Documents published in Scipedia

• FEM analysis of FRCM strengthened RC columns exposed to fire

  R. Talo, M. Kyaure, S. Khalaf, A. El Refai, F. Abed

  eccomas2022.

  
  

  Abstract

  Reinforced concrete (RC) structures deteriorate over time and therefore, need to be strengthened. Despite the fact that RC structurtes have a decent fire rating, the performance of the strengthening system under fire exposure needs to be evaluated. One of the main restrictions associated with Fibre Reinforced Polymer (FRP) systems is their poor resistance to high temperatures, which originates from the combustible polymer matrix. Therefore, Fibre Reinforced Cementitious Matrix (FRCM) systems have been introduced due to their improved performance during fire exposure. The potential of Poly-paraphenylene-ben-zobisoxazole (PBO) FRCM to strengthen circular RC columns is evaluated using a nonlinear finite element analysis (FEA). The commericial software ABAQUS is used to develop 3D FE models to investigate the axial performance of the strengthening system. The modeling approach is performed by first conducting a thermal analysis to generate the nodal tempertaures. The second step of the model includes a displacement-controlled loading condition with imported nodal temperatures from the first model. The temperature dependent material properties are incorporated in both models. The modeling approach is validated against published literature and a parametric study is conducted on PBO FRCM strengthened and unstrengthened columns heated at durations of 1, 2, and 4 hours following the ASTM standard fire temperature-time curve. Results indicated a decrease in the axial capacity and stiffness of the strengthened and unstrengthened columns upon heating. Moreover, an increase in the columns' ductility due to the increase in temperature was observed. A decrease in ultimate strength of up to 78 and 68% was observed for the unstrengthened and strengthened columns respectively.

  Abstract
  Reinforced concrete (RC) structures deteriorate over time and therefore, need to be strengthened. Despite the fact that RC structurtes have a decent fire rating, the performance [...]

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• Theoretical procedure to predict the local buckling resistance of aluminium members in elastic-plastic range

  V. Piluso, A. Pisapia

  eccomas2022.

  
  

  Abstract

  In the present research work, a theoretical approach to evaluate the ultimate resistance of aluminium alloy members subjected to local buckling under uniform compression is provided.

  Abstract
  In the present research work, a theoretical approach to evaluate the ultimate resistance of aluminium alloy members subjected to local buckling under uniform compression is [...]

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• A coupled multiphysics approach for modelling in-stent restenosis

  S. Reese, K. Manjunatha, M. Behr, F. Vogt

  eccomas2022.

  
  

  Abstract

  Drug-eluting stents were developed to counteract the severe restenosis observed after bare-metal stent implantation. The risk of restenosis still prevailed due to the inhibitory effect of the drug on endothelial healing. The current work focuses on extending a multiphysics-based modeling framework to include the effect of anti-inflammatory drugs embedded in the drugeluting stents. An additional advection-reaction-diffusion equation governing the drug transport is introduced herein. Additionally, the effect of drugs, specifically rapamycin-based ones, on the proliferation of smooth muscle cells is captured. An optimal level of drug embedment is realized through the modeling framework.

  Abstract
  Drug-eluting stents were developed to counteract the severe restenosis observed after bare-metal stent implantation. The risk of restenosis still prevailed due to the inhibitory [...]

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• Uncertainties of Parameters Quantification in SHM

  M. Miah, W. Lienhart

  eccomas2022.

  
  

  Abstract

  The uncertainties of parameters quantification due to various known and unknown conditions are crucial to understand structural health monitoring (SHM) systems. For instance, the amplitudes and the variation of loading conditions play a vital rule how the structural parameters are going to be changed. Hence, the aforementioned issue leads to an additional challenge in the area of SHM that requires attention. This study observed the behaviour of a steel bridge experimentally by employing multi-sensors scenarios e.g. accelerometers and laser triangulation sensor. The dynamical properties such as the peak (e.g. maximum-minimum) accelerations and displacements are evaluated. Additionally, the frequencies and damping ratio from the measured data of the tested bridge has been estimated by utilizing the fast Fourier transform (FFT) estimation. The outcome shows that the variation of input excitations (i.e., random, free-decay, extra-loading) effects the investigated properties as well as on their magnitudes considerably. Therefore, the findings suggest that before making a final judgement based on the identified/estimated properties from measured data, the underlying uncertainties need to be considered to avoid sub-optimal assessment strategy.

