A semi-analytical matrix formalism for stress singularities in anisotropic multi-material corners with frictional boundary and interface conditions

A new general semi-analytic procedure for the characterisation of singular asymptotic elastic states in the vicinity of the apex of linearly elastic anisotropic multi-material corners, including frictional contact, is developed and tested. The corners can consist of any finite number of homogeneous wedges defined by polar sectors. The variability of configurations covered is enormous as frictional contact can be considered on one or more outer boundary surfaces or interfaces, in addition to a large variety of homogeneous boundary conditions and perfect bonding or frictionless sliding interface conditions between wedges in the corner. The Coulomb rate-independent and dry frictional contact law is assumed. One of the novelties is that, in addition to the singularity exponent , the angle of the friction tangential stress vector on each frictional contact surface is an a priory unknown to be determined by solving a nonlinear corner eigensystem. The procedure, which considers power-law stress singularities, is based on the Stroh formalism of anisotropic elasticity, assuming generalised plane strain (2.5D) conditions, and on the semi-analytic matrix formalism for wedge transfer-matrices and boundary and interface condition matrices. This makes it, firstly, very suitable for computational implementations, secondly, very efficient especially in cases with several perfectly bonded homogeneous wedges, and, thirdly, very accurate due to its fully semi-analytic nature. The code developed is tested by solving a large variety of examples, comparing the present results with those obtained by solving closed-form corner-eigenequations deduced by previous authors for specific useful practical configurations, confirming the extremely high accuracy of the present code in the computation of and . The differences observed in some cases with anisotropic materials are explained by the fact that some of the previous authors did not take the true 3D Coulomb friction law into account

Determinación del modelo de comportamiento hasta rotura de los aceros corrugados tempcore mediante modelado 3D

El estudio del comportamiento real hasta rotura de los metales resulta de gran interés en la industria ya que permite determinar la tenacidad o energía absorbida durante el proceso de deformación y rotura. En cuanto a los aceros estructurales, existe el interés añadido de conocer su respuesta real ante cargas asociadas a situaciones límites como son los movimientos sísmicos. En este trabajo se aborda el comportamiento tenso-deformacional de los aceros corrugados Tempcore. La peculiar geometría de estas barras, diseñadas a tal efecto para aumentar la adherencia acero-hormigón, dificulta el análisis de la fase de estricción desde la metodología que tradicionalmente se sigue para probetas cilíndricas, basada en diversas hipótesis de partida que no se cumplen en probetas corrugadas. Por tanto, se hace necesario el planteamiento de nuevos principios y, por ende, de nuevos procesos que permitan abordar su estudio. En este trabajo se presentan algunos de los avances realizados referentes a la evolución del perfil del cuello y a las deformaciones sufridas por las diferentes secciones transversales del mismo para estas barras.The real tensile behavior of metals beyond the UTS must be considered to calculate toughness or absorbed energy till fracture. Structural steels, designed to withstand earthquakes, are the typical material where post necking behavior can be of paramount importance. This paper deals with the tensile stress-strain behavior of TEMPCORE Rebar, a specifically shaped structural steel. Helical, short ribs, formed by rolling, protrude from the cylindrical basic shape of the Rebar. This help in increasing concrete/steel adherence in reinforced structures. On the other hand, those ribs make it difficult to assess strain distribution in the necking area, according to wellknown theories describing neck shape. New or modified experimental methods, along with new theoretical approaches must be developed to help in studying neck shape evolution and corresponding stresses in Rebar. Advances in such methods and theories are presented in this paper

Campos de tensiones y desplazamientos en grietas de interfaz en bimateriales anisótropos con contacto con fricción

