JP2024064667A - Acting load calculation system - Google Patents

Abstract

The present invention provides a method for calculating a previously applied load that can calculate a previously applied load that is already applied to an object at the time of measurement more easily than conventional methods by using a stress-luminescent material.
[Solution] A method for calculating a previously applied load that has already been applied to an object at the time of measurement using a stress-stimulated luminescent material, the calculation method includes a calibration step of applying a dynamic load to a test object to which a stress-stimulated luminescent material is installed and a predetermined previously applied load has been applied, and confirming the relationship between the degree of luminescence in response to the dynamic load and the predetermined previously applied load applied to the test object;
A method for calculating a previously applied load, comprising: a measurement step of applying a dynamic load to a measurement object having a stress-stimulated luminescent material placed thereon, and measuring the degree of luminescence in response to the dynamic load; and a step of calculating a previously applied load that is already applied to the measurement object at the time of measurement, from the relationship between the degree of luminescence in response to the dynamic load obtained in the calibration step and a predetermined previously applied load applied to the test object, and the degree of luminescence in response to the dynamic load measured in the measurement step.
[Selection diagram] None

Description

The present invention relates to a system for calculating applied loads.

Traditionally, known methods for measuring the stress state of various objects such as structures include calculating the stress by multiplying the amount of strain measured using a strain gauge by the Young's modulus of the material, analyzing the stress distribution by photographing temperature changes caused by small repeated loads with infrared light, and analyzing the stress state from birefringence using a transparent, uniform photoelastic material. In addition to these methods, in recent years, methods have been considered for evaluating the stress state of objects such as structures using mechanoluminescent materials that emit light when subjected to external mechanical stimuli. Proposed methods include a measurement method that uses mechanoluminescent materials to visualize stress distribution in real time (see Patent Document 1), a paint composition made by mixing a resin such as an epoxy resin with a mechanoluminescent material so that it can be used to grasp the stress state of a wide range of materials (see Patent Document 2), a load measurement method that applies a mechanoluminescent paint composition to a structure and determines the level of load applied to the structure from the brightness and pattern of the light emitted (see Patent Document 3), a method of calculating residual stress, etc. by photographing the light emission state of the mechanoluminescent material when a load is applied and when the load is released (see Patent Document 4), and a structure external force detection device that uses an external force response means that combines a first material that is light-transmitting and flexible, a second material that emits light when an external force is applied, and a third material that is not light-transmitting and flexible (see Patent Document 5).

JP 2001-215157 A International Publication No. 2018/135106 JP 2017-044634 A JP 2019-158437 A JP 2003-262558 A

As mentioned above, various methods have been proposed for measuring and understanding the stress state of objects such as structures using mechanoluminescent materials. However, with conventional measurement methods, in order to measure the load state of an object to be measured that is already under load, it is necessary to measure all of the excitation states and the light emission process due to loading from the unloaded state to the time of measurement. In cases where a complex load history is applied, it is difficult to measure the already-applied load state.

In view of the above-mentioned current situation, the present invention aims to provide a method for calculating a pre-applied load that uses a stress-luminescent material and can more easily calculate the pre-applied load that is already applied to an object at the time of measurement than conventional methods.

The inventors have investigated a method for calculating the applied load already applied to an object at the time of measurement more easily than conventional methods, and have found that when a dynamic load is applied to an object on which a stress-stimulated luminescent material is installed and to which a stress-stimulated luminescent load is applied, the degree of luminescence changes depending on the magnitude of the applied load. Then, after performing a calibration process to confirm the relationship between the magnitude of a predetermined applied load applied to a test object on which a stress-stimulated luminescent material is installed and the degree of luminescence in response to a dynamic load when the dynamic load is applied to the test object, a measurement process is performed to apply a dynamic load to a measurement object on which a stress-stimulated luminescent material is installed and measure the degree of luminescence, and the degree of luminescence in response to the obtained dynamic load and the relationship between the degree of luminescence in response to the dynamic load obtained in the calibration process and the predetermined applied load applied to the test object, and have found that the applied load already applied to the measurement object at the time of measurement can be calculated, thereby completing the present invention.

In other words, the present invention is a method for calculating a previously applied load that is already applied to an object at the time of measurement using a stress-stimulated luminescent material, the calculation method being characterized by including a calibration step of applying a dynamic load to a test object to which a stress-stimulated luminescent material is installed and a predetermined previously applied load is applied, and confirming the relationship between the degree of luminescence in response to the dynamic load and the predetermined previously applied load applied to the test object; a measurement step of applying a dynamic load to a measurement object to which a stress-stimulated luminescent material is installed, and measuring the degree of luminescence in response to the dynamic load; and a step of calculating the previously applied load that is already applied to the measurement object at the time of measurement from the relationship between the degree of luminescence in response to the dynamic load obtained in the calibration step and the predetermined previously applied load applied to the test object, and the degree of luminescence in response to the dynamic load measured in the measurement step.

The above-mentioned stress-stimulated luminescent material is preferably placed in an object or by applying a stress-stimulated luminescent coating composition to the surface of the object.

It is also preferable that the above-mentioned stress-stimulated luminescent material is placed on the object by placing a piece of stress-stimulated luminescent material having a stress-stimulated luminescent material or a stress-stimulated luminescent coating composition on the inside or surface of the piece.

The load already applied to the object to be measured at the time of measurement is preferably a compressive load, a tensile load, a torsional load or a shear load.

It is also preferable that the dynamic load in the calibration process and the dynamic load in the measurement process are either a compressive load, a tensile load, a torsional load or a shear load.

It is also preferable that the characteristic quantity (load index) of the dynamic load in the measurement process is the same as or different from the characteristic quantity of the dynamic load in the calibration process.

