Departament de Resistència dels Materials i Estructures en Enginyeria
http://hdl.handle.net/2117/4001
Sun, 04 Oct 2015 15:18:58 GMT2015-10-04T15:18:58ZExperimental study on ferritic stainless steel decks in constructions stage according to Eurocode-3
http://hdl.handle.net/2117/77306
Experimental study on ferritic stainless steel decks in constructions stage according to Eurocode-3
Real Saladrigas, Esther; Arrayago Luquin, Itsaso; Marimón Carvajal, Federico; Ferrer Ballester, Miquel
The aesthetic appeal and thermal capacity of ferritic stainless steels, together with the combination of good mechanical properties and excellent corrosion resistance, makes them ideal for exposed composite slabs using profiled decks. Cold-formed members are very slender, with a high resistance-to-weight ratio, so they are highly sensitive to buckling phenomena and the behaviour of these elements is very complex.
Although the use of composite floor slabs with carbon steel sheeting is well established, a study into the structural performance of composite slabs using ferritic stainless steel decking is required due to the complex nonlinear behaviour of stainless steels, which is very different to carbon steel. This paper presents some tests characterizing the resistance of a deck profile which is approximately 60mm in depth in the construction stage.
Six simply supported tests (undergoing positive and negative bending moment) have been conducted for the determination of the flexural resistance of the decks, as part of a major European project looking at ferritic stainless steel in structural applications. These results are compared with some similar previous tests on galvanized carbon steel decks. The resistance of a continuous sheet over two or more spans under combinations of moment and shear loads at the internal supports is assessed by performing three continuous decking tests. Internal support tests have also been conducted to analyse the bending moment-support reaction for different spans and finally, some end support tests have been carried out to characterize the outer support reaction resistance of the decks.
All the experimental results have been compared with the predicted ultimate loads in Standards, showing that expressions proposed in EN 1993-1-3 for carbon steel are, in general, applicable to ferritic stainless steel, although some changes may be introduced in order to get more accurate results and make ferritic stainless steel a competitive option in construction.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/2117/773062014-01-01T00:00:00ZA stochastic model for soft tissue failure using acoustic emission data
http://hdl.handle.net/2117/77287
A stochastic model for soft tissue failure using acoustic emission data
Sánchez Molina, David; Martínez González, Eva; Velázquez Ameijide, Juan; Llumà Fuentes, Jordi; Rebollo Soria, María Carmen; Arregui Dalmases, Carlos
The strength of soft tissues is due mainly to collagen fibers. In most collagenous tissues, the arrangement of the fibers is random, but has preferred directions. The random arrangement makes it difficult to make deterministic predictions about the starting process of fiber breaking under tension. When subjected to tensile stress the fibers are progressively straighten out and then start to be stretched. At the beginning of fiber breaking, some of the fibers reach their maximum tensile strength and break down while some others remain unstressed (this latter fibers will assume then major stress until they eventually arrive to their failure point). In this study, a sample of human esophagi was subjected to a tensile breaking of some fibers, up to the complete failure of the specimen. An experimental setup using Acoustic Emission to detect the elastic energy released is used during the test to detect the location of the emissions and the number of micro-failures per time unit. The data were statistically analyzed in order to be compared to a stochastic model which relates the level of stress in the tissue and the probability of breaking given the number of previously broken fibers, i.e. the deterioration in the tissue). The probability of a fiber breaking as the stretch increases in the tissue can be represented by a non-homogeneous Markov process which is the basis of the stochastic model proposed. This paper shows that a two-parameter model can account for the fiber breaking and the expected distribution for ultimate stress is a Fréchet distribution.
Wed, 15 Jul 2015 00:00:00 GMThttp://hdl.handle.net/2117/772872015-07-15T00:00:00ZMultilevel Monte-Carlo methods applied to the stochastic analysis of aerodynamic problems
http://hdl.handle.net/2117/77253
Multilevel Monte-Carlo methods applied to the stochastic analysis of aerodynamic problems
Bugeda Castelltort, Gabriel; Pons Prats, Jordi
This paper demonstrates the capabilities of the Multi-Level Monte Carlo Methods (MLMC) for the stochastic analysis of CFD aeronautical problems with uncertainties. These capabilities are compared with the classical Monte Carlo Methods in terms of accuracy and computational cost through a set of benchmark test cases. The real possibilities of solving CFD aeronautical analysis with uncertainties by using MLMC methods with a reasonable computational cost are demonstrated.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/2117/772532015-01-01T00:00:00ZMulti-input genetic algorithm for experimental optimization of the reattachment downstream of a backward-facing step with surface plasma actuator
http://hdl.handle.net/2117/77252
Multi-input genetic algorithm for experimental optimization of the reattachment downstream of a backward-facing step with surface plasma actuator
Benard, N.; Pons Prats, Jordi; Periaux, Jacques Francis; Bugeda Castelltort, Gabriel; Bonnet, J.P.; Moreau, E.
