GB/T 42871-2023 Non-destructive testing - Acoustic emission testing - Measurement method for acoustic emission signals in concrete
1 Scope
This document establishes a measurement method for acoustic emission signals in concrete.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 12713 Non-destructive testing - Acoustic emission inspection - Primary calibration of transducers
Note: GB/T 19800-2005, Non-destructive testing - Acoustic emission inspection - Primary calibration of transducers (ISO 12713:1998, IDT)
ISO 12714 Non-destructive testing - Acoustic emission inspection - Secondary calibration of acoustic emission sensors
Note: GB/T 19801-2005, Non-destructive testing - Acoustic emission inspection - Secondary calibration of acoustic emission sensors (ISO 12714:1999, IDT)
ISO 12716 Non-destructive testing - Acoustic emission inspection - Vocabulary
Note: GB/T 12604.4-2005, Non-destructive testing – Terminology - Terms used in acoustic emisson testing (ISO 12716:2001, IDT)
ISO/TR 13115 Non-destructive testing - Methods for absolute calibration of acoustic emission transducers by the reciprocity technique
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 12716 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
——ISO Online browsing platform: available at https://www.iso.org/obp
——IEC Electropedia: available at http://www.electropedia.org/
3.1
acoustic emission
AE
transient elastic waves generated by the release of energy within a material
3.2
AE signal
electrical signal detected at a sensor, which is converted through the detection of AE wave (3.3) (elastic wave)
3.3
AE wave
wave that can be detected in the form of hits (3.5) on one or more channels (3.4)
3.4
channel
one line of AE signal (3.2) detected by AE (3.1) sensor and processed by the other devices
3.5
hit
given AE (3.1) channel (3.4) that has detected and processed one AE transient
3.6
event
group of AE (3.1) hits (3.5) received from a single source by two or more channels (3.4), of which spatial coordinates can be located
3.7
array
spatial arrangement of AE (3.1) sensors for spatially locating AE sources
3.8
attenuation
observed loss of a signal as it travels through a medium
3.9
noise
signal produced by causes other than AE (3.1) phenomena
Note: Elimination of noises is essential for effective detection of AE signals (3.2).
4 Detection of AE waves
Microscopic fracture in concrete takes place with the release of stored strain energy as nucleating micro-cracks and generating elastic waves. These waves due to crack nucleation are referred to as AE waves, which propagate inside a material and are detected by an AE sensor as shown in Figure 1.
5 Measuring system
5.1 General
A basic system is illustrated in Figure 2, where only analog devices are shown. Following this system, a digital signal-processor is usually applied.
5.2 Sensor
AE sensors shall be sensitive enough to detect AE signals generated in the target structure, taking acoustic coupling into consideration. They convert elastic waves (motions) on the surface of a material into electric signals, preferably, without any distortions. A resonance-type sensor is most sensitive around the resonant frequency, while a broad-band sensor has approximately flat response in the range but is less sensitive than the resonance-type. AE sensor shall be robust enough against temperature
change, moisture condition and mechanical vibrations in the environments.
Refer to Annex A for recommended types of sensors to be used in the concrete.
Sensitivity calibration of AE sensors shall be performed by employing the standard source, in addition to the calibration methods prescribed in ISO 12713 and ISO 12714. A simulated AE source due to pencil-lead break is defined in ASTM E976. This standard source is illustrated in Figure 3, where a guide ring is recommended to be employed.
Absolute calibration of AE sensors shall be made on the basis of ISO/TR 13115.
5.3 Amplifier
Amplifiers normally consist of the pre-amplifier and the main amplifier as shown in Figure 2. The preamplifier shall be located as close as possible to AE sensor. The internal noise of the amplifier shall be inherently low and less than 20 µV (26 dBAE for 0 dBAE = 1 µV) as the peak voltage converted by input voltage. Here, the gain of the amplifier is given in dBAE (decibels AE),