  Abstract
  The uncertainties of parameters quantification due to various known and unknown conditions are crucial to understand structural health monitoring (SHM) systems. For instance, [...]

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• Multi-objective optimization for understanding tree design rules with finite element modelling.

  E. Moreno-Zapata, J. Cabrero-Ballarín, G. Ramos-Ruiz, G. Vargas-Silva

  eccomas2022.

  
  

  Abstract

  This research presents an optimization problem, which aims to understand the inherent design rules of the shape of a tree. It makes use of a classical optimization problem, the Nowacki beam, which consists of a cantilever beam with a point load at the end which seeks to obtain the lowest cross-sectional area and bending stress under a set of constraints [1]. Forrester et al. developed an algorithm to address this problem [2] by means of machine learning techniques. They began defining the beam properties and building a distributed random sampling plan and then computed the objective function and constraint functions. The process starts from an initially computed dataset that is used to train Kriging models, which are later used as a filling strategy, and genetic algorithms, as an optimization strategy. The result of each iteration is added to the dataset, and the process is repeated until convergence is found. In this way, the Pareto front with the optimal solutions is obtained. 

  Abstract
  This research presents an optimization problem, which aims to understand the inherent design rules of the shape of a tree. It makes use of a classical optimization problem, [...]

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• Constitutive model for the analysis of the behavior and mechanics of wood damage

  R. Quinteros-Mayne, I. de Artega Jorda, J. Cabrero

  eccomas2022.

  
  

  Abstract

  Wood is a heterogeneous material, whose morphology and topology make the prediction of its mechanical behavior complex under different boundary conditions [1-3]. In this way, different constitutive models with different scale lengths have been developed since the middle of the 20th century to predict the behavior and mechanics of wood damage [3-8]. However, there is still no agreement on which constitutive model or scale length allows for a more consistent representation of behavior and damage mechanics mentioned. This article seeks to contribute to the discussion a new constitutive model for the analysis of the behavior and mechanics of wood damage. To do this, we present the implementation in a user subroutine for Abaqus [9], of a viscoelastic constitutive model based on the generalized well criterion for the elastic regime with a macroscale model [10] [11]; the onset and the damage evolution law are analyzed under a mesoscale model based on the progressive degradation of cracking parallel and perpendicular to the fiber [12-14]

  Abstract
  Wood is a heterogeneous material, whose morphology and topology make the prediction of its mechanical behavior complex under different boundary conditions [1-3]. In this way, [...]

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• Taut domain analysis of transversely isotropic dielectric elastomer membranes

  A. Khurana, G. Zurlo, M. Joglekar

  eccomas2022.

  
  

  Abstract

  Actuation devices made of dielectric elastomers are prone to compression induced wrinkling instabilities, which can adversely affect their performance and may lead to device failure. On the other hand, wrinkles can be used constructively in certain applications demanding a controlled alternation of the surface morphology. The idea of taut states and the natural width under simple tension plays an important role in the analysis of compression generated instability (wrinkling). In case of electrically driven DE membranes, the domain of taut states in the plane of principal stretches is influenced substantially by the applied voltage and the film's constitutive properties. In the recent past, there has been an increasing interest in exploiting anisotropy in the material behavior of dielectric elastomers for improving their actuation performance. Spurred with these ongoing efforts, this paper presents a continuum mechanics based electromechanical model for predicting the thresholds on the domain of taut states of transversely isotropic planar dielectric elastomers. The developed analytical framework uses an amended energy function that accounts for the electromechanical coupling for a class of incompressible transversely isotropic dielectric membranes. The required expressions for the total Cauchy stress tensor and the associated principal stress components are evaluated utilizing the amended energy function. Finally, the concept of natural width under simple tension is implemented to obtained the nonlinear coupled electromechanical equation that evaluates the associated taut states domain of the transversely isotropic planar dielectric elastomers. Our results indicate that the extent of taut domain can be controlled by modifying the level and the principal direction of the transverse isotropy. The taut states domain for a particular level of applied electric field increases with increase in the anisotropy parameter, while the taut domains depleted with the increase in fiber orientations from 00to 900for an applied level of electrical loading. The fiber-reinforced wrinkle-tunable surfaces can be effectively designed and developed using the underlying analytical framework and the trends obtained in this study.

