Analýza poškození nízkocyklovou únavou při proporcionálním a neproporcionálním zatěžování

This thesis deals with the study of determination fatigue life of aluminum alloy AA2124-T851 prediction of materials at multiaxial fatigue. The first part of the thesis introduces uniaxial fatigue going to multiaxial fatigue. The next part focuses on the elaboration of separate criteria of multiaxial fatigue mainly for low-cycle fatigue for the estimation of life prediction of testing materials. Because the testing specimens were controlled strained at non-proportional low-cycle fatigue, these criteria were also selected in order to correspond with the given loading. The last part of this thesis is devoted to the evaluation of individual tests from different loading paths in the half of the life prediction of the component and following evaluation using specific criteria.Diplomová práce se zabývá stanovením životnosti hliníkové slitiny AA2124-T851 v případě víceosé napjatosti. V první části diplomové práce je vysvětlena všeobecná problematika únavy materiálu a to jednak při jednoosé napjatosti a dále při napjatosti víceosé. Další část se zabývá stanovením únavové životnosti v případě porušení nízkocyklovou únavou. Cílem práce je stanovení životnosti zkušebních vzorků, zatěžovaných deformačně, a to jednak pro případy proporcionálního a neproporcionálního zatěžování. Jsou zde vysvětleny jednotlivé přístupy. V poslední části práce je provedeno vyhodnocení jednotlivých kritérií únavové životnosti a jejich srovnání s experimenty.330 - Katedra aplikované mechanikydobř

A comprehensive review of techniques for natural fibers as reinforcement in composites::preparation, processing and characterization

Designing environmentally friendly materials from natural resources represents a great challenge in the last decade. However, the lack of fundamental knowledge in the processing of the raw materials to fabricate the composites structure is still a major challenge for potential applications.Natural fibers extracted from plants are receiving more attention from researchers, scientists and academics due to their use in polymer composites and also their environmentally friendly nature and sustainability. The natural fiber features depend on the preparation and processing of the fibers. Natural plant fibers are extracted either by mechanical retting, dew retting and/or water retting processes. The natural fibers characteristics could be improved by suitable chemicals and surface treatments. This survey proposes a detailed review of the different types of retting processes, chemical and surface treatments and characterization techniques for natural fibers. We summarize major findings from the literature and the treatment effects on the properties of the natural fibers are being highlighted

Physicochemical, tensile, and thermal characterization of new natural cellulosic fibers from the stems of Sida cordifolia

Natural fibers are the one worthy substitute for replacing synthetic fibers and used as a polymer reinforcement due to their eco-friendly nature. This investigation deals with the newly identified Sida cordifolia fibers (SCFs) characterized by chemical analysis, single fiber tensile test, thermogravimetric analysis (TGA/DTG), Fourier transform-infrared spectroscopy (FT-IR) analysis, X-ray diffraction (XRD), and atomic force microscopy (AFM). The chemical constituents of SCFs contains cellulose (69.52%), hemicellulose (17.63%), and lignin (18.02. %). The SCFs are thermally stable up to a temperature of 338.2°C evidenced by TGA analysis. The X-ray diffraction confirmed that SCFs were rich in cellulose fraction with a crystallinity index of 56.92%