On the material invariant of 110°-conjugate angle of shear bands—Reply to Gomez-Rivas and Griera (2015)

Abstract

After their experimental data were re-explained in terms of the maximum-effective-moment (MEM) criterion, Gomez-Rivas and Griera (2015) challenge the validity of the MEM-Criterion in terms of shear fractures, which have mixed up with shear fractures and shear bands. The two features are similar in appearance but different in deformation mechanism (s). The MEM-criterion proves that ±55° to σ1 are the maximum effective moment directions and the shear bands that formed by material-line (beddings or fabrics) rotation mechanism have a constant conjugate angle of 110°. Theoretically, the 55° or 110° is a material-invariant, and practically, a statistic-invariant or preferred direction with average deviation of ~10°. By this angle, shear bands can be easily recognized from shear fractures with conjugate angle never over 90°. The High-strain deformation in the lozenges usually predates the surrounding shear bands. Two stress states can not coexisted simultaneously in the same place and the resolving σ1′ normal to the related shear zone represents 0–100% deformation partitioning, depending on the original kinematic vorticity of the shear zones.