The practical interest of flow control approaches is no more debated as flow control provides an effective mean for considerably increasing the performances of ground or air transport systems, among many others
applications. Here a fundamental configuration is investigated by using non-thermal surface plasma discharge. A dielectric barrier discharge is installed at the step corner of a backward-facing step (Reh=30000, Re¿=1650). Wall pressure sensors are used to estimate the reattaching location downstream of the step. The primary objective of this paper is the coupling of a numerical optimizer with an experiment. More specifically, optimization by genetic algorithm is implemented experimentally in order to minimize the reattachment point downstream of the step model. Validation through inverse problem is firstly demonstrated. When coupled with the plasma actuator and the wall pressure sensors, the genetic algorithm finds the optimum forcing conditions with a good convergence rate, the best control design variables being in agreement with the literature that uses other types of
control devices than plasma. Indeed, the minimum reattaching position is achieved by forcing the flow at the shear layer mode where a large spreading rate is obtained by increasing the periodicity of the vortex street and by enhancing the vortex pairing phenomena. At the best forcing conditions, the mean flow reattachment is reduced by 20%. This article, with its experiment-based approach, demonstrates the robustness of a single-objective multi-design optimization method, and its feasibility for wind tunnel experiments.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/2117/772522015-01-01T00:00:00ZA generalized finite-strain damage model for quasi-incompressible hyperelasticity using hybrid formulation
http://hdl.handle.net/2117/77100
A generalized finite-strain damage model for quasi-incompressible hyperelasticity using hybrid formulation
Comellas Sanfeliu, Ester; Bellomo, Facundo J.; Oller Martínez, Sergio Horacio
A new generalized damage model for quasi-incompressible hyperelasticity in a total Lagrangian finite-strain framework is presented. A Kachanov-like reduction factor (1 - D) is applied on the deviatoric part of the hyperelastic constitutive model. Linear and exponential softening are defined as damage evolution laws, both describable in terms of only two material parameters. The model is formulated following continuum damage mechanics theory such that it can be particularized for any hyperelastic model based on the volumetric–isochoric split of the Helmholtz free energy. However, in the present work, it has been implemented in an in-house finite element code for neo-Hooke and Ogden hyperelasticity. The details of the hybrid formulation used are also described. A couple of three-dimensional examples are presented to illustrate the main characteristics of the damage model. The results obtained reproduce a wide range of softening behaviors, highlighting the versatility of the formulation proposed. The damage formulation has been developed to be used in conjunction with mixing theory in order to model the behavior of fibered biological tissues. As an example, the markedly different behaviors of the fundamental components of the rectus sheath were reproduced using the damage model, obtaining excellent correlation with the experimental results from literature.
This is the accepted version of the following article: [Comellas, E., Bellomo, F. J., and Oller, S. (2015) A generalized finite-strain damage model for quasi-incompressible hyperelasticity using hybrid formulation. Int. J. Numer. Meth. Engng, doi: 10.1002/nme.5118.], which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/nme.5118/abstract
Tue, 01 Sep 2015 00:00:00 GMThttp://hdl.handle.net/2117/771002015-09-01T00:00:00ZComputational modeling of high-performance steel fiber reinforced concrete using a micromorphic approach
http://hdl.handle.net/2117/77099
Computational modeling of high-performance steel fiber reinforced concrete using a micromorphic approach
Huespe, Alfredo Edmundo; Oliver Olivella, Xavier; Mora, Diego Fernando
A finite element methodology for simulating the failure of high performance fiber reinforced concrete composites (HPFRC), with arbitrarily oriented short fibers, is presented. The composite material model is based on a micromorphic approach. Using the framework provided by this theory, the body configuration space is described through two kinematical descriptors. At the structural level, the displacement field represents the standard kinematical descriptor. Additionally, a morphological kinematical descriptor, the micromorphic field, is introduced. It describes the fiber–matrix relative displacement, or slipping mechanism of the bond, observed at the mesoscale level. In the first part of this paper, we summarize the model formulation of the micromorphic approach presented in a previous work by the authors. In the second part, and as the main contribution of the paper, we address specific issues related to the numerical aspects involved in the computational implementation of the model. The developed numerical procedure is based on a mixed finite element technique. The number of dofs per node changes according with the number of fiber bundles simulated in the composite. Then, a specific solution scheme is proposed to solve the variable number of unknowns in the discrete model. The HPFRC composite model takes into account the important effects produced by concrete fracture. A procedure for simulating quasi-brittle fracture is introduced into the model and is described in the paper. The present numerical methodology is assessed by simulating a selected set of experimental tests which proves its viability and accuracy to capture a number of mechanical phenomenon interacting at the macro- and mesoscale and leading to failure of HPFRC composites.
