A preload electromagnetic ultrasonic sound time recognition monitoring method

Abstract

The present invention discloses a method for identifying and monitoring the ultrasonic time of flight of pre-tightening force by electromagnetic ultrasonic, which comprises the following steps: when the bolt is in a state without pre-tightening force, search for the echo envelope from the trailing edge of the starting wave through the electromagnetic ultrasonic pre-tightening force measurement system, and identify the highest continuous j-cycle echo envelopes during the period without pre-tightening force of the bolt through the peak algorithm; store the ultrasonic time of flight during the period without pre-tightening force of the bolt as t0; apply pre-tightening force to the bolt, search for the echo envelope from the trailing edge of the starting wave through the electromagnetic ultrasonic pre-tightening force measurement system, and identify the highest continuous j-cycle echo envelopes during the period with pre-tightening force of the bolt through the peak algorithm, and store the ultrasonic time of flight during the period with pre-tightening force of the bolt as t1; according to the formula F = KΔt, obtain F = K(t1 - t0), calculate the accurate time of flight Δt, and accurately calculate the pre-tightening force F of the bolt. The present invention can automatically re-identify and calculate the ultrasonic time of flight of the echo envelope, improving the accuracy and stability of bolt pre-tightening force measurement.

Description

Technical Field

[0001] The invention relates to the technical field of electromagnetic ultrasound for measuring preload force, and in particular to a method for electromagnetic ultrasound sound-time recognition and monitoring of preload force. Background Art

[0002] As important parts of wind turbines, wind turbine blades, towers, nacelles, and main shafts are all connected with high-strength bolts. Whether the preload force of high-strength bolts meets the construction requirements is an important monitoring link in the installation and maintenance of wind turbines, which is related to whether wind turbines can operate reliably and safely for a long time.

[0003] According to the acoustoelastic effect, when sound waves propagate in solids, the propagation speed has a linear relationship with the stress state of the solid medium. As the stress on the solid changes, the speed of the sound wave will also change accordingly. From Hooke's law, it can be seen that the stress σ in the solid is proportional to the strain ε, that is, σ=Εε, where σ is the material stress (force per unit area), E is the elastic modulus (Young's modulus), and ε is the strain (deformation per unit length). When a preload is applied to the bolt, the applied preload is the stress in the bolt. Different preloads will result in different propagation speeds of ultrasonic waves in the bolt, and the corresponding acoustic time will also be different.

[0004] By monitoring the change of ultrasonic sound time in the bolt under different preloads, the mathematical function relationship between the transit time and the bolt preload is obtained to indirectly measure the bolt preload. The mathematical function relationship between the transit time of ultrasonic waves in the bolt and the bolt preload is F=KΔt=K(t1-t0), where F is the bolt preload; K is the test calibration acoustic elastic coefficient; Δt is the change of sound time when the bolt is preloaded (i.e., the transit time of ultrasonic waves in the bolt); t1 is the sound time when the bolt is preloaded; t0 is the sound time when there is no preload on the bolt. Therefore, it is very critical to accurately identify and monitor the sound time when the bolt is without preload and when the preload is applied.

[0005] The echo of bolts measured by electromagnetic ultrasound is generally a multi-cycle echo envelope. Due to the different preloads or bolt differences, the amplitude height of each cycle of the echo envelope will change. When the period position corresponding to the highest amplitude changes, the ultrasonic sound time measured by the highest amplitude position of the traditional ultrasonic monitoring echo envelope will deviate by at least 1 cycle. If the ultrasonic frequency of the bolt is 2.5MHz, the vibration period of the ultrasonic wave is 400 nanoseconds, and the measured ultrasonic sound time deviates by at least 400 nanoseconds, which is much larger than the tens of nanoseconds or even a few nanoseconds of ultrasonic sound time change caused by the change of preload, which seriously affects the accuracy of preload measurement. Summary of the invention

[0006] The problem to be solved by the present invention is to provide a preload electromagnetic ultrasonic sound time recognition monitoring method, which can automatically re-recognize and calculate the ultrasonic sound time of the echo envelope, thereby improving the accuracy and stability of bolt preload measurement.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0008] A preload electromagnetic ultrasonic sound recognition monitoring method, characterized by comprising the following steps:

