Analysis of adiabatic shear banding in orthogonal cutting of Ti alloy

This work is focused on the numerical analysis of adiabatic shear banding in orthogonal cutting of Ti6Al4V alloy. Segmented chip results from adiabatic shear banding, depending on the competition of thermal softening and strain and strain rate hardening. The influence of cutting velocity and feed in the chip segmentation is studied. Also the role of friction at the tool-chip interface and the effect of rheological parameters of the constitutive equation are analyzed. Experimental tests obtained from previous work of the authors [Molinari A, Musquar C, Sutter G, Adiabatic shear banding in high speed machining of Ti-6Al-4V experiments and modeling, Int J Plast, vol. 18, 2002, p. 443-4591 and others were used as a reference to validate the models. Cutting forces and the mechanism of plastic flow localization are analyzed in terms of frequency of segmentation and shear band width and compared to experimental data.The financial support of this work to the Ministry of Economy and Competitiveness of Spain with the project DPI2011-25999 and to the Universidad Carlos III de Madrid —Banco de Santander for the program "Chair ofExcellence". This work was also supported by the French State through the program “Investmentin the future” operated by the NationalResearch Agency (ANR) and referenced byLabEx DAMAS.Publicad

Wobbling kinks and shape mode interactions in a coupled two-component ϕ4\phi^4 theory

The dynamics of a wobbling kink in a two-component coupled $\phi^4$ scalar field theory (with an excited orthogonal shape mode) is addressed. For this purpose, the vibration spectrum of the second order small kink fluctuation is studied in order to find the corresponding vibration modes associated to the first (longitudinal) and second (orthogonal) field components. By means of this analysis, it was found that the number of possible shape modes depends on the value of the coupling constant. It is notable that when one of the orthogonal field shape modes is initially triggered, the unique shape mode of the longitudinal field is also activated. This coupling causes the kink to emit radiation with twice the frequency of excited mode in the first field component. Meanwhile, in the orthogonal channel we find radiation with two different frequencies: one is three times the frequency of the orthogonal wobbling mode and another is the sum of the frequencies of the longitudinal shape mode and the triggered mode. All the analytical results obtained in this study have been successfully contrasted with those obtained through numerical simulations.Comment: 20 pages, 12 figure

La comunidad de coleópteros y hemípteros acuáticos de un arroyo costero cantábrico (norte de España): composición, variación estacional e influencia de los factores ambientales

The aquatic Coleoptera and Hemiptera assemblages have been studied in a short Cantabrian coastal stream (La Llantada, Asturias, North Spain). We aim to know the assemblage composition and to detect the environmental factors that affected it, consideringseasonalchanges(samplings in spring and autumn during two annual cycles). Most(89%)of the identified species (thirty-three of Coleoptera and eleven of Hemiptera) shows a high range distribution. It is remarkable the presence of some Southern species (Hydrochus grandicollis, Dryops striatellus, Velia caprai bertrandi). Chaetarthria simillima (Coleoptera: Hydrophilidae) is recorded for the second time in the Iberian Peninsula. The results show a clear decrease of richness towards the mouth that seems to be related to the decrease of water quality. Seasonal changes of assemblage composition are related to organic pollution, particularly during the months of summer with low rainfall and greater anthropic impact. CCA shows that most species of both groups respond negatively to high nutrient pollution, mainly total nitrogen and ammonium. A small group associated to samples with a high load of nutrients is detected and can be considered tolerant to pollution, for instance the water beetles Hydroporus vagepictus, Stictotarsus duodecimpustulatus, Helophorus minutus, Helophorus brevipalpis and Octhebius dilatatus.Se ha estudiado la comunidad de coleópteros y hemípteros acuáticos en un pequeño arroyo costero cantábrico (La Llantada, Asturias). Se pretende conocer su composición e identificar los factores ambientales que influyen en ella, teniendo en cuenta los cambios estacionales (muestreos en primavera y otoño durante dos años consecutivos). La mayoría (89%) de las 33 especies de coleópteros y 11 de hemípteros identificadas muestran una amplia distribución geográfica. Pese a ello, destaca la presencia de especies meridionales (Hydrochus grandicollis, Dryops striatellus, Velia caprai bertrandi). Se señala el segundo registro ibérico de Chaetarthria simillima (Coleoptera: Hydrophilidae). Los resultados muestran un claro gradiente de disminución de la riqueza hacia la desembocadura del arroyo que parece estar relacionado con el descenso de la calidad del agua. La variación estacional de la composición de la comunidad se ve afectada por el efecto de la contaminación orgánica, especialmente durante los meses de verano, cuando disminuyen las precipitaciones y el impacto antrópico es mayor. El ACC muestra que la mayoría de las especies de ambos grupos responden negativamente a elevadas concentraciones de contaminantes, principalmente nitrógeno total y amonio. Se detecta un pequeño grupo de especies asociadas a muestras con una fuerte carga de nutrientes y que pueden considerarse tolerantes a la contaminación, como los coleópteros Hydroporus vagepictus, Stictotarsus duodecimpustulatus, Helophorus minutus, Helophorus brevipalpis y Ochthebius dilatatus

