JPH01156662A - Non-destractive inspection method for fiber reinforced piston - Google Patents

Abstract

PURPOSE:To improve the accuracy for an inspection by detecting an acoustic emission in a temperature variation process of a fiber reinforced piston by using a waveguide plate. CONSTITUTION:To one end of a plate-like stainless steel waveguide plate 20, an acoustic emission (AE) sensor 22 is attached, and on the other end, a fiber reinforced piston 10 taken out of a casting metallic mold is placed. In such a way, an AE generated from the piston 10 is transmitted through the waveguide plate 20 and can be detected by the AE sensor 22, but heat does not reach the vicinity of the AE sensor 22, and the AE sensor 22 can be used without being subjected to a thermal load. A transfer loss of the AE extending from the piston 10 to the waveguide plate 20 and a transfer loss by the waveguide plate 20 are only a little, therefore, the AE generated from the piston 10 can be detected with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for non-destructive testing of fiber-reinforced pistons using an AE sensor, and particularly to improving the accuracy thereof.

[Prior Art] With the aim of reducing the noise of engines for automobiles and the like, the development of pistons in which a portion of the piston is reinforced with fibers such as carbon, silicon carbide, and alumina is underway. For example, as shown in FIG. 11, an annular fiber-reinforced part 12 made of reinforcing fibers is disposed coaxially with a part of the cylindrical part 10a of the piston 10. In such a fiber-reinforced piston,
Since the radial coefficient of thermal expansion of the cylindrical portion 10a of the piston 10 becomes small, the outer diameter of the cylindrical portion 10a of the piston 10 and
It becomes possible to design a small difference in the inner diameter of the corresponding cylinder liners, and the swinging motion of the piston 10 at the time of engine startup is suppressed, thereby reducing engine vibration noise.

When installing such a fiber-reinforced piston,
The fiber bundle shaped into an annular shape is placed in a predetermined position in a casting mold, and then, for example, aluminum hot water is poured into the mold and treated under high pressure to impregnate the fiber bundle with the aluminum hot water, and at the same time, the entire piston 10 is integrated. A fiber-reinforced piston is produced in which a part of the cylindrical portion 10a of the piston 10 is coaxially reinforced with fibers.

However, if the casting pressure is not appropriate, the fiber reinforced part 1
Poor impregnation of the aluminum hot water in No. 2 occurs, and when the piston 10 is taken out from the casting mold and cooled, cracks may occur from the defective impregnation area A as shown in FIG. 12. Furthermore, even if the casting pressure is appropriate and there is no impregnation defect, buckling failure B or delamination failure C may occur when the cast piston 10 cools, as shown in FIG.

This is because the coefficient of thermal expansion of the fiber-reinforced portion 12 is smaller than that of the single aluminum portion surrounding the fiber-reinforced portion 12, so compressive stress f is generated in the fiber-reinforced portion 12.
This is because the compressive stress f generated may be higher than the compressive strength of the fiber-reinforced portion 12 depending on the content of fibers No. 2 or the type of fibers.

Generally, after the piston 10 is cast, it is heat treated to develop an aluminum structure and improve the surface hardness and thermal deformability of the piston 10. Cracks may occur in the fiber reinforced portion 12.

As mentioned above, a piston with such a defect has little effect in suppressing the thermal expansion in the radial direction of the piston 10, and as a result, the intended goal of noise reduction cannot be achieved.
Even if a piston with a defect exhibits an effect of suppressing thermal expansion, repeated use of the engine will cause a thermal load to act on the piston 10, and cracks in the fiber-reinforced portion of the piston 10 will develop, leading to destruction of the piston. can also be considered. Therefore, it is extremely important to detect defects that occur during manufacturing in advance from the perspective of quality assurance.

However, the X-ray method, ultrasonic flaw detection method, thermal expansion measurement, etc. can be considered as non-destructive detection methods for the above defects, but none of them have sufficient accuracy and require a long time for inspection, making them impractical. isn't it. Therefore, when putting fiber-reinforced pistons into practical use, the probability of a non-destructive testing method that can detect the above-mentioned defects accurately and in a short period of time has become an issue.

