DETERMINATION OF THE CONNECTION BETWEEN THE STRUCTURE OF CARBON FIBER SAMPLES AND THE PARAMETERS OF ACOUSTIC EMISSION SIGNALS DURING SIMULTANEOUS STATIC AND THERMAL LOADING

Abstract

The effects of positive and negative temperature and static load on the main informative parameters (structure coefficient, partial energy, location) of acoustic emission (AE) signals, which determined the mechanism for changing the structure of carbon fiber and the beginning of its destruction, are investigated. Tests of specimens of carbon fiber T800, made of nine monolayers with laying [±45/90/О3/90/±45], size 600x100x0.9 mm. Each sample was subjected to static loading and the effects of positive (+20, +40, +60, +80, +100 °С) or negative (–20, –40, –60, –80 °C) temperatures in the area of the concentrator in the form of a 12 mm diameter hole. Using fractography, changes in the structure of carbon plastic from the applied static load and temperature and changes informative parameters were analyzed. It was shown that the lamination of the material with simultaneous exposure to static load and temperatures from –80 to –20 °C and from +60 to +100 °C corresponded to an increase in the structural coefficient and partial energy, which caused an energy shift in the frequency range 125…250 kHz. Under the same static loads, but temperatures of +20 and +40 °C, informative parameters took on minimal values, that meant the energy was shifted to the frequency range 250…500 kHz, characterized the crumbling of the matrix and breaking of the fibers without lamination of the CFRP. Under all temperature conditions, the location of the signals began in the hole area and spread in the direction of the static load. The detection the disturbance of the CFRP structure by the informative parameters of AE signals makes it possible to reduce the risk of emergency situations during working of the composite construction.