Numerical modelling of orthogonal cutting: Influence of cutting conditions and separation criterion

6 pages, 5 figures.-- Issue title: "EURODYMAT 2006 - 8th International Conference on Mehanical and Physical Behaviour of Materials under Dynamic Loading" (Dijon, France, Sep 11-15, 2006).Chip formation is a high strain rate process studied with analytical and numerical models. Analytical models have the advantage of a small calculation time, however, they are often based on some assumptions which are difficult to verify. Finite element modelling (FEM) of chip formation process provides more details on the chip process formation, such as plastic strain, strain rate or stress fields. FEM can be used to improve the analytical models' assumptions. There is still a wide dispersion of formulations and numerical parameters adopted in order to obtain accurate results in numerical models. In the Lagrangian approach, it is of crucial importance to establish realistic criteria for element deletion, allowing chip separation from original workpiece. In the arbitrary Lagrangian Eulerian (ALE) formulation no element deletion is needed. This work is focused in modelization of orthogonal cutting. A comparison between both numerical approaches, Lagrangian and ALE is shown. The effects of geometrical parameters, erosion criterion and cutting speed are evaluated. Comparisons between numerical and theoretical results are performed, and the results obtained from the numerical approach are used as an input of analytical model, improving its accuracy."Program of Creation and Consolidation of Research Teams" University Carlos III of Madrid (2005).Publicad

Wobbling kinks in a two-component scalar field theory: Interaction between shape modes

In this paper the interaction between the shape modes of the wobbling kinks arising in the family of two-component MSTB scalar field theory models is studied. The spectrum of the second order small kink fluctuation in this model has two localized vibrational modes associated to longitudinal and orthogonal fluctuations with respect to the kink orbit. It has been found that the excitation of the orthogonal shape mode immediately triggers the longitudinal one. In the first component channel the kink emits radiation with twice the orthogonal wobbling frequency (not the longitudinal one as happens in the $\phi^4$-model). The radiation emitted in the second component has two dominant frequencies: one is three times the frequency of the orthogonal wobbling mode and the other is the sum of the frequencies of the longitudinal and orthogonal vibration modes. This feature is explained analytically using perturbation expansion theories.Comment: 28 pages, 11 figure

Residual stresses in orthogonal cutting of metals: the effect of thermo-mechanical coupling parameters and of friction

21 pages, 13 figures.The generation of residual stresses in orthogonal machining is analysed by using an Arbitrary Lagrangian Eulerian (ALE) finite element approach. It is shown that a substantial level of tensile residual stresses can be obtained in the vicinity of the machined surface without any contribution of thermal effects. This motivates the development of a parametric study to analyse the effects of the thermomechanical coupling parameters on residual stresses. The roles of thermal expansion, of thermal softening and of the Taylor-Quinney coefficient (controlling the heat generated by plastic flow) are considered separately. The influence of friction is also analysed by assuming dry cutting conditions and a Coulomb friction law. The friction coefficient has a complex effect by controlling heat generation (frictional heating) along the tool rake and clearance faces and the propensity for the chip to stick to the tool. Geometrical effects such as the tool rake angle and the tool edge radius are also discussed.The authors are indebted, for the financial support of this work, to the Ministry of Science and Education of Spain (under project DPI2005-08018) and to the Comunidad Autónoma de Madrid and University Carlos III of Madrid (under project CCG07-UC3M/DPI-3396).Publicad

Identifying explanatory factors of bitcoin price with artificial neural networks

This study aims to develop a new model that allows determining with high precision the factors that explain the price of bitcoin. To do this, an extensive database of variables related to bitcoin and artificial neural network techniques has been used. The results obtained have made it possible to identify that aspects related to the number of forum posts, the volume of transactions on the blockchain, and the hash rate provide an excellent strategy for predicting the price of bitcoi

Numerical analysis for design of bioinspired ceramic modular armors for ballistic protections

