Documents published in Scipedia

• Post-buckling behaviour and delamination growth in defected variable angle tow composite laminates

  D. Gaetano, F. Greco, L. Leonetti, A. Pranno, G. Zucco

  ECCOMAS 2024.

  
  

  Abstract

  Due to their specific strength and stiffness properties, composite materials are largely used in lightweight structural applications in aerospace, automotive and mechanical engineering. Understanding how these materials fail under service loads is a challenging aspect of designing advanced composite structures. In fact, the failure of composite laminated structures is often governed by complex interactions of multiple interlaminar failure and damage mechanisms. Among them, delamination is one of the damage modes requiring large attention due to the low interlaminar resistance between the different layers comprised in a composite laminate. In addition, this phenomenon may be triggered by defects introduced in the construction phase or by the presence of connections leading to stress concentrations. When coupled with buckling phenomena, delamination inevitably decreases the load-carrying capacity of lightweight composite structures. Variable Angle Tow (VAT) laminates have been proven to improve the buckling and post-buckling response of those structures significantly. However, little is known about the geometrically nonlinear behaviour of VAT composite laminates with delaminations. This work applies the cohesive finite element method to model delamination growth in VAT composite laminates containing initial defects under compressive loading conditions. Numerical simulations investigate the effects of the fibre angle variation on the geometrically nonlinear static response of VAT composite laminates compared to that of their classical straight fibre counterparts.

  Abstract
  Due to their specific strength and stiffness properties, composite materials are largely used in lightweight structural applications in aerospace, automotive and mechanical [...]

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• Numerical and analytical evaluation of resin flow during PCB pressing cycles

  C. Schipfer, J. Zuendel, Q. Tao, T. Krivec, P. Fuchs, M. Gramueller

  ECCOMAS 2024.

  
  

  Abstract

  This paper presents a comprehensive sequence of analytical methods for evaluating printed circuit board (PCB) pressing processes, augmented by numerical finite element (FE) simulations. The study considers the properties of the prepreg material, the structure of the PCB copper layer, and various pressing process parameters, all of which can be adjusted according to specific requirements. Our results are validated through experiments and compared with the established Squeeze Flow Model. The pro posed methodology identifies potential weaknesses in the design of the copper layer, material selection, and pressing parameters prior to production. Additionally, the implementation of this methodology in an interactive user interface allows for rapid and efficient results, facilitating timely decision-making and process optimization

  Abstract
  This paper presents a comprehensive sequence of analytical methods for evaluating printed circuit board (PCB) pressing processes, augmented by numerical finite element (FE) [...]

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• Computational analysis of non-proportional biaxial shear reverse experiments superimposed by different cyclic loads

  Z. Wei, S. Gerke, M. Brünig

  ECCOMAS 2024.

  
  

  Abstract

  This paper deals with anisotropic ductile damage and fracture behavior under low positive stress triaxialities. Novel tension–shear biaxial low–cycle experiments with different numbers of loading cycles (up to twenty) have been performed using a cruciform biaxially loaded specimen. During the experiment, a tensile preload is first imposed on the horizontal axis until it reaches 3kN; then, it is kept constant while different shear cyclic loading sequences are superimposed on the vertical axis until failure. All cyclic loadings are driven to a large strain range to investigate ductile damage, and the same amplitude is maintained for each repeated reverse loading cycle within a single loading pattern. In addition, numerical simulations are performed with an anisotropic stress-state-dependent plastic-damage continuum model, also considering the Bauschinger effect. The experimental and numerical analysis of the evolution of the first principal total strain and damage strains highlights the influence of the cyclic loading history on the material behavior. Moreover, fracture surfaces are examined by scanning electron microscopy to analyze the different mechanical performances at the micro-level

  Abstract
  This paper deals with anisotropic ductile damage and fracture behavior under low positive stress triaxialities. Novel tension–shear biaxial low–cycle experiments with [...]

