JPH05209874A - Method and apparatus for detecting microfine cracking of metal part having insulation coating - Google Patents

Abstract

PURPOSE:To obtain a method and apparatus for detecting microfine cracking in a structure which is repetitively subjected to load including car components. CONSTITUTION:An insulating coating 1 is formed in advance on a metallic surface for the purpose of detecting microfine cracking caused on the metallic surface of a metallic part, and electrolytic solution 3 containing electrochromic substance is applied. The metal is made into a cathode and potential is applied between the cathode and an anode 5, whereby only a cracking portion 4 is colored to have the cracking detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting minute surface cracks in a metal part having an insulating film, and more particularly to a method and a device for detecting fatigue cracks in aluminum parts for automobiles and airframes of aircraft.

[0002]

2. Description of the Related Art In structural members such as automobile parts that are subjected to repeated loading, it is an important subject to compensate the strength reliability against fatigue. And in order to guarantee the high durability and reliability required for automobile parts,
Strict shock or endurance test is done. It is natural that through these tests, it is confirmed that cracks do not occur, but from the viewpoint of optimizing the part design shape and material development, these parts are oversized, for example, exceeding the allowable value. Information such as the shape, position, and size of cracks generated when a load is applied is very useful, and an excellent crack detection method is required. Conventionally, magnetic powder flaw detection and fluorescent flaw detection have been used as a simple method for detecting cracks, but the size of surface cracks that can be detected by these is at most about 2 mm, and whether they are newly caused by load or not. However, there was a drawback that it was difficult to judge. In order to solve this problem, and particularly for crack detection of aluminum parts, which have recently been greatly expanded in use, an electrochemical method (SAE840122) as shown in FIG. 1 has been proposed. As shown in the figure, when a crack 4 occurs due to a load on the surface of a metal part 2 having an insulating film 1, for example, a surface of an aluminum part that has been subjected to chemical conversion treatment, the insulating film 1 is broken, and the position of the crack 4 has conductivity. Like Therefore, a gel-like solution 3 that is a detection liquid that develops color on the surface of the component 2 by means of energization, for example, a mixed solution of KI and starch (shows a dark blue color when energized)
When the probe 2 of the anode is scanned with the component 2 applied to the cathode side and the component 2 is on the cathode side, the crack site becomes 2I ⁻ → I ₂ + 2e ⁻ , and iodine reacts with starch. Can be detected. This method has the advantages that it is simpler, has higher sensitivity than conventional flaw detection methods such as magnetic particle flaw detection and fluorescence flaw detection, and that only cracks after chemical conversion treatment can be detected. However, when it is attempted to detect a microcrack of 1 mm or less by the above-mentioned electrochemical crack detection method, (a) the crack site is colored dark navy blue, and it is unclear to distinguish it from the shadow of a black gel. (B) Due to excessive precipitation of iodine, the surrounding area becomes polluted,
The contour, especially the tip, is unclear. Moreover, after the gel solution 3 of the detection liquid was included in gauze or the like and applied to the surface of the component, the bare probe 5 was attached to the applied gel solution 3, so (c) the gel would flow if the viscosity was low. On the contrary, if it is too high, it is difficult to apply it uniformly, so it is necessary to keep it at an appropriate temperature.
In the conventional method, it is difficult to keep the gel at an appropriate temperature and eliminate uneven coating. (D) Since the exposed electrode is used, when the electrode comes into contact with the surface of the component, the electrode may be burned or the surface of the component may be damaged. On the contrary, if the electrode is too far away from the component, the coloring reaction is delayed and the working efficiency is deteriorated. It is necessary to keep a proper gap between the electrode and the component. On the other hand, in recent years, as a method to quantitatively understand the fatigue phenomenon, a fracture mechanics method focusing on the growth of fatigue cracks has been developed, and when the conditions such as shape and load are simple like a test piece, the fatigue fracture is fairly accurate. The behavior can be estimated. However, there are many problems in applying the method to parts with complicated shapes, and one of them is the measurement of crack opening and closing in actual parts. 5 and 6 (a) and 6 (b) are explanatory views of the crack opening / closing port, FIG. 5 is a time change of load stress, and FIGS. 6 (a) and 6 (b) are schematic diagrams of the crack. The crack 4 does not always open even when it is subjected to repeated tensile stress (amplitude Δσ1) (Fig. 6 (a)), is in a crack closed state (σ <σOP), and contributes to fatigue crack growth. , After all cracks have opened (σOP) (Fig. 6 (b)
, The stress amplitude Δσ2 of the crack opening state σ> σOP). Various factors that affect the crack growth behavior, such as residual stress and load fluctuation, can be sorted out by using the effective stress amplitude.Therefore, for the material of the metal part 18, the crack growth characteristic data for the effective stress should be investigated and The crack behavior can be accurately estimated by measuring the crack opening stress of 18. Conventionally, as a method for measuring the crack opening stress, a strain gauge is attached near the crack to detect a change in strain associated with the crack opening / closing, or a change in reflected wave associated with the crack opening / closing using ultrasonic waves. There is a detection method, but the sensitivity is insufficient for a real part that has a complicated load input fluctuation and is noisy, or the device and operation become large. Further, when there are a plurality of cracks of different sizes, it is difficult to measure with either method. Therefore, there is no suitable crack opening / closing observation method for actual parts.

