Effect of cyclic loading on hydrogen diffusion in low carbon steels

Carbon steels or low-alloyed steels may be affected by damaging phenomena due to Hydrogen Embrittlement (HE), which is a particular form of Environmental Assisted Cracking (EAC). The insurgence of HE depends on the intrinsic susceptibility of the steel, the applied stress, and the concentration of hydrogen inside the metal. It occurs by a mechanism of absorption and subsequent diffusion of atomic hydrogen through the metal lattice. On steels with a yield strength lower than 700 MPa, HE occurs in the plastic deformation field, in the presence of dynamic loading at slow strain rates or cyclic fatigue loading at very low frequencies. Although several important studies were carried out on the effect of loading conditions on hydrogen diffusion into the metal and HE mechanism, HE phenomena are not fully understood. In this work, the effect of the application of cyclic loads on hydrogen diffusion parameters was studied both in the elastic and in the plastic deformation field. The influence of mean load and amplitude was analyzed. Hydrogen permeation tests were performed on API 5L X65 steel, in accordance with ISO 17081:2014. The specimen behaved as bi-electrode between the two compartments of a Devanathan-Stachurski cell. The anodic side of the specimen was polarized at +340 mV vs Ag/AgCl in a 0.1 M NaOH aerated solution, while the cathodic compartment was filled with an aerated borate solution. A controller enabled temperature adjustment at 20±0.5°C. Once the passivity current registered in the anodic side reached values of 0.05 µA/cm2, a cathodic current density of 0.50 mA/cm2 was applied to charging cathodic side. The study included tests with sine waveform cycling loading, with a maximum level equal to 110% TYS, at a frequency of 10-2 Hz. The results confirmed the values of hydrogen diffusion coefficient usually indicated for low-alloyed steels with a sorbitic microstructure. Strain hardened specimens - stretched above yield strength - showed an increase of steady state current and an extension of the time lag, denoting a slight decrease in the apparent hydrogen diffusion coefficient due to traps effect in the cold deformed steel matrix. Under cyclic loading, an instantaneous peak of current with a subsequent significant transient decrease occurred after cyclic load application, whereas no relevant variation of permeation curve compared to unloaded specimens was observed if specimens were already loaded before hydrogen charging. The instantaneous current peak reached values much higher than the steady state current. This is ascribed to the rupture of the passive film – caused by loading – and its subsequent reformation; in fact, this can also be noted during tests performed on specimens without hydrogen permeation. The following transient, in which the permeation current decreases below the steady state and then returns to it, denotes a relevant trapping effect that causes the instantaneous reduction of mobile hydrogen concentration in the lattice. This becomes more significant for loads closer and closer to the yield strength, mainly beyond this, and can only be noted at the first loading step. Subsequent unloading and loading step at the same mean value showed no transient in the permeation curren

Linear response of light deformed nuclei investigated by self-consistent quasiparticle random-phase-approximation

We present a calculation of the properties of vibrational states in deformed, axially--symmetric even--even nuclei, within the framework of a fully self--consistent Quasparticle Random Phase Approximation (QRPA). The same Skyrme energy density and density-dependent pairing functionals are used to calculate the mean field and the residual interaction in the particle-hole and particle-particle channels. We have tested our software in the case of spherical nuclei against fully self consistent calculations published in the literature, finding excellent agreement. We investigate the consequences of neglecting the spin-orbit and Coulomb residual interactions in QRPA. Furthermore we discuss the improvement obtained in the QRPA result associated with the removal of spurious modes. Isoscalar and isovector responses in the deformed ${}^{24-26}$Mg, $^{34}$Mg isotopes are presented and compared to experimental findings

Hydrated metal salt pretreatment and alkali catalyzed reactive distillation: A two-step production of waste cooking oil biodiesel

In this work, a novel method was proposed for the conversion of waste cooking oil into biodiesel. A two-step approach based on a pretreatment with AlCl3•6H2O to convert FFA into the relevant methyl esters, followed by the complete transesterification of glycerides, under KOH catalysis in a reactive distillation column, was considered. The pretreatment with AlCl3•6H2O allowed to obtain two different phases: an oily phase, rich in FAME and triacylglycerols and with a very limited content of water (100 ppm), and residual FFA (1 mgKOH /goil), and a methanol phase, in which most of the catalyst, water and monoacylglycerols were dissolved in. The esterified stream was characterized by its composition and used to obtain new kinetic parameters to be used in the setting of the reactive distillation. The reactive distillation column was proved to be efficient in obtaining a biodiesel stream with a purity requirement conform to the EN14214 standards. The transesterification step was characterized by a specific heating requirement of 701.3 kJ per kg of biodiesel produced

