Stress space
In continuum mechanics, Haigh–Westergaard stress space, or simply stress space is a 3-dimensional space in which the three spatial axes represent the three principal stresses of a body subject to stress. This space is named after Bernard Haigh and Harold M. Westergaard.
In mathematical terms, H-W space can also be interpreted as a set of numerical markers of stress tensors orbits ; every point of H-W space represents one orbit.
Functions of the principal stresses, such as the yield function, can be represented by surfaces in stress space. In particular, the surface represented by von [Mises stress|von Mises] yield function is a right circular cylinder, equiaxial to each of the three stress axes.
In 2-dimensional models, stress space' reduces to a plane and the von Mises yield surface reduces to an ellipse.