Finite Element Simulation of the In

146 Pages·2016·5.21 MB·English

by  Gautam Kumar Jeyakodi

Master of Science Thesis
Finite Element Simulation of
the In - Situ AFP process for
Thermoplastic Composites using
Abaqus
Gautam Kumar Jeyakodi
Faculty of Aerospace Engineering · Delft University of Technology

Finite Element Simulation of the In -
Situ AFP process for Thermoplastic
Composites using Abaqus
Master of Science Thesis
For obtaining the degree of Master of Science in Aerospace Engineering
at Delft University of Technology
Gautam Kumar Jeyakodi
September 30th,2016
Faculty of Aerospace Engineering · Delft University of Technology
Copyright © Gautam Kumar Jeyakodi
All rights reserved.
Delft University of Technology
Faculty of Aerospace Engineering
Department of Aerospace Structures and Materials
The undersigned hereby certify that they have read and recommend to the Faculty of
Aerospace Engineering for acceptance a thesis entitled
Finite Element Simulation of the In - Situ AFP process for Thermoplastic
Composites using Abaqus
by
G. K. JEYAKODI
in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE
Dated: September 30th,2016
Chair holder:
Prof. Dr. ir. Rinze Benedictus
Committee members:
Dr. ir. Sonell Shroff
Dr. ir. Javad Fatemi

