JP7804985B2 - Stress recording material, stress recording structure, stress recording method, stress recording system, and method of use as a stress recording material - Google Patents

Description

The present invention relates to a stress recording material, a stress recording structure , a stress recording method , a stress recording system and a method of use as a stress recording material .

Conventionally, mechanoluminescent materials have been known as materials that emit luminescence correlated with the energy of a mechanical stimulus.

Mechanoluminescent materials with these properties are being applied in a wide variety of fields, including sensors, non-destructive testing, visualization of stress distribution, stress sensing, and detection of abnormalities and dangers in structures.

Stress-luminescent materials can be made into paint or dispersed in a resin sheet, which can then be applied or stuck to the surface of the object being measured to form a detection area, making it possible to observe the stress applied to this detection area.

However, because mechanoluminescent materials emit light the moment stress is applied, it is possible to observe the moment stress is applied, i.e., to know in real time that stress has been applied, but it is not possible to know after the fact.

In order to enable the applied stress to be known after the fact, a stress recorder has been proposed that combines a mechanoluminescent material with a photoreactive functional material such as a photosensitive material (see, for example, Patent Document 1).

With this type of stress recording system, the applied stress can be determined after the fact by examining the presence or absence of photosensitive traces from mechanoluminescent light recorded on the photoreactive functional material and the intensity of the photosensitive traces.

JP 2017-053679 A

However, stress recording media combined with the above-mentioned conventional photoreactive functional materials have a complex structure and are not satisfactory in terms of the dark reaction of the photoreactive layer, quantitativeness, and long-term record retention.

The present invention was made in consideration of these circumstances, and provides a stress recording material that is not affected by dark reactions due to chemical reactions, has excellent quantitative properties and long-term record retention, and allows the application of stress to be determined after the fact simply by observing the afterglow.

The present invention also provides a stress recording structure, stress recording body, stress recording body forming agent, stress recording coating film forming paint, stress recording method, and stress recording system using the above stress recording material.

In order to solve the above-mentioned conventional problems, one embodiment of the stress recording material according to the present invention is (1) a composition represented by the general formula Li _x Na _y NbO _{3+(x+y-1)/2+Σ(zk*Lk/2)} : M1 _z1 , M2 _z2 , M3 _z3 (where M1 is any one metal ion selected from rare earth ions and transition metal ions, M2 or M3 is none or any one metal ion selected from rare earth ions and transition metal ions, zk is a generalized expression of z1 to z3, Lk is a generalized expression of the valence L1 of the ion M1, the valence L2 of the ion M2, and the valence L3 of the ion M3, and when M2 is none, z2 is 0, and when M3 is none, z3 is 0), wherein x=0.02 to 2, y=0.01 to 1, and z1+z2+z3=0.0001 to 0.2 , By placing the material in a recordable area formed in a predetermined region of the object to be measured, it is possible to know after the fact information about the stress that the object to be measured has received by irradiating the recordable area with readout light of a wavelength of 200-480 nm and observing the difference between the afterglow observed before the application of stress, which has a peak in the 500-1100 nm band, and the afterglow observed after the application of stress, which has a peak in the 500-1100 nm band that changes depending on the past load history of the object to be measured.Furthermore, the stress recording material for emitting afterglow can erase the recorded traces of stress by irradiating reset light of approximately the same wavelength as the readout light and 100 to 1000 times the intensity of the readout light .
(2) A stress recording material having a composition represented by the general formula Li _x Na _y NbO _{3+ (x+y-1)/2 + Σ(zk*Lk/2)} : M1 _z1 , M2 _z2 , M3 _z3 (where M1 is any one metal ion selected from rare earth ions and transition metal ions, M2 or M3 is none or any one metal ion selected from rare earth ions and transition metal ions, zk is a generalized expression of z1 to z3, Lk is a generalized expression of the valence L1 of the ion M1, the valence L2 of the ion M2, and the valence L3 of the ion M3, and when M2 is none, z2 is 0, and when M3 is none, z3 is 0), where x=0.02 to 2, y=0.01 to 1, and z1+z2+z3=0.0001 to 0.2 (wherein, in the general formula Li _(1-P)(1+α) NaPNbO3 : _{QR (} where Q is at least one metal ion selected from transition metal ions), excluding materials _where the value of P is in the range of 0.10 to 0.98, the value of R is in the range of 0.0001 to 0.2, and α is in the range of 0 or more) .

Furthermore, one aspect of the stress recording structure according to the present invention is ( 3 ) a recordable area formed as a coating layer or sheet layer in a predetermined area of an object to be measured, in which powder of a stress recording material is dispersed in a light-transmitting resin matrix , and the recordable area is configured so that after the stress is applied, an afterglow appears due to the irradiated readout light, making it possible to know after the fact that stress has been applied to the object to be measured .

Furthermore, one aspect of the stress recording system according to the present invention is ( 4 ) a stress recording system including: a recordable area for stress formed in a measurement object; a readout light irradiating unit that irradiates the recordable area with excitation light for afterglow emission; an afterglow intensity acquiring unit that acquires information on the afterglow intensity of the recordable area; and an afterglow intensity reporting unit that reports the information on the afterglow intensity, wherein the recordable area is represented by a general formula Li _x Na _y NbO _{3+ (x+y-1)/2 + Σ(zk*Lk/2)} : M1 _z1 , M2 _z2 , M3 _z3 (wherein M1 is any one kind of metal ion selected from rare earth ions and transition metal ions, M2 or M3 is none or any one kind of metal ion selected from rare earth ions and transition metal ions, zk is a generalized expression of z1 to z3, Lk is a generalized expression of the valence L1 of the M1 ion, the valence L2 of the M2 ion, and the valence L3 of the M3 ion, and when M2 is none, z2 is 0, and when M3 is none, z3 is 0), and x = 0.02 to 2, y = 0.01 to 1, and z1 + z2 + z3 = 0.0001 to 0.2 is present in a predetermined region of the measurement object, and the stress recording system is formed by placing a stress recording material having a composition represented by the formula: (wherein M1 is any one kind of metal ion selected from rare earth ions and transition metal ions, M2 or M3 is none or any one kind of metal ion selected from rare earth ions and transition metal ions, zk is a generalized expression of z1 to z3, Lk is a generalized expression of the valence L1 of the M1 ion, the valence L2 of the M2 ion, and the valence L3 of the M3 ion, and when M2 is none, z2 is 0, and when M3 is none, z3 is 0), and the stress recording material has a composition represented by the formula :

