The effect of geometry on acoustic emission.

El-Dardiry, Samir M.A.

Abstract

Acoustic emissions are impulsive elastic waves which are part of the total energy release from many metallurgical phenomena. The emissions signature carry information about the source mechanisms and the present interest of investigators is to identify the acoustic emission sources in terms of material fatigue and fracture parameters in order to determine their severity on the structure components. In practice, the acoustic emission signature from the receiving transducer output is strongly affected by the structure geometry, structure/transducer couplant layer, transducer components and instrumentation characteristics. The aim of this study was to develop an acoustic emission data processing system and to investigate the effect of piezoelectric transducer structure, couplant and the geometry of test specimen on the transducer output. Theoretical interpretation of acoustic emission parameters are carried out on an arbitrary emission burst and relationships between different parameters, in both time and frequency domains, are investigated in order to achieve a better understanding of the physical meaning of such measures. Data processing systems to record the waveforms of emissions and computer programs to extract several statistical parameters and transform the waveforms to frequency spectra are developed and tested. To simplify the propagation problem, the theoretical study only predicted the pressure transmission coefficient for the case of a plane longitudinal wave incident on the couplant and transducer components in normal direction. Several transmission cases are considered theoretically, and an emerged test system was devised to determine experimentally the applicability of the theoretically predicted transmission curves. The study shows how the observed acoustic emission parameters are influenced by the transmission geometry and variation in couplant thickness. It is suggested that a PVC adhesive tape, under certain conditions, is a good selection as transducer couplant. An attempt was made, using the developed data processing system and couplant, to touch on the important highlights of the effect of the specimen geometry on the received acoustic emission waveforms. It is found that the series of the theoretical relationships between different acoustic emission parameters correspond rather well with the experimental results. In the case of simulated acoustic emission source in plates, the results indicated that the received bursts are of normal distribution with zero mean as well as the bursts derivative function. The linear relationship between the natural logarithm of the burst number of counts and the corresponding threshold squared value for an individual burst can be used to characterise the burst energy, duration time and the central frequency.

Citation

EL-DARDIRY, S.M.A. 1980. The effect of geometry on acoustic emission. Robert Gordon's Institute of Technology, PhD thesis. Hosted on OpenAIR [online]. Available from: https://doi.org/10.48526/rgu-wt-1993200

• Thesis Type: Thesis
• Deposit Date: Oct 10, 2024
• Publicly Available Date: Oct 10, 2024
• DOI: https://doi.org/10.48526/rgu-wt-1993200
• Public URL: https://rgu-repository.worktribe.com/output/1993200
• Award Date: Feb 29, 1980