L'activitat científica general del grup es el desenvolupament de mètodes de la mecànica computacional per a la modelització de problemes a l'Enginyeria. Dins d'aquest context, el grup treballa més específicament en les següents àrees: a) Modelització numèrica de processos de fabricació industrial. b) Modelització numèrica del comportament mecànic de materials i estructures. c) Eines avançades per al disseny computacional de materials d'enginyeria.
Roca, D.; Lloberas-Valls, O.; Cante, J.C.; Oliver, J. Computer methods in applied mechanics and engineering Vol. 330, p. 415-446 DOI: 10.1016/j.cma.2017.10.025 Data de publicació: 2018-03 Article en revista
A framework, based on an extended Hill–Mandel principle accounting for inertial effects (Multiscale Virtual Work principle), is developed for application to acoustic problems in the context of metamaterials modelling. The classical restrictions in the mean values of the micro-displacement fluctuations and their gradients are then accounted for in a saddle-point formulation of that variational principle in terms of Lagrange functionals. A physical interpretation of the involved Lagrange multipliers can then be readily obtained.
The framework is specifically tailored for modelling the phenomena involved in Locally Resonant Acoustic Metamaterials (LRAM). In this view, several additional hypotheses based on scale separation are used to split the fully coupled micro-macro set of equations into a quasi-static and an inertial system. These are then solved by considering a projection of the microscale equations into their natural modes, which allows for a low-cost computational treatment of the multiscale problem. On this basis, the issue of numerically capturing the local resonance phenomena in a FE
context is addressed. Objectivity of the obtained results in terms of the macroscopic Finite Element (FE) discretization is checked as well as accuracy of the homogenization procedure by comparing with direct numerical simulations (DNS). The appearance of local resonance band-gaps is then modelled for a homogeneous 2D problem and its extension to multi-layered macroscopic material is presented as an initial attempt towards acoustic metamaterial design for tailored band-gap attenuation.
In this paper, conserving time-stepping algorithms for frictionless and full stick friction dynamic contact problems are presented. Time integration algorithms for frictionless and full stick friction dynamic contact problems have been designed in order to preserve the conservation of key discrete properties satisfied at the continuum level. Energy and energy-momentum preserving algorithms for frictionless and full stick friction dynamic contact problems, respectively, have been designed and implemented within the framework of the direct elimination method, avoiding the drawbacks linked to the use of penalty-based or Lagrange multipliers methods. An assessment of the performance of the resulting formulation is shown in a number of selected and representative numerical examples, under full stick friction and slip frictionless contact conditions. Conservation of key discrete properties exhibited by the time stepping algorithm is shown.
This is the peer reviewed version of the following article: [Agelet de Saracibar C, Di Capua D. Conserving algorithms for frictionless and full stick friction dynamic contact problems using the direct elimination method. Int J Numer Methods Eng. 2018;113:910–937. https://doi.org/10.1002/nme.5693], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/nme.5693. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.
Caicedo, M.; Mroginski, J.; Toro, S.; Raschi, M.; Huespe, A.; Oliver, J. Archives of computational methods in engineering p. 1-22 DOI: 10.1007/s11831-018-9258-3 Data de publicació: 2018-02 Article en revista
A High-Performance Reduced-Order Model (HPROM) technique, previously presented by the authors in the context of hierarchical multiscale models for non linear-materials undergoing infinitesimal strains, is generalized to deal with large deformation elasto-plastic problems. The proposed HPROM technique uses a Proper Orthogonal Decomposition procedure to build a reduced basis of the primary kinematical variable of the micro-scale problem, defined in terms of the micro-deformation gradient fluctuations. Then a Galerkin-projection, onto this reduced basis, is utilized to reduce the dimensionality of the micro-force balance equation, the stress homogenization equation and the effective macro-constitutive tangent tensor equation. Finally, a reduced goal-oriented quadrature rule is introduced to compute the non-affine terms of these equations. Main importance in this paper is given to the numerical assessment of the developed HPROM technique. The numerical experiments are performed on a micro-cell simulating a randomly distributed set of elastic inclusions embedded into an elasto-plastic matrix. This micro-structure is representative of a typical ductile metallic alloy. The HPROM technique applied to this type of problem displays high computational speed-ups, increasing with the complexity of the finite element model. From these results, we conclude that the proposed HPROM technique is an effective computational tool for modeling, with very large speed-ups and acceptable accuracy levels with respect to the high-fidelity case, the multiscale behavior of heterogeneous materials subjected to large deformations involving two well-separated scales of length.
Carreño, M.L.; Lantada, N.; Jaramillo, N. Revista internacional de métodos numéricos para cálculo y diseño en ingeniería Vol. 34, num. 1, p. 1-13 DOI: 10.23967/j.rimni.2017.7.001 Data de publicació: 2018-01 Article en revista
The urban areas may be exposed to different natural hazards; in order to jointly evaluate the potential risk, this article proposes a methodology for the qualitative assessment of the multi-hazard physical risk by using a fuzzy inference system called MuHRA by its abbreviations MUlti-Hazard Physical risk assessment. This methodology is based on the fuzzy sets theory and uses expert opinions. It is applicable to the risk evaluation involving a maximum of three natural hazards and uses five levels of risk: very low, low, medium, high and very high. The proposed methodology considers the physical risk in an urban area involving at least three potential effects: predominant damage that varies with the type of hazard; impact on the population, and damage in lifelines. According to the available information for the urban area to be assessed, the physical risk to a natural hazard can be evaluated, either through expert opinion or a more detailed assessment, and then they are combined and synthesized into a single multi-hazard physical risk index (RFmh).
The MuHRA methodology is applied to the multi-hazard risk evaluation for the city Merida-Venezuela considering both, the seismic hazard and the landslides. This application shows the versatility and robustness of the methodology, which can be adapted according to the information available in each case study.
In this work, a new strategy for solving multiscale topology optimization problems is presented. An alternate direction algorithm and a precomputed offline microstructure database (Computational Vademecum) are used to efficiently solve the problem. In addition, the influence of considering manufacturable constraints is examined. Then, the strategy is extended to solve the coupled problem of designing both the macroscopic and microscopic topologies. Full details of the algorithms and numerical examples to validate the methodology are provided.
In this work, a new strategy for solving multiscale topology optimization problems is presented. An alternate direction algorithm and a precomputed offline microstructure database (Computational Vademecum) are used to efficiently solve the problem. In addition, the influence of considering manufacturable constraints is examined. Then, the strategy is extended to solve the coupled problem of designing both the macroscopic and microscopic topologies. Full details of the
algorithms and numerical examples to validate the methodology are provided.