[EN] The exigent requirements for personal protections in terms of energy absorption and ergonomics have led to increasing interest in bioinspired protections. This work focuses on the numerical analysis of ballistic behavior of different bioinspired geometries under impact loadings. Ceramic armors based on ganoid fish scales (the type exhibited by gars, bichirs and reedfishes), placoid fish scales (characterizing sharks and rays) and armadillo natural protection have been considered. Different impact conditions are studied, including perpendicular and oblique impacts to surface protection, different yaw angle, and multiple impacts. Main conclusion is related to the improved efficiency of modular armors against multiple shots exhibiting more localized damage and crack arrest properties. Moreover, its potential ergonomic is a promising characteristic justifying a deeper study.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work has been carried out within the framework of the research program Juan de la Cierva Incorporacion 2015, and research projects DPI2017-88166-R, and RTC-2015-3887-8 of FEDER program financed by the Ministerio de Economia, Industria y Competitividad of Spain. The support of the Generalitat Valenciana, Programme PROMETEO 2016/007 is also acknowledged.González Albuixech, VF.; Rodríguez-Millán, M.; Ito, T.; Loya, JA.; Miguélez, MH. (2019). Numerical analysis for design of bioinspired ceramic modular armors for ballistic protections. International Journal of Damage Mechanics. 28(6):815-837. https://doi.org/10.1177/1056789518795203S815837286Chen, I. H., Kiang, J. H., Correa, V., Lopez, M. I., Chen, P.-Y., McKittrick, J., & Meyers, M. A. (2011). Armadillo armor: Mechanical testing and micro-structural evaluation. Journal of the Mechanical Behavior of Biomedical Materials, 4(5), 713-722. doi:10.1016/j.jmbbm.2010.12.013Chintapalli, R. K., Mirkhalaf, M., Dastjerdi, A. K., & Barthelat, F. (2014). Fabrication, testing and modeling of a new flexible armor inspired from natural fish scales and osteoderms. Bioinspiration & Biomimetics, 9(3), 036005. doi:10.1088/1748-3182/9/3/036005Deka, L. J., Bartus, S. D., & Vaidya, U. K. (2009). Multi-site impact response of S2-glass/epoxy composite laminates. Composites Science and Technology, 69(6), 725-735. doi:10.1016/j.compscitech.2008.03.002Duro-Royo, J., Zolotovsky, K., Mogas-Soldevila, L., Varshney, S., Oxman, N., Boyce, M. C., & Ortiz, C. (2015). MetaMesh: A hierarchical computational model for design and fabrication of biomimetic armored surfaces. Computer-Aided Design, 60, 14-27. doi:10.1016/j.cad.2014.05.005Flores-Johnson, E. A., Shen, L., Guiamatsia, I., & Nguyen, G. D. (2014). Numerical investigation of the impact behaviour of bioinspired nacre-like aluminium composite plates. Composites Science and Technology, 96, 13-22. doi:10.1016/j.compscitech.2014.03.001Grujicic, M., Pandurangan, B., & Coutris, N. (2011). A Computational Investigation of the Multi-Hit Ballistic-Protection Performance of Laminated Transparent-armor Systems. Journal of Materials Engineering and Performance, 21(6), 837-848. doi:10.1007/s11665-011-0004-3Grunenfelder, L. K., Suksangpanya, N., Salinas, C., Milliron, G., Yaraghi, N., Herrera, S., … Kisailus, D. (2014). Bio-inspired impact-resistant composites. Acta Biomaterialia, 10(9), 3997-4008. doi:10.1016/j.actbio.2014.03.022Klasztorny, M., & Świerczewski, M. (2015). NUMERICAL MODELLING AND VALIDATION OF 12.7 MM FSP IMPACT INTO ALFC SHIELD – ARMOX 500T STEEL PLATE SYSTEM. Journal of KONES. Powertrain and Transport, 19(4), 291-299. doi:10.5604/12314005.1138463Liu, P., Zhu, D., Yao, Y., Wang, J., & Bui, T. Q. (2016). Numerical simulation of ballistic impact behavior of bio-inspired scale-like protection system. Materials & Design, 99, 201-210. doi:10.1016/j.matdes.2016.03.040Morka, A., & Nowak, J. (2015). NUMERICAL ANALYSES OF CERAMIC/METAL BALLISTIC PANELS SUBJECTED TO PROJECTILE IMPACT. Journal of KONES. Powertrain and Transport, 19(4), 465-472. doi:10.5604/12314005.1138618Pandya, K., Kumar, C. V. S., Nair, N., Patil, P., & Naik, N. (2014). Analytical and experimental studies on ballistic impact behavior of 2D woven fabric composites. International Journal of Damage Mechanics, 24(4), 471-511. doi:10.1177/1056789514531440Poniżnik, Z., Nowak, Z., & Basista, M. (2015). Numerical modeling of deformation and fracture of reinforcing fibers in ceramic–metal composites. International Journal of Damage Mechanics, 26(5), 711-734. doi:10.1177/1056789515611945Porter, M. M., Ravikumar, N., Barthelat, F., & Martini, R. (2017). 3D-printing and mechanics of bio-inspired articulated and multi-material structures. Journal of the Mechanical Behavior of Biomedical Materials, 73, 114-126. doi:10.1016/j.jmbbm.2016.12.016Reaugh, J. E., Holt, A. C., Welkins, M. L., Cunningham, B. J., Hord, B. L., & Kusubov, A. S. (1999). Impact studies of five ceramic materials and pyrex. International Journal of Impact Engineering, 23(1), 771-782. doi:10.1016/s0734-743x(99)00121-9Rostamiyan, Y., & Ferasat, A. (2016). High-speed impact and mechanical strength of ZrO2/polycarbonate nanocomposite. International Journal of Damage Mechanics, 26(7), 989-1002. doi:10.1177/1056789516644312Russell, B. P. (2014). Multi-hit ballistic damage characterisation of 304 stainless steel plates with finite elements. Materials & Design, 58, 252-264. doi:10.1016/j.matdes.2014.01.074Serjouei, A., Chi, R., Sridhar, I., & Tan, G. E. B. (2015). Empirical Ballistic Limit Velocity Model for Bi-Layer Ceramic–Metal Armor. International Journal of Protective Structures, 6(3), 509-527. doi:10.1260/2041-4196.6.3.509Shaktivesh, Nair, N., & Naik, N. (2014). Ballistic impact behavior of 2D plain weave fabric targets with multiple layers: Analytical formulation. International Journal of Damage Mechanics, 24(1), 116-150. doi:10.1177/1056789514524074Yang, W., Chen, I. H., Gludovatz, B., Zimmermann, E. A., Ritchie, R. O., & Meyers, M. A. (2012). Natural Flexible Dermal Armor. Advanced Materials, 25(1), 31-48. doi:10.1002/adma.20120271

