Evaluation of Anisotropy of Fracture Toughness in Brittle Rock, Migmatized Gneiss

Most rocks in nature are affected by a certain degree of anisotropy. They contain cracks mostly with certain distributions. Therefore their mechanical behaviour is dependent on the direction of the strength distribution, which is different in each direction. We can distinguish the directions in which the rock is relatively firm and conversely the directions in which it is weak. The strength anisotropy and the direction of weakening is useful information for engineering applications. Metamorphic foliation with the specific orientation of rock grains also influences the mechanical behaviour, and the mechanical properties, i.e. strength, are changed in different directions of loading. This change of strength is called the strength anisotropy. The main purpose of this research is to analyze the effect of the orientation of metamorphic foliation distinguished within the rock specimens on their strength anisotropy. In the article, the anisotropy of a mechanical property, i.e. the fracture toughness, of migmatized gneiss is discussed. For this purpose, series of semi-circular bend tests were carried out on specimens of migmatized gneiss with a metamorphic foliation. The methodology used in this research is effective for evaluating the strength anisotropy of a brittle rock