Prediction of critical state and load carrying capacity of structures is the fundamental issue in engineering practice. Critical states are often govemed by formation and growth of tension and/or shear cracks. The safety assessment of a concrete arch dam against large earthquake excitation, for example, requires consideration of shear crack growth at the rock foundation. The studies of shear crack growth in geological materials consist of three aspects; 1) formation of shear cracks (or strain localization), 2) localization of shear cracks, and 3) instability of crack growth. The present study focuses on the condition for the initiation of unstable growth of a localized shear crack. Experimental studies have shown that the growth of localized shear crack in soft rock is captured with the initiation condition and the softening law for shear cracks obtained from element tests. The instability of shear crack growth in structural tests is found to occur before the released energy reaches the fracture energy. Hence, it is necessary to find the initiation condition of unstable crack growth. In the present study, a rate dependent softening law is introduced in the softening law of the shear crack. Effect of the rate dependence in softening law is at first investigated for a one-dimensional model. Then, mode I crack propagation is investigated with interface elements that satisfy the rate dependent softening relationship along the crack. The ability to predict unstable crack growth by means of a rate dependent softening law is demonstrated. Finally, analysis of shear crack propagation in soft rock is conducted. It is shown that the unstable crack growth and associated sudden load drop observed in structural tests are captured by the present analysis. It is concluded that the rate dependence of the softening behavior along the shear crack is a promising candidate for the goveming mechanism of unstable crack growth in geological materials.
A displacement rate dependent softening model applied to the unstable propagation of shear crack in soft rock
PUNTEL, Eric;
2002-01-01
Abstract
Prediction of critical state and load carrying capacity of structures is the fundamental issue in engineering practice. Critical states are often govemed by formation and growth of tension and/or shear cracks. The safety assessment of a concrete arch dam against large earthquake excitation, for example, requires consideration of shear crack growth at the rock foundation. The studies of shear crack growth in geological materials consist of three aspects; 1) formation of shear cracks (or strain localization), 2) localization of shear cracks, and 3) instability of crack growth. The present study focuses on the condition for the initiation of unstable growth of a localized shear crack. Experimental studies have shown that the growth of localized shear crack in soft rock is captured with the initiation condition and the softening law for shear cracks obtained from element tests. The instability of shear crack growth in structural tests is found to occur before the released energy reaches the fracture energy. Hence, it is necessary to find the initiation condition of unstable crack growth. In the present study, a rate dependent softening law is introduced in the softening law of the shear crack. Effect of the rate dependence in softening law is at first investigated for a one-dimensional model. Then, mode I crack propagation is investigated with interface elements that satisfy the rate dependent softening relationship along the crack. The ability to predict unstable crack growth by means of a rate dependent softening law is demonstrated. Finally, analysis of shear crack propagation in soft rock is conducted. It is shown that the unstable crack growth and associated sudden load drop observed in structural tests are captured by the present analysis. It is concluded that the rate dependence of the softening behavior along the shear crack is a promising candidate for the goveming mechanism of unstable crack growth in geological materials.| File | Dimensione | Formato | |
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