  Abstract
  Actuation devices made of dielectric elastomers are prone to compression induced wrinkling instabilities, which can adversely affect their performance and may lead to device [...]

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• Energy-momentum conserving dynamic variational modeling of fiber-bending stiffness in composites

  I. Kalaimani, J. Dietzsch, M. Groß

  eccomas2022.

  
  

  Abstract

  We propose a new variational formulation for large deformations in dynamical systems made of 3D-fiber-reinforced composites. The formulation emanates from the dynamic variational approach based on the principle of virtual power. The use of higher-order gradient theory along with multi-field mixed-finite element method enables us to model the fiber-bending stiffness in fiber reinforced composites for numerical simulations accurately. Our proposed model capture higher-order energy contributions exhibited by fibers that influence the fiber-bending curvature, and consequently the fiber-bending stiffness behaviour. For this, we introduce a higher-order gradient of the deformation mapping as an independent field in the internal energy functional formulation. Along with the energy-momentum scheme, our new time integrator makes possible to perform long-term dynamic simulations with larger time steps and efficient CPU-time. We demonstrate our model using transient dynamical simulations on thre geometrical examples that exhibit hyperelastic, transversely isotropic, polyconvex gradient material behaviour. In the first example, a cantilever beam is self-excited due to its body weight, in the second, a L-shaped block tumbles free in the ambient space after an initial loading phase and in the third a turbine rotor is rotated due to hydrodynamic pressure. It is observed that our model conserves total momenta and total energy and preserves their time evolution in all these examples along with spatial and temporal convergence.

  Abstract
  We propose a new variational formulation for large deformations in dynamical systems made of 3D-fiber-reinforced composites. The formulation emanates from the dynamic variational [...]

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• From freezing-induced to injection-induced non-isothermal saturated porous media fracture

  Y. Heider

  eccomas2022.

  
  

  Abstract

  The focus of this contribution is laid on different aspects and instances related to porous media fracture under non-isothermal conditions. This includes the extreme case of fracturing due to pore-fluid freezing, where the micro-cryo-suction plays an important role in generating the required stresses for crack onset. This also includes studying the instances related to hydraulic fracturing and heat transfer under non-isothermal conditions. In all cases, the continuum mechanical modeling of the induced fractures is based on macroscopic porous media mechanics together with the phase-field method (PFM) for fracture modeling. For the micro-cryo-suction in saturated porous media, the water freezing is treated as a phase-change process. This is modeled using a different phase-field approach, in which the thermal energy derives the phase change and, thus, leads to the occurrence of micro-cryo-suction. Two numerical examples are presented to show the effectiveness of the proposed modeling frameworks.

  Abstract
  The focus of this contribution is laid on different aspects and instances related to porous media fracture under non-isothermal conditions. This includes the extreme case [...]

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• Efficient dispersion curve computations for periodic vibro-acoustic structures using the (generalized) Bloch mode synthesis

  V. Cool, F. Naets, L. Van Belle, W. Desmet, E. Deckers

  eccomas2022.

  
  

  Abstract

  Periodic structures such as metamaterials and phononic crystals hold potential as promising compact and lightweight solutions for noise and/or vibration attenuation in targeted frequency ranges. The performance of these structures is usually investigated by means of dispersion curves. The input for dispersion curve computations is often a finite element model of the corresponding unit cell. Nowadays, the vibration and noise attenuation of the periodic structures are generally tackled as separate problems and their performance is investigated with either structural or acoustic dispersion curves, respectively. Recently, vibro-acoustic unit cell models have come to the fore which can exhibit simultaneous structural and acoustic stopbands. However, the vibro-acoustic coupling inside the unit cell is usually not taken into account during the dispersion curve computations. To consider this coupling during their performance assessment, the computation of vibro-acoustic dispersion curves is required. Although these dispersion curves provide valuable information, the associated computational cost rapidly increases with unit cell model size. Model order reduction techniques are important enablers to overcome this high cost. In this work, the Bloch mode synthesis (BMS) and generalized BMS (GBMS) unit cell model order reduction techniques are extended to be applicable for 2D and 3D periodic vibro-acoustic systems. Through a verification case, the methodologies are shown to enable a strongly reduced dispersion curve calculation time while maintaining accurate predictions.

  Abstract
  Periodic structures such as metamaterials and phononic crystals hold potential as promising compact and lightweight solutions for noise and/or vibration attenuation in targeted [...]

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