[0009] (1) Place the electromagnetic ultrasonic transverse and longitudinal wave probe on the stress-free bolt end face. When the bolt is in a state without preload, search for the echo envelope from the trailing edge of the starting wave through the electromagnetic ultrasonic preload measurement system, and identify the highest continuous j-cycle echo envelope in the bolt without preload time period through the peak algorithm;

[0010] (2) Record the peak sound time of the j-period echo envelope identified in step (1), sort them in chronological order, and store the peak sound time of the j-period echo envelope as t 01 ,t 02 ,……,t 0j ,j≧1;

[0011] (3) Selecting the Nth peak sound time from the peak sound time of the j-cycle echo envelope in step (2) as the designated ultrasonic sound time to be monitored, N ≧ 1;

[0012] (4) The ultrasonic sound time during the period when the bolt has no pre-tightening force is stored as t0;

[0013] (5) Apply preload force to the bolt, search for the echo envelope from the trailing edge of the starting wave through the electromagnetic ultrasonic preload force measurement system, and identify the highest continuous j-cycle echo envelope during the bolt preload force application period through the peak algorithm;

[0014] (6) Record the peak sound time of the j-period echo envelope identified in step (5), sort them in chronological order, and store the peak sound time of the j-period echo envelope as t 11 ,t 12 ,……,t 1j ,j≧1;

[0015] (7) Selecting the Nth peak sound time from the peak sound time of the j-cycle echo envelope in step (6) as the designated ultrasonic sound time to be monitored, N ≧ 1;

[0016] (8) The ultrasonic sound time during the period of time when the bolt applies pre-tightening force is stored as t1;

[0017] (9) According to the formula F=KΔt, where F is the bolt preload, K is the test calibration acoustic elastic coefficient, and Δt is the transit time of the ultrasonic wave in the bolt, we can get F=K(t1-t0), calculate the accurate transit time Δt, and accurately calculate the bolt preload F;

[0018] (10) When the bolt preload is different, the ultrasonic sound time t1 of the bolt preload period is re-identified and calculated according to steps (5)-(8) and saved, and then the accurate transit time Δt and bolt preload F are re-calculated according to step (9).

[0019] In the above steps (2) and (6), j of the j period echo envelopes is ≥ 1. The number of the identified j period echo envelopes can be expanded to 3 or more, so that the data of multiple period echo envelopes can be cross-validated, the characteristics of the echo envelope can be captured more accurately, and the measurement error can be reduced.

[0020] The reason for the different bolt preloads in the above step (10) is due to inaccurate bolt construction or changes in the bolts after long-term operation.

[0021] In the preferred embodiment, in the steps (1) and (5), the highest continuous j period echo envelopes are obtained by selecting the peak of the highest period echo envelope and then selecting the peak of the period echo envelope that is continuous with it forward or backward.

[0022] In the preferred embodiment, in the steps (3) and (7), the ultrasonic sound time to be monitored is the peak sound time of any one cycle in the j-cycle echo envelope. Selecting the peak sound time of any one cycle as the ultrasonic sound time to be monitored can simplify the complexity of the algorithm and improve the processing speed.

[0023] Of course, in the above steps (3) and (7), the ultrasonic sound time to be monitored is designated as the zero-crossing sound time of any cycle in the j-cycle echo envelope. The change of the zero-crossing sound time is relatively stable, especially when the preload force changes slightly, the measurement error is usually small, which can reduce the error caused by the change of the peak position and improve the accuracy of the measurement result.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] This preload electromagnetic ultrasonic sound time recognition and monitoring method calculates the accurate transit time Δt of the ultrasonic wave in the bolt by recording the ultrasonic sound time t0 when the bolt has no preload and the ultrasonic sound time t1 when the bolt has preload respectively. It can automatically re-identify and calculate the ultrasonic sound time of the echo envelope, solve the sound time deviation problem caused by the change of the period corresponding to the highest amplitude of the ultrasonic echo envelope, and improve the accuracy and stability of the bolt preload measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of ultrasonic sound time t1 and t0 of the bolt with and without pre-tightening force in Example 1 of the present invention;

[0027] Figure 2 is a schematic diagram of ultrasonic sound times t1 and t0 of a bolt with or without pre-tightening force in Example 2 of the present invention;

[0028] Figure 3 It is a schematic diagram of ultrasonic sound times t1 and t0 of a bolt with or without pre-tightening force in Example 3 of the present invention. DETAILED DESCRIPTION

[0029] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] Embodiment 1, as Figure 1 As shown, the preload electromagnetic ultrasonic sound recognition monitoring method in this embodiment includes the following steps:

