The following references are cited in this guide:
F. Barlat and J. Lian. "Plastic Behavior and Stretchability of Sheet Metals. Part I: A Yield Function for Orthotropic Sheets Under Plane Stress Conditions". Int. Journal of Plasticity, Vol. 5. pg. 51-66. 1989.
F. Barlat, D. J. Lege, and J. C. Brem. "A Six-Component Yield Function for Anistropic Materials". Int. Journal of Plasticity, Vol. 7. pg. 693-712. 1991.
R. Hill. "A Theory of the Yielding and Plastic Flow of Anisotropic Metals". Proceedings of the Royal Society of London, Series A., Vol. 193. pg. 281–197. 1948.