A thermo-viscoplastic constitutive model for FCC metals with application to OFHC copper

In this paper a physical-based constitutive relation for defining the thermo-viscoplastic behaviour of FCC metals with dependence on strain on thermal activation processes is presented. The model, based on previous considerations reported by Rusinek and Klepaczko [Rusinek A, Klepaczko JR. Shear testing of sheet steel at wide range of strain rates and a constitutive relation with strain-rate and temperature dependence of the flow stress. Int J Plasticity 2001;17:87-115], is founded on physical aspects of the material behaviour. The proposed constitutive relation is applied to define the behaviour of oxygen-free high conductivity (OFHC) copper using the experimental data reported in Nemat-Nasser and Li [Nemat-Nasser S, Li Y. Flow stress of FCC polycrystals with application to OFHC copper. Acta Mater 1998;46:565-77]. The description of the material behaviour provided by the model gets satisfactory agreement with the experiments. The analytical predictions of this constitutive description are compared with those obtained from the models due to Voyiadjis and Almasri [Voyiadjis GZ, Almasri AH. A physically based constitutive model for fcc metals with applications to dynamic hardness. Mech Mater 2008;40:549-63], and Nemat-Nasser and Li. This comparison reveals that the original formulation proposed in this paper is a suitable alternative to other physically based relations for modeling OFHC copper.The researchers of the University Carlos III of Madrid are indebted to the Comunidad Autónoma de Madrid (ProjectCCG08UC3M/MAT4464) and to the Ministerio de Ciencia e Innovación de España (ProjectDPI/200806408)Publicad

Numerical simulations of impact behaviour of thin steel plates subjected to cylindrical, conical and hemispherical non-deformable projectiles

In this paper, a numerical study of normal perforation of thin steel plates impacted by different projectile shapes is reported. The numerical simulations of this problem have been performed using a finite element code, ABAQUS-Explicit with a fixed and an adaptive mesh for the plate. To define the thermoviscoplastic behaviour of the material constituting the plate, the Johnson-Cook model has been used. This homogeneous behaviour has been coupled with the Johnson-Cook fracture criterion to predict completely the perforation process. Three kinds of projectile shape (blunt, conical and hemispherical) have been simulated with a large range of impact velocities from 190 to 600 m/s. The analysis considers the influence of adiabatic shear bands, plastic work and the gradient of temperature generated in the plate. The numerical results predict correctly the behaviour projectile-plate in agreement with experimental data published by other authors.Publicad

Thermo-viscoplastic behaviour of 2024-T3 aluminium sheets subjected to low velocity perforation at different temperatures

This paper deals with the mechanical behaviour of the aluminium alloy 2024-T3. This alloy has particular relevance since it is widely used in the aeronautical industry for building aircraft structures. The deformation behaviour of this material has been characterised in tension under wide ranges of strain rate and temperature. Among the aluminium alloys, the AA 2024-T3 highlights due to its high flow stress and strain hardening. Moreover, the material temperature sensitivity has been found dependent on plastic strain. The Modified Rusinek-Klepaczko constitutive description [Rusinek A, Rodriguez-Martinez JA, Arias A. A thermo-viscoplastic constitutive model for FCC metals with application to OFHC copper. Int. J. Mech. Sci. 52 (2010) 120-135], which takes into account such dependence of the temperature sensitivity on plastic strain, has been applied for modelling the thermo-viscoplastic response of the material. Satisfactory agreement between experiments and analytical predictions provided by the Modified Rusinek-Klepaczko model has been found. In order to study the material behaviour under impact loading, low velocity perforation tests on AA 2024-T3 sheets have been performed at different initial temperatures using a drop weight tower. Plastic instabilities formation and progression are identified as the cause behind the target collapse for all the impact tests conducted. The results from these perforation tests are compared with those reported in [Rodriguez-Martinez JA, Pesci R, Rusinek A, Arias A, Zaera R, Pedroche DA. Thermo-mechanical behaviour of TRIP 1000 steel sheets subjected to low velocity perforation by conical projectiles at different temperatures. Int. J. Solids Struct. 47 (2010) 1268-1284.] for TRIP 1000 steel sheets. The comparison reveals that the amount of specific energy absorbed by the aluminium targets is much lower than that corresponding to the steel targets. The role played by inertia on delaying plastic instabilities formation is determined as potential responsible for such behaviour.Publicad

A dislocation-based constitutive description for modeling the behavior of FCC metals within wide ranges of strain rate and temperature

