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Determination of residual stress distribution in high strength aluminum alloy after EDM

Mehmood S., Sultan A., Anjum N. A., Anwar W., Butt Z.

Advances in Science and Technology. Research Journal

2017

Vol. 11, no 1

29--35

Thermal energy produced by discrete and random electric sparks in electric discharge machining (EDM) melts surface material. A portion of this molten material is removed and the remaining material resolidified by rapid cooling in a hydrocarbon oil. The effect of repeated heating and cooling of the surface and sub surface material with complex temperature gradients results in residual stresses in machined parts. The aim of this investigation is to determine the distribution of residual stresses in the depth of machined material with respect to discharge current, most important electric parameter during EDM. It is well known that surface finish is dependent on discharge current. Therefore, investigations were carried out for smaller discharge current levels i.e. 3, 6, 9, 12 ampere. Hole-drill strain gauge method is used for the determination of residual stresses in the depth of material. For comparison purposes, residual stresses are also determined for conventionally turned specimens. This study provided quantitative analysis of the residual stresses for various discharge current in EDM which is a key parameter in deciding the service life of material.

Poly(N-isopropylacrylamide-co-methacrylic acid) microgel stabilized copper nanoparticles for catalytic reduction of nitrobenzene

Farooqi Z. H., Butt Z., Begum R., Khan S. R., Sharif A., Ahmed E.

Materials Science Poland

2015

Vol. 33, No. 3

627--634

Pakistan Poly(N-isopropylacrylamide-co-methacrylic acid) microgels [p(NIPAM-co-MAAc)] were synthesized by precipitation polymerization of N-isopropylacrylamide and methacrylic acid in aqueous medium. These microgels were characterized by dynamic light scattering and Fourier transform infrared spectroscopy. These microgels were used as micro-reactors for in situ synthesis of copper nanoparticles using sodium borohydride (NaBH4) as reducing agent. The hybrid microgels were used as catalysts for the reduction of nitrobenzene in aqueous media. The reaction was performed with different concentrations of catalyst and reducing agent. A linear relationship was found between apparent rate constant (kapp) and amount of catalyst. When the amount of catalyst was increased from 0.13 to 0.76 mg/mL then kapp was increased from 0.03 to 0.14 min−1. Activation parameters were also determined by performing reaction at two different temperatures. The catalytic process has been discussed in terms of energy of activation, enthalpy of activation and entropy of activation. The synthesized particles were found to be stable even after 14 weeks and showed catalytic activity for the reduction of nitrobenzene.