JPH0894592A - Method and device for inspecting brittle material - Google Patents

Abstract

PURPOSE: To enable non-destructively evaluating the breaking characteristics of a brittle material by applying a tensile stress to subjects to be inspected, measuring the frequency of occurrence of acoustic emission generated from them, and calculating the damping characteristic of the frequency of occurrence. CONSTITUTION: About 40 test pieces each of which is about 8cm by about 2cm by about 1.15cm are cut from a cordylite ceramics pipe which is about 14cm in bore, about 17cm in outside diameter and about 70cm in length, and the average bending strength is calculated from 10 of the test pieces. Next, two acoustic emission sensors are attached to each test piece, and the test piece is bent at three points for a destructive test, so that the number of acoustic emission (AE event number) per minute is measured. As tensile stress approaches the breaking stress of the test piece, the gradient of the damping curve of the AE event number gets gentler. Therefore, when a constant tensile stress is applied to a number of subjects to be inspected and the gradient of the damping curve of the AE event number generated is gentle, the breaking stress of the subjects to be inspected can be judged to be small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection method and an inspection apparatus for brittle materials such as ceramics, and more particularly to an inspection method and an inspection apparatus for porous brittle materials (for example, filter tubes used in high temperature gas dedusting purification apparatus). .

[0002]

2. Description of the Related Art As a device for cleaning high-temperature dust-containing gas, a dust-removing device has been proposed which uses a filter body such as a tube or honeycomb made of porous ceramics as a filtering material. This type of dust removing device is, for example, as shown in FIG.
The dust-containing gas is fed into the porous ceramic tube 11 having air permeability, and the clean gas is taken out through the filter wall of the ceramic tube 11. Also, in order to prevent dust in the dust-containing gas from accumulating on the filter wall inside the ceramic tube and causing excessive increase in ventilation pressure loss, a high-pressure backwash airflow is made to flow in a pulsed manner from the compressed air cylinder 12 and is accumulated on the filter wall. The dust is blown off to the hopper for regeneration.

[0003]

By the way, in the process of manufacturing a filter tube made of porous ceramics, material defects such as scratches and cavities may occur, and a filter tube having such a material defect may be used as a dust removing device. When used, the filter tube is sometimes damaged due to the temperature change of the dust-containing gas and thermal shock caused by backwash regeneration. Therefore, conventionally, non-destructive 100% inspection is performed on the filter tube products.

However, since the filter tube is an opaque porous material, it cannot be evaluated by visual inspection or optical inspection. Further, since it is a porous material, it is not possible to apply an inspection method such as an ultrasonic flaw detection method or a penetration flaw detection method used for inspecting a dense material such as iron.

The present invention has been made in view of the above-mentioned problems of the prior art, and it is brittle so that even an object to be inspected made of an opaque and porous material can be evaluated for its breaking characteristics without breaking. An object is to provide a material inspection method and an inspection apparatus.

[0006]

Means for Solving the Problems As a result of intensive studies for achieving the above object, the present inventors have found that when a tensile stress is applied to a ceramic filter tube, an acoustic wave generated from the ceramic tube after the tensile stress rises. By examining the attenuation characteristics of the emission frequency, it was found that the fracture characteristics of this ceramic tube due to delayed fracture or fatigue can be evaluated nondestructively and with high precision, and the present invention has been completed. That is, according to what the inventors of the present invention have sought, when tensile stress is applied to a brittle material (hereinafter simply referred to as “material”), the frequency of acoustic emission generated from this material has a peak value at the time of rising of the tensile stress. And then decreases when the tensile stress becomes constant (hereinafter, the range in which the tensile stress is kept constant is referred to as “after the rising of the tensile stress”). In the case of an inspected object that breaks down, the frequency of acoustic emission that occurs after the rise of the tensile stress is once attenuated, but increases again with the passage of time. Further, the frequency of occurrence of acoustic emission generated after the rise of the tensile stress increases as the tensile stress closer to the fracture stress of the material is applied, and the slope of the attenuation curve of the frequency of occurrence also becomes gentle. This is because when the applied tensile stress approaches the fracture stress of the material, it is considered that delayed fracture extension occurs inside the material even after the tensile stress rises.

