Františka Pešlová

Degradation of propeller shaft surface during mechanical proccessing

The paper deals with identifying the causes of surface failure of a propeller shaft made of material 42CrMoS4. On the basis of microstructural analysis completed by hardness testing, the occurrence of undesirable phases, such as non-metallic inclusions in the structure of the shaft, can be demonstrated. In the presence of various heterogeneous phases in the material structure, plucking of particles can occur during chip machining which leads to surface damage. In the conclusion, the authors recommend checking the starting material, which can eliminate problems that cause the degradation of the surface of the propeller shaft. The failure of the surface causes the notch effect which initiates further failures of the material.

Material Criteria for Parts Exposed to Liquid Medium Loading

The paper is focused on the study of the material changes which can occur on the basis of mechanical and thermal loading in relation to the functional surfaces of the construction parts. The structural or the mechanical changes can be influenced by ambient environment and in this case, it is the influence of liquid media. The water, hot metal as well as molten glass can be the representatives of the mentioned liquid medium. In relation to the influence of the liquid medium, there is the danger of superposed wears while one of these wears is considered as dominant. Furthermore, occurrence of the corrosion process leads to the increases of the given dominant wear. In relation to the analysis and evaluation of the wear, the simulated tests under the critical conditions are necessary for the correct and precise prediction of the degradation processes. Experimental measurements can be used for the prediction of the material behaviour under the critical operation conditions. In the given work, the attention was paid to the selected materials which were exposed to the mechanical as well as mechanical-thermal loading. The important parameters were achieved with help of the testing device which was modified in a special way. Moreover, the structure changes were observed for the different time intervals or periods. On the basis of the susceptibility to the loading, the conclusions as well as recommendations were summarized for the selected materials.

Structural Changes of Hot Work Tool Steel due to Heat load

The paper deals with the influence of thermal load on functionality of the Toolox 33 hot work tool steel equivalent to the materials of W.Nr. 1.2311, 1.2312, 1.2738 and P20 in order to assess its suitability as a material for glass manufacture preform. Using light and electron microscopy it was shown that the steel was highly unfitting for this application where the steel comes into contact with the hot glass. Regarding the evaluation of the microstructure, it was shown that intense decarburization reflecting on the fracture behaviour of the surface layer during the thermal load has occurred. This fact was confirmed by a static tensile test and hardness measurements. Moreover, the thick layer of flakes has formed on the surface.

MICROSCOPIC EVALUATION OF THE QUALITY OF DENTAL REPLACEMENT

The permanent tooth replacements including metal-ceramic crowns are a convenient solution for the renewing of the original function of the whole set of teeth as well as of the natural appearance. Development and preparation of suitable tooth replacement presents a real challenge for dental engineers as the replacement has to meet all the conditions and requirements of the dental medicine as well as patient’s needs and wishes. The preparation of the metal-ceramic crown is a sophisticated process and the dental engineer has to prepare alwaysa unique replacement on demand. In dental medicine there is a wide spectrum of inorganic and organic materials used formanufacturing of dental replacements. Each of the material has specific properties leading to distinct applications.Besides the material properties, the attention has to be paid to the aesthetic function and biocompatibility of the material to ensure thecomplete restoration of the whole set of teeth.

The Surface Treatment Influence on the Occurrence of the Critical State Relating to the Needle as the Operating Tool

The research work deals with the evaluation of limit states of machine needles failure where significant operational wear was anticipated. It focuses on the description of limit states, their causes and subsequent brittle fracture as a result of degradation. The experiment dealt with an evaluation of prepared microstructures followed by the fractography observation. Due to the fact that chemical composition of the material was not originally determined distribution of the chemical elements by linear and area method was performed within the experimental part. The work confirmed incorrect selection of the base material that although coated was typical by rapid degradation and failure which resulted in economic losses.