[0003]

The first object of the present invention is to solve the above-mentioned problems, and to use a detection liquid which can easily control the color development and decolorization of a crack portion, especially when the crack is opened, and which is made of metal. It is an object to provide a method for detecting minute surface cracks in a component. In order to solve the above problems, a second object of the present invention is to properly maintain the distance between the electrode of the detection liquid container and the component and the viscosity of the detection liquid in the microcrack detection device.
It is an object of the present invention to provide a microcrack detection device capable of efficiently performing an electrochemical crack detection operation.

[0004]

The method for detecting microcracks according to the present invention is such that an insulative film is formed in advance on a metal surface for the purpose of detecting microcracks generated on the surface of a metal part, and is used as a detection liquid. The present invention is characterized in that an electrolytic solution containing an electrochromic substance is applied, the metal serves as a cathode, and a potential is applied between the metal and the anode so that only the cracked portion is colored. In this detection method, the potential applied between the cathode and the anode is preferably a rectangular wave of 0.5 to 2.0 V, 1 to 100 Hz, and a coloring reaction occurs by applying a potential in this range. Therefore, the applied potential is 0.5
It is advisable to apply a rectangular wave of V, 1 to 100 Hz, repeat coloring and erasing according to the pulse, and emphasize the crack tip to perform continuous observation. The crack detection method of the present invention is to clearly detect the crack generated on the metal surface having the insulating film as described above by the coloring reaction based on the electrochromic reaction. Hereinafter, a method of continuously observing cracks while subjecting the Al alloy test piece for fatigue test to a fatigue test will be described. The test piece has an insulating film adhered to the surface after molding. In the case of Al alloy, the most convenient and reliable method for producing the insulating film is by anodic oxidation. However, when anodic oxidation is not possible, for example, in the case of iron type, vapor deposition or coating may be used.
The electrolytic solution is prepared with the following specifications. First, heptyl viologen bromide is dissolved in a supporting electrolyte. In order to make the electrolyte viscous, add agar powder as appropriate and heat to melt. Next, the operation will be described. The viologen is represented by the following formula 1.

[Chemical 1] (In the formula, R represents an electron withdrawing group such as an alkyl group or a benzyl group, and X ⁻ represents a halogen ion). The coloring mechanism of viologen will be described. Viologen is present in an aqueous solution by being dissociated into a dication and a halogen anion. Now, if a potential difference is applied between the electrode to be colored and the cathode as a cathode and the probe 5 shown in FIG. 1, the viologen radical is attracted to the surface of the cathode and receives one electron.

