**Principal Plane is the Plane in which no Shear Stresses are acting.**

**The normal stresses which are acting on Principal Plane are called as Principal Stress.**

**Stresses on Oblique Plane**

**The normal stresses (s***x*and s*y*) and the shear stress (t*xy*) are acting vary smoothly on a body, the normal and tangential stresses or shear stress acting on a Oblique plane making a rotation of an angle q to the vertical face are given by,

**Normal stress on inclined plane**

**sq = (**

**s***x***+**

**) / 2 + (****s***y***-****s***x***)/2cos2q +****s***y***sin2q -- (1)****t***xy*

**Shear stress in the inclined plane**

**t****q =**

**(**sin

**-****s***x***)/2****s***y***2q**-

**t***xy***cos2q - (2)**

**In above equations, there exist a couple of particular angles where the stresses take on special values.**

**First, there exists an angle q**

*p*where the shear stress t*xy*becomes zero. That angle is found by setting t*xy*to zero in the above shear transformation equation and solving for q (set equal to q*p*). The result is, t**he principal palenes are located at**

**tan**

**q**

*p***= 2 xy / (x - y) ---(3)**

**The principal stresses are**

**--(4)**

**The angl…**