CN108775984B - Baseliness time reversal guided wave bolt pretightening force monitoring method - Google Patents
Baseliness time reversal guided wave bolt pretightening force monitoring method Download PDFInfo
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- 238000000034 method Methods 0.000 title claims abstract description 58
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- 230000005284 excitation Effects 0.000 claims abstract description 25
- 239000000919 ceramic Substances 0.000 claims description 9
- 230000004044 response Effects 0.000 claims description 3
- 230000000737 periodic effect Effects 0.000 claims description 2
- 230000007613 environmental effect Effects 0.000 abstract description 3
- 238000001514 detection method Methods 0.000 description 6
- 239000002131 composite material Substances 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 230000036541 health Effects 0.000 description 2
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- 239000000853 adhesive Substances 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L5/00—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes
- G01L5/24—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for determining value of torque or twisting moment for tightening a nut or other member which is similarly stressed
- G01L5/246—Apparatus for, or methods of, measuring force, work, mechanical power, or torque, specially adapted for specific purposes for determining value of torque or twisting moment for tightening a nut or other member which is similarly stressed using acoustic waves
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Abstract
The invention relates to a baseline-free ultrasonic guided wave bolt pretightening force monitoring method which comprises the steps of obtaining refocusing signals of excitation signals under different pretightening forces by adopting a time reversal method or an improved time reversal method, and then calculating tightening indexes under different torques by utilizing the refocusing signals. According to the method, the tightening index is calculated without a reference signal, so that the environmental adaptability of the monitoring of the pretightening force is improved, and the monitoring precision of the pretightening force of the bolt can be effectively guaranteed.
Description
Technical Field
The patent refers to the field of 'investigating or analysing materials by determining their chemical or physical properties'.
Background
The bolt connection can bear larger load, is convenient to install and disassemble, and is widely applied to structures in the fields of aerospace and civil engineering. However, under the influence of factors such as time-varying load and the like on the condition that the initial pretightening force is incorrect or the service process is affected, the bolt connection is easy to loosen in service, the loosening of the bolt can directly reduce the bearing capacity of the structure and affect the reliability and safety of the structure, and therefore, the monitoring of the pretightening force of the bolt connection is an important means for ensuring the reliability and safety of the structure. The ultrasonic guided wave becomes an important structural health monitoring means due to large measurement range and high sensitivity, and the bolt pretightening force monitoring technology based on the ultrasonic guided wave is widely concerned at home and abroad.
Due to the effects of frequency dispersion, multi-modal and boundary reflection of the guided wave, the received guided wave signal is extremely complex and difficult to analyze. The Time reversal method is proposed for the foreign scholars to process the guided wave signals, and the Time reversal method can realize refocusing of the guided wave signals and reconstruct excitation signals, thereby more conveniently realizing defect monitoring. Thus, the time reversal method-based bolt pretension monitoring method was proposed by the scholars at home and abroad (see [1] Tao W, Shaopeng L, Junhua S, et al, health monitoring of bottom joints using the time reversal method and piezoelectric transducers [ J ]. Smart Materials & Structures,2016,25(2):025010.[2] Paravasi S M, Ho S C M, Kong Q, et al, real time bolt preloading using piezoelectric ceramics transducers and time reversal technology-a numerical test with experimental modification [ J ]. Materials and Structures,2016,25(8): 085015). The method has poor sensitivity in the initial loosening stage, and thus, domestic researchers improve the method and propose an improved time reversal method (see the accepted invention patent: Xuchao, Wuguan man, Dufei, a bolt pretension torque ultrasonic guided wave monitoring method based on the improved time reversal method, 2017102607258[ P ] 2017.). The methods all utilize a time reversal method or a modified time reversal method to refocus the guided wave signals in the bolt connection structure. After refocusing signals in a tightening state (a healthy state) and a loosening state (an unhealthy state) are respectively obtained, the amplitude or the phase of a refocusing wave packet in the healthy state is utilized to normalize the peak value or the phase of the refocusing wave packet in the unhealthy state, and a tightening index is further obtained to evaluate the bolt pretightening force.
