Fracture toughness transition of ferritic-pearlitic steel at static and dynamic loading evaluated by Master curve concept

The paper focuses on assessing the usability of fatigue pre-cracked Charpy type specimens when evaluating the resistance of steel with ferritic-pearlitic structure to the initiation of unstable fractures. The suitability of using the specimens is evaluated on the basis of comparing experimentally established values of fracture toughness on pre-cracked Charpy type specimens and the values of this characteristics determined using Compact Tension (CT) specimens. For the evaluation and comparison of the fracture toughness temperature dependences determined on individual specimen types the master curve concept quantifying fracture toughness transition was applied. In the case of the steel employed, very good agreement was found to exist between the characteristics determined on individual types of specimen. It was shown that fracture toughness determined on pre-cracked Charpy type specimens can be regarded as a representative measure of resistance of the material employed to the brittle fracture occurrence

Residual life of external steel constructions

The contribution is focused to the aspects of prevention untimely damage of exterior steel constructions at variable climatic conditions. The aspects for assurance of continual service of strategic steel constructions (bridges, pipelines, pylons, pressure vessels, containers, frameworks, cranes, chimneys, towers, etc.) is by action of severe climatic conditions in our climatic zones deteriorative. The service safety of construction mentioned is decreasing and could cause preterm damages. To avoid preterm damage there are two ways. First is to create conditions excluding the damage and second is proposal of construction safety also after expected limit state. During the lifetime is needed to assure failure free service of external steel constructions stressed by variable loading. At the same time is needed to calculate with action of aggressiveness of external environment as well as worsen atmospheric conditions. From load and conditions analysis could be calculated the residual life of external steel constructions

The effect of high temperature annealing in different atmospheres on microstructure of ODS materials

Mechanically alloyed oxide dispersion strengthened materials MA 6000 and MA 956 have been annealed at 1100ºC for 24 and 240 hours in air, vacuum of 10 -3 Pa and hydrogen atmosphere.. Mass changes due to oxidation and evaporation were measured. Fracture surfaces, microstructure of the materials and changes in chemical composition were examined along with surface layers  evolution and pores formation. On fracture surfaces and polished sections, formation of voids and altered microstructure sub-surface zones in both materials has been studied. Different mechanisms causing void formation are discussed and proposed in discussion. Also the mechanisms and reaction sequences of surface oxidation reactions are examined

Examination and Polishing of Surface Scratches on Handheld Devices

Pollution is a current environmental problem. Personal used mobile phones and devices with LCD displays are often thrown away only the optical matter. The renewal of these device surfaces is at the focus of common interest. Our examination was a well-defined micro-scratch test using a special microhardness and scratch tester equipment (MCT). This equipment provides four different means of analyzing the scratch: acoustic emission detection, tangential force measurement, scratch depth measurement, optical observation through a digital microscope. The scratches were made with normal force from 0.5 to 15 N, the same length (20 mm) with the same diamond indenter. The scratches were analyzed with contact and non-contact methods, laser surface topographical analysis, optical microscopic examination, and surface roughness testing. On the LCD display we created specified scratches with the MCT scratch tester and after these scratches had to be repaired by polishing. Three different polishing speeds and loads were used. The measured wear rates show that higher polishing loads result increased wear rates but this trend does not true for the polishing speed

Mechanical properties of AlSi10Mg alloy processed by SLM

The paper deals with mechanical properties of AlSi10Mg aluminium alloy processed by the selective laser melting (SLM) technique. The influence of surface quality and building orientation of the samples on mechanical properties was evaluated. It was found that orientation of the samples had no effect on tensile properties (UTS, 0.2% proof stress) whereas surface quality had a significant effect. An 11% increase in ultimate tensile strength was found in the case of samples of lower surface roughness, and an increase of almost factor two in elongation at break was found for machined samples in comparison to as-built samples

Corrosion resistance of AZ31 magnesium alloy influenced by conventional cutting fluid

This paper deals with the evaluation of cutting fluid impact on corrosion resistance of AZ31 magnesium alloy in aggressive environment containing chloride ions supported by photo documentation. Ground samples were immersed in the standard commercial cutting fluid for 5 minutes to simulate conditions during machining process at the temperature of 22 ± 2 °C and subsequently cleaned and immersed in 0.1M NaCl solution at the temperature of 22 ± 2°C in order to measure electrochemical corrosion characteristics. Cyclic potentiodynamic polarization (CPP) tests were chosen as a testing method. The measured CPP curves of immersed samples and ground samples were analysed by Tafel extrapolation method. The values of obtained electrochemical characteristics show that the chosen cutting fluid has negative effect on corrosion resistance of AZ31 magnesium alloy in sodium chloride solution.

Production of hydroxyapatite-titanium composite powders by high-energy ball milling suitable for spark plasma sintering processes

Hydroxyapatite-titanium (HA-Ti) composite powders were prepared by high-energy ball milling for subsequent production of samples by spark plasma sintering (SPS). Different milling times for the preparation of HA-Ti composite powders were used. The microstructural properties and phase composition of the composite powders were studied by scanning electron microscopy and X-ray analysis. The results showed no formations of new phases in the structure during high-energy ball milling and a gradual reduction of the particles size with increasing milling time. Sintered samples from HA-Ti composite powder were prepared. A cross section analyzed by SEM and phase composition obtained by X-ray diffraction was studied. The results showed changes of phase compositions in the structure.

Examination of metal side heating of LAMP joint by CO2 laser beam

Nowadays the vehicle industry is focusing on making materials and technologies for automotive parts that satisfy the newest requirements. Reduction of the manufactured vehicle’s weight is such a requirement. There exist many solutions to satisfy this requirement. One of them is when hybrid materials is combined and fixed together. In this research some aspects of the hybrid joining process of steel and PMMA sheet were investigated. Due to the non-transparent type joining CO2 laser were applied from the metal parts and the laser power and the speed of spot movement were changed in order to roughly determine the process window. In case of adhesive based joining the surface conditions have high importance on the bond strength, therefore the effect of cleaning and blasting of the metal surface was also examined. To determine the role of the value of clamping force it was also changed in some cases. Tensile tests were carried out and the tearing force and the bonded area were measured. In this way the joint strength was determined in case of different setting. New bubble formation was also detected during the process

EVALUATION OF WEAR BEHAVIOR OF Al-Si ALLOY USING SiC AS THE REINFORCEMENT

The current study investigates the wear behavior of the SiC particles reinforced Al-Si alloy composites developed using the stir casting process. The results were obtained from the wear tests of the cast Al-Si alloy and prepared SiC reinforcement composites containing 3 % wt and 9 % wt using fine and coarse size SiC particles. The wear test of all the developed composites were done at different testing conditions with varying loads. The analysis of wear traces, as well as the wear debris, was done at every composition but at higher loads. It was observed that the wear resistance was improved with increasing the amount as well as decreasing the size of the SiC particles. However, the wear rate of the composites increases with increasing the applied load. From the microstructural study of specimen after the wear test one can conclude that both adhesive and abrasive wear mechanisms contribute for wear of SiC particle composites

ZnO THIN FILMS PREPARED BY ATOMIC LAYER DEPOSITION

The purpose of this paper is present the influence of deposition conditions of nanometric zinc oxide thin films using atomic layer deposition on the mechanical and optical properties. The influence of the deposition temperature and the number of cycles on the transparency and adhesion of the ZnO, thin films was investigated. In addition, the results of chemical and phase composition analysis of the layers and their topography and structure were discussed. As a substrate for the investigated thin films was used glass. For the preparation of ZnO thin films was used ALD method. Selecting this method is justified by the high quality and good properties of the deposited layers