[Chemical 2] As shown by the formula (3), it becomes a blue cation radical, which further reacts with a halogen ion and is deposited on the cathode surface to exhibit a reddish purple color. The voltage to cause this reaction is 0.
6 to 1.0V is good. Further, if the potential difference is given as a rectangular wave, coloring and decoloring are continuously repeated. Experiments have shown that this response is possible up to 100Hz. Not limited to viologen, phthalocyanine or the like can be used as long as it is a substance exhibiting electrochromism. Practically, it is selected from those having a low coloring voltage and a vivid color and easily decoloring. Implementation of the above-described method for detecting microcracks
When a small crack detection device equipped with a crack detection liquid container is set on a metal part with an insulating film to detect cracks, the crack detection work is much more accurate and efficient than before. Can be done on a regular basis. Therefore, the present invention also relates to a microcrack detecting device used in the above-described microcrack detecting method. The device used for such a method for detecting microcracks has (1) a plurality of rollers covered with an insulator whose surface is in contact with the insulating coating of a metal part in the lower portion of the crack detection liquid container, and the rollers between the rollers. (2) Further, between each roller, electrodes having a length substantially equal to the roller axis length, which is parallel to the roller axis and connected to a metal part through a power source, are provided. ,
(3) It is characterized by having a heating element in the vicinity of the rotation axis of the roller and the crack detection liquid discharge portion. Next, a microcrack detecting device will be described with reference to the drawings. FIG. 2 is a diagram showing a microcrack detecting apparatus according to an example of the present invention. Reference numeral 6 denotes a gel container which is a detecting liquid container, and stores a gel 8 of the detecting liquid supplied from a supply port 7 therein. Reference numeral 9 denotes a roller attached to the gen container 6, the surface portion of which is made of a hygroscopic insulator. Reference numeral 11 denotes a rotary shaft that rotates together with the roller 9 and is connected to a power source 10 to generate heat. roller
The roller 12 has the same structure as the roller 9,
It is arranged in parallel with. Gel 8 is roller 9 and roller
It is designed to be discharged only from between 12, and a gel pool 14 is formed between the roller 9 and the roller 12 and the metal part 18. Reference numeral 13 is a heating element, which is connected to the power source 10 and is arranged in the vicinity of the two rollers to keep the viscosity of the gel moderate. Reference numeral 15 denotes an electrode, which has substantially the same length as the roller shaft length so that electricity can be uniformly applied along the roller shaft length, and is arranged in the gel pool 14 in parallel with the roller shaft. Further, the electrode 15 can change the distance to the component by moving the electrode moving mechanism 17 in the direction of the arrow. 16
Is a potentiostat, and the cathode and the anode are connected to the component 13 and the electrode 15. In order to detect microcracks using the above device, as shown in the figure, the gel container 6 is placed on the insulating film of the metal part 18, the rollers 9 and 12 are kept at a predetermined temperature, and the heating element 13 is operated. After the viscosity of the gel 8 of the detection liquid stored in the container is maintained at an appropriate level, the gel pool 14 is formed, the electrode 15 is positioned by the electrode moving mechanism 17, and then a pulse current is passed by a potentiostat to cause the device to flow. Move while pressing on the insulating film of the metal part.
When the device reaches the crack portion, the electrochromic substance is colored vividly and the crack can be detected.
In the above device, by using the rotating shaft 11 as a heating element,
The gel viscosity near the most important exit is optimized and the gel does not stick to the roller when the roller is moved.
Further, since the roller surface is made of an insulator, it does not burn even if it touches the electrode, and the heating element 11 which is the roller rotating shaft and the electrode 15 are not short-circuited. The roller functions to keep the distance between the metal part and the electrode constant, and even if the device is moved while being pressed against the metal part, the friction is small and there is no fear of damaging the surface of the metal part. FIG. 4 shows a crack detecting device according to another example of the present invention. The illustrated apparatus is characterized in that, in addition to the configuration of the apparatus shown in FIG. 2, a heating element 13 and a temperature control mechanism 24 for the rotating shaft 11, which is the heating element, are provided. It is desirable that the viscosity of the gel be low when detecting cracks in a wide horizontal area, and slightly higher so that the gel does not flow down at a portion where the inclination is severe. The temperature control mechanism 24 allows the viscosity of the gel to be optimally controlled according to the condition of the metal part.

[0005]

In the crack detecting device of the present invention, the viscosity of the gel from which the above-mentioned heating element is discharged can be properly maintained, and the gel discharge amount and the distance between the electrode and the component can be made constant by a plurality of rollers. The accuracy of can be improved and the work efficiency can be greatly improved.

