Experimental Studies Of The Deformation,Failure And The Principal Strain Axis Rotational Angles For Clay Specimens Based On The Digital Image Correlation Method

In order to reveal the deformation and failure,the distributions and evolution of principal strain axis rotational angles for clay specimens.Using the developed digital image correlation method based on the particle swarm optimization algorithm and the Newton-Raphson method,the maximum shear strain and the principal strain axis rotational angles for clay specimens are calculated and interpolated by use of the bicubic spline interpolation method.For the cuboid clay specimens under uniaxial compression,we arrange two different monitored lines.Some straight monitored lines are arranged according to the positions of apparent shear bands along shear bands in maximum shear strain fields at higher longitudinal strains.Some curved monitored lines are arranged according to the positions of higher maximum shear strains in apparent shear bands at higher longitudinal strains,and some straight monitored lines are arranged at both sides of the curved monitored lines.For clay specimens with holes under plane strain biaxial compression,the latter is adopted.For clay specimens under uniaxial compression,it is found that after the uniform deformational stage,with the increase of the longitudinal strains,the maximum shear strains in shear bands increase rapidly,while the maximum shear strains outside shear bands increase slowly;the distributions of the principal strain axis rotational angles inside and outside shear bands are nonuniform,and with the increase of the longitudinal strain the standard deviations of the principal strain axis rotational angles first decrease and then reach a stable status;for dextral shear bands,the mean of the principal strain axis rotational angles are basically negative,but not vice versa;when microcracks just occur,the principal strain axis rotational angles of dextral shear bands are mainly in the range of-10° to 0°,and the principal strain axis rotational angles of sinistral shear bands are mainly in the range of 0° to 10°;usually,positions of higher and lower values principal strain axis rotational angles correspond to or are adjacent to those of higher or lower of maximum shear strains.For clay specimens with holes under plane strain biaxial compression,it is found that one or two shear bands among multiple unclear shear bands develop to macroscopical cracks with the increase of the longitudinal strains;at higher longitudinal strains,the mean of principal strain axis rotational angles is in the range of 15° for sinistral shear bands,while it is in the range of-13° for dextral shear bands.