WEB A localized slip model for the simulation of microcrystalsFriday (25.09.2020) 11:35 - 11:50 M: Modelling and Simulation 2 Part of:
Microcompression and microtensile experiments have a great potential because it can be used to isolate certain features. However, the many microcrystal experiments done since the introduction of micropillar compression testing in 2004 have revealed significantly different behavior compared to bulk metals. Consequently, one should be careful with one-to-one translations of measured properties to bulk metals. Simulations can be used to help understand experimental observations. However, continuum plasticity models do not account for spatial fluctuations within single crystals. Therefore, discrete dislocation dynamics have been used extensively to study the dislocation behavior in single crystals. However, due to the computational cost and complexity of DDD, simulations are only done up to small strains and with simple geometries. Consequently, geometric effects and the influence of boundary constraints cannot be studied.
We present a numerical framework in which the crystallographic slip on a slip plane resulting from dislocation motion over that slip plane is modeled, without considering individual dislocations. In this way, plastic deformation of the crystal is localized into discrete planes. The properties of these discrete planes are varied based on microstructural statistics, such as the distribution of dislocation sources. For example, slip occurs at much lower stresses on planes that contain a dislocation source compared to planes without a dislocation source. We show that if these properties are sampled from appropriate probability distributions, many experimental observations are predicted by the model. By using weakest-link statistics, the model can be implemented in a conventional crystal plasticity finite element framework. This results in a model which does take spatial variations and microstructural statistics within a single crystal into account, but does not have the computational cost and complexity of DDD. Finally, the model is applied to micro-tensile tests of interstitial free ferrite. Here we show that Schmid’s law can already break down due to the microstructural statistics within a small sample. Furthermore, we show that small changes in boundary conditions can have a significant effect on the stress state within the crystal and the activation of slip systems.