KR20110014400A - Method ang computer-readable recording medium for measuring length of bolt gas turbine bolt contracting - Google Patents

Abstract

PURPOSE: A method for measuring the elongation of a fastening bolt for a gas turbine and a computer-readable recording medium used for the method are provided to prevent the vibration of a turbine by accurately measuring the elongation and fastening load of a bolt at the same time. CONSTITUTION: A method for measuring the elongation of a fastening bolt for a gas turbine is as follows. The speed of ultrasonic wave varying according to the material of a fastening bolt is calculated using equations reflecting temperature and load compensation components. The equations are Elongation=Stresscorrected*Effective elongation/E0 and Load=Stresscorrected*Cross-Sectional Area, where Stresscorrected is corrected stress value applied to a bolt, Effective elongation is the fastening force of the bolt, E0 is the coefficient of elasticity, and Cross-Sectional Area is the cross section of the bolt.

Description

METHODO ANG COMPUTER-READABLE RECORDING MEDIUM FOR MEASURING LENGTH OF BOLT GAS TURBINE BOLT CONTRACTING}

The present invention provides a method of efficiently measuring the length (fastening load) state of bolts being used for fastening gas turbines in order to prevent turbine vibration accidents and to reduce bolt replacement costs, and a computer readable recording to which the method is applied. It is about the medium.

In general, a gas turbine rotor (Rotor) has a variety of components such as compressor, gas turbine, large bolts. The large bolt is a high speed operation of 3600rpm in a state that is fastened to the gas turbine for a long time, and the state of the bolt material is changed due to the aging change of the bolt material and the thermal stress of the fastening part because it is operated under frequent starting stop and high temperature The phenomenon usually occurs.

In other words, even if the length and the fastening load of the bolt at the beginning of use is operating within a certain range over time, the elastic deformation is reduced by high-speed operation, the plastic deformation is increased to change the length and fastening load of the bolt. Therefore, there is a need to measure the length and tightening load of the bolt, and as a method for measuring the length and the fastening load of the bolt, a method using a dial gage or an ultrasonic method has been mainly used.

Before describing the above method, the purpose of measuring the length of the bolt is usually a process for checking whether the bolts are uniformly fastened to each other, for example, when 18 bolts are fastened, before the bolts are fastened After measuring each bolt length, the average value of 18 bolt lengths is obtained, and it is regarded as a normal bolt only when the bolt length is within 15% of the reference value. The bolt after tightening is safe to ensure that the bolt length is within a certain range.

However, the above fastening method has two problems. First, the length measurement point before the bolt fastening is different from the time after the bolt fastening. For example, when the time before fastening is morning and the time after fastening is afternoon, There is a problem that length is affected by temperature. Secondly, even if the bolts before and after fastening are within a certain range, there has been a problem in that there is no relative comparison of how fast the bolts are fastened after fastening.

For example, if the length of the bolt 'A' is 156mm before the fastening and the length of the bolt 'B' is 157mm, assuming that the lengths of the A and B bolts are the same after the fastening, the lengths of the A and B bolts are the same. It is natural that the tightening loads of the A and B bolts can be the same, and it is also impossible to know how different the difference is if they are not the same.

As a result, when using a dial gauge when comparing the fastening load after fastening between bolts, as shown in Figure 1 can be confirmed that the difference between the fastening load (Load) and strain (Stress) between the bolts. Similarly, the conventional method using ultrasonic wave simply measures the length before and after fastening the bolts, or because the fastening loads between the bolts are not the same, so that vibration occurs frequently in the gas turbine during operation, and the blades of the gas turbine are damaged. There are many problems.

The present invention is to solve the above-mentioned conventional problems, and to measure the fastening load between the bolts at the same time as well as the temperature correction coefficient that significantly affects the ultrasonic speed under the judgment of varying the load correction according to the change in the fastening force, respectively It is an object of the present invention to provide a computer-readable recording medium by recording a method and a method for accurately measuring a bolt length and a fastening load by deriving different load correction coefficients according to a load change on a recording medium.

In addition, by using the temperature and load correction factors as described above to accurately measure the length and load of the bolt at the same time to prevent the turbine vibration accident, and to record the method and method for reducing the bolt replacement cost to the recording medium It is another object to provide a computer readable recording medium.

