NXms_dislocation_setΒΆ
Status:
base class, extends NXobject
Description:
Base class to describe details about dislocations observed in microstructures.
Dislocations are one-dimensional crystal defects whose primary interest is that they are the carrier of plastic deformation. Conceptually dislocations are a continuum-scale description of how atoms arrange spatio-temporally on the one hand as a persistent defect which on the other hand though, when inspected in detail for the atom dynamics and their interaction with other crystal defects manifest as an involved microstructural feature for which very different descriptions are used depending which length-, time-scale, and research question people address.
This is manifested in the large amount of literature on the topic:
Dislocations are one prominent group of representatives for one-dimensional features, other defects include disconnections and/or disclinations, and even more complicated configurations, especially when one considers not-necessarily crystalline materials, quasi crystals. It would be rude to claim that a single base class can encompass the entire complexity that this effectively coarse-graining of atomic spatio-temporal configurations has, in an effort to simplicify the description in the hope to arrive at physical models which do not need to take into account the location and movement of every atom.
However, it is also a fact that not every description, research question, and thus use cases that one could think of what one should store as data and metadata for one-dimensional, primarily line-type crystal defects, is equally relevant for an ensemble of research studies.
Thus, for the design of concrete schemata for the purpose of structured storage of research data on dislocations or studies where dislocations are measured or characterized, one has to prioritize which descriptors and aspects about dislocations are likely relevant for a large number of users of a research infrastructure. Consequently, it is possible to narrow down the scope of the base class and application definition.
It is noteworthy to mention that this applies not only to description using NeXus, but points to the problem of creating a golden-bullet schema capable of handling all possible subtleties.
For now we have to accept that is not yet an ontology of e.g. the above understanding of what dislocations are. Pragmatically we thus make the following assumptions:
This base class is essentially a template how specific often referred quantities for one-dimensional crystal defects can be stored.
In practice dislocations have a finite length as they are embedded in a finite specimen and wired into an ensemble of adjoining dislocations or other adjoining crystal defects.
There are the following general approaches of studying/characterizing
1. Indirect measurements where dislocations characterized statistically. In this case different types of dislocations are distinguished (geometrically-necessary, mobile, immobile), mainly motivated by different constitutive, continuum-models how they are threated in computer simulations with respect to what their effect is on ms evolution.
2. Electron microscopy measurements of single or several dislocation (bundles) In this case post-processing strategies are necessary which can extract statistical descriptors or d-dimensional reconstructions
3. Atomic-scale-resolved simulations. In this case the most frequently performed tasks are again post-processing into polyline networks, detailed local investigations of the atomic configurations, or both with or without some correlation.
4. Analytical approaches whereby dislocations are resolved at the continuum scale, as line defects containing other elementary defects (for instance) in models of disconnection motion), or again atomically resolved treatments.
From this we can conclude that an NXms_dislocation_set can primarily be useful as a wrapper class in which specific details about dislocations can be stored in an arbitrarily nested manner.
Symbols:
The symbols used in the schema to specify e.g. dimensions of arrays.
- Groups cited:
none
Structure:
