ABSTRACT
The concept of stress is developed by considering the equilibrium of a solid subjected to general loading. It is shown that six independent stress components define the state of stress at a point. The equations of equilibrium are obtained in terms of the variation of stress from one point to another in Cartesian and cylindrical polar coordinates. The stress components at a point change when changing the reference coordinates; the stress components and the directions of the axes are related by the stress transformation law. The expressions of the stress equations of equilibrium depend on the coordinate axes. In curvilinear coordinates, the space axes and coordinates are all curved and the curvature from one point to another is not usually constant. They are the most general form of coordinates, and it will be observed that Cartesian, cylindrical, and spherical coordinates are special cases of curvilinear coordinates.
