Brittle creep, damage and time-to-failure in rocks
نویسندگان
چکیده
We propose a numerical model based on static fatigue laws in order to model the time-dependent damage and deformation of rocks under creep. An empirical relation between time-to-failure and applied stress is used to simulate the behavior of each element of our finite element model. We first review available data on creep experiments, in order to study how the material properties and the loading conditions control the failure time. The main parameter that controls the failure time is the applied stress. Two commonly used models, an exponential tf ∼ exp(−bσ/σ0) and a power law function tf ∼ σ/σ0 b′ fit the data as well. These time-to-failure laws are used at the scale of each element to simulate its damage as a function of its stress history. An element is damaged by decreasing its young modulus, to simulate the effect of increasing crack density at smaller scales. Elastic interactions between elements and heterogeneity of the mechanical properties lead to the emergence of a complex macroscopic behavior, which is richer than the elementary one. In particular, we observe primary and tertiary creep regimes associated respectively with a power-law decay and increase of the rate of strain, damage event and energy release. Our model produces a power-law distribution of damage event sizes, with an average size that increases with time as a power-law until macroscopic failure. Damage localization emerges at the transition between primary and tertiary creep, when damage rate starts accelerating. The final state of the simulation shows highly damaged bands, similar to shear bands observed in laboratory experiments. The thickness and the orientation of these bands depend on the applied stress. This model thus reproduces many properties of rock creep, which were previously not modeled simultaneously.
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