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

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

Surface property control by electron beam deflection during hardening

The usage of the high-energy electron beam source enables repeated surface quenching of chosen locations of an engineering part surface. Different techniques of electron beam deflection allow creating hardened layers of different shapes, hardness levels and thicknesses. Experiments were carried out with 42CrMo4 (1.7225) steel. The deflection modes tested were one-point, 6-point, line, field, and meander. The influence of process speed and defocusing of the electron beam was also taken into account. The electron beam surface quenching resulted in a very fine martensitic microstructure with a hardness of over 700 HV0.5. The thickness of the hardened layers depends on the deflection mode and is affected directly (except field deflection) by process speed. The maximum hardened depth (NCHD) was 1.49 mm. Electron beam defocusing affects the width of the hardened track and can cause extension of the trace up to 40%. The hardness values continuously decrease from the surface to the material core

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

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

Mechanical Properties of Stellite-6 coated AISI 316L Stainless Steel

Present paper describes the mechanical properties of Stellite-6 coated AISI 316 L stainless steel. Specimens were coated using Detonation Gun thermal spray process, with different coating thicknesses of Stellite-6 ranging from 50 µm to 150 µm. Afterwards their properties like tensile strength, impact strength and micro hardness were evaluated on the basis of the results obtained from the experimentation. For comparison of substrate and coated material the graphs were plotted. The coated specimens exhibited superior impact strength and microhardness than that of the bare specimens, whereas the tensile strength of coated specimens decreased marginally with the increase in coating thickness

Characteristics of diamond – like carbon(DLC) film deposited by PACVD process

Diamond – like carbon (DLC) film is promising materials for many technical and engineering applications. DLC films are used in many different industries for example: in medicine, in electronics, in optics and the automotive industry. They have excellent tribological properties (low friction coefficient), chemical inertness and high mechanical hardness. This paper provides an analysis of the microstructure, mechanical and tribological properties of DLC films. In the study of the coating used several surface sensitive techniques and methods, i.e. High Resolution Transmission Electron Microscopy (HRTEM), Scanning Electron Microscopy (SEM), Raman spectroscopy and tribological tests like ball-on-disc. HRTEM investigation shows an amorphous character of DLC layer. In sliding dry friction conditions the friction coefficient for the investigated elements is set in the range between 0.02-0.03. The investigated coating reveals high wear resistance. The coating demonstrated a good adhesion to the substrate.

The variable contact pressure influence on the tensile force in the process of strip sliding in the flat die in ironing

Possibilities to influence the deep drawing process during its duration are limited and generally consist of influences at the flange of the thin sheet, mainly by the contact pressure (the blank holding force). The common characteristics of previous investigations were setting of the fixed values of the blank holding force or the holder's pressure within the ironing tool. The objective of this investigation was the continuous setting of the variable pressure during the sliding process, via the preset functions, in order to analyze the variable pressure influence on the ironing process. This is why an experimental computerized device was designed and constructed for analyzing the influence of the variable contact pressure on the sliding process of the model strip during the flat-die test. The multi-parameter experiment was conducted; various materials of the tested pieces were applied (primarily thin sheet made of Al alloys and low-carbon steels sheet, with and without coating); different versions of the tool's contact elements were used, with various friction regimes and influential parameters (variable contact pressure during the sliding process, etc.). This experimental device practically represents a simulator for realization and studying of the physical model of an important segment of the ironing process in the completely realistic conditions (materials, tools, etc.). The aim was to find the optimal combination of the variable contact pressure and the tribological parameters, so that the punch force, as one of the process output parameters, would have the minimal value, as well as to avoid the undesired effects during the forming (difficult sliding of the flange, appearance of thin sheet's wrinkling, structural destruction, etc.). Understanding the mutual dependence of the holder's variable pressure and other influences should enable improvement of the ironing process control and should contribute to better understanding of the phenomena occurring at the thin sheet's flange.

Zirconia / Alumina Composite Foams with Calcium Phosphate Coating

In this study, mechanical properties of calcium phosphate foams were enhanced by zirconia/alumina porous cores prepared by polymer replica technique. This technique was chosen to ensure interconnected pores of optimal size for cell migration and attachment. The porosity of ZA cores (50 – 99%) was controlled by multistep impregnation process, the size of pore windows was 300 – 500 μm. Sintered ZA cores were impregnated by hydroxyapatite or β-tricalcium phosphate slurry to improve bioactivity. The bone like apatite layer was formed on coatings when immersed in a simulated body fluid. Neither of tested materials was cytotoxic. Thus, the composite foam can be potentially used as a permanent substitute of cancellous bone

Wear resistance of layers hard faced by the high-alloyed filler metal

The objective of this work was to determine the wear resistance of layers hard faced by the high-alloyed filler metal, with or without the austenite inter-layer, on parts that operate at different sliding speeds in conditions without lubrication. The samples were hard faced with the filler metal E 10-UM-60-C with high content of C, Cr and W. Used filler metal belongs into group of alloys aimed for reparatory hard facing of parts damaged by abrasive and erosive wear and it is characterized by high hardness and wear resistance. In experiments, the sliding speed and the normal loading were varied and the wear scar was monitored, based on which the volume of the worn material was calculated analytically. The contact duration time was monitored over the sliding path of 300 mm. The most intensive wear was established for the loading force of 100 N and the sliding speed of 1 m.s-1, though the significant wear was also noticed in conditions of the small loading and speed of 0.25 m.s-1, which was even greater that at larger speeds.