Modelado de grieta y estimación de vida en Fretting Fatiga mediante el Método de los Elementos Finitos Extendido X-FEM

El Método de los Elementos Finitos (MEF) ha sido y es uno de los métodos numéricos más utilizados para la estimación de parámetros caracterizantes en Mecánica de la Fractura. En el caso de la Mecánica de la Fractura Elástico-Lineal (MFEL), existe una gran cantidad de métodos que permiten estimar el factor de intensidad de tensiones K (o equivalentemente, la tasa de liberación de energía G) a partir de un análisis de elementos finitos (EF). Este tipo de análisis ha permitido estudiar la propagación de grieta en fase II y la estimación de vida. En los últimos años la aplicación del método de elementos finitos (X-FEM) ha demostrado ser una herramienta muy eficaz para el modelado numérico de grietas en MFEL, donde proporciona beneficios significativos en la elaboración de modelos numéricos de propagación de grietas. Las principales ventajas son que la malla de elementos finitos no necesita ajustarse a los límites de la grieta para modelar la discontinuidad geométrica, y, además, la regeneración de la malla no es necesaria en las simulaciones de crecimiento de la grieta. Por lo tanto, una única malla, que a menudo se genera con facilidad, puede ser utilizada para cualquier longitud de grieta y orientación. Las aportaciones realizadas en esta Tesis están relacionadas con tres aspectos: el modelado del contacto con fricción de caras de grieta con X-FEM, el modelado de la orientación de propagación en fretting fatiga en casos de contacto completo y la estimación de vida, también en contacto completo. En estos dos últimos casos se ha realizado una correlación con los resultados obtenidos mediante ensayos experimentales. En ciertos problemas de fatiga se pueden presentar situaciones de contacto entre caras de grieta a lo largo del ciclo, y por tanto, las grietas experimentan procesos de cierre con contacto entre sus caras. En esta Tesis se utiliza una formulación integral para establecer el contacto entre los segmentos de caras de grieta dentro de cada elemento.Sabsabi ., M. (2010). Modelado de grieta y estimación de vida en Fretting Fatiga mediante el Método de los Elementos Finitos Extendido X-FEM [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/7521Palanci

Equilibrium and dynamic behaviour of (weakly) interacting assemblies of magnetic nanoparticles

A still open issue related with the study of assemblies of magnetic nanoparticles, deposited on a substrate or embedded in a matrix, is that of the interplay between intrinsic features of the nanoparticles pertaining to their finite-size and boundary effects, and the collective effects entailed by their mutual interactions and their interactions with the hosting matrix or substrate. In this work we develop a semi-analytical approach that allows us to derive expressions for the magnetization and the susceptibility of interacting assemblies of single-domain ferromagnetic nanoparticles. We find that upon tuning the physical parameters pertaining to each nanoparticle or the shape of the assembly and its spatial arrangement, surface and inter-particle interactions may be set up to play additive or competitive roles leading to assemblies with optimal magnetic properties

Structural Performance of Ordinary and Laminated Glass during Fire Exposure

Façade and glazing elements constitute the skin of buildings. They are the interface between the inside and outside environment. Glass has low fire resistance and can quickly break during fire events. This creates new vents, which increase the oxygen supply and promote the flashover phenomenon. Existing methods for evaluating the structural fire safety of glass require expensive experimental tests or extensive knowledge of finite element (FE) modeling. This research provides simplified, rational, and reliable methods to assess the behavior of ordinary and laminated glass panels during fire exposure. The proposed methods provide the means to determine the glass temperature and its maximum thermal stress during fire exposure. These methods can be utilized by structural engineers, while designing buildings using performance-based design criteria

Interplay between surface anisotropy and dipolar interactions in an assembly of nanomagnets

We study the interplay between the effects of surface anisotropy and dipolar interactions in monodisperse assemblies of nanomagnets with oriented anisotropy. We derive asymptotic formulas for the assembly magnetization, taking into account temperature, applied field, core and surface anisotropy, and dipolar interparticle interactions. We find that the interplay between surface anisotropy and dipolar interactions is well described by the analytical expression of the assembly magnetization derived here: the overall sign of the product of the two parameters governing the surface and the dipolar contributions determines whether intrinsic and collective terms compete or have synergistic effects on the magnetization. This is illustrated by the magnetization curves of γ-Fe2O3 nanoparticle assemblies in the low concentration limit

A simple thermodynamical witness showing universality of macroscopic entanglement