The final publication is available at Springer via http://dx.doi.org/10.1007/s00466-013-0873-4
Sun, 01 Dec 2013 00:00:00 GMThttp://hdl.handle.net/2117/770992013-12-01T00:00:00ZReal losses compared with modelled ones using probabilistic approaches : the Lorca 2011 case
http://hdl.handle.net/2117/77088
Real losses compared with modelled ones using probabilistic approaches : the Lorca 2011 case
Salgado Gálvez, Mario Andrés; Barbat Barbat, Horia Alejandro; Carreño Tibaduiza, Martha Liliana; Cardona Arboleda, Omar Dario
A loss assessment was performed for the buildings of Lorca, Spain, considering an earthquake hazard scenario with similar characteristics to those of the real event which occurred on May 11th 2011, in terms of epicentre, depth and magnitude. This low-to moderate earthquake caused severe damage and disruption in the region and especially on the city. A building by building resolution database was developed and used for damage and loss assessment. The portfolio of buildings was characterized by means of relevant indexes capturing information from a structural point of view such as age, main construction materials, number of stories, and building class. A replacement cost approach was selected for the analysis in order to calculate the direct losses incurred by the event. Hazard and vulnerability were modelled in a probabilistic way, considering their inherent uncertainties which were also taken into account in the damage and loss calculation process. Losses have been expressed in terms of the mean damage ratio of each dwelling and since the analysis has been performed on a geographical information system platform, the distribution of the
damage and its categories was mapped for the entire urban centre. The simulated damage was compared with the observed damage reported by the local authorities that inspected the city after the event.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/2117/770882015-01-01T00:00:00ZMultiscale formulation for material failure accounting for cohesive cracks at the macro and micro scales
http://hdl.handle.net/2117/77059
Multiscale formulation for material failure accounting for cohesive cracks at the macro and micro scales
Toro, Sebastian; Sánchez, Pablo J.; Blanco, Pedro J.; de Souza Neto, E.; Huespe, Alfredo Edmundo; Feijóo, R.A.
This contribution presents a two-scale formulation devised to simulate failure in materials with heterogeneous micro-structure. The mechanical model accounts for the nucleation of cohesive cracks in the micro-scale domain. The evolution and propagation of cohesive micro-cracks can induce material instability at the macro-scale level. Then, a cohesive crack is nucleated in the macro-scale model which considers, in a homogenized sense, the constitutive response of the intricate failure mode taking place at the smaller length scale. The two-scale semi-concurrent model is based on the concept of Representative Volume Element (RVE). It is developed following an axiomatic variational structure. Two hypotheses are introduced in order to build the foundations of the entire theory, namely: (i) a mechanism for transferring kinematical information from macro-to-micro scale along with the concept of “Kinematical Admissibility”, and (ii) a Multiscale Variational Principle of internal virtual power equivalence between the involved scales of analysis. The homogenization formulae for the generalized stresses, as well as the equilibrium equations at the micro-scale, are consequences of the variational statement of the problem. The present multiscale technique is a generalization of a previous model proposed by the authors (Sánchez et al., 2013; Toro et al., 2014) and could be viewed as an application of a recent contribution (Blanco et al., 2014). The main novelty in this article lies on the fact that failure modes in the micro-structure involve a set of multiple cohesive cracks, connected or disconnected, with arbitrary orientation, conforming a complex tortuous failure path. Following the present multiscale modeling approach, the tortuosity effect is introduced as a kinematical concept and has a direct consequence in the homogenized mechanical response. Numerical examples are presented showing the potentialities of the model to simulate complex and realistic fracture problems in heterogeneous materials. In order to validate the multiscale technique in a rigorous manner, comparisons with the so-called DNS (Direct Numerical Solution) approach are also presented.
Fri, 01 Jan 2016 00:00:00 GMThttp://hdl.handle.net/2117/770592016-01-01T00:00:00ZA two-scale failure model for heterogeneous materials: numerical implementation based on the finite element method
http://hdl.handle.net/2117/77051
A two-scale failure model for heterogeneous materials: numerical implementation based on the finite element method
Toro, Sebastian; Sánchez, Pablo J.; Huespe, Alfredo Edmundo; Giusti, Sebastian Miguel; Blanco, Pedro J.; Feijóo, R.A.
