CN105115652A - Method for quantified monitoring bolt pre-tightening torque through active ultrasonic guided wave - Google Patents

Abstract

The present invention proposes a method for quantitatively monitoring the pretightening torque of bolts using active ultrasonic guided waves, using MFC (Macro-Fiber? Composite) macro-fiber piezoelectric composite elements as excitation and sensors, orienting the excitation structure and collecting fluctuation responses, and establishing The bolt pretightening torque reference comparison database, so that the bolt pretightening torque can be monitored online based on the reference database. The invention can quickly monitor the tightness state of the bolt without dismantling the structure, reduce the assembly cost and improve the efficiency; moreover, the method is simple to operate and has high quantitative monitoring accuracy for the torque value of a single bolt; in addition, the macro fiber The piezoelectric composite material element is very thin (about 0.2mm), and does not affect the structural performance after pasting.

Description

A Method for Quantitatively Monitoring Bolt Pretightening Torque Using Active Ultrasonic Guided Waves

technical field

The invention relates to the technical field of structural health monitoring, in particular to a method for quantitatively monitoring bolt pretightening torque by using active ultrasonic guided waves.

Background technique

Bolted connections are widespread in the fields of mechanical, civil, energy and aerospace engineering. Controlling and maintaining the bolt preload is an important prerequisite to ensure the safe service of engineering structures. However, the stress relaxation of bolts during long-term service, as well as mechanical environments such as external vibration and impact may lead to a decrease in bolt preload and loose connections, which seriously endanger the safety of the structure.

At present, the monitoring methods of bolt pretension in engineering are conventional non-destructive monitoring methods, such as the use of ultrasonic imaging, X-ray flaw detection and other methods; the other method is to fix strain gauges or force sensors on Bolt strain changes or pressure changes monitor changes in bolt preload. The former requires large-scale equipment support, and may require dismantling of the structure, which is not suitable for real-time online monitoring; the latter requires lead wires for bolt drilling or changes in the structure of the joint, which is difficult for practical application.

In recent years, the damage monitoring method using the ultrasonic guided wave method has been applied to the damage monitoring of structures such as single-material pipes and flat plates, but there are few researches on bolt loosening monitoring in the open literature and the following limitations: using energy-directed Active ultrasonic excitation elements with poor performance cause the excitation energy to diverge, resulting in insufficient wave energy in the desired direction; a systematic method for monitoring the reference database cannot be established; the sensitivity and resolution of the characteristic parameters are low, so that it is impossible to quantitatively evaluate the bolt pretension state.

Contents of the invention

technical problem to be solved

The present invention aims at solving one of the above technical problems at least to a certain extent or at least providing a useful commercial choice. For this reason, an object of the present invention is to provide a kind of method that utilizes active ultrasonic guided wave quantitative monitoring bolt pretightening torque, adopts MFC (Macro-FiberComposite) macrofiber piezoelectric composite material element as excitation and sensor, directional excitation structure and The fluctuation response is collected, and a bolt pretightening torque reference comparison database is established, so that the bolt pretightening torque can be monitored online based on the reference database.

Technical solutions

In one aspect of the present invention, the present invention proposes a method for quantitatively monitoring bolt pretightening torque using active ultrasonic guided waves, which is characterized in that it includes the following steps:

Step 1: Create a reference database offline:

Step 1.1: Manually tighten the bolt to be tested on the connection structure with a digital display torque wrench, and record the value of the torque wrench;

Step 1.2: Glue two pieces of macro-fiber piezoelectric composite material components on the connection structure, which are respectively used as actuators and sensors; the two pieces of macro-fiber piezoelectric composite material components are respectively located on both sides of the bolt to be tested, the center of the bolt and two macro The principal deformation directions of the fiber piezoelectric composite elements are collinear;

Step 1.3: The macro-fiber piezoelectric composite element as an exciter is sequentially connected to a power amplifier and a waveform generator; the macro-fiber piezoelectric composite element as a sensor is sequentially connected to a digital oscilloscope and a computer;

Step 1.4: Store the sinusoidal signal modulated by the Hanning window for 3-5 cycles in the waveform generator, the center frequency of the sinusoidal signal is 100-300KHz; the waveform generator outputs the stored sinusoidal signal in the form of a single pulse, and the output signal passes through the power amplifier After being amplified, it is applied to both ends of the electrode of the macro-fiber piezoelectric composite element as an exciter, and the peak-to-peak value of the signal pulse amplified by the power amplifier is 80-100V;