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• Adaptive Refinement Techniques using Multiresolution Wave Propagation Simulations Guided by Inherent Convergence Indicators

  D. Dimitriou, A. Samara, D. Saravanos

  ECCOMAS 2024.

  
  

  Abstract

  The multiresolution finite wavelet domain method has been meticulously studied in wave propagation simulations. The multiresolution procedure always starts with the coarse solution, and then finer solutions can be superimposed on the coarse solution, until convergence is achieved. Based on remarkable observations on the multiple resolution components of the method, a residual-based convergence indicator that reveals convergence at the coarse solution is developed. This convergence metric is rapidly applicable and straightforward and can also divulge the spatial and temporal ranges/domains that the already obtained solution needs to be enhanced. In that way, an automatic adaptive refinement technique is proposed for the local enrichment of the solution, only in the specific grid points and time-steps that it is needed. A numerical case study regarding wave propagation in an inhomogeneous rod manifests the effectiveness and accuracy of the proposed automatic refinement methodology, as also the performance of the suggested convergence indicator.

  Abstract
  The multiresolution finite wavelet domain method has been meticulously studied in wave propagation simulations. The multiresolution procedure always starts with the coarse [...]

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• Seismic Performance Assessment of Bouçã Arch Dam. Non-Linear Analysis Considering Joint Movements and Concrete Damage Under Tension and Compression

  S. Oliveira, A. Alegre, C. Serra, R. Ramos, J. Silva, J. Proença, P. Mendes

  ECCOMAS 2024.

  
  

  Abstract
  Download

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• Simultaneous, Dynamical Analysis of Structural Ropes and Membranes on all Level-sets

  T. Fries, M. Kaiser

  ECCOMAS 2024.

  
  

  Abstract

  Thelevel sets of scalar functions may imply the geometries of individual ropes and membranes. All level sets within an interval, considered in some bulk domain, define infinitely many geometries at once. A mechanical model is proposed which enables the simultaneous, dynamic analysis of all such geometries. For the solution of the governing equations, a tailored numerical method coined Bulk Trace FEM is employed for the spatial discretization, using higher-order background meshes in the bulk domains. The HHT-α method is used for the temporal discretization. Numerical results are presented that demonstrate the potential of the proposed mechanical model and numerical method

  Abstract
  Thelevel sets of scalar functions may imply the geometries of individual ropes and membranes. All level sets within an interval, considered in some bulk domain, define infinitely [...]

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• Micro-scale analysis of rough surfaces using non-conforming meshes

  M. Oliveira, D. Neto, L. Menezes

  ECCOMAS 2024.

  
  

  Abstract

  This work presents a finite element model of the contact between a flat rigid surface and a rough deformable elastoplastic body, enabling the micro-scale analysis of the contact conditions. To assure the computational efficiency a non-conforming mesh is adopted to describe the deformable body. The results show that the model can capture the main effects of the bulk material constitutive behaviour, which is known to have a significant impact on the problem, as well on local changes on the friction conditions.

  Abstract
  This work presents a finite element model of the contact between a flat rigid surface and a rough deformable elastoplastic body, enabling the micro-scale analysis of the contact [...]

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• Offline and Online Performance Contrast of Optimal Control

  M. Miah, W. Lienhart

  ECCOMAS 2024.

  
  

  Abstract

  Civil structures are quite vulnerable to extreme dynamic loads as well as to nat ural disasters. The aforementioned problem is well-known and interestingly, unavoidable as it is almost impossible to know when that type of loads or disasters are going to hit the existing structures. Due to such unpredictability, many are interested to adopt the online or real-time control and monitoring strategy instead of conventional approach. However, still offline moni toring and vibration control strategies are useful to understand the overall performance of the investigated dynamical problem as it might not be an option to go for online due to feasibility or other constrains. In order to hold a debate, herein, the controlled performance of a multi degree-of-freedom system has investigated both adopting offline and online approaches. The linear-quadratic regulator (LQR) algorithm has been employed as the control law and it is as sumed that controller will behave as an active control system. In order to understand the effect of the optimal control, the displacements and velocities at different degree-of-freedom’s level have considered and compared. The outcome suggests that both approaches have advantages and disadvantages such as offline approach is quite useful to understand at the design phase of the project, while, online approach might be very effected after the construction.

