shearband

A shear band (also written as shearband) is a narrow zone in which shear deformation concentrates, creating localized strain in a material or rock.

In geology, shear bands are localized zones of intense differential shear strain within rocks subjected to tectonic forces. They can form during ductile deformation at high temperature and pressure or during brittle slip at lower temperatures. Typical thickness ranges from millimeters to centimeters, while their extent can reach meters to kilometers depending on conditions. Microstructural evidence includes grain-size reduction, development of foliations, and dynamic recrystallization, with many bands evolving into or alongside mylonites and ultramylonites. If rapid frictional slip occurs, pseudotachylyte veins may form along the band. The orientation of a geological shear band is controlled by the principal stress directions and pre-existing rock fabric.

In materials science, a shear band is a narrow region where plastic strain localizes under applied load, often preceding macroscopic failure. They arise from factors such as material heterogeneity, damage accumulation, thermal softening, and high strain rates. Shear bands can sharply concentrate deformation and promote crack initiation and propagation, affecting the performance and reliability of metals, ceramics, and polymers.

Significance: shear bands are key indicators of localized deformation and failure mechanisms in both natural and engineered systems. Related concepts include shear zones, faults, doling of fabric in rocks, and the distinction between ductile and brittle deformation.