Se presenta una generalización del modelo de la grieta de interfaz de Comninou para bimateriales anisótropos desarrollada a partir de la aplicación del formalismo de Stroh y la matriz de impedancia de Ting, y considerando la ley de Coulomb para fricción isótropa en la interfaz de la grieta. De esta forma, tenemos una solución analítica con la que obtener los diferentes exponentes de singularidad que definen los campos asintóticos de tensiones y desplazamientos en el entorno de la punta de la grieta. A diferencia de los casos encontrados en la literatura, en este trabajo no se impone una dirección relativa de deslizamiento entre ambos materiales, considerando así el ángulo de deslizamiento una incógnita. Una vez se tienen los exponentes de la serie asintótica y los correspondientes ángulos de deslizamiento, se pueden obtener los campos de desplazamientos y tensiones en el entorno de la grieta asociados a cada modo. Entre los casos especiales que se han analizado debido a su importancia, están las soluciones para λ=0.5 y λ=1, así como el estudio completo de la variación de los exponentes de singularidad y del ángulo de deslizamiento en el caso de una grieta de interfaz entre dos láminas del mismo material con diferente orientación.A generalization of the Comninou interface crack model for anisotropic materials is presented, it is developed by applying the Stroh formalism and Ting's impedance matrix and considering the Coulomb law for isotropic friction at a crack interface. In this way, we have an analytical solution allowing us to obtain the singularity exponents that define the asymptotic stress and displacement fields near the crack tip. In contrast to the cases found in the literature, in this work we do not specify the relative sliding direction between the two materials, so we consider the sliding angle as an unknown. Once the exponents of the asymptotic series and the corresponding slip angles are obtained, the displacement and stress fields near the crack tip associated with each mode are calculated. As special cases, the solutions for λ=0.5 and λ=1 are analysed due to their significance, and a complete analysis of the variations of the singularity exponent and the sliding angle in the case of a crack in the interface of two laminates of the same material with different orientations is presented

Characterization of the mechanical behaviour of Tempcore 500C rebar steel during tensile test necking: Experimentation and simulation

The calculation of the true stress and strain values during the tensile test necking phase of smooth ductile metals specimens has been extensively pursued by several authors. A symmetrical neck profile, which leads to axial-symmetrical behaviour, is usually considered. In this study, the neck geometry of Temp-core ribbed bars, the most commonly used steel in reinforced concrete today, is analysed. Knowledge of the true stress and strain values up to failure of this steel is vital since these describe the real behaviour of the steel under extreme conditions. Due to the limited effectiveness of the previously reported theories, an experimental methodology is proposed in order to analyze ribbed bar neck 3D geometry. The results obtained are compared to those of smooth bars of similar steel, both of which are then validated through Finite Element analysis. As a result, the influence of ribbed geometry is found to involve a reduction of true strain values on failure, due to stress concentration occurring in proximity to the root of the transverse ribs affected by necking.El cálculo de los valores de tensión y deformación verdaderos en probetas cilíndricas de metales dúctiles durante la estricción ha sido ampliamente estudiado por diversos autores partiendo, en todos los casos, de una geometría simétrica del cuello. En este estudio se analiza la evolución del perfil del cuello en las barras corrugadas de los aceros Tempcore, proponiendo una metodología experimental mediante análisis en 3D. Conocer el verdadero comportamiento hasta rotura de este acero es de vital importancia para describir su respuesta ante situaciones límites. Los resultados experimentales obtenidos son comparados con los de barras cilíndricas de acero similar, siendo ambos validados mediante análisis por Elementos Finitos. Dicha comparativa permite comprobar que la existencia de corrugas implica una reducción de la deformación en rotura debido a la concentración de tensiones que se origina en zonas próximas al arranque de las mismas

Efficacy of clozapine versus standard treatment in adult individuals with intellectual disability and treatment-resistant psychosis (CLOZAID): study protocol of a multicenter randomized clinical trial