In addition, as an optional aspect of the stress recording system according to the present invention, it is also characterized in the following respects.
( 5 ) The recording device is provided with a memory unit that stores information on the afterglow intensity of the measurement object in the recordable area before it is subjected to stress and information on the afterglow intensity of the measurement object after it is subjected to stress, which information is obtained from the afterglow intensity acquisition unit, and a difference information generation unit that generates information on the difference between the information on the afterglow intensity of the measurement object before it is subjected to stress and the information on the afterglow intensity of the measurement object after it is subjected to stress, and the afterglow intensity notification unit is capable of notifying the information on the difference.
( 6 ) The memory unit is capable of storing information on the difference, and the afterglow intensity notification unit is capable of notifying information on the difference or predetermined afterglow intensity stored in the memory unit.
( 7 ) The information on the afterglow intensity is image information on the afterglow.
One embodiment of the method of use as a stress recording material is (8) a compound of the general formula Li _x Na _y NbO _{3+(x+y-1)/2+Σ(zk*Lk/2)} : M1 _z1 , M2 _z2 , M3 _z3 (where M1 is any one metal ion selected from rare earth ions and transition metal ions, M2 or M3 is none or any one metal ion selected from rare earth ions and transition metal ions, zk is a generalized expression of z1 to z3, Lk is a generalized expression of the valence L1 of the ion of M1, the valence L2 of the ion of M2, and the valence L3 of the ion of M3, and when M2 is none, z2 is 0, and when M3 is none, z3 is 0.) where x = 0.02 to 2, y = 0.01 to 1, and z1 + z2 + z3 = 0.0001 to 0.2 is placed in a recordable area formed in a predetermined area of an object to be measured, and the material is used as a stress recording material for emitting afterglow, which allows information about the stress received by the object to be measured to be known after the fact based on the difference between an afterglow image before stress application and an afterglow image after stress application, observed by irradiating the recordable area with readout light of a predetermined wavelength.

The stress recording material according to the present invention has a composition represented by the general formula Li _x Na _y NbO _{3+ (x+y-1)/2 + Σ(zk*Lk/2)} : M1 _z1 , M2 _z2 , M3 _z3 (wherein M1 is any one metal ion selected from rare earth ions and transition metal ions, M2 or M3 is none or any one metal ion selected from rare earth ions and transition metal ions, zk is a generalized expression of z1 to z3, Lk is a generalized expression of the valence L1 of the ion M1, the valence L2 of the ion M2, and the valence L3 of the ion M3, and when M2 is none, z2 is 0, and when M3 is none, z3 is 0), wherein x=0.02 to 2, y=0.01 to 1, and z1+z2+z3=0.0001 to 0.2 , and the object to be measured By irradiating the recordable area with readout light of wavelength 200-480 nm, the recordable area is observed to have an afterglow having a peak in the 500-1100 nm band before the stress is applied, and by observing the difference between the afterglow having a peak in the 500-1100 nm band after the stress is applied and the afterglow having a peak in the 500-1100 nm band that changes depending on the past load history of the measurement object, it is possible to know after the fact information on the stress that the measurement object has received. Moreover, the recorded trace of stress can be erased by irradiating reset light of approximately the same wavelength as the readout light and 100 to 1000 times the intensity of the readout light. A stress recording material having a composition represented by _x Na _y NbO _{3+ (x+y-1)/2 + Σ(zk*Lk/2)} : M1 _z1 , M2 _z2 , M3 _z3 (wherein M1 is any one metal ion selected from rare earth ions and transition metal ions, M2 or M3 is none or any one metal ion selected from rare earth ions and transition metal ions, zk is a generalized expression of z1 to z3, Lk is a generalized expression of the valence L1 of the ion M1, the valence L2 of the ion M2, and the valence L3 of the ion M3, and when M2 is none, z2 is 0, and when M3 is none, z3 is 0), where x=0.02 to 2, y=0.01 to 1, and z1+z2+z3=0.0001 to 0.2 (wherein the general formula is Li _(1-P)(1+α) Na _P NbO ₃ : Q _R (where Q is at least one metal ion selected from transition metal ions), excluding materials where the value of P is in the range of 0.10 to 0.98, the value of R is in the range of 0.0001 to 0.2, and α is in the range of 0 or more.) This makes it possible to provide a stress recording material that is not affected by dark reactions due to chemical reactions, has excellent quantitative properties and long-term record retention, and allows the application of stress to be known after the fact simply by observing the afterglow.

Furthermore, the stress recording structure of the present invention has a recordable area formed as a coating layer or sheet layer in which powder of a stress recording material is dispersed in a light-transmitting resin matrix in a predetermined area of the object to be measured, and the recordable area is configured so that after stress is applied, an afterglow is generated by irradiating a readout light, making it possible to know retrospectively that stress has been applied to the object to be measured.Therefore , it is not affected by dark reactions due to chemical reactions, and has excellent quantitativeness and long-term record retention properties, and a stress recording structure can be provided that allows the application of stress to be known retrospectively simply by observing the afterglow.

Furthermore, a stress recording system according to the present invention includes a recordable area for stress formed in a measurement object, a readout light irradiation unit that irradiates the recordable area with excitation light for afterglow emission, an afterglow intensity acquisition unit that acquires information on the afterglow intensity of the recordable area, and an afterglow intensity notification unit that notifies the information on the afterglow intensity, wherein the recordable area is a compound represented by the general formula Li _x Na _y NbO _{3+ (x+y-1)/2 + Σ(zk*Lk/2)} : M1 _z1 , M2 _z2 , M3 _z3 (wherein M1 is any one metal ion selected from rare earth ions and transition metal ions, M2 or M3 is none or any one metal ion selected from rare earth ions and transition metal ions, zk is a generalized expression of z1 to z3, Lk is a generalized expression of the valence L1 of the ion of M1, the valence L2 of the ion of M2, and the valence L3 of the ion of M3, and when M2 is none, z2 is 0, and when M3 is none, z3 is 0), and x=0.02 to 2. The stress recording system is formed by placing a stress recording material in a predetermined region of the object to be measured , where y=0.01 to 1 and z1+z2+z3=0.0001 to 0.2, and the stress recording material is provided with a reset light irradiation unit that irradiates the recordable region with high-intensity reset light at approximately the same wavelength as the excitation light for the afterglow emission. This makes it possible to provide a stress recording system that is not affected by dark reactions due to chemical reactions, has excellent quantitativeness and long-term record retention, and allows the application of stress to be known after the fact simply by observing the afterglow.

The recording device also includes a storage unit that stores information on the afterglow intensity of the object to be measured in the recordable area before it is subjected to stress, which information is obtained from the afterglow intensity acquisition unit, and information on the afterglow intensity of the object to be measured after it is subjected to stress; and a difference information generation unit that generates information on the difference between the information on the afterglow intensity of the object to be measured before it is subjected to stress and the information on the afterglow intensity of the object to be measured after it is subjected to stress. If the afterglow intensity notification unit is capable of reporting this difference information, it can remove noise and background that exist both before and after the application of stress and obtain information on the afterglow intensity that occurs in response to the stress.

Furthermore, if the memory unit is capable of storing information about the difference, and the afterglow intensity notification unit is capable of reporting information about the difference or predetermined afterglow intensity stored in the memory unit, it is possible to store and display the history of stress exposure.