  Abstract
  Civil structures are quite vulnerable to extreme dynamic loads as well as to nat ural disasters. The aforementioned problem is well-known and interestingly, unavoidable as [...]

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• Determination of Neutral Axis and Effect of the Variation of Cross Sectional Area on the Mechanical Properties of Smart Meta-Structure

  S. Sahana, A. Singh, B. Bhattacharya

  ECCOMAS 2024.

  
  

  Abstract

  In recent years, manufacturing has paved the way to enhance structural properties using 3D printed structures by constructing complex shapes. The properties of such structures depend on the arrangement of the internal lattices. Honeycomb is one such simple lattice struc ture that is widely used by researchers as it exhibits a high strength-to-weight ratio. However, the elastic properties of the lattice structures are intrinsic functions of the material properties and the geometric shape. Hence, it is impossible to modulate the elastic properties once constructed. Recent studies have shown that the active modulation of the elastic properties can be achieved by incorporating smart materials over the substrate layers of the lattice. The analytical expressions have been developed for honeycomb/ auxetic honeycomb lattice considering the Euler-Bernoulli bi-layer beam to determine its elastic properties. The expression is well valid for lattices where the thickness of the smart material is relatively less compared to the substrate thickness. How ever, it does not produce consistent results as the thickness of the smart material increases due to the shift of the position of the neutral axis, which was earlier assumed to be at the geomet ric centre of the substrate beam. This paper presents a modified formulation that considers the change in the position of the neutral axis as the thickness of the smart material patches varies. This modification allows the use of the analytical expression for beams with higher thickness ratios and can be used to understand the impact of forces in shear deformation. In addition, the variation in the elastic properties has also been investigated for different cross-sectional shapes such as I-section, T-section, and rectangular cross-section. The formulation presented here is generic, and the concept can be used in various futuristic multi-functional structural systems and devices across different length scales

  Abstract
  In recent years, manufacturing has paved the way to enhance structural properties using 3D printed structures by constructing complex shapes. The properties of such structures [...]

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• ψ − flow: A Novel Physics-Constrained Architecture to Enforce Incompressibility and Boundary Conditions for Fast and Accurate Flow Predictions

  M. Cabral, B. Font, G. Weymouth

  ECCOMAS 2024.

  
  

  Abstract

  Deeplearning models have demonstrated remarkable capabilities at producing fast predictions of complex flow fields. However, incorporating known physics is essential to ensure that physical solutions can generalize to flow regimes not used for training. In this study, a formulation that, by construction, enforces flow incompressibility and respects the invariance of physical laws across different unit systems is introduced. We demonstrate that this approach can achieve performance improvements of up to 100 times compared to purely data-driven methods, all while maintaining fidelity to other crucial physical quantities. Moreover, we show that for canonical flow test cases, such a physics-constrained model can yield accurate results even with training datasets as small as a few hundred points and neural networks containing only a handful of neurons. It is also shown, however, that physics-constrained machine learning models are not silver bullets out of the box, and require careful consideration in their application and integration with other constraints. Specifically, this study addresses how a problem that is mathematically simple may not necessarily be straightforward in machine learning terms, and discusses ongoing efforts to bridge this gap. We conclude by discussing the place of physics-constrained machine learning models within a landscape primarily dominated by physics-informed approaches, in particular in the context of real-world problems where data and computational resources are often limited

  Abstract
  Deeplearning models have demonstrated remarkable capabilities at producing fast predictions of complex flow fields. However, incorporating known physics is essential to ensure [...]

  • 197
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