[0006]

EXAMPLES The present invention will be described with reference to Examples and Comparative Examples. Example 1 First, after forming a fatigue test piece, an insulating film was formed on the surface by the following procedure. That is, after the process of etching with a 1 mol / l sodium hydroxide solution → washing with water → neutralization with 1 mol / l dilute nitric acid → washing with water, a current density of 20 A / dm ² was applied for 30 seconds in a 30% phosphoric acid solution at 70 ° C. Anodization was performed. Then, it was washed with water and dried. The above test piece is 10Hz, stress ratio 0.
A fatigue test was performed under the condition of 1. Around the cutout area, apply agar to an aqueous solution containing 5 mg of methylviologen and 2% by weight of potassium chloride (KCl), apply the solution, and apply a probe shown in Fig. 1 or 2 to apply a voltage of 0.8V. I put it in between. Electrons were donated by the mechanism described above at the location where cracks occurred and the insulating film was destroyed at the same time, resulting in color development. The crack progress was observed by observing it with an optical moving microscope. Since the color can be erased by turning off the voltage, there is no contamination around the crack as in the conventional method. Further, since the tip portion of the crack has high electrochemical activity, it was possible to observe the tip portion of the crack in detail by utilizing the fact that the color development is concentrated. Example 2 In Example 1, a rectangular wave of 0.8 Hz and 1 Hz was applied to cause continuous color development and decolorization, and the progress of cracks was observed in detail by a continuous photograph or video camera with the tip portion emphasized. I was able to do it. COMPARATIVE EXAMPLE 1 Instead of the electrolytic solution used in Example 1, a mixed solution of KI and starch was applied, and when the probe of the anode was scanned with the component on the cathode side, the color reaction was irreversible. However, it was not possible to observe the growth of the tip part by accumulating around the crack. Example 3 In the detection device shown in FIG. 2, the size of the roller 9 and the roller 12 was 3 mm in diameter × 5 mm in axial length, and the gel 8 was an aqueous solution containing 5 mg of methylviologen and 2% by weight of KCl and agar added thereto. .. The temperature of the rotating shaft 11 was 40 ° C, and the temperature of the heating element near the roller was 35 ° C. Metal parts 18 are JIS A2
618 is a 14 × 14, R4 semicircular notched bending test piece that has been subjected to chemical conversion treatment. After repeatedly applying a load to this test piece and observing a surface crack having a length of 1 mm at the notch bottom with an optical microscope, the test piece was connected to the cathode side of the potentiostat 16. The electrode 15 was connected to the anode side, and a pulse current of 10 V and 50 ms was supplied from the potentiostat 16. After that, the detection device was pressed against the crack generation position of the test piece. By the heating element 13, the gel 8 was supplied to the gel pool 14 without excess or deficiency.
Further, since the rotating shaft 11 is a heating element, the gel viscosity near the most important outlet is optimized, and the cracked portion can be colored sharply. 3 (a) and 3 (b) schematically show the crack detection results of the conventional crack detection device and the example product. FIG. 3 (a) shows the result of a conventional method in which a mixed solution of gel KI and starch was applied to the surface of a test piece and the test piece was placed on the cathode side and the probe of the anode was scanned. The electrode causes a scratch 20 or the electrode is too close to the test piece, causing seizure or excessive reaction 21 and the crack shape is unknown. Further, if the viscosity of the gel is too high and unevenness is generated, a shadow 22 is formed, which may be mistaken for a crack. FIG. 3 (b) shows the results of this embodiment, but the above problems did not appear, and it was possible to easily color the crack portion 23 clearly and to improve the crack detection accuracy. Example 4 After molding a test piece for fatigue test, an insulating film was formed on the surface by the following procedure. That is, 1 mol / l
After etching with sodium hydroxide solution → washing with water → neutralization with 1 mol / l dilute nitric acid → washing with water, 30% phosphoric acid solution, 70
Anodization was performed for 30 seconds at a current density of 20 A / dm ² at ℃. Then, it was washed with water and dried. 10H for the above test piece
A fatigue test was conducted under the conditions of z and stress ratio of 0.1. The electrolytic solution was applied around the notch, and the probe shown in FIG. 2 was applied to apply a voltage of 0.8 V between them. At the same time as the crack was generated, the insulating film was also destroyed, but the reaction did not occur because the crack was closed until the crack opening stress was applied. When a load was applied to the test piece, a crack eventually opened, and at the same time, a metal surface having electrical conductivity was exposed, so that electrons were donated by the mechanism described above to develop color. The opening stress can be found by obtaining the stress at the time when color development is recognized from a triaxial strain gauge (not shown) attached near the crack. Even when a plurality of cracks having different sizes are present as in this example, the above-mentioned stress occurs for each crack, so that the opening / closing port of any crack can be observed. Further, the position of the crack may not be particularly clear. Example 5 A test piece was prepared according to the procedure of Example 4, and a fatigue load was applied at a load speed of 1 Hz. A rectangular wave of 0.8 Hz and 1 Hz was applied in synchronism with the load cycle so that the color was erased when the load stress was at a minimum, and the color was continuously developed and erased. The behavior of crack opening and closing during the fatigue process can be continuously observed by continuous photographs or video cameras.

