Eberhardsteiner, Josef, Manfred Gingerl, Lubomir Ondris, and Rudolf Beer. 2000. “Experimental Investigation of the Strength of Anisotropic Solids under Biaxial Loading Oblique to the Principal Material Directions”. Communications - Scientific Letters of the University of Zilina 2 (3), 4-7. http://journals.uniza.sk/index.php/communications/article/view/1059.