Experimental Studies Of The Deflection Angles Of Principal Strain Axes For Wet Sand Specimens Under Uniaxial Compression Based On The Digital Image Correlation Method

In order to deeply understand the fracture mechanism and process for geotechnical materials, the deflection or rotation angles of principal strain axes for wet sand specimens in uniaxial compression are investigated. Using the developed digital image correlation method based on the particle swarm optimization algorithm, the spatiotemporal distributions of the deflection or rotation angles of principal strain axes for sand specimens are obtained. Using the bicubic spline interpolation, the deflection angles of principal strain axes at any position are obtained to study the evolution of the deflection angles of principal strain axes with the longitudinal strains before the occurrence of a shear band, at its center, in the vicinity and at both sides of the band.It is found that with an increase of the longitudinal strain, the deflection angles of principal strain axes changes from a scattered distribution to a stable one, and at last, its range in most regions is -10?10°. After the occurrence of an apparent shear band at the late stage of strain-hardening, at the center of the band, the deflection angles of principal strain axes tend to be at -5?5° or descend slightly, while those at both sides of the band still increase. In some cases, without the influence of other bands, the deflecting directions at the center and the both sides of the apparent band are opposite. At tip of the band, the evolution of the deflection angles of principal strain axes is complex.