A Micromechanical Anisotropic Damage Model for Brittle Rocks With Non-Associated Plastic Flow Rule Under True Triaxial Compressive Stresses

A micromechanical anisotropic damage model with a non-associated plastic flow rule is developed for describing the true triaxial behaviors of brittle rocks. We combine the Eshelby’s solution to the inclusion problem with the framework of irreversible thermodynamics. The main dissipative mechanisms of inelastic deformation due to the frictional sliding and damage by microcrack propagation are strongly coupled to each other. A Coulomb-type friction criterion is formulated in terms of the local stress applied onto the microcracks as the yielding function. The back-stress term contained in this local stress plays a critical role in describing the material’s hardening/softening behaviors. With a non-associated flow rule, a potential function is involved. Some analytical analysis of the non-associated micromechanical anisotropic damage model are conducted, which are useful for the model parameters calibration. The proposed model is used to simulate the laboratory tests on Westerly granite under true triaxial stresses. Comparing the numerical simulation results provided by the models with associated/non-associated plastic flow rule and experimental results, it is clear that the proposed non-associated model gives a better prediction than the previous associated model.

Surface plastic flow of 3D printed PLA in tribological study of surface patterned polymer

The potential of three-dimensional (3D) printing in polymer tribology is poorly explored. Material alignment and composition plays a vital role in altering the friction and wear characteristics of 3D printed materials. In the current study 3D patterns using fused deposition modeling are used to print advanced tribo-composites. Two different surface patterns (line and circular) are provided through 3D printing using white and silver Poly Lactic Acid (PLA). The deformation and the distribution of white and silver PLA over the samples surface are observed after the wear test. Results showed that the coefficient of friction is not being influenced by changing in the surface pattern. However, the wear rate increased for samples with line patterns on the contact surface, since the plastic flow was more significant in this case. Moreover, the filling factor exhibited an influence on increasing the plastic flow of the contact surface in case of the samples with line pattern.