Test Conditions in Stress Wave Factor Measurements for Fiber Reinforced Composites and Laminates
The acousto-ultrasonic technique using Vary’s definition of the stress wave factor has been evaluated (SWF = g.r.n.). It was found that the technique needed to be reappraised and conditions under which the stress wave factor is reproducible defined carefully. The Acoustic Emission Technology Model AU 206 was used for the study. Instrument variables were sequentially eliminated and reduced to the instrument gain and the background noise. Regions of validity were then defined in terms of the background noise levels, and of the instrument gain on various unreinforced and glass reinforced polyester resins, with and without introduced defects. The stress wave factor is found to be most reproducible when independent of background noise, and at high gains. The equivalence of readings taken using through transmission, and those taken by placing transducers on the same side is investigated. These were found to be equivalent only at high gain, with doubtful results for low gain. The stress wave factor is interpreted in light of the present study.
KeywordsAcoustic Emission Background Noise Threshold Voltage High Gain Polyester Resin
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