which are the equations of the three Mohr's circles for stress C 1 , C 2 , and C 3 , with radii R 1 = 1 2 ( σ σ 2 − − σ σ 3 ) , R 2 = 1 2 ( σ σ 1 − − σ σ 3 ) , and R 3 = 1 2 ( σ σ 1 − − σ σ 2 ) , and their centres with coordinates [ 1 2 ( σ σ 2 + σ σ 3 ) , 0 ] , [ 1 2 ( σ σ 1 + σ σ 3 ) , 0 ] , [ 1 2 ( σ σ 1 + σ σ 2 ) , 0 ] , respectively.