Papers by Keyword: Ultrasonics

Abstract: Non-destructive testing (NDT) of thin-walled parts is being considered. This technique is based on registration of changes in thermal fields created by sources on internal defects of the material. Mathematical model calculating surface temperatures of the part in each time-step has been built. The deduced system has been transformed into matrix format by the finite elements method. Solution has been found by the finite difference method. Actual tests has been conducted registering changes in surface temperature of the plate with symmetrical and asymmetrical internal source position. The model has been fine-tuned based on comparison of actual tests’ results with numerical calculations.

Abstract: The paper deals with a solution to increase the machining rate at electrical discharge machining aided by ultrasonics (EDM+US), i.e. the overlapping the voltage pulses provided by EDM generator on the cumulative microjets stage (CMS), which occurs at every final of an ultrasonic period by collective implosion of the gas bubbles from the working gap. This overlapping moves the limit of the removed material by a discharge from the boiling isothermal (at classic EDM) to melting isothermal (at EDM+US) as it is emphasized by the results of finite element analysis. The preliminary experimental data analyzed in the paper are obtained in case of random overlapping at ultrasonic frequency of 20 kHz. They demonstrate an increase of machining rate with more than 300% at EDM+US in comparison with classic EDM in the same working conditions.

Abstract: The paper deals with Finite Element Method (FEM) of thermal and mechanical-hydraulic components of material removal mechanism at micro-electrical discharge machining aided by ultrasonics (μEDM+US), due to EDM and US contribution. The dimensions of craters produced by single discharges under μEDM+US conditions are determined with different pulse durations in order to establish a machining strategy with correlation of pulses and tool elongations.

Abstract: The paper deals with finite element modelling (FEM) of the process of micro-electrical discharge machining of micro-holes aided by ultrasonic longitudinal oscillations of workpiece (μEDM+US). FEM of the process comprises two components: the thermal one due to μEDM removal mechanism, and the ultrasonic one caused by cavitation effect generated inside the lateral working gap. The FEM results obtained are validated by experimental data in terms of craters dimensions produced by single discharges, leading to optimization strategy of process parameters.

Abstract: Non-destructive testing techniques are widely used for testing ceramic materials. In our studies, two different types of ultrasonic test methods (A-scan and C-Scan) were investigated as non-destructive testing methods for characterization of porcelain tiles. Tiles were sintered in different temperatures to change their porosity and density properties. By changing of ultrasonic time and velocity related with samples’ some physical properties (such as bulk density, apparent density, apparent porosity (%), water absorption (%)) inspected via contact A-scan ultrasonic test method. The results show that without necessity of traditional test methods, some physical properties of ceramics can be determined by using obtained ultrasonic velocity-bulk density, apparent density, apparent porosity (%) and water absorption (%) calibration plots. Additionally, various defects were inspected in samples by using water immersion ultrasonic C-scan method. These results supported this study to obtain the information about defects’ size and place in the ceramic tiles. To support this non-destructive method results scanning electron microscope (SEM) characterization was done and images give the information about the place of the defect.

Abstract: Ultrasonic Non-destructive testing is a well known technique for inspecting fiber reinforced composite structures however; its capability is severely limited by the high attenuation in thick and multi layer structures. Guided wave ultrasonic inspection has been reported to be useful tool for quantitative identification of composite structures. It takes advantage of tailoring / generating desired ultrasonic wave modes (Symmetric and anti-symmetric) for improved transmission through the composite structure. For this, guided waves have to be generated selectively by precisely placing transducer at an angle to the test surface. Automation of two axis fixture for transmission and reception of transducers have to be used for avoiding manual errors. The captured signals have to be processed in order to extract useful information from the received ultrasonic signals. The proposed project aims at developing automated guided wave inspection methods along with digital signal processing for generating dispersion curves for thick composited. Using test laminates with implanted defects, methodology for thick composite inspection with guided wave ultrasonic’s will be established. For this data will be captured and analyzed using Labview software.

Abstract: Ultrasonic vibrations of electrode-tool and workpiece were applied successfully in specific cases to increase some parameters at micro-EDM, this working mode being characterized through machining instability due to vary narrow working gap. Our researches proved that all main technological parameters of micro-EDM can be improved by ultrasonic aiding (μEDM+US) in terms of machining rate, volumetric relative wear and surface roughness if some optimization conditions of working parameters are fulfilled. A multiphysics Finite Element Analysis (FEA) of material removal mechanism was achieved using two time dependent modules of Comsol 4.2 in order to attain the working parameters optimization. The FEA results compared to experimental data aiming at model validation led to some useful measures to optimize the working parameters. The knowledge management process was approached in order to suggest how human resource from an organization that uses μEDM+US can apply and improve the research results. Our EDM+US strategy is based on relative long pulse time with very low current overlapped on collective bubbles implosion occurring at the final of a liquid ultrasonic stretching semiperiod, and relative low consumed power on ultrasonic chain, contributing to increase the main output technological parameters mentioned above.

Abstract: Lanthanide-doped semiconductors find usage in a wide variety of applications. In this work, Eu³⁺-doped rutile TiO₂ nanocrystals have been successfully prepared at room temperature by a sonochemical method. The nanocrystalline sample has been characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. A possible mechanism is proposed to explain the formation of Eu³⁺-doped TiO₂ nanomateirals. Additionally, the characteristic emissions of Eu³⁺ can be found upon excitation in the region of TiO₂ absorption, indicating that an energy transfer from TiO₂ to Eu³⁺ occurs for the doped sample.

Abstract: Air-coupled ultrasonic non-destructive testing technology, possessing the characters of complete non-contact and non-destruction, can be used in some situations in which traditional testing is hardly applicable. This article summarized the development of air-coupled ultrasonic non-destructive testing technology briefly, the main existing problems that restrict its progress are analyzed respectively from three processes, concluded and summarized the development and progress of the current solutions to these problems. People can promote the development of this technology more efficiently and directly by the research of its present development.

Abstract: Zircaloy-2, an useful nuclear material is studied here by photoacoustics to correlate with the measurements of X-rays. The microstructure variations observed in X-rays could be explained on the basis of thermal diffusivity measured by photoacoustics technique.