In this work we put the method proposed by van Hinsberg et al.  to the test, highlighting its accuracy and efficiency in a sequence of benchmarks of increasing complexity. Furthermore, we explore the possibility of systematizing the way in which the method's free parameters are determined by generalizing the optimization problem that was considered originally. Finally, we provide a list of worked-out values, ready for implementation in large-scale particle-laden flow simulations.
Chiumenti, M.; Neiva, E.; Salsi, E.; Cervera, M.; Badia, S.; Moya, J.; Chen, Z.; Lee, C.; Davies, C. Additive Manufacturing Vol. 18, p. 171-185 DOI: 10.1016/j.addma.2017.09.002 Data de publicació: 2017-12 Article en revista
In this work a finite-element framework for the numerical simulation of the heat transfer analysis of additive manufacturing processes by powder-bed technologies, such as Selective Laser Melting, is presented. These kind of technologies allow for a layer-by-layer metal deposition process to cost-effectively create, directly from a CAD model, complex functional parts such as turbine blades, fuel injectors, heat exchangers, medical implants, among others. The numerical model proposed accounts for different heat dissipation mechanisms through the surrounding environment and is supplemented by a finite-element activation strategy, based on the born-dead elements technique, to follow the growth of the geometry driven by the metal deposition process, in such a way that the same scanning pattern sent to the numerical control system of the AM machine is used. An experimental campaign has been carried out at the Monash Centre for Additive Manufacturing using an EOSINT-M280 machine where it was possible to fabricate different benchmark geometries, as well as to record the temperature measurements at different thermocouple locations. The experiment consisted in the simultaneous printing of two walls with a total deposition volume of 107 cm3 in 992 layers and about 33,500 s build time. A large number of numerical simulations have been carried out to calibrate the thermal FE framework in terms of the thermophysical properties of both solid and powder materials and suitable boundary conditions. Furthermore, the large size of the experiment motivated the investigation of two different model reduction strategies: exclusion of the powder-bed from the computational domain and simplified scanning strategies. All these methods are analysed in terms of accuracy, computational effort and suitable applications.
Mendez, C.; Podestá, J.; Lloberas-Valls, O.; Toro, S.; Huespe, A.; Oliver, J. International journal for numerical methods in engineering Vol. 112, num. 10, p. 1353-1380 DOI: 10.1002/nme.5560 Data de publicació: 2017-12 Article en revista
A topology optimization technique based on the topological derivative and the level set function is utilized to design/synthesize the micro-structure of a pentamode material for an acoustic cloaking device. The technique provides a micro-structure consisting of a honeycomb lattice composed of needle-like and joint members. The resulting metamaterial shows a highly anisotropic elastic response with effective properties displaying a ratio between bulk and shear moduli of almost 3 orders of magnitude. Furthermore, in accordance with previous works in the literature, it can be asserted that this kind of micro-structure can be realistically fabricated. The adoption of a topology optimization technique as a tool for the inverse design of metamaterials with applications to acoustic cloaking problems is one contribution of this paper. However, the most important achievement refers to the analysis and discussion revealing the key role of the external shape of the prescribed domain where the optimization problem is posed. The efficiency of the designed micro-structure is measured by comparing the scattering wave fields generated by acoustic plane waves impinging on bare and cloaked bodies.
In this paper we present an accurate stabilized FIC-FEM formulation for the multidimensional steady-state advection-diffusion-absorption equation.The stabilized formulation is based on the Galerkin FEM solution of the governing differential equations derived via the Finite Increment Calculus (FIC) method using two stabilization parameters. The value of the two stabilization parameters ensuring an accurate nodal FEM solution using uniform meshes of linear elements is obtained from the optimal values for the 1D problem.The accuracy of the new FIC-FEM formulation is demonstrated in the solution of 2D steady-state advection-diffusion-absorption problems for a range of physical parameters and boundary conditions.
Los métodos numéricos son decisivos en la ingeniería para la conservación de estructuras de mampostería existentes y el diseño de estructuras nuevas. Entre ellos, los métodos ma-cro-mecánicos de elementos finitos, basados en el concepto de fisuras distribuidas, son habitualmente los preferidos como opción asequible para el análisis de grandes estructuras de mampostería. Sin embargo, suelen resultar en a una representación poco realista del daño, distribuido en grandes áreas de la estructura, lo que impide la correcta interpretación del patrón de daño. Además, esta metodología presenta una patología más crítica, la de-pendencia de la malla, que influye notablemente en las predicciones de seguridad y estabi-lidad.Para superar estas limitaciones, esta tesis propone una nueva herramienta numérica basada en el enriquecimiento del clásico enfoque de fisuras distribuidas con un algoritmo de tra-zado local. El objetivo de este modelo de daño localizado es el análisis no-lineal de las estructuras de mampostería de manera realista y eficiente con una representación mejora-da de fisuras.El comportamiento no lineal de la mampostería se simula a través de la adopción de un modelo de mecánica de daño continuo con dos índices de daño, permitiendo la diferen-ciación entre las respuestas mecánicas de tensión y compresión de la mampostería. En este contexto, se propone e implementa una nueva formulación explícita para la evolución de deformaciones irreversibles. Se derivan dos nuevas expresiones para la regularización del ablandamiento de tracción y compresión según el ancho de banda de la fisura, garantizan-do la objetividad del modelo de daño al respecto del tamaño de la malla.La simulación del comportamiento estructural de las estructuras de mampostería en condi-ciones de carga y contorno generales precisa de algunos desarrollos en el contexto de los algoritmos locales de trazado. Con este objetivo, se presenta la mejora de los algoritmos locales de trazado con nuevos procedimientos que posibilitan la simulación de fisuración múltiple, arbitraria e secante bajo cargas monótonas y cíclicas. Además, se investiga el efecto de diferentes criterios de propagación de fisuras y se aborda la selección entre más de un plano de falla posible.El modelo de daño localizado propuesto se valida mediante la simulación de una serie de ejemplos estructurales. Éstos van desde pruebas a pequeña escala en probetas de hormi-gón, con pocas fisuras dominantes, hasta estructuras de mampostería de mediana y gran escala con fisuración múltiple de tracción, de cortante y de flexión. Los análisis se compa-ran con los resultados analíticos, experimentales y numéricos obtenidos con métodos al-ternativos disponibles en la literatura. El modelo de daño localizado mejora en gran medi-da la independencia de la malla del clásico método de fisuras distribuidas y reproduce patrones de daño y mecanismos de colapso de una manera eficiente y realista.Palabras clave: Mampostería, Materiales cuasi-frágiles, Método de elementos finitos, Lo-calización de deformaciones, Algoritmo de trazado, Mecánica de daño continuo, Defor-maciones irreversibles, Fisuración de tracción/cortante/flexión, Fisuras secantes, Depen-dencia de la malla, carga cíclica de cortante
This paper discusses the finite element modeling of cracking in quasi-brittle materials. The problem is addressed via a mixed strain/displacement finite element formulation and an isotropic damage constitutive model. The proposed mixed formulation is fully general and is applied in 2D and 3D. Also, it is independent of the specific finite element discretization considered; it can be equally used with triangles/tetrahedra, quadrilaterals/hexahedra and prisms. The feasibility and accuracy of the method is assessed through extensive comparison with experimental evidence. The correlation with the experimental tests shows the capacity of the mixed formulation to reproduce the experimental crack path and the force–displacement curves with remarkable accuracy. Both 2D and 3D examples produce results consistent with the documented data. Aspects related to the discrete solution, such as convergence regarding mesh resolution and mesh bias, as well as other related to the physical model, like structural size effect and the influence of Poisson’s ratio, are also investigated. The enhanced accuracy of the computed strain field leads to accurate results in terms of crack paths, failure mechanisms and force displacement curves. Spurious mesh dependency suffered by both continuous and discontinuous irreducible formulations is avoided by the mixed FE, without the need of auxiliary tracking techniques or other computational schemes that alter the continuum mechanical problem.