The present invention also provides a method for confirming the relationship between a previously applied load and the degree of luminescence in response to a dynamic load applied to an object on which a stress-stimulated luminescent material is installed, the method being characterized in that a dynamic load is applied to an object on which a stress-stimulated luminescent material is installed and to which a previously applied load is applied, and the degree of luminescence in response to the dynamic load at that time is confirmed.

In the above-mentioned method for confirming the relationship between the applied load and luminescence, the applied load applied to the object in which the stress-luminescent material is placed is preferably a compressive load, a tensile load, a torsional load, or a shear load.

It is also preferable that the dynamic load applied to the object to which the applied load has been applied in the method for confirming the relationship between the applied load and luminescence is a compressive load, a tensile load, a torsional load, or a shear load.

The method for calculating the previously applied load of the present invention is a method that can calculate the previously applied load that is already applied to the object to be measured at the time of measurement without checking the history of the load acting on the object to be measured, and therefore can be suitably used as a method for checking the load state of various objects.

1 is a conceptual diagram showing the relationship between the load index and the luminescence intensity of a stress-stimulated luminescent material when a dynamic load is applied to an object in which the stress-stimulated luminescent material is placed. FIG. FIG. 2 is a conceptual diagram showing the relationship between the slope of the load index-luminescence intensity line in FIG. 1 and the axial strain rate. 1 is a conceptual diagram showing the relationship between the load index and luminescence intensity of a stress-stimulated luminescent material when a dynamic load is applied to an object in which a stress-stimulated luminescent material is placed and to which a load has already been applied. FIG. FIG. 4 is a conceptual diagram showing the relationship between the previously applied load and the contribution of the previously applied load in the slope of the line of the load index vs. luminous intensity in FIG. 3. 1 is a graph plotting the load measurement value and average luminescence intensity against time when a load of 10 N was applied using pellet A1 in Example 1, and photographed images showing the luminescence during measurement. FIG. 1 shows the relationship between the load (excluding the previously applied load) applied in addition to the previously applied load and the average luminescence intensity under conditions where a previously applied load of 10 N for holding was applied using pellet A1 in Example 1 and four types of axial strain rate were applied, and the regression line and correlation coefficient for each plot are also shown (corresponding to FIG. 1 ). FIG. 2 shows the relationship between the slope of the regression line (corresponding to α in FIG. 1 ) in the load-average luminescence intensity relationship at an applied load of 10 N in Example 1 and the axial strain rate, and also shows the regression line and correlation coefficient in this plot (corresponding to FIG. 2 ). FIG. 1 shows the relationship between the additional load (not including the previously applied load) and the average luminescence intensity at previously applied loads of 10 N, 100 N, 200 N, and 300 N in Example 1, and also shows the regression line and correlation coefficient for each plot. FIG. 9 is a graph showing the relationship between the slope of the regression line in the relationship between the applied load and the average luminescence intensity at an axial strain rate of 1.67% strain s in ^FIG. 8 and the applied load for three pellets in Example 1, and the average value is plotted. FIG. 10 is a graph showing the relationship between the average slope of the regression line in the applied load-average luminescence intensity relationship in FIG. 9 and the applied load for each axial strain rate in Example 1. FIG. 1 is a schematic diagram of a process for calculating a pre-applied load with reference to Example 1. 1 is a graph plotting the load measurement value and average luminescence intensity against time when a load of 1 N was applied using pellet A2 in Example 2, and photographed images showing the luminescence during measurement. FIG. 13 is a graph (corresponding to FIG. 10 in Example 1) showing the relationship between the average slope of the regression line in the applied load-average luminescence intensity relationship and the applied load for each axial strain rate in Example 2.

The following describes in detail preferred embodiments of the present invention, but the present invention is not limited to the following description, and can be modified as appropriate without departing from the spirit of the present invention.

The method for calculating the previously applied load of the present invention includes a calibration step of confirming the relationship between a predetermined previously applied load applied to a test object on which a stress-stimulated luminescent material is placed and the degree of luminescence in response to a dynamic load, a measurement step of applying a dynamic load to a measurement object on which a stress-stimulated luminescent material is placed and measuring the degree of luminescence, and a step of calculating the previously applied load already applied to the measurement object at the time of measurement from the relationship between the degree of luminescence in response to the dynamic load obtained in the calibration step and the predetermined previously applied load applied to the test object and the degree of luminescence in response to the dynamic load measured in the measurement step.
These steps will be described in order below.

