Abstract
This paper presents a new algorithm to obtain principal stress trajectory grid. Grid points are calculated as the intersections of three mutually orthogonal isoplethic surfaces of direction functions which are evaluated from the result of FEM. The system to form equal force flow grid is developed, where the line density corresponds to the magnitude of principal stress. The line density of the principal stress trajectory which occurs subsidiarily from free boundary it faces to free boundary does not correspond to the magnitude of principal stress. Then, attenuations of the principal stress in the vicinity of free boundary surface are denoted by darker color of trajectories.
