Acoustic Emission at the Crack Tip during Cooling of a Moisture-Saturated Composite

The effect of low temperature on the properties of moisture-saturated glass-fiber-reinforced plastic KAST-B was investigated by studying acoustic emission. During cooling of dried and moisture-saturated specimens with surface defects, the rms acoustic emission and the acoustic emission count rate remain within the background noise. It was determined for the first time that, if water is localized in a crack in the glass-fiber-reinforced plastic, then its cooling leads to an intense acoustic emission. It was assumed that this emission is caused by local damages of the polymer matrix because of the increase in the internal stresses as water turns to ice.