The final publication is available at Springer via http://dx.doi.org/10.1007/s00466-017-1438-8
Dialami , N.; Chiumenti, M.; Cervera, M.; Segatori, A.; Osikowicz, W. International journal of mechanical sciences Vol. 133, p. 555-567 DOI: 10.1016/j.ijmecsci.2017.09.022 Data de publicació: 2017-11 Article en revista
Friction is one of the main heat generation mechanisms in Friction Stir Welding (FSW). This phenomenon occurs between the pin and the workpiece as the rotating tool moves along the weld line. An accurate friction model is essential for obtaining realistic results in a FSW simulation in particular temperature, forces and torque. In this work, a modified Norton's friction law is developed. The suggested enhanced friction model aims at providing not only the realistic temperature field but also the forces and torque. This model does not exclusively relate the frictional shear stress to the sliding velocity; conversely it takes into account the effect of non-uniform pressure distribution under the shoulder, as this latter has an important role in the process of heat generation. Longitudinal, transversal and vertical forces and torque are numerically calculated. The effect of the enhanced friction model is reflected in these forces. In particular, it leads to a more realistic estimation of the transversal and longitudinal forces in comparison with the results obtained using former models. The friction model is successfully validated by the experimental measurements provided by the industrial partner (Sapa). The experimental analysis is performed for the material characterization, the calibration of the friction model and, more generally, the assessment of the overall numerical strategy proposed for the FSW simulation.
This work adopts a fast and accurate two-stage computational strategy for the analysis of FSW (Friction stir welding) processes using threaded cylindrical pin tools. The coupled thermo-mechanical problem is equipped with an enhanced friction model to include the effect of non-uniform pressure distribution under the pin shoulder. The overall numerical strategy is successfully validated by the experimental measurements provided by the industrial partner (Sapa). The verification of the numerical model using the experimental evidence is not only accomplished in terms of temperature evolution but also in terms of torque, longitudinal, transversal and vertical forces.
The advances in information and communication technologies led to a general trend towards the availability of more detailed information on dam behaviour. This allows applying advanced data-based algorithms in its analysis, which has been reflected in an increasing interest in the field. However, most of the related literature is limited to the evaluation of model prediction accuracy, whereas the ulterior objective of data analysis is dam safety assessment. In this work, a machine-learning algorithm (boosted regression trees) is the core of a methodology for early detection of anomalies. It also includes a criterion to determine whether certain discrepancy between predictions and observations is normal, a procedure to compute a realistic estimate of the model accuracy, and an original approach to identify extraordinary load combinations. The performance of causal and noncausal models is assessed in terms of their ability to detect different types of anomalies, which were artificially introduced on reference time series generated with a numerical model of a 100-m-high arch dam. The final approach was implemented in an online application to visualise the results in an intuitive way to support decision making.
In this work the numerical simulation of metal Additive Manufacturing (AM) processes is addressed . In most metal AM systems, a high energy and focused laser melts metal powder or wire to sinter each layer of the object. A layer of added material is created according to the scanning path defined by the user. As a result, a layer-by-layer metal deposition (with titanium, Inconel, steel, or other metals) can be carried out to build complex shapes for components such as turbine blades, aircraft stiffeners, cooling systems, medical implants, among others. The advantage of these kind of processes is the rapid cooling of each deposited layer that results in a finer grain size of the material, if compared to other metal forming technologies such as casting or forming. The Finite-Element (FE) framework developed to simulate the metal deposition process has already been addressed and experimentally validated for both wire-feeding  and blown-powder technologies . However, in the case of powder technologies (powder bed or blown powder), the number of layers to be simulated is much higher than in other technologies, leading to massively large problems that must be dealt with in a computationally efficient manner. This work enhances the FE framework presented in  to run it in a HPC platform. This is achieved by adopting a parallel FE activation technique to follow in time the growth of the geometry driven by the movement of the laser. Moreover, the global linear system of equations is preconditioned with the weakly-scalable Balancing Domain Decomposition by Constraints (BDDC) . The BDDC solver has been implemented in such a way that it can dynamically handle the growth of the geometry in an efficient way. This solution strategy has been implemented in FEMPAR, an advanced high-performance and object-oriented research software. A weak scalability analysis to show the performance of this new framework is shown.
