A constitutive model for analyzing martensite formation in austenitic steels deforming at high strain rates

This study presents a constitutive model for steels exhibiting SIMT, based on previous seminal works, and the corresponding methodology to estimate their parameters. The model includes temperature effects in the phase transformation kinetics, and in the softening of each solid phase through the use of a homogenization technique. The model was validated with experimental results of dynamic tensile tests on AISI 304 sheet steel specimens, and their predictions correlate well with the experimental evidence in terms of macroscopic stress–strain curves and martensite volume fraction formed at high strain rates. The work shows the value of considering temperature effects in the modeling of metastable austenitic steels submitted to impact conditions. Regarding most of the works reported in the literature on SIMT, modeling of the martensitic transformation at high strain rates is the distinctive feature of the present paper.The researchers of the University Carlos III of Madrid are indebted to the Comunidad Autónoma de Madrid (Project CCG10-UC3M/DPI-5596)) and to the Ministerio de Ciencia e Innovación de España (Project DPI/2008-06408) for the financial support received which allowed conducting part of this work. The authors express their thanks to Mr. Philippe and Mr. Tobisch from the company Zwick for the facilities provided to perform the tensile tests at high strain rates

A constitutive model for analyzing martensite formation in austenitic steels deforming at high strain rates

This study presents a constitutive model for steels exhibiting SIMT, based on previous seminal works, and the corresponding methodology to estimate their parameters. The model includes temperature effects in the phase transformation kinetics, and in the softening of each solid phase through the use of a homogenization technique. The model was validated with experimental results of dynamic tensile tests on AISI 304 sheet steel specimens, and their predictions correlate well with the experimental evidence in terms of macroscopic stress–strain curves and martensite volume fraction formed at high strain rates. The work shows the value of considering temperature effects in the modeling of metastable austenitic steels submitted to impact conditions. Regarding most of the works reported in the literature on SIMT, modeling of the martensitic transformation at high strain rates is the distinctive feature of the present paper.The researchers of the University Carlos III of Madrid are indebted to the Comunidad Autónoma de Madrid (Project CCG10-UC3M/DPI-5596)) and to the Ministerio de Ciencia e Innovación de España (Project DPI/2008-06408) for the financial support received which allowed conducting part of this work. The authors express their thanks to Mr. Philippe and Mr. Tobisch from the company Zwick for the facilities provided to perform the tensile tests at high strain rates

Rhodium and Iridium complexes with a new scorpionate phosphane ligand

A straightforward synthesis of a new hybrid scorpionate ligand [(allyl)2B(CH2PPh2)(Pz)]− ([A2BPN]−) is reported. Coordination to rhodium resulted in square-planar complexes [Rh(κ2-A2BPN)(L)(L′)] [L = L′ = 1/2cod (1,5-cyclooctadiene), CNtBu, CO (6); L = CO, L′ = NH3, pyridine, PPh3, PMe3] for which spectroscopic data and the molecular structure of [Rh(κ2-A2BPN)(CO)PPh3] (11) indicate the ligand to be κN,κP-bound to rhodium with two dangling free allyl groups. Studies in solution point out that the six-membered Rh–N–N–B–C–P metallacycle undergoes a fast inversion in all of them. The bis(carbonyl) complex 6 easily loses a CO group to give [{Rh(A2BPN)(CO)}2], a dinuclear compound in which two mononuclear subunits are brought together by two bridging allyl groups. Coordination to iridium is dominated by a tripodal κN,κP,η2-C═C binding mode in the TBPY-5 complexes [Ir(κ3-A2BPN)(L)(L′)] [L = L′ = 1/2cod (3), CNtBu (5), CO (7); L = CO, L′ = PPh3 (13), PMe3 (14), H2C═CH2, (17), MeO2CC≡CCO2Me (dmad, 18)], as confirmed by the single-crystal structure determination of complexes 3 and 18. A fast exchange between the two allyl arms is observed for complexes having L = L′ (3, 5, and 7), while those having CO and L ligands (14, 17, and 18) were found to be nonfluxional species. An exception is complex 13, which establishes an equilibrium with the SP-4 configuration. Protonation reactions on complexes 13 and 14 with HCl yielded the hydride complex [Ir(κ2-A2BPN)(CO)(Cl)(H)PPh3] (15) and the C-alkyl compound [Ir{κ3-(allyl)B(CH2CHCH3)(CH2PPh2)(Pz)}(Cl)(CO)PMe3] (16), respectively. The bis(isocyanide) complex 5 reacts with dmad to form [Ir(κ2-A2BPN)(CNtBu)2(dmad)]. On the whole, the electronic density provided to the metal by the [A2BPN]− ligand is very sensitive to the coordination mode. The basicity of the new ligand is similar to that of the TpMe2 ligand in the κN,κP mode but comparable to Tp if coordinated in the κN,κP,η2-C═C mode.This research was supported by the MICINN/FEDER (Project CTQ2011-22516, Spain), Gobierno de Aragón (GA)/FSE (E70), and GA-La Caixa (Grant 2012/GA LC 057). A.L.S. thanks MICINN/FEDER for a fellowship.Peer Reviewe

