with three or more temperature sensors and detect the temperature of the structure at three or more detection positions. In this case, the stress measurement unit 10 may select two temperatures suitable for stress measurement from the temperatures detected at the three or more detection positions and calculate the temperature difference.

Alternatively, the stress measuring unit 10 may select two or more combinations of temperatures detected at three or more detection positions, with two detection positions being one combination, and calculate the temperature difference for each combination. For example, for three detection positions, the first detection position, the second detection position, and the third detection position, the first temperature difference between the first detection position and the second detection position and the second temperature difference between the second detection position and the third detection position are calculated. A correspondence relationship between the combination of the time gradients of the first temperature difference and the second temperature difference (the ratio of the first time gradient in the first temperature range to the second time gradient in the second temperature range) and the strain is set in advance. The stress measuring unit 10 refers to this correspondence relationship and estimates and measures the existing stress of the structure based on the temperatures detected at the first detection position, the second detection position, and the third detection position.

The correspondence data between the time gradient of the temperature difference and the stress of the structure is not limited to being stored in advance in the memory unit 4, but may be input from an external memory or by wired or wireless communication.

In addition, the correspondence data between the time gradient of the temperature difference and the stress of the structure is not limited to a specific type of structure, and the correspondence data may be stored or input for various types of structures. At the start of the stress measurement operation, the type of structure may be specified using the operation unit 7, and the correspondence data for the specified structure may be read out.

The description of the embodiment shows one aspect of the stress measurement method and stress measurement device according to the present invention, and the technical scope of the present invention is not limited to the above embodiment. The present invention may be modified, substituted, or altered in various ways without departing from the spirit of the technical idea, and the claims include all embodiments that may be included within the scope of the technical idea.

REFERENCE SIGNS LIST 1 Stress measuring device 2 Housing 3 Control unit 4 Memory unit 5 Heating unit 6 Temperature detection unit 7 Operation unit 8 Display unit 9 Power supply unit 10 Stress measuring unit 11 First temperature sensor 12 Second temperature sensor

Claims (4)

The structure to be measured is heated at a predetermined heating position.
Detecting a temperature of the structure at two or more detection positions spaced apart from the heating position in a stress direction applied to the structure;
an amount of change in state of the structure caused by heating is estimated, and an existing stress of the structure is measured based on a correspondence relationship between a time gradient of the temperature difference at the two or more detection positions and an existing stress of the structure as a thermal conductivity of the structure as an amount of change in state of the structure based on a temperature detection result of the structure ;
The stress measurement method, characterized in that the correspondence relationship is preset to indicate a relationship between a first time gradient of the temperature difference in a predetermined first temperature range and a second time gradient of the temperature difference in a predetermined second temperature range, and the existing stress . 2. The stress measurement method according to claim 1 , wherein the correspondence relationship is preset to indicate a relationship between a ratio of the first time gradient to the second time gradient and a strain of the structure corresponding to the existing stress. A heating unit that heats the structure to be measured at a predetermined heating position;
a temperature detection unit that detects a temperature of the structure at two or more detection positions spaced from the heating position in a stress direction applied to the structure;
a stress measurement unit that estimates an amount of change in state of the structure caused by heating, and measures an existing stress of the structure based on a correspondence relationship between a time gradient of a temperature difference at the two or more detection positions and an existing stress of the structure as a thermal conductivity of the structure as an amount of change in state of the structure based on a temperature detection result of the structure ,
The stress measuring device according to claim 1, wherein the correspondence relationship is preset to indicate a relationship between a first time gradient of the temperature difference in a predetermined first temperature range and a second time gradient of the temperature difference in a predetermined second temperature range, and the existing stress . 4. The stress measuring device according to claim 3, wherein the correspondence relationship is preset to indicate a relationship between a ratio of the first time gradient to the second time gradient and a strain of the structure corresponding to the existing stress.

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