Hintze, D., and J. Will. “Multisurface Plasticity Models under Yielding conditions/Multisurface-plastizitäts-Modelle Mit Zusammengesetzten Fliessbedingungen”. Journal of Civil Engineering and Management, vol. 5, no. 5, Oct. 1999, pp. 329-34, doi:10.3846/13921525.1999.10531484.