Asperity Height and Aperture of an Artificial Tensile Fracture of Metric Size

Summary

A tensile fracture of about 1 m in length was created by indenting wedges in a block of granite, and the heights of the two fracture surfaces were measured using a large, non-contact surface profile measurement system with a laser profilometer to determine the aperture distribution of the fracture. Based on the measured data, the frequency characteristics of the asperity heights, the initial aperture (the aperture when the surfaces are in contact at a single point), and the size effect on the statistical properties were analyzed. The results can be summarized as follows:

• 1. The relation between the power spectral density of the fracture surface and the spatial frequency shows linearity on a log–log plot and thus the fracture surfaces can be assumed to be fractal object. On the other hand, the power spectral of the initial aperture becomes almost constant for wavelengths greater than about 100 mm. Thus, the matedness between the two surfaces of a fracture of 1 m monotonously increases with wavelength.

• 2. The standard deviation of the initial aperture increases with fracture size until the fracture size is about 200 mm, beyond which the standard deviation is almost independent of the fracture size. On the other hand, the mean initial aperture still increases when the fracture size exceeds 200 mm, since the initial aperture depends on the minimum value of the aperture, which decreases with the number of data points.