Liebe, T., P. . Steinmann, and A. . Benallal. “Sorne Aspects of a Gradient Damage Formulation”. European Journal of Computational Mechanics, vol. 10, no. 2-4, Aug. 2001, pp. 157-72, https://journals.riverpublishers.com/index.php/EJCM/article/view/2709.