JPH0720121A - Method and equipment conducting guarantee test for ceramic component - Google Patents

Abstract

PURPOSE:To prevent the strength of a ceramic component from lowering during test by conducting load test of the ceramic component in a liquid at a temperature sufficiently lower than the freezing temperature of water. CONSTITUTION:When a guarantee test is conducted for a ceramic component 5 made of Si3N4, for example, the component 5 is immersed into a vessel 1 filled with liquid nitrogen 4 and mounted on the supporting member 2c of a lower jig 2. Under that state, an upper jig 3 is pushed down by means of a down press and bending load is applied at three points thus conducting the screening test. A component withstood against a specified load is selected as a passed component. Since the screening test is conducted in liquid nitrogen 4, influence of water on the ceramic material can be eliminated perfectly. This equipment can prevent stress corrosion crack during screening test and can discard low strength ceramic components without causing deterioration of strength.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, when using ceramic parts as mechanical structural parts, applies a predetermined load to all the ceramic parts, and judges all parts that have not been destroyed as acceptable products. The present invention relates to a screening assurance test method and an assurance test apparatus therefor.

[0002]

2. Description of the Related Art Ceramic materials have excellent properties such as heat resistance, corrosion resistance, wear resistance, and light ampacity, and are therefore being increasingly applied as high value-added mechanical structural parts. For example, ceramic materials such as turbochargers for automobile engine parts, auxiliary combustion chambers, and ceramic bearings that are expected to be used in special environments are typical examples. However, while ceramic materials have the above-mentioned excellent characteristics, However, it also has the drawback of being brittle and having a large variation in material strength. Therefore, in order to apply ceramic materials to mechanical structural parts, quality assurance that guarantees the minimum strength of the parts is an important technical issue.

In order to guarantee the quality of mechanical structural parts made of metallic materials, it is common to confirm the presence or absence of defects by a nondestructive inspection such as an X-ray transmission test or a fluorescent penetrant inspection test. However, in the case of ceramic materials, the size of defects that control strength is at most several tens of μm, and it is almost impossible to detect defects of such size with the current nondestructive inspection technology. Is. For this reason, as a means of guaranteeing the minimum strength of ceramic parts, an all-item screening guarantee test is generally performed in which a predetermined load is applied to all parts before actual use and surviving parts that have not been destroyed are accepted. There is.

[0004]

Ceramic materials generally exhibit delayed fracture characteristics such that their strength decreases with increasing load time. FIG. 9 shows, as an example, the delayed fracture characteristics of SiC ceramics at 1400 ° C. (Material, Vol. 38, No. 430, p783, July 1989). Such delayed fracture is based on crack growth from an initial defect due to stress corrosion cracking, and the amount of crack growth increases and the strength decreases as the loading time increases.

In the screening assurance test for all ceramic parts, the delayed fracture characteristics as described above, that is, the crack growth from the initial defect due to stress corrosion cracking, occurs due to the load during the screening test. The strength of the part will be lower than before the screening test.

FIG. 10 shows Sakata et al. (Journal of the Japan Society of Mechanical Engineers, Volume A, Volume 58, No. 550, p120, June 1992).
The results of the research on the assurance test effect of the ceramics performed by the above are shown, and the strength distributions of the ceramic materials before and after the screening test are compared and shown.

[0007] In this experiment, S = S for Al ₂ O ₃ ceramics having an initial strength distribution as shown by a triangle mark.
A foot-cutting test was carried out with a load of σ _p , and the strength distribution was further examined for the surviving test pieces which were not broken as indicated by a circle. As shown in FIG. 10, the strength of the surviving test piece is S
There are some that show lower strength than σ _p , even though they were cut off with a load of = σ _p .

As described above, in the guarantee test of the ceramic parts, the decrease in the strength of the parts due to the load during the screening test is a serious problem. Therefore, as a method for reducing such strength reduction, measures such as minimizing the load during the screening test and performing the unloading speed as quickly as possible after reaching a predetermined load are taken. For example, Ichikawa et al.
, P97, 1988) for details.

However, no specific proposal has been made yet for a method of guarantee testing of ceramic parts capable of completely eliminating the strength reduction during the screening test. An object of the present invention is to provide a guarantee test method for a ceramic component and a guarantee test apparatus for the same, which do not cause a decrease in strength during a screening test.

[0010]

In order to achieve the above object, the invention according to claim 1 applies a predetermined load to all the ceramic parts before use, and judges the parts which are not destroyed as acceptable products. In the method for guaranteeing all-parts screening of ceramic parts, the load test for the ceramic parts is performed in a liquid sufficiently lower than the freezing point of water.

