Process Simulation for Braiding - Fachkongress Composite Simulation

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www.
.uni-stuttgart.de
Institut für Flugzeugbau
ENTWICKLUNGSTRENDS IN DER
FASERVERBUND-SIMULATION
Prof. Dr.-Ing. Peter Middendorf
Dipl.-Ing. Karin Birkefeld
Institute of Aircraft Design
University of Stuttgart
www.
.uni-stuttgart.de
R&D Focus for (Composite) CAE: Key Topics
1. Early concept phase
 Fast modeling and analysis tools  on time reliable information
2. Pre-design phase
 Multi-disciplinary design and optimization  ensure design freeze
3. Final design phase
 Detailed (non-linear) analysis for sizing & justification  save weight
4. New technology developments
 Process simulation, modeling and sizing methods & implementations
 enabling factor
5. A/C certification support
 Virtual structural testing  reduction of experimental testing and
development time
2012-02-23
Fachkongress Composite Simulation, Ludwigsburg
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.uni-stuttgart.de
Outline of Presentation
1. Process Simulation for Braiding
2. Multi-level Modelling and Analysis of Textile
Composites
3. Virtual Testing of Sandwich Core Materials
4. Conclusions
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Braiding @ IFB
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.uni-stuttgart.de
Braiding machine (IFB)
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Introduction to Braiding
The braiding process and the material is
variable for a high number of parameters…
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
Braiding angle

Circumference of the mandrel

Type and number of rovings

Weave construction

Tension on the fibers during braiding

Compaction of braided layers

Fiber volume fraction after infusion
and curing (RTM, vacuum assisted
processes)
Generic Demonstrator
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Process Chain Braiding
Braiding process parameters
Geometry of the component
Optimisation
Identification of
fiber architecture
Structural analysis
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Micro- and meso-mechanical analysis
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Process Simulation for Braiding
Why braiding simulation?
 Failure analysis of the material based on detailed
meso-models
 Optimization of the production process
 Determination of fiber orientation for structures with
complex geometry
 Direct determination of component stiffness and its
behavior under loading
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Bias and zero
degree yarns
Braiding mandrel
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Braiding ring
Springs
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 Representation of
rovings with bar and
beam elements
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 Triaxial braid with 30° braiding angle
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Results from braiding simulation compared to experiments
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Advantage:
 Realistic behaviour of fibers in yarn
Disadvantage:
 Friction behavior not implemented
 Enormous increase in CPU time
Multi-bar approach
Advantages:
 Deformation of cross-section
 Friction between shells
Shell-bar approach
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Disadvantage:
 Enormous increase in CPU time
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 Realistic behavior of the rovings
due to modeling of friction in the
system with shell-bar approach
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Rovings are not aligned
directly to the mandrel
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Future – Design for the process (CAM)
Optimized machine
parameters from
braiding simulation
Information about
preform compaction
for tool development
Braiding Simulation
Braiding of the preform
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RTM-Tool (FHNW)
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•
Influenced material parameters like stiffness,
strength, permeability, drapability, …
 How to predict the average properties of a
complex textile reinforced composite?
•
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Proposed solution: multi-level modelling
– Micro: level of yarn / roving
– Meso: level of a representative volume
element
– Macro: part size
MESO
Textile reinforced composites are more complex
– textile architecture, base materials,
– local variations, defects
– damage behaviour, ...
MACRO
•
MICRO
Modelling and Analysis of Textile Composites
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Meso-mechanical Modelling Approach
Braiding angle
Geometric model (WiseTex [*])
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Geometric characterisation
RVE
RVE
Yarn width
Spacing
Yarn crimp
FE model
Cross section shape
Yarn height
[* ]
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http://www.mtm.kuleuven.ac.be/Research/C2/poly/software.html
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Geometry Validation
•
Micro Computer Tomography of infiltrated CFRP
– Specimen is scanned under different angles
– Image processing software transfers the
result to a 3D voxel model
– Widely used for medical applications
– Fast data processing
– Model validation / creation
2012-02-23
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.uni-stuttgart.de
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FE Modelling of Textile Composites (FETex)
 Translation of WiseTex description into FE model
• Mesh principle for yarns:
– Mimic geometric entities in FE pre-processor
• Create cross sections
• Make linear interpolation
– Use mesher in FE pre-processor
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•
Create volume entities
Mesh principle for resin material
– Duplicate outer element faces of existing yarn
elements
– Create surface mesh on RVE boundaries
– Combine and mesh volume
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Model cross sections
Mesh
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FE Modelling of Textile Composites
•
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Material property definition
– Resin: Isotropic
– Fibre reinforced materials
• Based on WiseTex
description
– Fibre volume fraction Vf
– Fibre orientation fx, fy, fz
• Elastic properties using
Chamis mixing formulas
• Fibre orientations using
reference coordinate
systems
– Loop over all elements
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MESO-LEVEL
Homogenization: Meso-Macro Approach
Geometric model
Meso FE Analysis
Translation
FE + Homogenisation
MACRO-LEVEL
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
Part simulation

