Avalanche behavior in creep failure of disordered materials

This work builds on this other one, where the model used the Kinetic Monte Carlo method to simulate thermally-activated plastic deformation as a Poisson process. However, the model now includes local damage accumulation, enabling it to simulate the approach to material fracture. Damage is the reduction of a material’s local strength due to local plastic deformation. It can lead to a feedback loop: deformation induces damage, which fosters future deformation, leading to more damage… When damage is severe enough, the material can fracture.

Moreover, if a material is loaded well below its limit capabilities over extended periods, fracture by damage accumulation and localization can still occur in a phenomenon known as creep failure. If this happens, a material can fail catastrophically and unexpectedly, which is especially dangerous in civil structures holding loads for long periods, such as, e.g. bridges or damns. Creep failure has also been related to natural catastrophic events such as landslides, cliff collapses, and some earthquakes and volcanic eruptions.

In this work, I studied creep failure. Analyzing the data from the simulated material samples, I looked at how the deformation process’s statistical properties change over time as the fracture point is approached. These changes might serve as early warning signals of an imminent catastrophic event and help enhance hazard assessment techniques. Moreover, the results prove a deep connection between this model –designed for the mesoscale simulation of plastic deformation– and models of earthquake activation (see ETAS model).

Here is a video of the mentioned creep failure simulation. On the left, we see the amount of plastic deformation versus time. On the right, the spatial activity map shows how the deformation is spread through the material. Initially, the activity is quite random, but as time passes, correlations emerge, and the deformation localizes into a shear band. Eventually, the deformation rate diverges, and the material fractures.