Stress and Strain

In Situ Stresses Mechanics of Earth Materials Outline

A load applied to a material results in a stress at any point within it. Stresses may be:

In rock mechanics and soil mechanics, compressive stresses are positive by convention and tensile stresses are negative. Shear stresses are positive if the implied rotation is anticlockwise.

STRESS

is defined as force per unit area. The units of stress are Pascals . Soil stresses are typically in the kilopascal range (kPa). Rock stresses are usually measured in Megapascals (MPa).

STRAIN

is defined as change in length per unit length (normal strain) or change in angle between lines in a deforming body (shear strain). Strain is dimensionless and in rocks and soils is usually counted in microstrains.

STRAIN RATE

is change in strain per unit time. In rock deformation strain rates are usually given in microstrains/sec. In explosive deformation, strain-rates can be be very high. For geological processes, strain-rates are extremely low.

In Situ Stresses Mechanics of Earth Materials Outline
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