GB/T 34370.8-2020Nondestructive testing of amusement equipments—Part 8: Acoustic emission testing (English PDF)

3.1 Acoustic emission source

The physical source point or location where transient elastic waves are generated by the rapid release of energy in a material.

3.2 Acoustic emission location source

The location of the acoustic emission source on the object under test determined by analyzing the acoustic emission data.

NOTE: several common source location methods include regional location, computational location and continuous signal location.

3.3 Activity

The degree, to which, the number of acoustic emission source events changes with the loading process or the time.

3.4 Intensity

The average elastic energy released by the acoustic emission source events.

3.5 Active defect

Defect that causes transient elastic wave release due to load.

8.1 General Testing Process Procedures

The organizations engaged in acoustic emission testing of amusement equipment shall develop general testing process procedures in accordance with the requirements of GB/T 34370.1 and this Part, which shall at least include the following elements:

a) Serial No. of the document;

components with a maximum side length greater than 400 mm, plane location should be adopted. For profile steel components, such as: I-beams, channel steels and angle steels, etc., line location should be adopted.

b) In a sensor array, if there are bolt connections, pin connections and riveting, etc. in metal components that may cause serious attenuation of sound energy, sensor arrays shall be respectively set up on both sides of the connection.

Appendix B provides a schematic diagram of the arrangement of acoustic emission sensors for some structural components.

9.1.5 Determination of loading scheme

In accordance with the purpose of acoustic emission testing and the actual conditions of the testing site, determine the loading scheme. The loading includes three modes: equipment operating status loading, independent static loading of the component under test, and natural wind loading. Each loading mode shall comply with the following requirements:

a) The loading of equipment operating status shall be carried out in accordance with the loading methods of no-load, full-load or eccentric test load specified in GB 8408 or relevant regulations and standards, or determined in consultation with the user in accordance with the actual use of the equipment;

b) For individual static loading of the component under test, water bags or water tanks, hoisting mechanisms (with tension gauges), etc. should be used to apply the static load, and the load shall be increased step by step;

c) For components affected by wind load, if meteorological conditions permit, the natural wind load loading mode may be adopted.

9.2 Installation of Sensors

9.2.1 Sensors shall be installed on the component under test in accordance with the determined sensor array. When testing the entire component, the installation location of the sensors shall be as far away from bolted connections, supports, reinforcing plates and welded parts as possible. When performing local testing, the tested part shall be located in the middle area of the sensor array as much as possible. When I-beams are connected by riveting or bolting, sensors shall be respectively arranged on both sides of the connection part.

9.2.2 The surface of the sensor installation part shall be treated to make it smooth and metallic.

If there is a smooth and dense protective layer on the surface, it can be retained, but the attenuation of the acoustic emission signal by the protective layer shall be measured.

9.2.3 Apply coupling agent onto the installation part of the sensors. The coupling agent shall be made of materials with good acoustic coupling performance. The operating temperature level of the coupling agent shall match the surface temperature of the component under test.

9.2.4 Good acoustic coupling between the sensors and the surface of the component under test shall be achieved.

9.2.5 Adopt magnetic clamps, adhesive tape or other modes to firmly fix the sensors on the component under test, and maintain the sensors insulated from the component under test and the fixture.

9.3 Debugging of Acoustic Emission Testing System

9.3.1 General

Use cables to connect the sensor to the pre-amplifier and system host, power on and pre-heat the system to a stable operating state. Set the preliminary working parameters of the acoustic emission testing system, then, in accordance with the provisions of 9.3.2 ~ 9.3.6, successively debug the system.

9.3.2 Simulated source

Use a simulated source to test the testing sensitivity and calibrate location. The simulated source shall be able to repeatedly emit elastic waves. An acoustic emission signal generator can be used as the simulation source, or the break signal of a pencil lead with phi0.3 mm and hardness 2H or phi0.5 mm and hardness HB can be used as the simulation source. The extension length of the pencil lead is about 2.5 mm, and the angle between it and the surface of the component under test is about 30°. It is broken 100 (± 5) mm away from the center of the sensor. The response amplitude value shall be the average value of more than three responses.

