A plasticity model for simulation of industrial powder compaction processes

A constitutive model, based on large strain plasticity, for simulation of industrial powder compaction processes is presented. The elastic response is stated in terms of a hyperelastic model based on a hookean elastic free energy. Plastic response is defined in terms of a two parameter yield surface that evolves in terms of the relative density. Two different flow rules are considered and tested in front of some available experimental results. Application to the simulation of an actual powder-metallurgy compaction process is also shown

Numerical modelling of crack formation in powder compaction processes

The primary objective of this work is precisely to fill this gap by developing a constitutive model that attempts to describe the mechanical behavior of the powder during both pressing and ejection phases, with special emphasis on the representation of the cracking phenomenon. The constitutive relationships are derived within the general framework of rate-independent, isotropic, finite strain elastoplasticity. The yield function is defined in stress space by three surfaces intersecting nonsmoothly, namely, an elliptical cap and two classical Von Mises and Drucker-Prager yield surfaces. The distinct irreversible processes occurring at the microscopic level are macroscopically described in terms of two internal variables: an internal hardening variable, associated with accumulated compressive (plastic) strains, and an internal softening variable, linked with accumulated (plastic) shear strains. The innovative part of our modeling approach is connected mainly with the characterization of the latter phenomenological aspect: strain softening. Incorporation of a softening law permits the representation of macroscopic cracks as high gradients of inelastic strains (strain localization). Motivated by both numerical and physical reasons, a parabolic plastic potential function is introduced to describe the plastic flow on the linear Drucker-Prager failure surface. A thermodynamically consistent calibration procedure is employed to relate material parameters involved in the softening law to fracture energy values obtained experimentally on Distaloy AE specimens

Variational approach to relaxed topological optimization: closed form solutions for structural problems in a sequential pseudo-time framework

The work explores a specific scenario for structural computational optimization based on the following elements: (a) a relaxed optimization setting considering the ersatz (bi-material) approximation, (b) a treatment based on a non-smoothed characteristic function field as a topological design variable, (c) the consistent derivation of a relaxed topological derivative whose determination is simple, general and efficient, (d) formulation of the overall increasing cost function topological sensitivity as a suitable optimality criterion, and (e) consideration of a pseudo-time framework for the problem solution, ruled by the problem constraint evolution. In this setting, it is shown that the optimization problem can be analytically solved in a variational framework, leading to, nonlinear, closed-form algebraic solutions for the characteristic function, which are then solved, in every time-step, via fixed point methods based on a pseudo-energy cutting algorithm combined with the exact fulfillment of the constraint, at every iteration of the non-linear algorithm, via a bisection method. The issue of the ill-posedness (mesh dependency) of the topological solution, is then easily solved via a Laplacian smoothing of that pseudo-energy. In the aforementioned context, a number of (3D) topological structural optimization benchmarks are solved, and the solutions obtained with the explored closed-form solution method, are analyzed, and compared, with their solution through an alternative level set method. Although the obtained results, in terms of the cost function and topology designs, are very similar in both methods, the associated computational cost is about five times smaller in the closed-form solution method this possibly being one of its advantages. Some comments, about the possible application of the method to other topological optimization problems, as well as envisaged modifications of the explored method to improve its performance close the workPeer ReviewedPostprint (author's final draft

An implicit/explicit integration scheme to increase computability of non-linear material and contact/friction problems

An implicit/explicit integration scheme for non-linear constitutive models is presented. It aims at providing additional computability to those solid mechanics problems were robustness is an important issue, i.e. material failure models equipped with strain softening, soft materials, contact-friction models, etc., although it can also provide important advantages, in terms of computational cost, with respect to purely implicit integration schemes. The proposed scheme is presented based on general families of constitutive models (continuum damage and elasto-plasticity) and its properties, in terms of robustness and accuracy, are analytically derived and computationally assessed by means of numerical simulations. An adaptive time stepping algorithm, based on a priori control of the committed error and the application of the proposed scheme to contact/friction interfaces are also presented

Propuesta para diseñar un programa de negocios sostenibles que desarrollen competencias en emprendimiento social para el programa institucional Yomasa.

Práctica SocialSe diseñó una propuesta de programa de negocios sostenibles que busca enseñarle a la comunidad del programa institucional Yomasa las ventajas de tener un negocio propio, pues este será una forma de generar ingresos de manera sostenible supliendo las necesidades de su comunidad. Se consideró como la mejor opción para este la elaboración de capacitaciones que contarán con una cartilla como material didácticoINTRODUCCIÓN 1. GENERALIDADES 2. ESTADO ACTUAL DE LAS COMPETENCIAS ADQUIRIDAS EN EMPRENDIMIENTO SOCIAL POR LA COMUNIDAD QUE ENMARCA EL TERRITORIO DEL PROGRAMA INSTITUCIONAL YOMASA 3. PROPUESTA DE MATERIAL DIDÁCTICO PARA EL PROGRAMA DE NEGOCIOS SOSTENIBLES QUE DESARROLLE HABILIDADES EN EMPRENDIMIENTO SOCIAL 4. DIVULGACIÓN DEL PROGRAMA DE NEGOCIOS SOSTENIBLES QUE DESARROLLE HABILIDADES EN EMPRENDIMIENTO SOCIAL 5. CONCLUSIONES 6. RECOMENDACIONES 7. TRABAJOS FUTUROS A REALIZARPregradoIngeniero Industria