Symbol-asynchronous transmission in multibeam satellite user down-link : rate regions for novel superposition coding schemes

We consider the forward link of a multibeam satellite system with high spectral reuse and the novel low-complexity transmission and detection strategies from [1]. More specifically, we study the impact of a time offset between the antenna beams that cooperate to simultaneously serve a given user. Assuming Gaussian signaling, we provide closed-form expressions for the achievable rate region. It is demonstrated that, in the absence of timing information at the gateway, this region is not affected by a time offset. Our numerical results further show that, in case timing is known at the gateway, an offset of half a symbol period at both user terminals is optimal in terms of spectral efficiency.Grant numbers : Satellite Network of Experts IV. © 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works

Non-coherent rate-splitting for multibeam satellite forward link : practical coding and decoding algorithms

Non-Coherent Rate-Splitting (NCRS) was recently proposed as a practical multiuser coding and decoding scheme to increase the spectral efficiency of multibeam satellite communication systems. In this paper, we further study the practical realization of NCRS. We propose a modified coding scheme (NCRS*) that is robust to a nonzero time offset among beams. In NCRS*, as opposed to NCRS, the beams send independently channel encoded and modulated waveforms. We assess the performance of NCRS* in terms of the achievable rate region. It is shown that NCRS* performs worse than NCRS, but better than or comparable to other competing schemes, which, as opposed to NCRS*, require flexible bandwidth allocation or perfect synchronization at the transmitter. We also propose a new N-MAP algorithm for the practical implementation of NCRS* receivers. Similar to the existing UMAP algorithm, N-MAP takes into account the modulation used by, and the time offset between, the signals received from the different beams. In most cases, however, N-MAP has a significantly lower complexity than U-MAP

A taxonomic study of Jacquemontia evolvuloides (Moric.) Meisn. and related species (Convolvulaceae).

Made available in DSpace on 2018-01-09T16:14:10Z (GMT). No. of bitstreams: 1 a2017n2a60.pdf: 6004543 bytes, checksum: 622a8fd20f952479c74b285593d34289 (MD5) Previous issue date: 2018-01-09bitstream/item/170613/1/a2017n2a6-0.pd

Ab-initio Molecular Dynamics study of electronic and optical properties of silicon quantum wires: Orientational Effects

We analyze the influence of spatial orientation on the optical response of hydrogenated silicon quantum wires. The results are relevant for the interpretation of the optical properties of light emitting porous silicon. We study (111)-oriented wires and compare the present results with those previously obtained within the same theoretical framework for (001)-oriented wires [F. Buda {\it et al.}, {\it Phys. Rev. Lett.} {\bf 69}, 1272, (1992)]. In analogy with the (001)-oriented wires and at variance with crystalline bulk silicon, we find that the (111)-oriented wires exhibit a direct gap at ${\bf k}=0$ whose value is largely enhanced with respect to that found in bulk silicon because of quantum confinement effects. The imaginary part of the dielectric function, for the external field polarized in the direction of the axis of the wires, shows features that, while being qualitatively similar to those observed for the (001) wires, are not present in the bulk. The main conclusion which emerges from the present study is that, if wires a few nanometers large are present in the porous material, they are optically active independently of their specific orientation.Comment: 14 pages (plus 6 figures), Revte

Corrosion rate of high CO2 pressure pipeline steel for carbon capture transport and storage

The paper deals with the effect of pressure, temperature and time on corrosion rate of pipeline steels in CO2saturated water and in humid saturated CO2 gas in the range from 25 to 60°C and pressure from 20 to 145 bar,up to 400 hours of exposure. The results of weight loss tests show very high rates in the aqueous phase, oneor two order of magnitude higher than the values obtained in CO2 saturated with water, but remaining in anycase much lower than values extrapolated by De Waard and Milliams model at high partial pressure. Dependingon temperature and pressure, cementite and iron carbonate scales can grow on metallic surface reducingcorrosion rate. SEM and metallographic analysis evidenced the evolution of scale from defective cementitebasedlayer to protective compact carbonate scale