Determination of Crack Initiation Point in J_Ic Testing Using Acoustic Emission Frequency Analysis

Abstract

A classification method of acoustic emissions (AE) accompanied by the crack initiation in fracture toughness testing was proposed. The AE signals during fracture testing of compact specimens of hot rolled steel, HT-60 steel and 7075-T6 aluminum alloy were measured and the frequency spectra of the initial part of the observed signals were obtained. The source rise time and the characteristic AE energy were calculated from each power spectrum.
It was found that the high energy AE events were closely related to the crack initiation determined by the electric potential method. Fracture initiation in hot rolled steel and 7075-T6 aluminum alloy was precisely determined by using the energy above method, but not easily determinable from the conventional AE parameters, RMS, event count and rate, AE energy by V_p² or the observed waveform. High energy events corresponding to the stable crack initiation were not observed in ductile HT-60 steel. From the source rise time analysis, it was revealed that the sampling time was too short to evaluate the energy.