Franci, A.; Oñate, E.; Carbonell, J.M.; Chiumenti, M. Computer methods in applied mechanics and engineering Vol. 325, p. 711-732 DOI: 10.1016/j.cma.2017.07.028 Data de publicació: 2017-10 Article en revista
The aim of this paper is to present a Lagrangian formulation for thermo-coupled fluid–structure interaction (FSI) problems and to show its applicability to the simulation of hypothetical scenarios of a nuclear core melt accident. During this emergency situation, an extremely hot and radioactive lava-like material, the corium, is generated by the melting of the fuel assembly. The corium may induce collapse of the nuclear reactor devices and, in the worst case, breach the reactor containment and escape into the environment. This work shows the capabilities of the proposed formulation to reproduce the structural failure mechanisms induced by the corium that may occur during a meltdown scenario. For this purpose, a monolithic method for FSI problems, the so-called Unified formulation, is here enhanced in order to account for the thermal field and to model phase change phenomena with the Particle Finite Element Method (PFEM). Several numerical examples are presented. First, the convergence of the thermo-coupled method and phase change algorithm is shown for two academic problems. Then, two complex simulations of hypothetical nuclear meltdown situations are studied in 2D as in 3D.
Turmo, J.; Estela, M. Rosa; Chacon, R.; Gironella, X.; Lloberas-Valls, O.; Oliver, J.; Poblet-Puig, J.; Puigvi, M.; Valls, S.; Diez, P. International Forum for High-Rise and Special Constructions p. 49-58 Data de presentació: 2017-10 Presentació treball a congrés
The educational programs of Civil Engineering schools have evolved to adapt to changes in society demands and regulations. Specifically, Civil Engineering curricula in Spain was highly impacted by the Bolonia Declaration as the European Higher Education Area (EHEA) was launched to promote homogeneous Civil Engineering programs in all European countries. Moreover, in the last years, the construction crisis has changed significantly the Civil Engineering profession panorama in Spain. This scenario has reduced significantly the demand for studying in Civil Engineering Schools. These are forced, for the first time, to attract students. Furthermore, the world economy has been globalized and construction has been industrialized. This asks for professionals able to work worldwide and with new capabilities. To face these new challenges, the School of Civil Engineering of Barcelona (ETSECCPB)
considered the EHEA modifications as an opportunity to reinvent itself to become more attractive for students and more useful to society. This paper will show which are the paths chosen to shift from a teacher to a student centered education and how the communication of the School has improved. Specific examples will be given (flipped classroom, project based learning, Massive Open Online Course-MOOCs, workshops) focusing not only on the results, but also on the challenges that were overcome in order to educate professionals able to excel in a worldwide market.
This contribution presents a numerical investigation of experimental tests on skew notched beams with the mixed strain-displacement finite element method . Mode III and mixed mode loading conditions are often encountered in tests involving torsion and asymmetrical bending for the mechanical characterization of quasi-brittle materials. Recently, the authors showed that the mixed strain displacement finite elements are capable of delivering very accurate results in the analysis of experimental pull-out tests on unreinforced concrete . This is possible thanks to the enhanced convergence that the mixed formulation provides in a non-linear mechanical problem involving localization and failure, by solving the displacement and strains field as independent variables . In this work, the proposed FE technology is applied to three study cases: firstly, a three point bending test of a Plexiglas beam; secondly, the torsion test of a plain concrete prismatic beam; finally, the torsion test of a cylindrical beam made of plain concrete as well. All three specimens present a notch at the midspan with a 45 degrees inclination. To take into account the complex non-linear mechanical behaviour, Rankine and Drucker-Prager failure criteria are implemented in both plasticity and isotropic continuum damage models. It is shown that the mixed strain displacement formulation is able of overcoming the common issues encountered with the standard irreducible FEM. Indeed, it predicts fracture surfaces, peak loads and
global loss of carrying capability close to the experimental ones. Finally, taking advantage of the compatibility between the displacement-based and the mixed formulations, an enhancement in terms of computational time is presented.
Barbu, L.; Escudero-Torres, C.; Cornejo, A.; Martinez, X.; Oller, S.; Barbat, A. H. International Conference on Computational Plasticity p. 471-482 Data de presentació: 2017-09-07 Presentació treball a congrés
The main purpose of this paper is to develop a reliable method based on a three-dimensional (3D) finite-element (FE) model to simulate the constitutive behaviour of reinforced concrete structures strengthened with post-tensioned tendons. A 3D FE model was used, where the nonlinear material behaviour and geometrical analysis based on incremental–iterative load methods were adopted. The pre-tensioned concrete is modelled as a composite material whose behaviour is described with the serial-parallel rule of mixtures (S/P RoM) [1-3]. The effective pre-tensioning stress was applied as an initial strain imposition in the steel material used to model the tendons. The methodology is valid for both straight and curvilinear steel tendons. Examples of both cases will be shown. Validation by comparison with the analytic solution is done for the case of a concrete beam with a straight pre-tensioned steel tendon embedded. Other examples are also included.
This work presents the computational strategy adopted for the numerical simulation of the Selective Laser Melting (SLM) technology used in Additive Manufacturing (AM). SLM is used to fabricate industrial components by powder bed technology in a layer-by-layer manner. Hence, firstly the CAD geometry is sliced, and later, the scanning sequence is generated to allow for the selective melting of the different sections of the sliced geometry. The SLM machine makes use of a high power laser beam for the powder melting, while Titanium-64 powder is our reference material. The objective of this work consists of: (i) assessing the inherent shrinkage method to reproduce the manufacturing process in a layer-by-layer manner; (ii) calibrating the model parameters according to the experimental evidence provided by IK4-LORTEK. The transient coupled thermomechanical analysis defined for the high-fidelity simulation of the AM process [1,2] is replaced by a faster sequence of quasi-static mechanical computations according to
the metal deposition in the building sequence. The scanning path is not faithfully reproduced; instead, a layer-by-layer strategy is adopted. This is feasible because, compared to other available AM technologies (e.g. wire-feeding or blown powder), the scanning speed is much faster (almost 10 times) and the power source used for the melting process is much smaller (almost 10 times). Hence, the laser spot and the corresponding Heat Affected Zone (HAZ) is much smaller and the cooling process much faster than for other manufacturing technologies. Avoiding the transient thermal analysis, the thermal stresses are computed by defining an inherent strain field as a function of the material shrinkage and the process parameters that characterise the manufacturing process. The solution strategy proposed is calibrated by the experimental work carried out at IK4-LORTEK, where the distortions and residual stresses induced by the manufacturing process are measured for a number of samples.