(1) Calibration Step The calibration step in the present invention is a step of applying a dynamic load to a test object having a stress-stimulated luminescent material placed thereon and having various predetermined pre-applied loads applied thereto, and confirming the relationship between the degree of luminescence in response to the dynamic load and the pre-applied loads applied to the test object.
When a dynamic load is applied to an object on which a stress-luminescent material is placed, the luminescence intensity increases according to the magnitude of the load, and the luminescence intensity relative to the load index based on the load and load increment increases as the axial strain rate (the strain of an object in the axial direction per unit time due to loading; also known as the longitudinal strain rate; in the case of a torsional load, this corresponds to the torsional angular velocity) applied to the object increases. Figures 1 and 2 conceptually illustrate this relationship. Note that in Figures 1 and 2, the relationship between luminescence intensity and load index, and the relationship between α (slope of load index - luminescence intensity) and axial strain rate are both shown as linear relationships, but these are not necessarily linear and may be curved.
The present inventors have studied the relationship between the load index and the luminescence intensity when a dynamic load is applied to an object on which a stress-luminescent material is installed and to which a previously applied load is applied, and have found that the luminescence intensity for the load index increases according to the axial strain rate and the magnitude of the previously applied load applied to the object, and that when the axial strain rate is constant, the luminescence intensity for the load index increases according to the previously applied load applied to the object. Figures 3 and 4 conceptually illustrate this relationship. Note that in Figures 3 and 4, the relationship between the load index and the load increment, and the relationship between β (the slope of the load index-luminescence intensity including the influence of the previously applied load) and the axial strain rate are both shown as linear relationships, but these are not necessarily linear relationships and may be curved. In addition, depending on the value of β, for example, the relationship between the slope of the load index-luminescence intensity based on α1 and the previously applied load may be smaller than the relationship based on α2, and the positional relationship between the luminescence intensity-load increment line may differ from that shown in Figure 3.
The inventors have utilized this knowledge and found that by confirming the relationship between the load index and the luminescence intensity when a dynamic load is applied at one or more predetermined axial strain rates to a test object in which the same mechanoluminescent material as that installed in the measurement object is installed and which is in two or more previously applied load states (a no-load state, a state in which a predetermined previously applied load is applied, or a state in which two or more previously applied loads are applied), it is possible to confirm the relationship between the axial strain rate, the magnitude of the previously applied load on the object, and the luminescence intensity, and by using this relationship, it is possible to calculate the magnitude of the previously applied load on the measurement object from the luminescence intensity when a dynamic load is applied at a predetermined axial strain rate to the measurement object in which the mechanoluminescent material is installed, as described later in "(2) Measurement step". With this method, it is possible to calculate the previously applied load applied to the measurement object at the time of measurement without confirming the history of the load acting on the measurement object.
In the above description, the degree of light emission is explained using the light emission intensity for the load index based on the load, the load increment, etc. However, since it is sufficient to confirm a calibrable correspondence with the magnitude of the degree of light emission, in the calculation method of the applied load of the present invention, the load index based on the load, the load increment, etc. may be converted to stress, or indexes such as strain energy, strain energy increment, impulse, or feature values such as their cumulative value, increment value, normalized index, peak value, etc. may be used. As for the index related to the light emission intensity, feature values such as the cumulative value of the light emission intensity, the increment value of the light emission intensity, the normalized index, peak value, etc. may be used. In addition, the applied load may be the applied stress considering the area on which the load acts, or the strain energy increment may be used instead of the axial strain rate.

In the calibration step, it is sufficient to confirm the degree of luminescence by applying a dynamic load to the test object at least at one predetermined axial strain rate, but from the viewpoint of improving the accuracy of the calculation, it is preferable to confirm the degree of luminescence by applying a dynamic load at two or more predetermined axial strain rates, and more preferably, to confirm the degree of luminescence in response to a dynamic load at three or more predetermined axial strain rates.
In the calibration step, a dynamic load is applied at a predetermined axial strain rate to a test object to which at least two types of previously applied loads have been applied, and the degree of luminescence is confirmed, but in terms of improving the accuracy of calculation, it is preferable to apply a dynamic load at a predetermined axial strain rate to a test object to which three or more types of previously applied loads have been applied, and the degree of luminescence is confirmed. More preferably, it is preferable to confirm the degree of luminescence in response to a dynamic load at a predetermined axial strain rate to a test object to which four or more types of previously applied loads have been applied.
In addition, the accuracy of the calculation can be improved by carrying out loading several times under the same loading conditions of axial strain rate and applied load and averaging the results.
The calibration process may use a single test object or may use multiple test objects.

In the above calibration process, a dynamic load is applied at a predetermined axial strain rate to the test object on which the stress-stimulated luminescent material is placed, and the degree of luminescence is confirmed. In this case, in order to fully confirm the degree of luminescence, it is preferable to wait a predetermined time after irradiating the test object on which the stress-stimulated luminescent material is placed with excitation light before applying the dynamic load.

(2) Measuring Step The measuring step in the present invention is a step of applying a dynamic load to the measurement object on which the stress-stimulated luminescent material is placed, and measuring the degree of luminescence.
The measurement process involves applying a dynamic load at a constant axial strain rate (or, in the case of torsional loading, torsional angular rate).
If the degree of luminescence is confirmed by applying a dynamic load at one specific axial strain rate in the calibration process, then in the measurement process, it is necessary to apply a dynamic load to the object to be measured at the same axial strain rate as in the calibration process.
On the other hand, if the degree of luminescence is confirmed by applying dynamic loads at two or more predetermined axial strain rates in the calibration step, the relationship between the luminescence intensity and the load index can be obtained regardless of which axial strain rate is used when applying a dynamic load to the measurement object in the measurement step. Therefore, in this case, the axial strain rate used in the measurement step may be the same as or different from that used in the calibration step.
In the measurement step, in order to thoroughly check the degree of luminescence, it is preferable to irradiate the measurement object on which the stress-stimulated luminescent material is placed with excitation light, wait a predetermined time, and then apply a dynamic load.

(3) Step of calculating the applied load The step of calculating the applied load in the present invention is a step of calculating the applied load already applied to the object to be measured at the time of measurement from the relationship between the degree of light emission in response to the dynamic load obtained in the calibration step and the applied load already applied to the test object, and the degree of light emission in response to the dynamic load measured in the measurement step.
As described above, by using the relationship between the axial strain rate obtained in the calibration process, the magnitude of the load already applied to the test object, and the light emission intensity for a load index based on the load, load increment, etc., the load already applied to the object being measured at the time of measurement can be determined from the degree of light emission for the dynamic load measured in the measurement process.
In the method of calculating the applied load of the present invention, it is not necessary to continuously observe the applied load on the object to be measured, and it is also not necessary to use equipment that requires a power supply and wiring, such as conventional strain gauges and load cells, so that it is possible to reduce the costs required for measurement and the maintenance costs of sensors. Furthermore, since the power required to excite the mechanoluminescent material is about that of a portable battery such as a dry cell, the measurement process of the object to be measured can be performed remotely or unmanned using a drone or the like.