Furthermore, if the afterglow intensity information is image information of the afterglow, the afterglow intensity information can be notified in a manner that is easy to view.

Furthermore, by providing a reset light irradiation unit that irradiates the recordable area with high-intensity reset light of approximately the same wavelength as the excitation light for the afterglow emission, it is possible to erase the recorded traces of stress.

FIG. 2 is an explanatory diagram showing an SEM image of the stress recording material according to the embodiment. FIG. 2 is an explanatory diagram showing the appearance of the prepared stress recording pellet. FIG. 2 is an explanatory diagram showing the configuration of a test device. FIG. 10 is an explanatory diagram showing a test situation. FIG. 2 is an explanatory diagram showing the state of stress-luminescence emitted from a stress-recording pellet. FIG. 10 is an explanatory diagram showing the state of afterglow emitted by a stress recording pellet. FIG. 10 is an explanatory diagram showing the results of an FEM analysis. 1 is a graph showing the relationship between stress distribution and stress recording distribution intensity. 1 is a graph showing the long-term retention of stress records. FIG. 10 is an explanatory diagram showing the relationship between the number of weightings and MR. FIG. 10 is an explanatory diagram of stress recording intensity under maximum load. FIG. 1 is an explanatory diagram of an experiment to examine the spatial resolution of stress history. FIG. 10 is an explanatory diagram showing the results of an experiment examining the spatial resolution of stress history. FIG. 10 is an explanatory diagram showing the results of line distribution analysis.

The present invention provides a stress recording material that can record applied stress. In particular, it is not affected by dark reactions due to chemical reactions, has excellent quantitative properties and long-term record retention, and allows the application of stress to be known after the fact simply by observing the afterglow.

As mentioned above, there have been several stress recording methods in the past that allow the applied stress to be known after the fact.

Specific examples include stress recorders that combine a mechanoluminescent material with a photoreactive functional material, as in Patent Document 1, as well as devices that apply writing pressure to silicone gel with stress recording properties, allowing the stress record to be obtained (hereinafter also referred to as readout) using a thermoluminescence camera (Zhuang et al. Light: Science & Applications 9:182 (2020)). Other devices also include microcapsules containing a specific core substance as a stress detection means, which are scattered on a coating or resin sheet formed on the surface of the measurement object, allowing the stress record to be obtained by observing the core substance released from the microcapsules that are crushed by the application of stress.

However, stress recording means using the above-mentioned silicone gel require heating to read data, so reading is not possible at room temperature. Furthermore, stress recording means using microcapsules cannot be reused by their nature, as the destruction of the microcapsules is irreversible.

In this regard, the stress recording material according to this embodiment allows for the recording (traces) of applied stress to be read at room temperature (hereinafter also referred to as room temperature readout), and also allows for repeated recording and reading (hereinafter also referred to as repeated recording and reading). Furthermore, by using this as a means of detecting stress, it is possible to realize a stress recording structure, stress recording body, stress recording body forming agent, stress recording coating film forming paint, stress recording method, and stress recording system that are capable of room temperature readout and repeated recording and reading.

It should also be noted that previous mechanoluminescent materials were not capable of reading out recorded stress through afterglow. In other words, previous mechanoluminescent materials possessed mechanoluminescence (ML) properties and could only measure mechanical information in real time, requiring a separate recording means and the construction of a complex stress recording system. Furthermore, in addition to their complex structure, there were issues with the dark reaction of the photoreactive layer, as well as issues with stability, quantitation, and long-term record retention. Furthermore, the readout system required heating, making the system cumbersome. This is because previous mechanoluminescent materials themselves were not capable of recording applied stress.

In contrast, this application provides a material that can quantitatively record stress history and easily read and display it simply by observing the afterglow after irradiation with readout light of a specified wavelength. In other words, it can be said that this application provides a material with stress recording (mechanical recording, MR) and stress history display (mechanical report) functions, and a stress recording material that can record the applied stress itself.

This invention was completed after the inventors discovered that LiNaNbO ₃ (LNNO) can exhibit a new stress recording (mechanical recording, MR) function, i.e., a material that can record and read out past load application information and stress history at any time using light. In addition, this invention is based on the new discovery of stress recording, that is, it is possible to read out stress records (MR) that correlate with luminescence intensity using only afterglow.

In particular, whereas previous mechanoluminescent materials could only measure mechanical information in real time, mechanoluminescent materials with MR functionality are extremely useful in that they can not only measure in real time, but also extract information on past load application and the history of stress distribution.

The specific experiments and results will be described later, but as a multi-piezo element, LiNaNbO ₃ (LNNO) powder was synthesized using a solid-phase method, and this synthesized powder was mixed with epoxy resin. The resin pellets created were also used to evaluate the ML/MR characteristics using a material testing machine and a camera system with LED illumination, and the MR function was evaluated using optical readout images (afterglow images) after light irradiation before and after stress application.

As a result, when a load was applied, a luminescence image proportional to the dynamic stress distribution was displayed. After the load was applied, the mechanoluminescence disappeared, but by irradiating it with an LED and observing the afterglow image, it was possible to read out the record of the applied stress. Comparing the MR images before and after the load test, it was found that the recorded image was proportional to the history of the stress distribution.

In this way, previous mechanoluminescent materials showed no difference in afterglow before and after stress history, making it impossible to read out the recorded stress history using afterglow. However, with the present invention, stress history can be quantitatively recorded and read out simply by observing the afterglow after LED irradiation. MR can also record and read out past load application information and stress history at any time using light. It can be said to be a new principle and material with a non-volatile memory function that has never been seen before, and is highly stable and retains data, allowing for long-term recording without the need for electrical or thermal energy. It also excels in quantitatively recording stress distribution. Furthermore, mechanoluminescent materials with MR functionality can not only measure in real time, but also extract past load application information and stress distribution history.

The stress recording material according to this embodiment can be said to be a lithium sodium niobium composite oxide to which one or more types of metal ions are added, and is characterized by the general formula Li _x Na _y NbO _{3+ (x+y-1)/2 + Σ(zk*Lk/2)} : M1 _z1 , M2 _z2 , M3 _z3 (wherein M1 is any one metal ion selected from rare earth ions and transition metal ions; M2 or M3 is none or any one metal ion selected from rare earth ions and transition metal ions; zk is a generalized expression of z1 to z3; Lk is a generalized expression of the valence L1 of the M1 ion, the valence L2 of the M2 ion, and the valence L3 of the M3 ion; when M2 is none, z2 is 0; and when M3 is none, z3 is 0), and x = 0.02 to 2, preferably x = 0.1 to 0.9; y = 0.01 to 1, preferably y = 0.1 to 0.95; and z1 + z2 + z3 = 0.0001 to 0.2, preferably z1 + z2 + z3 = 0.0001 to 0.1.

