Publications

The information comes from the university database V3S.

Authors:
Ing. Lukáš Zeman; Ing. Jaroslav Valach, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; Ing. Nela Krčmářová; Koudelková, V.; Zeman, J.
Published:
2023, Young Transportation Engineers Conference 2022, Praha, České vysoké učení technické v Praze), p. 89-97), ISBN 978-80-01-07224-0, ISSN 2336-5382
Annotation:
The article presents a study of the mechanical processes occurring during the aluminothermic reaction using experimental methods (strain gauges, digital image correlation, thermography, scanning electron microscopy, profilometry). The aluminothermic reaction is a highly efficient welding method due to its exothermic behaviour, however, it places considerable demands not only on the welding technique, but also on the capabilities of the experimental methods used; these limitations are also discussed in the article. The aluminothermic reaction is associated with the formation of a localised heat source with a time evolution dictated by the technological procedure, which manifests itself in heat propagation to the surrounding weld material. The unequal evolution of the temperature field is the fundamental cause of the appearance of the heat affected zone or local deformations or surface curvature, which was the focus of the experimental methods deployed above and the results of which are shown in the article.
DOI:

Authors:
Ing. Tomáš Fíla, Ph.D.; doc. Ing. Petr Zlámal, Ph.D.; prof. Ing. Ondřej Jiroušek, Ph.D.; Ing. Jan Falta; Ing. Petr Koudelka, Ph.D.; doc. Ing. Daniel Kytýř, Ph.D.; Ing. Tomáš Doktor, Ph.D.; Ing. Jaroslav Valach, Ph.D.
Published:
2017, Advanced Engineering Materials, 19 (10), ISSN 1438-1656
Annotation:
In this paper, impact testing of auxetic structures filled with strain rate sensitive material is presented. Two dimensional missing rib, 2D re-entrant honeycomb, and 3D re-entrant honeycomb lattices are investigated. Structures are divided into three groups according to type of filling: no filling, low expansion polyurethane foam, and ordnance gelatine. Samples from each group are tested under quasi-static loading and dynamic compression using Split Hopkinson Pressure Bar. Digital image correlation is used for assessment of in-plane displacement and strain fields. Ratios between quasi-static and dynamic results for plateau stresses and specific energy absorption in the plateau are calculated. It is found out that not only the manufactured structures, but also the wrought material exhibit strain rate dependent properties. Evaluation of influence of filling on mechanical properties shows that polyurethane increases specific absorbed energy by a factor of 1.05–1.4, whereas the effect of gelatine leads to increase of only 5–10%. Analysis of the Poisson's function reveals influence of filling on achievable (negative) values of Poisson's ratio, when compared to unfilled specimens. The results for the Poisson's function yielded apparently different values as the assessed minima of quasi-static Poisson's ratio in small deformations are constrained by a factor of 15.
DOI: