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• Combination of an adaptive remeshing technique with a coupled FEM-DEM approach for analysis of crack propagation problems (preprint)

  A. Cornejo, V. Mataix, F. Zarate, E. Oñate

  Computational Particle Mechanics (2020). Vol. 7, pp. 735–752, doi: 10.1007/s40571-019-00306-4

  
  

  Abstract

  This paper presents an enhanced coupled approach between the Finite Element Method (FEM) and the Discrete Element Method (DEM) in which an adaptative remeshing technique has been implemented. The remeshing technique is based on the computation of the Hessian of a selected nodal variable, i.e. the mesh is refined where the curvature of the variable field is greater. Once the Hessian is known, a metric tensor is defined node-wise that serves as input data for the remesher (MmgTools) that creates a new mesh. After remeshing, the mapping of the internal variables and the nodal values is performed and a regeneration of the discrete elements on the crack faces of the new mesh is carried out. Several examples of fracturing problems using the enhanced FEM-DEM formulation are presented. Accurate results in comparison with analytical and experimental solutions are obtained.

  Abstract
  This paper presents an enhanced coupled approach between the Finite Element Method (FEM) and the Discrete Element Method (DEM) in which an adaptative remeshing technique has [...]

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• Modelling torque and temperature in Friction Stir Welding of Aluminium Alloys

  D. Andrade, C. Leitão, N. Dialami, M. Chiumenti, D. Rodrigues

  International Journal of Mechanical Sciences (2020). Vol. 182 (2020), 105725

  
  

  Abstract

  An analysis of the evolution of the torque and of the temperature with welding conditions, in Friction Stir Welding (FSW) of aluminium alloys, was conducted. More precisely, torque and temperature results from a large number of publications, on FSW of AA2xxx, AA5xxx, AA6xxx and AA7xxx aluminium alloys series, were collected. The literature data was complemented with results from a fully coupled thermomechanical analysis of the FSW welding process. Coupling the experimental data, from the literature, with numerical simulation results, the individual influence of the main process parameters, tools and plates characteristics, on the torque and on the temperatures in FSW was assessed. It was found that the tool rotational speed govern the heat generation, while the tool dimensions have a very important influence, not only on the heat generation but also on the volume of material being stirred during welding, which is another important factor determining the welding torque. The traverse speed and the base material thickness were also found to be important factors governing the torque during welding. However, the influence of the traverse speed on torque evolution is conditioned by the tool dimensions. A parametric analysis enabling to understand the relation between process parameters, heat generation, heat dissipation and base material stirring, was conducted. Analytical relations, which enable calculating the torque and the temperature, in FSW of aluminium alloys, were developed based on numerical results and tested using the data from the literature review.

  Abstract
  An analysis of the evolution of the torque and of the temperature with welding conditions, in Friction Stir Welding (FSW) of aluminium alloys, was conducted. More precisely, [...]

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• Defect formation and material flow in Friction Stir Welding

  N. Dialami, M. Cervera, M. Chiumenti

  European journal of mechanics. A, Solids (2020). Vol. 80, pp. 1-13

  
  

  Abstract

  This work addresses the issue of the simulation and prediction of defect formation through the analysis of the material mixing during Friction Stir Welding (FSW). A coupled thermomechanical model is used for the FSW simulation. To follow the flow of the material, a tracing technique of the material particles is incorporated in the numerical model. A fast and accurate two-stage numerical strategy is adopted to analyse the FSW process. The speed-up stage intends to reach the steady state quickly. The material tracing is performed in the periodic stage where the rotation of the tool is modelled. The effect of the process parameters and the pin features on the defect formation is studied. The model is capable of predicting defects such as void, wormhole, flash and joint line remnant, as well as the formation of “onion rings” in a single simulation. The results show that the proposed model has significant capability to explain and predict the post-FSW defects

  Abstract
  This work addresses the issue of the simulation and prediction of defect formation through the analysis of the material mixing during Friction Stir Welding (FSW). A coupled [...]