In this work a dislocation based constitutive description for modeling the thermo visco plastic behavior of FCC metals has been developed. The constitutive description, which is founded on the concepts of thermal activation analysis and dislocation dynamics, assumes the plastic flow additively decomposed into internal stress and effective stress. The internal stress represents the applied stress required for the transmission of plastic flow between the polycrystal grains and it is defined by the Hall Petch relationship. The effective stress formulation, which is the main innovative feature of this work, represents the thermally activated deformation behavior. This is defined taking into account the interrelationship between strain rate and temperature, and gathers structural evolution dependence. This structural evolution is described as a function of dislocations density, which acts as internal state variable in the material deformation behavior. A systematic procedure for identifica tion of the material parameters is developed and the model is applied to define the behav ior of annealed OFHC copper. The analytical predictions of the constitutive description are compared with the experimental data reported by Nemat Nasser and Li (Nemat Nasser, S., Li, Y., (1998). Flow stress of FCC polycrystals with application to OFHC Copper. Acta Mater. 46, 565 577). Good correlation between experiments and analytical predictions is found within wide ranges of strain rate and temperature.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 conduct ing part of this work.Publicad

The deterministic nature of the fracture location in the dynamic tensile testing of steel sheets

This paper investigates the key mechanisms which determine the fracture location in the dynamic tensile testing of steel sheets. For that purpose we have conducted experiments and finite element simulations. Experiments have been performed using samples with six different gauge lengths, ranging from 20 mm to 140 mm, that have been tested within a wide spectrum of loading velocities, ranging from 1 m/s to 7.5 m/s. Three are the key outcomes derived from the tests: (1) for a given gauge length and applied velocity, the repeatability in the failure location is extremely high, (2) there is a strong interplay between applied velocity, gauge length and fracture location and (3) multiple, and largely regular, localization patterns have been observed in a significant number of the experiments performed using the samples with the shorter gauge lengths. Our experimental findings are explained using the finite element simulations. On the one hand, we have shown that variations in the applied velocity and the gauge length alter the processes of reflection and interaction of waves taking place in the sample during the test, which leads to the systematic motion of the plastic localization along the gauge (as experimentally observed). On the other hand, we have detected that the emergence of multiple localization patterns requires short and equilibrated specimens with uniform stress and strain distributions along the gauge. We conclude that the experimental and numerical results presented in this paper show that, in the absence of significant material and/or geometrical defects, the location of plastic strain localization in the dynamic tensile test is deterministic.The authors are indebted to the Ministerio de Ciencia e Innovación de España (Project DPI/2011-24068) for the financial support received which allowed conducting this work.Publicad

Análisis del juego de ataque en balonmano femenino

.- This study focuses on the specific organization of the attacking strategies in women's handball. In particular, we explore the specific weight of the two possible modalities of attack: positional and counterattack. To do so, during the 2008/2009 season, we have analyzed through a systematic observation methodology, direct and non-participant, the matches of a team that plays in the First Division of Women's Handball. To determine the rates of effectiveness, we have studied more than 2000 attacks and 900 throws on goal. Statistical analysis revealed that counterattack is more effective than positional play, and that it has a closer relationship with victory.Este estudio examinó la específica organización del juego de ataque en balonmano femenino. En concreto, hemos explorando el peso específico de los dos posibles tipos de ataque: posicional y contraataque. Para ello, hemos analizado los partidos de un mismo equipo de División de Honor Femenina durante la temporada 2008/2009 mediante metodología de la observación sistemática, directa y no participante. Hemos estudiado más de 2000 jugadas de ataque y 900 lanzamientos a portería, determinando de esta manera los índices de efectividad. El análisis estadístico reveló que existe una mayor eficacia del contraataque frente al juego posicional, además de una mayor relación con la victoria final

Meta-evaluation of ESO in the Canary Islands in early xxi century: proposals

El Departamento de Psicología y Sociología de la ULPGC ha llevado a cabo recientemente la investigación titulada: «Metaevaluación de la ESO en Canarias: análisis y propuestas», en este artículo se muestran algunas conclusiones. El objetivo principal fue conocer la práctica real de la evaluación en un sentido amplio: del rendimiento del alumnado, de la práctica docente, de la evaluación, la atención a la diversidad, etc. El diseño es el de una investigación descriptiva; como herramienta principal utilizamos un Cuestionario que se envió a los 250 centros del Archipiélago que imparten dicha etapa, además de entrevistas a expertos y usuarios de dicha evaluación. Asimismo analizamos la evaluación en tres países de la CE a través de entrevistas con sus Equipos Directivos, seleccionamos tres centros extranjeros en Gran Canaria: inglés, francés y alemán.The Psychology and Sociology Department of the University of Las Palmas de Gran Canaria (ULPGC) has recently developed an investigation named: «Meta-evaluation of ESO in the Canary Islands: analysis and proposals», herein we include the conclusions of this investigation. The main aim of this investigation was to discover the assessment in its broad meaning: pupils’ performance, teaching, attention to diversity, etc. Its design is from a descriptive investigation and as a main tool we used a questionnaire sent to the 250 schools that teach ESO in the archipelago. Also interviewed experts and users of this assessment method. Besides, we analysed the assessment in three countries of the European Union as we interviewed the headmaster and chief of studies of three foreign schools: an English school, a French school and a German school

