ISO 16838:2019 pdf free.Non-destructive testing – Acoustic emission testing – Test method for lassification of active cracks in concrete structures .
4 Measurement system
4.1 AE sensor
AE sensors shall be calibrated properly in advance of the measurement in accordance with ISO 12713, ISO 12714 and ISO/TR 13115. AE sensors shall be sensitive enough to detect AE signals generated in a concrete structure, taking acoustic coupling into consideration. AE sensor shall also be robust enough against temperature change, moisture condition and mechanical vibrations in the environments.
For the parameter analysis, a broad-band sensor is recommended; but resonance-type sensors are also available, in the case that their resonance frequencies are higher than 60 kHz in concrete.
4.2 System for signal analysis
The system of AE devices shall be specified, depending on the target. AE sensors are attached at proper locations to cover the target area. The internal noise of the amplifier shall be inherently low and less than 20 1iV (26 dBAE for 0 dBAE = 1 iiV) as the peak voltage converted by input voltage. The amplifier shall be robust enough against the environmental conditions and be protected properly. The frequency range shall be determined prior to the measurement, taking into account the performance of AE sensor and the amplifier. The range from several kHz to several 100 kHz is recommended in concrete. The duration of the measurement shall be prescribed, depending on the propagation property of AE signals in the target structure.
5 Environmental noises
In advance to AE measurement, the noise level shall be estimated. Then, counteract against external noises, wind, rain, sunshine and so forth shall be conducted to decrease the noise level as low as possible. In the case that the noises have similar frequency contents, while amplitudes to AE signals or sources of the noises are unknown, characteristics of the noises shall be estimated prior to the measurement. Based on this result, separation of AE signals from the noises shall be achieved. In this respect, the use of filters is applicable after determining the proper frequency range.
The sensitivity of AE channels shall be checked routinely by employing the standard source. The variation within the channels shall be less than ±3 dBAE.
6 Test procedure
AE signals due to cracking shall be detected properly for the duration of the measurement. The test shall be conducted under loads which shall not fundamentally make any critical damage on functions of the structure to detect and locate active cracks. In advance to the test, attenuation properties of the target structure shall be estimated, by employing the standard source or the equivalent.
AE measurement is conducted in accordance with Iso 16836 and AE data is recorded with conventional AE parameters. RA values as well as average frequency are calculated based on the definition described in 3J..
By applying these parameters, classification of cracks into tensile cracks and other-types of cracks including shear cracks is performed as shown in Figure 1. It is noted that the RA values may vary depending on the threshold level; but the figure shows that the selection of AE sensors does not provide much effect on the results as shown in the figure.
For plotting data, here, the ratio of the abscissa scale to the ordinate scale is set to 10; but it just means a suggestive value. A proper ratio shall be determined, depending on materials and structures. It is recommended to set the ratio in advance to the classification of active cracks in consideration of the threshold, attenuation rate and the propagation distances.ISO 16838 pdf download.