A constitutive model for analyzing martensite formation in austenitic steels deforming at high strain rates

This study presents a constitutive model for steels exhibiting SIMT, based on previous sem inal works, and the corresponding methodology to estimate their parameters. The model includes temperature effects in the phase transformation kinetics, and in the softening of each solid phase through the use of a homogenization technique. The model was validated with experimental results of dynamic tensile tests on AISI 304 sheet steel specimens, and their predictions correlate well with the experimental evidence in terms of macroscopic stress strain curves and martensite volume fraction formed at high strain rates. The work shows the value of considering temperature effects in the modeling of metastable austen itic steels submitted to impact conditions. Regarding most of the works reported in the lit erature on SIMT, modeling of the martensitic transformation at high strain rates is the distinctive feature of the present paper.The researchers of the University Carlos III of Madrid are indebted to the Comunidad Autónoma de Madrid (Project CCG10 UC3M/DPI 5596)) and to the Ministerio de Ciencia e Innovación de España (Project DPI/2008 06408) for the financial support received which allowed conducting part of this work. The authors express their thanks to Mr. Philippe and Mr. Tobisch from the company Zwick for the facilities provided to perform the tensile tests at high strain rates.Publicad

Optimization of Components of Superstructure of High-Speed Rail: The Spanish Experience

The performance of rail transport has increased significantly in recent decades, in particular due to the gradual introduction of high-speed rails worldwide. In 1981, the first high-speed line of the world was inaugurated; nowadays, high-speed is operating in more than 20 countries, the high-speed network covering more than 35,000 kms (with more than 25,000 additional kms under construction). Spain is the second country by total distance of railways installed (only behind China) and the first in terms relative to the population and surface. Since the installation of the first high-speed line in Spain in 1992, the elements of the superstructure have undergone a continuous evolution, in order to improve the performance, the durability of the components and the comfort of the passengers. This evolution rests on an adequate selection of materials based on the characterization of their physical and mechanical properties to ensure the optimum in-service conditions. This chapter includes an overview of the different elements present in the railway superstructure of the high-speed lines in Spain. Throughout the text, the innovations incorporated over time are analyzed, as well as the methods used to validate them. In particular, a description of the mechanical characterization procedures is presented

General approach for dealing with dynamical systems with spatiotemporal periodicities