The evaluation of the bolt pretightening force in the above monitoring method depends on a baseline signal in a healthy state, however, since the propagation of a guided wave signal is easily influenced by environmental factors such as temperature, the baseline-free monitoring method has higher reliability in application (see Huang L, Zeng L, Lin J. Baseline-free damagedetection in composites based on the reliability of the baseline priority [ J ]. Smart Materials and Structures,2017,27(1): 015026.). Therefore, the method for monitoring the bolt pretightening force without the base line is constructed, and has important significance for improving the reliability of the method for monitoring the bolt pretightening force.
Disclosure of Invention
Technical problem to be solved
In order to avoid the defects of the prior art, the invention provides a baseline-free time reversal guided wave bolt pretightening force monitoring method, wherein the pretightening force is monitored without a reference signal in a healthy state in the calculation of a pretightening force index, and the monitoring precision of the pretightening force is guaranteed.
Technical scheme
A baseline-free time reversal guided wave bolt pretightening force monitoring method is characterized by comprising the following steps:
step 1: PZT piezoelectric ceramic pieces are respectively pasted on two sides of a bolt on a tested bolt connecting structure and respectively used as an exciter and a sensor, and the center of the bolt and the main deformation directions of the two PZT piezoelectric ceramic pieces are collinear;
step 2: a signal generator is adopted to generate a sine pulse signal modulated by a periodic Hanning window, the frequency is 100-300 kHz, the sine pulse signal is amplified by a power amplifier and then serves as an initial excitation signal, the initial excitation signal is applied to a PZT piezoelectric ceramic piece serving as an exciter, and a data acquisition card or an oscilloscope is used for acquiring a response signal;
and step 3: obtaining refocusing signals of the excitation signals under different pretightening forces by using a time reversal method or an improved time reversal method;
and 4, step 4: the tightening index at different torques was calculated using the following formula:
in the formula, vrm(t) obtaining a refocusing signal by using a time reversal method or a modified time reversal method; t is t2And t3Defining a time window of a refocusing wave packet in the refocusing signal, wherein the center point of the window is the maximum amplitude of the whole signal, and the length of the window is the same as the pulse width of the initial excitation signal; t is t1And t4Defining the time window of the whole refocusing signal, wherein the central point is the maximum amplitude of the whole signal and the length is 20-60 times of the pulse width of the initial excitation signal;
and 5: the above tightening index TIEThe method is used for measuring bolt pretightening force.
The PZT is 10mm multiplied by 8mm multiplied by 1mm in size, model P5H.
Advantageous effects
According to the baseline-free time reversal guided wave bolt pretightening force monitoring method, the tightening index is calculated without a reference signal, the environmental adaptability of pretightening force monitoring is improved, and meanwhile the pretightening force monitoring precision of the bolt can be effectively guaranteed.