In the method for calculating the applied load of the present invention, the specific procedures of the measuring step and the step of calculating the applied load are not particularly limited, but an example of the specific procedures is shown below.
(1) A load applied to a measurement object on which a stress-stimulated luminescent material is placed is transmitted to generate a minute strain.
(2) The stress-stimulated luminescent material is excited by an excitation light in a darkroom frame.
(3) After waiting for a predetermined time, a dynamic load is applied to the stress-stimulated luminescent material.
(4) The luminescence intensity of the mechanoluminescent material due to the application of a dynamic load and the change in the dynamic load or its characteristic quantity (load index based on load, load increment, etc.) are measured using a sensor.
(5) The measured emission intensity and the changes in the load index are stored in a data recording device.
(6) The emission intensity for the load index is compared with the calibration database obtained in the calibration process to calculate the applied load of the object to be measured.
The waiting for a predetermined time in the above step (3) is for keeping the luminescence intensity under constant conditions during loading in the measurement step, since the stress-stimulated luminescent material phosphoresses upon excitation and the phosphorescence intensity decreases over time.
The dynamic load applied in the above step (3) can be applied so that the axial strain rate is constant, or can be calculated as a load index based on the load, load increment, etc.
The calibration database in the above step (6) is obtained by a calibration step, and is a function of a calibration coefficient created by investigating in advance the luminescence intensity versus load index of the applied load, waiting time, and dynamic load. If the load index acting on the mechanoluminescent material is considered to be approximately the same by predetermining the waiting time for loading and the axial strain rate in the measurement step, a calibration database in which only the relationship between the applied load and the luminescence intensity is investigated will suffice.

In the method of calculating the applied load of the present invention, the object to be measured and the stress-luminescent material must be placed so that the load is transmitted between them. This may be done by placing the stress-luminescent material inside the object, or by using a coating-type stress-luminescent material and applying a stress-luminescent paint composition to the surface of the object. Alternatively, it may be done by placing a piece of stress-luminescent material with a stress-luminescent material placed inside or on the surface of the object as a sensor on the object to be measured.

When the stress-stimulated luminescent material piece is installed as a sensor on an object to be measured, a load may be applied directly to the stress-stimulated luminescent material piece using a jig that transmits the load, or the load may be applied via the jig and a frame with known rigidity.
The sensor-type measurement system is composed of a piece of mechanoluminescent material, an excitation illuminator, a previously applied load transmission jig, a loading device for applying the load in the measurement process, a darkroom frame, a luminescence intensity measurement sensor, a data recording device, and a data processing device. The excitation illuminator, the loading device for applying the load in the measurement process, the darkroom frame, the luminescence intensity measurement sensor, the data recording device, and the data processing device may be attached after the sensor is placed on the object. The data recording device may be an external communication device, and data may be recorded on an external information processing terminal, or a data processing device (load index calculation, feature extraction, calibration processing) may be provided within the sensor.
By using the sensor type, it is possible to install a stress-stimulated luminescent material on an object later, and therefore it is possible to use the method of calculating the applied load of the present invention for a larger number of objects. By using the sensor type using a frame, it is possible to adjust the measurable load by selecting the rigidity of the frame.

When a mechanoluminescent material is placed inside or on the surface of a measurement object, the measurement system is composed of the mechanoluminescent material, an excitation illuminator, a loading device for applying load in the measurement process, a darkroom frame, a luminescence intensity measuring sensor, a data recording device, and a data processing device. The excitation illuminator, the loading device for applying load in the measurement process, the darkroom frame, the luminescence intensity measuring sensor, the data recording device, and the data processing device may be attached to the sensor later. The data recording device may be an external communication device, and data may be recorded on an external information processing terminal, or a data processing device (load index calculation, feature extraction, calibration processing) may be provided inside the sensor.
In addition, when a coating type stress-stimulated luminescent material is used, the stress-stimulated luminescent material can be placed on the object later, making it possible to use the method of calculating the previously applied load of the present invention on a larger number of objects. In order to measure the load acting on the object before coating, it is necessary to remove the load after coating and measure the luminescence.

In the method of calculating the applied load of the present invention, the applied load applied to the object to be measured can be measured whether it is a static load or a dynamic load (however, if the applied load is a dynamic load, the dynamic load applied in the calibration process or the measurement process must be a load that acts in a sufficiently shorter time than the applied load). It is also possible to calculate the overall load distribution of the object to be measured from the data of a plurality of measurement points on the object to be measured.
Furthermore, the applied load applied to the test object in the calibration process and the applied load applied to the measurement object in the measurement process may be any of a compressive load, a tensile load, a torsional load, and a shear load.
If the direction of the applied load applied to the test object in the calibration process differs from the direction of the dynamic load applied to the test object, effects such as a decrease in the emission intensity for the applied load will occur. By utilizing this property, even if a dynamic load cannot be applied to the measurement object in the same direction as the applied load, it is possible to calculate the applied load that is already applied to the measurement object at the time of measurement using the calculation method of the applied load of the present invention.

In the method of calculating the applied load of the present invention, the dynamic load applied to the test object in the calibration process and the dynamic load applied to the measured object in the measurement process may be any of a compressive load, a tensile load, a torsional load, and a shear load. If calibration is possible, the type of dynamic load applied to the test object in the calibration process and the type of dynamic load applied to the measured object in the measurement process may be different, but usually the type of dynamic load applied to the test object in the calibration process and the type of dynamic load applied to the measured object in the measurement process are the same.

2. Method for confirming the relationship between the previously applied load and the degree of luminescence As described above, the present inventor has found that when a dynamic load in the same load direction is applied to an object on which a mechanoluminescent material is installed and on which a previously applied load is applied, the luminescence intensity for a load index based on the load and load increment increases according to the axial strain rate applied to the object and the magnitude of the previously applied load already applied to the object, and when the axial strain rate is constant, the luminescence intensity for a load index based on the load and load increment increases according to the previously applied load on the object. By utilizing this relationship, the previously applied load of the object can be calculated easily. For this calculation, a method for confirming the relationship between the load applied to the object and the luminescence, that is, a method for confirming the relationship between the load applied to the object on which a mechanoluminescent material is installed and the degree of luminescence for a dynamic load, which method is characterized in that a dynamic load is applied to a test object on which a mechanoluminescent material is installed and on which various predetermined previously applied loads are applied, and the degree of luminescence for the dynamic load at that time is confirmed, is also one of the present inventions.