Programa de Conservación del Merino Negro: Caracterización de la aptitud productiva y valoración genética para caracteres de crecimiento

A pesar de que el merino negro como miembro del tronco merino nativo español, ha sufrido la mayoría de los vaivenes del merino blanco, no ha existido paralelismo en la evolución de los censos de ambas poblaciones a lo largo de la historia, principalmente debido al color de su fibra. En la actualidad está considerada una raza en peligro de extinción. Dentro de las actuaciones llevadas a cabo por la Asociación Nacional de Criadores para su conservación in situ, y en el ámbito del proyecto de investigación lNIA (RZ- 2004-00024), se ha realizado el control productivo de 170 corderos hijos de 5 moruecos pertenecientes al Censyra de Extremadura (Badajoz) que fueron sometidos a prueba de descendencia. Se realizaron 4 pesadas por cordero desde el nacimiento hasta el sacrificio (edad media 75 días). La ganancia media diaria osciló en el caso de los machos entre los 0,223 Kg. (ganancia en el primer mes de vida) hasta los 0,265 Kg. (en la última fase del cebo) y los 0,195 Kg. a 0,221 Kg. en los mismos periodos para las hembras. Esto determinó que los pesos medios obtenidos fueron en todos los casos estadísticamente menores a los del merino blanco que se controla dentro del Esquema de Selección de la raza (alrededor de 1 Kg. de media a los 30 días de edad, y 2 kgs. al final del cebo). Esto justifica en parte la situación en la que se encuentra actualmente esta raza. No obstante consideramos que las diferencias detectadas son más bien un reflejo de la diferente historia selectiva de ambas razas en la última década. Finalmente se ha realizado la primera valoración genética de esta raza empleando la metodología BLUP modelo animal para caracteres de crecimiento utilizando para ello los mismos parámetros y modelo que el merino blanco, contando en la actualidad con el valor genético de 898 animales para 4 caracteres de crecimiento (gmd hasta los 30 días y de 30 a los 75 dias, peso a los 3O y 75 días), y la calificación morfológica

Membership duration in a Spanish Union : a survival analysis

This article presents an analysis of the characteristics that are associated with union membership duration using data from the membership registers of the largest Spanish trade union: Comisiones Obreras (CCOO, Workers' Commissions). Making use of survival analysis techniques, the results indicate that the shortest membership durations and the highest risks of leaving are associated with workers with poor employment conditions, mainly youth and foreigners, as well as those in firms, economic sectors, and territories where the union has a rather weak presence. As workers in these situations represent the majority of both current joining and leaving rates, the article concludes that retention policies should focus on the early stages of union membership