Experimental Study on the Perforation Process of 5754-H111 and 6082-T6 Aluminium Plates Subjected to Normal Impact by Conical, Hemispherical and Blunt Projectiles

This paper presents an experimental investigation on the perforation behaviour of 5754-H111 and 6082-T6 aluminium alloys. The mechanical response of these materials has been characterized in compression with strain rates in the range of . Moreover, penetration tests have been conducted on 5754-H111 and 6082-T6 plates of thickness using conical, hemispherical and blunt projectiles. The perforation experiments covered impact velocities in the range of . The initial and residual velocities of the projectile were measured and the ballistic limit velocity obtained for the two aluminium alloys for the different nose shapes. Failure mode and post-mortem deflection of the plates have been examined and the perforation mechanisms associated to each projectile/target configuration investigated. It has been shown that the energy absorption capacity of the impacted plates is the result of the collective role played by target material behaviour, projectile nose shape and impact velocity in the penetration mechanisms.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/2011-24068) for the financial support received which allowed conducting part of this work

An evaluation framework to support optimisation of scenarios for energy efficient retrofitting of buildings at the district level

Producción CientíficaEnergy-efficient retrofitting of buildings has become essential to achieve the environmental objectives of the European Union’s (EU) strategies towards reducing carbon emissions and energy dependency on fossil fuels. When tackling retrofitting projects, the issue of scale becomes essential as sometimes this can determine the sustainability of the project. Therefore, a comprehensive approach is essential to ensure effective decision-making. A platform has been designed within the EU funded OptEEmAL project to support stakeholders in this process, providing functionalities that can automatically model and evaluate candidate retrofitting alternatives considering their priorities, targets and boundary conditions. A core element of this platform is the evaluation framework deployed which implements a multi-criteria decision-making approach to transform the priorities of stakeholders into quantifiable weights used to compare the alternatives. As a result, more informed decisions can be made by the stakeholders through a comprehensive evaluation of the candidate retrofitting scenarios. This paper presents the approach followed to develop and integrate this evaluation framework within the platform as well as its validation in a controlled environment to ensure its effectiveness

Mecanismos de fallo en placas de acero sometidas a impacto de proyectiles cilíndricos, cónicos y hemisféricos

6 pages, 14 figures.-- Contributed to: "XXV Encuentro del Grupo Español de Fractura" (Sigüenza, Spain, Mar 5-7, 2008).[EN] In this work a numerical study is presented of the behaviour of Weldox 460 E steel plates of 12 mm thickness subjected to perpendicular impact of rigid projectiles of different nose shapes: cylindrical, hemispherical and conical. The numerical simulations have been carried out using the FE commercial code ABAQUS/Explicit. The validation of the numerical results using experimental results available in the international literature has been done considering failure time, ballistic limit and the energy absorbed by the plate. In order to evaluate the influence of the thermoviscoplastic material behaviour on the results obtained, two different constitutive relations have been compared: Johnson-Cook and Rusinek-Klepaczko.[ES] En este trabajo se presenta un análisis numérico del comportamiento de placas de acero Weldox 460 E de 12 mm de espesor sometidas al impacto normal de proyectiles rígidos de diferentes geometrías: cilíndrica, hemisférica y cónica. Las simulaciones numéricas se han llevado a cabo utilizando el código comercial de elementos finitos ABAQUS/Explicit. La validación de los resultados numéricos con los datos experimentales disponibles en la bibliografía se ha realizado considerando el tiempo de fractura, el límite balístico y la energía absorbida por la placa. Para evaluar la influencia de la definición del comportamiento termoviscoplástico del material en los resultados obtenidos, se han empleado dos ecuaciones constitutivas: Johnson-Cook y Rusinek-Klepaczko.Los investigadores de la Universidad Carlos III de Madrid desean agradecer al Ministerio de Educación (proyecto DPI2005-06769) y a la Comunidad Autónoma de Madrid (proyecto CCG06-UC3M/DPI-0796) el soporte económico que ha permitido la realización de este trabajo. Los investigadores de la Universidad Paul Verlaine de Metz (LPMM) desean agradecer el soporte financiero recibido del CNRS-France.Publicad