JPH0566544B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention is applicable to cast iron materials, cast iron product types, tensile strength,
The present invention relates to a method and apparatus for nondestructively evaluating the degree of deterioration caused by cracks using a vibration method. <Conventional technology> For example, JIS G5501 "Gray cast iron products" specifies gray cast iron types 1 to 6, including FC10, FC15, FC20, FC25, FC30, and FC35.
It is represented by the symbol. The numbers in these symbols are based on the strength of the as-cast material with a diameter of 30 mm. Destructive tests such as tensile tests, anti-deposition tests, and chemical analyzes were used to test these cast iron products, and there was no method or device to non-destructively measure the product type or tensile strength. In addition, methods for measuring the deterioration of cast iron products include the eddy current method, which uses the fact that the induced current excited in the sample changes depending on the crack, and the penetration method, which uses a penetrant solution near the crack and visually checks it. , the ultrasonic method that uses the reflection of incident ultrasonic waves from cracks, and the AE method that counts the number of acoustic emissions (AE) that propagate as cracks occur and develop. In addition, methods and devices using vibration analysis were mainly used for analyzing structures. <Problems to be solved by the invention> As described above, conventional methods have no choice but to use destructive tests to measure the tensile strength of cast iron products, and there is also a non-destructive method for measuring deterioration due to cracks. It required skill, and was lacking in terms of ease of use and short measurement time. Furthermore, there was no method to simultaneously measure tensile strength and deterioration in a non-destructive manner. The present invention has been made to solve these problems, and provides a method and apparatus for nondestructively and simultaneously measuring the material quality, tensile strength, and degree of deterioration due to cracks of cast iron products using a vibration analysis method. It provides: <Means for solving the problem> In the present invention, a cast iron product is struck to cause vibration, the tensile strength is calculated and displayed from the resonance frequency, and the tensile strength and The type of cast iron product is determined, and the degree of deterioration due to cracks according to the load history is calculated and displayed from the amount of movement of the resonance frequency toward the lower frequency side. FIG. 1 is a diagram showing the configuration of the device of the present invention,
1 is a cast iron product, 2 is a striking tool such as a hammer, and 3 is a vibration probe that detects the mechanical vibration of the cast iron product by directly contacting the surface of the cast iron product and converts it into an electrical signal, and an acceleration pickup coil or the like can be used.
Reference numeral 4 indicates an amplifier, and reference numeral 5 indicates a waveform analyzer, which is comprised of a frequency measuring section 6 that measures the resonance frequency of mechanical vibration of the cast iron product from the output of the amplifier 4, and a waveform measuring section 7 that measures the amplitude over time. 8 is a memory section such as a floppy disk that stores the measurement results from the frequency measurement section and the waveform measurement section, and also stores necessary data such as constant terms; 9 is an operation that calculates the tensile strength, attenuation rate, etc. from the measurement results. A microcomputer is used in the department. 10 is an output unit such as a printer.
Preferably, the cast iron product 1 is placed on a cushion material 11 such as sponge. <Operation> When the cast iron product 1 is struck, it vibrates at a resonant frequency corresponding to its shape. The resonance frequency i is given by i=(λi/l) ² (EI/ρA) ^1/2 (1). However, i is the order of vibration, l is the length of the cast iron product, I is the second moment of area, A is the cross-sectional area, E is Young's modulus, ρ is the density, λi is a constant, and λ ₁ =
4730, λ ₂ = 7853, λ ₃ = 10996, ... Furthermore, in the case of cast iron, what are the tensile strength σ and Young's modulus E?
Since they are related by McEleeMoore's equation σ=(E/2900) ^2.32 (2), in advance,
The shape, density and λ of the cast iron product are stored in the memory section 8 in Figure 1.
If you memorize it and measure the resonant frequency,
The tensile strength σ can be obtained from (1) and (2). σ={1/2900・ρA/I(l/λi) ⁴・fi} ^2.32 (
3) can be calculated by the calculation section 9 in FIG. 1, and the result can be outputted onto the output section 10 together with the resonance frequency. The resonant vibration of a cast iron product caused by impact is transferred to damped vibration, and the inventors have found that the damping rate differs depending on the type and tensile strength of the cast iron product. By measuring the vibration damping rate of the cast iron product 1 with the waveform analyzer 5, the tensile strength and type of the cast iron product 1 can be determined, and the results can be displayed. Furthermore, the present inventor found that the resonant frequency of a cast iron product shifts to a lower frequency side depending on its load history, and that this is due to cracks caused by the load history. By storing the resonant frequency of a healthy cast iron product or a previously prepared calibration curve in the memory section 8 and comparing the resonant frequency of a deteriorated sample with them, the degree of deterioration can be determined, and the historical load can be compared with the breaking load. It is also possible to quantify and output the ratio. <Example> A detailed description will be given below based on an example. (Example 1) Tensile strength was measured from the resonance frequency. Among JISG5501 gray cast iron products, FC15, FC20,
A sample was made from a round bar of FC30. Sample length 460
mm, a round bar with a diameter of 32 mm was cut into a plate shape with a thickness of 20 mm. Each sample was placed on a sponge, hit with a hammer, the vibration was converted into an electrical signal by probe 3, and the resonance frequency was measured. In advance, the sample length, cross-sectional area, second moment of area,
The density, λ, was stored in the memory unit 8, and the tensile strength σ was calculated from the resonance frequency fi using equation (3) in the calculation unit 9. The results obtained are shown in FIG.
