Residual stress state after the laser surface remelting process

Residual stresses are a result of elasto-plastic deformations induced in the workpiece material during the heat treatment process. The extent and magnitude of internal stresses depend on temperature conditions in heating and cooling and physical properties of the workpiece material. This contribution discusses the extent and distribution of residual stresses after laser remelting a thin surface layer on ductile iron 80-55-06 (ASTM specification) or Gr 500-7 according to ISO. Residual stresses are not only induced by temperature differences but also result from stresses due to microstructural changes between the surface and the core of the specimen subsequent to cooling to the ambient temperature. The distribution and extent of residual stresses in the remelted thin surface layer depend mostly on melt composition and cooling conditions. Different rates of solidification and subsequent cooling of the remelted layer are reflected in the volume proportions of the created cementite, residual austenite, and martensite in the microstructure. The rate of heating and cooling of the thin surface layer is a function of laser power, beam diameter on the workpiece surface, and interaction time. In addition, the number of passes of the laser beam over the workpiece surface and different degrees of laser trace overlapping were increased to see how these can affect the thermal conditions in the workpiece. To determine the residual stresses, the relaxation method was used. This is based on measuring the specimen strain during electrochemical material removal.     

Asphalt concrete modification with waste PMMA/ATH

This paper presents recycling of waste PMMA/ATH powder in asphalt concrete mixture. Waste PMMA/ATH is generated in large amounts during shaping process of acrylic sheets. Recycling waste polymers rationally and efficiently has become one of the priorities of road pavement industry in recent years. Therefore, in this study waste PMMA/ATH powder was incorporated in an asphalt mixture. In one case waste PMMA/ATH was used as an asphalt binder modifier and in other case as a partial replacement for fine aggregate fraction. Basic performance characteristics of asphalt mixtures were evaluated by measuring material properties such as rutting potential and stripping resistance. Binder characteristics were determined also on artificially aged samples. With both modification methods, improved performance characteristics of asphalt mixture were achieved which can increase road pavement durability. Finally, waste PMMA/ATH allowed us to prepare an asphalt mixture that had strongly enhanced mechanical properties regarding to the wheel tracking test and could also have less negative effects on the environment as indicated by moisture susceptibility test results.     

Hidden logistic potentials of working systems

Nowadays, the companies operate in a turbulent environment caused by various effects of global market, quick expansion of new products and production processes, fastidious customers and increased competition.In these circumstances only those companies are successful which can respond to market changes as fast as possible—i.e. they have the shortest response time regarding fulfilment of customer requirements (short delivery time and reliable delivery in addition to price and quality).Consequently, a reduction of mean inventory, range and lead time of working systems in the company is an ever increasing strategy that ensures an increase of growth and profit of the company.The article shows how the tools for modelling the flow of orders through working systems can be used in order to discover the hidden logistic potentials of working systems in a company.Presented are the results of finding hidden logistic potentials of working systems in the tool-production department of "ETI d.d." company from Izlake, Slovenia.     

Online assessment of power transmission belt geometry by using laser triangulation and profile parameterisation

We present a method that enables an automated assessment of the geometrical dimensions of power transmission belts and the detection of surface defects and small deviations from the ideal shape that are difficult to detect with a visual inspection. The method is based on the acquisition of belt surface profiles using a laser triangulation and automated profile assessment based on a custom-developed algorithm. The algorithm uses a novel approach to profile segmentation, featuring a template that defines the expected profile shape in advance and so, allows a faster implementation of the algorithm. It enables an automated calculation of the basic geometrical dimensions, which define the profile shape in the technical drawing and are important for online quality control in the production line. A macrolanguage was developed for a rapid and flexible definition of the mathematical operations used in the calculation of the profile's dimensions and thus, an adaptation to the requirements of a particular application. We demonstrate the use of the automatic belt profile geometry assessment on randomly chosen samples.     

Single-step preparation of rutile-type CrNbO4 and CrTaO4 oxides from oxalate precursors–characterization and properties

Chromium niobate and tantalate (CrNbO₄ and CrTaO₄) were synthesized by pyrolysis of the oxalate-based heterometallic complexes [Cr₂(bpy)₄(μ-O)₄Nb₂(C₂O₄)₄]·3H₂O (Cr-Nb) and [Cr(bpy)₂(H₂O)(μ-O)Ta(C₂O₄)₃]₂·3.5H₂O (Cr-Ta) (bpy = 2,2'-bipyridine). Compared to conventional solid-state synthesis, herein studied oxides are prepared at lower temperatures, in one step without repeating grinding procedures. The structure, morphology, and optical properties of the as-synthesized oxides were characterized using powder X-ray diffraction (PXRD), field emission scanning electron microscopy (SEM), the thermogravimetric and differential thermal analysis (TG/DTA) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The determined band gap energies of CrNbO₄ and CrTaO₄ are 2.39 and 2.82 eV, respectively, which prompted us to investigate photocatalytic activity of these oxides in degradation of dyes. Microscopy studies show that the particles of both oxides began to aggregate into bigger particles, leading to an increase in grain size. Additionally, magnetization measurements on both oxides revealed spin-glass behavior at low temperatures.     

Depassivation and repassivation of stainless steels by stepwise pH change

Immersion tests with different stainless steels have been performed, while the pH was stepwise decreased and then increased again. During 8.5-day exposure, the depassivation and repassivation pH values as a function of pitting resistance equivalent number were determined. There is always a gap between both pH values (depassivation and repassivation), indicating that for every steel, there are conditions where an existing passive layer can be maintained but cannot be rebuilt after depassivation. In such environments, the passive layer is thicker, consisting mainly of molybdenum and iron rich oxides, while chromium is dissolved. Usually, depending on conditions, the passive layer is more chromium-rich, especially the inner layer. This is relevant, for example, for acidizing jobs in oil and gas industry, proving that repassivation after acidizing will happen promptly, when the pH is increased again.     

Numerical simulation of rotational symmetric tube bulging with inside pressure and axial compression

The process of rotational symmetric tube bulging with inside pressure and axial compression enables the standard tubes to be formed into different rotational symmetric hollow parts in such a way that their central part is expanded into a desired shape while the ends remain unchanged. The superposition of axial compression contributes to a more favorable forming stress state, which is reflected in larger forming limits and smaller wall thinning in the widened area. The problems characterizing the process are a limited range of compression stability and difficulties met when establishing and optimizing the technological parameters of the process whose course cannot be defined in an analytical way. Based on a physical model of the forming process a numerical model was built. Using ABAQUS code the model was simulated over the entire stress/forming region. The comparison of the computer simulated forming process with the experimentally obtained results showed that the model was highly accurate. Finally, the paper studies the influences of particular parameters on the stability of the process, showing on a practical example how it is possible to achieve tube bulging without wall thinning.