In the present work, different Cu-alloyed model ductile irons with ferritic (0%Cu-0.09%Mn), mixed ferritic-pearlitic (0.38%Cu-0.40%Mn) and pearlitic (0.69%Cu-0.63%Mn) microstructure were produced and analyzed in terms of their electrochemical corrosion behavior in a 3.5wt.%NaCl aqueous solution containing naturally dissolved oxygen at room temperature (25°C). The remaining elements such as Si and Mg were kept at balanced levels in an attempt to minimize variations in graphite size and distribution among different samples. The corrosion resistance was evaluated by electrochemical impedance spectroscopy and potentiodynamic polarization. Microstructure analysis of the cast alloys confirmed similarity in the graphite morphology among the different cast samples and the expected variations in the metallic matrix. In the absence of passivation, it was found that the addition of copper led to an increase in corrosion resistance, which could be attested by higher values polarization resistance and corrosion potential.
An implemented impedance measuring instrument is described in this paper. The device uses a dsPIC (Digital Signal Peripheral Interface Controller) as a processing unit, and a DDS (Direct Digital Synthesizer) to stimulate the measurement circuit composed by the reference impedance and the unknown impedance. The voltages across the impedances are amplified by programmable gain instrumentation amplifiers and then digitized by analog to digital converters. The impedance is measured by applying a seven-parameter sine-fitting algorithm to estimate the sine signal parameters. The dsPIC communicates through RS-232 or USB with a computer, where the measurement results can be analyzed. The device also has an LCD to display the measurement results.
The problem of sequencing jobs on a single machine to minimize total cost (earliness and
tardiness) is nowadays not just important due to traditional concerns but also due to its
importance in the context of Collaborative Networked Organizations and Virtual Enterprises,
where precision about promptly responses to customers’ requests, along with other
important requirements, assume a crucial role. In order to provide a contribution in this
direction, in this paper the authors contribute with an applied constructive heuristics that
tries to find appropriate solutions for single machine scheduling problems under different
processing times and due dates, and without preemption allowed. In this paper, two different
approaches for single-machine scheduling problems, based on external and internal
performance measures are applied to the problem and a comparative analysis is performed.
Computational results are presented for the problem under Just-in-Time and agile conditions
on which each job has a due date, and the objective is to minimize the sum of holding costs
for jobs completed before their due date and tardiness costs for jobs completed after their
due date. Additional computational tests were developed based on different customer and
enterprise oriented performance criteria, although preference is given to customer-oriented
measures, namely the total number of tardy jobs and the maximum tardiness.