Documents published in Scipedia

• 50 Years of Form Finding by the Force Density Method

  K. Bletzinger

  membranes2023.

  
  

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• Thinking to close the loop in membrane architecture

  C. Monticelli

  membranes2023.

  
  

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• The Evolution in the Design Tools for Membrane Structures

  P. Beccarelli

  membranes2023.

  
  

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• Progressive Damage in thin 2D Woven CFRP Laminates due to Stress Concentrations at Free Edges and Notches

  L. Heinzlmeier, S. Siberer, C. Kralovec, M. Schagerl, T. Wolfsgruber

  composites2023.

  
  

  Abstract

  Stress concentrations are present at cut-outs, notches, and generally at free edges in woven CFRP structures. Under cyclic loading, damage initiates from these stress raisers and progresses into the laminate, leading to strength reduction and structural failure. The present contribution provides a literature review summarizing analytical, experimental and numerical investigations regarding damage initiation and propagation in the presence of free edges and at notches in thin plain-woven 2D CFRP laminates. For free edges, initiation of damage is given as interlaminar matrix cracking. Modelling approaches for the progression by cohesive zone models or linear-elastic fracture mechanics are summarized. Recent advances using image correlation and numerical modelling are presented. In terms of notches, a brief survey of relevant literature is given, followed by a more detailed treatment of the damage progression originating from a circular hole. Additionally, the shortcomings of standard specimens with holes for fatigue damage progression investigations are addressed, since both mechanisms, damage from the free edge and the hole, interact. Latest research to uniquely identify the damage emanating from the hole is presented

  Abstract
  Stress concentrations are present at cut-outs, notches, and generally at free edges in woven CFRP structures. Under cyclic loading, damage initiates from these stress raisers [...]

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• Investigation into the Manufacture of Hybrid Wear Resistant Forging Tools using Tailored Forming Technology

  M. Till

  composites2023.

  
  

  Abstract

  Forging tools that are subject to high thermo-mechanical loads require a correspondingly high heat resistance, hardness and ductility to prevent undesirable failure patterns due to wear, plastic deformation and crack formation. These properties are mainly required in the layer of the tool engraving close to the surface, as this area is exposed to the highest loads due to the contact with the hot workpiece. With the heat transfer from the workpiece to the tool, a cyclic tempering process of the tool material often occurs in this area, resulting in a decrease in wear resistance. Diffusion treatments of the tool surface, such as additional nitriding, cannot provide sufficient protection in thermally highly stressed tool areas, as the heat-affected zone in these areas extends beyond the surface modification. As a result, a tempered layer forms under the nitrided layer, on which it can slide off or break as a result of the high process loads and the wear protection is lost. The use of nickel-based alloys promises an improvement in service life due to their high specific heat. However, these alloys are much more expensive than hot-work tool steels and are more difficult to machine, which has a negative effect on the economic use as a die material. Furthermore, nickel-based alloys do not have the high strength of steel that is often required in the base material that is subject to low thermal loads. To reduce the material usage of nickel-based alloys, but to fully take advantage of their positive properties, the suitability of the Tailored Forming concept in thermo-mechanically highly stressed areas were investigated within the scope of this research. For this reason, hybrid forging tool inserts with a base material of hot-work tool steel and a protective nickel-based alloy surface layer were produced. The hybrid tools are manufactured through a process combination of rotatory friction welding and die forging. The surface enlargement as a result of the forming process is to be used specifically to protect the relevant tool areas with a layer of nickel-based alloy and at the same time minimize the use of the expensive material. The effects of the thermo mechanical treatments occurring in the joining zone were examined and the potential of the technology was investigated

  Abstract
  Forging tools that are subject to high thermo-mechanical loads require a correspondingly high heat resistance, hardness and ductility to prevent undesirable failure patterns [...]

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• Evaluation of Bend-Twist Coupling in Shape Memory Alloy Integrated Fiber Rubber Composites

  A. Annadata, A. Endesfelder, M. Koenigsdorf, J. Mersch, T. Gereke, M. Zimmernann, C. Cherif

  composites2023.