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• A pseudo-DNS method for the simulation of incompressible fluid flows with instabilities at different scale

  S. Idelsohn, N. Nigro, A. Larreteguy, J. Gimenez, P. Ryzhakov

  Computational Particle Mechanics (2020). Vol. 7 (1), pp. 19-40

  
  

  Abstract

  In this work, a new model for the analysis of incompressible fluid flows with massive instabilities at different scales is presented. It relies on resolving all the instabilities at all scales without any additional model, i.e., following the direct numerical simulation style. Nevertheless, the computation is carried out at two levels or scales, termed the coarse and the fine. The fine-scale simulation is performed on representative volume elements providing the homogenized stress tensor as a function of several dimensionless numbers characterizing the flow. Consequently, the effect of the fine-scale instabilities is transferred to the coarse level as a homogenized stress tensor, a procedure inspired by standard multi-scale methods used in solids. The present proposal introduces a new way for the treatment of the flow at the fine scale, simulating not only the coarse scale but also the fine scale with all the necessary detail, but without incurring in the excessive computational cost of the classical DNS. Another interesting aspect of the present proposal is the use of a Lagrangian formulation for convecting the eddies simulated on the fine mesh through the coarse domain. Several examples showing the potentiality of this methodology for the simulation of homogeneous flows are presented.

  Abstract
  In this work, a new model for the analysis of incompressible fluid flows with massive instabilities at different scales is presented. It relies on resolving all the instabilities [...]

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• A particle finite element-based model for droplet spreading analysis

  E. Mahrous, A. Jarauta, T. Chan, P. Ryzhakov, A. Weber, R. Roy, M. Secanell

  Physics of Fluids (2020). Vol. 32 (4), pp. 1-15 (Preprint)

  
  

  Abstract

  A particle finite element method-based model is proposed to analyze droplet dynamics problems, particularly droplet spreading on solid substrates (wetting). The model uses an updated Lagrangian framework to formulate the governing equations of the liquid. The curvature of the liquid surface is tracked accurately using a deforming boundary mesh. In order to predict the spreading rate of the droplet on the solid substrate and track the corresponding contact angle evolution, dissipative forces at the contact line are included in the formulation in addition to the Navier-slip boundary conditions at the solid–liquid interface. The inclusion of these boundary conditions makes it possible to account for the induced Young’s stress at the contact line and for the viscous dissipation along the solid–liquid interfacial region. These are found to be essential to obtain a mesh-independent physical solution. The temporal evolution of the contact angle and the contact line velocity of the proposed model are compared with spreading droplets and micro-sessile droplet injection experiments and are shown to be in good agreement.

  Abstract
  A particle finite element method-based model is proposed to analyze droplet dynamics problems, particularly droplet spreading on solid substrates (wetting). The model uses [...]

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• Bond assessment for corroded steel bars in structural concrete

  M. Prieto, P. Tanner, C. Andrade

  (2014). Resúmenes de comunicaciones, pp. 115-116

  
  

  Abstract

  Corrosion can affect bond between reinforcing bars and concrete and with it the transfer of longitudinal stresses between both materials. Loss of bond is normally characterized by brittle behaviour thus it should be analysed within the framework of the assessment of damaged structures in order to avoid it. Factors that affect bond strength include the weakening of the steel bar confinement due to cracking of the concrete cover and/or stirrup corrosion, development of corrosion products at the interface, and, in the case of ribbed bars, reduction of the relative rib area due to cross-section loss in the steel. A number of experimental studies have been conducted in recent years on bond failure, the findings have diverged rather widely, however, due primarily to differing test conditions. In an attempt to surmount the inconsistencies in bond prediction with corroded steel bars, eccentric pull-out tests were carried out with specimens subjected to both accelerated and natural corrosion [1]. In this study a semi-empirical formulation accounting for both pull-out and splitting failures is proposed to assess bond of corroded and non-corroded steel bars. This formulation is obtained by means of multiple linear regression analysis of a database of more than 650 tests of corroded and non-corroded bond tests, including the tests performed in [1]. The database used includes a wide range of influencing variables regarding to bond, such as bar diameter, concrete strength, concrete cover, anchorage length, confinement ratio and cross-section loss due to corrosion. Several statistical criteria have been used to analyse the proposed formulation and the influence of the explanatory variables. Also a comparison with several formulations found in literature, including the proposal of Fib Model Code 2010 for corroded bars is performed. The proposed formulation could be used in the structural assessment of corroded reinforced concrete beams.

  Abstract
  Corrosion can affect bond between reinforcing bars and concrete and with it the transfer of longitudinal stresses between both materials. Loss of bond is normally characterized [...]