We show that if the ground state entanglement exceeds the total entropy of a given system, then this system is in an entangled state. This is a universal entanglement witness that applies to any physical system and yields a temperature below which we are certain to find some entanglement. Our witness is then applied to generic bosonic and fermionic many body systems to derive the corresponding "critical" temperatures that have a very broad validity.Comment: 3 pages, Torun conference, June 25-28, 200

Development of Laser-Induced Breakdown Spectroscopy (LIBS) for Nuclear Safety Inspections and Pharmaceutical Process Analytical Chemistry Applications

NRC publication: Ye

Simplified structural analysis of framed ordinary non-tempered glass panels during fire exposure

Ordinary non-tempered glass is one of the most widely used materials in the construction industry. Knowing its fire resistance is essential to ensure the safety of emergency personnel as its failure increases the oxygen supply and causes a rapid spread of the fire (flashover phenomenon). Existing approaches for evaluating the structural fire safety of glass façades require expensive experimental tests and/or extensive knowledge of Finite Element modeling. This paper provides a simplified, rational, and reliable approach to assess the structural capacity of ordinary glass panels during fire exposure. A simplified method is developed to predict the temperature difference between the edge and the center of the glass panel. Afterward, a method, based on strain-equilibrium, is developed to predict the corresponding maximum thermal stress. The developed methods are validated by comparisons with experimental work by others

Direction of crack propagation in a complete contact fretting-fatigue problem

In this work, the orientation and propagation of a crack in a fretting fatigue problem is analyzed numerically and correlated experimentally. The analysis is performed using a 2D model of a complete-contact fretting problem, consisting of two square indenters pressed onto a specimen subjected to cyclic fatigue. For the simulation, we use the extended finite element method (X-FEM), allowing for crack face contact during the corresponding parts of the fatigue cycle. The problem is highly non-linear and non-proportional and an orientation criterion is introduced to predict the crack direction in each step of the crack growth simulation. It is shown that the proposed criterion predicts crack orientation directions that are in good agreement with those found experimentally, in contrast to the directions found by application of conventional orientation criteria used in LEFM, such as the MTS criterion.The authors gratefully acknowledge the financial support given by the SGPI of the Spanish Ministry of Economics and Competitiveness (Projects DPI2007-66995-C03-02 and DPI2010-20990). The support of the Generalitat Valenciana, Programme PROMETEO 2012/023, is also acknowledged. The authors thank the collaboration of Mr. Pere Dasi Rodriguez.Giner Maravilla, E.; Sabsabi, M.; Ródenas García, JJ.; Fuenmayor Fernández, FJ. (2014). Direction of crack propagation in a complete contact fretting-fatigue problem. International Journal of Fatigue. 58:172-180. https://doi.org/10.1016/j.ijfatigue.2013.03.001S1721805

Fretting fatigue life prediction using the extended finite element method

In this work, fretting fatigue tests available in the literature are modeled using the extended finite element method (XFEM). The aim is to numerically evaluate the stress intensity factors (SIFs) for cracks of different lengths emanating at the end of the contact zone and to estimate the propagation life corresponding to each of the tests. This propagation life is combined with the initiation life calculated analytically using a multiaxial fatigue criterion (Fatemi-Socie), following a initiation-propagation approach for life estimation. The predicted lives are then compared with the reported experimental lives. It is shown that the consideration of the crack-contact interaction through the numerical models tends to improve the life estimation when compared with a fully analytical approach for the calculation of both initiation and propagation lives.Ministerio de Ciencia y Tecnología DPI2007-66995-C0301Ministerio de Ciencia y Tecnología DPI2007-66995-C03-02

In vitro infection of primary chicken lymphocytes with Marek’s disease virus

Marek’s disease virus (MDV) is a highly oncogenic alphaherpesvirus that infects immune cells and causes a deadly lymphoproliferative disease in chickens. Cytokines and monoclonal antibodies promote the survival of chicken lymphocytes in vitro. Here, we describe protocols for the isolation, maintenance, and efficient MDV infection of primary chicken lymphocytes and lymphocyte cell lines. This facilitates the investigation of key aspects of the MDV life cycle in the primary target cells of viral replication, latency, genome integration, and reactivation. For complete details on the use and execution of this protocol, please refer to Schermuly et al.,1 Bertzbach et al. (2019),2 and You et al.3 For a comprehensive background on MDV, please see Osterrieder et al.4 and Bertzbach et al. (2020).5 Subject areas: Cell Biology, Cell isolation, Cell-based Assays, Microbiolog