Here, rare earth ions refer to ions of rare earths (rare earth metal elements), and can be understood as ions of, for example, Sc (scandium), Y (yttrium), La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), and Lu (lutetium).

Transition metal ions are ions of transition metal elements, and can be understood as ions of transition metal elements that exist between Group 3 and Group 11 elements.

By placing such a stress recording material in a specified area of an object, it becomes possible to know after the fact that stress has been applied to that area. In other words, the stress recording material of this embodiment can be said to be a material that, by placing it in a specified area of an object, makes it possible to know after the fact that stress has been applied to that area.

Here, "presence in a predetermined region" means that the stress recording material is present in a predetermined region of the object in a state where stress applied to the object can be transmitted, and there are no particular limitations on how it is present. For example, a coating containing the stress recording material may be formed on the surface of the object, or a stress-luminescent material may be distributed over all or part of the object. There are no limitations on how it is present, and it can be applied, sprayed, mixed, or otherwise.

Furthermore, to aid in understanding the stress recording material according to this embodiment, an example of how the stress recording material can be used will be further explained. The object in which the stress recording material is placed is not particularly limited as long as it is an object for measuring the applied stress, and may be, for example, a structure such as a vehicle or furniture, a building such as a tunnel or bridge, or even an instrument applied to a living body such as a bone, tooth, or implant.

Furthermore, the predetermined area of an object in which the stress recording material is present is not particularly limited, and may be the entire object or only a portion of the object. In the following description, the predetermined area of an object in which the stress recording material is present is also referred to as the recordable area (of stress).

The recordable area may be a dot-like, linear, or planar area, or it may be a three-dimensional area.

Although it is difficult to read the recorded stress distribution in a point-like recordable area, it is useful because it is possible to read the recorded presence or absence of stress. Note that point-like here does not, of course, mean a point in the strict sense, which has no area or volume, but rather something roughly like a dot; the same applies to the line-like shape described below.

It is also useful for linear areas, as it allows recording of whether or not stress is applied, and reading out records of stress propagation in the linear direction.

A planar area is not limited to the surface of an object, but can also be a surface in the direction of cutting the object. Furthermore, a surface is not limited to a flat surface, but can also be a curved surface, and can be continuous or discontinuous. Note that planar refers to an area that is realistically treated as a curved or flat surface, such as an uneven surface of an object, as well as a coating, sheet, or film, and is not limited to being strictly two-dimensional.

The three-dimensional region may be a three-dimensional region having a portion exposed on the surface of the object, or the entire recordable region may be formed within the object. However, to facilitate readout, it is desirable that the recordable region and object be configured so that at least the portion of the recordable region where stress recording is to be observed can be irradiated with readout light from the readout light irradiating unit described below, and that information on the afterglow intensity can be acquired by the afterglow intensity acquiring unit. In simpler terms, it is desirable that the recordable region and object be configured to be sufficiently transparent to the readout light and afterglow (enough to allow excitation for afterglow emission and to enable reading).

Furthermore, the recordable area may be located in only one place on the object, or in multiple places.

In this way, the present application can be said to provide a stress recording structure that is characterized by having a recordable area in a predetermined area of an object to be measured, where the stress recording material according to this embodiment is present, and is configured to enable subsequent detection of the application of stress to the recordable area.

The present application also provides a stress recording medium in which the stress recording material according to this embodiment is present, for example, dispersed, in a predetermined matrix material. For example, by using a curable resin as the matrix material and dispersing powdered stress recording material in the resin before hardening and then hardening it, a stress recording medium of the desired shape capable of recording applied stress can be easily formed. The matrix material used is one that is at least transmissive to the readout light used to induce afterglow emission from the stress recording material mixed in the matrix material, and the afterglow emitted from the stress recording material.

The present application also provides a stress recording medium forming agent that contains the stress recording material according to this embodiment in a liquid, viscous, or viscoelastic base, and that forms a stress recording medium by solidifying the base.

Here, a liquid base can be understood as, for example, paint, adhesive, or UV-curable resin before solidification, a viscous base as putty or clay, and a viscoelastic base as slime.

In addition, the solidification is not limited to a degree that allows the stress applied to the measurement object or recordable area to be transmitted to the stress recording material, and includes solidification reactions such as evaporation of the solvent (dispersion medium) or crosslinking.

In other words, in the example above, the matrix material with the stress recording material dispersed therein before solidification corresponds to the stress recording material forming agent according to this embodiment.

As a further specific embodiment of the stress recording material forming agent, the present application also provides a stress recording coating film forming paint that contains a stress recording material in a base paint. The manner in which the paint is used is not particularly limited, and it may be applied or sprayed.

Furthermore, with this type of stress-recording coating paint, a stress-recording coating can be formed on the surface of the object to be measured, making it easy to create a recordable area. This stress-recording coating can also be considered a stress recording medium.

The present application also provides a method for recording stress applied to a predetermined region of an object, in which the stress recording material according to this embodiment is present in the predetermined region; in other words, a predetermined region of an object in which it is desired to record the presence or absence and strength of stress is made a recordable region by having the stress recording material present.

In particular, in the case of the stress recording method according to this embodiment, if stress is applied multiple times, the record that is read out is an accumulated record of the repeatedly applied stress, which is useful for understanding the total amount of applied stress.

The present application also provides a stress recording system capable of recording and reading stress. The stress recording system according to this embodiment is characterized by including a recordable area, a readout light irradiation unit, an afterglow intensity acquisition unit, and an afterglow intensity notification unit.

As explained above, the recordable area is a predetermined area of the object to be measured in which the mechanoluminescent material according to this embodiment is present. In the stress recording system according to this embodiment, the recordable area may be a recordable area located in an environment where stress can be applied, or a recordable area located in an environment where stress cannot be applied. For example, when recording stress at a certain part of a bridge, even if the bridge is sound and there is no load on the recordable area, and no record of stress application is ultimately left behind, that is, even if the recordable area is located in an environment where stress cannot be applied, the stress recording system according to this embodiment is still useful in indicating the soundness of the bridge, and such an aspect is also included in the stress recording system according to this embodiment.

The read light irradiation unit is a part that irradiates the recordable area with excitation light for afterglow emission. The excitation light to be irradiated is not particularly limited as long as it has a wavelength and intensity that can cause the stress recording material present in the recordable area to emit afterglow, and the type of light source can be selected appropriately as long as it does not conflict with the purpose.

The afterglow intensity acquisition unit is a component that acquires information about the afterglow intensity of the recordable area. To cite a specific example, it can be configured with an imaging unit equipped with an image sensor and an afterglow intensity information generation unit that generates afterglow intensity information from the image signal obtained by the imaging unit. The imaging unit and afterglow intensity information generation unit may be integrated into one unit like an imaging camera, or the imaging unit may be configured specifically for generating image signals while the afterglow intensity information generation unit is configured with a specific circuit or computer capable of generating afterglow intensity information.