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• Cold Drawn Steel Surface Analysis in Contact with Saline Solution: Analysis Using Electrochemical Atomic Force Microscopy

  A. Pachón, J. Sánchez, C. Andrade, E. Menéndez, J. Fullea

  (2014). Durability of Reinforced Concrete from Composition to Protection. Andrade C., Gulikers J., Polder R. (eds)., pp. 57-68, Springer, Cham

  
  

  Abstract

  High strength steels in concrete structures used as reinforcement are usually passivated due to the physical barrier that concrete provides and by a protective passive film developed on the surface by the high alkaline media. Chloride ions can break the passive film. These ions can be found dissolved in the water or in structures in marine environment. This work is focused on the study, by Electrochemical Atomic Force Microscopy (EC-AFM), of the early stages of corrosion of such steels during exposure to a sodium chloride solution in order to better understand the evolution of the dissolution of steel phases. Additionally, it is estimated the corrosion rate by topographical images and simultaneously by means of measuring the corrosion rate through the linear polarization technique performed in an electrochemical cell specially developed in the AFM microscope. The results show the evolution of the topographical profiles which are compared during some period of time with the electrochemical results.

  Abstract
  High strength steels in concrete structures used as reinforcement are usually passivated due to the physical barrier that concrete provides and by a protective passive film [...]

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• Electronic and Electrolytic Conduction of Cement Pastes with Additions of Carbonaceous Materials

  C. Andrade, P. Garcés, F. Baeza, Ó. Galao, E. Zornoza

  (2014). Andrade C., Gulikers J., Polder R. (eds) Durability of Reinforced Concrete from Composition to Protection. Springer, Cham

  
  

  Abstract

  Additions to concrete may change some of its basic properties in several ways depending on the nature of these additions. The addition of fibers, in particular, has enabled new concrete characteristics, making standard concrete a very modern composite material. If the fibers are electrical conductors, the properties that change in addition to the mechanical ones, are the thermal and electrical conductivities. The results indicate that the arrangement of the electrodes and the electrode-material interface are relevant, because the use of sponges between electrode and concrete prevents the contact between the metallic electrode and the carbon material which ends in different values of electrical resistance with and without sponges. Moisture conditions, that critically influence the electrical resistance of concrete without additions, resulted, also very relevant when conductive substances are present in the matrix. If the proportion of the carbonaceous addition, that lowers significantly the resistivity, is to be quantified, the best procedure seems to measure in dry concrete (0 % relative humidity) with sponges or, alternatively, wet concrete (100 % relative humidity) with silver painted electrodes (without sponges).

  Abstract
  Additions to concrete may change some of its basic properties in several ways depending on the nature of these additions. The addition of fibers, in particular, has enabled [...]

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• Application of DIC to monitor reinforced concrete structures

  L. Saucedo-Mora, C. Andrade, C. López, J. Barroso, A. Zamora

  (2017).

  
  

  Abstract

  The reinforced concrete structures need to be monitored to ensure their structural integrity, but sometimes those measurements are very local and the instrument is complex to locate physically in the structure and may interfere on it. Digital Image Correlation, DIC, is a non-contact and non-destructive experimental technique capable to measure the displacement field in a big region of a structure with a great accuracy. This allows extracting valuable information from the fracture processes of reinforced concrete structures. Critical for the evaluation of the structural integrity. The identification of the energy dissipated by the structure is essential for the identification of the strength mechanisms that are failing in the structure, and to identify a proper repair. In this paper the penetration of a prestress rebar in concrete is measured with this technique and the energy dissipated by different fractures is fully observed. Comparison is made with traditional measurement techniques. Also, using Fracture Mechanics other valuable information is extracted from the fracture processes of the reinforced concrete beam, such as the Mode I and Mixed Mode fracture energy released at each loading step, which is essential to evaluate the elastic energy that the structure can accumulate before collapse. The examples enable to anticipate the importance of DIC for future studies at large scale of fracture in concrete and other materials related to construction. 

  Abstract
  The reinforced concrete structures need to be monitored to ensure their structural integrity, but sometimes those measurements are very local and the instrument is complex [...]

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• Correction to: Propagation of reinforcement corrosion: principles, testing and modelling

  C. Andrade

  Materials and Structures (2019). Vol. 53 (1),

  
  

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