The Fourier transform method was used to quantitatively analyze an intergranular fracture surface in 45# steel and a fatigue fracture surface in commercial aluminum. It was found that there is a direct correspondence between the Fourier spectrum of the profile and the microstructure features. Utilization of the secondary electron line scanning facilitated the analysis of the fracture surface in this case. The results of the analysis showed that the autocorrelation length can be related to the average grain size. For the 45# steel, the power intensity corresponds to the impact energy of the fracture surface. Through autocorrelation analysis of the fatigue striations, the salient character of the surface morphology at high magnification, the local crack propagation rate can be deduced. The superiority of the correlation analysis method over the ordinary method (by measuring the striation distance) is obvious especially for those fracture surfaces without apparent striations. From the power spectrum function, the energy spectra of the secondary electron scanning line show an inverse relationship between the power amplitude G(k) and wave number k. A parameter n was indexed by curvefitting the power spectrum peaks in the function G(k) = c.k~(-n). It was found that for the brittle intergranular fracture surface the exponent n changes in the same trend of the fractal dimension of the fracture surface and for the fatigue fracture surface n stands in a close relation to the crack propagation rate. The study shows that Fourier transform method is feasible in quantitative analysis of the fracture surface.
修改评论