Documents published in Scipedia

• Micromechanical Homogenization Methods of Short Glass Fiber-reinforced Injection-molded Bio-based Composite Material

  O. Schwahofer, K. Dreschler, F. Otero, P. Camanho

  composites2023.

  
  

  Abstract

  Herein, microscale approaches were explored to determine the homogenized properties of short fibre reinforced polymer material. The analytical homogenization follows the shear lag principle to approximate elastic modulus in the case of longitudinally oriented short fibres. For the finite element-based homogenization, a periodic 3D representative volume element of the composite is constructed to apply forward numerical homogenization. This unit cell is discretized by tetrahedral 3D finite elements resulting in a periodic mesh. An effective spring element method was further developed to homogenize the properties of short fibre-reinforced material. The reduced order spring method predicted the elastic properties almost equally to the finite element-based homogenization. A novel bio-based polyamide matrix with 40% glass fibre content and a traditional polyamide with 30% glass fibre reinforcement serve for the application and validation of the developed micromechanical methods. An additional effectivity parameter must be considered to capture the manufacturing imperfections of the injection molding process. This parameter can be calibrated based on experimental data from tensile testing. The developed numerical frameworks show good potential for extensions to more advanced modelling of the composite, such as nonlinear behaviour or failure mechanism.

  Abstract
  Herein, microscale approaches were explored to determine the homogenized properties of short fibre reinforced polymer material. The analytical homogenization follows the shear [...]

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• Impact damage modelling in composite laminates – numerical implementation of a strain rate dependent damage model

  D. Ivančević, J. Ratkovic

  composites2023.

  
  

  Abstract

  In this work, a numerical methodology for simulation of impact damage in laminated CFRP structures has been developed and implemented into the Abaqus/Explicit software. The methodology is based on the recent insights into the mechanical behaviour of CFRP materials at various strain rates. Failure initiation is modelled using the failure theory that was introduced in Coles et al. (2019). This approach has been modified to include the strain rate effects according to work presented in Raimondo et al. (2012) and to account for the mesh objectivity of the damage process in this work. The model has been implemented into Abaqus/Explicit using the user material subroutine VUMAT and details of the implementation are discussed in the work. The model has been applied to the simulation of two impact simulations demonstrating that the damage modes of the composite plate, as well as damage scope and displacement fields, have been simulated accurately. The methodology has been previously developed for application in unidirectional composite plates, whereas this work and current research phase focus on woven composites. Additionally, only the in-plane failure modes are currently considered whereas the out-of-plane damage modes will be investigated in the future research.

  Abstract
  In this work, a numerical methodology for simulation of impact damage in laminated CFRP structures has been developed and implemented into the Abaqus/Explicit software. The [...]

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• SHM system for bonding line monitoring of composite wing box skin-spar cap during manufacturing

  M. Ciminello, A. Concilio, U. Mercurio, G. Apuleo

  composites2023.

  
  

  Abstract

  The CFRP wing box section under investigation is a stringer less wing-box (develop within the OPTICOMS research project) and consists of two portions: an upper part, made of co-cured spars and a top skin panel, and a bottom cured skin panel. The two portions are joined with a bonding process, giving rise to the final wing-box. During that final assembly step, distributed fibre optics were embedded between the spar caps and the bottom skin panel along the bonding lines. The embedded FO consists of six distributed fibres running within the bonding layer for about 1 m along the span direction. An irregular damage map was defined, by simulating the presence of manufacturing bonding defects by the intersection of teflon patches, different for width and length, to check an SHM system capabilities in detecting such flaws. The SHM system was tested after the final bonding process, by exploring the info contained within the “residual strains” data of the unloaded structure. Results obtained by post processing data for each fibre optic, are reported. The damage index associated to the eligible sensors is provided. Based on the available data, the SHM algorithm appeared to be sensible enough to hundreds of microstrain signals. Concerning faults detection, sensor density seems a key. Errors in the estimate of the damage extension can be assessed to be around 25%

  Abstract
  The CFRP wing box section under investigation is a stringer less wing-box (develop within the OPTICOMS research project) and consists of two portions: an upper part, made [...]

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• 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 [...]

  • 4
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