A statistical study of the relationship between crack length and frequency bandwidth emitted from the crack

In structure of rocks, there are a number of pores, joints and small cracks which called discontinuities. Studies showed that these discontinuities propagate under load and emit acoustic wave (signals). Acoustic emission (AE) method is used to study these signals. In AE method, a rock sample is loaded and a number of sensors are placed around it. Then during the loading test by growing the cracks signals emit and collecting by sensors. By collecting and analyzing these signals in the frequency dimension, mechanism of crack propagation could be studied. In this research, frequency bandwidth of the waves emitted from a rock sample under increasing load has been investigated. Data which obtained from an experiment on rock sample have been used for study. A sample of granite with dimensions of 1*3*6 inches was subjected to uniaxial loading. A code was written to change the data and executed in MATLAB. By execution the code, initially, raw data is transmitted into domain-time signals. Then, time-amplitude dimension signals converted to the frequency dimension using wavelet transform. Analyses were carried out with outputs of code and in form of diagrams and figures are presented. Analysis showed that by elapse of time and crack growth in the experiment, there was an inverse relationship between the length of the growing crack and frequency bandwidth of the emitted wave, and the frequency bandwidth decreased.