Modelling Time Dependency
This chapter describes the theories of sub-critical crack growth and numerical procedures implemented in FRACOD. Classical fracture mechanics postulates that a fracture tip with a stress intensity equal to the material’s critical fracture toughness will accelerate to speeds approaching the elastic wave speed in a medium. However, in cases of long-term loading, fractures can grow at stress intensities significantly lower than the critical values. This process is called subcritical fracture growth (SCG); SCG and propagation velocities can vary over many orders of magnitude as a function of stress intensity. In FRACOD the subcritical crack growth is modelled by considering the crack length as a function of time. Using the subcritical crack growth function, the time-dependent stability of fractured rock masses can be modelled.
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