In addition, in general destructive inspection of metal and FRP materials,
Acoustic emission (hereinafter referred to as AE) can be detected, for example, in JP-A-60-135861, JP-A-61-184456, "Kuchihon Hakusei Materials Society Journal, 10.3 (1984), p. 102. ~106''.

Purpose of the Invention The present invention solves the above-mentioned technical problems, and detects AE during the temperature change process of the fiber-reinforced piston using a waveguide plate, thereby accurately and quickly detecting defects that occur during the manufacturing of the fiber-reinforced piston. This provides a non-destructive testing method for detecting

[Means for Solving the Problems] The non-destructive testing method for fiber-reinforced pistons of the present invention includes: a plate-shaped waveguide plate; an AE sensor attached to one end of the waveguide plate to detect acoustic emissions; The other end of the waveguide plate is brought into contact with a metal piston containing a circular fiber-reinforced part made of inorganic continuous fibers or short fibers, and the acoustic emission emitted during the temperature change process of this piston is - A defect in the piston is detected by measuring with the AE sensor via the waveguide plate.

[Operation] The defects that can be detected by the above-mentioned inspection method of the present invention are as follows.

First, impregnation failure occurs due to the aluminum hot water not being sufficiently impregnated into the fiber bundle due to insufficient casting pressure during casting or insufficient preheating of the fiber bundle shaped into an annular shape, or insufficient impregnation. However, because the coefficient of thermal expansion of the fiber-reinforced part and the single aluminum part that surrounds it is significantly different, large compressive stress is applied to the fiber-reinforced part during manufacturing cooling or heat treatment, resulting in damage to the fiber-reinforced part. (
(buckling failure or interlaminar failure between fibers).

The destruction of this fiber-reinforced part depends on the mechanical properties of the fiber-reinforced part, such as elastic modulus, thermal expansion coefficient, compressive strength, adhesive strength between fiber and aluminum, etc., and these depend on the cellulose a ratio of the fiber-reinforced part, It is related to the bundled state of the fibers, as well as the type and surface condition of the fibers.

In the present invention, these defects are detected by AE generated during the temperature change process of the piston, for example, the cooling process during casting, and the heating and cooling process during heat treatment.
The principle of occurrence is thought to be as follows. In other words, one is when a crack occurs in the material due to stress, and as a result, the stress that existed around the crack is released all at once, which becomes an elastic wave and becomes AE. This is called "crack AE". Name it. The other type of AE occurs when the defective surfaces that already exist are deformed by heat load and the defective surfaces rub against each other, and this is called "friction AE."

Named in this manner, it can be said that the AE that occurs during the manufacture of fiber-reinforced pistons is caused by two types of mechanisms: crack AE and friction AE.

In fiber-reinforced pistons, the annular fiber-reinforced part has a very small coefficient of thermal expansion, and the difference in coefficient of thermal expansion between the fiber-reinforced part and the aluminum part surrounding it is large. When taken out from the mold and allowed to cool naturally, compressive stress is generated in the fiber-reinforced part, and if the compressive stress exceeds the compressive strength of the fiber-reinforced part, buckling failure or delamination failure may occur in the fiber-reinforced part. At that time, the above-mentioned crack AE occurs. Therefore, by measuring the AE during cooling of the casting, it is possible to detect the destruction (cracks) of the fiber-reinforced portion that occurs at that time.

In addition, when manufacturing fiber-reinforced pistons, the casting pressure may be insufficient, or the fiber bundle formed into an annular shape before casting is preheated to improve impregnation with aluminum hot water, but the heating is insufficient. In such a case, poor impregnation may occur in the fiber-reinforced portion when aluminum hot water is poured and cast. When this piston is taken out of the casting mold and cooled, the compressive stress mentioned above is generated in the fiber-reinforced portion, causing cracks to occur from the defective impregnation portions, and at this time, cracks AE occur. Furthermore, even if no cracks occur, the defective impregnation portion is deformed by thermal stress, and at this time, rubbing occurs within the defective impregnation portion, causing the aforementioned friction AE. Therefore, by measuring the AE during casting cooling, it is possible to detect the presence or absence of poor impregnation during casting.

Furthermore, when the piston is taken out of the casting mold and allowed to cool naturally, thermal stress is generated in the fiber-reinforced part, which causes interlaminar failure or buckling failure in the fiber-reinforced part, and as a result, cracks AE occur. .

