Fig. 10. The method of calculating the traction stress. (A) Each triangle element has three nodes, A₁, A₂ and A₃, whose original positions are (x₁, y₁), (x₂, y₂), (x₃, y₃) and displacement vectors are (u₁, v₁), (u₂, v₂), (u₃, v₃), respectively. The strains at each point in one element are assumed to be distributed linearly. P is an arbitrary point whose original position is (x, y) and the displacement vector is (u, v). (B) The longitudinal and shearing strains, _x, _y and _xy, at the minute square in the element. (C) The normal and shearing stresses, _x, _y and _xy, at the minute square in the element.