Özet:

The application and understanding of fracture mechanics has great importance in the analysis of the performance of brittle engineering materials such as rock, cemented sand,dry soil, clay and concrete structures. The fundamental questions in geotechnical engineering relate to predicting the failure load of those brittle structures consisting of both pre-existing and stres-induced flaws and cracks, and to revealing the combination of load and flaw geometry that lead to failure. The prediction of the direction of any crack propagation and orientation of fracture in a brittle material becomes crucial because, once a crack has opened, the state of stress in the vicinity of the crack tip is altered significantly. Existing failure criteria and theories, such as the well-known Mohr-Coulomb Criterion and Hoek-Brown Criterion often deal directly with failure processes; however, they cannot be expected to deal with crack propagation in terms of the length of the stable and/or unstable crack or the direction of crack propagation. In contrast, fracture mechanics, sometimes called crack mechanics, is concerned with the behaviour of individual crack or cracks. Cracks and/or discontinuities are common structural features of engineering structures. Lineer Elastic Fracture Mechanics (LEFM) is based on the stress intensity factor (SIF), K, which quantifies the intensity of the stress singularity at the crack tip. Fracture mechanics states that a crack will propagate when its stress intensity reaches a critical value, KC, assuming that the crack tip is in a state of plane strain. The stress intensity factor depends on the fracture displacement modes and crack geometry. Both experimental and numerical analyses were done in this study to investigate the relationship between loading direction and crack axis for analysing the strength of brittle materials; concrete and rock. In order to check the validity of the numerical modelling, a comparison of numerical results and experimental findings regarding crack extension (θ) and crack inclination (β) angles was made. A good agreement was found between numerical and experimental findings regarding crack extension (θ) and crack inclination (β) angles. The crack initiation angle was found to increase with increasing crack inclination angles.

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