TEMStrain    

Plane stress case

In order to calculate strain with respect the reference lattice parameters under the assumption of plane stress in the foil,  select PSts option and click on “Strain ” command button (on main interface). This activates “Plane stress case” dialog box. There is a possibility to select some of three free stress components which are subject of determination. The components of the stress tensor are given in the Cartesian coordinate system linked to the sample. One can also request fitting of voltage and/or camera length. Camera length is then calculated separately for each diffraction pattern. Voltage and is either calculated separately for each diffraction pattern or the same value is fitted to all patterns of the project (if "=" is checked).  

The calculation requires the stiffness tensor of the material. Values of particular components of that tensor can be modified in "Stiffness tensor / C_11" dialog box, which is activated by clicking on "Stiffness" command button of  “Plane stress case” dialog box. The numbers in the text boxes should be equal to C_ij/C_11.

Stress components (and other fitted parameters) are calculated by locating a (supposedly global) minimum  of a goodness-of-fit function. A number of distinct goodness-of-fit functions are available by selecting “Strategy” in “Plane stress case”. Optimization  strategies, bounds,  domain of intersection points are as in the case of  general  calculation of strain in the crystal coordinate system (CCS). 

After completion of the calculation, results are displayed in the “Results” dialog box. The box allows for displaying four different groups of results.

• The first one contains values (times 10000) of strain and/or relative values of voltages and/or relative values of camera lengths.  If the optimization bounds are reached they are considered to  be incorrect.
• The second group are estimated errors (times 10000/C_11) of stress and/or relative values of voltages and/or relative values of camera lengths.
• The third group contains absolute values (times 10000) of lattice parameters and/or voltages and/or camera lengths.
• The fourth group contains absolute values (times 10000/C_11) of stress and/or relative values of voltages and/or relative values of camera lengths. 

The “Update” in the “Results” dialog box command button will change the current settings for all patterns in terms of orientations,  lattice parameters and/or voltages and/or camera lengths, whichever were subject of fitting.