Dialamishabankareh, N.; Cervera, M.; Chiumenti, M.; Segatori, A.; Osikowicz, W.; Olsson, B. International Conference on Computational Plasticity p. 1 Data de presentació: 2017-09-07 Presentació treball a congrés
This work presents the results of the numerical simulation and experimental validation of a fast and accurate FEM model for FSW simulation [1,2]. In this model, the fully coupled thermomechanical problem is solved using an apropos kinematic framework, a mixed pressure-velocity formulation and an accurate stabilization procedure with optimal numerical dissipation. The model considers the friction between the tool and the workpiece and the plastic dissipation as the
main sources of heat generation. The friction model proposed is a modified viscoplastic Norton’s law that not only relates the frictional shear stress to the sliding velocity but also accounts for the pressure
distribution. The constitutive model proposed is calibrated by the experimental material characterization provided in terms of stress/strain rate. The study shows that the proposed modelling approach can be used to predict and interpret the FSW behaviour for a given pin geometry. The results obtained in terms of forces, torque and temperature evolution are validated against the measurement provided by the industrial partner (SAPA).
Modelling of cracking in quasi-brittle materials has been the object of intensive study in computational solid mechanics over the last five decades. In most of the studies carried out with standard irreducible elements, the attempts to predict the crack path fail because the obtained solution suffers from spurious bias mesh dependency. The problem is addressed via a mixed strain/displacement finite element formulation [1-4].
In this presentation, a mixed strain/displacement finite element formulation is applied to the solution of nonlinear solid mechanics problems. For this, an enhanced version of the finite element program COMET  has been developed. The proposed mixed formulation is fully general and is applied in 2D and 3D. Also, it is independent of the specific finite element discretization considered; it can be equally used with triangles/tetrahedra, quadrilaterals/hexahedra and prisms.
The feasibility and accuracy of the method is assessed through extensive comparison with experimental evidence. The correlation with the experimental tests shows the capacity of the mixed formulation to reproduce the experimental crack path, failure mechanism and the force-displacement curves with remarkable accuracy. Both 2D and 3D examples produce results consistent with the documented data.
Spurious mesh dependency suffered by both continuous and discontinuous irreducible formulations is avoided by the mixed FE, without the need of auxiliary tracking techniques or other computational schemes that alter the continuum mechanical problem.
In this work the numerical simulation of metal Additive Manufacturing (AM) processes is addressed . In most metal AM systems, a high energy and focused laser melts metal powder or wire to sinter each layer of the object. A layer of added material is created according to the scanning path defined by the user. As a result, a layer-by-layer metal deposition (with titanium, Inconel, steel, or other metals) can be carried out to build complex shapes for components such as turbine blades, aircraft stiffeners, cooling systems, medical implants, among others. The advantage of these kind of processes is the rapid cooling of each deposited layer that results in a finer grain size of the material, if compared to other metal forming technologies such as casting or forming.
The Finite-Element (FE) framework developed to simulate the metal deposition process has already been addressed and experimentally validated for both wire-feeding [3,4] and blown-powder technologies . However, in the case of powder technologies (powder bed or blown powder), the number of layers to be simulated is much higher than in other technologies, leading to massively large problems that must be dealt with in a computationally efficient manner.
This work enhances the FE framework presented in  to run it in a HPC platform. This is achieved by adopting a parallel FE activation technique to follow in time the growth of the geometry driven by the movement of the laser. Moreover, the global linear system of equations is preconditioned with the weakly-scalable Balancing Domain Decomposition by Constraints (BDDC) . The BDDC solver has been implemented in such a way that it can dynamically handle the growth of the geometry in an efficient way. This solution strategy has been implemented in FEMPAR, an advanced high-performance and object-oriented research software. A weak scalability analysis to show the performance of this new framework is shown.
Carreño, M.L.; Cardona, O.D.; Barbat, A. H.; Suarez, D.; Perez, M.; Narvaez, L. International journal of disaster risk science Vol. 8, num. 3, p. 258-269 DOI: 10.1007/s13753-017-0136-7 Data de publicació: 2017-09 Article en revista
Disaster risk depends on both the physical vulnerability and a wide range of social, economic, and environmental aspects of a society. For a better risk understanding, a holistic or integrated perspective was considered when risk was assessed for the city of Manizales, Colombia. This assessment accounts not only for the expected physical damage and loss, but also for the socioeconomic vulnerability factors that favor secondorder effects in a disaster. This comprehensive approach allows the identification of different aspects related to physical vulnerability, social fragility, and lack of resilience that can be improved, thus enhancing integrated disaster risk management actions. The outcomes of this comprehensive assessment are currently being used as input to update the disaster risk management plan of Manizales.
The Particle Finite Element Method, a lagrangian finite element method based on a continuous Delaunay re-triangulation of the domain, is used to study machining of Ti6Al4V. In this work the method is revised and applied to study the influence of the cutting speed on the cutting force and the chip formation process. A parametric methodology for the detection and treatment of the rigid tool contact is presented. The adaptive insertion and removal of particles are developed and employed in order to sidestep the difficulties associated with mesh distortion, shear localization as well as for resolving the fine-scale features of the solution. The performance of PFEM is studied with a set of different two-dimensional orthogonal cutting tests. It is shown that, despite its Lagrangian nature, the proposed combined finite element-particle method is well suited for large deformation metal cutting problems with continuous chip and serrated chip formation.
Escudero-Torres, C.; Oller, S.; Martinez, X.; Barbat, A. H. Journal of engineering mechanics Vol. 143, num. 9, p. 04017080-1-04017080-19 DOI: 10.1061/(ASCE)EM.1943-7889.0001275 Data de publicació: 2017-09 Article en revista
The construction of confined masonry buildings has become a good choice to meet the housing needs of low-income families inbig cities. Despite this, current building codes for such construction allow the use of highly simplified analysis techniques that have hardlychanged in the last 40 years. This paper is based on numerical simulation and discusses the need to combine and improve existing techniquesin finite-element method (FEM) analysis for composite materials, to assess the overall structural behavior of reinforced concrete structureswith masonry in-fills, and consequently to support the derivation of rational rules for analysis and design. Through the use of a simpleyet powerful shell finite element (FE), state-of-the-art theories of mixtures to analyze composite materials, a computational tool to generatethe volume fraction of composites, and the Mexican building code, this paper attempts to be a guide to numerical reproduction ofthe overall behavior of confined masonry structures.
