Multiscale computational homogenization: review and proposal of a new enhanced-first-order method

This is a copy of the author 's final draft version of an article published in the Archives of computational methods in engineering. The final publication is available at Springer via http://dx.doi.org/10.1007/s11831-016-9205-0The continuous increase of computational capacity has encouraged the extensive use of multiscale techniques to simulate the material behaviour on several fields of knowledge. In solid mechanics, the multiscale approaches which consider the macro-scale deformation gradient to obtain the homogenized material behaviour from the micro-scale are called first-order computational homogenization. Following this idea, the second-order FE2 methods incorporate high-order gradients to improve the simulation accuracy. However, to capture the full advantages of these high-order framework the classical boundary value problem (BVP) at the macro-scale must be upgraded to high-order level, which complicates their numerical solution. With the purpose of obtaining the best of both methods i.e. first-order and second-order, in this work an enhanced-first-order computational homogenization is presented. The proposed approach preserves a classical BVP at the macro-scale level but taking into account the high-order gradient of the macro-scale in the micro-scale solution. The developed numerical examples show how the proposed method obtains the expected stress distribution at the micro-scale for states of structural bending loads. Nevertheless, the macro-scale results achieved are the same than the ones obtained with a first-order framework because both approaches share the same macro-scale BVP.Peer ReviewedPostprint (author's final draft

Designing experiments using digital fabrication in structural dynamics

In engineering, traditional approaches aimed at teaching concepts of dynamics to engineering students include the study of a dense yet sequential theoretical development of proofs and exercises. Structural dynamics are seldom taught experimentally in laboratories since these facilities should be provided with expensive equipment such as wave generators, data-acquisition systems, and heavily wired deployments with sensors. In this paper, the design of an experimental experience in the classroom based upon digital fabrication and modeling tools related to structural dynamics is presented. In particular, all experimental deployments are conceived with low-cost, open-source equipment. The hardware includes Arduino-based open-source electronics whereas the software is based upon object-oriented open-source codes for the development of physical simulations. The set of experiments and the physical simulations are reproducible and scalable in classroom-based environments.Peer ReviewedPostprint (author's final draft

New methodology for calculating damage variables evolution in Plastic Damage Model for RC structures

The behavior of reinforced concrete (RC) structures under severe demands, as strong ground motions, is highly complex; this is mainly due to joint operation of concrete and steel, with several coupled failure modes. Furthermore, given the increasing awareness and concern for the important seismic worldwide risk, new developments have arisen in earthquake engineering. Nonetheless, simplified numerical models are widely used (given their moderate computational cost), and many developments rely mainly on them. The authors have started a long-term research whose final objective is to provide, by using advanced numerical models, solid basis for these developments. Those models are based on continuum mechanics, and consider Plastic Damage Model to simulate concrete behavior. Within this context, this paper presents a new methodology to calculate damage variables evolution; the proposed approach is based in the Lubliner/Lee/Fenves formulation and provides closed-form expressions of the compressive and tensile damage variables in terms of the corresponding strains. This methodology does not require calibration with experimental results and incorporates a strategy to avoid mesh-sensitivity. A particular algorithm, suitable for implementation in Abaqus, is described. Mesh-insensitivity is validated in a simple tension example. Accuracy and reliability are verified by simulating a cyclic experiment on a plain concrete specimen. Two laboratory experiments consisting in pushing until failure two 2-D RC frames are simulated with the proposed approach to investigate its ability to reproduce actual monotonic behavior of RC structures; the obtained results are also compared with the aforementioned simplified models that are commonly employed in earthquake engineering.Postprint (published version

Collision-free path planning for robots using B-splines and simulated annealing

This thesis describes a technique to obtain an optimal collision-free path for an automated guided vehicle (AGV) and/or robot in two and three dimensions by synthesizing a B-spline curve under geometric and intrinsic constraints. The problem is formulated as a combinatorial optimization problem and solved by using simulated annealing. A two-link planar manipulator is included to show that the B-spline curve can also be synthesized by adding kinematic characteristics of the robot. A cost function, which includes obstacle proximity, excessive arc length, uneven parametric distribution and, possibly, link proximity costs, is developed for the simulated annealing algorithm. Three possible cases for the orientation of the moving object are explored: (a) fixed orientation, (b) orientation as another independent variable, and (c) orientation given by the slope of the curve. To demonstrate the robustness of the technique, several examples are presented. Objects are modeled as ellipsoid type shapes. The procedure to obtain the describing parameters of the ellipsoid is also presented

Analysis of ultra low cycle fatigue problems with the barcelona plastic damage model

This paper presents a plastic formulation based on the Barcelona plastic damage model ([1], [2]) capable of predicting the material failure due to Ultra Low Cycle Fatigue. This is achieved taking into account the fracture energy dissipated during the cyclic process. This approach allows the simulation of ULCF in regular cyclic tests, but also in non-regular cases such as seismic loads

Numerical validation of the incremental launching method of a steel bridge through a small-scale experimental study

The final publication is available at Springer via http://dx.doi.org/10.1007/s40799-016-0037-5This article presents an experimental and a numerical study of an incremental launching process of a steel bridge. The former is deployed in a scale-reduced laboratory,whereas the latter is performed using the finite elementmethod. The numerical simulation is based upon realistic transient boundary conditions and accurately reproduces the elastic response of the steel bridge during launching. This numerical approach is validated experimentally with the scale-reduced test performed at the laboratory. The properly validated numerical model is subsequently systematically employed as a simulation tool of the process. The proposed simulation protocol might be useful for design and monitoring purposes of steel bridges to be launched. Results concerning strains, stresses, and displacements might be inferred from the model and thus compared to field measurements obtained in situ. The conditions presented at the end of the article are potentially useful for researchers and practice engineers alike.Peer ReviewedPostprint (author's final draft