In order to achieve the above object, the invention according to claim 2 is such that all the ceramic parts before use are immersed in a container containing liquid nitrogen and a bending load is applied to the ceramic parts. , A load consisting of a compressive load or internal pressure is applied at a constant speed, then a constant load is applied for a fixed time, and finally at the unloading speed, the ceramic parts that have not been destroyed at this stage are regarded as acceptable products. This is a guarantee test method for ceramic parts.

In order to achieve the above object, the invention according to claim 3 provides a container containing a liquid having a temperature sufficiently lower than the freezing point of water, and a ceramic component to be tested inside the container. And a load supply device for applying a bending load, a compressive load, or an internal pressure,
This is a screening guarantee tester for all ceramic parts that applies a predetermined load to all the ceramic parts before use and accepts the parts that are not destroyed as a result.

[0013]

According to the invention described in any one of claims 1 to 3, since the screening test of the ceramic parts is performed in a liquid which is sufficiently lower than the freezing point of water,
It is possible to perform a load test on a ceramic component while completely removing the influence of water molecules on the ceramic material. As a result, it is possible to prevent crack growth due to stress corrosion cracking during the load test, that is, reduction in strength of the ceramic component.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram for explaining a first embodiment of a guarantee test method for ceramic parts of the present invention. A test apparatus for carrying out the guarantee test method comprises a container 1, a lower jig 2 and , Upper jig 3, and liquid nitrogen 4 is stored in container 1.

The lower jig 2 has a V-shaped groove 2a formed in the upper portion thereof, and support member storage grooves 2b are formed at the left and right edges of the groove 2a.
Are formed at intervals (spans) L, and support members 2c each having a circular cross section are stored in the support member storage groove 2b. The lower jig 2 penetrates the bottom surface from the outside of the container 1,
The support member storage groove 2b is fixed so as to be located inside the container 1.

The upper jig 3 is formed in a taper shape so that the main body 3a fits in the supporting member accommodating groove 2b, and the punch 3c is supported and fixed to the tip of the main body 3a by the pin 3d, which is not shown. It can be moved up and down by a rolling down device.

In order to perform a guarantee test of the ceramic component 5 made of, for example, Si ₃ N ₄ with the test apparatus having such a configuration, first, the ceramic component 5 is dipped in the container 1 in which the liquid nitrogen 4 is stored. It is placed on the support member 2c of the side jig 2. In this state, a lowering device (not shown) pushes down the upper jig 3 to apply a 3-point bending load, and a screening test is performed.

FIG. 2 shows the time change σ (t) of the load stress (bending stress) due to the load applied in the screening test. As is clear from this figure, the constant load speed σ
The load is increased by 1 and the load is held at the guaranteed test load σa for the time t0, and then the load is removed at the unloading speed σ2. That is, in the guarantee test of the present embodiment, the ceramic component 5 that is not destroyed by the load as shown in FIG. 2 is selected as an acceptable product.

FIG. 3 shows S for carrying out a guarantee test in this embodiment.
Initial stage of ceramic parts 5 made of i ₃ N ₄ (before warranty test)
3 is a Weibull distribution diagram showing the variation distribution of the three-point bending immediate fracture strength σf. In the figure, the solid line represents the strength in normal temperature atmosphere, and the broken line represents the strength in liquid nitrogen.

Here, the three-point bending immediate fracture strength σf is the stress at the time of increasing the load at a constant load speed σ1 using a test apparatus as shown in FIG. 1 until the ceramic component 5 breaks. is there. In the Weibull distribution diagram, the horizontal axis represents the natural logarithm lnσf of the fracture strength σf, and the vertical axis represents the value ln [ln {1 / (1-P
f}] is taken and the strength of each test piece is plotted.

However, the destruction probability Pf corresponding to each test piece
Is the strength ranking i (i = 1 to k) within the total number k of test pieces
Is calculated by the equation (1). Pf = 1 / (1 + k) (1) As shown in FIG. 3, the initial strength distribution of the present ceramic component 5 is represented linearly in the Weibull distribution diagram. That is,
The distribution of the immediate fracture strength σf in the atmosphere and liquid nitrogen is approximated as a two-parameter Weibull, and in the atmosphere, it is expressed as in equation (2).

Pf = 1-exp {-(σf / β1) ^m1 } (2) Further, in the case of liquid nitrogen, it is expressed by the equation (3). Pf = 1-exp {-([sigma] f / [beta] 2) ^m2 } (3) Here, [beta] 1, m1 and [beta] 2, m2 are Weibull distribution parameters of the respective intensity distributions, but since they are m1 and m2, In the description of, m = m1 m2.