On the other hand, when a tensile stress at a level close to the fracture stress of this material is repeatedly applied to the material, delayed fracture may occur. When a tensile stress is repeatedly applied to a material, a decay curve of the frequency of acoustic emission that occurs after the tensile stress rises is observed for a material that does not cause delayed fracture. Decays at.
On the other hand, in the attenuation curve of the frequency of occurrence of acoustic emission of a material in which delayed fracture occurs, when tensile stress is repeatedly applied to the material, the attenuation gradient becomes gentler than before the same time. This is because the frequency of acoustic emission, which occurs after the rise of tensile stress, is once attenuated in the material leading to fracture, but the above-mentioned phenomenon of re-increasing over time is acceleratedly realized. As described above, it is possible to predict this phenomenon by applying a single tensile stress,
Judgment as to whether delayed destruction occurs with this method is when the absolute value of the frequency of occurrence of acoustic emission is small, so if the gradient is small, even a small amount of noise from the outside will greatly affect the discrimination accuracy. .

Based on such knowledge, the present invention focuses on the attenuation characteristic of the frequency of acoustic emission occurring after the rise of tensile stress among the frequencies of acoustic emission, and the attenuation characteristic when the same tensile stress is applied. Is compared between the inspected objects to determine the magnitude of the fracture stress of each inspected object. That is, according to the present invention, a tensile stress is applied to the inspection object,
At this time, a frequency of acoustic emission generated from the inspection object is measured, and a fracture characteristic of the inspection object is evaluated based on a damping characteristic of the generation frequency. It

As described above, by examining the attenuation characteristic of the frequency of occurrence of acoustic emission that occurs after the rise of tensile stress, noise from the outside is relatively reduced, and the tensile stress application speed and sensor sensitivity difference. Also, the influence of the inspection conditions such as the degree of adhesion of the sensor to the inspection object is reduced, and the evaluation accuracy of the destruction characteristics is improved.

In this case, the steepness of the attenuation of the acoustic emission occurrence frequency after the rise of the tensile stress, in other words, in the attenuation curve of the acoustic emission occurrence frequency, occurs when a predetermined time has elapsed after the rise of the tensile stress. It is preferable to inspect the destruction characteristics of the object to be inspected based on the rate at which the frequency is attenuated (hereinafter also referred to as the attenuation rate). When such an attenuation rate is used, it is determined that the inspected object having a smaller attenuation rate (that is, the slope of the attenuation curve of the occurrence frequency being gentler) has a smaller fracture stress. In addition, the frequency of occurrence of acoustic emission after the rise of tensile stress is
It is also possible to evaluate the destruction characteristics of the object to be inspected based on the decay time until the occurrence frequency is multiplied by a predetermined ratio to decrease the occurrence frequency. When this decay time is used, it is determined that the fracture stress is smaller for the test object having a longer decay time when the same tensile stress is applied. By inspecting on the basis of the attenuation rate or the attenuation time defined in this way, the magnitude of the fracture stress of the inspected object can be determined with almost no influence on the absolute value of the frequency of occurrence of acoustic emission.

On the other hand, when the absolute value or the peak value of the frequency of occurrence of acoustic emission generated from the object to be inspected is taken as the frequency of occurrence of acoustic emission, these are regarded as a crack generation position and a sensor for detecting acoustic emission. Since it is affected by the distance and the distance or the degree of adhesion between the object to be inspected and the sensor, it is difficult to uniformly evaluate the destructive characteristics for many objects to be inspected. Also, for the absolute value and peak value of acoustic emission, the frequency of occurrence of acoustic emission at the rise of tensile stress is important, but mechanical vibration from an external device is transmitted at the rise of applied stress, and this vibration is transmitted by the sensor. Since it is received as noise, it is not preferable to use these absolute values and peak values as the frequency of acoustic emission.

In another aspect of the present invention, a tensile stress is repeatedly applied to the object to be inspected, and the repeated application of the tensile stress accelerates the damping characteristic of the frequency of occurrence of acoustic emission generated after the rising of the tensile stress to appear.
By comparing the damping characteristics, it is possible to evaluate whether or not delayed fracture occurs in the inspection object. That is, according to the present invention,
Tensile stress is repeatedly applied to the object to be inspected, each time the tensile stress is applied, the frequency of occurrence of acoustic emission after the tensile stress is applied after the tensile stress is applied is measured from the object to be inspected, and the tensile stress There is provided a brittle material inspection method characterized by evaluating the fracture characteristics of the object to be inspected based on a change in the attenuation characteristic of the frequency of occurrence of acoustic emission.

Here, the strength of the acoustic emission after the rise of the tensile stress is defined as a value obtained by integrating the function f (t) of the frequency of occurrence of the acoustic emission for a predetermined time, and the strength of the acoustic emission is repeatedly applied with the tensile stress. It is preferable to predict whether delayed fracture will occur in the inspection object depending on how it changes with respect to the number of times. That is, if the strength of the acoustic emission generated after the first rise of the tensile stress shows the maximum value and the strength becomes smaller with each subsequent application of the tensile stress, delayed fracture does not occur in the inspected object. Predict. On the other hand, if the intensity of the acoustic emission becomes larger than the previous one at a certain number of repetitions, it is predicted that delayed destruction will occur in the inspected object. By inspecting for delayed destruction by such a change in the intensity of acoustic emission, the influence of noise from the outside can be made relatively small, and the evaluation accuracy can be improved. In this case, if the tensile stress is repeatedly applied at least four times, delayed fracture can be predicted and the time required for evaluation can be shortened.

The objects to be inspected according to the present invention include brittle materials such as ceramics, glass and composite materials, and are particularly preferably applied to various ceramics sintered bodies and polycrystalline bodies such as crystallized glass. It is preferably used for inspection of porous polycrystals. Such inspected objects include porous filter tubes, heat exchanger pipes, bricks, SiC, Si ₃
An example is a semiconductor process tube made of N ₄ .

The tensile stress repeatedly applied to the inspection object made of a porous material is preferably 20% or more and 70% or less of the fatigue limit stress of the inspection object. Repeated application of a tensile stress greater than 70% of the fatigue limit stress causes delayed fracture in many inspected objects, which is not preferable for nondestructive inspection. Also, 20% of fatigue limit stress
Even if a smaller tensile stress is repeatedly applied, it is difficult for the crack to spread, so that it is not possible to distinguish between an inspected object that causes delayed fracture and an inspected object that does not cause delayed fracture.

Further, according to the present invention, when the object to be inspected is a hollow body, it is pulled to the object to be inspected by the expansion of the expandable and contractible bag body inside which the pressurizing fluid is introduced. There is provided a brittle material inspection device comprising a means for applying stress and a sensor for detecting acoustic emission generated from the inspection object.

If tensile stress is applied to an object to be inspected using such a bag, it is possible to apply substantially uniform tensile stress to the object to be inspected. Further, as the pressurizing fluid introduced into the inside, various fluids such as water and oil can be selected according to the magnitude of applied stress, etc., which facilitates the handling of the inspection device and applies a high pressure. Is possible.
Furthermore, since the pressurizing fluid does not come into direct contact with the object to be inspected,
Especially when it is used for a porous inspection object, it can prevent the surface of the inspection object from being contaminated or the surface condition being damaged, or the fluid from entering the inspection object and impairing the filtration performance. It is suitable.

For an object to be inspected, which is a porous tubular body, an expandable bag is inserted into the object to be inspected, and a pressurizing fluid is introduced into the bag to inflate the object to be inflated. It is preferable to apply tensile stress due to internal pressure to the inspection object.

[0019]

Embodiments of the present invention will be described below with reference to the drawings. Example 1 First, the tensile stress close to the fracture stress of the inspection object is applied once, and the magnitude of the fracture stress of the inspection object is determined from the attenuation characteristic of the occurrence frequency of acoustic emission generated from the inspection object after the tensile stress rises. It was verified whether it could be determined.

Inner diameter 140 mm, outer diameter 170 mm, length 7
00 mm cordierite ceramics (2MgO
・ 40 pieces of 80 mm × 20 mm × 11.5 mm test pieces TP are cut out from one ceramic tube made of (2Al ₂ O ₃ .5SiO ₂ ), and the bending strength is measured with 10 of these, and the average bending strength is measured. I asked. Next, as shown in FIG. 1, the acoustic emission sensor 1 (hereinafter referred to as AE) is attached to each of the test pieces.
Two sensors (referred to as sensors) were attached, and then a destructive test was performed by bending at three points. Then, as shown in FIG. 2, 20%, 40%, 60% of the average bending strength is applied to the inspection object every step.
%, 80%, ... Stress rise rate 0.1 mm / m
This stress was held constant for 2 minutes each, for example, by loading in. At the same time, acoustic emission generated from the test piece TP was detected. The AE sensor 1
The acoustic emission, which is a piezoelectric element utilizing the piezo effect, was measured using an acoustic emission measuring instrument equipped with this AE sensor 1.

The results are shown in FIG. The “number of AE events” shown on the vertical axis of FIG. 3 is the number of acoustic emission waves generated per second, that is, the frequency of occurrence. The relationship between the load W applied to the test piece and the generated stress σ is σ = 2.
It is represented by 27W. According to this result, when a certain tensile stress is applied (at the time of rising until the tensile stress becomes constant), the number of AE events shows a peak value, and this peak value indicates that the applied tensile stress causes the destruction of the test piece. The value becomes large as the stress approaches. This is because when the tensile stress increases, the cracks generated inside or on the surface of the test piece expand, which increases the cross-sectional area of the crack.

Further, according to this result, the number of AE events is attenuated after the rise of the tensile stress, and the gradient of the attenuation curve of the number of AE events becomes gentle as the tensile stress approaches the fracture stress of the test piece. If the “decay time” of the number of AE events is defined as the time from when the number of AE events shows a peak value until the number of AE events decreases to, for example, 15% of the number of AE events after the rise of tensile stress, The decay time of the number of AE events increases as the tensile stress approaches the fracture stress of the test piece.
This is because it is considered that when the tensile stress becomes large, a delayed destructive crack extension occurs inside or on the surface of the test piece even if the tensile stress is constantly applied. Therefore, if a constant tensile stress is applied to a large number of objects to be inspected and the gradient of the attenuation curve of the number of AE events that occurs in a certain object to be inspected is gentle, or if the attenuation time of the number of AE events is long, the It can be judged that the fracture stress of the inspection object is small.

As the frequency of acoustic emission occurring during the material destruction process, the peak value and absolute value of the number of AE events can be considered. Where AE
As can be seen from the results shown in FIG. 3, the peak value and the absolute value of the number of events are values that appear when the tensile stress applied to the test piece is increasing (at the time of rising).
However, when the tensile stress rises, mechanical vibration from the outside such as the test equipment is transmitted, and this vibration is detected by the AE.
Since the sensor 1 receives the noise as noise, it is difficult to inspect the destructive characteristics of the material even if the peak value or absolute value of the number of AE events is adopted as the frequency of acoustic emission. Moreover, since the peak value and the absolute value of the number of AE events greatly vary depending on the distance between the crack and the AE sensor generated in the test piece and the degree of adhesion between the test piece and the AE sensor, many objects can be inspected. It is extremely difficult to evaluate uniformly.

On the other hand, the slope of the decay curve of the number of AE events after the rise of the tensile stress and the decay time of the number of AE events are such that the tensile stress is kept constant as can be seen from the results shown in FIG. Since it is the frequency of occurrence when it is present, there is relatively little mechanical vibration transmitted from the test equipment and the like, and the mixing of noise is small. Also, the decay time of the number of AE events after the rise of the tensile stress is
“After the number of AE events shows a peak value, the number of AE events is the maximum value after the rise of tensile stress, for example, 15
If it is defined as "time until it decreases to%", the absolute value of the number of AE events does not matter. Therefore, the distance between the crack generated in the test piece TP and the AE sensor 1,
A large number of inspected objects can be uniformly evaluated without being affected by inspection conditions such as the degree of adhesion between the test piece TP and the AE sensor 1.

Example 2 Next, a tensile stress close to the fracture stress of the object to be inspected is repeatedly applied, and a delayed fracture of the object to be inspected due to a change in the damping characteristic of acoustic emission generated from the object to be inspected after the tensile stress rises. It was verified whether the presence or absence can be evaluated.

