Pic of the day #13 (Brittle deformation)

Fracture formation.
(a) Stress–strain plot (differential stress versus axial shortening) showing the stages (I–IV) in a confined compression experiment. The labels indicate the process that accounts for the slope of the curve.
(b) The changes in volume accompanying the axial shortening illustrate the phenomenon of dilatancy; left of the dashed line, the sample volume decreases, whereas to the right of the dashed line the sample volume increases.
(c–f) Schematic cross sections showing the behavior of rock cylinders during the successive stages of a confined compression experiment and accompanying stress–strain plot, emphasizing the behavior of Griffith cracks (cracks shown are much larger than real dimensions).
(c) Pre-deformation state, showing open Griffith cracks.
(d) Compression begins and volume decreases due to crack closure.
(e) Crack propagation and dilatancy (volume increase).
(f) Merging of cracks along the future throughgoing shear fracture, followed by loss of cohesion of the sample (mesoscopic failure).


    1. When a body is under stress it starts to accumulate strain, which we say deformation. Now in starting the deformation is elastic, which means as soon as the stress is removed body goes back to its initial shape of zero strain. If the stress is kept on increasing, strain reaches a point where deformation becomes permanent. The stress at that point is called Yield Stress

      Young’s modulus (E) is the ratio of stress to strain in Uniaxial deformation (Hooke’s law).
      E = stress/strain
      SI unit : Pascal
      Young’s modulus hence is mechanical property of material.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.