JPH03229133A - Method for evaluating and testing ceramics - Google Patents

Abstract

PURPOSE:To easily know the stress corrosion cracking with the natural corrosion in various corrosive environments as a starting point by packing various kinds of gases into a hermetic vessel holding a test piece and carrying out a bending test or tensile test by an acoustic emission (AE) measurement in the atmosphere of these gases. CONSTITUTION:The test piece 11 supported at 4 points by roll-shaped parts 12 is put into the hermetic vessel 10 and, for example, CO2, CO, ammonia, H2S, N2, etc., are filled into this vessel 10 to form the corrosive environments; thereafter, a load is applied on the test piece 11 by the parts 12. The cracks occurring in natural cracks are generated in the test piece 11 in such a manner and the AEs are simultaneously generated. The total number of the generated AEs is gradually increased with the slow growth of the cracks by the increase of the load. The subsequently generated AEs are measured by an AE sensor 13 and are sent to a preamplifier 15 which increases a signal level up to the degree to allow easy processing. The AE signal separated from noises by a discriminator 16 is counted by a counter 17 and is recorded in a recorder 18.

Description

[Detailed Description of the Invention] The present invention is a ceramic evaluation test method, more specifically, it is used for the development of various ceramics and the safety evaluation in a corrosive environment at the design stage. Concerning test methods.

Conventionally, as an evaluation test method for this type of ceramics, there has been research on the stress corrosion cracking of ceramics itself, which examines the crack propagation characteristics from cracks or snots created artificially in test pieces. For example, Weider
DCB (Double Canti
Research conducted using the Lever Beaml test method iJ, Am, ceram, soc, 50[8]19
67) and D T (Double
e Torsion) test method (J
, Mat, Sci, , 7 f19721). In the above research, stress corrosion cracking is determined by the relationship between the stress intensity factor (KI) and the crack growth rate m, fKI-V.
diagram), and as a result,
It has been revealed that stress corrosion cracking occurs in ceramics containing 5iO- due to the action of water vapor components in the atmosphere.

However, cracks are artificially created in the test specimens used in the DCB test method and DT test method, and the cracks can be propagated by applying stress while artificially controlling the stress after the crack is manufactured. We are investigating the characteristics. Therefore, it cannot be said that the destruction of ceramics due to stress corrosion cracking caused by defects naturally formed in ceramics in a corrosive environment (hereinafter referred to as natural defects) is evaluated.

Therefore, the AE method was used to investigate the destruction of ceramics starting from natural defects. For example, in a bending test, Gogotsi et al. measured the AE (Acoustic Emission) and predicted the breaking strength from the AE obtained (Proc, Ultrason, Int.
, 83i198311, and JP-A-58-2211
No. 62 discloses that stress is applied to a ceramic sintered body,
A non-destructive testing method has been disclosed in which strength is predicted by analyzing the AE signal generated from the ceramic sintered body.

On the other hand, in addition to the above-mentioned mechanical stress, thermal stress caused by a laser (Japanese Unexamined Patent Publication No. 59-221657) or thermal stress caused by a tungsten lamp (Japanese Unexamined Patent Application No. 60-135860) is partially applied, and AE1 occurs. There is a report that evaluates the crack propagation characteristics from natural defects in product-sized samples by measuring .

Furthermore, studies using DT tests using various samples have been reported regarding the relationship between crack growth rate and AE. For example, Evans et al.
ram, Soc, 56 [11] 1973), Kishi et al.
19861 was used as the sample, and the crack growth rate and A
We are considering the relationship with E.

Problems that Ming tried to solve However, the above-mentioned ceramic evaluation test method had the following problems.

(2) Conventionally, the main method was to artificially create cracks such as brick cracks or notches in a test piece, and then examine the stress corrosion cracking characteristics caused by the cracks. For this reason, although it is possible to quantitatively evaluate the Kl-V characteristics of ceramics, the fracture characteristics of ceramics due to stress corrosion cracking starting from natural defects have not been clarified.

(2) Processing of the test piece, such as surface polishing in the preparation stage of the test piece and the above-mentioned manufacturing work, is difficult and requires a relatively large sample, making it unsuitable.

(2) Regarding the stress loading on the test piece, it is necessary to have a sophisticated technique to apply the stress while delicately adjusting it, since it is artificially applied to one loaf.

■In addition, in conventional tests, the test is conducted in the air without setting various atmospheres during the test, and AE measurements are performed to evaluate the fracture behavior of the test piece. Corrosion cracking characteristics have not been clarified.

The present invention was made in view of the above-mentioned problems, and in simple mechanical tests such as bending tests and tensile tests,
Ceramics that can easily and accurately evaluate the stress corrosion cracking characteristics of ceramics without the need for complex analysis by generating natural defects under various atmospheres and performing AE measurements as a result. The purpose is to provide an evaluation test method for

In order to accomplish Section 1 to 2, the method for evaluating ceramics according to the present invention is to hold a test piece in a closed container, fill the container with various gases, It is characterized by conducting a bending test or a tensile test using AE measurement in a gas atmosphere.

