Showing papers by "Miroslav Karlík published in 2020"
01 Jan 2020
TL;DR: In this article, a one-dimensional version of the heat diffusion equation was used to reconstruct heat sources originating from deformation processes in metals, and the sensitivity of the method to the degree of spatio-temporal filtering was also tested.
Abstract: The study deals with the reconstruction of heat sources originating from deformation processes in metals. A one-dimensional method to be applied on wires or bars is introduced and tested on superelastic NiTi wire subjected to force-controlled loading and unloading. Infrared thermography was used for this purpose. Thermal data were then processed by heat source reconstruction technique using a one-dimensional version of the heat diffusion equation. Attention was paid to the identification of the heat exchanges with the specimen’s environment, in particular by convection to the air of ambient temperature. The sensitivity of the method to the degree of spatio-temporal filtering was also tested. Finally, the localization of martensitic transformation in superelastic NiTi was evaluated using the proposed method. It is shown that under force-control regime the phase transformation proceeds in two time-shifted bursts, where each of bursts consists in several displaced and nearly simultaneous transforming zones. This transformation sequence is rationalized by fast latent heat release from the transforming zone upon load control regime, which leads to overheating of surrounding zones thus temporarily suppressing their transformation.
3 citations
TL;DR: In this paper, a similar test was carried out using multiple methods including standard compress tests with strains evaluated by using video extensometer as well as digital image correlation of the stack surface and instrumented indentation method.
Abstract: Elastic properties of wound rolls are used as an input for simulations of stress-strain state in the roll after winding in order to optimize quality of foils. The effective elastic modulus in direction perpendicular to the layers of foil is challenging to measure because it is dependent on interlayer pressure and is generally much smaller than the bulk elastic modulus of the material. Normally, stacks of many layers of foil are pressed in order to determine the interlayer-pressure dependence on effective elastic modulus. In this study, a similar test was carried out using multiple methods including standard compress tests with strains evaluated by using video extensometer as well as digital image correlation of the stack surface and instrumented indentation method. The results given by all methods were compared. Moreover, multiple stack thicknesses were tested in order to evaluate the influence of stack size on the effective modulus. The tested foil was made from aluminum alloy AA8079 and was 13 μm thick.
TL;DR: The financial support of the European Regional Development Fund (project No. CZ.0000485) is gratefully acknowledged as discussed by the authors, which is used to support the work of as discussed by the authors.
Abstract: Financial support of the European Regional Development Fund (project No. CZ.02.1.01/0.0/0.0/15_003/0000485) is gratefully acknowledged
01 Jan 2020
TL;DR: In this paper, the microstructure was characterized by means of scanning and transmission electron microscopy and electron backscattered diffraction (EBSD), mechanical properties were monitored by hardness measurements and tensile tests.
Abstract: Unhomogenized and homogenized AA8006 (Al-Fe-Mn-Si) alloy sheets twin-roll cast to strip 8.5 mm thick, processed by accumulative roll-bonding (ARB) on 2 mm thick sheets up to 6 cycles were studied. The microstructure was characterized by means of scanning and transmission electron microscopy and electron backscattered diffraction (EBSD), mechanical properties were monitored by hardness measurements and tensile tests. The macroscopic texture was determined by X-ray diffraction. The initial texture of the unhomogenized sheet is rotated cubic {001}<110> combined with recrystallization R texture {011}<211>, while the homogenized sheet has a cubic texture {001}<100> with remaining rolling component C {112}<111>. One ARB cycle leads to the formation of low-angle grain boundaries (LAGB) in original coarser grains and to a low angle rotation of the subgrains bounded by LAGB. After the 3rd and 6th ARB cycle unhomogenized and homogenized sheets show a common rolling texture of cold-rolled aluminium. The thermal stability of sheets processed by 6 ARB cycles was tested by isochronal annealing for 30 min up to 450°C. The homogenized sheet starts to recrystallize at 250°C, while the fine grain structure of the unhomogenized sheet is thermally stable up to 400°C.