Influence of Strength Heterogeneity Factor on Influence of Strength Heterogeneity Factor on Crack Shape in Laminar Rock Crack Shape in Laminar Rock- Like Materials Like Materials Jerzy Podgórski * Józef Jonak ** * * Faculty Faculty of of Civil Civil Engineering Engineering ** ** Faculty Faculty of of Mechanical Mechanical Eng Eng. Lublin Lublin University University of of Technology Technology Poland Poland