Drawings
FIG. 1: the tested bolt connection structure and the pasted PZT piezoelectric piece;
FIG. 2: the shape of refocusing wave packet in refocusing signal obtained by time reversal method (a) refocusing signal under 8Nm torque (b) refocusing signal under 1Nm torque (c) refocusing signal is compared with that of excitation signal;
FIG. 3: the mean value and the standard deviation of the baseline-free pretightening force detection result based on a time reversal method;
FIG. 4: the shape of refocusing wave packet in refocusing signal under the condition of 12Nm torque (a) refocusing signal under the condition of 8Nm torque (c) refocusing signal under the condition of 1Nm torque (d) refocusing signal obtained by using improved time reversal method is compared with that of excitation signal;
FIG. 5: the mean value and the standard deviation of the baseline-free pretightening force detection result based on the improved time reversal method;
Detailed Description
The invention will now be further described with reference to the following examples and drawings:
step 1: piezoelectric ceramic (PZT) sheets are respectively stuck to two sides of a bolt in the connecting structure and are respectively positioned on two sides of the bolt to be detected, and the main deformation directions of the bolt and the PZT sheets are collinear;
step 2: a waveform generator and the like send out a sine pulse signal modulated by a Hanning window, the signal frequency can be selected to be 100-300 kHz, and the initial signal is amplified by a power amplifier and then serves as an initial excitation signal;
and step 3: obtaining refocusing signals of the excitation signals under different pretightening forces by using a time reversal method or an improved time reversal method;
and 4, step 4: utilizing the ratio of the energy of the refocusing wave packet to the energy of the whole signal to construct a new tightening index which measures the refocusing capacity of the refocusing wave-guiding signal, as shown by TI in the following formulaEShown in the figure:
in the formula, vrm(t) obtaining a refocusing signal by using a time reversal method or a modified time reversal method; t is t2And t3Defining a time window of a refocusing wave packet in the refocusing signal, wherein the center point of the window is the maximum amplitude of the whole signal, and the length of the window is the same as the pulse width of the initial excitation signal; t is t1And t4Defining the time window of the whole refocusing signal, and the central point is the whole signal amplitudeAt maximum, the length is 20-60 times the pulse width of the initial excitation signal.
And 5: using the above tightening index TIEThe bolt pretightening force can be measured.
The first embodiment is as follows: baseliness pretension monitoring based on time reversal method
Step 1: referring to the attached figure 1, two PZT piezoelectric ceramic pieces are adhered to a connection structure of a bolt to be tested by using epoxy resin adhesive and are respectively used as an exciter and a sensor, and the two PZT piezoelectric pieces are respectively positioned at two sides of the bolt to be tested. PZT has a size of 10mm × 8mm × 1mm, model P5H. The center of the bolt and the main deformation directions of the two PZT elements are collinear.
Step 2: and applying an excitation signal to the piezoelectric plate by using a signal generator and a signal amplifier, and acquiring a response signal by using a data acquisition card or an oscilloscope. A sinusoidal signal modulated by a Hanning window with 3.5 cycles is used as an excitation signal, the center frequency of the sinusoidal signal is 150kHz, and the peak value of a signal pulse amplified by a power amplifier is 50V.
And step 3: torque is applied to the bolt to be tested by a torque wrench, and the M8 bolt is connected with the two building components. The rated torque of M8 is set to 16Nm, and the tightening state is taken as a healthy state, and other loosening torque states are taken as unhealthy states, and other torques adopted in the embodiment are as follows: 1Nm,2Nm,4Nm,6Nm,8Nm,10Nm,12Nm,14Nm, and with Hand Tightness (HT) in a completely loosened state.
And 4, step 4: refocusing signals in different torque states are obtained by using a time reversal guided wave method, see fig. 2.
And 5: the tightening indexes at different torques were calculated using the following formula.
In the formula, vrm(t) obtaining a refocusing signal by using a time reversal method or a modified time reversal method; t is t2And t3Defining the time window of refocusing wave packet in refocusing signal, its window central point is the maximum position of amplitude value of whole signal, window length and pulse width of initial excitation signalThe degrees are the same; t is t1And t4The time window of the whole refocusing signal is defined, the central point is also the position with the maximum amplitude of the whole signal, and the length is 41 times of the pulse width of the initial excitation signal.
Step 6: and comparing the tightening indexes obtained by calculation to judge whether the bolt is loosened. The detection steps are repeated for three times to obtain the result shown in the attached figure 3, so that the tightening index is far higher than the situation with pretightening force under the condition of Hand Tightening (HT), the repeatability is better, and whether the bolt is loosened or not can be distinguished by using the index.
The second embodiment is as follows: baseliness pretension monitoring based on improved time reversal method
And 4, step 4: refocusing signals in different torque states were obtained using the modified time reversed guided wave method, see figure 4 for results.