Therefore, by measuring the AE during cooling of the casting, it is possible to detect interlaminar fractures and buckling failures that occur during cooling of the casting.

Furthermore, normally cast pistons are subjected to heat treatment, but at that time, if a piston with poor impregnation in the fiber-reinforced part during casting or a piston with cracks in the fiber-reinforced part due to thermal stress during casting is heated, the inside of the defective impregnation part may occur. Alternatively, friction occurs due to deformation due to thermal load within an already existing crack, causing friction AE. Therefore, the AE during heat treatment
By measuring this, pistons with poor impregnation and cracks in casting cooling can be selected.

In addition, during the cooling process of heat treatment, thermal stress is generated in the fiber-reinforced part in the same way as during casting cooling, so this may cause poor impregnation in the fiber-reinforced part, or the type and amount of fibers may be incorrect. If not, a new rack will be generated,
Therefore, crack AE occurs. Therefore, by measuring the AE during the cooling process of heat treatment Al11, it is possible to select pistons having these defects.

As described above, by checking the AE during the temperature change process such as the heating and cooling process during casting cooling and heat treatment, it is possible to detect the occurrence of defects and to select pistons with defects.

Next, regarding the method for measuring AE, AE generally consists of an AE sensor, an amplifier, and a counter, all of which can be commercially available. It is desirable to place the AE sensor on the surface of the test object, which in this case is a fiber-reinforced piston, but the surface temperature of the piston immediately after casting is approximately 300°C, and during heat treatment it is heated to nearly 500°C. . There are very few sensors that can be used in such high temperature areas. Therefore, for example, as shown in FIG. 1, an AE sensor 22 is attached to one end of a stainless steel plate 20, which is a plate-shaped waveguide plate, and a piston 10 taken out from a casting mold is placed on the other end to measure AE. is possible. In this way, the AE generated from the piston 10 is transmitted through the stainless steel plate 20 and detected by the AE sensor 22. On the other hand, the heat of the piston 10 is transferred to the stainless steel plate 20, but since stainless steel has a low thermal conductivity, the heat does not reach the vicinity of the AE sensor 22, and the AE sensor 22 can be used without being subjected to a heat load. The transmission loss of AE from the piston 10 to the stainless steel plate 20 and the transmission loss at the stainless steel plate are negligible, and the piston 10
It is possible to accurately detect AE generated from

Note that the stainless steel plate 20 was placed on a stand 26 with a rubber plate 24 in between so as not to pick up noise. Also, AE sensor 2
The measurement results of step 2 are counted by a counter 30 via an amplifier 28.

Further, an example of measurement during heat treatment is shown in FIG.

In this case as well, insert the stainless steel plate 20 into the electric furnace 32,
The piston 10 is placed on it, and the AE
A sensor 22 can be attached to measure AE generated during heat treatment.

Note that by measuring the temperature of the piston at the same time as the AE measurement, it is possible to know at what temperature defects are likely to occur.

[Effect] Fiber-reinforced pistons are highly effective in reducing noise. However, if poor impregnation occurs in the fiber-reinforced part during manufacturing or cracks occur in the fiber-reinforced part due to thermal stress, etc., not only will noise reduction not be possible, but the cracks will develop due to continuous use of the piston, resulting in There may also be cases where the functions of the above are not met. Therefore, it is very important to detect these defects in advance for piston quality control.

The defect detection method proposed in the present invention can be carried out simultaneously during cooling and heat treatment of casting without creating a new process for measurement, and can be carried out simultaneously during cooling and heat treatment of casting, and without missing a single fiber. Defects can be detected with high accuracy.

In addition, conventionally, the fiber-reinforced part was cut and the state of internal defects was observed, but the present invention can detect the occurrence of defects non-destructively, and by applying this to all pistons. It is possible to accurately select only pistons with defects.

In addition, the present invention is not only applied to detecting defects, but also considers how to construct a fiber-reinforced part that does not cause defects, such as optimization of casting pressure, selection of reinforcing fibers, It can also be used to determine the fiber content, consider the placement of fiber-reinforced parts, and can also be useful in the development of fiber-reinforced pistons.

[Example] Hereinafter, the method for non-destructive testing of fiber-reinforced pistons of the present invention will be described based on Examples.