In order to achieve the object of the present invention as described above, and to perform the characteristic functions of the present invention described below, the characteristic configuration of the present invention is as follows.

According to one aspect of the present invention, the bolt using the following equation (1) or equation (2) reflecting the temperature and load correction factors in the ultrasonic speed measurement method that varies the propagation speed according to the material of the gas turbine fastening bolt A method of measuring the length of Elongation and the load of fastening is provided.

Elongation = Stress _corrected × Effective length / E ₀ ..... Equation (1)

Load = Stress _corrected × Cross-Sectional Area ..... Equation (2)

At this time, the stress _corrected is the corrected stress value applied to the bolt, Effective length is the clamping force length of the bolt, E ₀ is the elastic modulus, Cross-Sectional Area represents the cross-sectional area of the bolt.

Here, the stress _corrected can be calculated by the following equation (3).

Stress _corrected = Stress _uncorrected (3) (1 + Stress Radio / 100) + Stress Offset ..... Equation (3)

In this case, the stress _uncorrected is a stress value applied to the bolt, the stress radio is a load ratio by the correlation between the actual fastening load of the bolt and the fastening load of the bolt measured by the calculation, Stress Offset represents the load difference.

In addition, the stress _uncorrected can be calculated by the following equation (4).

Stress _uncorrected = (V / K ₁ , ₂ , ₃ , ....) × (Change of Ultrasonic Length) / (Change of Ultrasonic Length + Effective Length) ..... Equation (4)

Here, K ₁ , ₂ , ₃ , ... are the load vectors according to the tightening force of the bolt, V is the ultrasonic velocity propagated according to the material of the bolt (inherent longitudinal velocity of the bolt), Change of Ultrasonic Length is the load of the bolt The change in length is shown.

In addition, the Change of Ultrasonic Length may be calculated by the following Equation (5).

Change of Ultrasonic Length = (V × TOF _{normal-stressed} )-(V × TOF _{normal-reference} ) ..... Equation (5)

In this case, the TOF _{normal-stressed} is the first reaction time when the ultrasonic wave is reflected by reflecting the temperature factor before and after the bolt is tightened in the state in which the tensile load is applied to the bolt, and the TOF _{normal-reference} does not apply the tensile load to the bolt. The second reaction time is reflected by the ultrasonic wave reflecting the temperature component before and after tightening the bolt in the non-state state.

In addition, the reference lengths of the bolts according to the TOF _normal and TOF _reference may be calculated by the following equations (6), (7) and (8).

TOF _normal = TOF _measured × {1 + (Cp × (Temp _measured -22.22))} ..... Equation (6)

TOF _measured = Sound Path Duration / 2 ..... Equation (7)

_P = [C ₁ / T ₂ -T 1] [L ₂ / L ₁ - _1] ..... (8)

LREF (Reference Length of Bolts) = TOF _measured × V

In this case, the sound path duration is the reaction time when the ultrasonic wave is reflected back in the volt, TOF _measured is the reaction time when the longitudinal wave passes through the volt, C _p is the temperature correction coefficient, T ₁ , T ₂ is the temperature coefficient, L ₁ and L ₂ are the ultrasonic reach lengths and Temp _measured represents the test temperature.

In addition, the temperature and load correction factors are preferably calculated by calculating differently depending on the section to be changed.

The method of measuring the length and the fastening load of the bolt may be a result of selecting an optimal probe through a speed measurement test on a new material and a used material.

According to another aspect of the present invention, there is provided a computer readable recording medium having recorded thereon a computer program for executing a method of measuring the length of the bolt and the load thereof.

According to the present invention, by accurately calculating the length and tightening load of the bolt as a result of reflecting the temperature and load correction factors in the ultrasonic velocity measuring method, to solve the non-uniform fastening load between the bolts, the gas due to the uneven tightening of the bolt It prevents the rotor rotor vibration in advance, and greatly increases the utilization rate of the power plant gas turbine through stable operation of the plant, and also prevents component damage, thereby reducing the cost of repairing and replacing parts. Done.

