Aplikace vhodných optických metod pro stanovení pole přetvoření v elasto-plastické oblasti

Abstract

The dissertation describes the basic knowledge from the field of continuum mechanics and theory of plasticity, which are subsequently used for solving the key problem of the thesis - verification of the methodology of accelerated creep and fatigue tests in terms of obtaining more information about the stress-strain behaviour of the material under incorporation of suitable optical method. Creep tests are performed on solder alloys SAC305 and SACX0807. The low cycle fatigue tests were performed on specimens produced by additive manufacturing from AlSi10Mg aluminium alloy. The investigation of deformation on the specimens for both types of tests was carried out using digital image correlation, abbreviated as DIC. In the first chapters of the thesis, the principles of the basic optical methods commonly used in practice, photoelasticity, digital image correlation and laser speckle interferometry, are described. An electronically controlled polariscope is developed for more efficient measurements by photoelasticity. Creep tests are complemented by numerical modelling, by finite element method, considering a viscoplastic model based on the theory of Perzyna, Chaboche and Norton. The accelerated creep methodology by using DIC was validated on hourglass-shaped specimens to determine the parameters of the Norton creep model. For strain-controlled low cycle tests, it was shown that a cyclic stress strain curve can be obtained, for cyclically stable materials, from DIC measurements of the strain on the curved surface of the specimen. The methodology was applied on three different loading strain paths: Tension compression, torsional, and circular strain path.