  
  

  Abstract

  Advancements in textile technologies such as the integration of wire shaped Shape Memory Alloys (SMAs) on to the fabric with the help of Tailored-Fiber-Placement (TFP) method, and weft insertion of SMAs during manufacturing of textiles using knitting machines are helping to create composites capable of bending deformations without any external loads. These advancements laid the foundations for versatile applications especially in soft robotics. One such application is Interactive Fiber Rubber Composites (IFRC). The aim of this project is to evaluate the bend-twist coupling in the IFRC. The SMA reinforced composite is made of polydimethylsiloxane (PDMS) and has two layers of glass fibers stacked upon one another and joined with the help of TFP machine. This work focuses on the simulation of this approach in ANSYS with the Woodworth & Kaliske material model for SMA. The important feature of this model is that the shape memory effect can be achieved for different profiles of SMA, thus eliminating the necessity for a pre-stretch in contrast to the built-in model. The experimental values are evaluated from Multi-DIC technique, which is capable of determining deformations with respect to all directions. A comparative study with simulation and experimental results of the deformation and twisting angles is carried out. The derived conclusions will be helpful in obtaining and evaluating 3D spatial movements in IFRC structures with multiple joints in the future projects

  Abstract
  Advancements in textile technologies such as the integration of wire shaped Shape Memory Alloys (SMAs) on to the fabric with the help of Tailored-Fiber-Placement (TFP) method, [...]

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• Analysis of Cure Behaviour Uncertainties in Thermoset Composite Parts using Particle Filter

  A. Balaji, C. Sbarufatti, D. Dumas, O. Pierard, F. Cadini

  composites2023.

  
  

  Abstract

  Process-induced deformations result from internal residual stress caused by the anisotropic properties of thermoset composite parts. The study’s focus is diagnosing the polymerization process, or curing, and considering how uncertainties in boundary conditions affect cure kinetics. This is achieved through a Particle Filter approach, utilizing a Bayesian framework. This framework recursively estimates the evolving cure state’s posterior distribution based on observed measurements from Differential Calorimetry Scanning tests and thermocouples. The algorithm simultaneously estimates the cure state parameters and predicts part temperature and process-induced deformations, which are closely tied to cure behaviour. This is accomplished using diffusion cure kinetics and analytical deformation models. Furthermore, it introduces an augmented cure state formulation to address uncertainties in cure boundary conditions, which conventional models overlook. The developed stochastic approach adeptly captures uncertainties related to cure evolution while providing comparable deformation predictions with minimal computational costs and memory usage. Experimental measurements of process-induced deformations in C-shaped thermosetting parts, made of unidirectional 8552/AS4 fibres and cured following the Manufacturing Recommended Curing Cycle, are validated using the developed algorithm. After validation, the proposed model is employed to predict outcomes, which are then utilized to determine the optimal curing cycle using a Genetic Algorithm.

  Abstract
  Process-induced deformations result from internal residual stress caused by the anisotropic properties of thermoset composite parts. The study’s focus is diagnosing the [...]

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• Numerical Simulation of the Fatigue Damage Growth in Unidirectional Composites based on Fibre-Matrix Debonding

  A. Seidel, B. Sørensen, K. Drechsler

  composites2023.

  
  

  Abstract

  A methodology for investigating the micromechanical fatigue behaviour of unidirectional composites based on fibre-matrix debonding is developed. The fatigue damage mechanism is based on the progressive failure of fibres caused by debond crack tip stress fields resulting from fibre breaks in previous load cycles. The methodology combines an analytical model to describe the debond crack initiation and growth with a numerical finite element model to calculate resulting stresses. The methodology is applied on a two-fibre model composite. It can qualitatively predict the stress development within the simulation domain as well as the mechanism of a debond crack tip stress field triggering a break in a neighbouring fibre. Both is consistent with microscale observations in the literature.

  Abstract
  A methodology for investigating the micromechanical fatigue behaviour of unidirectional composites based on fibre-matrix debonding is developed. The fatigue damage mechanism [...]

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• 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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