Petracca, M.; Pelà, L.; Rossi, R.; Zaghi, S.; Camata, G.; Spacone, E. Construction & building materials Vol. 149, p. 296-314 DOI: 10.1016/j.conbuildmat.2017.05.130 Data de publicació: 2017-09 Article en revista
A novel damage mechanics-based continuous micro-model for the analysis of masonry-walls is presented and compared with other two well-known discrete micro-models. The discrete micro-models discretize masonry micro-structure with nonlinear interfaces for mortar-joints, and continuum elements for units. The proposed continuous micro-model discretizes both units and mortar-joints with continuum elements, making use of a tension/compression damage model, here refined to properly reproduce the nonlinear response under shear and to control the dilatancy. The three investigated models are validated against experimental results. They all prove to be similarly effective, with the proposed model being less time-consuming, due to the efficient format of the damage model. Critical issues for these types of micro-models are analysed carefully, such as the accuracy in predicting the failure load and collapse mechanism, the computational efficiency and the level of approximation given by a 2D plane-stress assumption.
Turbulent boundary layer control (TBLC) for skin-friction drag reduction is a relatively new technology made possible through the advances in computational-simulation capabilities, which have improved the understanding of the flow structures of turbulence. Advances in micro-electronic technology have enabled the fabrication of active device systems able to manipulating these structures. The combination of simulation, understanding and micro-actuation technologies offers new opportunities to significantly decrease drag, and by doing so, to increase fuel efficiency of future aircraft. The literature review that follows shows that the application of active control turbulent skin-friction drag reduction is considered of prime importance by industry, even though it is still at a low technology readiness level (TRL). This review presents the state of the art of different technologies oriented to the active and passive control for turbulent skin-friction drag reduction and contributes to the improvement of these technologies.
The simulation of penetration problems in geomaterials is a challenging problem as it involves large deformations and displacements as well as strong non-linearities affecting material behaviour, geometry and contact surfaces. The paper presents examples of modelling of the cone penetration test using two procedures: a discrete approach and a continuum approach. The discrete approach is based on the Discrete Element Method where a granular material is represented by an assembly of separate particles. Cone penetration has been successfully simulated for the case of crushable sands. For the continuum approach, the Particle Finite Element Method has been adopted. The procedure has been effectively applied to the modeling of undrained cone penetration into clays. Although not exempt of problems, both approaches yield realistic results leading to the possibility of a closer examination and an enhanced understanding of the mechanisms underlying penetration problems in geomechanics.
Cornejo, A.; Barbu, L.; Escudero-Torres, C.; Martinez, X.; Oller, S.; Barbat, A. H. International Conference on Structural Integrity and Durability p. 1 Data de presentació: 2017-08-17 Presentació treball a congrés
Rodríguez, J.; Carbonell, J.M.; Cante, J.C.; Oliver, J. International journal of solids and structures Vol. 120, p. 81-102 DOI: 10.1016/j.ijsolstr.2017.04.030 Data de publicació: 2017-08-01 Article en revista
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.
This work presents a general formulation and implementation in solid-shell elements of the refined zigzag theory and the trigonometric shear deformation theory in an unified way. The model thus conceived is aimed for use in the analysis, design and verification of structures made of composite materials, in which shear strains have a significant prevalence. The refined zigzag theory can deal with composite laminates economically, adding only two nodal degrees of freedom, with very good accuracy. It assumes that the in-plane displacements have a piece-wise linear shape across the thickness depending on the shear stiffness of each composite layer. The trigonometric theory assumes a cosine variation of the transverse shear strain. A modification of this theory is presented in this paper allowing its implementation with C0 approximation functions. Two existing elements are considered, an eight-node tri-linear hexahedron and a six-node triangular prism. Both elements use a modified right Cauchy-Green deformation tensor View the MathML source where five of its six components are linearly interpolated from values computed at the top and bottom surfaces of the element. The sixth component is computed at the element center and it is enhanced with an additional degree of freedom. This basic kinematic is improved with a hierarchical field of in-plane displacements expressed in convective coordinates. The objective of this approach is to have a simple and efficient finite element formulation to analyze composite laminates under large displacements and rotations but small elastic strains. The assumed natural strain technique is used to prevent transverse shear locking. An analytic through-the-thickness integration and one point integration on the shell plane is used requiring hourglass stabilization for the hexahedral element. Several examples are considered on the one hand to compare with analytical static solutions of plates, and on the other hand to observe natural frequencies, buckling loads and the non-linear large displacement behavior in double curved shells. The results obtained are in a very good agreement with the targets used.
El sistema de pretensado ha sido ampliamente utilizado con el objetivo de mejorar la eficiencia de las estructuras de hormigón armado convencionales. Dicha tecnología emplea tendones de acero de alta resistencia para incrementar la capacidad última de las estructuras de hormigón armado.
El objetivo principal del presente artículo es desarrollar un método fiable basado en elementos finitos en tres dimensiones (3D) para simular el comportamiento de estructuras de hormigón armado reforzadas con tendones de pretensado. Para ello se ha utilizado un modelo 3D, el cual tiene en cuenta el comportamiento no lineal y geométrico del material basado en métodos incrementales-iterativos.
El hormigón pretensado se modela como un material compuesto cuyo comportamiento está regido por la teoría de mezclas serie-paralelo (S-P). Las tracciones debidas al pretensado se aplican al material como una deformación inicial impuesta en la capa de acero activo que simula el efecto de los tendones.
Mediante la teoría de mezclas S-P [1,2] se alcanza un equilibrio en cada punto de integración entre el acero activo y el hormigón. Esto hace que el tensor de deformaciones se actualice para tener en consideración el mencionado efecto del hormigón. En iteraciones globales posteriores, el campo de desplazamientos es actualizado y se alcanza una convergencia global para el sistema de cargas definido.
La teoría de mezclas S-P permite el uso de diferentes modelos constitutivos para cada uno de los materiales simples que constituyen el material compuesto (acero activo, pasivo y hormigón). Esto implica que se puede simular el decaimiento de tensión en el acero mediante un modelo reológico (Maxwell Generalizado) y, por otra parte, la fluencia del hormigón.
La metodología es apta para geometrías lineales y curvas de tendones. Ejemplos de ambos casos serán presentados. Adicionalmente se mostrarán validaciones de la formulación frente a soluciones analíticas para el caso de vigas de hormigón pretensado. Posteriormente se presentarán otros ejemplos de aplicación.
Commonly, the simulation of Fluid Structure Interaction (FSI) problems uses an Arbitrary Lagrangian Eulerian (ALE) formulation in the fluid domain. This allows the structure interface tracking but might yield large element distortion, which usually requires remeshing, when large displacements occur. To get rid of this limitation we present the use of an embedded formulation in the fluid domain. The main features of the embedded formulation is that the fluid mesh is fixed and that the interface tracking is done with a signed distance function. This completely avoids mesh distortion, allowing the simulation of large displacement FSI problems. The show the capabilities of the presented formulation it has been applied to the simulation of mud motors. Mud motors are progressive cavity positive displacement pumps (PCPD) used in the drilling industry to increase the power of the drilling bit. The presented formulation is capable of dealing with the large displacements arising from the mud motor inner rotation that produces the power. Advances towards the development of a Virtual Wind Tunnel (VWT) capable of dealing with large displacement structures will be also shown.
