Statistical analyses of principal strain axis rotational angles in shear bands and outside for clay specimens in uniaxial compression

Statistical analyses of maximum shear strains obtained by use of the digital image correlation method and principal strain axis rotational angles are conducted for low liquid limit clay specimens in uniaxial compression. Some curved monitored lines are arranged according to higher maximum shear strain positions in apparent shear bands at higher longitudinal strains, and some straight monitored lines are arranged at both sides of curved monitored lines. The following results are found. With an increase of the longitudinal strain, the percentage of positive values(anticlockwise rotation) of principal strain axis rotational angles shows an increasing or invariable trend for straight monitored lines arranged by sinistral shear bands, while it shows a decreasing trend for curved monitored lines arranged by dextral shear bands. The percentage of positive values of principal strain axis rotational angles shows a decreasing trend for straight monitored lines arranged by sinistral shear bands, while it shows an increasing trend for curved monitored lines arranged by dextral shear bands. When microcracks just occur, most of principal strain axis rotational angles for dextral shear bands are negative(clockwise rotation), most of principal strain axis rotational angles for sinistral shear bands are positive, and principal strain axis rotational angles near shear bands are usually opposite to those in shear bands. Positions of higher and lower values of principal strain axis rotational angles are consistent with or adjacent to those of higher or lower of maximum shear strains. Once an apparent shear band occurs, current rotational directions of principal strain axes outside the shear band are usually opposite to total rotational directions of principal strain axes in the shear band.