arXiv subjects

Timothy J. Rupert

Publications and source records attributed to Timothy J. Rupert.

76 records · Page 5Linked to original sources

arXiv2014

Strain localization in a nanocrystalline metal: Atomic mechanisms and the effect of testing conditions

Molecular dynamics simulations are used to investigate strain localization in a model nanocrystalline metal. The atomic mechanisms of such catastrophic failure are first studied for two grain sizes of interest. Detailed analysis shows that the formation of a strain path across the sample width is crucial, and can be achieved entirely through grain boundary deformation or through a combination of grain boundary sliding and grain boundary dislocation emission. Pronounced mechanically-induced grain growth is also found within the strain localization region. The effects of testing conditions on strain localization are also highlighted, to understand the conditions that promote shear banding and compare these observations to metallic glass behavior. We observed that, while strain localization occurs at low temperatures and slow strain rates, a shift to more uniform plastic flow is observed when either strain rate or temperature is increased. We also explore how external sample dimensions influence strain localization, but find no size effect for the grain sizes and samples sizes studied here.

cond-mat.mtrl-sci↗

arXiv2014

Tracking Microstructure of Crystalline Materials: A Post-Processing Algorithm for Atomistic Simulations

Atomistic simulations have become a powerful tool in materials research due to the extremely fine spatial and temporal resolution provided by such techniques. In order to understand the fundamental principles which govern material behavior at the atomic scale and directly connect to experimental works, it is necessary to quantify the microstructure of materials simulated with atomistics. Specifically, quantitative tools for identifying crystallites, their crystallographic orientation, and overall sample texture do not currently exist. Here, we develop a post-processing algorithm capable of characterizing such features, while also documenting their evolution during a simulation. In addition, the data is presented in a way that parallels the visualization methods used in traditional experimental techniques. The utility of this algorithm is illustrated by analyzing several types of simulation cells which are commonly found in the atomistic modeling literature, but could also be applied to a variety of other atomistic studies which require precise identification and tracking of microstructure.

cond-mat.mtrl-sci↗

arXiv2014

Solid Solution Strengthening and Softening Due to Collective Nanocrystalline Deformation Physics

Solid solution effects on the strength of the finest nanocrystalline grain sizes are studied with molecular dynamics simulations of different Cu-based alloys. We find evidence of both solid solution strengthening and softening, with trends in strength controlled by how alloying affects the elastic modulus of the material. This behavior is consistent with a shift to collective grain boundary deformation physics, and provides a link between the mechanical behavior of very fine-grained nanocrystalline metals and metallic glasses.

cond-mat.mtrl-sci↗

arXiv2014

Damage nucleation from repeated dislocation absorption at a grain boundary

Damage nucleation from repeated dislocation absorption at a grain boundary is simulated with molecular dynamics. At the grain boundary-dislocation intersection site, atomic shuffling events determine how the free volume brought by the incoming dislocation is accommodated. This process in turn determines the crack nucleation mechanism, as well as the critical strain and number of dislocations that can be absorbed before cracking. Slower strain rates promote earlier crack nucleation and a damage nucleation mode where cracking is preceded by dislocation emission. The simulation methodology presented here can be used to probe other types of boundaries as well, although multiple thermodynamically equivalent starting configurations are required to quantify the damage resistance of a given grain boundary.

cond-mat.mtrl-sci↗