The following detailed description of the invention refers to the accompanying drawings, which illustrate, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that the various embodiments of the invention are different, but need not be mutually exclusive. For example, specific shapes, structures, and characteristics described herein may be embodied in other embodiments without departing from the spirit and scope of the invention in connection with one embodiment. In addition, it is to be understood that the location or arrangement of individual components within each disclosed embodiment may be changed without departing from the spirit and scope of the invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention, if properly described, is defined only by the appended claims, along with the full range of equivalents to which such claims are entitled. Like reference numerals in the drawings refer to the same or similar functions throughout the several aspects.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention.

The method for measuring the length of the bolt (Elongation) and fastening load (Load) according to an embodiment of the present invention is a temperature and load correction element in the ultrasonic speed measurement method of varying the propagation speed according to the material of the gas turbine fastening bolt It can be achieved by deriving Equation (1) or Equation (2) as follows.

Elongation = Stress _corrected × Effective length / E ₀ ..... Equation (1)

Load = Stress _corrected × Cross-Sectional Area ..... Equation (2)

Stress _corrected described in Equations (1) and (2) above is the corrected stress value applied to the bolt, and Effective length is the tightening force of the bolt, E ₀ Is the modulus of elasticity and Cross-Sectional Area represents the cross-sectional area of the bolt.

Hereinafter, the process for deriving Equation (1) and Equation (2) will be described in detail by tracking back.

First, the measurement of the bolt length and the fastening load of the present invention uses an ultrasonic speed measuring method of varying the speed according to the state of the solid material. For example, the ultrasonic wave is represented by the following formula (10) for the material of IN 718 bolts. The speed is measured.

Ｖ = ｆλ ..... Equation (10)

V described in Equation (9) is a speed (m / sec), f is a frequency (cycles / sec), and λ represents a wavelength (m / cycle).

Subsequently, the bolt length and the fastening load measurement according to the present invention use an ultrasonic flaw detector to obtain a reflected TOF _measured (Time of Flight) by transmitting a longitudinal wave through the IN 718 bolt, which is the time when the ultrasonic wave is reflected back (Sound Path). Duration) divided by 2, and can be expressed as shown in Equation (7).

TOF _measured = Sound Path Duration / 2 ..... Equation (7)

Next, the bolt length and the fastening load measurement of the present invention is obtained by multiplying the TOF _measured obtained from the experiment by the intrinsic longitudinal velocity of the bolt to obtain a reference length LREF (Reference Length) of the bolt. This can be expressed as Equation (9), and V is an experimentally obtained value using a reference block as the intrinsic longitudinal velocity of the material of IN 718 volts.

LREF (Reference Length of Bolts) = TOF _measured × V ..... Equation (9)

Here, the length of the bolt for fastening the gas turbine is usually affected by the temperature, and as the temperature increases, the longitudinal wave speed decreases, which means that the length of the bolt also increases. Therefore, the bolt length and the fastening load measurement of the present invention can obtain the TOF _normal by reflecting the temperature effect, which can be expressed as Equation (6).

TOF _normal = TOF _measured × {1 + (Cp × (Temp _measured -22.22))} ..... Equation (6)

Equation (6) is a result calculated using the TOF _measured , Cp and the test temperature (Temp _measured ) considering the temperature effect, TOF _measured is the reaction time to return the longitudinal _wave through the volt, C _p is temperature correction Means coefficient. After all, the temperature correction coefficient is a result of correcting the temperature affecting the length and load of the bolt. Here, Cp can be expressed by the following equation (8) for correlation between the ultrasonic reach lengths L ₁ and L ₂ using ultrasonic waves for different temperature coefficients, for example, T ₁ and T ₂ .

_P = [C ₁ / T ₂ -T 1] [L ₂ / L ₁ - _1] ..... (8)

When C _p1 is calculated through Equation (8), C _p1 = [1 / T ₂ -T ₁ ] [L ₂ / L _1-1 ], and when C _{p2 , 3 ...} is calculated, C _{p2 , 3 ...} = [1 / T ₃ -T ₂₁ [L ₃ / L _2-1 ].

Subsequently, the measurement of the bolt length and the fastening load of the present invention is a result of considering the temperature without a tensile load as shown in Equation (8), but it is intended to further reflect the load correction factor here.

