Electrically Assisted Wire Drawing Polarity Effects

Electrically assisted manufacturing is the direct application of an electric current or field to a workpiece during a manufacturing operation. In addition to resistive heating, various anomalous effects have been observed experimentally. Since its conception in the 1950s, scientists continue to debate the existence of these so called electroplastic effects (EPEs) due to conflicted results shown throughout literature. A popular theory of electroplasticity is the electron wind, which postulates that there is a transfer of momentum between electrons and dislocations, which assists their motion during deformation. Though refuted both mathematically and experimentally in other types of tests, the electron wind theory, and therefore the existence of electroplasticity, is interestingly supported by the existence of polarity effects in wire drawing. A detailed review of the literature that has shown polarity effects in wire drawing is conducted. While the authors of these publications failed to fully disclose all test parameters, requiring several assumptions to be made, it appears that no mathematical/logical trends could be established. It is hypothesized herein that the velocity of the wire in a wire drawing application can influence the drift velocity of electrons, thereby increasing or decreasing current flow explicitly through the moving section of the wire. In order to test this hypothesis, a fixture was constructed which is capable of passing a current through a moving wire at common wire drawing speeds. Modern sensing equipment was used to measure various electrical parameters during testing. The wire speed effect hypothesis was refuted by experimental testing. While the results of experimental testing thus far indicate the existence of electroplasticity, further testing that includes drawing and force measurements must be conducted in order to fully conclude its existence in the wire drawing application.

Polarity effects in 4-fluoro- and 4-(trifluoromethyl)prolines

Fluorine-containing analogues of proline are valuable tools in engineering and NMR spectroscopic studies of peptides and proteins. Their use relies on the fundamental understanding of the interplay between the substituents and the main chain groups of the amino acid residue. This study aims to showcase the polarity-related effects that arise from the interaction between the functional groups in molecular models. Properties such as conformation, acid–base transition, and amide-bond isomerism were examined for diastereomeric 4-fluoroprolines, 4-(trifluoromethyl)prolines, and 1,1-difluoro-5-azaspiro[2.4]heptane-6-carboxylates. The preferred conformation on the proline ring originated from a preferential axial positioning for a single fluorine atom, and an equatorial positioning for a trifluoromethyl- or a difluoromethylene group. This orientation of the substituents explains the observed trends in the pK a values, lipophilicity, and the kinetics of the amide bond rotation. The study also provides a set of evidences that the transition state of the amide-bond rotation in peptidyl-prolyl favors C4-exo conformation of the pyrrolidine ring.