State of Pure Shear  
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Four points j k m n are marked on a grid system. J k m n forms a square of side d x. After torsion is applied the points k and m move to points k prime m prime. The length of each side remains d x.

After torque T is applied, the shaft twists. The right-hand end of element jkmnrotates with respect to the left-hand end by a small angle of twist dϕ. Points k and m move to new positions k' and m', respectively.

Notice that the element sides do not elongate or contract. However, the corners of the element are no longer equal to 90∘. The element is in a state of pure shear.