In other words, the change of the length according to the load is obtained by using the TOFnormal-reference for the unloaded state and the TOF _{normal - stressed} for the unloaded state. The TOF _{normal - stressed} is a reaction time when the ultrasonic wave is reflected by reflecting the temperature factor before and after the bolt is tightened in the state where the tensile load is applied to the bolt, and thus the change of ultrasonic length can be obtained. This can be expressed as (5) below.

Change of Ultrasonic Length = (V × TOF _{normal-stressed} )-(V × TOF _{normal-reference} ) ..... Equation (5)

TOF _{normal - reference} shown in Equation (5) means the reaction time when the ultrasonic wave is reflected by reflecting the temperature factor before and after tightening the bolt without applying the tension load to the bolt.

The stress value (stress _uncorrected ) applied to the bolt can be obtained through the change in the length of the bolt determined by Equation (5), which can be expressed as Equation (4) below.

Stress _uncorrected = (V / K ₁ , ₂ , ₃ , ....) × (Change of Ultrasonic Length) / (Change of Ultrasonic Length + Effective Length) ..... Equation (4)

Stress _uncorrected shown in Equation (4) above Is the stress value applied to the bolt, and K ₁ , ₂ , ₃ , ... are coefficients representing the change of sound velocity according to the change of tensile load in the longitudinal wave. Since the sound wave length increases, this value is considered. In other words, K ₁ , ₂ , ₃ , ... are the load vectors according to the clamping force of bolts. In addition, V shown in Equation (4) represents the ultrasonic velocity propagated according to the material of the bolt (intrinsic longitudinal velocity of the bolt) as described above, and Effective Length means the tightening force of the bolt, that is, the bolt is fastened in some way Depending on whether or not it can be shown as shown in FIG. Figure 2 shows an exemplary result of the effective length applied in the shape of the gas turbine fastening bolt.

Subsequently, in the bolt length and the fastening load measurement of the present invention, the stress offset and the stress ratio can be obtained through the correlation between the actual load and the load measured by the calculation, which can be represented as shown in FIG. 3. The stress offset and stress ratio of the present invention shown in Fig. 3 are used for the stress _corrected to be obtained by calculation of the following equation (3).

Stress _corrected = Stress _uncorrected (1 + Stress Radio / 100) + Stress Offset ..... Equation (3)

Here, the stress _corrected is a _corrected stress value applied to the bolt, Stress Radio means a load ratio by the correlation between the actual tightening load of the bolt and the tightening load of the bolt measured by the calculation, Stress Offset is the load difference Respectively.

By obtaining the stress _corrected in the above formula (3), it is possible to obtain the length or tightening load of the bolt which is the final target value of the present invention. That is, the tightening load can be obtained by multiplying the _corrected stress value, Stress _corrected , by the cross-sectional area as shown in Equation (2). In addition, the relationship between the stress _corrected , the effective length, and the elastic modulus is expressed by Equation (1) to obtain the increased length of the gas turbine fastening bolt.

Bolt geometry example

4a to 4c are views showing the shape of the gas turbine fastening bolt for measuring the length of the bolt material according to an embodiment of the present invention, IN 718 used in the above-described bolt length and fastening load measurement experiment Shows the shape of the bolt.

As shown, the IN 718 bolts used in the present invention have a height of 5 mm, 10 mm, 15 mm, 20 mm and a length of 80 mm, respectively. Therefore, in order to measure the length of the IN 718 bolt material, it is necessary to measure the longitudinal and transverse velocity in the material, and the speed was obtained by measuring the time when the ultrasonic wave is reflected in the transverse length direction of the manufactured IN 718 bolt. To measure the longitudinal velocity at IN 718, a transducer with a frequency of 5 MHz was used, and the longitudinal velocity was calculated using the time between the third and fourth peak points for each height as shown in FIG. As shown in Fig. 3c, the longitudinal velocity average for each height of IN 718 volts was measured at 5856.58 m / s, which can be summarized as shown in Table 1.

TABLE 1

Temperature coefficient Cp ) Measurement example

The above-mentioned bolt length and load measurement method reflects the temperature coefficient factor, which depends on the media, which is proportional to the young modulus (E) of the media and is temperature-related density (ρ). ) Is inversely related to the sonic velocity, which ultimately affects the sonic velocity. Therefore, in order to measure the exact volt length, it is necessary to correct the sound velocity according to temperature, and this relationship can be expressed as shown in Equation (11).

C ∝ Eρ ..... (11)

As the temperature rises in the solid through the relationship as shown in Equation (11), the sound velocity becomes slower, which indicates that the density decreases due to volume expansion as the temperature rises. As a result, the experimental results as shown in Tables 2 and 3 are obtained. Could be obtained.

TABLE 2

TABLE 3

Table 2 shows the results of the sound path duration of the new and used materials with the Marriage Bolt and Turbine bolt test specimens. The temperature is 50 ° C and 70 ° C in the IN 718 bolt material without a tensile load using a 5 MHz transducer. The longitudinal velocity at ° C and the results of two measurements at each temperature are shown.

On the other hand, Table 3 shows the result of calculating Cp, which is a factor indicating the change of ultrasonic speed according to temperature, by using Equation (8), and the moving time of ultrasonic wave moving inside the material as the temperature increases It can be seen that the movement time of the ultrasonic wave is longer in the IN 718 bolt material used than the new material, and even the same material is used for longer ultrasonic movement time in the bolt that is placed in the higher temperature environment. It can be seen that. That is, it was proved that the Cp value should be different according to the temperature at the time of measurement because the coefficient according to the temperature change that is overlooked in the conventional method is not constant in every temperature section.

Example of measurement of load factor (K)

In the above-described method of measuring the length of the bolt and the load, the factor of the load factor is reflected. The length of the bolt varies according to the increase or decrease of the tightening load, so the change in the tightening load must be reflected. In order to calculate the load correction coefficient, in this example, a 5 MHz transducer was used, and a tensile load of 0 ton, 1 ton, 2 ton, 3 ton, 4 ton, and 5 ton was applied to three types of test specimens collected from new and used material bolts. While observing the change in longitudinal velocity according to the deformation of IN 718 bolt material, the result can be shown in Table 4, and the change in longitudinal velocity due to the change in tensile stress can be expressed as 5. In this way, like the temperature correction coefficient, the load correction coefficient is not the same value in every load section, so it should be reflected in each load section.

Table 4

Table 5

Ultrasonic speed measurement method and dial gauge Dial gage)  Example of comparison

5A and 5B are views exemplarily comparing the ultrasonic velocity measuring method and the d-diameter method according to an embodiment of the present invention.

First, before describing the experimental results of FIGS. 4A and 4B, the length and fastening load measuring equipment used in this embodiment has a frequency of 2.25 Mhz for 32 volts of new and used materials having the same frequency as the ultrasonic probe. (0.25 inch), 2.5 Mhz (0.5 inch), 5.0 Mhz (0.2 inch) probe was tested 25 times, 5.0Mhz (0.5inch) showing the most stable signal characteristics were used to select.

4A and 4B, first, the ultrasonic velocity before and after the fastening of nine Marriage bolts out of 32 bolts is measured, and the ultrasonic waves according to the temperature and the load at the time of measurement using Equations (1) to (9) are measured. It is the result of calculating the exact length and tightening load by compensating the speed change differently according to the temperature and load. As a result, in FIG. 4, the conventional dial gauge and the ultrasonic wave were simultaneously measured, and the measurement results of the length and the fastening load were compared with each other.

Here, the result of the dial gauge method is a result obtained by comparing and measuring the dial gauge with respect to the reference bolt as described above, by measuring only the length of the bolt rather than the tightening load of the bolt.

Accordingly, in the present embodiment, even if the fastening by the conventional dial gauge method and the length before and after the fastening between the bolts is a certain standard (within 15%), it can be seen that there is a large difference in the fastening load between the bolts, ultrasonic speed method Unlike the measurement results using the dial gauge, the length measurement results show the amount of extension and tightening force, etc., so that it is possible to check the length of the bolt as well as whether it is tightened at the same time. By applying the difference according to the load section, it can be seen that the vibration generating factor of the gas turbine can be removed.

Embodiments according to the present invention described above may be implemented in the form of program instructions that may be executed by various computer components, and may be recorded in a computer-readable recording medium. The computer-readable recording medium may include program instructions, data files, data structures, etc. alone or in combination.