[0031] (1) Place the electromagnetic ultrasonic transverse and longitudinal wave probe on the stress-free bolt end face. When the bolt is in a state without preload, search for the echo envelope from the trailing edge of the starting wave through the electromagnetic ultrasonic preload measurement system, and identify the highest two consecutive cycle echo envelopes in the bolt no preload period through the peak algorithm;

[0032] (2) Record the peak sound time of the two-cycle echo envelope identified in step (1), sort them in chronological order, and store the peak sound time of the two-cycle echo envelope as t 01 ,t 02 ;

[0033] (3) Select the first peak time t from the peak times of the two-cycle echo envelope in step (2) 01 When used as the designated monitoring ultrasonic sound;

[0034] (4) The ultrasonic sound time during the period when the bolt has no pre-tightening force is stored as t0;

[0035] (5) Apply preload force to the bolt, search for the echo envelope from the trailing edge of the starting wave through the electromagnetic ultrasonic preload force measurement system, and identify the two most continuous echo envelope cycles during the bolt preload force application period through the peak value algorithm;

[0036] (6) Record the peak sound time of the two-cycle echo envelope identified in step (5), sort them in chronological order, and store the peak sound time of the two-cycle echo envelope as t 11 ,t 12 ;

[0037] (7) Select the first peak sound time t from the peak sound times of the two-cycle echo envelope in step (6) 11 When used as the designated monitoring ultrasonic sound;

[0038] (8) The ultrasonic sound time during the period of time when the bolt applies pre-tightening force is stored as t1;

[0039] (9) According to the formula F = KΔt, where F is the bolt preload, K is the test calibration acoustic elastic coefficient, and Δt is the transit time of the ultrasonic wave in the bolt, we can obtain F = K(t1-t0) = K(t 11 -t 01 ), calculate the accurate transit time Δt, and accurately calculate the bolt preload F;

[0040] (10) When the bolt preload is different, the ultrasonic sound time t1 of the bolt preload period is re-identified and calculated according to steps (5)-(8) and saved, and then the accurate transit time Δt and bolt preload F are re-calculated according to step (9).

[0041] The reason for the different bolt preloads in the above step (10) is due to inaccurate bolt construction or changes in the bolts after long-term operation.

[0042] In steps (1) and (5), the two highest consecutive period echo envelopes are obtained by selecting the peak of the highest period echo envelope and then selecting the peak of the consecutive period echo envelope forward or backward.

[0043] Of course, in the above steps (3) and (7), the ultrasonic sound time to be monitored can be the peak sound time of any one cycle in the two-cycle echo envelope. Selecting the peak sound time of any one cycle as the ultrasonic sound time to be monitored can simplify the complexity of the algorithm and improve the processing speed.

[0044] Embodiment 2, as Figure 2 As shown, the difference between the preload electromagnetic ultrasonic sound recognition monitoring method in this embodiment and that in embodiment 1 is as follows:

[0045] (1) When the bolt is in a state without pre-tightening force, the electromagnetic ultrasonic pre-tightening force measurement system searches for the echo envelope from the trailing edge of the starting wave, and the peak algorithm is used to identify the highest three consecutive cycle echo envelopes during the period without pre-tightening force of the bolt;

[0046] (2) Record the peak sound time of the three-cycle echo envelope identified in step (1), sort them in chronological order, and store the peak sound time of the three-cycle echo envelope as t 01 ,t 02 ,t 03 ;

[0047] (3) Select the second peak sound time t from the peak sound time of the three-cycle echo envelope in step (2) 02 When used as the designated monitoring ultrasonic sound;

[0048] (4) The ultrasonic sound time during the period when the bolt has no pre-tightening force is stored as t0;

[0049] (5) Apply preload force to the bolt, search for the echo envelope from the trailing edge of the starting wave through the electromagnetic ultrasonic preload force measurement system, and identify the two most continuous echo envelope cycles during the bolt preload force application period through the peak value algorithm;

[0050] (6) Record the peak sound time of the three-cycle echo envelope identified in step (5), sort them in chronological order, and store the peak sound time of the three-cycle echo envelope as t 11 ,t 12 ,t 13 ;

[0051] (7) Select the second peak time t from the peak times of the three-cycle echo envelope in step (6) 12 When used as the designated monitoring ultrasonic sound;

[0052] (8) The ultrasonic sound time during the period of time when the bolt applies pre-tightening force is stored as t1;

[0053] (9) According to the formula F = KΔt, where F is the bolt preload, K is the test calibration acoustic elastic coefficient, and Δt is the transit time of the ultrasonic wave in the bolt, we can obtain F = K(t1-t0) = K(t 12 -t 02 ), calculate the accurate transit time Δt, and accurately calculate the bolt preload F;

[0054] (10) When the bolt preload is different, the ultrasonic sound time t1 of the bolt preload period is re-identified and calculated according to steps (5)-(8) and saved, and then the accurate transit time Δt and bolt preload F are re-calculated according to step (9).

