Non-destructive testing. Acoustic emission. General principles of AE testing for the detection of corrosion within metallic surrounding filled with liquid

Acoustic emission (AE) was originally developed for non-destructive testing of static structures, but over the years its application has been extended to health monitoring of rotating machines and bearings. It offers the advantage of earlier defect detection in comparison with vibration analysis. However, limitations in the successful application of the AE technique for monitoring bearings have been partly due to the difficulty in processing, interpreting and classifying the acquired data. The investigation reported in this paper was centred on the application of standard AE characteristic parameters on a radially loaded bearing. An experimental test rig was modified such that defects could be seeded onto the inner and outer races of a test bearing. As the test rig was adapted for this purpose, it offered high background acoustic emission noise providing a realistic test for fault diagnosis. In addition to a review of current diagnostic methods for applying AE to bearing diagnosis, the results of this investigation validated the use of r. m. s., amplitude, energy and AE counts for diagnosis. Furthermore, this study determined the most appropriate threshold level for AE count diagnosis, the first known attempt.

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Study of Initial Stages of Fatigue Process Using Non-Destructive Testing Methods

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.592-593.553 ◽

2013 ◽

Vol 592-593 ◽

pp. 553-556

Author(s):

František Vlasic ◽

Josef Volák ◽

Libor Nohál ◽

Pavel Mazal ◽

Filip Hort

Keyword(s):

Acoustic Emission ◽

Crack Nucleation ◽

Electrical Potential ◽

Fatigue Loading ◽

Non Destructive Testing ◽

Testing Methods ◽

Destructive Testing ◽

Fatigue Process ◽

Cyclic Damage ◽

Non Destructive

This paper deals with the basic research of cyclic damage during the initial stages of fatigue process using the non-destructive testing methods. The acoustic emission method was used for monitoring of the microstructure changes during fatigue loading. The electrical potential measurements of specimen and microscopic observation were used mainly to detect the first short cracks and their propagation. The fatigue tests at room temperature were conducted on titanium alloy and creep-resistant steel specimens under bending and tension loading. The aim of the study was to compare the acoustic emission signal at different types of loading until fracture and to analyze in detail the signal changes in initial stages of fatigue process. This analysis was primarily based on the waveform similarity and division into classes. The results show the high sensitivity of the acoustic emission technology in the transition from the stage of surface relief evolution to the stage of crack nucleation and propagation.

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