Summary
The out - of autoclave processing technology of thermoplastic composite has seen significant
development over the past decades. The in - situ processing in Automated Fibre Place-
ment (AFP), combines the additive manufacturing technology and the philosophy of out -
of autoclave process. To emulate the processing quality of parts produced using autoclave
processes, it is imperative to study the interactions between the processing parameters and
thecompositematerialduringthein-situAFPprocess. Mathematicalmodelsofthein-situ
processing,weredevelopedbyseveralresearcherstoidentifyprocessingwindowsforproducing
good laminates. The increase in computational power and simulation capabilities supported
the development of process modelling. From a literature review on the process modelling of
the in - situ AFP technology, it was identified that an application-oriented simulation tool
couldbedevelopedthatcanserveasaprocessingguideforanysetofprocessingconfiguration
or thermoplastic composite material. Moreover, the development of residual stresses in the
tapesduringprocessingwerestudiedonlybyafewresearchersusingmathematicalsimulation
models. Many assumptions were made in the calculations to estimate the final residual stress
state. Therefore, a new approach to simulate the in - situ AFP process was developed using
ABAQUS. The goal was to determine the effects of processing parameters on the develop-
ment of residual stresses in the laminate. The in - situ process was first modelled to obtain
the thermal distributions in the laminate. The set-up of the model is aimed to predict the
effects of the processing parameters on the thermoplastic composite material. The simulation
is also combined with a bonding model to predict the development of interlaminar bonding
in the laminate during processing. The established simulation methodology/procedure would
serve as a good tool to predict the effects of processing conditions for a certain thermoplastic
composite laminate.
The numerical simulation was performed in ABAQUS using a Coupled Temperature Dis-
placement analysis. A fully scripted procedure in PYTHON was developed to allow for a
fast and efficient pre- and post-processing. Parametric studies can be performed easily by
modifying the user defined input variables in the PYTHON code. The ABAQUS input files
are generated based on the PYTHON script that specifies the entire processing procedure.
Basedonthelaminatestackingsequenceandthenumberoflayersinthelaminate,thepython
code generates the correspondingly along with all the interactions and boundary conditions.
To apply the transient laser heat and roller pressure, the USER SUBROUTINES - DFLUX
and DLOAD were developed in FORTRAN. The ABAQUS input files were uploaded to the
TU Delft cluster to run the simulations. The results of the simulations were extracted from
viii Summary
query nodal sets created in each tape layer. These nodes store the temperature and stresses
induced during processing. The material selected for this simulation study is Aromatic Poly-
mer Composite 2 (APC-2). This composite is composed of high strength, standard modulus
carbon fibres (AS-4) embedded at 61% f/v ratio in a thermoplastic matrix of Polyther Ether
Ketone (PEEK).
Asetofpreliminarytestswereconductedtoset-upthesimulationofthein-situAFPprocess
in ABAQUS. An optimised part model dimension was determined and a mesh convergence
study was conducted to determine the minimum mesh size. The interface of the laminate was
modelled based on a user defined solution by specifying the thermal and mechanical contact
properties. A parametric study for GAPCON (Gap conductance) was performed to evaluate
the thermal contact resistance at the interfaces of the laminate. The simulation of the in -
situ process comprises of three main studies: Thermal analysis, Degree of Bonding (DOB)
analysis and Stress Analysis.
First, a thermal analysis of the in - situ AFP process was performed to determine the thermal
distributions induced in the laminate for various process configurations. In total, 15 different
processmodelsweresimulatedtoanalysetheeffectoftoolheating,variableheating,combined
toolheating&variableheating,long&shorttoolreturntimes,rollervelocityandtheeffectof
an insulated mould. A verification of the simulation model was made to a similar simulation
study from literature. The results of the thermal analysis showed a great depths of detail
in capturing the material response during the in - situ processing. The obtained thermal
distribution results were then passed on to the bonding model for evaluating the DOB.
The high temperatures and pressures applied while placement leads to consolidation of the
tape layers in the laminate. A bonding model was implemented to estimate the level of
bonding developed at the interfaces of the laminate during processing. A solution procedure
wasdevelopedinMATLAB.Thethermalhistoryandpressurehistoryateverytimeincrement
of the process simulation are imported into the MATLAB program. The DOB calculations
are continued as long as the temperature of the tape remains above 270 (◦C). Below this
temperaturethepolymerdoesnotparticipateinthebondingprocessasthemolecularmotion
is very slow. The DOB results for each of the 15 process models were analysed. A comparison
of the DOB results with a previous master thesis based on the simulation of in - situ tape
placement process in PAM-FORM work for identical process models was performed. The
effectofvariousrollervelocitieswasstudiedandsuggestionswereproposedtoimprovebonding
within the laminate layers.
Finally,theresidualstressesdevelopedduringthein-situprocesswereanalysed. Thestresses
induced in the laminate are simultaneously calculated along with the thermal results during
the simulation in ABAQUS. Five different laminates were simulated with tool temperatures
at 25 (◦C) and 120 (◦C). The relation between the stacking sequence of the laminate to the
process parameters was analyzed.
Conclusions were drawn based on the analysis of the various simulation results. Recom-
mendations for further research in this field were proposed, based on the shortcomings and
opportunities identified to improve the simulation model of the in - situ process.
Table of Contents
Summary vii
Acknowledgments xiii
Nomenclature xv
List of Acronyms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv
1 Introduction 1
2 Literature Review 3
2.1 In - Situ AFP Process Description . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1.1 Placement Head Configurations. . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Process Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2.1 Thermal Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.2 Thermal degradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.2.3 Crystallization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2.4 Void Reduction and Growth . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.5 Bonding Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.6 Shear Thinning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.2.7 Residual Stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.2.8 Process Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
2.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.3.1 Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.3.2 Process Simulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.3.3 Residual Stress Development . . . . . . . . . . . . . . . . . . . . . . . . 19
2.3.4 Simulation Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.3.5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.4 Research Question and Objectives . . . . . . . . . . . . . . . . . . . . . . . . . 20
x Table of Contents
3 Numerical Modelling: Methodology 23
3.1 Finite Element (FE) Software Selection . . . . . . . . . . . . . . . . . . . . . . . 23
3.2 Key Process Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
3.3 Simulation Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.3.1 ABAQUS/Standard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.3.2 Transient Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.3.3 Non - Linear Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.3.4 Coupled Temperature and Displacement Analysis . . . . . . . . . . . . . 27
3.3.5 Modelling Space - 3D . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.3.6 Element type - C3D8T . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.3.7 Material - APC-2 (Carbon/PEEK) . . . . . . . . . . . . . . . . . . . . . 29
3.4 Outline of the Simulation Process . . . . . . . . . . . . . . . . . . . . . . . . . 30
3.4.1 Pre-Processing: Python Script . . . . . . . . . . . . . . . . . . . . . . . 31
3.4.2 Submitting the Jobs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
3.4.3 Post- Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4 Preliminary Tests and Modelling 37
4.1 Thermoplastic Material data . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.1.1 Material Data Collection . . . . . . . . . . . . . . . . . . . . . . . . . . 37
4.1.2 Material Behaviour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4.2 Part Modelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.2.1 Placement of tapes layers - Steps and Passes . . . . . . . . . . . . . . . 42
4.2.2 Modelling the build up of a Laminate . . . . . . . . . . . . . . . . . . . 43
4.2.3 Assembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.2.4 DFLUX & DLOAD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.2.5 Boundary Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
4.2.6 Interface & Interaction modelling . . . . . . . . . . . . . . . . . . . . . . 48
4.3 Model Size Optimization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.4 Mesh convergence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.5 Heat Sensitivity Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
4.5.1 Effect of Heating length . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4.5.2 Effect of Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.6 GAPCON Sensitivity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
4.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64