Engineering■ Ceramics break down starting from natural defects due to stress being applied in a corrosive environment. The natural defects grow slowly based on stress corrosion, and as the natural defects grow, the total number of AEs increases, and at the same time, the number of AEs increases.
The load at which this occurs will decrease.

It has been found that the stress corrosion cracking characteristics of such ceramics vary depending on the pore distribution of the ceramic, and that the occurrence of the above-mentioned AE is influenced by the shape and size of defects formed in the ceramic.

Therefore, in bending or tensile tests,
By holding the test piece in a sealed container, filling the container with various gases, and performing AE measurements in the atmosphere of the various gases, it is possible to perform AE measurements in each atmosphere without the need for complex analysis. The stress corrosion cracking characteristics of ceramics, which are dominated by natural defects, can be easily clarified with high precision.

- Absolute and Comparative Examples Examples and comparative examples according to the present invention will be described below based on the drawings.

FIG. 1 is a conceptual diagram schematically showing an apparatus used for evaluation testing of ceramics according to the present example.

The device 1 is a conventional test device sealed in a sealed container 10. Inside the sealed container 10, there is a test piece 11 to which a load is applied from four points by a roll-shaped part 12.
is retained. At both left and right ends of this test piece 11, there is an AE
A sensor 13 is provided, and this AE sensor 13
is connected to a preamplifier 15 via a cord 14.

The AE measured by the AE sensor 13 is sent to a preamplifier 15, and then a discriminator 16 removes noise.
After being counted by the counter 17, the recorder 18
Recorded at

That is, various gases such as co2. c.
After forming various corrosive environments by filling with o, ammonia, H2S, N2, etc., a load of 4. A bending test is performed by applying a load from a ton.

Due to the above-mentioned load, cracks caused by natural defects occur in the test piece 11, and at the same time, AE occurs. The total number of AE occurrences increases with the gradual growth of cracks due to an increase in load. This kind of AE sensor 13
After that, the signal is multiplied by AE and sent to the preamplifier 15.
send to The preamplifier 15 increases the signal level of the AE signal to a level that facilitates signal processing, and then sends it to the discriminator 16. The AE signal separated from noise by the discriminator 16 is counted by a counter 17 and then recorded by a recorder 18.

Details of the test M device near the test piece 11 will be explained based on FIG. 2.

In FIG. 2, reference numeral 21 denotes a load cell fixed to the lower surface of a crosshead 20 that is suspended between support columns (not shown). Below this load cell 21 are jigs 22a, 22b and two roll-shaped parts 12. A test piece 11 is disposed with the test piece 11 interposed therebetween. AE sensors 13 are disposed at both left and right ends of the test piece 11, and a cord 14 connected to a preamplifier 15 (FIG. 1) is attached to the AE sensors 13. Further, below the test piece 11, there are two roll-shaped rollers for applying a load to the test piece 11.
The individual parts 12 and the jig 27 are placed on the pedestal 28. On the right side of the jig 27, the gas introduction pipe 29 is also connected to the jig 27.
A gas exhaust pipe 30 is arranged on the left side. and,
The bending test apparatus having the above structure is sealed so as to be wrapped in a bag-shaped sealed container 10 made of a flexible material (such as vinyl) whose top part is fixed to a jig 22a.

That is, by forming the airtight container 1O using a flexible material, various devices such as the bending test device or the tensile test device can be integrated into one airtight container 1.
Since it can be sealed at zero, there is no need to prepare large, hard vacuum containers, atmosphere containers, etc. exclusively for each type of equipment.

Furthermore, when adjusting the atmosphere during testing, it is possible to replace the atmosphere with various gases with simple operations, and it is possible to easily create various corrosive environments.

Furthermore, since the sealed container IO is deformable due to its flexibility, the cord 14 connected to the AE sensor 13
can be easily taken out, and even when a plurality of test pieces 11 are used for consecutive tests, the test pieces 11 can be easily replaced and the test can be carried out smoothly.

Further, even in experimental operations, when delicate adjustments from the outside are required, the operations can be performed easily and quickly.

In this example, the test piece 11 is mullite (3Aff20
．． -23 i 02 ) was prepared, an atmospheric atmosphere and a N2 atmosphere were formed as corrosive environments, and the test was conducted according to the above method. The results of the AE measurement obtained in this example were
Shown in the figure. The curve ■ represents the results in an atmospheric atmosphere;
Curve ■ shows the results in N2 atmosphere.

On the other hand, as a comparative example, a DCB test was conducted.

FIG. 5 is a conceptual diagram schematically showing a DCB test apparatus, and the DCB test will be explained based on this diagram.