El análisis con incertidumbres es un concepto importante a tener en cuenta para la simulación y la optimización. El manejo adecuado de las incertidumbres proporciona mejores resultados desde el punto de vista de la robustez del diseño. Normalmente, estas incertidumbres están relacionadas con los datos de entrada del análisis que representan la naturaleza del fenómeno a analizar, o algunos parámetros de fabricación (geometría) o tolerancias. La caracterización de estas incertidumbres se realiza a través de su distribución estadística de valores.
Este trabajo se basa en la utilización de una metodología para la resolución de problemas de optimización que permita la definición estocástica de los datos con incertidumbres. Esta metodología debe ser eficiente y robusta. Hay que tener en cuenta que en la mayor parte de problemas de ingeniería en general, y en aerodinámica y problemas acoplados en particular, se requieren las mejores configuraciones para operar con eficacia no sólo en unas condiciones muy determinadas sino también dentro de un cierto rango de condiciones.
La metodología utilizada lleva a cabo un análisis estocástico de cada diseño, lo cual permite obtener no sólo los valores medios de la función de mérito utilizada sino también su varianza. Ello permite la resolución de problemas de diseño robusto mediante la minimización simultánea del valor medio de la función de mérito y de su varianza.
Uno de los métodos clásicos de análisis estocástico para problemas en los que algunos de los parámetros presentan valores con incertidumbres es el de Montecarlo (MC). Éstos se basan en la generación de una serie de valores de los parámetros inciertos de acuerdo con su distribución estadística. Para cada valor se genera el correspondiente caso determinista. El análisis de los resultados de todos los casos proporciona la información necesaria para un tratamiento estadístico de la solución del problema estocástico.
Para un correcto análisis estadístico es necesario que el número de casos sea estadísticamente representativo, lo que normalmente conduce a un número de casos elevado. Por otro lado, si el análisis de cada caso requiere de una discretización en el espacio entonces su coste computacional puede ser relevante, y el coste total de la resolución puede ser prohibitivo. Ello impone limitaciones en cuanto al número de casos a analizar y en cuanto a la calidad de la discretización para el análisis de cada caso. Ambos tipos de limitación se traducen en las correspondientes fuentes de error numérico en la solución final.
Los métodos de Monte Carlo Multi Nivel (MLMC) mejoran esta situación mediante la combinación del análisis de un gran número de casos utilizando discretizaciones pobres en el espacio para proporcionar una buena representación estadística de la solución, con un número más bajo de análisis con discretizaciones de calidad que proporcionan buenos resultados en cuanto al error de discretización. Este tipo de combinación proporciona unos costes computacionales más razonables.
En este trabajo se presenta la resolución de problemas de diseño robusto en los que el análisis estocástico de cada diseño se lleva a cabo mediante métodos MLMC.
This paper presents a computational framework for the numerical analysis of fluid-saturated porous media at large strains. The proposal relies, on one hand, on the particle finite element method (PFEM), known for its capability to tackle large deformations and rapid changing boundaries, and, on the other hand, on constitutive descriptions well established in current geotechnical analyses (Darcy’s law; Modified Cam Clay; Houlsby hyperelasticity). An important feature of this kind of problem is that incompressibility may arise either from undrained conditions or as a consequence of material behaviour; incompressibility may lead to volumetric locking of the low-order elements that are typically used in PFEM. In this work, two different three-field mixed formulations for the coupled hydromechanical problem are presented, in which either the effective pressure or the Jacobian are considered as nodal variables, in addition to the solid skeleton displacement and water pressure. Additionally, several mixed formulations are described for the simplified single-phase problem due to its formal similitude to the poromechanical case and its relevance in geotechnics, since it may approximate the saturated soil behaviour under undrained conditions. In order to use equal-order interpolants in displacements and scalar fields, stabilization techniques are used in the mass conservation equation of the biphasic medium and in the rest of scalar equations. Finally, all mixed formulations are assessed in some benchmark problems and their performances are compared. It is found that mixed formulations that have the Jacobian as a nodal variable perform better.
Lafontaine, N.; Cervera, M.; Rossi, R.; Chiumenti, M. Revista internacional de métodos numéricos para cálculo y diseño en ingeniería Vol. 33, num. 3-4, p. 250-261 DOI: 10.1016/j.rimni.2016.06.001 Data de publicació: 2017-07 Article en revista
This paper presents the application of stabilized mixed explicit strain/displacement formulation (MEX-FEM) [23,24] for solving non-linear plasticity problems in solid mechanics with strain localization. In order to use the same linear interpolation order for displacements and strains, the formulation uses the variational subscales method. Compared to the standard irreducible formulation, the proposed formulation yields improved strain and stress fields, and it is capable of addressing nearly incompressible situations. This work investigates the effects of the improved strain and stress fields in problems involving strain softening and localization leading to failure for the Mohr-Coulomb and Drucker Prager plasticity models. Numerical examples validate the ability of the proposed formulation to correctly predict failure mechanisms with localized patterns of strain, virtually free of mesh dependence and without using tracking algorithm.
Chacon, R.; Oller, S. Journal of professional issues in engineering education and practice Vol. 143, num. 3, p. 1-9 DOI: 10.1061/(ASCE)EI.1943-5541.0000315 Data de publicació: 2017-07 Article en revista
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.
Marti, J.; Ortega, E.; Idelsohn, Sergio R. International journal of numerical methods for heat and fluid flow Vol. 27, num. 8, p. 1748-1764 DOI: 10.1108/HFF-06-2016-0219 Data de publicació: 2017-07 Article en revista
The purpose of this paper is to propose a new elemental enrichment technique to improve the accuracy of the simulations of thermal problems containing weak discontinuities. Design/methodology/approach - The enrichment is introduced in the elements cut by the materials interface by means of adding additional shape functions. The weak form of the problem is obtained using Galerkin approach and subsequently integrating the diffusion term by parts. To enforce the continuity of the fluxes in the "cut" elements, a contour integral must be added. These contour integrals named here the "inter-elemental heat fluxes" are usually neglected in the existing enrichment approaches. The proposed approach takes these fluxes into account. Findings - It has been shown that the inter-elemental heat fluxes cannot be generally neglected and must be included. The corresponding method can be easily implemented in any existing finite element method (FEM) code, as the new degrees of freedom corresponding to the enrichment are local to the elements. This allows for their static condensation, thus not affecting the size and structure of the global system of governing equations. The resulting elements have exactly the same number of unknowns as the non-enriched finite element (FE). Originality/value - It is the first work where the necessity of including inter-elemental heat fluxes has been demonstrated. Moreover, numerical tests solved have proven the importance of these findings. It has been shown that the proposed enrichment leads to an improved accuracy in comparison with the former approaches where inter-elemental heat fluxes were neglected.
