José Julio de C. Pituba,   An Anisotropic Model of Damage and Unilateral Effect for Brittle Materials .   journal   = {International Journal of Materials and Metallurgical Engineering}, [online]. World Academy of Science, Engineering and Technology.
    February 2007, vol. 2(2). 29 - 34
    [viewed 29 March 2020]. Available from: https://publications.waset.org/pdf/1895.