FIG. 4 shows the delayed fracture strength characteristics of the present ceramic component, where the horizontal axis shows the effective load time teff and the vertical axis shows the strength σf. In the figure, the solid line shows the characteristics in air, and the broken line shows the characteristics in liquid nitrogen. The effective load time teff is the holding time of the maximum stress σmax converted so that the crack growth amount becomes equivalent when the load stress varies. The crack growth law for stress corrosion cracking is based on the stress intensity factor K1.
[= Σ (πa) ^1/2 , a: crack size, σ: load stress] is used to express as in equation (4).

Da / dt = CK1 ⁿ (4) Here, C: crack growth rate constant n: crack growth rate exponent When the variable stress σ (t) is expressed by the equation (4), The effective load time teff is calculated by the equation (5).

[0025]

[Equation 1]

As shown in FIG. 4, the delayed fracture strength characteristics are
Expressed linearly in a logarithmic display, the characteristics in the atmosphere are
It becomes like the formula (6). σfteff ^{1 / n} = D (6) Here, D: strength constant of delayed fracture strength characteristic in the atmosphere In contrast, the characteristic in liquid nitrogen is effective load time teff
It is a constant value regardless of Considering the above-mentioned material characteristics, the strength distributions of the ceramic parts after the screening test will be compared and compared when the screening test is performed in the air and in liquid nitrogen. In the proof test in this example, if the lower 30% strength component is cut off from the initial strength distribution, the proof test load in the atmosphere and in liquid nitrogen is calculated by the equation (2). It can be determined from the equation (3). That is, the guaranteed test load σa1 in the atmosphere is σa1 = β1 ^m {ln [1 / (1-0.3)]} ^1/2 (7). Further, the guaranteed test load σa2 in liquid nitrogen can be determined as σa2 = β2 ^m {ln [1 / (1-0.3)]} ^1/2 (8).

When the guarantee test load is set as described above and a load as shown in FIG. 2 is applied as the screening test, the effective load time tes in the screening test in the atmosphere is
It can be obtained by integration of the equation (5), and becomes as shown in the equation (9).

Tes = t0 + {σa1 / σ1 (n + 1)} + {σa1 / σ2 (n + 1)} (9) In the screening test in the atmosphere, the stress σ1 should be applied for the effective load time tes as described above. Due to
The crack grows according to the crack growth rule as expressed by equation (4), and the strength decreases. Residual strength after screening test σR
Is dependent on the initial immediate fracture strength σfi that the ceramic part had before the screening test, and when the effective load time te1 in the immediate fracture test is expressed by equation (10).

ΣR = σa1 {(σfi / σa1) ⁿ -tes / te1} ^{1 / n} (10) Therefore, in the case of (σfi / σa1) ⁿ -tes / te1 >> 1, σR and σfi are almost equal. Is 1 ≧ (σfi
/ Σa1) ⁿ −tes / te1> 0, σR ≦
σa1 and further (σfi / σa1) ⁿ −tes /
When te1 <0, the ceramic parts are destroyed by delayed fracture during the screening test.

FIG. 5 is a diagram showing the results of the immediate destruction test in the atmospheric air at room temperature compared with the Weibull plots for the ceramic parts subjected to the screening test in the air and liquid nitrogen, respectively. in this way,
By conducting a screening test for ceramic parts in liquid nitrogen, it is possible to prevent crack growth due to such stress corrosion cracking, so it is possible to cut off low-strength parts without lowering the strength of the ceramic parts. it can.

According to the first embodiment described above, the screening test of ceramic parts is performed in liquid nitrogen, so that the influence of water on the ceramic material can be completely prevented. That is, since it is possible to prevent stress corrosion cracking during the screening test, it is possible to cut off the low-strength component without lowering the strength of the ceramic component.

FIG. 6 is a view for explaining a second embodiment of the guarantee test method for ceramic parts of the present invention. The test apparatus for carrying out this guarantee test method is a container 1 and a lower compression. It comprises a jig 8 and an upper compression jig 7, and the liquid nitrogen 4 is housed in the container 1. The ceramic component to be subjected to the proof test is a ceramic vane component 6 used for a vane of a gas turbine, which is sandwiched from above and below by an upper compression jig 7 and a lower compression jig 8 during actual use. Held in. For this reason, the ceramic stationary blade component 6 receives a compressive force from above and below by the upper compression jig 7 and the lower compression jig 8.

In the guarantee test method of this embodiment, as shown in FIG. 6, the ceramic stationary vane component 6 is placed in liquid nitrogen 4 and a compressive load similar to that in actual use is applied to the upper compression jig 7 and the lower compression jig. In addition to the compression jig 8, a part that is not destroyed by a predetermined compression load is adopted as an acceptable product. The operation and effect of this embodiment are exactly the same as those of the above-described first embodiment. In this embodiment as well, it is possible to cut off low-strength parts without lowering the strength of the parts.