40 in the figure is a DCB test piece, and cracks 49 are sandwiched between holes 41 and 44 at the upper and lower right side of the figure in the DCB test F40.
is formed. A string 42 fixed to a substrate 43 is attached to the wire 41, and a cord 42 fixed to the substrate 43 is attached to the blade hole 44.

A string 45 is fixed. Load cell 46 is code 4
7 to the XY recorder. Further, a microscope 52 is arranged below the left end of the crack 49, and a clip gauge 50 is arranged overlapping the crack 49. This clip gauge 50 is connected to an XY recorder by a cord 51.

That is, the string 4 is tied to the load cell 46 on the DCB test piece 4o.
When an upward load is applied through the hole 41, since the string 4 attached to the hole 41 is fixed to the substrate 43, the crack 49 in the OCS specimen 4o is torn vertically, causing the crack 49 to grow. happen. In order to investigate the growth characteristics of this crack 49, the position of the left end of the crack 49 is measured using a microscope 52, and the length of the crack 49 is measured. Further, the spread width of the crack 49 is measured by a total of 75jl by the clip gauge 5o, and then transmitted to the XY recorder 48. This XY recorder 4
8 creates a KI-Vts diagram based on the crack width of the crack 49 and the load value information sent from the load cell 46, and shows the relationship between the stress intensity factor fKI) and the crack growth rate.

A DCB test was conducted according to the above method and used as a comparative example.

At that time, the test piece 4o was mullite (3Af) as in this example.
220s.2S i Oz) was prepared, and a DCB test was conducted by forming an atmospheric atmosphere and a N2 atmosphere as corrosive environments. FIG. 4 shows the obtained Kl-V diagram. The curve (■) represents the results in an air atmosphere, and the curve (2) represents the results in an N2 atmosphere.

Comparing with the above Figures 3 and 4, in the test method in this example, the sample mullite (3AJ22
0!・Differences in stress corrosion cracking characteristics due to differences in corrosion environment of 2S10□) were clearly and easily understood. In other words, the number of AEs generated increases by about 2 times on average in the air atmosphere compared to the N2 atmosphere, and the number of AEs generated increases by about 20 times in the generated load.
% has decreased. Therefore, mullite (3Aε203
It has become clear that 2S102) is destroyed by stress corrosion cracking caused by water vapor components in the atmosphere.

On the other hand, in FIG. 4 relating to the comparative example, the KI-V curve ■ obtained in the air atmosphere is different from the KI obtained in the N2 atmosphere.
Stress corrosion cracking characteristics were observed, including an overall shift to the left (lower stress side) than the -V curve (■) and the presence of a region A called a "tana" degree.

As described above, in the ceramic evaluation test method according to the present example, the stress at which a natural defect starts to cause stress corrosion cracking can be easily determined under various corrosive environments. moreover,
From the obtained results, stress corrosion cracking characteristics originating from natural defects in ceramics can be easily investigated with high precision without the need for complicated analysis. On the other hand, calculating the stress at which stress corrosion cracking begins to occur from the Kr-V curve is complicated and cannot be easily determined.

Furthermore, the above allows comparison of the fracture risk between various types of ceramics, or when using the same ceramic, the difference in the fracture risk of the ceramics due to differences in the shape and size of natural defects. Safety can be easily known.

Furthermore, in the test in this example, the stress corrosion cracking characteristics of the sample could be easily investigated by measuring only the load and AE. However, in the DCB test in the comparative example, it is necessary to measure the load and COD (opening displacement), and usually also to read the length of the crack, which lacks simplicity.

As is clear from the above explanation, in the method for evaluating ceramics according to the present invention, a test piece is held in a closed container, and the container is filled with various gases. By performing a bending test or a tensile test using AE measurement in an atmosphere of various gases, it is possible to easily investigate the stress corrosion cracking characteristics caused by natural defects under various corrosive environments.

Furthermore, based on the above-obtained results, the fracture characteristics of ceramics can be easily and highly accurately investigated without performing complicated analysis. For this reason, it is possible to compare the fracture risks between various types of ceramics, or when using the same ceramic, to understand the differences in the fracture risks of the ceramics due to differences in the shape and size of natural defects. You can easily know the gender.

[Brief explanation of drawings]

Fig. 1 is a conceptual diagram schematically showing an apparatus for implementing the ceramic evaluation test method according to the present example, and Fig. 2 illustrates the vicinity of the closed container for implementing the method according to the present invention. FIG. 3 is a graph showing the measurement results of this example, and FIG. 4 is a graph showing the measurement results of the comparative example.
The V diagram and FIG. 5 are conceptual diagrams schematically showing a DCB test apparatus in a comparative example. 0 ■ ■ Sealed container test piece 3 AE sensor (AE measurement)

Claims (1)

[Claims] (1) Ceramics evaluation test characterized by holding a test piece in a sealed container, filling the container with various gases, and performing a bending test or tensile test by AE measurement in the atmosphere of the various gases. Method.