3. Stimuli-luminescent Material The following describes the stress-luminescent material used in the present invention.
The mechanoluminescent material used in the present invention is not particularly limited as long as it has the property of emitting light when subjected to an external mechanical stimulus, but a material classified as elastico-luminescence that emits light according to the magnitude of a mechanical stimulus in the elastic region of the substance is preferable, and more preferably a mechanoluminescent material based on strontium aluminate, such as a europium-activated strontium aluminate-based mechanoluminescent material.

_{Strontium aluminate} is a compound generally represented by _SrxAlyOz (0<x, 0< _y , 0<z). Although not particularly limited _, various compounds such as _{SrAl2O4 , SrAl4O7} , _Sr4Al14O25 , _SrAl12O19 , _{and Sr3Al2O6} are known as specific _examples of _{strontium aluminate} .

The above strontium aluminate is preferably synthesized from an alumina raw material or aluminum hydroxide containing at least one type of alumina selected from θ-alumina, κ-alumina, δ-alumina, η-alumina, χ-alumina, γ-alumina, and ρ-alumina, and a strontium source. Although "alumina" usually refers to inexpensive and general-purpose α-alumina, if so-called activated alumina such as θ-alumina or aluminum hydroxide is used as a raw material, a higher luminescence intensity can be achieved than when α-alumina is used.

As an activator, it is desirable to contain europium (Eu) ions. The amount of Eu ions contained in the above-mentioned stress-stimulated luminescent material is not particularly limited, but is 0.0001 to 0.01 mol, preferably 0.0005 to 0.01 mol, and more preferably 0.0005 to 0.005 mol per mol of strontium aluminate. If the amount of Eu ions is too small, sufficient luminescence intensity cannot be achieved, and if the amount is too large, the luminescence intensity will saturate, but other physical properties may also be affected.

The stress-stimulated luminescent material may further include a co-activator. The co-activator is not particularly limited, but may be a compound or ion of a rare earth element other than Eu. Examples of the rare earth element other than Eu include one or more elements selected from Sc, Y, Zr, La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, etc. These are preferable because lattice defects are formed by replacing them with elements having different ionic radii or valences, making the crystal structure more likely to be distorted, thereby improving the stress-stimulated luminescent ability. Among them, Nd, Dy, and Ho are particularly preferable as co-activators in that they provide high luminescence brightness.
Furthermore, examples of the compounds of the rare earth elements include carbonates, oxides, hydroxides, chlorides, sulfates, nitrates, acetates, and the like of the elements.

The stress-luminescent material may further contain a dispersant to enhance the dispersibility of the particles. Examples of dispersants include, but are not limited to, anionic surfactants and nonionic surfactants. Examples of anionic surfactants include ammonium polycarboxylate, sodium polycarboxylate, and sodium hexametaphosphate, while examples of nonionic surfactants include polyoxyethylene alkyl ether, polyoxyethylene hydrogenated castor oil, polyoxyethylene mono fatty acid ester, and polyoxyethylene sorbitan mono fatty acid ester. These may be used alone or in combination of two or more.

The stress-luminescent material may further contain a flux component to enhance the crystallinity of the particles. The flux component is not particularly limited, but may include compounds such as calcium fluoride, magnesium fluoride, aluminum fluoride, ammonium fluoride, sodium chloride, potassium chloride, lithium chloride, ammonium bromide, ammonium iodide, potassium iodide, sodium hydroxide, potassium hydroxide, ammonium sulfate, sodium sulfate, potassium sulfate, sodium nitrate, ammonium nitrate, boric acid, and sodium borate. These may be used alone or in combination of two or more.

Alternatively, the surface of the stress-stimulated luminescent material may be coated with a silane coupling agent and heat-treated to increase the water resistance of the stress-stimulated luminescent material.
The silane coupling agent preferably contains a trialkoxysilane.
Moreover, it is preferable that the substituent other than the alkoxy group of the above trialkoxysilane is a hydrocarbon group having 3 or more carbon atoms.
The above-mentioned silane coupling agent can enhance hydrophobicity due to the structure of the substituent other than the alkoxy group, and can therefore be used as a stress-stimulated luminescent material with even better water resistance.

The silane coupling agent is preferably a silane coupling agent having a fluoroalkyl group.
When the silane coupling agent has a fluoroalkyl group, the hydrophobicity can be increased, and therefore the material can be used as a stress-stimulated luminescent material having even better water resistance.

The silane coupling agent is preferably 3,3,3-trifluoropropyltrimethoxysilane.
When 3,3,3-trifluoropropyltrimethoxysilane is used, it can be used as a stress-stimulated luminescent material having particularly excellent water resistance.

Alternatively, the stress-stimulated luminescent material may have a surface-treated layer formed by mixing the stress-stimulated luminescent material with a phosphate compound in a dry or wet manner to modify the surface of the stress-stimulated luminescent material with the phosphate compound.
A stress-stimulated luminescent material having such a surface treatment layer is also desirable because it has sufficient water resistance.

The phosphate compound is not particularly specified, and both inorganic and organic phosphates can be used. Among them, water-soluble salts (including phosphoric acid) are preferable, and specifically, at least one selected from the group consisting of ammonium phosphate, sodium phosphate, potassium phosphate, sodium polyphosphate, sodium hexametaphosphate, and phosphoric acid is preferable.

The method for producing the stress-stimulated luminescent material is not particularly limited, but it can be produced by the method described in JP 2017-044634 A, for example.