Step 1.5: Monitor the voltage signal of the electrodes at both ends of the macrofiber piezoelectric composite element as a sensor, and perform high-pass filtering on the monitored signal to obtain a filtered response signal;

Step 1.6: Calculate the root mean square of the filtered response signal, and use the root mean square as the characteristic parameter for identifying the bolt pretightening torque;

Step 1.7: Loosen the bolts completely, and then start with the torque value of manual tightening in step 1.1, select several bolt pre-tightening torques greater than the manual tightening torque value; for each bolt pre-tightening torque value, repeat steps 1.4-step 1.6 to get The characteristic parameters corresponding to the bolt pre-tightening torque value; establish a reference database composed of pre-tightening torque and characteristic parameters;

Step 2: Online monitoring of bolt pre-tightening torque:

The waveform generator repeatedly outputs the stored sinusoidal signal in the form of pulses according to the set time interval, and then monitors the voltage signal of the electrodes at both ends of the macrofiber piezoelectric composite element as a sensor, and performs high-pass filtering on the monitored signal to obtain The filtered response signal; calculate the root mean square of the filtered response signal; compare the obtained root mean square with the reference database to obtain the bolt pre-tightening torque value.

In addition, according to the embodiments of the present invention, it may also have the following additional technical features:

The method for quantitatively monitoring the pretightening torque of bolts by using active ultrasonic guided waves is characterized in that: 3MDP460 industrial adhesive is used to paste macro-fiber piezoelectric composite material elements on the connection structure, and the thickness of the adhesive layer is 0.04-0.06mm. And curing for two hours at a temperature of 50°C to 60°C.

The method for quantitatively monitoring bolt pretightening torque by using active ultrasonic guided waves is characterized in that: the cut-off frequency of the high-pass filter in step 1.5 is not less than 1.5 times the center frequency in step 1.4.

The method for quantitatively monitoring bolt pre-tightening torque using active ultrasonic guided waves is characterized in that: in step 1.7, for each bolt pre-tightening torque value, repeat step 1.4-step 1.6 several times to obtain the bolt pre-tightening torque The 95% confidence interval of the average value of the characteristic parameters corresponding to the torque value; establish a reference database composed of the preload torque and the 95% confidence interval of the average value of the characteristic parameters.

According to the embodiment of the present invention, the method of quantitatively monitoring the bolt pretightening torque by using active ultrasonic guided waves can quickly monitor the tightness state of the bolt without dismantling the structure, reduce assembly costs, and improve efficiency; The single bolt torque value has high quantitative monitoring accuracy; in addition, the macro-fiber piezoelectric composite material element used is very thin (about 0.2mm), and the structural performance will not be affected after pasting.

Description of drawings

The above and/or additional aspects and advantages of the present invention will become apparent and comprehensible from the description of the embodiments in conjunction with the following drawings, wherein:

Figure 1: Bolt pre-tightening torque monitoring system;

Figure 2: Measurement process of the bolt pretightening torque monitoring system;

Figure 3: The structural size of the test piece and the location of the excitation and monitoring points of the example;

Figure 4: A five-period sinusoidal pulse signal modulated by a Hanning window;

Figure 5: The original signal and the filtered signal of the monitoring point of the bolt under the torque of 2N.m;

Figure 6: The RMS of the monitoring point response filtering under different preloads of the example (multiple repeated experiments);

Figure 7: 95% confidence interval of the RMS mean of the examples as a function of different preload torques (reference database).

Detailed ways

Embodiments of the present invention are described in detail below, examples of which are shown in the drawings, wherein the same or similar reference numerals designate the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the figures are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

In describing the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", " Orientation indicated by rear, left, right, vertical, horizontal, top, bottom, inside, outside, clockwise, counterclockwise, etc. The positional relationship is based on the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, Therefore, it should not be construed as limiting the invention.

In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be interpreted as indicating or implying relative importance or implicitly specifying the quantity of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of these features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

This embodiment is a quantitative monitoring method for bolted connection pretightening torque using active ultrasonic guided wave technology. This method uses P1-type MFC to apply directional excitation to generate ultrasonic guided waves in the structure. After the guided wave propagates through the bolted connection, the wave response is measured. The signal is processed, and the obtained characteristic information is compared with the reference database to judge the current pretightening torque state of the bolt, so as to realize the non-destructive and online quantitative monitoring of the bolt pretightening force.

