Papers by Author: Algirdas Vaclovas Valiulis

Abstract: In a modern environment, during the evolution of international activities, from mobility to international education hubs, universities are searching for new internationalization tools to implement those undertakings more effectively in terms of finance and time. Co-operation with other regions of the world and international openness are the key factors in the development of the European Higher Education Area. To illustrate the situation arising from student mobility of studying technological sciences, the paper analyses information about student mobility in the fields of mechanical engineering and mechatronics for the period 2009–2013.

Abstract: This paper present the result obtained from new experimental STEIN-MESYFIL 953 V; STEIN-MESYFIL 954 V coatings. The surfacing material was wires of 1.6 mm diameter. The tests aimed at determining wear resistance of coatings sprayed on steel substrate. The investigation shows that the tribological behaviour of new experimental thermal arc sprayed coatings is greatly affected by its microstructural constituents such as porosity, oxide inclusions, and microhardness of coatings. Results show that increasing porosity of coatings twice, it doubles the mass loss. Results for thermal sprayed coatings of all experiments showed their high wear resistance and are discussed.

Abstract: On covering aluminum and its alloys with coatings resistant to high-temperature corrosion and attrition, abundant technological problems arise. The key problem is a removal of the film of aluminum oxide Аl₂O₃ from the aluminum substrate. This permanent, chemically continuous film of oxide reduces adhesion between the substrate and the coating. For improving cohesion of the coating with the substrate, an appropriate pre-treatment of aluminum is required. In the paper, cleaning of aluminum alloy AW 5754 by electric discharge is investigated. This method is considered one of most environmentally friendly methods of surface cleaning. The impact of the parameters of aluminum alloy cathodic cleaning on the surface cleaning width, its roughness and free energy of the surface were examined. In addition, the topography, microstructure and chemical composition of the surface of cleaned aluminum alloy were estimated.

Abstract: Lithuania, as a small country, cannot afford creating new knowledge in all the fields of science. It is reasonable to firstly focus on those fields in which Lithuania already has scientific and industrial potential and that clearly declare the biggest demand for innovations as well as capability to invest into innovations. Research institutions here usually focus on fundamental research but both the revenues and the human resources of research institutions are rather poor. Dispersion of the Lithuanian potential of science and studies and the absence of critical mass represent the main reasons why R&D lacks effectiveness. The paper presents the main research fields and high-tech research institutions in Lithuania.

Abstract: Presented work analyses the impact of heat treatment parameters on the mechanical properties and operational reliability of P5 (5%Cr0.5%Mo) steel welded joints. The key objects of research are heat-treated chrome-molybdenum steel welded joints and piping elements operated at high temperature for an extensive period of time, where degradation of mechanical properties has been observed. The main objective is to investigate the causes of degradation of alloy steel mechanical properties during fabrication and operation of the equipment, and to develop a methodology for identification of optimum heat treatment parameters for chrome-molybdenum steel welded joints. A few key issues are addressed herein: identification of dependence of chrome-molybdenum (5%Cr-0.5%Mo) steel welded joint mechanical properties on heat treatment parameters, identification of the optimum value of temperature/time parameter, and identification of causes of mechanical property changes and degradation of the steel.

Abstract: The existence of residual stresses induced by the welding process is an important reason of cracking and distortion in welded metal structures that may affect the fatigue life and dimensional stability significantly [1]. Heat treatment is one of the traditional methods to relieve the residual stresses. But it is often limited by the manufacturing condition and the size of the structures. In this paper a procedure called vibratory stress relief (VSR) is discussed. VSR is the process to reduce and re-distribute the internal residual stresses of welded structures by means of weldment mechanical vibration during welding. Parameters of VSR procedure are described in the paper. Residual stresses on weld bead are measured in three different specimens by X-ray diffraction method. Mechanical tests of welded specimens were also performed with purpose to evaluate VSR effect in weld metal and heat affected zone (HAZ).

Abstract: Consistent patterns for transfer of chromium and carbon from the electrode coating into the fused metal, impact of their amounts on transfer of other alloying elements into the alloy are considered. Respective compositions of electrode coatings are made so, that Cr content in coated layers would change from 2 % up to 40 % (content of C ~ 3 %). At research of transfer of carbon patterns, the compositions of electrode coatings are made so, that C content in coated layers would change from 0.1 % up to 4 % (content of chromium in this case is approximately 20 %). In both cases the content of other alloying elements remain in a settled level (Si ~ 2 %, Mn ~ 1.1 %, Ti ~ 0.5 %, B ~ 0.6 %).

Abstract: Rapid advances in technology have blurred traditional boundaries between engineering disciplines and forced mechanical engineering graduate courses to embrace new subject areas. These are not negative influences, but are simply a healthy response to rapidly advancing technologies. A particular example is the combining in one study program, studies of different engineering and structural materials (including composite materials, ceramics, polymers, etc.) and methods and technologies of brazing, joining by welding, bonding by glue, etc of these materials. Among all engineering programs, materials and mechanical engineering requires huge laboratories and expensive facilities, as students need to develop practical experience. In order to maintain an educational standard and quality, a university is forced to look for alternatives to handson practical laboratories. One of the alternatives is to utilize a wide variety of computer-aided learning packages and the simulation of physical-chemical processes in a welding pool and near to its border. This paper sets forth a case for integrating aspects of materials and joining technologies throughout a graduate curriculum.

Abstract: The number of potentially dangerous equipment that has completed its established operational time, but is still being used, is permanently increasing. Therefore there is a problem of its further operations. A decision to continue to operate power-generating plants, when the initial resource of the equipment’s working time is ended, and its further operation without considerable expenditures on repair and the diagnostic of a metal state is possible only with the help of long-term research of metal in power-generating plants. Only a complex of research techniques can estimate the real state of a construction. In the article problems connected with the definition of operation reliability of steam pipeline elbows are investigated. Different areas of an elbow were researched. Results of a microstructure analysis, and mechanical characteristics (time history) research of an elbow metal are presented. Also results of calculation of an elbow on low - cyclic thermal fatigue are presented.