Kossel pattern     KSLStrain    Kossel pattern

 

How to proceed in order to determine strain tensor from multiple patterns?

A complete strain tensor (complete set of lattice parameters) can be determined form one or multiple Kossel diffraction patterns originating from the same point of the sample. Assuming that a set of patterns in (proper digital format) is given, use the interface in the following way:

  1. enter correct settings using “Settings” command button,
  2. mark Kossel lines in the experimental pattern,
  3. if pattern center, camera length and/or orientation are not known, use the 'PC', 'Indexing' and 'PCL' buttons to determine their approximations, 
  4. fine tune the orientation (and other parameters, if necessary) using geometrically simulated pattern (which can be displayed by clicking on  “Simulate pattern” command button) and the “Fine-tuning”  frame box,
  5. save the data for the pattern using “Save data” command button.

When saved, projects are written in .kspr files. These files should be kept in the same directory as all .bmp files containing patterns of the project. If this directory is changed, the path specified in the .kspr file must be corrected. 

It must stressed again that  the optimization calculations are influenced by distortions and dynamic effects present in experimental patterns. No matter how many patterns are used, one needs to be accurate with input data and very scrupulous in marking the Kossel lines. Results need to be confirmed by applying a number of computational approaches (with various combinations of patterns, diverse sets of marking lines, changing starting and bounding values of parameters et cetera) and by visual inspection. Even if the resulting parameters lead to apparently perfect fit between the experimental and simulated patterns, one should remain skeptical and double-check each detail.

KSLStrain v.1.2,   Mar. 2020