As shown in Figure 2, the method consists of two parts:

Step 1: Create a reference database offline:

Step 1.1: Use a digital display torque wrench to manually tighten the bolts to be tested on the connection structure, and record the value of the torque wrench.

Step 1.2: Use 3MDP460 industrial adhesive to paste two pieces of macro-fiber piezoelectric composite elements (M2814-P1 type MFC, 0.2mm thick) on the connection structure, which are respectively used as actuators and sensors. The positions are shown in Figure 3; the two pieces of macro The fiber piezoelectric composite elements are located on both sides of the bolt to be tested, 0.1m away from the bolt center, and the main deformation directions of the bolt center and the two macro fiber piezoelectric composite elements are collinear. 3MDP460 industrial adhesive layer is thin and uniform, the thickness of the adhesive layer is 0.04-0.06mm, and it is cured at a temperature of 50°C to 60°C for two hours.

Step 1.3: As shown in Figure 1, the macrofiber piezoelectric composite element as an actuator is connected to a power amplifier and a waveform generator in sequence; the macrofiber piezoelectric composite element as a sensor is sequentially connected to a digital oscilloscope and a computer.

Step 1.4: Store the sinusoidal signal modulated by the Hanning window for 3-5 cycles in the waveform generator, the center frequency of the sinusoidal signal is 100-300KHz; the waveform generator outputs the stored sinusoidal signal in the form of a single pulse, and the output signal passes through the power amplifier After being amplified, it is applied to both ends of the electrode of the macro-fiber piezoelectric composite material element as an exciter, and the peak-to-peak value of the signal pulse amplified by the power amplifier is 80-100V. In this embodiment, the sinusoidal signal modulated by the Hanning window for 5 periods is stored in the waveform generator, as shown in Figure 4, the center frequency is 150KHz, amplified by the power amplifier, the signal peak-to-peak value is 80V, and applied to both sides of the exciter electrode end.

Step 1.5: Due to the inverse piezoelectric effect, the piezoelectric element produces a time-varying deformation, and the disturbance is transmitted to the structure through the shear action of the adhesive layer. Elastic waves propagate in the structure, through the bolted connection, and are affected by the state of the connection (contact surface, contact stiffness, etc.). Different preload states have different effects on wave propagation behavior, and the connection state is identified accordingly. The wave continues to propagate and reaches the other end of the structure. According to the piezoelectric effect, monitor the voltage signal of the electrodes at both ends of the macrofiber piezoelectric composite element as a sensor, and perform high-pass filtering on the monitored signal. The cut-off frequency of the high-pass filtering is not less than step 1.4 1.5 times of the center frequency, remove the power frequency signal interference, remove the interference generated by the surrounding electric field induction, and obtain the filtered response signal, as shown in Figure 7.

Step 1.6: Calculate the root mean square (RMS) of the filtered response signal, and use the root mean square as the characteristic parameter for identifying the bolt pretightening torque.

Step 1.7: Loosen the bolts thoroughly with a wrench, then start with the torque value of manual tightening in step 1.1, select several bolt pre-tightening torques greater than the manual tightening torque value; for each bolt pre-tightening torque value, repeat steps 1.4-step 1.6 , to obtain the characteristic parameters corresponding to the bolt pre-tightening torque value; establish a reference database composed of pre-tightening torque and characteristic parameters. In this example, start from the torque value of manual tightening in step 1.1, and then select four bolt pretightening torque values of 1N m, 2N m, 3N m, 4N m, for each bolt pretightening torque value , repeat step 1.4-step 1.6 ten times to obtain the 95% confidence interval of the average value of the characteristic parameter corresponding to the bolt pretightening torque value; establish a reference database composed of the 95% confidence interval of the pretightening torque and the average value of the characteristic parameter.

Step 2: Online monitoring of bolt pre-tightening torque:

The waveform generator outputs the stored sinusoidal signal in the form of a pulse every second to ensure that the last guided wave is effectively attenuated in the structure, and then monitors the voltage signal of the electrodes at both ends of the macrofiber piezoelectric composite element as a sensor, and The monitored signal is high-pass filtered to obtain the filtered response signal; the root mean square of the filtered response signal is calculated; the obtained root mean square is compared with the reference database to obtain the bolt pre-tightening torque value.