In a simpler example, for example, where the recordable area is in the form of a dot and it is only necessary to confirm the presence or absence of stress and its intensity, without needing to record the stress distribution, it is possible to configure it with a light-receiving element placed opposite the dot-shaped recordable area, and a specific circuit or computer that generates information on the afterglow intensity based on the signal generated by the received light. Of course, the image sensor or imaging unit of the imaging camera mentioned above, or the light-receiving element, etc., that can respond to afterglow wavelengths, should be used.

The afterglow intensity notification unit is a component for reporting information about the afterglow intensity acquired (generated) by the afterglow intensity acquisition unit. This reporting mode can be selected appropriately according to the situation, such as when it is sufficient to know only whether or not stress is being applied, as described above, when it is also desired to know the intensity of the stress, or even when it is desired to know the stress distribution.

In other words, if you only need to know whether or not stress is being applied, you can use any means that humans can perceive with their five senses, such as whether or not an LED is lit, whether or not there is sound, whether or not there is printing, or whether or not there is a display on a screen. If you also want to know the strength of stress in addition to whether or not it is being applied, you can use any means, such as the intensity of light or sound, the magnitude of the printed value, or differences in the values or colors displayed on a screen. If you also want to know the stress distribution, you can express it using differences in brightness or color on a displayed image, print it, or in some cases express it numerically.

This type of stress recording system is not affected by dark reactions caused by chemical reactions, has excellent quantitative properties and long-term record retention, and allows the application of stress to be determined after the fact simply by observing the afterglow.

The stress recording system according to this embodiment may further include a storage unit and a difference information generation unit, which may store data before and after the application of stress and generate and report the difference. If stress is applied multiple times, the system may store data before and after the application of the first stress (before the application of the second stress) and generate and report the difference, or may store data before and after the application of the second stress (before the application of the third stress) and generate and report the difference, and this process may be repeated. With this configuration, noise and background data present before and after the application of stress can be removed, making it possible to obtain information on the afterglow intensity that occurs in response to the stress.

The storage unit stores information about the afterglow intensity in the recordable area before and after the stress to be measured, both of which are obtained from the afterglow intensity acquisition unit. "Information about the afterglow intensity before the stress to be measured" refers to cases where stress is applied only once, as well as cases where stress is applied multiple times. If the stress to be measured is the first stress, this refers to information about the afterglow intensity before the first stress, i.e., information about the afterglow intensity in a state where no substantial stress (to be measured) has yet been applied since the irradiation of the reset light described below (hereinafter also referred to as the reset state). However, if the stress to be measured is applied a second time (when it is the second stress), this does not refer to information about the afterglow intensity in the reset state, but rather information about the afterglow intensity after the application of the first stress (before the application of the second stress). The same applies to "information about the afterglow intensity after the stress to be measured."

The storage unit is not particularly limited as long as it can store information on the afterglow intensity before and after the measurement target is subjected to stress in a format that allows the difference information generation unit, described below, to generate difference information. For example, any storage medium can be used, including RAM (Random Access Memory), EEPROM (Electrically Erasable Programmable Read-Only Memory), HDD (Hard Disk Drive), SSD (Solid State Drive), optical disk, or magnetic disk.

The difference information generation unit generates information on the difference between information on the afterglow intensity before the measurement target is subjected to stress and information on the afterglow intensity after the measurement target is subjected to stress. The difference information can be generated using a known method depending on the type of afterglow intensity information, such as by subtraction if the information is numerical, or by subtracting brightness information if the information is image information.

In a configuration further comprising such a memory unit and a difference information generation unit, if the afterglow intensity notification unit can report the difference information generated by the difference information generation unit, it will be possible to remove noise and background that exist before and after the application of stress, and provide information on the afterglow intensity that occurs in response to the stress.

Furthermore, the stress recording system according to this embodiment may be further configured so that the difference information generated by the difference information generation unit can be stored in the memory unit, and the afterglow intensity notification unit can be configured to notify the predetermined afterglow intensity information or difference information stored in the memory unit.

With this configuration, afterglow intensity information and difference information can be stored as a history, and information can be displayed from this history. In particular, when stress is applied multiple times, it becomes possible to refer to afterglow intensity information and difference information for a specific stress. If necessary, a search and extraction unit can be implemented by a program or the like to search for and extract desired information from the stored afterglow intensity information and difference information for stress.

Furthermore, as mentioned above, if the afterglow intensity information described above is image information of the afterglow, the afterglow intensity information can be reported in a manner that is easy to view.

Furthermore, the stress recording system according to this embodiment may be further configured to include a reset light irradiation unit that irradiates the recordable area with high-intensity reset light having approximately the same wavelength as the excitation light for afterglow emission.

One interesting feature of the stress recording material according to this embodiment is that the recorded stress traces can be erased by irradiating it with high-intensity light (reset light) at approximately the same wavelength as the excitation light used for afterglow. This makes it possible to reset the recordable area. The intensity of the reset light must be adjusted to suit various conditions, such as the composition of the stress recording material and the distance between the reset light irradiation area and the recordable area, but a rough guideline is approximately 100 to 1,000 times that of the read light.

The stress recording material, stress recording structure, stress recording body, stress recording body forming agent, stress recording coating film forming paint, stress recording method, and stress recording system according to this embodiment will be further described below with reference to the drawings.

1. Preparation of stress recording material
The stress recording material according to this embodiment, Li _0.35 Na _0.80 NbO _4.168 :Pr _0.01 , Nd _0.005 , Cr _0.003 , was prepared by a solid-state reaction method.

First, _Na2CO3 , _{Li2CO3 ,} and _Nb2O5 as _the raw materials for the base material _, and _Pr2O3 , _{Nd2O3 ,} and _Cr2O3 as metal ion supply compounds to be added to the base material were weighed according to the _above composition (based on a non-stoichiometric ratio) _, and then thoroughly mixed and crushed in an agate mortar.

Next, the crushed mixture was pre-fired in an electric furnace at 850°C in an air atmosphere for a predetermined time (for example, 3 to 10 hours, more specifically, 4 to 6 hours), and the pre-fired product was crushed.

The calcined and pulverized material was then sintered at 1100°C for a predetermined time (for example, 3 to 100 hours, more specifically, 20 hours) in an _O2 atmosphere (100% _O2 ), and the sintered material was pulverized. The sintered and pulverized material can be sintered and pulverized again (sometimes more than once) as needed to prepare a more stable stress recording material.

Next, the sintered and pulverized product that had undergone one or more sintering and pulverization steps was sized as necessary to obtain a powder sample of _{Li0.35Na0.80NbO3.102} : _Pr0.01 , _Nd0.005 , _Cr0.003 (hereinafter referred to as stress recording material A1) as the stress recording material according to this _embodiment . Figure 1 shows an SEM image of _the prepared stress recording material A1.