When the method of calculating the applied load of the present invention is carried out by placing a stress-stimulated luminescent material in an object, the method can be carried out by kneading particles of the stress-stimulated luminescent material with a ceramic material and sintering the mixture to obtain a hardened product, or by mixing particles of the stress-stimulated luminescent material with a hardening resin and hardening the mixture to obtain a hardened product, and placing the hardened product in the object. The hardening resin that can be used is as described below.

The particles of the stress-luminescent material are preferably mixed with a ceramic material and sintered to obtain a hardened product, or the particles of the stress-luminescent material are mixed with a curable resin and hardened to obtain a hardened product (100% by mass), and the proportion of the particles of the stress-luminescent material in this 100% by mass hardened product is preferably 1 to 90% by mass. With such a proportion, the degree of luminescence can be more fully confirmed when used in the method of calculating the applied load of the present invention. More preferably, it is 5 to 80% by mass.

When a stress-luminescent coating composition is used in the method of calculating the applied load of the present invention, a coating composition containing a resin is used as the coating composition. In addition to the resin, the coating composition may contain, as necessary, coating additives such as solvents, dispersants, fillers, thickeners, surface conditioners or leveling agents, curing agents, crosslinking agents, pigments, defoamers, antioxidants, light stabilizers including ultraviolet absorbers, flame retardants, curing catalysts, bactericides, antibacterial agents, and adhesion enhancers.

The resins used in the paint composition can be various types such as thermosetting resins, room temperature curing resins, ultraviolet curing resins, and radiation curing resins, and examples thereof include epoxy resins, acrylic resins, fluororesins, alkyd resins, polyurethane resins, unsaturated polyester resins, amino resins, organosilicates, and organotitanates. Ink film forming materials include urethane resins, acrylic resins, polyamide resins, vinyl chloride-vinyl acetate resins, and chlorinated propylene resins. Among these resins, it is preferable to include epoxy resins or polyurethane resins. When the paint composition is an epoxy resin-based paint containing an epoxy resin or a polyurethane resin-based paint containing a polyurethane resin, the correspondence between the magnitude of the load applied to the object and the brightness of the emitted light is clear, and it is easy to determine the degree of the load applied to the object.

Solvents include aliphatic hydrocarbons, aromatic hydrocarbons (C7-10, e.g., toluene, xylene, and ethylbenzene), esters or ether esters (C4-10, e.g., methoxybutyl acetate), ethers (C4-10, e.g., tetrahydrofuran, monoethyl ether of EG, monobutyl ether of EG, monomethyl ether of PG, and monoethyl ether of DEG), ketones (C3-10, e.g., methyl isobutyl ketone, di-n-butyl ketone), alcohols (C1-10, e.g., methanol, ethanol, n- and i-propanol, n-, i-, sec-, and t-butanol, 2-ethylhexyl alcohol), amides (C3-6, e.g., dimethylformamide, dimethylacetamide, N-methylpyrrolidone, etc.), sulfoxides (C2-4, e.g., dimethylsulfoxide), and mixed solvents of two or more of these, water, or the above-mentioned mixed solvents.

The stress-luminescent coating composition may contain dispersants, fillers, thickeners, leveling agents, curing agents, crosslinking agents, pigments, defoamers, antioxidants, light stabilizers including ultraviolet absorbers, flame retardants, curing catalysts, and bactericides, such as those described in JP 2017-044634 A.

The proportion of particles of the stress-luminescent material in 100% by mass of the stress-luminescent coating composition (after drying) is preferably 40 to 95% by mass. With such a proportion, the degree of luminescence can be more fully confirmed when used in the method of calculating the applied load of the present invention. More preferably, it is 50 to 90% by mass.

In the method for calculating the applied load of the present invention, a stress-luminescent kneaded resin composition in which a stress-luminescent material is kneaded into a resin can also be used. In this case, the resin can be a polyolefin such as polyethylene or polypropylene, a polyacrylic resin, a urethane resin, a styrene resin, an acrylonitrile styrene, an acrylonitrile-butadiene-styrene copolymer, a polyamide resin, a polyimide resin, an epoxy resin, an acrylonitrile styrene, a polyvinyl chloride, a polyvinylidene fluoride, a polyacetal, a polycarbonate, a phenolic resin, a urea resin, a melamine resin, an alkyd resin, a silicone resin, a fluororesin, a polyester resin, an unsaturated polyester, a furan resin, nitrocellulose, a cellulose propionate, an ethyl cellulose, a polymethylpentene, a polyphenylene ether, an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, or a polyphenylene oxide. In order to confirm the stress-luminescence, a transparent resin is preferable, and the ratio of particles of the stress-luminescent material in a sample of 100% by mass of the stress-luminescent kneaded resin composition is preferably 1 to 50% by mass. With such a ratio, the degree of luminescence can be confirmed more sufficiently when used in the calculation method of the applied load of the present invention. More preferably, it is 3 to 30 mass%.

The above-mentioned stress-luminescent kneaded resin composition may contain additives such as dispersants, thickeners, surface conditioners or leveling agents, curing agents, crosslinking agents, defoamers, antioxidants, light stabilizers including ultraviolet absorbers, flame retardants, curing catalysts, bactericides, and adhesion promoters, as necessary.
Specific examples of these additives include those described in JP-A-2017-165947.

The method for calculating applied loads of the present invention is a method that can easily calculate the loads applied to an object, and can be used for a variety of objects, including structures such as buildings, viaducts, bridges, roads, railway rails, pillars, towers, pipelines, and tunnels; building materials such as flooring, tiles, wall materials, block materials, paving materials, wood, steel, and concrete; power transmission components such as gears and cams; exterior and internal parts (engine parts, tires, belts, etc.) used in bicycles, automobiles, trains, ships, airplanes, etc., bearing parts, bearing retainers, and fastening parts such as bearings with optical sensors, screws, bolts, nuts, and washers; and natural objects such as trees and rocks.

Specific examples are given below to explain the present invention in detail, but the present invention is not limited to these examples. Unless otherwise specified, "%" and "wt%" mean "weight % (mass %)."