Numerical modeling of crack formation in powder forming processes

This paper presents a constitutive model describing the mechanical behavior of metal powders during (uniaxial) cold die compaction processes, placing special emphasis on the modeling of cracks formed during the ejection stage. The constitutive relationships are derived within the general framework of rate-independent, isotropic, finite strain elastoplasticity. The yield condition is determined by three surfaces intersecting non-smoothly in stress space, namely, an elliptical cap and the classical Von Mises and Drucker–Prager yield surfaces. The distinct irreversible processes are described in terms of two internal variables: an internal hardening variable, associated with accumulated compressive (plastic) strains, and an internal softening variable, linked with accumulated (plastic) shear strains. Motivated by both numerical and physical reasons, a parabolic plastic potential function is introduced to characterize the plastic flow on the linear Drucker–Prager failure surface. A thermodynamically consistent calibration procedure is employed to relate the softening modulus to fracture energy values obtained experimentally on Distaloy AE powder specimens. The predictive capability of the constitutive model is checked by simulating three representative cases: a diametral compression test, the ejection of an over-densified thin cylindrical part and the compaction of an axially symmetric multilevel part in an advanced CNC press machine. These simulations demonstrate the ability of the model to detect evidence of macroscopic cracks, clarify and provide reasons for the formation of such cracks, and evaluate, at least qualitatively, the influence of variations in the input variables on their propagation through the green compac

Simulación numérica de procesos de compactación de pulvimateriales. Parte 2: Validación y aplicaciones industriales

En la primera parte de este trabajo se describió el modelo numérico propuesto para la simuación del proceso de compactación de pulvimateriales. En esta segunda parte se estudia el comportamiento del modelo mediante la comparación de resultados experimentales con resultados numéricos. Se desarrollan también una serie de ejemplos axisimétricos, que muestran la robustez del modelo numérico, y su utilidad como herramienta de diseño de procesos de compactación de piezas de uso industrial.In Part 1 of this work a numerical model to simulate the compaction of powder materials was proposed. In this second part, the behaviour of the model is studied by means of the comparison between experimental and numerical results. Robustness and usefullness of the numericd model as a design tool are shown through the simulation of the compaction of severa1 axisymmetric industrial parts.Peer Reviewe

On the contact domain method: a comparison of penalty and Lagrange multiplier implementations

This work focuses on the assessment of the relative performance of the so-called contact domain method, using either the Lagrange multiplier or the penalty strategies. The mathematical formulation of the contact domain method and the imposition of the contact constraints using a stabilized Lagrange multiplier method are taken from the seminal work (as cited later), whereas the penalty based implementation is firstly described here. Although both methods result into equivalent formulations, except for the difference in the constraint imposition strategy, in the Lagrange multiplier method the constraints are enforced using a stabilized formulation based on an interior penalty method, which results into a different estimation of the contact forces compared to the penalty method. Several numerical examples are solved to assess certain numerical intricacies of the two implementations. The results show that both methods perform similarly as one increases the value of the penalty parameter or decreases the value of the stabilization factor (in case of the Lagrange multiplier method). However there seems to exist a clear advantage in using the Lagrange multiplier based strategy in a few critical situations, where the penalty method fails to produce convincing results due to excessive penetration

Simulación numérica de procesos de compactación de pubimateriales

En esta tesis se presenta un modelo numérico para simular la fase de compactación de pulvimateriales y su implementación en ordenadores de cálculo paralelo, con el ánimo de facilitar y mejorar el diseño de los procesos de fabricación por compactación de polvos metálicos. El estudio se inicia llevando a cabo una breve descripción fenomenologica del proceso de compactación, se estudian las principales propiedades y métodos de producción del material en polvo y su efecto sobre las propiedades finales del compacto, se analizan cada una de las operaciones que intervienen en el proceso y se estudian las modificaciones de las propiedades físicas a medida que avanza la compactación. El estudio continua con una breve descripción del estado del arte de los modelos constitutivos empleados hasta ahora y las diferentes técnicas numéricas propuestas para la solución del sistema de ecuaciones asociado a la modelizacion.En el núcleo de la tesis se presenta la formulación matemática del modelo numérico. Se describen las variables básicas y su interpretación física, se formulan las ecuaciones básicas necesarias para la simulación numérica: ecuaciones cinemáticas, ecuación constitutiva, función de fluencia, reglas de flujo y disipación. Se formula el algoritmo de integración de la ecuación constitutiva y el cálculo del tensor constitutivo tangente. Adicionalmente, se describen los modelos numéricos de contacto y de fricción, que permiten simular los efectos que producen las paredes tanto del molde como de los punzones, sobre el material en polvo y en general sobre las propiedades mecánicas finales del compacto.El estudio del comportamiento del modelo numérico propuesto, se lleva a cabo mediante dos grupos de ejemplos.En el primer grupo se calibra y compara el modelo frente a una campaña de resultados experimentales. El segundo grupo, muestra la utilidad que tiene la herramienta numérica en el diseño de piezas complejas

Continuous chip formation in metal cutting processes using the Particle Finite Element Method (PFEM)

This paper presents a study on the metal cutting simulation with a particular numerical technique, the Particle Finite Element Method (PFEM) with a new modified time integration algorithm and incorporating a contact algorithm capability . The goal is to reproduce the formation of continuous chip in orthogonal machining. The paper tells how metal cutting processes can be modelled with the PFEM and which new tools have been developed to provide the proper capabilities for a successful modelling. The developed method allows for the treatment of large deformations and heat conduction, workpiece-tool contact including friction effects as well as the full thermo-mechanical coupling for contact. The difficulties associated with the distortion of the mesh in areas with high deformation are solved introducing new improvements in the continuous Delaunay triangulation of the particles. The employment of adaptative insertion and removal of particles at every new updated configuration improves the mesh quality allowing for resolution of finer-scale features of the solution. The performance of the method is studied with a set of different two-dimensional tests of orthogonal machining. The examples consider, from the most simple case to the most complex case, different assumptions for the cutting conditions and different material properties. The results have been compared with experimental tests showing a good competitiveness of the PFEM in comparison with other available simulation tools