2. Creation of stress recorder
Next, a stress recording pellet B1 was prepared as a stress recording medium using the stress recording material A1.

0.5 g of stress recording material A1 was mixed with 4.5 g of epoxy resin as a base, and the epoxy resin was solidified to prepare stress recording material forming agent C1 for forming stress recording pellets B1.

Next, the stress recording material forming agent C1 was placed in a specified mold and allowed to solidify, creating a composite resin pellet (25 mm in diameter, 10 mm in thickness) called the stress recording pellet B1 of this embodiment. Figure 2 shows the created stress recording pellet B1. Note that this stress recording pellet B1 has a stress recordable area formed throughout its entirety, and the stress recording pellet B1 itself was used as the measurement object in the tests described below.

3. Construction of the test equipment
Next, a test device D was constructed to perform stress recording tests using the stress recording pellet B1. Figure 3 is a conceptual diagram showing the configuration of the constructed test device D.

As shown in Figure 3, the test device D includes a load tester 10, a light source unit 11, an imaging unit 12, and a computer 13.

The load testing machine 10 is a device for applying a predetermined stress to a stress recording pellet B1, which is the measurement object placed on the testing stage 10a. The load testing machine 10 is electrically connected to a computer 13 via a cable (not shown), enabling it to control the load and acquire various data.

The light source unit 11 is a component for irradiating the stress recording pellet B1, or more specifically, the recordable area E1 of the stress recording pellet B1, with excitation light and reset light for afterglow emission. The light source unit 11 is electrically connected to the computer 13, for example, via a communication cable 14 or other wired or wireless means, and is configured to emit excitation light and reset light by changing the intensity of the light emitted from the light source unit 11 under the control of the computer 13. In other words, the light source unit 11 functions as part of the read light irradiation unit and reset light irradiation unit in cooperation with the computer 13.

The imaging unit 12 is a component that captures the afterglow emitted from the stress recording pellet B1 (recordable area E1), and is equipped with an optical system for capturing the afterglow, an imaging element that electrically converts the light incident through the optical system, and an image information generation unit that generates image information based on the electrical signal from the imaging element.

The optical system is also directed toward the stress recording pellet B1 (recordable area E1) through the gap 11a of the light source unit 11. The imaging unit 12 is also electrically connected to the computer 13 via a communication cable 14, etc., making it possible to control the imaging unit 12 and obtain information. The imaging unit 12 must be sensitive to at least the afterglow emitted from the recordable area E1, but may also be configured to be sensitive to mechanoluminescence if necessary.

The computer 13 is a component that transmits and receives data between the load testing machine 10, light source unit 11, and imaging unit 12, performs control, acquires information, and displays information, and is composed of a computer main unit 13a and a display 13b.

The computer main unit 13a has a built-in CPU, ROM, RAM, etc., and is capable of performing the aforementioned control and acquiring and displaying information in accordance with a predetermined program. The computer main unit 13a also has a built-in HDD as a storage unit, which is capable of storing afterglow intensity information supplied from connected peripheral devices, such as information about the afterglow intensity before the stress to be measured is applied, information about the afterglow intensity after the stress to be measured is applied, and information about the difference between these (along with chronological information such as the date and time when the afterglow intensity was obtained and the date and time when the difference information was generated, as necessary). The difference information is generated by the CPU, etc., executing predetermined processing in accordance with a program to obtain the difference between the afterglow intensity information before the stress to be measured is applied and the afterglow intensity information after the stress to be measured is applied. In this embodiment, the afterglow intensity information and difference information are image information, but as mentioned above, this is not necessarily limited to this.

The computer main unit 13a is also configured so that the user can select the desired information from the afterglow intensity information and difference information stored in the memory unit via a specified input means such as a keyboard or mouse, allowing the information to be extracted along with time-series information as needed.

The display 13b is a component for displaying information on afterglow intensity and difference information, along with time-series information as needed. In this embodiment, the display is configured to display an image of the afterglow based on image information supplied from the imaging unit 12 or stored in the memory of the computer main unit 13a.

As such, the testing device D includes a stress recording system F1 according to this embodiment, which includes a stress recordable area E1 formed in the stress recording pellet B1, which is the measurement object; a readout light irradiation unit constituted by a computer 13 and a light source unit 11 for irradiating the recordable area E1 with excitation light for afterglow emission; an afterglow intensity acquisition unit constituted by a computer 13 and an imaging unit 12 for acquiring information on the afterglow intensity of the recordable area E1; and an afterglow intensity notification unit constituted by a computer 13 (particularly, a display 13b) for reporting the afterglow intensity information.

4. Verification of stress records
Next, stress recording was verified using the above-mentioned test device D. Specifically, as shown in Figure 4, the ML/MR characteristics were evaluated using a materials testing machine and a camera system with LED illumination. The MR function was also evaluated using optical readout images (afterglow images) taken after light irradiation before and after stress application. The wavelengths of the readout and reset lights were 200 to 480 nm, with the readout light irradiated at 0.1 to 3 mW/ ^cm² and the reset light irradiated at 100 to 1000 mW/ ^cm² .

As a result, applying a load produced a luminescence image proportional to the dynamic stress distribution, as shown in Figure 5. After the load was applied, the mechanoluminescence disappeared, but by irradiating the light source 11 with readout light and observing the afterglow image, the record of the stress history could be read out. Comparing the MR images before and after the load test, it can be seen that the recorded image is proportional to the history of the stress distribution. Figure 6(a) shows an image generated based on the afterglow intensity information (image information) before the measurement target was subjected to stress, and Figure 6(b) shows an image generated based on the difference between the afterglow intensity information before the measurement target was subjected to stress and the afterglow intensity information after the measurement target was subjected to stress.

In this way, it has been demonstrated that the stress recording material according to this embodiment is capable of recording stress. Furthermore, it has been demonstrated that the stress recording material, stress recording structure, stress recording body, stress recording method, and stress recording system according to this embodiment make it possible to know after the fact that stress has been applied simply by observing afterglow. Furthermore, it has been demonstrated that the stress recording body according to this embodiment is a stress recording body that can express the presence or absence of stress and its strength as differences in afterglow intensity. Furthermore, it has been demonstrated that the stress recording body forming agent according to this embodiment is a stress recording body forming agent that can form the stress recording body described above.

[5. Verification of stress distribution and MR strength distribution]
Next, we examined the stress distribution and MR intensity distribution. Figure 7 shows the results of FEM analysis. As can be seen from comparing Figures 5 and 7, the results of FEM analysis are in good agreement with the observed results of mechanoluminescence.

Furthermore, as can be seen by comparing Figure 6(b) and Figure 7, the MR intensity distribution shown in the stress recording image closely matches the stress distribution shown in the FEM analysis results.

