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Carbon fibre reinforced composites (CFRP) are construction material, which is viewed as a perspective for its ratio of mechanical properties to weight. In recent years the research was focused on implementing the carbon-based composites among smart materials. Nevertheless, extent and volume of use of these composites in technical practice is still not up to the potential, which this modern material offers. One of substantial reasons is the lack of adequate instruments for continuous manufacturing quality control and for mechanical condition monitoring of ready-made construction parts. For this reason the presented dissertation thesis is focused on effectiveness enhancement of detection of deformation response in composites subjected to mechanical loading with uniaxial tension with employment of passive acoustic emission (AE) detection, optical method for detection of surface deformation fields digital image correlation (DIC) and electron microscopy scanning electron microscopy (SEM). Combination of used methods proved as a robust instrument for identification and monitoring of entire degradation process in composite material in course of mechanical loading.

This work deals with fatigue life and fractographycal analysis of plasma-nitrided and virgin specimen made of the low-alloy high-strength steel. Specimens were subjected to in-phase combined bending-torsion loading. The work is focused on three groups of problems. The first group of problems was associated with the fatigue life and its prediction. The objective was to examine a relationship between the presence of the nitrided layer and fatigue life. The application of surface layers has significantly improved the fatigue life in the high-cycle region. An extended comparison between classical and advanced multiaxial criteria was performed. Criterions proposed by Marin and Matake were found to be most precise. The second objective of this work was to examine a relationship between the loading ratio ( is the bending amplitude and is the torsion amplitude ) and the fracture surface topography in the highcycle fatigue. Properties of fracture surfaces were quantified by many roughness and fractal parameters. Many roughness parameters start to incrise rapidly above a critical value of the loading ratio zc = 0,5. The last part of this work deals with the fractographical analysis of fish-eye cracks that were formed in plasma-nitrided steel specimens under symetrical bending, symetrical torsion and biaxial in-phase bending-torsion combinations.

The subject of this master’s thesis was to find the causes of impact toughness scattering of forgings of the test disk with dimension range of 540 – 170 mm. The experimental samples were developed from steel A694 F60. To reach the main aim light microscopy, electron microscopy, EBSD technique, fractographic analysis and hardness measurement HV10 were utilized.

Dissertation thesis deals with basic research in the field of materials from pure Zn powders and Mg, Zn, and Ca binary mixtures prepared by powder metallurgy. General powder metallurgy principles and methods, a brief description of Mg, Zn, and Ca structure and properties, and the latest research in the field of bulk materials preparation from these elements via powder metallurgy are summarized in the theoretical part of the thesis. The experimental part focuses on the preparation of materials from finer and coarser Zn powder particles by hot pressing at 300 and 400 °C using the pressure of 100, 200, 300, 400, and 500 MPa. Binary mixtures based on Mg with the addition of Zn or Ca were prepared by hot pressing in the solid-state (300 °C) and hot pressing in the semi-solid state (400 °C, 450 °C in the case of Mg-Ca system) using the pressure of 500 MPa. Binary mixtures based on Zn with the addition of Mg or Ca were prepared by hot pressing in the semi-solid state (400 °C) using the pressure of 500 MPa. The prepared materials were evaluated in terms of microstructure, elemental and phase composition, microhardness, flexural strength, and fractography. The results showed that in the case of processed from pure Zn powders, a better combination of the flexural strength and displacement was achieved in the case of the finer Zn powder, namely in the material prepared at a temperature of 400 °C and a pressure of 500 MPa. In the case of mixtures, the best connection between the powder particles was achieved in the case of a material based on finer Zn powder with 0.5 wt.% of Mg, which had a significant effect on the achieved values of flexural strength and displacement. The amount of minor powder in the mixture had a significant effect on the prepared material structure and phase composition, while the processing conditions influenced the reached strength characteristics and fracture mechanism.

In this work have been identified mechanical and fatigue properties of magnesium alloy AZ31 with 0.5% calcium, which was cast using squeeze casting. In addition, it was observed microstructure of the alloys and made fractographic assessment of fracture surfaces after fatigue loading.

This work is focused on the realization of experiment allowing simultaneous loading under mode II and III in a single circular specimen. Proposed experiment allowed to minimize crack closure during the cyclic loading and obtained values of thresholds of stress intensity range can be considered to be very close to effective values. This was attained by means of an unique experimental devices and procedure of preparation of pre-crack of specimen with circumferential notch, which was made of stainless austenitic steel. The obtained values were compared with theoretical models with the support of molecular dynamics and ab-anitio calculation. Based on observation was found out, that fatigue crack propagation is controlled by decohesion model in austenitic steel. The morphology of fracture surfaces was studied by means of optical chromatographie and 3D stereophotogrammetry, which allowed a comparison of created morphology under shear modes II and III. Morphology of fracture surface formed (static and cyclic loading) by pre-crack was also studied by means of selected roughness parameters. The mechanism of deflection (kink) of crack growth under mode II was defined.

Práce je zaměřena na šíření únavových trhlin v módech II, III a II + III v prahové oblasti v kovových materiálech. Byly provedeny experimenty pro ARMCO železo, titan, nikl a austenitickou ocel na třech druzích vzorků pro zatěžování trhliny ve smykových módech. Byl použit zvláštní způsob vytváření iniciační trhliny, který eliminoval efekt zavírání trhliny na začátku smykového zatěžování. Ve všech zkoumaných materiálech byly efektivní prahové hodnoty v módu II přibližně 1,7 krát nižší než v módu III. Měřením úhlů lokálních odklonů a natočení lomových faset s použitím stereofotogrammetrie v SEM bylo usuzováno na tendenci trhliny k vyhýbání do lokálního módu I. Nejmenší úhly byly zjištěny u ARMCO železa pro trhliny v módech II i III, středně velké úhly u titanu a niklu a největší úhly (vyhnutí do čistého módu I) byly pozorovány u austenitické oceli. Tyto rozdíly lze vysvětlit různým počtem dostupných skluzových systémů v krystalových mřížkách daných materiálů. Poměry mezi naměřenými prahovými hodnotami v módu I, II a III byly srovnány s předpověďmi teoretických modelů. Byl navržen analytický vztah pro efektivní prahové hodnoty v módu II, který byl v dobré shodě s experimentálními výsledky. Pomocí efektivních prahových hodnot bylo vyčísleno kritérium pro vyhýbání do módu I, které vedlo ke kritickému úhlu odklonu 40° souvisejícímu s přechodem z lokálního smykového módu do otevíracího módu.