Program instructions recorded on the computer-readable recording medium may be those specially designed and configured for the present invention, or may be known and available to those skilled in the computer software arts. Examples of computer-readable recording media include magnetic media such as hard disks, floppy disks and magnetic tape, optical recording media such as CD-ROMs, DVDs, and magneto-optical media such as floptical disks. media), and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. Examples of program instructions include not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like. The hardware device may be configured to operate as one or more software modules to perform the process according to the invention, and vice versa.

1 is a graph for explaining the fastening load between bolts in the conventional dial gauge method.

2 is a view showing an exemplary effective length applied in the shape of the gas turbine fastening bolt in accordance with an embodiment of the present invention.

3 is a graph illustrating stress _corrected according to an embodiment of the present invention.

4A to 4C are views exemplarily showing shapes of a gas turbine fastening bolt for measuring a length of a bolt material according to an embodiment of the present invention.

5A and 5B are views exemplarily comparing the ultrasonic velocity measuring method and the d-diameter method according to an embodiment of the present invention.

Claims (8)

Elongation and fastening load of the bolt using Equation (1) or Equation (2) below reflecting temperature and load correction factors in the ultrasonic velocity measuring method that varies the propagation speed depending on the material of the gas turbine fastening bolt. How to measure Load. Elongation = Stress _corrected × Effective length / E ₀ ..... Equation (1) Load = Stress _corrected × Cross-Sectional Area ..... Equation (2) The stress _corrected is the corrected stress value applied to the bolt, effective length is the tightening force of the bolt, E ₀ is the elastic modulus, Cross-Sectional Area represents the cross-sectional area of the bolt. The method of claim 1, _Wherein the Stress _corrected is calculated by the following equation (3). Stress _corrected ＝ Stress _uncorrected (1 + Stress Radio / 100) + Stress Offset ..... Equation (3) The stress _uncorrected is a stress value applied to the bolt, the stress radio is a load ratio based on the correlation between the actual tightening load of the bolt and the tightening load of the bolt measured by calculation, and Stress Offset represents a load difference. The method of claim 2, The stress _uncorrected is calculated by the following equation (4). Stress _uncorrected = (V / K ₁ , ₂ , ₃ , ....) × (Change of Ultrasonic Length) / (Change of Ultrasonic Length + Effective Length) ..... Equation (4) K ₁ , ₂ , ₃ , ... are the load vectors according to the tightening force of the bolt, V is the ultrasonic velocity propagated according to the material of the bolt (intrinsic longitudinal velocity of the bolt), Change of Ultrasonic Length is in accordance with the load of the bolt Indicates a change in length. The method of claim 3, The Change of Ultrasonic Length is calculated by the following equation (5). Change of Ultrasonic Length = (V × TOF _{normal-stressed} )-(V × TOF _{normal-reference} ) ..... Equation (5) The TOF _{normal-stressed} is a first reaction time in which ultrasonic waves are reflected by reflecting temperature components before and after the bolt is tightened in a state where a tension load is applied to the bolt, and a TOF _{normal-reference} is a state in which the tension load is not applied to the bolt. Represents the second reaction time in which ultrasonic waves are reflected by reflecting the temperature component before and after the bolt is tightened. The method of claim 4, wherein The reference length of the bolt according to the TOF _normal and TOF _reference is calculated by the following equations (6), (7) and (8). TOF _normal = TOF _measured × {1 + (Cp × (Temp _measured -22.22))} ..... Equation (6) TOF _measured = Sound Path Duration / 2 ..... Equation (7) _P = [C ₁ / T ₂ -T 1] [L ₂ / L ₁ - _1] ..... (8) LREF (Reference Length of Bolts) = TOF _measured × V ..... Equation (9) The Sound Path Duration is the reaction time when the ultrasonic wave is reflected back in the volt, TOF _measured is the reaction time when the longitudinal wave passes through the volt, C _p is the temperature correction coefficient, T ₁ , T ₂ is the temperature coefficient, L ₁ , L ₂ is the ultrasonic reach length and Temp _measured represents the test temperature. The method of claim 1, The temperature and load correction factors are calculated by calculating differently depending on the section to be changed. The method of claim 1, The length and the load measurement method of the bolt, Method characterized in that the result of selecting the optimum probe (Probe) through the speed measurement test for new and used materials. A computer-readable recording medium having recorded thereon a computer program for executing the method according to any one of claims 1 to 7.

Images