Figure 8 is a graph showing the relationship between the stress distribution and the stress recording distribution intensity between the black arrows in Figure 6(b). Note that the stress recording distribution is shown in absolute values. As can be seen from Figure 8, the stress distribution and the MR intensity distribution are in good agreement.

These results demonstrate that the stress recording material, stress recording structure, stress recording body, stress recording body forming agent, stress recording coating film forming paint, stress recording method, and stress recording system according to this embodiment are capable of quantitatively recording and reading out stress, in particular, recording and reading out stress that corresponds to the stress distribution.

[6. Verification of long-term retention of stress records]
Next, we investigated how long the stress record could be maintained. As a result, as shown in Figure 9, it was shown that the stress record could be maintained for at least six months. This indicates that the stress recording material according to this embodiment can maintain the stress record for a long period of at least six months or more.

[7. Examination of the relationship between the number of weightings and MR]
Next, we investigated the relationship between the number of loads and MR. Specifically, as shown in Figure 10(a), we applied the same load to the stress-recording pellet B1 around its axis by 1 degree from 12 o'clock to 6 o'clock, 5 degrees from 10-11 o'clock to 4-5 o'clock, and 10 degrees from 9 o'clock to 3 o'clock, and measured the afterglow intensity, which is the difference from the intensity before and after the load.

Figure 10(b) shows the afterglow image after loading from three directions, and Figure 10(c) shows the afterglow recording intensity. As can be seen from Figures 10(b) and 10(c), it was shown that the cumulative stress has no effect on the MR intensity.

[8. Examination of stress record strength under maximum load]
Next, we investigated the stress recording intensity under maximum load. Specifically, to examine the relationship between load and MR intensity, loads of 500 N were applied from 1-2 o'clock to 7-8 o'clock, 750 N from 12 o'clock to 6 o'clock, and 1000 N from 9 o'clock to 3 o'clock, as shown in Figure 11(a), while moving the stress recording pellet B1 around its axis. MR intensity was evaluated from the afterglow images. The afterglow intensity after load application was defined as I, and the afterglow intensity before load application was defined as I0. The stress recording intensity (MRI) was calculated as MRI = |I - I0|.

Figure 11(b) shows the afterglow image after load application from three directions, and Figure 11(c) shows the calculated results of the afterglow recording intensity. As can be seen from Figures 11(b) and 11(c), an increase in MR intensity was confirmed as the load increased, demonstrating that MR is quantitative over a wide range.

Figure 11(d) is a graph showing the relationship between stress-induced luminescence intensity and stress-recording intensity. As shown by the dashed line in Figure 11(d), previous stress-induced luminescent materials exhibited luminescence in response to stress, but were unable to perform stress recording, and naturally no stress-recording intensity was observed. In contrast, it was confirmed that the stress-recording material A1 (stress-recording pellet B1) according to this embodiment exhibited stress-recording intensity that had an excellent correlation with stress-induced luminescence.

9. Consideration of the resolution of stress records
Next, using the stress recording pellet B1, we investigated how fine an area recording is possible, that is, the resolution of stress recording.

Figure 12 shows a load application jig and the experiment using it to examine the spatial resolution of stress history. Tests were conducted using various jigs shown in Figure 12(a), but here we will explain the test using jig 30, numbered 3 in Figure 12(a) (see Figure 12(b)), as a representative example.

As shown in Figure 12(c), the test was performed by placing the flat surface of the stress recording pellet B1 upside down, with the protrusion-forming surface 30a of the jig 30 facing the top surface 31a of the stress recording pellet B1, and applying a load from above the jig 30.

The MR images after load application are shown in Figures 13(a) and 13(b). Six cylindrical protrusions were molded on the jig 30, designated areas 1 to 6.

The MR image shown in Figure 13(b) confirms the record of stress history up to area 6. To examine spatial resolution, pixel size was calculated. Since the pellet diameter is constant, it was calculated from the proportion of the pellet in the MR image. Based on the calculation results, 3D surface analysis was performed centered on area 6.

The analysis results of the fitted surface are shown in Figure 13(c). The analysis results indicated that load application information of approximately 600 μm could be detected with high spatial resolution. The results of the line distribution analysis are shown in Figure 14.

In compression tests using a materials testing machine, it was discovered that it was possible to record the stress history of LNNO. Using this as a starting point, we attempted to examine the quantitativeness, strength, and resolution of MR. The strength of MR matched the stress distribution obtained from FEM analysis, and we were able to successfully read out the past history from the afterglow. Furthermore, experiments using a jig enabled us to read out the spatial distribution of the stress history record with a diameter of sub-mm, and in this study, we were able to observe the history at approximately 600 μm.

10. Other stress recording materials
So far, _we have _described the stress recording material A1 of this embodiment, i.e., _{Li0.35Na0.80NbO3.102} : _Pr0.01 , _Nd0.005 , _Cr0.003 , and the stress recording structure, stress recording body, stress recording body forming agent, stress recording method, and stress recording system using this material. However, the present invention is not limited to this composition. Therefore, here we will mention other stress recording materials.

Two stress recording materials A2 and A3 according to other embodiments were prepared using the same solid-state reaction method as described in [1. Preparation of Stress Recording Materials]. Stress recording material A2 has a composition of _{Li0.14Na0.89NbO3.017} : _Pr0.002 , and stress recording material A3 has _{a composition of Li0.21Na0.80NbO3.095} : _Nd0.05 , _{Cr0.01 .}

Furthermore, using the method described in [2. Preparation of stress recording medium], stress recording pellet B2 containing stress recording material A2 and stress recording pellet B3 containing stress recording material A3 were prepared.

Then, in the same manner as in [4. Verification of stress recording], it was confirmed whether stress recording was possible. In the test of stress-recorded pellet B2, the wavelengths of the read light and reset light were 250 to 400 nm, and the read light was irradiated at 0.1 to 1 mW/ ^cm2 and the reset light was irradiated at 100 to 500 mW/ ^cm2 . In the test of stress-recorded pellet B3, the wavelengths of the read light and reset light were 200 to 300 nm, and the read light was irradiated at 0.8 to 3 mW/ ^cm2 and the reset light was irradiated at 300 to 800 mW/ ^cm2 .

As a result, it was confirmed that stress could be recorded and read out in both stress recording pellets B2 and B3, just as it was in stress recording pellet B1. The afterglow of stress recording pellet B2 was red visible light centered at 605 nm and near-infrared light with a central wavelength of 1050 nm, while the afterglow of stress recording pellet B3 was green visible light centered at 500 nm and near-infrared light centered at 1100 nm.

