Acoustic Emission

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Acoustic emission

Definition

Acoustic emissions (sound emissions, SE for short) are elastic stress waves (sound waves) that are generated and propagate as a result of stress reduction in the material volume, specifically due to micromechanical damage processes, crack formation (see: fracture formation) and crack propagation, and the like. In particular, the boundary areas between the reinforcing material (often fibres) and the matrix (see: fibre–matrix adhesion) are to be regarded as sound sources in reinforced plastics. With the appropriate measurement technology (see: sound emission analysis), the acoustic emissions can be recorded and linked to ongoing damage mechanisms (see, for example: Instrumented notch impact test with damage-sensitive sound emission analysis – ICIT with AE) and structural variables.

Generation

Acoustic emissions are caused by stress concentrations in the material, which give way in the form of impulses when subjected to corresponding loads, i.e., they are broken down. This causes neighbouring volume elements to vibrate, generating sound waves (Fig. 1).

Fig. 1:

Generation of sound waves due to damage to the crack tip when an external load is applied

These are particularly intense when damage processes are involved. Examples include crack formation and crack propagation and associated fracture phenomena (see: fracture types).

Measurement

The sound waves reach the surface of the component or test specimen and can be detected by piezoelectric sound transducers (see also: piezo ceramic). These correspond to the basic design of ultrasonic standard sensors, but function only as receivers.

The sound transducers are coupled to the surface of the test object. They are tuned to the frequency range of the sound waves to be detected.

Evaluation

The received sound signals represent vibrations of the sound transducer, which are represented by HF-scans. However, to characterize the signal dynamics, the results are usually displayed in sum and rate form. In contrast, by displaying the amplitude values as an HF-scan and applying frequency analysis to it, conclusions can be drawn about the damage mechanisms, e.g., in the case of different types of failure in polymer-fibre composites (see also: fibre-reinforced plastics), and the temporal assignment to individual mechanisms. Further information on the evaluation is explained in the article on sound emission testing (SEP).

See also

• Acoustic properties
• Sound velocity
• Non-destructive testing (NDT)

References

• Bardenheier, R.: Schallemissionsuntersuchungen an polymeren Verbundwerkstoffen. Part I: Das Schallemissionsverfahren als quasi-zerstörungsfreie Werkstoffprüfung. Z. Werkstofftechnik 11 (1980) pp. 41–46
• Bohse, J.: Acoustic Emission Characteristics of Micro-Failure Processes in Polymer Blends and Composites. Compos. Sci. Technol. 60 (2000) 1213–1226 ; https://doi.org/10.1016/S0266-3538(00)00060-9 (access on November 19, 2025)
• Schoßig, M.: Mechanische und bruchmechanische Bewertung von kurzglasfaserverstärkten Polyolefinwerkstoffen unter quasistatischer und dynamischer Beanspruchung. Vieweg+Teubner | Springer Fachmedien Wiesbaden GmbH (2011), (ISBN 978-3-8348-1483-8; see also AMK-Library under B 1-21)