Failure probabilities and tough-brittle crossover of heterogeneous materials with continuous disorder

Intermittency and roughening in the failure of brittle heterogeneous materials

Stress enhancement in the vicinity of brittle cracks makes the macro-scale failure properties extremely sensitive to the micro-scale material disorder. Therefore: (i) Fracturing systems often display a jerky dynamics, socalled crackling noise, with seemingly random sudden energy release spanning over a broad range of scales, reminiscent of earthquakes; (ii) Fracture surfaces exhibit roughness a...

4 Effective toughness of heterogeneous brittle materials

A heterogeneous brittle material characterized by a random field of local toughness K c (x) can be represented by an equivalent homogeneous medium of toughness, K eff. Homogenization refers to a process of estimating K eff from the local field K c (x). An approach based on a perturbative expansion of the stress intensity factor along a rough crack front shows the occurrence of different regimes...

Multiscale failure modelling of quasi - brittle materials

Continuous wave MRI of heterogeneous materials.

A prototype continuous wave MRI system operating at 7T has been used successfully to study a variety of heterogeneous materials exhibiting T2 relaxation values ranging from 10 micros to 50 ms. Two-dimensional images of a poly(methly methacrylate) (PMMA) resolution phantom (T2=38 micros) exhibited a spatial resolution of approximately 1mm at a magnetic field gradient strength of 200 mT/m. The te...

Numerical Studies on the Failure Process of Heterogeneous Brittle Rocks or Rock-Like Materials under Uniaxial Compression

In rocks or rock-like materials, the constituents, e.g. quartz, calcite and biotite, as well as the microdefects have considerably different mechanical properties that make such materials heterogeneous at different degrees. The failure of materials subjected to external loads is a cracking process accompanied with stress redistribution due to material heterogeneity. However, the latter cannot b...