BackgroundIntellectual disability (ID) affects approximately 1% of the worldwide population and individuals with ID have a higher comorbidity with mental illness, and specifically psychotic disorders. Unfortunately, among individuals with ID, limited research has been conducted since ID individuals are usually excluded from mental illness epidemiological studies and clinical trials. Here we perform a clinical trial to investigate the effectiveness of clozapine in the treatment of resistant psychosis in individuals with ID. The article highlights the complexity of diagnosing and treating psychopathological alterations associated with ID and advocates for more rigorous research in this field.MethodsA Phase IIB, open-label, randomized, multicenter clinical trial (NCT04529226) is currently ongoing to assess the efficacy of oral clozapine in individuals diagnosed with ID and suffering from treatment-resistant psychosis. We aim to recruit one-hundred and fourteen individuals (N=114) with ID and resistant psychosis, who will be randomized to TAU (treatment as usual) and treatment-with-clozapine conditions. As secondary outcomes, changes in other clinical scales (PANSS and SANS) and the improvement in functionality, assessed through changes in the Euro-QoL-5D-5L were assessed. The main outcome variables will be analyzed using generalized linear mixed models (GLMM), assessing the effects of status variable (TAU vs. Clozapine), time, and the interaction between them.DiscussionThe treatment of resistant psychosis among ID individuals must be directed by empirically supported research. CLOZAID clinical trial may provide relevant information about clinical guidelines to optimally treat adults with ID and treatment-resistant psychosis and the benefits and risks of an early use of clozapine in this underrepresented population in clinical trials.Trial registrationClinicaltrials.gov: NCT04529226. EudraCT: 2020-000091-37

Un acercamiento a la investigación multidisciplinar en la Universidad Autónoma de Aguascalientes

According to the World Health Organization\u27s (WHO) declaration of April 27, 2020, on December 31, 2019, the presence of a new coronavirus was confirmed, causing multiple cases of pneumonia in the city of Wuhan, China. Due to its spread and severity, on March 11, 2020, the WHO declared that a pandemic level had been reached (WHO, 2020). In Mexico, on March 24, 2020, an agreement was published in the Official Journal of the Federation (DOF) to establish preventive measures and mitigate the health risks caused by SARS-CoV2 (COVID-19). This pandemic has made 2020 an extremely challenging year for the entire world. In Aguascalientes, Mexico, we continued with our usual lives during the first quarter; however, in the last week of March, our university implemented health measures to protect its community, which included confinement, the implementation of distance learning, and the suspension of all academic meetings scheduled for that year. This situation, recognized as the "new normal," spurred the creativity of the university community to adapt planned activities and design emerging projects. In July, the 21st edition of the Research Seminar, convened annually by the General Directorate of Research and Postgraduate Studies with the purpose of disseminating "results of scientific, humanistic, and technological research, as well as strengthening the integration of networks and research groups" (SI, 2020), should have been held. Given that the Seminar could not be held this year, the Department of