[0007]

As shown in the above embodiments, the crack detection method of the present invention makes it possible to clearly observe a crack generated on the surface of a metal having an insulating film by a coloring reaction based on an electrochromic reaction. Now, it becomes possible to observe the crack growth process in detail, and it is now possible to easily observe the opening / closing behavior of surface cracks in actual parts, which had no suitable method until now. Furthermore, in addition to the effects described above in these examples, since the test piece is colored by negative polarization, the conventional method uses the component side as the anode, so the broken insulating film is regenerated and crack detection is performed. The disadvantage of reduced sensitivity can be prevented, while the cracks are colored so that the crack growth behavior can be observed very easily and the relationship between the measured effective stress and the crack growth behavior can be known. Be done. Further, in the microcrack detection device of the present invention, at the tip of the crack detection liquid discharge portion, the surface portion has a plurality of rollers that are hygroscopic insulators, and between each roller is approximately the roller axis length in parallel with the roller axis. Equipped with electrodes of the same length and having a heating element in the vicinity of the rotation axis of the roller and the crack detection liquid discharge part, the crack detection work should be much more accurate and the work efficiency should be greatly improved. The effect of being able to do is obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a crack detection method for a metal component that shakes an insulating film.

FIG. 2 is a cross-sectional view of a microcrack detection device according to an example of the present invention.

FIG. 3A is a diagram schematically showing a detection result by a conventional detection method, and FIG. 3B is a diagram schematically showing a detection result by the detection method of the present invention.

FIG. 4 is a cross-sectional view of a microcrack detecting device of another example of the present invention.

FIG. 5 is a graph showing a time change of a load stress of a metal part for detecting a microcrack.

FIG. 6 (a) shows a closed state of a crack generated when a metal part is subjected to repeated tensile stress, and (b) is an opening of a crack generated when the metal part is subjected to repeated tensile stress. Indicates the state.

[Explanation of symbols]

 1 Insulating film 2 Metal parts 3 Detection liquid or electrolyte 4 Crack 5 Anode or probe 6 Crack detection liquid container or gel container 7 Detection liquid supply port 8 Gel 9 Roller 10 Power supply 11 Roller 12 Roller 13 Heating element 14 Gel accumulation 15 Electrode 16 Potentiostat 17 Electrode moving direction 18 Metal part 19 Arbitrary waveform generator 20 Scratch 21 Burn or overreaction 22 Shade 23 Crack 24 Temperature control mechanism

[Procedure amendment]

[Submission date] February 16, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

[Fig. 2]

[Figure 3]

[Figure 4]

[Figure 5]

[Figure 6]

Claims (2)

[Claims] 1. An insulating film is previously formed on a metal surface for the purpose of detecting microcracks generated on the metal surface of a metal component, and an electrolytic solution containing an electrochromic substance is applied to the metal as a cathode. None A method for detecting microcracks in a metal part having an insulating film, wherein a color is developed only in the cracked portion by applying a potential between the anode and the anode. 2. An apparatus used for the method for detecting microcracks in a metal part having an insulating film according to claim 1,
(1) The crack detection liquid container has a plurality of rollers whose surface is covered with an insulating material in contact with the insulating film of the metal part in the lower portion, and is provided with a detection liquid discharge unit formed by the rollers between the rollers. (2) Further, between each roller, an electrode having a length substantially equal to the roller shaft length in parallel with the roller shaft and connected to a metal part through a power source is provided, (3) the rotation shaft of the roller and cracks. A device for detecting a microcrack, which has a heating element in the vicinity of a detection liquid discharge part.