9.3.3 Channel sensitivity test

Before starting the testing, the channel sensitivity shall be tested. It is required that each channel be tested for simulated source acoustic emission amplitude value response. The difference between the amplitude value of each channel response and the average amplitude value of all channels shall not be greater than ± 3 dB.

9.3.4 Attenuation measurement

Measurement of attenuation characteristics shall be performed under the same conditions as for acoustic emission testing. If there is already attenuation characteristic data with the same testing conditions, the attenuation characteristic measurement does not need to be performed, but the attenuation characteristic data shall be indicated in the current testing record and report.

9.3.5 Location calibration

When adopting computational location, at any part of the array of the component under test, the elastic waves generated by the acoustic emission simulated source can at least be received by the sensors in the location array, and a unique location result can be obtained. The location error shall not exceed ± 5% of the maximum sensor spacing in the array of sensors.

When adopting regional location, the elastic waves generated by the acoustic emission simulated source shall be received by at least one sensor in the region.

9.3.6 Background noise measurement

By lowering the threshold voltage, measure the background noise of each channel. The threshold voltage setting value of each channel shall be at least 6 dB greater than the background noise. Then, measure the background noise of the entire testing system, and the measurement time shall not be less than 5 minutes. If the background noise is close to or greater than the intensity of the acoustic emission signal generated by active defects in the material of the object under test, the interference of the background noise shall be eliminated as much as possible, otherwise, the acoustic emission testing should not be performed.

9.4 Testing

9.4.1 Loading

In accordance with the determined loading scheme, load the component under test.

9.4.2 Noise during testing

During the loading process, attention shall be paid to the impact of the following factors on the testing results:

a) External mechanical vibration;

b) Mechanical friction;

c) Electromagnetic interference;

d) Weather conditions, such as: interference from wind, rain and hail, etc.;

e) Leakage of pneumatic and hydraulic parts, etc.

9.4.3 Testing data collection and process observation

9.4.3.1 The testing data shall collect at least the parameters specified in Appendix A. When time difference location is adopted, the data on the arrival time shall also be collected; when regional location is adopted, information on the sequence, in which, the acoustic emission signals arrive at each sensor, shall also be collected.

9.4.3.2 During the testing, the variation tendency of the number of acoustic emission impacts and / or location source over time shall be observed. For parts where acoustic emission location sources are concentrated, check whether there are external interference factors. If external interference factors are found, stop loading and eliminate the interference factors as much as possible.

9.4.3.3 During the test, if it is found that the number of acoustic emission impacts received by a certain channel is significantly lower than that of an adjacent channel, then, the sensitivity measurement of the channel shall be carried out again. During the testing, if the testing is suspended for more than 1 hour due to loading or other reasons, when the testing is resumed, the sensitivity measurement of each channel shall be performed again.

9.4.3.4 If strong noise interference is encountered during the testing, the testing shall be suspended, and the testing shall be carried out after the strong noise interference is eliminated.

9.4.4 Testing data analysis and determination of acoustic emission source locations

9.4.4.1 Noise data occurring during the testing process shall be identified in the testing data and indicated in the testing record.

9.4.4.2 Utilize software filtering or data graphic display and analysis methods to separate non-correlated acoustic emission signals from the testing data and indicate them in the testing record.

9.4.4.3 In accordance with the testing data, determine the location of the relevant acoustic emission locating sources. If further confirmation of the acoustic emission sources is required, the specific location of the acoustic emission sources shall be determined through simulated source location. The determination method is to emit a simulated source at a certain location in the testing area. If the obtained location display is consistent with the location display of acoustic emission location source in the testing data, then, the location of the simulated source is the location of the detected acoustic emission location source.

9.5 Testing Record

9.5.1 The main content of the testing record shall not be less than the content of 8.2 and Chapter 12.

9.5.2 During the testing, if there is noise interference from factors that cannot be eliminated, such as: wind, rain and friction, etc., they shall be truthfully recorded and indicated in the testing record.

9.5.3 The testing record and acoustic emission data shall be kept for at least 6 years. For the type test process, the manufacturing organization shall keep the testing record and acoustic emission data, until the equipment is scrapped.