Research Support generated an emerging project through which it invited professors from all UAA centers, who had completed research projects, to develop a book chapter for a publication that would allow the recognition of the different disciplines from which research is conducted at our university. In the act of bringing together in a single publication the diversity of projects - from Agricultural Sciences, Biomedical Sciences, Design and Construction Sciences, Economic and Administrative Sciences, Natural and Exact Sciences, Social Sciences, Arts, and Humanities - carried out by an academic community that shares the values, mission, vision, and resources - human and material - provided by an institution, an opportunity is recognized to reflect on the notion of system exposed by Mario Bunge, who was one of the Spanish-speaking scientists who has marked a large number of Latin American research.De acuerdo con la declaración del 27 de abril de 2020 de la Organización Mundial de la Salud (OMS), el 31 de diciembre de 2019 se confirmó la presencia de un nuevo coronavirus, causante de múltiples casos de neumonía en la ciudad de Wuhan, China. Por su propagación y gravedad, el 11 de marzo de 2020 la OMS declaró que se había alcanzado el nivel de pandemia (OMS, 2020). En México, el 24 de marzo de 2020, en el Diario Oficial de la Federación (DOF) se publicó un acuerdo para establecer medidas preventivas y mitigar los riesgos de salud provocados por el SARS-CoV2 (covid-19). Esta pandemia ha hecho del 2020 un año sumamente retador para el mundo entero. En Aguascalientes, México, continuamos con la vida habitual durante el primer trimestre; sin embargo, la última semana de marzo nuestra universidad emprendió medidas sanitarias para proteger a su comunidad, entre las que se encontraban el confinamiento, la implementación de cursos a distancia y la suspensión de todos los encuentros académicos programados para ese año. Esta situación, reconocida como “nueva normalidad” impulsó la creatividad de la comunidad universitaria para adecuar las actividades planeadas y para diseñar proyectos emergentes. En el mes de julio debió haberse realizado la emisión 21 del Seminario de Investigación convocado anualmente por la Dirección General de Investigación y Posgrado con el propósito de difundir “resultados de investigaciones científicas, humanísticas y tecnológicas, así como reforzar la integración de redes y grupos de investigación” (SI, 2020). Dado que el Seminario no pudo realizarse este año, el Departamento de Apoyo a la Investigación generó un proyecto emergente mediante el cual convocó a profesores de todos los centros de la UAA, que tuvieran proyectos de investigación concluidos, a elaborar un capítulo de libro para una publicación que permitiera reconocer las distintas disciplinas desde las cuales se realiza investigación en nuestra universidad. En el acto de hacer converger en una misma publicación la diversidad de proyectos –de las Ciencias Agropecuarias, las Ciencias Biomédicas, las Ciencias del Diseño y la Construcción, las Ciencias Económicas y Administrativas, las Ciencias Naturales y Exactas, las Ciencias Sociales, las Artes y las Humanidades–, realizados por una comunidad académica que comparte los valores, misión, visión y recursos –humanos y materiales– dispuestos por una institución, se reconoce una oportunidad para reflexionar sobre la noción de sistema expuesta por Mario Bunge, quien fue uno de los científicos de habla hispana que ha marcado una gran cantidad de investigaciones latinoamericanas

