Documents published in Scipedia

• Application of Model-based Design Approach on Dynamic Tensile Testing of Carbon/Epoxy Composites at Intermediate Strain Rates

  S. Yoo, E. Kim, N. Toso, H. Voggenreiter

  composites2023.

  
  

  Abstract

  The reliable strain rate-dependent material properties at intermediate strain rate levels (1-200 s-1 ) are crucial for an accurate crashworthy design of fibre-reinforced polymer (FRP) composite structures. However, the presence of unacceptable oscillations in measured force signals hinders the precise identification of the dynamic mechanical response of materials. The current work reports the results of gained in an initial study using a novel numerical model developed through a Model-based Design (MBD) approach. A multi-degree of-freedom (MDOF) mass-spring-damper model is employed to investigate the dynamic characteristics of a whole experimental test setup to gain insights into the dynamic interaction between the test machine and the test specimen. The developed model was calibrated by the results from dynamic tension testing of Aluminium Alloy 2024-T3. Then, the model parameters were optimised using a genetic algorithm (GA). Subsequently, the adaptability of the developed model to carbon/epoxy composites, IM7/8552, was examined. The proposed model is promising to identify the influence of the test setup on the measurements and effectively distinguish excessive oscillations caused by its inertial effect at intermediate strain rate levels. The model will offer a robust solution to identify oscillations and, therefore, expand the testing capabilities to a broader range of strain rates.

  Abstract
  The reliable strain rate-dependent material properties at intermediate strain rate levels (1-200 s-1 ) are crucial for an accurate crashworthy design of fibre-reinforced polymer [...]

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• Tensile Testing of Pinned Hybrid CFRP/Titanium Joints and Damage Monitoring with Electrical Resistance Measurements

  A. Dengg, C. Kralovec, M. Schagerl

  composites2023.

  
  

  Abstract

  This contribution presents a new evaluation approach for Structural Health Monitoring of a pinned hybrid CFRP/titanium single-lap shear joint with the help of direct current electrical resistance measurements. The result is a dimensionless, load-independent damage indicator that is similar to an already developed evaluation approach by the authors but is simpler and more robust in comparison. Readily published test data is re-evaluated with the new evaluation approach and compared with the existing structural as well as the electrical resistance results. Finally, further test setup improvements for future tests are discussed.

  Abstract
  This contribution presents a new evaluation approach for Structural Health Monitoring of a pinned hybrid CFRP/titanium single-lap shear joint with the help of direct current [...]

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• Effect of Ply Thickness on Dynamic Damage Progression in Cross-ply Laminates Under Low-velocity Impact

  O. Batmaz, D. Coker

  composites2023.

  
  

  Abstract

  : In this study, we have conducted in-situ LVI experiments on cross-ply CFRP beams having stacking layups [04/904/02]s and [02/902/02/902/02]s. The progression of damage is observed through high-speed photography. In addition to LVI, quasi-static indentation (QSI) experiments are performed to reduce challenges in monitoring damage progression during the short impact loading interval. QSI experiments provide magnified in-situ observations on the free edge of the beam using a traveling digital microscope. Numerical simulations of these experiments are carried out using the finite element method in ABAQUS/Explicit. The orthotropic constitutive material model, predicting fiber and matrix damage initiation and evolution, is implemented through a VUMAT subroutine. The comparison between numerical simulations and experimental observations allowed us to investigate the influence of ply clustering on the LVI-induced damage mechanisms.

  Abstract
  : In this study, we have conducted in-situ LVI experiments on cross-ply CFRP beams having stacking layups [04/904/02]s and [02/902/02/902/02]s. The progression of damage is [...]

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• Investigation of Several Impact Angles for Predicting Bird-Strike Damage in a Riveted eVTOL Composite Wing

  E. Kayar, G. Abdelal, B. Falzon, Z. Kazanci

  composites2023.

  
  

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• A 3D Damage Model for Simulating Damage Modes in Fibre Metal Laminates

  I. Abuzayed, J. Curiel, N. Wiravan, C. Zhang

  composites2023.

  
  

  Abstract

  This paper presents a 3D damage model utilized for studying the failure characteristics of GLARE. The current damage model adopted the 3D forms of Hashin’s and Puck’s failure criteria for predicting the onset of failure of fibres and matrix in the composite plies. Whilst the damage evolution is modelled based on the dissipation of fracture energy. In addition, a ductile damage model was employed to study the failure of metal layers and the delamination was assessed via a cohesive interface model. The current damage model was adopted to predict the failure modes and the blunt notch strength of GLARE; where various failure modes were observed, such as Fibre breakage, matrix cracking, delamination and plastic damage of aluminium layers. The model showed strong agreement with experimental results.

  Abstract
  This paper presents a 3D damage model utilized for studying the failure characteristics of GLARE. The current damage model adopted the 3D forms of Hashin’s and Puck’s [...]

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• Virtual manufacturing of thick composite beams, investigating cure cycle and shrinkage induced stress

  J. Vroon, N. van Hoorn

  composites2023.

  
  

  Abstract

  Investigating cure shrinkage-induced stress in thick composite beams by virtual manufacturing is the focus of this study. The research aims to understand the behaviour of thick-walled composite structures, particularly in relation to curing shrinkage-induced damages. The curing process of resin is simulated thermally and mechanically to investigate the residual cure-induced stress. The study utilizes a finite element model in Abaqus, considering material properties, mesh, boundary conditions, and user subroutines. Ten different cure cycles are investigated, showing improvements in reducing internal stresses after curing compared to the manufacturer's cycle of about 20%. However, during curing, the investigated cycles provide marginal improvements. This study demonstrates the potential for optimizing cure cycles to reduce internal stresses in thick-walled applications. It is important to note that the proposed method is not experimentally validated and requires accurate measurements for validation.