Part behaviour
Element average
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Damage Prediction and Failure
www.
•
 How does a complex textile
reinforced composite behaves
beyond initial damage?
Find out using multi-level
modelling:
– Apply damage model on small
scale
– Look at average response of
meso-mechanical RVE
•
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Local fibre orientation in yarn
elements enables application of
UD composite damage model
(here: Ladevèze) + damage
model for pure matrix material
(here: Weibull based)


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Virtual Testing
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Dynamic VST of Cellular Sandwich Core Structures
•
Objective: Obtain effective mechanical
properties of (existing/innovative) core
structures in various load cases, reducing
experimental (prototype) tests
•
Explicit dynamic simulations of compression/tensile/shear tests
•
Model development: Parametric model generation
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•
Modeling issues:
– Cell wall material modeling (e.g. resin-impregnated Nomex® paper)
– Imperfection modeling e.g.
• Global geometry distortion of individual cells
• Local distortion of node coordinates (node
shaking)
• Superposition of first buckling modes
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• Stochastically distributed property variation of
individual elements
– Model size
• Single unit cell with periodic boundary
conditions = unlimited honeycomb size
• Larger model with free edges
= test specimen behavior
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Nomex® honeycomb unit cell deformation under compression:
•
hexagonal cells:
over-expanded cells:
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Experiment
Simulation
2,5
2
1,5
1
0,5
0
Experiment
Simulation
2,5
2
1,5
1
0,5
0
0
20
40
compressive strain [%]
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compressive stress [MPa]
3
60
0
20
40
60
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Flatwise compression:
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Transverse shear:
In-plane compression:
•
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Application: Development of new cellular core geometries,
geometry optimization for special applications
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Extension to folded core materials (collaboration with DLR-BK)
– Aramid paper
Stress-strain diagram
buckling
www.
Aramid folded core
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Experiment
3
2
1
Simulation
0
0
20
40
60
folding/kinking
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•
Extension to folded core materials (collaboration with DLR-BK)
– CFRP folded core
CFRP folded core
Stress-strain diagram
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6
Experiment
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Simulation
2
0
0
5
10
15
20
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Conclusions
Future trends for composite simulation

Horizontal extension: capture full process chain

Vertical (in-depth) extension: multi-scale approaches

Multi-disciplinary: optimization of composite system

Increased reliability: towards virtual testing / certification
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.uni-stuttgart.de
Institute of Aircraft Design
middendorf@ifb.uni-stuttgart.de
www.ifb.uni-stuttgart.de/en/forschung/simulation
2012-02-23
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.uni-stuttgart.de
References
[1] Middendorf, P.: Virtual Design & Analysis of innovative Aeronautic
Structures: From Research to Application. MSC Aerospace Summit,
Toulouse, 2008
[2] Middendorf, P.; van den Broucke, B.: Multi-level Modelling and
Analysis of Textile Composites. Leichtbau-Seminar, Universität der
Bundeswehr, München, 2009
[3] Birkefeld, K.; von Reden, T.; Böhler, P.: Analysis and Process
Simulation of Braided Structures. EUCOMAS Conference, Hamburg,
2012
[4] Pickett, A et. al.: Braiding Simulation and Prediction of Mechanical
Properties. App. Comp. Mat. 2009; 16 (6): 345-364
[5] Middendorf, P.; Heimbs, S., Kilchert, S.; Johnson, A.: Numerical
Analysis of Aircraft Sandwich Structures with Composite Folded Core
in Compression. EuroPAM, Prague, 2008
2012-02-23
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Process Simulation for Braiding - Fachkongress Composite Simulation

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