And 5: the tightening indexes at different torques were calculated using the following formula.
In the formula, vrm(t) obtaining a refocusing signal by using a time reversal method or a modified time reversal method; t is t2And t3Defining a time window of a refocusing wave packet in the refocusing signal, wherein the center point of the window is the maximum amplitude of the whole signal, and the length of the window is the same as the pulse width of the initial excitation signal; t is t1And t4The time window of the whole refocusing signal is defined, the central point is also the position with the maximum amplitude of the whole signal, and the length is 41 times of the pulse width of the initial excitation signal.
Step 6: in order to compare with the detection result of the tightening index, the index measuring the waveform change in the existing guided wave damage detection is used as the tightening index 2, and the calculation formula is shown as follows (see the Watkins R, Jha R.A modified sample reversal method for Lamb wave based diagnostics of composite structures [ J ]. Mechanical Systems and Signal Processing 2012,31:345-354.)
In the formula, va(t) is a 3.5 cycle hanning window modulated sinusoidal excitation signal; n is the number of data points of the signal, according to t in step 52And t3Determining the number of data points in a defined time window; at this time vrm(t) represents a refocused focal packet, the same as the refocused focal packet in step 5.
Step 6: the two tightening indexes are calculated simultaneously, and the detection steps are repeated three times to obtain the result shown in the attached figure 5, so that the proposed tightening index TI can be seenEThe bolt pre-tightening torque can be distinguished by using the index, the torque is reduced along with the reduction of the torque, the repeatability is very good, and different pre-tightening torques of the bolt can be distinguished by using the index. However, with tightening index 2: TIL2The repeatability of the obtained result is very poor, which shows that the method provided by the invention can obtain the tightening index without a base line signal, and the index can guarantee the precision of the monitoring result.
Claims (2)
1. A baseline-free time reversal guided wave bolt pretightening force monitoring method is characterized by comprising the following steps:
step 1: PZT piezoelectric ceramic pieces are respectively pasted on two sides of a bolt on a tested bolt connecting structure and respectively used as an exciter and a sensor, and the center of the bolt and the main deformation directions of the two PZT piezoelectric ceramic pieces are collinear;
step 2: a signal generator is adopted to generate a sine pulse signal modulated by a periodic Hanning window, the frequency is 100-300 kHz, the sine pulse signal is amplified by a power amplifier and then serves as an initial excitation signal, the initial excitation signal is applied to a PZT piezoelectric ceramic piece serving as an exciter, and a data acquisition card or an oscilloscope is used for acquiring a response signal;
and step 3: obtaining refocusing signals of the excitation signals under different pretightening forces by using a time reversal method or an improved time reversal method;
and 4, step 4: the tightening index at different torques was calculated using the following formula:
in the formula, vrm(t) obtaining a refocusing signal by using a time reversal method or a modified time reversal method; t is t2And t3Defining a time window of a refocusing wave packet in the refocusing signal, wherein the center point of the window is the maximum amplitude of the whole signal, and the length of the window is the same as the pulse width of the initial excitation signal; t is t1And t4Defining the time window of the whole refocusing signal, wherein the central point is the maximum amplitude of the whole signal and the length is 20-60 times of the pulse width of the initial excitation signal;
and 5: the above tightening index TIEThe method is used for measuring bolt pretightening force.
2. The method for monitoring the pre-tightening force of the baseless time-reversal guided wave bolt according to claim 1, wherein the PZT is 10mm x 8mm x 1mm in size, model P5H.
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| CN110068454A (en) * | 2019-04-23 | 2019-07-30 | 西北工业大学 | The electromechanical impedance monitoring method of bolt pretightening under a kind of vibrational excitation |
| CN113916411B (en) * | 2021-09-18 | 2022-05-27 | 哈尔滨工业大学 | Pre-tightening force measurement method based on global linearization Koopman state observer |
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