An inner diameter of 140 m as in the first embodiment.
m, outer diameter 170 mm, length 700 mm from one ceramic tube made of cordierite ceramics
80mm x 20mm x 11.5mm test piece TP
40 pieces were cut out, and the average bending strength was obtained using 10 of these test pieces. Next, two AE sensors 1 were attached to each of the test pieces, and then a destructive test was performed in the same manner as in Example 1 shown in FIG. And
High tensile stresses of about 75% and 85% of the average flexural strength of these test pieces TP were repeatedly applied 5 times for 2 minutes each, as shown in FIG. 4, so as to cause delayed fracture in the test pieces TP. At the same time, acoustic emission was detected.

The results are shown in FIGS. All of the 6 test pieces show delayed fracture when a high stress of 85% of the average breaking stress is applied, and 6 of 24 test pieces are loaded when a bending stress of 75% of the average breaking stress is applied. Delayed destruction occurred in the piece. 5 to 7,
The number of AE events due to the repeated application of tensile stress is shown. Fig. 5 shows the test piece A that failed and delayed after the second application of tensile stress, and Fig. 6 shows the test piece that failed and delayed after the fifth application of tensile stress. B and FIG. 7 show the results regarding the test piece C in which delayed fracture did not occur.

According to this result, tensile stress is repeatedly applied as shown in FIG. 7 in the decay curve of the crack extension wave (which is an acoustic emission generated when the crack extends) of the test piece in which delayed fracture did not occur. It turns out that the gradient becomes steep every time. On the other hand, in the damping curve of the crack extension wave of the test piece in which delayed fracture occurred in Fig. 6, almost no change was observed in the damping curve at the first and second tensile stresses, and at the third tensile stress. Although the slope of the curve once becomes large, the slope of the attenuation curve when the fourth tensile stress is applied becomes gentle.

FIG. 8 is a graph in which the crack extension wave, that is, the intensity ratio of acoustic emission, is plotted against the number of times the tensile stress is repeatedly applied, for the test pieces B and C shown in FIGS. Here, the intensity of the crack extension wave is an integral value of the function f (t) over time t when the number of AE events (occurrence frequency) is a function f (t) of time, and is the intensity ratio of the crack extension wave. Is the ratio of the strength of the crack extensional wave due to the second and subsequent tensile stresses when the strength of the crack extensional wave due to the first tensile stress is "1". In the test piece C in which the delayed fracture did not occur, the strength ratio of the crack extension wave decreased each time the tensile stress was repeatedly applied.
In the test piece B in which the delayed fracture occurred, the test piece B once decreased and then increased. From these results, the acoustic emission when the tensile stress is repeatedly applied n times is detected, and the damping ratio α _n of each strength ratio of the frequency of occurrence of the crack extension wave is not reduced to, for example, 70% or less. The material is judged to be defective due to delayed fracture.

Example 3 Next, an example of an inspection apparatus for applying the above-described inspection method of the present invention using a porous ceramic filter tube as an inspection object will be described. FIG. 9 is an external perspective view showing a material inspection apparatus according to an embodiment of the present invention, and FIG. 10 is a main part for explaining a step of injecting water into a pressure rubber sleeve inserted into a filter tube of porous ceramics. Sectional view, Figure 1
1 is a cross-sectional view of a main part showing a measurement position of acoustic emission.

The porous ceramics filter tube 2 used in this embodiment is assembled by connecting four filter elements 2a using an annular joint 2b as shown in FIGS. Element 2a
Only the inspection object may be used. This filter tube 2 is held in a soundproof case 3 of the inspection apparatus, and as shown in FIG. 11, an AE sensor 1 is provided at approximately the center of each element 2a. For the AE sensor 1, the same piezoelectric element as that used in Examples 1 and 2 described above was used. Further, as shown in FIG. 9, in order to sequentially inspect a large number of filter tubes, the AE sensor 1 is not directly attached to the filter tube 2 but is attached to the annular bracket 4.

The tensile stress is applied to the filter tube 2 by inserting a stretchable rubber sleeve (bag) 5 into the filter tube and pouring water into the rubber sleeve 5. This makes it possible to apply a substantially uniform tensile stress to the wall of the filter tube 2. As the fluid to be introduced into the pressing rubber sleeve, oil can be used in addition to water. If water is used as the pressurizing fluid, handling such as post-treatment is easy.