  Abstract
  Investigating cure shrinkage-induced stress in thick composite beams by virtual manufacturing is the focus of this study. The research aims to understand the behaviour of [...]

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• Free Vibration Analysis of Thermally Prestressed Constant and Variable Stiffness Laminated Beams using Strong Unified Formulation

  S. Ojo, G. Zucco, P. Weaver

  composites2023.

  
  

  Abstract

  Free vibration analysis is an essential requirement to capture the behaviour of composite structures subject to dynamic loading environment. To enhance the vibratory behaviour of composite structures, variable stiffness (VS) concept offers increased design flexibilities to tailor the structural response to meet a wide range of applications. Mechanically, the increased design space created by VS techniques leads to complexities of non-classical stiffness couplings which necessitate robust computational frameworks with enriched kinematics to predict the dynamic response accurately and efficiently. In this regard, this study proposes an enhanced differential quadrature based Strong Unified Formulation (SUF) to investigate the free vibration behaviour of thermally prestressed constant and variable stiffness composite beams. The proposed SUF model exploits the flexible kinematical description of the Theory of Unified Formulation to combine a hierarchical serendipity Lagrange-based 2D finite element (FE) with 1D differential quadrature method beam element for efficient free vibration characterisation of composite beams induced with prestress at different temperatures. The proposed SUF free vibration solutions of constant stiffness and VS beams demonstrate satisfactory accuracy and achieved improved efficiency with up to 99.9% computational savings when benchmarked against ABAQUS 3D FE solutions. Finally, a numerical study reveals that the effects of thermal prestress significantly contribute to the free vibration response of constant stiffness and VS laminated beams underscoring the importance of the study.

  Abstract
  Free vibration analysis is an essential requirement to capture the behaviour of composite structures subject to dynamic loading environment. To enhance the vibratory behaviour [...]

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• On the Importance of Fibre Direction Mesh Alignment for Artificial Lightning Strike Simulations

  S. Millen, B. Navagel, A. Murphy

  composites2023.

  
  

  Abstract

  Composite materials, used in primary aircraft structures, produce weight reduction and improved fuel efficiency over legacy metal airframes but are more susceptible to lightning strike damage. Therefore, research into lightning strike damage and protection systems, through experiments and simulations, is an important research topic. For any FE simulation appropriate representation of the material behaviour, the loading and boundary conditions are key to accurate predictions. In addition, an aspect which has been under reported in many studies is the meshing strategy. Fibre direction mesh alignment has been reported to yield more accurate results in the modelling of mechanical damage (intralaminar damage initiation and propagation) in unidirectional fibre reinforced composite structures. However, this model meshing strategy has not found wide application and has not been used for the modelling of thermal damage events, e.g. lightning strike direct effect simulation. Instead, authors have typically refined the mesh around the arc attachment area. This paper, for the first time, examines the influence of fibre direction mesh alignment for artificial lightning strike simulations and the prediction of thermal damage. Initially, the mesh alignment is introduced partially in the central region of the specimen. The paper uses a mature modelling approach with a transient, fully coupled, thermal-electric step in ABAQUS with a lightning test Waveform A (40 kA, 4/20 µs) applied to the specimen. Specimen boundary conditions match those typically used in experiments and a mesh convergence study is undertaken to ensure no element size influence on the results. The use of this meshing strategy has been shown to significantly improve the prediction of both moderate and severe thermal damage profiles, when compared with the standard meshes used in previous research. The predicted moderate (2659 mm2 vs 2833 mm2 ) and severe (1059 mm2 vs 1061 mm2 ) damage areas were improved to within 4% and 1% of experimental results, respectively, using this meshing strategy.

  Abstract
  Composite materials, used in primary aircraft structures, produce weight reduction and improved fuel efficiency over legacy metal airframes but are more susceptible to lightning [...]

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• Coupled problems in bio-inspired robotics

  A. Simone

  coupled2023.

  
  

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• FEM Simulations for Nonlinear Multifield Coupled Problems: Application to thixoviscoplastic flow

  N. Begum, A. Ouazzi, S. Turek

  coupled2023.

  
  

  Abstract

  In this note, we are concerned with the solvability of multifield coupled problems with different, often conflictual types of non-linearities. We bring into focus the challenges of getting EFM numerical solutions. As for instance, we share our investigations of the solvability of thixoviscoplastic flow problems in FEM settings. On one hand, nonlinear multifield coupled problems are often lacking unified FEM analysis due to the presence of different nonlinearities. Thus, the importance of treating auxiliary subproblems with different analysis tools to guarantee existence of solutions. Moreover, the nonlinear multifield problems are extremely sensitive to the coupling. On other hand, monolithic Newton-multigrid FEM solver shows a great success in getting numerical solutions for multifield coupled problems. Thixoviscoplastic flow problem is a perfect example in this regard. It is a two field coupled problem, by means of microstructure dependent plastic-viscosity as well as microstructure dependent yield stress, and microstructure and shear rate dependent buildup and breakdown functions. We adapt different numerical techniques to show the solvability of the problem, and expose the accuracy of FEM numerical solutions via the simulations of thixoviscoplastic flow problems in channel configuration.

  Abstract
  In this note, we are concerned with the solvability of multifield coupled problems with different, often conflictual types of non-linearities. We bring into focus the challenges [...]

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