Stresses can also be expressed in matrix forms as indicated below. Strain Strain is defined as the elongation of an element with respect to its original length. In 3-D, it is also a tensor quantity. Similar to stresses, therefore, it can be expressed in matrix forms as well. When a deformation is in a direction perpendicular to the original length, it is called a shear strain.
Normal strains preserve the angles of a control element, but change the lengths of the sides.
Shear strains, on the other hand, preserve the lengths of the sides, but change the angles of the control element. One must first know particle displacements before deformation can be described. Consider the line element below. Let be the stretching of the line element. The amount of displacement of each particle along the line element varies from left to right.