[0055] The identified j period echo envelopes can be expanded to 3 or more, and the data of multiple period echo envelopes can be cross-validated to more accurately capture the characteristics of the echo envelope and reduce measurement errors.

[0056] Embodiment 3, as Figure 3As shown, the difference between the preload electromagnetic ultrasonic sound time identification monitoring method in this embodiment and that in embodiment 1 is that in steps (3) and (7), the ultrasonic sound time to be monitored is the zero-crossing sound time of any one cycle in the two-cycle echo envelope. The change of the zero-crossing sound time is relatively stable, especially when the preload change is small, the measurement error is usually small, which can reduce the error caused by the change of the peak position and improve the accuracy of the measurement result.

[0057] In addition, it should be noted that the names of the various parts of the specific embodiments described in this specification may be different, and any equivalent or simple changes made based on the structure, features and principles described in the patent concept of the present invention are included in the protection scope of the patent of the present invention. The technicians in the technical field of the present invention can make various modifications or supplements to the specific embodiments described or replace them in a similar manner, as long as they do not deviate from the structure of the present invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

Claims

1. A preload electromagnetic ultrasonic sound recognition monitoring method, characterized in that The steps include: (1) Place the electromagnetic ultrasonic transverse and longitudinal wave probe on the stress-free bolt end face. When the bolt is in a state without preload, search for the echo envelope from the trailing edge of the starting wave through the electromagnetic ultrasonic preload measurement system, and identify the highest continuous j-cycle echo envelope in the bolt without preload time period through the peak algorithm; (2) Record the peak sound time of the j-period echo envelope identified in step (1), sort them in chronological order, and store the peak sound time of the j-period echo envelope as t 01 ,t 02 ,……,t 0j ,j≧1; (3) Selecting the Nth peak sound time from the peak sound time of the j-cycle echo envelope in step (2) as the designated ultrasonic sound time to be monitored, N ≧ 1; (4) The ultrasonic sound time during the period when the bolt has no pre-tightening force is stored as t0; (5) Apply preload force to the bolt, search for the echo envelope from the trailing edge of the starting wave through the electromagnetic ultrasonic preload force measurement system, and identify the highest continuous j-cycle echo envelope during the bolt preload force application period through the peak algorithm; (6) Record the peak sound time of the j-period echo envelope identified in step (5), sort them in chronological order, and store the peak sound time of the j-period echo envelope as t 11 ,t 12 ,……,t 1j ,j≧1; (7) Selecting the Nth peak sound time from the peak sound time of the j-cycle echo envelope in step (6) as the designated ultrasonic sound time to be monitored, N ≧ 1; (8) The ultrasonic sound time during the period of time when the bolt applies pre-tightening force is stored as t1; (9) According to the formula F=KΔt, where F is the bolt preload, K is the test calibration acoustic elastic coefficient, and Δt is the transit time of the ultrasonic wave in the bolt, we can get F=K(t1- t0), calculate the accurate transit time Δt, and accurately calculate the bolt preload F; (10) When the bolt preload is different, the ultrasonic sound time t1 of the bolt preload period is re-identified and calculated according to steps (5)-(8) and saved, and then the accurate transit time Δt and bolt preload F are re-calculated according to step (9).

2. The preload electromagnetic ultrasonic sound recognition monitoring method according to claim 1, characterized in that: In the steps (1) and (5), the highest continuous j period echo envelopes are obtained by selecting the peak of the highest period echo envelope and then selecting the peak of the period echo envelopes that are continuous with it forward or backward.

3. The preload electromagnetic ultrasonic sound recognition monitoring method according to claim 1, characterized in that: In the steps (3) and (7), the ultrasonic sound time to be monitored is designated as the peak sound time of any one cycle in the j-cycle echo envelope.

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