Example 1 In the configuration shown in FIG. 1, width 150ffla + length 5
Place a stainless steel plate 20 with a thickness of 0ff1m and 5Illfil on the rubber plate 24, and connect the AE sensor 22 (resonance frequency 1) to one end of the stainless steel plate 20 through silicone grease.
40kllz) is installed, and the signal from the AE sensor 22 is first amplified by 40dB with a preamplifier (with a 100kllz bypass filter), and then further amplified by 55dB with the main amplifier.
A total of 71pr systems (Duncg
A total of 7111 AEs were obtained during cooling of the casting using the following method.

In Example 1, when the casting pressure is appropriate (1200 kg/
cd ) and when the casting pressure is half the optimum value ([10
A cast product of the piston 10 (0 kg/c+#) immediately after casting was placed on a stainless steel plate, and the AE during the cooling process was compared.

Note that carbon fiber (M30J manufactured by Toshi) was used as the reinforcing fiber. The lhJ degree of the piston was measured using a surface thermometer.

The results are shown in FIGS. 3 and 4. When the casting pressure was appropriate, very little AE was generated, whereas when the casting pressure was half of the appropriate value, a large amount of AE was generated during the cooling process. After cooling, we cut the fiber-reinforced parts of both pistons and observed their cross-sections, and found that no poor impregnation was observed in the pistons with the proper casting pressure, but in the case of the pistons with the casting pressure half of the proper value. In the manufactured piston, there were several locations with poor impregnation. From the above results, it is clear that defects (poor impregnation) in fiber-reinforced pistons can be detected by the present non-destructive testing method.

Example 2 In Example 2, the present invention was applied to detecting cracks that occur during casting cooling. The configuration of the AE method is exactly the same as in Example 1, but here, a fiber-reinforced piston was cast using a different fiber (carbon fiber [Toshi M40J]) at an appropriate casting pressure. did.

FIG. 5 shows the measurement results of the casting cooling process, and a large amount of AE was generated during the cooling process. After the measurement, when the cross section of this piston was observed, many buckling failure points were observed in the fiber reinforced portion.

From the above results, it is clear that defects (cracks) in fiber-reinforced pistons can be detected by the present non-destructive testing method.

Example 3 Example 3 was also applied to the detection of cracks that occur during casting cooling. The AE method is exactly the same as in Example 1, but here the same fiber as in Example 1,
The amount of fiber was halved based on the cross-sectional area of Example 1 and placed in a casting mold, and a fiber-reinforced piston was cast at an appropriate casting pressure. FIG. 6 shows the measurement results of the casting cooling process, and a large amount of AE was generated during the cooling process. After the measurement, when the cross section of this piston was observed, many cracks were observed in the fiber-reinforced portion due to thermal stress due to the small amount of fiber filling.

From the above results, it is clear that defects (cracks) in fiber-reinforced pistons can be detected by the present non-destructive testing method.

Embodiment 4 As shown in FIG. 2, one end of a stainless steel plate 20 with a width of 150 mm, a length of 500 a+n, and a thickness of 5 mm is inserted into an electric furnace 32 having a window large enough to insert the stainless steel plate, and the other end is inserted into the electric furnace 32. Arrange the stainless steel plate 20 so that it is outside the electric furnace 32, attach the AE sensor 22 to the end of the stainless steel plate located outside the electric furnace 32 via silicone grease, and first output the signal from the AE sensor 22 to the preamplifier.
Amplify by 0dB and further amplify by 55dB with the main amplifier,
Using a measurement system that can count the number of amplified signals whose amplitude value exceeds a threshold of 1 V generated per unit time using a counter 30, the piston after casting is placed on a stainless steel plate 20 in an electric furnace 32. AE generated during heat treatment
was measured.

In this Example 4, as in Example 1, the occurrence of AE during heat treatment was compared between a piston cast under appropriate casting pressure conditions and a piston cast under half the appropriate casting pressure. In this example, the heat treatment conditions were 5°C/min and 300°C.
After heating to °C and holding for 1 hour, it was cooled at 5 °C/min. The results are shown in Figure 7.8. Pistons cast with proper casting pressure generate very little AE even during heat treatment, whereas pistons with insufficient casting pressure generate a lot of AE even during casting cooling, as described in Example 1. Furthermore, a large amount of AE was generated during the heating process of the heat treatment. In particular, it often occurs during the heating process of heat treatment.