As described above, the stress recording material according to this embodiment has the general formula Li _x Na _y NbO _{3+ (x+y-1)/2 + Σ(zk*Lk/2)} : M1 _z1 , M2 _z2 , M3 _z3 (wherein M1 is any one metal ion selected from rare earth ions and transition metal ions, M2 or M3 is none or any one metal ion selected from rare earth ions and transition metal ions, zk is a generalized expression for z1 to z3, Lk is a generalized expression for the valence L1 of the M1 ion, the valence L2 of the M2 ion, and the valence L3 of the M3 ion, and when M2 is none, z2 is 0, and when M3 is none, z3 is 0), and x = 0.02 to 2, y = 0.01 to 1, and z1 + z2 + z3 = 0.0001 to 0.2, it is possible to provide a stress recording material that is not affected by dark reactions due to chemical reactions, has excellent quantitative properties and long-term record retention, and allows the application of stress to be known after the fact simply by observing the afterglow.

Finally, the above-mentioned embodiments are merely examples of the present invention, and the present invention is not limited to the above-mentioned embodiments. Therefore, it goes without saying that various modifications can be made to the design, etc., even in the above-mentioned embodiments, as long as they do not deviate from the technical concept of the present invention.

REFERENCE SIGNS LIST 10 Load tester 11 Light source unit 12 Imaging unit 13 Computer 13a Computer main body 13b Display A1, A2, A3 Stress recording material B1, B2, B3 Stress recording pellet C1 Stress recording body forming agent D Test device E1 Recordable area F1 Stress recording system

Claims (8)

It has a composition represented by the general formula Li _x Na _y NbO _{3+ (x + y - 1)/2 + Σ (zk * Lk/2)} : M1 _z1 , M2 _z2 , M3 _z3 (wherein M1 is any one metal ion selected from rare earth ions and transition metal ions, M2 or M3 is none or any one metal ion selected from rare earth ions and transition metal ions, zk is a generalized expression of z1 to z3, Lk is a generalized expression of the valence L1 of the M1 ion, the valence L2 of the M2 ion, and the valence L3 of the M3 ion, and when M2 is none, z2 is 0, and when M3 is none, z3 is 0), x = 0.02 to 2, y = 0.01 to 1, and z1 + z2 + z3 = 0.0001 to 0.2 , and a measurement By placing the stress recording material in a recordable area formed in a predetermined region of the object to be measured, it is possible to know after the fact information about the stress experienced by the object to be measured by irradiating the recordable area with readout light of a wavelength of 200-480 nm and observing the difference between the afterglow observed before the stress is applied, which has a peak in the 500-1100 nm band, and the afterglow observed after the stress is applied, which has a peak in the 500-1100 nm band that changes depending on the past load history of the object to be measured; and further, the traces of the recorded stress can be erased by irradiating reset light of approximately the same wavelength as the readout light and 100 to 1000 times the intensity of the readout light . A stress recording material having a composition represented by the general formula Li _x Na _y NbO _{3+ (x+y-1)/2 + Σ(zk*Lk/2)} : M1 _z1 , M2 _z2 , M3 _z3 (wherein M1 is any one metal ion selected from rare earth ions and transition metal ions, M2 or M3 is none or any one metal ion selected from rare earth ions and transition metal ions, zk is a generalized expression of z1 to z3, Lk is a generalized expression of the valence L1 of the ion M1, the valence L2 of the ion M2, and the valence L3 of the ion M3, and when M2 is none, z2 is 0, and when M3 is none, z3 is 0), wherein x=0.02 to 2, y=0.01 to 1, and z1+z2+z3=0.0001 to 0.2 (wherein the general formula is Li _(1-P)(1+α) Na _P NbO ₃ :QR ₍ where Q is at least one metal ion selected from transition metal ions), excluding materials where the value of P is in the range of 0.10 to 0.98, the value of R is in the range of 0.0001 to 0.2, and α is in the range of 0 or more) . A stress recording structure comprising a recordable area formed as a coating layer or sheet layer in a predetermined area of an object to be measured, in which powder of the stress recording material described in claim 1 or claim 2 is dispersed in a light-transmitting resin matrix , and the recordable area is configured so that after stress is applied, an afterglow is generated by irradiating a readout light, thereby making it possible to know after the fact that stress has been applied to the object to be measured . a region where stress formed on the measurement object can be recorded;
a read light irradiation unit that irradiates the recordable area with excitation light for afterglow emission;
an afterglow intensity acquisition unit that acquires information about the afterglow intensity of the recordable area;
an afterglow intensity reporting unit that reports information about the afterglow intensity,
The recordable area has a general formula Li _x Na _y NbO _{3+ (x+y-1)/2 + Σ(zk*Lk/2)} : M1 _z1 , M2 _z2 , M3 _z3 (wherein M1 is any one metal ion selected from rare earth ions and transition metal ions, M2 or M3 is none or any one metal ion selected from rare earth ions and transition metal ions, zk is a generalized expression of z1 to z3, Lk is a generalized expression of the valence L1 of the M1 ion, the valence L2 of the M2 ion, and the valence L3 of the M3 ion, and when M2 is none, z2 is 0, and when M3 is none, z3 is 0), and x=0.02 to 2, y=0.01 to 1, and z1+z2+z3=0.0001 to 0.2, is present in a predetermined region of the measurement object,
A stress recording system comprising a reset light irradiation unit that irradiates the recordable area with high-intensity reset light having substantially the same wavelength as the excitation light for afterglow emission . a storage unit that stores information on the afterglow intensity in the recordable area before the stress to be measured is applied and information on the afterglow intensity after the stress to be measured, the information being obtained from the afterglow intensity acquisition unit;
a difference information generating unit that generates difference information between information on afterglow intensity before the measurement object is subjected to stress and information on afterglow intensity after the measurement object is subjected to stress,
5. The stress recording system according to claim 4 , wherein the afterglow intensity notifying unit is capable of notifying information on the difference. the storage unit is capable of storing information about the difference;
6. The stress recording system according to claim 5 , wherein the afterglow intensity notifying unit is capable of notifying information on a predetermined afterglow intensity or information on a difference stored in the storage unit. 7. The stress recording system according to claim 4 , wherein the information on the afterglow intensity is image information on the afterglow. General formula Li _x Na _y NbO _{3+ (x+y-1)/2 + Σ(zk*Lk/2)} : M1 _z1 , M2 _z2 , M3 _z3 (where M1 is any one metal ion selected from rare earth ions and transition metal ions, M2 or M3 is none or any one metal ion selected from rare earth ions and transition metal ions, zk is a generalized expression of z1 to z3, Lk is a generalized expression of the valence L1 of the ion of M1, the valence L2 of the ion of M2, and the valence L3 of the ion of M3, and when M2 is none, z2 is 0, and when M3 is none, z 3 is 0.) where x = 0.02 to 2, y = 0.01 to 1, and z1 + z2 + z3 = 0.0001 to 0.2 , is placed in a recordable area formed in a predetermined area of an object to be measured, and readout light of a predetermined wavelength is irradiated onto the recordable area, and the difference between an afterglow image before stress application and an afterglow image after stress application is observed. This method of use is as a stress recording material for emitting afterglow, which allows information about the stress received by the object to be measured to be obtained after the fact.