10.1 General

The evaluation of the testing results is based on the acoustic emission signals of the previous two load-holding processes, and the signals of the loading process or other load-holding processes are used as a reference.

10.2 Determination of Acoustic Emission Source Area

When adopting time difference location, the acoustic emission location source area is […]

A.1 Sensors

The response frequency of the sensors is recommended to be within the range of 100 kHz ~ 400 kHz, and its sensitivity shall not be less than 60 dB. When selecting sensors in other frequency bands, changes in sensitivity shall be considered, so as to ensure sufficient receiving sensitivity within the selected frequency band.

The sensors shall be able to shield radio wave or electromagnetic noise interference. The sensitivity change value of the sensors within the response frequency and operating temperature range shall not be greater than 3 dB. Electrical insulation shall be maintained between the sensors and the surface of the object under test.

A.2 Signal Line

The length of the signal line between the sensor and the pre-amplifier shall not exceed 2 m. The signal line shall be able to shield electromagnetic noise interference.

A.3 Signal Cable

The signal cable between the pre-amplifier and the system host shall be able to shield electromagnetic noise interference. Within any 30 m range, the attenuation loss of the signal cable shall not be greater than 1 dB/30 m. The length of the signal cable should not exceed 150 m.

A.4 Coupling Agent

The coupling agent shall be able to maintain good acoustic coupling effect during the test period. Vacuum grease, petroleum jelly and butter can be selected.

A.5 Pre-amplifier

The effective voltage value of the pre-amplifier short-circuit noise shall not be greater than 7 µV. Within the operating frequency and operating temperature range, the frequency response of the pre-amplifier shall not change by more than 3 dB. The frequency response of the pre-amplifier and the sensor shall match, and its gain shall match the gain setting of the system host, usually 40 dB or 34 dB. When the pre-amplifier adopts a differential circuit, its common-mode noise suppression shall not be lower than 40 dB.

A.6 Filter

The frequency response range of the filters placed within the pre-amplifier and system host processor shall match the frequency response of the sensor.

A.7 System Host

A.7.1 The host of the acoustic emission system shall have the number of channels covering the testing area. It shall be able to display and store at least the following acoustic emission signal parameters in real time: arrival time, threshold, amplitude, ring count, energy, rise time, duration and number of impacts.

A.7.2 The system host should have the function of receiving and recording electrical signals output by external sensors, such as: force and temperature, etc.

A.7.3 The independent sampling frequency of each channel shall not be lower than ten times the center point frequency of the sensor response frequency.

A.7.4 The threshold accuracy shall be within the range of ± 1 dB.

A.7.5 The accuracy of the acoustic emission signal count measurement value shall be within the range of ± 5%.

A.7.6 Within 10 seconds from the start of the signal impact, the acoustic emission system shall have the short-term processing capability of collecting, processing, recording and displaying no less than 20 acoustic emission impact signals per second for each channel. When continuously monitoring, the acoustic emission system shall have the processing capability of collecting, processing, recording and displaying no less than 10 acoustic emission impact signals per second for each channel. When data congestion occurs, the system shall be able to send out an alarm signal.

A.7.7 The accuracy of the peak amplitude measurement value shall be within the range of ± 2 dB. Meanwhile, the dynamic range of signals without distortion shall not be less than 65 dB.

A.7.8 The accuracy of energy measurement value shall be within the range of ± 5%.

A.7.9 For the acoustic emission testing system by time difference location, the resolution of the rise time, duration and arrival time of each channel shall be at least 0.25 µs, the accuracy shall be within the range of ± 1 µs, and the error between channels shall not be greater than ± 3 µs of the average value.

A.7.10 The accuracy of the system in measuring the voltage value of external parameters shall not be lower than 2% of the full scale.

A.7.11 The acoustic emission acquisition software shall be able to realize real-time display of the parameters of the acoustic emission signals, and the correlation diagrams between the parameters of the acoustic emission signals and the parameter variation with force or time, as well as the line location and plane location diagrams of the acoustic emission location sources.

The lag time of real-time display shall not exceed 5 seconds.

A.7.12 The acoustic emission analysis software shall be able to play back the original acoustic emission testing data and perform analysis and processing on the acoustic emission testing data, […]