The purpose of this paper is to propose a new elemental enrichment technique to improve the accuracy of the simulations of thermal problems containing weak discontinuities. Design/methodology/approach - The enrichment is introduced in the elements cut by the materials interface by means of adding additional shape functions. The weak form of the problem is obtained using Galerkin approach and subsequently integrating the diffusion term by parts. To enforce the continuity of the fluxes in the
Este trabalho apresenta a extensão a 3D das técnicas de injeção de modos de deformação, que foram usadas anteriormente na modelação numérica de propagação de fissuras em 2D num conjunto de exemplos académicos de validação , em barragens de gravidade  e, mais recentemente, no estudo de problemas de propagação de fratura dinâmica .
As técnicas de injeção de modos de deformação foram desenvolvidas no âmbito do método dos elementos finitos e utilizam modelos constitutivos do continuum equipados com leis de enfraquecimento devidamente regularizadas com a energia de fratura material. A ideia chave do método consiste na divisão do domínio em dois subdomínios distintos: o domínio de injeção, que contém os elementos finitos atravessados pelas fissuras, no qual são injetados modos de deformação específicos (constantes e descontínuos) para melhorar o desempenho dos elementos na modelação de processos de fratura e a parte remanescente do domínio, onde nenhum melhoramento é efetuado, sendo usadas, portanto, formulações correntes de elementos finitos. Para injetar os modos de deformação descontínuos, a posição da fissura dentro dos elementos finitos deve ser conhecida antecipadamente, sendo esta informação obtida através de uma técnica auxiliar denominada por “crack path field technique”.
Devido às interessantes propriedades da metodologia em termos da independência dos resultados da malha elementos finitos, do seu custo computacional e da sua robustez, os autores consideram do máximo interesse a sua extensão a 3D o que permitirá o estudo de qualquer tipo de estrutura de interesse prático. Alguns resultados preliminares de aplicações a 3D evidenciam as potencialidades e vantagens do método.
Rossi, R.; Zorrilla, R.; Mataix, V.; Celigueta, M.A.; Larese, A.; Gandikota, V.; Oñate, E. International Conference on Computacional Methods for Coupled Problems in Science and Engineering p. 1 Data de presentació: 2017-06-14 Presentació treball a congrés
The petrol Industry relies on the use of “mud motors” for the generation of the torque needed by the drill bit . Mud motors are essential inverse pumps in which a rotor is set into motion by the passage of a high pressure fluid. The simulation of such devices presents major challenges, since it requires taking into account the details of the contact between the rotor and the stator as well as considering the wetting and drying of large portions of the fluid domain, which “open” or “close” to the fluid flow due to the motion of the rotor with respect to the stator. Curent work focuses on the simulation aspects, detailing in particular the FSI-related aspects. A description of the contact technique employed will also be provided together with details on the MPI implementation employed in the project ,. We remark in particular that an Immersed fluid solver is employed in following the motion of the rotor, thus making the FSI problem different from both classic FSI approaches  and of porous FSI problems . Adaptive remeshing is used adopting the algorithm in .
Dialami , N.; Cervera, M.; Chiumenti, M.; Agelet De Saracibar, C. International Conference on Computacional Methods for Coupled Problems in Science and Engineering p. 1 Data de presentació: 2017-06-13 Presentació treball a congrés
Pin geometry is a fundamental consideration in friction stir welding (FSW). It influences the thermal behaviour, material flow and forces during the weld and reflects on the joint quality.
This work studies four pin tools with circular, triflute, trivex, and triangular profiles adopting a validated model of FSW process developed by the authors [1-3]. The effect of the rotating tool geometry on the flow behaviour and process outcomes is analysed. Additionally, longitudinal and transversal forces and torque are numerically calculated and compared for the different pin shapes. The study is carried out for slip and stick limiting friction cases between pin and workpiece.
The Norton-Hoff constitutive model is adopted to characterize the material behaviour during the weld. The piecewise linear version of the model developed by the authors greatly facilitates the convergence of the numerical solution ensuring both computational efficiency and accuracy. A two-stage computational procedure is applied. In the first stage, a forced transient is carried out; in the second one, the magnitudes of interest are computed.
The study shows that the proposed modelling approach can be used to predict and interpret the FSW behaviour when using specific pin geometry.
Larese, A.; Rossi, R.; Zorrilla, R.; Wüchner, R.; Oñate, E. International Conference on Computacional Methods for Coupled Problems in Science and Engineering p. 1 Data de presentació: 2017-06-13 Presentació treball a congrés
The maturity of numerical techniques both in Structural Mechanics and in Computational Fluid Dynamics (CFD), accompanied by the availability of affordable high-performance hardware, allows the use of virtual rapid-prototyping facilities (for example virtual wind tunnels) as realistic alternatives to traditional wind tunnel experiments. This work aims to present the strategy developed by the authors for the creation of a virtual wind tunnel (VWT) especially designed for the analysis of lightweight structures. An embedded approach in the context of Variational Multi Scale (VMS) techniques is proposed to face FSI problems involving the movement of arbitrary objects within a fixed fluid domain. This method is based on an efficient intersection procedure which allows detecting how a given surface mesh, representing the shape of the object of interest, “cuts” the fixed fluid mesh. On the basis of such information, the underlying finite element formulation is modified at purely local level so to embed a discontinuity into the finite element space. The method is completed by a technique to weakly impose slip (or wall) boundary conditions on the cut interfaces. A distinctive feature of the proposed method is to allow the simulation of membrane structures, typically challenging for embedded solvers due to the need of modelling a strong discontinuity of the flow field in correspondence of the structural position. The method is evaluated in application to real deformable structures for which experimental results are available. All the presented strategies are developed inside Kratos Multiphysics open source platform (http://www.cimne.com/kratos/).