The calculation results are in good agreement with the standard values. (Example 2) The tensile strength and type of cast iron products were determined from the attenuation of resonance amplitude. A sample having the same shape and dimensions as in Example 1 was used. Figure 3 schematically shows the vibration waveform when a cast iron product is struck and vibrates. The amplitude reaches its maximum value after a certain period of time after being hit, and then transitions to a damped oscillation. FC15,
The vibration waveforms were measured for each of the FC20 and FC30 samples. The amplitude envelope is shown in FIG. Even if they are made of the same gray cast iron, the manner of attenuation differs depending on the type. In Figure 3 or Figure 4, if the time when the amplitude reaches its maximum is t = 0, and the amplitude at that time is u ₀ , then the amplitude u(t) of the subsequent damped oscillation will change with time t as u(t) = u ₀ e ^- 〓 ^t (4). α is the attenuation rate. From equation (4), α=1/tlnu ₀ /u(t) (5) Therefore, based on the attenuation waveform measured by the waveform measurement unit 6, the calculation unit 9 calculates the attenuation α, and outputs the let FC15, FC20 obtained in this way,
Table 1 shows the attenuation rate of FC30.

[Table] As seen in the table, the attenuation rate varies depending on the type of cast iron, so the type and, in turn, the tensile strength can be determined from the attenuation rate. (Example 3) The degree of deterioration due to cracks in the cast iron material was measured from the shift of the resonant frequency to the lower frequency side. Example 1
A sample with the same shape and dimensions was prepared, and an anti-deposition test was first conducted using an ordinary anti-deposition tester. Maximum drag load is 420Kg for FC15, 700Kg for FC20, FC30
It weighed 900Kg. Next, using the same anti-analytical tester,
FC15 from 100Kg to 400Kg in 50Kg increments, FC20 from 300Kg to 680Kg in 100Kg increments, FC30 from 450Kg, 600Kg, 750Kg,
A bending load of 890 kg was applied in advance. When the resonant frequency of each of these samples was measured using the apparatus shown in FIG. 1, it was found that the resonant frequency shifted to the lower frequency side with the hysteresis load. The resonance frequency of a cast iron material with no load history is measured in advance and stored in a memory section 8. The resonant frequency of the cast iron material subjected to a historical load is measured, and the difference Δ from the resonant frequency when there is no load history is calculated by the calculation unit 9 and outputted by the output unit 10. FIG. 5 shows the relationship between hysteretic load and Δ. Δ increases with hysteretic load, and the manner of increase differs depending on the type of cast iron. Using the Δ-history load curve in FIG. 5 as a calibration curve, the load history of the cast iron product can be determined from the resonance frequency of the cast iron product. The following experimental facts show that this load history indicates the degree of deterioration of the cast iron product. When applying a bending load as a hysteresis load to each sample, the acoustic emission (AE) is measured at the same time. Figure 6 shows the results, and Figure 7 shows Δ and AE obtained from Figures 5 and 6.
It shows the relationship between numbers. As is well known, the number of AEs is proportional to the amount of cracks that occur in the specimen, that is, the crack area, so the amount of shift Δ of the resonant frequency toward the lower frequency side due to the load history is the amount of cracks that occur due to cracks, and the amount of deterioration caused by cracks. It corresponds to this. We measured the resonance frequency for each type of FC15, FC20, and FC30 when there is no load history and when a known historical load is applied, and the table of historical load, resonance frequency, and Δ value for each type (hereinafter referred to as historical load) was measured. A table (referred to as a table) is stored in the memory section.The resonant frequency of a cast iron product of known type is measured, and the calculation section refers to this historical load table to output the historical load from the output section. It is also possible to output the 100-minute ratio of the historical load (W) to the breaking load (W _B ) as the degree of deterioration. (Example 4) The material quality of the cast iron product and the degree of deterioration due to cracks were measured from the resonance frequency and amplitude attenuation rate. The shape and dimensions of the sample are the same as in Example 1. As in Example 3, after applying a bending load (W) as a hysteresis load to each sample, vibration was generated by impact, and the damping rate at the damped vibration portion was measured. Figure 8 shows the results. In order to normalize the historical load, it is expressed as a 100% ratio to the anti-destructive load (breaking load (W _B )) for each of FC15, FC20, and FC30. What should be noted in FIG. 8 is that although the resonant frequency depends on the hysteresis load as described above, the damping rate is not affected by the hysteresis and is almost constant depending on the product type. It was mentioned above that the tensile strength and type of cast iron products can be determined based on the damping rate, but the type of cast iron products that have a load history can also be determined from the damping rate. Figure 9 shows various types of FC15, FC20, and FC30.
