Equations (3.46) for stresses at a point O can be represented conveniently by Mohrs circle (Fig. 3.16). Normal stress Æ’ is taken as the abscissa, and shear stress v is taken as the ordinate.

The center of the circle is located on the Æ’ axis at (Æ’1 + Æ’2) /2, where Æ’1 and Æ’2 are the maximum and minimum principal stresses at the point, respectively. The circle has a radius of (Æ’1 - Æ’2) /2. For each plane passing through the point O there are two diametrically opposite points on Mohrs circle that correspond to the normal and shear stresses on the plane. Thus Mohrs circle can be used conveniently to find the normal and shear stresses on a plane when the magnitude and direction of the principal stresses at a point are known.

Use of Mohrs circle requires the principal stresses Æ’1 and Æ’2 to be marked off on the

abscissa (points A and B in Fig. 3.16, respectively). Tensile stresses are plotted to the right of the v axis and compressive stresses to the left. (In Fig. 3.16, the principal stresses are indicated as tensile stresses.) A circle is then constructed that has radius (Æ’1 + Æ’2)/2 and passes through A and B. The normal and shear stresses Æ’x, Æ’y, and vxy on a plane at an angle with the principal directions are the coordinates of points C and D on the intersection of