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Influence of Monitoring Conditions on the Stress Wave Emission Data Recorded During Tensile Testing of a GRP,

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The stress wave or acoustic emission monitoring technique is a potentially valuable tool for the detection of failures in reinforced plastics. The monitoring conditions used may vary under different test circumstances and influence the actual data recorded. It is not yet possible to predict these effects from a basic understanding of the stress wave source event, its propagation and interaction with the detection system. In this report the results of an empirical study of these monitoring conditions using a practical test situation are reported. Repeat tensile tests have been conducted using a standardised procedure for a glass-fibreepoxy laminate of low variability for several monitoring parameters such as system gain, transducer type, transducer to failure site separation distance specimen dimensions, ringdown V. event and total count v. count rate. Under most conditions a similar trend of emission data with increased applied stress was obtained. In some cases only the final failure was detected and in all cases there was a considerable variation in the absolute count levels recorded. It was found in several cases that simple empirical relationships could be obtained which allowed for these changes in the monitoring condition. However, the potential dangers in accepting data without undertaking calibration-type experiments and without directly relating the emission data to actual failures were clearly apparent. In particular, there is a need to establish that an absence of emissions is in reality an absence of failures.

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  • Plastics
  • Mechanics
  • Laminates and Composite Materials

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