In the first part of this contribution, a brief theoretical revision of the mechanical and variational foundations of a Failure-Oriented Multiscale Formulation (FOMF) devised for modeling failure in heterogeneous
materials is described. The proposed model considers two well separated physical length scales, namely: (i) the “macro” scale where nucleation and evolution of a cohesive surface is considered as a medium to characterize the degradation phenomenon occurring at the lower length scale, and (ii) the “micro” scale where some mechanical processes that lead to the material failure are taking place, such as strain localization, damage, shear band formation, etc. These processes are modeled using the concept of Representative Volume Element (RVE). On the macro scale, the traction separation response, characterizing the mechanical behavior of the cohesive interface, is a result of the failure processes simulated in the micro scale. The traction
separation response is obtained by a particular homogenization technique applied on specific RVE subdomains. Standard, as well as, Non-Standard boundary conditions are consistently derived in order to
preserve “objectivity” of the homogenized response with respect to the micro-cell size. In the second part of the paper, and as an original contribution, the detailed numerical implementation of the two-scale model based on the Finite Element Method is presented. Special attention is devoted to the topics which are distinctive of the FOMF, such as: (i) the finite element technologies adopted in each scale along with their corresponding algorithmic expressions, (ii) the generalized treatment given to the kinematical boundary conditions in the RVE and (iii) how these kinematical restrictions affect the capturing of macroscopic material instability modes and the posterior evolution of failure at the RVE level. Finally, a set of numerical simulations is performed.
This is the accepted version of the following article: Toro, S., Sánchez, P.J., Huespe, A.E., Giusti, S.M., Blanco, P.J. and Feijóo, R.A. (2014), A two-scale failure model for heterogeneous materials: numerical implementation based on the finite element method. Int. J. Numer. Meth. Engng., 97: 313–351. doi: 10.1002/nme.4576, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/nme.4576/abstract
Sat, 01 Feb 2014 00:00:00 GMThttp://hdl.handle.net/2117/770512014-02-01T00:00:00ZOn the numerical modeling of granular material flows via the Particle Finite Element Method (PFEM)
http://hdl.handle.net/2117/77026
On the numerical modeling of granular material flows via the Particle Finite Element Method (PFEM)
Dávalos, César; Cante Terán, Juan Carlos; Hernández Ortega, Joaquín Alberto; Oliver Olivella, Xavier
The aim of this work is to describe a numerical framework for reliably and robustly simulating the different kinematic conditions exhibited by granular materials while spreading ---from a stagnant condition, when the material is at rest, to a transition to granular flow, and back to a deposit profile. The gist of the employed modeling approach was already presented by the authors in a recent work (Cante et al., 2014), but no proper description of the underlying numerical techniques was provided therein. The present paper focuses precisely on the detailed discussion of such numerical techniques, as well as on its rigorous validation with the experimental results obtained by Lajeunesse, et al. in Ref. ( Lajeunesse et al., 2004).
The constitutive model is based on the concepts of large strains plasticity. The yield surface is defined in terms of the Drucker Prager yield function, endowed with a deviatoric plastic flow and the elastic part by a hypoelastic model. The plastic flow condition is assumed nearly incompressible, so a u - p mixed formulation, with a stabilization of the pressure term via the Polynomial Pressure Projection (PPP), is employed. The numerical scheme takes as starting point the Particle Finite Element Method (PFEM) in which the spatial domain is continuously redefined by a different nodal reconnection, generated by a Delaunay triangulation. In contrast to classical PFEM approximations ( Idelsohn et al., 2004), in which the free boundary is obtained by a geometrical technique (a-shape method), in this work the boundary is treated as a material surface, and the boundary nodes are removed or inserted by means of an error function. One of the novelties of this work is the use of the so-called Impl-Ex hybrid integration technique to enhance the spectral properties of the algorithmic tangent moduli and thus reduce the number of iterations and robustness of the accompanying Newton-Raphson solution algorithm (compared with fully implicit schemes respectively). The new set of numerical tools implemented in the PFEM algorithm – including new discretization techniques, the use of a projection of the variables between meshes, and the constraint of the free-surface instead using classic a-shape – allows us to eliminate the negative Jacobians present during large deformation problems, which is one of the drawbacks in the simulation of granular flows.
Finally, numerical results are compared with the experiments developed in Ref. (Lajeunesse et al., 2004), where a granular mass, initially confined in a cylindrical container, is suddenly allowed to spread by the sudden removal of the container. The study is carried out using different geometries with varying initial aspect ratios. The excellent agreement between computed and experimental results convincingly demonstrates the reliability of the model to reproduce different kinematic conditions in transient and stationary regimes.
Thu, 01 Oct 2015 00:00:00 GMThttp://hdl.handle.net/2117/770262015-10-01T00:00:00Z