(Production Example 1)
Preparation of Stress-Stimulated Luminescent Material 1 Rare earth-activated strontium aluminate represented by SrAl ₂ O ₄ :Eu was prepared as the stress-stimulated luminescent material. This was mixed with polymethyl methacrylate resin at a weight ratio of 8%, and molded into pellets of 25 mm in diameter and 10 mm in thickness using a hot embedding device (manufactured by Marumoto Struers). The pellets were then cut to prepare stress-stimulated luminescent material 1 of a specified shape (prepared in accordance with the method for determining the compression characteristics of plastics specified in JIS K 7181:2011, in the shape of a B-type test piece measuring 10 mm in length x 10 mm in width x 4 mm in thickness).

Example 1
A calibration process for confirming the relationship between the magnitude of a load (pre-applied load) previously applied to a test object on which a stress-stimulated luminescent material was placed and the degree of luminescence when a dynamic load was applied to the test object was carried out using the stress-stimulated luminescent material 1 produced in Production Example 1, with a load in the compressive direction as the target.
In addition, from the viewpoint of improving the accuracy of calculation of the applied load, in this calibration process, three pellets (pellets A1, B1, and C1) are used to confirm the degree of luminescence under the same loading conditions, and the results are averaged.

The acrylic resin pellets mixed with the stress-luminescent material were placed in a micro strength evaluation tester (Shimadzu Micro Autograph MST-I type-HR) in a dark room, a pre-applied load was applied, and the pellets were irradiated with 365 nm ultraviolet light for one minute. After waiting for one minute, a compressive load was applied in accordance with the method for determining compressive properties of plastics specified in JIS K 7181:2011 to measure the changes over time in the luminescence intensity and axial deformation of the stress-luminescent pellets. In order to improve the accuracy of the calculations, compression tests were performed with applied loads of 10 N (load for holding the specimen), 100 N, 200 N, and 300 N, and the loading rates were changed to 20 mm/min, 10 mm/min, 5 mm/min, and 2 mm/min (converted to axial strain rates of 3.33% strain·s ^-1 , 1.67% strain·s ^-1 , 0.833% strain·s ^-1 , and 0.333% strain·s ^-1 ), and the luminescence intensity and axial deformation of the stress-induced luminescent pellets were measured over time.
The observation conditions for the luminescence behavior were as follows: a camera (manufactured by Black magic design) and a lens (manufactured by SIGMA, F value at time of shooting: 1.8), with a resolution of 6144 x 3456 pixels, ISO sensitivity of 6400, shooting speed of 50 fps, and shooting data of RGB 16 bit.
The average luminance value of the green component of each pixel on the observation surface (length 10 mm×width 10 mm) of the stress-stimulated luminescent pellet was used as an index of luminescence intensity (hereinafter, average luminescence intensity).
Figure 5 shows a graph plotting the load measurement value and the average luminescence intensity against the time axis when a load of 10 N was applied using pellet A1, and a photographed image showing the luminescence during the measurement. It can be clearly seen from Figure 5 that the luminescence brightness increases as the load applied to the structure increases and the axial strain (axial deformation) increases over time.
Figure 6 shows the relationship between the load (excluding the previously applied load) and the average emission intensity when pellet A1 is used and the previously applied load is 10N and the axial strain rate is set at the four types mentioned above, and also shows the regression line and correlation coefficient for each plot. (Equivalent to Figure 1) Figure 6 shows that there is a high correlation between the load and the average emission intensity at any axial strain rate, and that the emission intensity is higher for the same load as the axial strain rate is higher.
Figure 7 shows the relationship between the slope of the regression line in the load-average luminescence intensity relationship at a previously applied load of 10N (corresponding to α in Figure 1) and the axial strain rate, and also shows the regression line and correlation coefficient in this plot (corresponding to Figure 2). Figure 7 shows that there is a high correlation between the slope of the regression line in the load-average luminescence intensity relationship and the axial strain rate. Therefore, it is clear that the slope of the regression line in the load-average luminescence intensity relationship can be calculated according to the axial strain rate applied to the test object.

Based on the above relationship, the relationship between the load and average emission intensity at the previously applied loads ^of 10N, 100N, 200N, and 300N is shown in Figure 8, with the load-average emission intensity at the axial strain rate of 1.67% strain·s -1 shown as a representative example, and the regression line and correlation coefficient are also shown for each plot. From Figure 8, it can be seen that there is a high correlation between the load and the average emission intensity at all previously applied loads, and that the emission intensity is higher for the same applied load as the previously applied load is larger.
In Fig. 9, the relationship between the slope of the regression line in the relationship between the applied load and the average luminescence intensity at an axial strain rate of 1.67% strain·s ^- 1 in Fig. 8 and the previous load is plotted for three pellets, and the average value is graphed. From Fig. 9, it can be seen that the slope of the regression line in the relationship between the applied load and the average luminescence intensity tends to monotonically decrease as the previous load increases.
Figure 10 shows the relationship between the average slope of the regression line in the applied load-average luminescence intensity relationship in Figure 9 and the previously applied load for each axial strain rate. From Figure 9, it can be seen that the relationship between the average slope of the regression line in the applied load-average luminescence intensity relationship and the previously applied load monotonically decreases with an increase in axial strain rate. The calibration process was carried out by expressing the slope of the regression line in the load-average luminescence intensity relationship for the axial strain rate and the previously applied load as a function.
From the above, in the measurement step, the slope of the regression line in the relationship between load and average emission intensity is obtained at a predetermined axial strain rate (loading rate), and the previously applied load can be calculated by substituting the slope of the regression line in the relationship between the load and average emission intensity for the axial strain rate obtained in the calibration step and the previously applied load. An example of this series of steps is shown in Figure 11.

