Acoustic Emission Monitoring of the Destruction Process of Carbon Fiber Reinforced Plastic Samples in Different Temperature Ranges

Abstract

The paper provides the results of a study of the destruction process of carbon fiber reinforced plastic samples under simultaneous impact of static loads and positive or negative temperatures using acoustic emission (AE). Samples of T800 CFRP with dimensions 100 × 600 × 0.9 mm and a lamination pattern of nine monolayers at [±45/90/0₃/90/±45] were statically loaded. Heating or cooling was applied in the central region, where a stress concentrator as an opening with a diameter of 12 mm was provided. The destruction process was monitored with a certified digital acoustic emission diagnostic system DADS-16.10 with variable selection thresholds. The real time location of the sources of AE signal allowed monitoring sample destruction in the conditions of limited visual access. The main information bearing parameters of the AE signals (amplitude, dominant frequency and structural coefficient) were analyzed from their load dependences. The registered AE signals were evaluated using wavelet transformations, which also provided the structural coefficient. It was found that, at temperatures −20 °C and +20 °C, an increase in loading resulted in the most pronounced variations in AE signal parameters. A pre-destruction state of the material was revealed by characteristic points on the load dependences of the information bearing parameters. The developed monitoring technique may be used for AE diagnostics of composite structures operated at positive and negative temperatures.