As shown in FIGS. 10 and 11, a pipe 6 for bleeding air and for draining air is attached to one end of the rubber sleeve 5 for pressurization of this embodiment, and an opening / closing valve 7 is attached to this pipe 6. It is provided. In addition, the rubber sleeve 5 for press
A water injection pipe 8 is attached to the other end of the rubber sleeve 5 such as tap water by an electric pump 9 or a manual pump 10.
Is supplied in.

In the inspection device of this embodiment, after the filter tube 2 is set in the soundproof case 3, the pressurizing rubber sleeve 5 is inserted into the filter tube 2 so that the fixing frame 11 is fixed as shown in FIG. And a movable frame 12.
As shown in the figure, a movable frame 12 to which the soundproof case 3 is fixed is provided movably in the longitudinal direction of the filter tube 2 with respect to a fixed frame 11 to which the rubber pressing sleeve 5 is fixed. By moving 12 the pressing rubber sleeve 5 is quickly and smoothly inserted into the filter tube 2.

Next, a procedure for inspecting a filter tube for defects using the inspection apparatus of this embodiment will be described. First, four filter elements 2 are formed using the annular joint 2b.
The filter tube 2 produced by connecting a is set in the soundproof case 3. In this case, A provided in the soundproof case 3
The arrangement of the bracket 4 of the AE sensor 1 is considered so that the E sensor 1 is located substantially in the center of each element 2a of the filter tube 2. In addition, in the filter tube 2 used for the dust removing device, the empirical rule that the elements located at both ends are easily damaged, so that the bracket 4 to which the AE sensor for detecting acoustic emission of the elements 2a at both ends is attached is It is preferable to attach a plurality of AE sensors. In this embodiment, the three AE sensors are attached to the brackets at both ends in the circumferential direction at equal intervals (120 ° intervals), while only one AE sensor is attached to the bracket located in the middle.

By moving the movable frame 12, the pressing rubber sleeve 5 is moved with respect to the filter tube 2 set in the soundproof case 3, and the pressing rubber sleeve 5 is inserted into the inside of the filter tube 2. At this time, it is preferable to drain the water in the pressing rubber sleeve 5 in advance in order to smoothly perform the inserting work.

When the deflated rubber sleeve 5 for pressing is inserted into the inside of the filter tube 2, as shown in FIG.
Water for pressurization is supplied from a pipe 8 provided at the lower end of the rubber pressurization sleeve 5. In this step, it is preferable that the soundproof case 3 and the like be upright in order to remove air from the rubber sleeve 5 for pressurization. Since the air in the pressurizing rubber sleeve 5 is moved to the upper part of the pressurizing rubber sleeve 5 by the supply of this water, the air is provided at the upper end of the pressurizing rubber sleeve 5 until the pressurizing rubber sleeve 5 is filled with water. The on-off valve 7 thus opened is opened to bleed air.

When the air bleeding is sufficiently performed, the on-off valve 7 is closed and the water supply is continued. When the rubber sleeve 5 for pressurization is filled with water to some extent, the soundproof case 3 is placed horizontally as shown in FIG. 11, and the internal pressure is applied to the filter tube 2 by using the manual pump 10 while watching the water pressure gauge 13. Then, the acoustic emission generated from the filter tube 2 by the application of this internal pressure is detected by the AE sensor 1. Although not shown, the AE signal analysis system measures the number (occurrence frequency) of acoustic emissions generated per unit time from the output signal of the AE sensor 1. When evaluating the presence or absence of delayed fracture, after obtaining the total number of AE events (strength) after the rise of tensile stress when n times of repeated tensile stress is applied, n times each time, The attenuation rate of the total number of AE events after each rise of the stress is calculated, and when all the attenuation rates are smaller than a specified value (for example, 70%), it is determined that the delayed fracture does not occur. Thus, in applying tensile stress to the filter tube made of porous ceramics, since the bag body into which the pressurizing fluid is introduced is used in the present embodiment, the pressurizing fluid is directly applied to the porous filter tube. There is no contact and, as a result, no damage or clogging of the porous filter tube.

