Papers by Keyword: Oscillation

Abstract: Laser cladding of a Ni based powder on cast iron is performed by a 4kW continuous diode laser. For this, a robot programming method named “Wavering” is used. Indeed, this method allows to cover large surfaces (width higher than 5 mm and thickness higher than 4 mm). The cast iron substrate used during this work is employed for its thermal properties in glass mold Industry. However, it has drawbacks which are weak wear, corrosion, and abrasion resistance. Conventional techniques used to protect the molds, like Plasma Transferred Arc (PTA), affect the molds microstructure, but also the thermal and mechanical properties. The laser cladding of the Ni based alloy allows to protect the molds without affecting the cast iron thermal properties (low Heat Affected Zone). The purpose of this research is to produce a well bonded Ni based melted powder without pores or cracks on large and curvilinear surfaces. First, the coating, adapted to this substrate geometry, is optimized. Then, an investigation of the impact of the processing parameters (power, scanning speed and wavering frequency) on the microstructure is carried out. Besides, the mechanical behaviour is analysed by microhardness. In addition, the evolution of the Heat Affected Zone (HAZ) according to the processing parameters is observed. Two kinds of areas are inspected in terms of microstructure: a stable area obtained after a single pass and an interferenced area linked to superimposed passes. Those analyses led to a cladding parameter optimization to obtain perfect bonding, to avoid porosity propagation and to limit the HAZ emergence on curvilinear surfaces. Finally, in comparison with the PTA technique, it appears that laser cladding process with wavering method leads to a good coating of curvilinear surfaces.

Abstract: The relationship between substance characteristic temperatures: autoignition, melting, flash, boiling is demonstrated and analyzed. Based on the oscillatory and step changes presence, a conclusion was made about the supramolecular structures presence and periodicity in the n-alkanes homologous series. A method for modeling equivalent lengths of peroxide supramolecular structures for predicting the explosion and fire hazard parameters of n-alkanes is proposed. An approximation dependence was developed for predicting autoignition temperatures t_ai of n-alkanes. It is shown that stoichiometric concentrations of the various supramolecular peroxide structures formation accord to different flammability and explosion limits. A correlation between t_ai and Anti-Knock Index (AKI) was established. An approximation dependence was developed for predicting n-alkanes AKI. The detonation propensity index К_D was introduced based on cluster supramolecular structures modeling and melting temperatures. It is shown that К_D indicator correlates with the n-alkanes AKI and with the explosives detonation velocity. The possibility of taking into account during calculations the supramolecular structures presence at the combustion stage confirms their existence.

Abstract: In this paper, we consider a detailed technological process for manufacturing parts, namely, a gear wheel. The proposed method with the intervention of modern 3D modelling makes it possible to improve the main indicators of quality and strength of parts. Based on the results obtained, a cycloid transcendental system of circular motion of a gear wheel with the specified basic parameters was modelled. Using multifunctional modules, we studied the vibrations of the gear wheel at different points in time. It was found that due to the fatigue and contact strength, it is possible to ensure uniform flexural strength of the gear teeth. And also, by adjusting the profile of the teeth of the part, we selected the desired strengthening coefficient. The presented dependence of the angles of inclination of the gear teeth on the transformation coefficient allows you to improve the main indicators of quality and strength by at least 2 %.

Abstract: The presence of melting temperatures oscillatory and stepwise changes for hydrocarbons four homologous series is demonstrated and analyzed. The oscillating dependence is manifesteds on the principle of «even-odd» molecules with different deviations from linearity. According to the working hypothesis, this is due to the presence of the matter smallest structural unit in the cluster form of with a certain coordination number. The oscillation of melting temperatures in hydrocarbons series is explained by the fact that clustering can occur both at the site of the final carbon in the molecule and at other carbons in the molecule chain, and this fact depends on the «even-odd» effect. Based on the known values of melting temperatures in homologous series, the clusters probable structure is assumed. It is shown that graphs for the calculated values of equivalent lengths of these clusters correlate with corresponding graphs for hydrocarbons melting temperatures. An approximation formula has been developed to predict melting temperatures of hydrocarbons based on the values of the equivalent length and the cluster molecular weight, which operates with an approximation coefficient of 0.997 and a mean deviation of 4.2 K.