This is thought to be due to the friction AE mechanism in which poor impregnation caused by insufficient casting pressure or cracks generated during casting cooling are rubbed by the heat load. Further, it is considered that the AE generated during cooling is caused by the further propagation of cracks from the defective impregnation area due to thermal stress generated by cooling during heat treatment.

From the above results, it is clear that defects (poor impregnation) in fiber-reinforced pistons can be detected by the present non-destructive testing method during heat treatment.

Example 5 In Example 5, the present invention was applied to the detection of cracks that occur during heat treatment. The method for measuring AE is exactly the same as in Example 4, but here, as in Example 2, a fiber different from the appropriate fiber type (carbon fiber "M40 manufactured by Toshi") was used to obtain an appropriate casting pressure. The AE during heat treatment of the bis-i-n cast in the following manner was measured.

The results are shown in Figure 9. This piston also generated AE during casting cooling, but when it was further heat treated, the heating process
Many AEs occurred during the cooling process (during aging treatment).

When the cross section of the piston was observed after the heat treatment, more buckling failure points than those observed in Example 2 were observed in the fiber-reinforced portion. Therefore, the AE generated during the heating process is the friction A caused by the heat load rubbing the cracks generated during the cooling of the casting.
This is due to the E mechanism, and the AE generated during cooling is considered to be crack AE due to thermal stress.

From the above two results, it is clear that defects (cracks) in fiber-reinforced pistons can be detected by this non-destructive testing method during heat treatment.

Example 6 In Example 6, the presence of cracks was detected by AE generated during heat treatment. The AE measurement is exactly the same as in Example 4, but here, as in Example 3, an appropriate fiber (carbon fiber "Toshi M30J") was used, but the filling amount was less than the appropriate value. The AE was measured when the piston was heat treated (aging treatment), which had been cast in this state.Figure 10 shows the occurrence of AE during heat treatment, and a large amount of AE was generated during the heating process, and relatively little during the cooling process. few.

It is thought that the AE during this heating process is due to frictional AE caused by the cracks generated during casting cooling being rubbed by the heat load during heat treatment.

From the above results, it is clear that defects (cracks) in fiber-reinforced pistons can be detected by this non-destructive testing method during heat treatment.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a system to which one embodiment of the non-destructive testing method for fiber-reinforced pistons according to the present invention is applied. FIG. 2 is a configuration diagram of a system to which another embodiment is applied. 5, 6, 7, 8, 9, and 10 show temperature changes and A in the embodiments of the present invention.
A characteristic diagram showing the relationship between the E occurrence rate, Fig. 11 is for the piston 10.
12 is a horizontal and vertical sectional view showing the structure of the piston 10. FIG. 12 is a horizontal sectional view illustrating a defect in the piston 10. 10... Piston 12... Fiber reinforced part 20... Stainless steel plate (waveguide plate) 22...
AE sensor

Claims (5)

[Claims] (1) It has a plate-shaped waveguide plate, and an AE sensor attached to one end of the waveguide plate to detect acoustic emissions, and the other end of the waveguide plate is made of inorganic continuous fibers or short fibers. By contacting a metal piston with a built-in annular fiber-reinforced part and measuring the acoustic emissions emitted during the temperature change process of the piston with the AE sensor via the waveguide plate, defects in the piston can be detected. A method for non-destructive testing of fiber-reinforced pistons. (2) A non-destructive testing method for a fiber-reinforced piston according to claim 1, wherein the temperature change process is a cooling process after the piston is cast. (3) A non-destructive testing method for a fiber-reinforced piston according to claim 1, wherein the temperature change process is a heating process when the piston is heat-treated. (4) A non-destructive testing method for a fiber-reinforced piston according to claim 1, wherein the temperature change process is a cooling process when the piston is heat-treated. (5) In the method according to any one of claims 1 to 4, the waveguide plate and the piston both have flat surfaces, and the contact between the waveguide plate and the piston is on the waveguide plate. 1. A non-destructive testing method for a fiber-reinforced piston, characterized in that the piston is placed on the piston so that the flat surfaces thereof are in contact with each other.