(Production Example 2)
Preparation of Stress-Stimulated Luminescent Material 2 Rare earth-activated strontium aluminate represented by SrAl ₂ O ₄ :Eu was prepared as the stress-stimulated luminescent material. This was mixed with polymethyl methacrylate resin at a weight ratio of 8%, and molded into pellets 50 mm in diameter and 2 mm in thickness using a hot embedding device (manufactured by Marumoto Struers). The pellets were then machined to prepare stress-stimulated luminescent material 2 of a specified shape (shape of 1BB type test specimens prepared in accordance with JIS K 7161-2:2014 Plastics - Determination of tensile properties - Part 2: Mold molding).

Example 2
In Example 1, the load direction was changed from the compressive direction to the tensile direction, and the stress-stimulated luminescent material 2 produced in Production Example 2 was used.
In addition, from the viewpoint of improving the accuracy of calculation of the applied load, in this calibration process, three pellets (pellets A2, B2, and C2) are similarly used to confirm the degree of luminescence under the same loading conditions, and the results are averaged.

The acrylic resin pellets (for tensile load) mixed with the mechanoluminescent material were placed in a micro strength evaluation tester (Shimadzu Corporation Micro Autograph MST-I Type-HR) in a dark room, and a pre-applied load was applied. The pellets were irradiated with 365 nm ultraviolet light for 1 minute and then allowed to stand for 30 seconds. After that, a tensile load was applied in accordance with JIS K 7161-1:2014, Plastics - Determination of tensile properties - Part 1: General rules, to measure the changes over time in the luminescence intensity and axial deformation of the mechanoluminescent pellets. In order to improve the accuracy of the calculations, tensile tests were performed with applied loads of 1 N (load for holding the specimen), 10 N, 20 N, and 30 N, and the loading rates were changed to 20 mm/min, 10 mm/min, 5 mm/min, and 2 mm/min (converted to axial strain rates of 3.33% strain·s ^-1 , 1.67% strain·s ^-1 , 0.833% strain·s ^-1 , and 0.333% strain·s ^-1 ), and the luminescence intensity and axial deformation of the stress-induced luminescent pellets were measured over time.
Taking into account the cross-sectional area of the pellets, the applied loads were 0.25 N/ ^mm2 , 2.5 N/ ^mm2 , 5.0 N/ ^mm2 , and 7.5 N/ ^mm2 , which were the same as those in the compression test of Example 1. The axial strain rate was also the same because the gauge length was 10 mm, the same as that of the pellets in the compression test.
The observation conditions for the luminescence behavior and the index representing the luminescence intensity were the same as those in Example 1. The load was used as the load index. The average luminescence intensity was the average value of the luminescence intensity at the position of the gauge length.
FIG. 12 shows a graph plotting the load measurements and average luminescence intensity against time when a load of 1 N was applied using pellet A2, and also shows photographed images showing the luminescence during the measurement.

From the obtained measurement results, a calibration process was performed by creating a graph ( FIG. 13 ) showing the relationship between the average slope of the regression line in the applied load-average luminescence intensity relationship and the applied load for each axial strain rate, which corresponds to FIG. 10 in Example 1, using the same procedure as in Example 1.
Thereafter, in the same manner as in Example 1, in the measurement process, the slope of the regression line in the load-average luminescence intensity relationship at a predetermined axial strain rate is obtained, and the previously applied load can be calculated by substituting the slope of the regression line in the load-average luminescence intensity relationship for the axial strain rate obtained in the calibration process and the previously applied load.

Claims (9)

A method for calculating a load already applied to an object at the time of measurement using a stress-luminescent material, comprising:
The calculation method includes a calibration step of applying a dynamic load to a test object to which a stress-stimulated luminescent material is placed and to which a predetermined applied load is applied, and confirming a relationship between the degree of luminescence in response to the dynamic load and the predetermined applied load applied to the test object;
a measuring step of applying a dynamic load to the measurement object on which the mechanoluminescent material is placed and measuring the degree of luminescence in response to the dynamic load;
a step of calculating a pre-applied load that is already applied to the object to be measured at the time of measurement from the relationship between the degree of light emission in response to the dynamic load obtained in the calibration step and a predetermined pre-applied load applied to the test object, and from the degree of light emission in response to the dynamic load measured in the measurement step. The method for calculating the applied load according to claim 1, characterized in that the stress-stimulated luminescent material is placed in the object or by applying a stress-stimulated luminescent paint composition to the surface of the object. The method for calculating the applied load according to claim 1, characterized in that the stress-luminescent material is installed by installing a piece of stress-luminescent material having a stress-luminescent material or a stress-luminescent paint composition installed inside or on the surface of the object. A method for calculating a pre-applied load according to any one of claims 1 to 3, characterized in that the pre-applied load already applied to the object to be measured at the time of measurement is a compressive load, a tensile load, a torsional load or a shear load. The method for calculating the applied load according to claim 1, characterized in that the dynamic load in the calibration process and the dynamic load in the measurement process are either a compressive load, a tensile load, a torsional load or a shear load. The method for calculating the applied load according to claim 5, characterized in that the characteristic quantity of the dynamic load in the measurement process is the same as or different from the characteristic quantity of the dynamic load in the calibration process. A method for confirming the relationship between a load already applied to an object in which a stress-stimulated luminescent material is installed and a degree of luminescence in response to a dynamic load, comprising:
This method is a method for confirming the relationship between a previously applied load and luminescence, characterized in that a dynamic load is applied to an object to which a stress-luminescent material is installed and a previously applied load is applied, and the degree of luminescence in response to the dynamic load is confirmed. The method for confirming the relationship between applied load and luminescence described in claim 7, characterized in that the applied load applied to the object in which the stress-luminescent material is installed is a compressive load, a tensile load, a torsional load, or a shear load. The method for confirming the relationship between a previously applied load and luminescence described in claim 7, characterized in that the dynamic load applied to the object to which the previously applied load has been applied is a compressive load, a tensile load, a torsional load or a shear load.

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