New tension-compression damage model for complex analysis of concrete structures

A new damage model, based on continuum damage mechanics and simulating the opening, closing, and reopening of cracks in concrete using only one surface of discontinuity, is proposed in this article. The model complies with the thermodynamics principles of nonreversible, isothermal, and adiabatic processes. Two scalar internal variables have been defined: a tensile damage variable d+d+ and a compressive damage variable d-d-; the threshold of damage is controlled by only one surface of discontinuity and a new parameter controlling the damage variable that should be activated. This new parameter represents the ratio of tensile stress to compressive stress in the damaged material. The continuity of response under complex loads, which is one of the aims of this work, is ensured. An adequate response under different types of loads leads to the conclusion that the proposed model provides a powerful tool to numerically analyze reinforced concrete structures. Validation and illustrative examples are included in the article.Peer ReviewedPostprint (author's final draft

Simulation of delamination in composite materials using the serial/parallel mixing theory

Este artículo presenta un nuevo procedimiento con el que simular el fallo por delaminación en materiales compuestos. El método propuesto utiliza la teoría de mezclas serie/paralelo, desarrollada por Fernando Rastellini, para la caracterización constitutiva del material compuesto. Esta formulación obtiene el comportamiento del compuesto acoplando la respuesta constitutiva de los materiales componentes, fibra y matriz, imponiendo una relación de iso-deformación en la dirección de la fibra (dirección en paralelo) y una relación de iso-tensión en el resto de direcciones (direcciones en serie). Si bien la teoría de mezclas serie/paralelo permite simular los materiales componentes con cualquier ecuación constitutiva, el presente trabajo utiliza una formulación de daño para caracterizar la matriz y una formulación elástica para la fibra. Se mostrará que es posible, utilizando la teoría de mezclas serie/paralelo y una formulación de daño, simular el fallo del compuesto por delaminación. Además, éste se obtiene de forma natural, sin necesidad de definir elementos especiales en los que propagar la fractura, ni ser necesario utilizar costosas técnicas numéricas como el remallado o elementos de contacto. Con el procedimiento propuesto el fallo constitutivo de la matriz conduce a una reducción de la capacidad portante del compuesto en las direcciones en serie (entre otras, la dirección de las tensiones tangenciales) sin eliminar la capacidad resistente en la dirección de la fibra. Se probará que un material compuesto con este comportamiento corresponde a un material delaminado. La última sección de este artículo muestra la simulación del End Notch Failure Test y los resultados obtenidos son comparados con resultados experimentales. La similitud de los resultados numéricos y experimentales demuestra la validez del método propuesto para resolver problemas de delaminación en materiales compuestos.This paper presents a new procedure to deal with the delamination problem found in laminated com- posites, based in a continuum mechanics formulation. The procedure proposed obtains the composite constitutive performance with the Serial/Parallel mixing theory, developed by F. Rastellini. This theory characterizes composite materials by coupling the constitutive behaviour of the composite components, imposing an iso-strain relation among the components in the fibre (or parallel) direction and an iso-stress relation in the remaining directions (serial directions). The proposed procedure uses a damage formula- tion to characterize the constitutive behaviour of matrix component in order to obtain the stress-strain performance of this material. With these two formulations, the delamination phenomenon is characterized naturally by the nume- rical simulation, being unnecessary the definition of special elements or computationally expensive techniques like the definition of contact elements or mesh separation. Matrix failure, as a result of the stress state found in it, leads to a reduction of the stiffness and strength capacity of the composite in its serial directions, among them, the shear component. This stiffness reduction provides a composite performance equivalent to what is found in a delaminated material. To prove the ability of the formulation proposed to solve delamination problems, the End Notch Fai- lure test is numerically simulated and the results obtained are compared with experimental ones. The agreement found in the results with both simulations, numerical and experimental, validate the proposed methodology to solve the delamination problem.Peer Reviewe

Optimization method for the determination of material parameters in damaged composite structures

An optimization method to identify the material parameters of composite structures using an inverse method is proposed. This methodology compares experimental results with their numerical reproduction using the finite element method in order to obtain an estimation of the error between the results. This error estimation is then used by an evolutionary optimizer to determine, in an iterative process, the value of the material parameters which result in the best numerical fit. The novelty of the method is in the coupling between the simple genetic algorithm and the mixing theory used to numerically reproduce the composite behavior. The methodology proposed has been validated through a simple example which illustrates the exploitability of the method in relation to the modeling of damaged composite structures.Peer ReviewedPostprint (author’s final draft

El documental como tendencia productiva en la Comunicación contemporánea:“Tixca” una trilogía.

Contiene cuadro de cronología historica del Estado de MéxicoEl documento que a continuación describimos, traducido en memoria laboral, refleja, el proceso de realización por la que atraviesa una producción documentalista independiente. ¿Cuándo decidimos ser productores independientes? ¿Es fácil producir, siendo independiente? ¿El documental, es lucrativo? ¿Qué importancia tiene un documental histórico en la actualidad? ¿De qué vive un productor independiente? Éstas y algunas otras preguntas trataremos de respondernos durante el desarrollo de tal documento. Sin pretender indicar que ésta, es, la manera correcta para realizar dicho género. El objetivo es informar