TEMSTRAIN · Determination of the complete residual strain tensor by the CBED method

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Project objective

Residual stresses influence failure mechanisms in polycrystalline and composite materials and frequently lead to scrapping products. Of all methods of strain determination, the one using transmission electron microscopy and convergent beam electron diffraction (CBED) patterns has by far the best spatial resolution. In the CBED method, strain is obtained by fitting an experimental pattern to a simulated pattern. However, there is a serious problem with the method. It has been shown numerous times that its results are ambiguous. The causes of ambiguities are not understood, and this hinders the development of fully functional systems for strain determination.The problem is addressed by limiting the number of independent strain parameters. The procedures currently used calculate up to three (out of six) parameters. Despite that, strong instabilities of the calculated strain tensor entries are encountered. The scientific objective of the project is to remove the ambiguity in the CBED method and make it capable of providing complete strain tensor. We already know that the influence of some parameters on the differences between simulated and experimental patterns is many orders of magnitude weaker than the effect of other parameters. Thus, the initial step of the project will be the identification of the indeterminable parameters. With indeterminable parameters known, currently used 'educated assumptions' will be replaced by a robust approach.The goal is to create a reliable method of determination of the complete strain tensor based on multiple sample tilts. Computer programs for calculating the tensor based on multiple patterns will be written and extensive tests of the method will be performed. Development of a reliable method will definitely advance the work o n local analysis of residual strains, and it will open new capabilities in research on local strain. One of them, namely the creation of 'strain maps' analogous to popular orientation maps, will be explored.

Original text from CORDIS.

Participants

• UNIVERSITÉ DE METZ, ISGMP-LETAM · METZCoordinatorCity levelFrance

Links

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