The resonant frequency and damping rate of a device without a load history and a device with a history load shown in FIG. 8 are shown on one plane. Depending on the type of cast iron,
On this resonant frequency-attenuation factor surface, groups are formed that are separated from each other.
It becomes possible to evaluate cast iron materials whose history is unknown. The evaluation method will be explained based on the flowchart shown in FIG. 10 as an example. A test piece of a predetermined shape is cut out from a cast iron product, and it is struck and vibrated. Mechanical vibrations are converted into electrical signals and amplified using a vibrating probe that is in direct contact with the test piece, and the frequency and attenuation waveform are measured. Using this measured value and necessary data previously stored in the memory section, the tensile strength, damping rate, and movement amount Δ of the resonance frequency are calculated in the calculation section. Resonance frequency is 300<
If it is in the range of 340, FC15, if 340<390
If FC20, 390<420, it is preliminarily determined to be FC30, and if the resonance frequency is outside this range, it is determined to be an error. The case of 300<340 will be explained below.
If the calculated damping rate α is 8 < α < 11, then FC15
If α is outside this range, it is determined as an error.
If it is determined to be FC15, select the FC15 table from the history load table, refer to the table, and calculate the history load (W) from the Δ value.
is determined, and the 100% ratio of W to the breaking load (W _B ) is calculated as the degree of deterioration due to cracking. The determined product type, tensile strength, degree of deterioration due to cracks, resonance frequency, damping rate, and other desired items are output and the measurement is completed. The same applies to FC20 and FC30. In this way, the type of specimen, tensile strength, and degree of deterioration due to cracks can be determined from the resonance frequency and damping rate. In addition, in FIG. 10 and the explanation based on it, the resonant frequency is 300<340, 340<
390, 390<420 etc. are used,
This is the shape of the cast iron product specifically described in Example 1,
Standard data corresponding to the shape and dimensions of the test piece can be prepared and used. In addition, standard data can be obtained not only for test pieces such as round bars and plates, but also for iron lids and other cast iron products themselves, so that the material, strength, degree of deterioration due to cracks, etc. of unknown products can be determined. <Effects of the Invention> As explained above, the present invention allows the tensile strength of cast iron products and the degree of deterioration due to cracks to be evaluated simultaneously in a non-destructive manner through vibration analysis. It can be widely used for determining the degree of deterioration and predicting life from historical loads.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the configuration of the present invention, Figure 2 is a diagram showing the relationship between resonance frequency and tensile strength, Figure 3 is a schematic diagram of damped vibration of cast iron, and Figure 4 is an envelope of the vibration waveform. Figure 5 is a diagram showing the amount of movement of the resonant frequency due to the load history, Figure 6 is a diagram showing the load and the number of AEs, Figure 7 is a diagram showing the relationship between the amount of movement of the resonance frequency and the number of AEs, and Figure 8 is a diagram showing the relationship between the amount of movement of the resonance frequency and the number of AEs. The figure shows the relationship between historical load and damping rate.
Figure 9 is a diagram showing the resonance frequency and damping rate of cast iron products,
FIG. 10 is an example of a measurement flowchart. 1... Cast iron product, 2... Hitting hammer, 3... Vibration probe, 4... Amplifier, 5... Waveform analyzer,
6... Frequency measurement section, 7... Waveform measurement section, 8...
Memory section, 9... calculation section, 10... output section.

Claims (1)

[Scope of Claims] 1. Mechanical vibration is generated in a cast iron product, a damped waveform and a resonance frequency of the mechanical vibration are detected by a vibration probe that is brought into direct contact with the surface of the cast iron product, and the attenuation rate of the damped waveform is determined. The tensile strength and the type of the cast iron product are determined by comparing the damping rate and the preset type-specific damping rate. A method for evaluating cast iron products characterized by evaluating the degree of deterioration due to 2. A means for generating mechanical vibration in a cast iron product, a means for directly contacting the surface of the cast iron product to detect the mechanical vibration and converting it into an electrical signal, and a means for generating resonance of the mechanical vibration from the electrical signal. a means for measuring a frequency; a means for measuring an attenuation waveform of the mechanical vibration from the electrical signal; a memory section for storing each of the measurement results and a preset product-specific resonance frequency and attenuation rate; Determining the attenuation rate from the attenuation waveform of the cast iron product, determining the type of the cast iron product by comparing the attenuation rate with the preset type-specific attenuation rate, and determining the tensile strength from the determined type;
Further, a calculation unit that calculates the degree of deterioration of the cast iron product due to cracks from the difference between the resonant frequency of the cast iron product and the preset product-specific resonant frequency;
An evaluation device for cast iron products, comprising an output means for outputting the calculation results.