If the obtained root mean square is within the 95% confidence interval of the average value of the characteristic parameter corresponding to a certain pre-tightening torque in the reference database, it means that the bolt pre-tightening torque monitored at this time is the pre-tightening torque; if the obtained root mean square If it is outside the 95% confidence interval of the average value of the characteristic parameter corresponding to a certain pre-tightening torque in the reference database, then the monitored bolt pre-tightening torque is obtained by linear interpolation. For the characteristic parameter corresponding to the lower limit of the 95% confidence interval of the mean value of the corresponding characteristic parameter less than 1N·m, the bolt pretightening torque corresponding to the characteristic parameter is taken as the manual tightening torque value. As shown in Figure 7.

In this embodiment, the RMS measured twice is 0.00514V and 0.00827V respectively, and the measured pre-tightening torques are obtained through query as manual tightening (<1N·m) and 3N·m, and the confidence level of the measured values is 95%.

Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be construed as limitations to the present invention. Variations, modifications, substitutions, and modifications to the above-described embodiments are possible within the scope of the present invention.

Claims (4)

1. utilize a method for active ultrasonic guided wave quantification monitoring bolt pre-fastening moment, it is characterized in that: comprise the following steps:

Step 1: off-line sets up reference database:

Step 1.1: adopt force moment spanner with digital display manually to be tightened in syndeton by bolt to be measured, and record torque spanner numerical value;

Step 1.2: gluing two panels grand fiber piezo-electricity composite material element in syndeton, respectively as driver and sensor; Wherein two panels grand fiber piezo-electricity composite material element is in bolt both sides to be measured respectively, the principal deformation direction conllinear of bolt-center and two grand fiber piezo-electricity composite material elements;

Step 1.3: the grand fiber piezo-electricity composite material element as driver connects power amplifier and waveform generator successively; As grand fiber piezo-electricity composite material element digital oscilloscope and the computing machine successively of sensor;

Step 1.4: store the sinusoidal signal that the 3-5 cycle modulates through Hanning window in waveform generator, sinusoidal signal centre frequency is 100 ~ 300KHz; The sinusoidal signal stored exports according to monopulse form by waveform generator, output signal through power amplifier amplification after-applied to the grand fiber piezo-electricity composite material element electrode two ends as driver, the signal pulse peak-to-peak value after power amplifier amplifies is 80 ~ 100V;

Step 1.5: the voltage signal of monitoring the grand fiber piezo-electricity composite material element two end electrodes as sensor, and high-pass filtering is carried out to the signal monitored, obtain filtered response signal;

Step 1.6: the root mean square of the response signal after calculation of filtered, and using root mean square as the characteristic parameter identifying tools for bolts ' pretension moment of torsion;

Step 1.7: thoroughly loose bolts, then starts with the moment values of manually tightening in step 1.1, select several to be greater than the tools for bolts ' pretension moment of manual screw-down torque value; For each tools for bolts ' pretension moment value, repeat step 1.4-step 1.6, obtain this tools for bolts ' pretension moment value characteristic of correspondence parameter; Set up the reference database be made up of pre-fastening moment and characteristic parameter;

Step 2: on-line monitoring tools for bolts ' pretension moment:

Waveform generator repeated the sinusoidal signal of storage to export with impulse form according to the time interval of setting, then monitor the voltage signal of the grand fiber piezo-electricity composite material element two end electrodes as sensor, and high-pass filtering is carried out to the signal monitored, obtain filtered response signal; The root mean square of the response signal after calculation of filtered; The root mean square obtained is compared with reference database, obtains tools for bolts ' pretension moment value.

2. a kind of method utilizing active ultrasonic guided wave quantification monitoring bolt pre-fastening moment according to claim 1, it is characterized in that: with 3MDP460 industry glue grand fiber piezo-electricity composite material element in syndeton, bondline thickness is 0.04-0.06mm, and solidifies two hours at 50 DEG C ~ 60 DEG C temperature.

3. a kind of method utilizing active ultrasonic guided wave quantification monitoring bolt pre-fastening moment according to claim 1, is characterized in that: in step 1.5, the cutoff frequency of high-pass filtering is not less than 1.5 times of the centre frequency in step 1.4.

4. a kind of method utilizing active ultrasonic guided wave quantification monitoring bolt pre-fastening moment according to claim 1, it is characterized in that: in step 1.7, for each tools for bolts ' pretension moment value, repeat step 1.4-step 1.6 several times, obtain 95% fiducial interval of this tools for bolts ' pretension moment value characteristic of correspondence parameter mean value; Set up the reference database be made up of pre-fastening moment and characteristic parameter mean value 95% fiducial interval.