FIGS. 7 and 8 are views for explaining a third embodiment of the guarantee test method for ceramic parts of the present invention. The test apparatus for carrying out this guarantee test method uses liquid nitrogen 4. The container 1 stored, the rubber tube 10,
Pipe 117, pressure generator 12, and holding block 1
3 and this is a ceramic sleeve part 9
The ceramic sleeve component 9 is used for a rotor blade of a gas turbine, and is combined with a metal cored bar so that centrifugal force acts as a compressive force. .

In the rotor blade of the gas turbine used in such a configuration, a difference in thermal expansion occurs between the metal cored bar and the ceramic component due to temperature changes during use, and the ceramic sleeve component 9 is not affected. , The force that is pushed out from the inside acts. In the guarantee test of the present embodiment, the ceramic sleeve component 9 which is wet in the figure is put in the liquid nitrogen 4 and the load due to the difference in thermal expansion similar to that during actual use is reproduced. The internal pressure is applied by the rubber tube 10 filled with liquid nitrogen. The rubber tube 10 is housed in a holding block 13 and connected to a pressure generator 12 via a pipe 11 so that the internal pressure can be controlled to a predetermined pressure. In the screening test, the parts that did not break under a predetermined pressure are adopted as acceptable products. The operation and effect of this embodiment are exactly the same as those of the above-described first and second embodiments, and in this embodiment as well, it is possible to cut off low-strength parts without lowering the strength of the ceramic parts.

The present invention is not limited to the above embodiment,
Although the load test for the ceramic parts was performed in liquid nitrogen, the liquid test is not limited to liquid nitrogen, and any liquid having a temperature sufficiently lower than the freezing point of water may be used.

[0037]

According to the present invention described above, it is possible to provide a guarantee test method and a guarantee test apparatus for a ceramic component, which does not cause a decrease in strength during a screening test.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodying apparatus for explaining a first embodiment of a guarantee test method for ceramic parts according to the present invention.

FIG. 2 is a diagram showing changes in applied load in a screening test by the implementation apparatus of FIG.

FIG. 3 is a Weibull plot diagram of the immediate fracture strength of Si ₃ N ₄ ceramic parts in air and in liquid nitrogen.

FIG. 4 is a diagram showing delayed fracture strength characteristics of Si ₃ N ₄ ceramic parts in air and liquid nitrogen.

FIG. 5 is a Weibull plot diagram of the immediate fracture strength of Si ₃ N ₄ ceramic parts in the air at room temperature after performing a screening test in air and in liquid nitrogen.

FIG. 6 is a schematic configuration diagram of an implementation device for explaining a second embodiment of the guarantee test method for ceramic parts according to the present invention.

FIG. 7 is a schematic configuration diagram of an embodying apparatus for explaining a third embodiment of the method for guarantee testing ceramic parts according to the present invention.

8 is a cross-sectional view taken along the line AA of FIG. 7 and viewed in the direction of the arrow.

FIG. 9 is a diagram showing delayed fracture strength characteristics of a conventional SiC ceramic component in the atmosphere.

FIG. 10 is a Weibull plot diagram of the immediate fracture strength of a conventional Al ₂ O ₃ ceramic part before and after the guarantee test.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Lower jig, 3 ... Upper jig, 4 ... Liquid nitrogen, 5 ... Ceramic component, 6 ... Ceramic stationary blade component, 7 ... Upper compression jig, 8 ... Lower compression jig, 9 ... ceramic sleeve parts, 10 ... rubber tubes, 11 ... pipes, 12 ... pressure generators, 13 ... holding blocks.

Claims (3)

[Claims] 1. A method for screening and testing all ceramic parts that applies a predetermined load to all the ceramic parts before use and accepts unbroken parts as a passing product. A guarantee test method for ceramic parts, characterized in that the test is performed in a liquid at a temperature sufficiently lower than the temperature. 2. All the ceramic parts before use are immersed in a container containing liquid nitrogen, and a constant load of bending load, compression load or internal pressure is applied to the ceramic parts. This is a guarantee test method for ceramic parts, in which the ceramic parts that have not been destroyed at this stage are judged as acceptable products by adding at a speed, then applying a constant load for a fixed time, and finally unloading at an unloading speed. 3. A container containing a liquid having a temperature sufficiently lower than the freezing point of water, and a bending load, a compressive load, or an internal pressure applied to a ceramic part to be tested, which is contained in the container. This is a screening assurance tester for all ceramic parts, which is equipped with a load supply device that applies a load, applies a predetermined load to all ceramic parts before use, and judges the parts that are not destroyed as a result to be acceptable products.