Dynamical systems often contain oscillatory forces or depend on periodic potentials. Time or space periodicity is reflected in the properties of these systems through a dependence on the parameters of their periodic terms. In this paper we provide a general theoretical framework for dealing with these kinds of systems, regardless of whether they are classical or quantum, stochastic or deterministic, dissipative or nondissipative, linear or nonlinear, etc. In particular, we are able to show that simple symmetry considerations determine, to a large extent, how their properties depend functionally on some of the parameters of the periodic terms. For the sake of illustration, we apply this formalism to find the functional dependence of the expectation value of the momentum of a Bose-Einstein condensate, described by the Gross-Pitaewskii equation, when it is exposed to a sawtooth potential whose amplitude is periodically modulated in time. We show that, by using this formalism, a small set of measurements is enough to obtain the functional form for a wide range of parameters. This can be very helpful when characterizing experimentally the response of systems for which performing measurements is costly or difficult.This work has been supported by through Grants No. MTM2012-36732-C03-03 (R.A.N.), No. FIS2011-24540 (N.R.Q.), and PRODIEVO (J.A.C.), from the Ministerio de Economía y Competitividad (Spain), Grants No. FQM262 (R.A.N.), No. FQM207 (N.R.Q.), and Nos. FQM-7276 and P09-FQM-4643 (N.R.Q., R.A.N.), from the Ministerio de Ciencia e Innovación of Spain, Grant No. FIS2008-02873 (J.C.-P.), from Junta de Andalucía (Spain), and from the Alexander von Humboldt-Stiftung, Germany, through Research Fellowship for Experienced Researchers SPA, Grant No. 1146358 STP (N.R.Q.).Publicad

Two-state theory of nonlinear Stochastic Resonance

An amenable, analytical two-state description of the nonlinear population dynamics of a noisy bistable system driven by a rectangular subthreshold signal is put forward. Explicit expressions for the driven population dynamics, the correlation function (its coherent and incoherent part), the signal-to-noise ratio (SNR) and the Stochastic Resonance (SR) gain are obtained. Within a suitably chosen range of parameter values this reduced description yields anomalous SR-gains exceeding unity and, simultaneously, gives rise to a non-monotonic behavior of the SNR vs. the noise strength. The analytical results agree well with those obtained from numerical solutions of the Langevin equation.Comment: 4 pages, 1 figur

Dynamical Systems with Spatiotemporal Periodicities through the Symmetries

Ministerio de Economía, Industria y Competitividad FIS2014-54497-P, MTM2015-65888-C4-1-

Activity Patterns of Stenocercus iridescens in an Ecuadorian Coastal Agroecosystem: Is Temperature Important?

Circadian rhythms of Neotropical lizards have been poorly studied, which represents a problem when designing ecological studies or monitoring such species based on direct observations. In this work, 1000 m-long transects were established in an agroecosystem area of the Ecuadorian coast region to study the activity patterns of Stenocercus iridescens. The number of individuals (as a response variable) was correlated with local weather conditions: temperature, precipitation, and heliophany (duration of the solar brightness). We carried out the study in both dry and rainy seasons, and during different time ranges. The time range in which the transects were performed was the most important predictor, and the activity peak was established between 16:00 h and 18:00 h. Heliophany negatively affected lizard activity, but only on the days with higher heliophany during the dry season, whereas temperature was not a significant predictor. Our results suggest that in an area where temperature is relatively constant and the solar radiation is high, particularly during the dry season, the heliophany (an indirect measure of solar radiation) can affect ectotherm activity patterns more than temperature, particularly in open habitats such as agroecosystems

The potential of microextraction techniques for the analysis of bioactive compounds in food

For a long time, the importance of sample preparation and extraction in the analytical performance of the most diverse methodologies have been neglected. Cumbersome techniques, involving high sample and solvent volumes have been gradually miniaturized from solid-phase and liquid-liquid extractions formats and microextractions approaches are becoming the standard in different fields of research. In this context, this review is devoted to the analysis of bioactive compounds in foods using different microextraction approaches reported in the literature since 2015. But microextraction also represents an opportunity to mitigate the environmental impact of organic solvents usage, as well as lab equipment. For this reason, in the recent literature, phenolics and alkaloids extraction from fruits, medicinal herbs, juices, and coffee using different miniaturized formats of solid-phase extraction and liquid-liquid microextraction are the most popular applications. However, more ambitious analytical limits are continuously being reported and emergent sorbents based on carbon nanotubes and magnetic nanoparticles will certainly contribute to this trend. Additionally, ionic liquids and deep eutectic solvents constitute already the most recent forefront of innovation, substituting organic solvents and further improving the current microextraction approaches.info:eu-repo/semantics/publishedVersio