Abstract: The increasing demand for resource-efficient production methods is driving the development of new technologies. Sheet bulk metal forming (SBMF) offers the possibility to combine sheet metal and bulk forming operations. This allows the production of complex functional components with secondary forming elements from sheet metal. Compared to other production techniques such as machining, a more efficient use of material can be achieved. Further advantages are a near net shape production and increased strain hardening. SBMF processes are limited by forming technology boundaries. These include high forming forces, incomplete mould fillings and limited surface qualities. In this research, the possibility of enhancing the material flow, improving surface quality and reducing the tool loads in SBMF-processes is investigated by using a superimposed oscillation. The focus here is on achieving a high surface quality of components produced by forming technology and an enhanced material flow during forming. For this purpose, a forming process for ironing an axial gear geometry is superimposed with an oscillation in the main force flow.

Abstract: The known methods of calculation of oscillation amplitudes of massive foundations of machines taking into account damage are analyzed in the article. It is established that the method set out in the building codes allows to determine the amplitudes of the foundation oscillations at any point of the foundation, approximately enough. This technique does not take into account the interaction with the soil of the deepened foundations, but takes into account only the physical and mechanical characteristics under the sole of the foundation. The authors propose a finite element method (FEM) calculation using the Plaxis 7 software package installed on a personal computer and a vibrometer. The result is the oscillation amplitude of the massive foundation. The presence of cracks and damage increases the magnitude of the oscillation amplitudes from the dynamic impact. If you make timely planned repairs to the foundations, the amplitude of the oscillations can be reduced.

Abstract: The electron beam welding (EBW) parameters have significant influence on weld surface appearance and porosity formation. Besides basic welding parameters, such as acceleration voltage, welding current, focusing current and welding speed, the beam oscillation during EBW plays an important role in weld metal formation and directly impacts the final welded joints properties. The influence of technological movements during EBW on the properties of aluminium-lithium alloy welded joints was studied. The same frequency and different amplitude as well as same amplitude and different frequency were chosen. The other welding parameters were constant.

Abstract: The rheological behaviour of alkali-activated materials prepared by activation of a brick powder by alkaline solution (alkali + water glass) is described. The influence of the composition of activation solution (NaOH vs. KOH, varied silicate modulus) on the flow properties (yield stress, consistency coefficient, fluidity index) and the evolution of the elastic modulus (G ́) and the viscous modulus (G ́ ́) over time were studied. The rheological characterization was completed by frequency sweep tests with the aim of investigating the material behaviour more in detail. The results show that the pastes are thixotropic suspensions with very low yield stress. The potassium activator decreases the yield stress and viscosity of the pastes and retards the polymerization kinetic. The brick pastes become more rigid and more viscous with increasing silicate modulus. This also leads to an acceleration of gel formation in brick pastes.

Abstract: Unique conversions between stretched and contracted helices of mono-substituted polyacetylenes (SPA)s prepared with an organo rhodium complex-amine catalytic system were demonstrated. The conversions of aromatic SPAs with a drastic color change were caused by polymerization solvents used, substituents in the phenyl ring, and external stimuli like heat- and solvent-treatments which were induced in the solid state. The helices of aliphatic polyacetylenes was oscillating just like spring or coil which was synchronizing with the restricted rotation around the ester O-*C bond in the solution. The oscillation mode was named as an accordion-like helix oscillation “HELIOS”. All the conversions were attributed to the difference of the thermodynamical stability between stretched and contracted helices.

Abstract: In this contribution a theoretical basis of pendulum oscillations is described. The authors deal also with an experimental investigation of nonlinearity in oscillations of large displacement pendulum. High-speed correlation system was used for the registration of pendulum free motion. The obtained data were consequently processed in Matlab and depicted in a form of graphical visualizations and tables.