[0039]

As described above, according to the method for inspecting brittle materials of the present invention, since the attenuation characteristic of the frequency of acoustic emission generated when tensile stress is applied is utilized, it is opaque and porous. Even if the inspection object is made of a high quality material, the destruction characteristics can be accurately evaluated without breaking. In addition, since the attenuation characteristic of the frequency of acoustic emission when the tensile stress becomes constant after the rising of the tensile stress is used, the noise from the outside is mixed in relatively, and the inspection conditions such as the tensile stress application speed. It is rarely affected by. Further, according to another inspection method of the present invention, since the damping characteristic of the frequency of occurrence of acoustic emission after the rise of the tensile stress when the tensile stress is repeatedly applied is utilized, there is a possibility that delayed fracture may occur. It is possible to accelerate the evaluation of the inspection object in a short time and with high accuracy. Further, according to the brittle material inspection device of the present invention, since the expandable bag body is used which is arranged inside the hollow body and into which the pressurizing fluid is introduced, the fluid contacts the object to be inspected. The performance of the inspection object is not impaired or contaminated, and the tensile stress applied to the inspection object is substantially uniform.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing an example of a bending tester used in Examples 1 and 2 of the present invention.

FIG. 2 is a graph showing an application pattern of tensile stress in Example 1 of the present invention.

FIG. 3 is a graph showing the results of Example 1 of the present invention.

FIG. 4 is a graph showing an application pattern of tensile stress in Example 2 of the present invention.

FIG. 5 is a graph showing the relationship between the number of AE events and the time of a test piece that has been destroyed by repeated application of tensile stress twice in Example 2 of the present invention.

FIG. 6 is a graph showing the relationship between the number of AE events and the time of a test piece in which failure was caused by repeated application of tensile stress 5 times in Example 2 of the present invention.

FIG. 7 is a graph showing the relationship between the number of AE events and the time of a test piece that was not destroyed in Example 2 of the present invention.

FIG. 8 is a graph showing the relationship between the crack extension wave intensity ratio and the number of times tensile stress is repeated in Example 2 of the present invention.

FIG. 9 is an external perspective view showing a main part of an embodiment of the brittle material inspection apparatus of the present invention.

FIG. 10 is a cross-sectional view of a main part for explaining a step of pouring water into a pressurizing rubber sleeve inserted in a filter tube in the inspection device shown in FIG. 9.

FIG. 11 is a cross-sectional view of a main part for explaining a process of measuring acoustic emission in the inspection device shown in FIG.

FIG. 12 is a cross-sectional view showing an example of a conventional dust removing device.

[Explanation of symbols]

 1 ... AE sensor 2 ... Filter tube (inspection object) 2a ... Filter element 2b ... Annular joint 5 ... Rubber sleeve for pressurization (bag)

Claims (7)

[Claims] 1. A tensile stress is applied to an object to be inspected, an occurrence frequency of acoustic emission generated from the object to be inspected is measured after the tensile stress rises, and the object to be inspected is based on a damping characteristic of the occurrence frequency. A method for inspecting brittle materials, characterized by evaluating fracture characteristics. 2. The destruction characteristic of the object to be inspected is evaluated based on a decay time at which the frequency of occurrence of the acoustic emission decreases from a maximum value to a frequency of the maximum value multiplied by a predetermined ratio. Item 1. The method for inspecting a brittle material according to Item 1. 3. A tensile stress is repeatedly applied to an object to be inspected,
Each time the tensile stress is applied, the frequency of occurrence of acoustic emission generated from the object to be inspected after the tensile stress rises is measured, and the destruction characteristic of the object to be inspected is evaluated based on the change in the attenuation characteristic of the frequency of occurrence. A method for inspecting brittle materials, characterized by: 4. The strength of the acoustic emission generated each time the tensile stress is applied increases while the tensile stress is applied a predetermined number of times as an integrated value of the frequency of occurrence of the acoustic emission as the strength of the acoustic emission. The method for inspecting a brittle material according to claim 3, wherein it is determined that delayed fracture occurs in the inspected object when the inspection is performed. 5. The brittle material inspection method according to claim 1, wherein the inspection object is a porous polycrystalline material. 6. When the object to be inspected is a hollow body, a means for applying a tensile stress to the object to be inspected by the expansion of the expandable and contractible bag body in which the fluid for pressurization is introduced inside the hollow body. A brittle material inspection apparatus, comprising: a sensor for detecting acoustic emission generated from the object to be inspected. 7. The brittle material inspection apparatus according to claim 6, wherein the inspection object is a porous tubular body.