SUMMARYThis paper presents a study on the characterization of aging of transformer oil-pressboard insulation. Traditional and modern diagnostic tools and techniques were used to investigate aging of oil-paper insulation under controlled laboratory conditions. Insulation condition testing includes common chemical diagnostics such as acidity tests and new chemical techniques: determination of relative content of dissolved decay products by spectrophotometry, solid suspension by turbidimetry, Fourier Transform Infrared (FTIR) spectroscopy and electrical diagnostic techniques that have gained exceptional importance for utility professionals: polarisation/depolarisation current, recovery voltage measurement and frequency domain dielectric spectroscopy measurements. From the obtained results it is found that chemical tests depicted more sensitivity to insulation degradation. Also, different oil-pressboard insulation ratios were investigated to assess the influence of the relative amount of cellulosic materials on aged mineral oil decay products and vice versa. Emphasize is laid on the potentialities/avenues offered by FTIR to assess oil insulation condition. Notable experimental results have been reported, which could be valuable to researchers and practicing engineers in this field.

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The present work aims to investigate the fatigue characteristics of automotive lower suspension arm made of semi-solid A357 aluminum castings using metallurgical and analytical approaches. The fatigue life calculations of analytical model are used to identify and introduce the model parameters based on the suspension arm material followed by analyzing the load-number of cycles fatigue curve. The critical stress areas capable of initiating cracks during fatigue tests are detected using ABAQUS software followed by the installation of strain gages on the suspension arm to calculate maximum stress. The fatigue experiments are carried out to compare the results of the analytical method with the experimental endurance curves traced by lower suspension arm samples. Microstructure characteristics of the semi-solid A357 under T6 heat treatment conditions are examined using scanning electron microscope. The results show that the fatigue life and the quality index of alloys investigated are affected by casting technique, castings design, microstructural characterization, and heat treatment condition.