Asymptotic solutions in anisotropic elastic multi-material corners with frictional contact

El objetivo principal de esta tesis es proponer una metodología para caracterizar soluciones elásticas singulares en el entorno de puntos singulares en esquinas anisótropas de un solo material o de varios materiales a través de la expansión de la serie asintótica. La primera parte de esta tesis realiza un estudio del estado del arte, identificando varios aspectos aún por cubrir, lo que lleva a la definición de cinco objetivos específicos. En la segunda parte, se revisa y verifica un formalismo matricial general para el análisis de singularidades de tensiones bajo deformación plana generalizada, junto con su implementación en código MATLAB. Los resultados obtenidos mediante la implementación se verifican y se comparan con los resultados presentes en la literatura, revelando ciertas discrepancias, especialmente en casos que involucran contacto por fricción cuando el plano $x_3=0$ no es un plano de simetría elástica. Se presta especial atención a las soluciones en casos que presentan contacto con fricción, incluidas soluciones complejas y soluciones inesperadas que muestran acoplamiento entre los modos plano y antiplano a pesar de las simetrías elásticas presentes en la esquina. Estas últimas se validan utilizando un método numérico de elementos de contorno. La tercera parte de la tesis se centra en el desarrollo de metodologías semi-analíticas específicas para dos problemas relevantes: grieta de interfaz con contacto por fricción y contacto por fricción entre dos cuñas anisótropas. Estas metodologías se basan en el formalismo de Stroh y la ley de fricción de Coulomb, lo que permite la verificación de soluciones obtenidas a través del formalismo matricial general que no podrían verificarse mediante la comparación con otros autores. En la cuarta parte, se presenta la aplicación web SingSol. Esta aplicación web, basada en el lenguaje Python, representa una versión mejorada de la implementación MATLAB del formalismo matricial general. Incluye un módulo de optimización que permite el cálculo de soluciones de manera totalmente autónoma. Por último, con el objetivo de analizar la importancia de considerar el contacto con fricción en el análisis de aplicaciones ingenieriles reales, se realiza un análisis numérico del ensayo de flexión con entalla con apoyo en tres puntos, enfocandonos en la grieta de interfaz con contacto por fricción. Se desarrolla una metodología numérica para estudiar el crecimiento de grietas bajo carga de flexión, examinando cómo el coeficiente de fricción y las discrepancias de rigidez entre materiales afectan a la carga crítica y al incremento de longitud de grieta. En conclusión, esta tesis proporciona un marco integral para analizar singularidades de tensión en esquinas multi-materiales con contacto con fricción, desarrollando y validando metodologías semianalíticas específicas y aplicaciones de ingeniería práctica.The main objective of this thesis is to propose a methodology for characterizing singular elastic solutions near singular points in anisotropic single or multi-material corners through an asymptotic series expansion of power-law terms. The first part of this thesis conducts a state-of-the-art study, identifying various aspects yet to be covered, leading to the definition of five specific objectives. In the second part, a general matrix formalism for stress singularities analysis under generalized plane strain is reviewed and verified, along with its implementation in MATLAB code. Results obtained with its implementation are verified and compared with existing literature, revealing certain discrepancies, particularly in cases involving frictional contact when the plane x3 = 0 is not a plane of elastic symmetry. Special attention is paid to frictional solutions, including complex solutions and unexpected solutions showing coupling between in-plane and anti-plane modes despite elastic symmetries in the corner. The latter are validated using a numerical boundary element method. The third part of the thesis focuses on developing specific semi-analytical methodologies for two relevant problems: interface crack with frictional contact and frictional contact between two anisotropic wedges. These methodologies are based on the Stroh formalism and Coulomb friction law, allowing verification of solutions obtained through the general matrix formalism that could not be verified through comparison with other authors. In the fourth part, the SingSol web application is introduced. This web application, based on the Python language, represents an enhanced version of the MATLAB implementation of the general matrix formalism. It includes an optimization module that enables the computation of solutions in a fully autonomous way. Lastly, with the objective of analyzing the importance of considering frictional contact in the analysis of real engineering applications, a numerical analysis of the three-point end notched flexure test, is conducted, with a focus on the interface crack with frictional contact. A numerical methodology is developed to study crack growth under bending load, examining how the friction coefficient and stiffness discrepancies between materials affect the critical load and crack length increment. In conclusion, this thesis provides a comprehensive framework for analyzing stress singularities in multi-material corners with frictional contact, developing and validating specific semi-analytical methodologies and practical engineering applications

Computational semi-analytic code for stress singularity analysis

Problems of stress singularities in single or multi-material corners have been addressed by many authors over the years. Most of the authors presented closed-form corner-eigenequations for special cases, and often there is no easy way to check if the solution is correct. In this work, we present a general computational tool that can solve many different cases of stress singularity problems for multi-material corners under generalized plane strain. The semi-analytic code is based on the matrix formalism presented in Mantič et al. (1997, 2014); Barroso et al. (2003); Herrera-Garrido et al. (2022) and is developed in MATLAB. The following boundary conditions are implemented: stress-free, fixed, some restricted or allowed direction of displacements (defined either in the reference frame aligned with the cylindrical coordinate system or in an inclined reference frame), or frictional sliding. The following interface condition between two consecutive materials are implemented: perfectly bonded, and frictionless or frictional sliding. The code can analyze both open and closed (periodic) corners, composed of one or multiple materials with isotropic, transversely isotropic or orthotropic (with any orientation) constitutive laws. The code has proven to be a reliable, very accurate, robust and easy-to-use tool, which has been verified by comparing the results computed with those obtained by other authors. A summary of the corner singularity problems solved is presented. The results of the corner singularity analysis obtained by the code can be further used for prediction of crack onset at the corner tip by the Coupled Criterion of Finite Fracture Mechanics and FEM, see García and Leguillon (2012) and references therein