Measuring residual stresses at the micron scaleMaster thesis project: students applied and experimental physics
Residual stresses are present in almost all materials and arise whenever inelastic processes occur, like creep, plastic deformation, coating deposition, welding, cladding etc. They can have beneficial or detrimental effects to the materials properties, therefore the exact knowledge and control of residual stresses are of high practical relevance. A number of methods have been developed for measuring residual stresses. Most of these methods determine the mean stresses in large volumes or large areas of material investigated. They give useful results when the residual stresses are distributed uniformly and if no stress gradients are expected. Objective: The project consists of a new approach of stress measurement at the micron scale based on applying of dual beam microscopy like imaging-milling semidestructive instrument to realize mechanical relaxation method of measuring internal stress. Focused Ion Beam (FIB) is beeing used as a „sharp knife" to release local strain induced by internal stresses. Surface relaxation in the vicinity of such cut will be mapped using the Digital Image Correlation (DIC) and released stresses will be calculated on the base of these displacement maps. The main goal of the project is to prove the proposed concept for different type of materials: metals (crystalline and amorphous), ceramics, plastics and also for different coatings: laser clad, PVD and spin coatings. The project is a MSc thesis project for students, who are interested in using modern microscopy techniques, computer for DIC analysis and modeling. Experimental techniques: LYRA Tescan dual beam system with Focused Ion Beam and Electron beam guns, Aramis GOM GMbH Digital Image Correlation system and calculations of strain and stress fields. Figure: Illustration of the FIB cutting process with patterned surface. Contact: |