Transcript Dimensional Stability of Composite Structures Manufactured

CRIAQ COMP5
Modelling Work Progress
Erin Quinlan
McGill University
February 16, 2009
Structures and Composite Materials Laboratory
Outline
•
•
•
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Background
Objectives
Modelling approach
Work plan
Next steps
Structures and Composite Materials Laboratory
Thermoplastic Composites Processing
Comprehensive Composite Materials
Structures and Composite Materials Laboratory
Consolidation Steps
• Plies come into contact with
each other with added
temperature and pressure
• Resin flow begins to fill the
voids
• Polymer chains link together
(autohesion)
• Fibres impregnate through
the resin
• Cooling and crystallization
Structures and Composite Materials Laboratory
Processing Window
Economic limitations
Thermal degradation
Pressure
Restricted flow
Practical limitations
Equipment limitations
Uncontrolled flow
Fibre damage
Resin starvation
High void content
Cooling rate, log (dT/dt)
Comprehensive Composite Materials
Structures and Composite Materials Laboratory
Objectives
• Model the thermoplastic tape behaviour during the
Automated Fibre Placement (AFP) process
Temperature
Pressure
New ply
Laminate
Tool
Structures and Composite Materials Laboratory
Modelling Approach
‘raw’ material
composite
part
process
science of
processing
materials
characterization
equations
material
properties
numerical
implementation
solve
equations
data analysis
& verification
what does it
mean?
Structures and Composite Materials Laboratory
Typical Process Model Architecture
Input
Output
AFP Machine
State Variables
Database
Thermochemical
Void
Flow
Compaction
Structures and Composite Materials Laboratory
Thermochemical Module
• The thermochemical module is responsible for
calculation of
– temperature in the structure of interest
– degree of crystallinity in composite components
• The thermochemical module consists of a
combination of analyses for heat transfer and
crystallization kinetics.
Structures and Composite Materials Laboratory
Semicrystalline Thermoplastic Thermal
Analysis
z
Ply
Laminate
Tool
T   T 
dc*
cP
 K
Hu
  mm
t z  z 
dt
Heat generation due to
crystallization
Structures and Composite Materials Laboratory
Semicrystalline Thermoplastic
dc*
mm
Hu
dt
• Heat generation
– c*
– mm
– Hu
: crystallinity of matrix
: matrix mass fraction
: ultimate heat of crystallization of the polymer at 100%
crystallinity
• Rate of degree of crystallinity
– g
– dT/dt
: functional relationship
: heating rate (cooling rate)
dc*
 dT 
 g
,T 
dt
 dt 
Structures and Composite Materials Laboratory
Flow-compaction Module
• The flow-compaction module is responsible for calculation of
– prepreg consolidation
– degree of intimate contact
– autohesion
Phenomenon
Mechanism
Interfacial bond formation
(consolidation)
Autohesion
Interfacial deformation
(coalescence)
Viscoelastic deformation of
prepreg tows
Structures and Composite Materials Laboratory
Modelling Consolidation
• Intimate contact
• Interply bonding
Structures and Composite Materials Laboratory
Prepreg Interply Intimate Contact
• Modelling approach:
– Characterize prepreg surface roughness
– Measure neat resin viscosity
– Fluid mechanics
• Modelling results:
– Time required to achieve complete interply intimate contact
for a given set of temperature, pressure and prepreg
geometric parameters
• Verification
– Optical microscope
– Scanning acoustic microscope
Structures and Composite Materials Laboratory
Prepreg Surface Roughness Model
Structures and Composite Materials Laboratory
Single Ply Model
Rigid Flat Surface
ho
t=0
Prepreg
wo
bo
Papp
Rigid Flat Surface
t>0
h
Prepreg
w
b
Degree of intimate contact Dic
b
Dic 
w0  b0
Structures and Composite Materials Laboratory
Single Ply Model
• Assumptions:
–
–
–
–
Squeezing flow between two rigid parallel plates
Viscous laminar flow
Viscosity is independent of shear rate
w 0 = b0
1
Papp
ho h
1
Dic 
 1  10
1  w0 b0 2 
h0

Dic
Papp
h0
 h0 
 
 w0 
2
5
t

: degree of intimate contact
: consolidation pressure
: zero-shear rate viscosity
Structures and Composite Materials Laboratory
Neat Resin Rheology
Structures and Composite Materials Laboratory
Degree of Intimate Contact Versus Time
APC-2 Prepreg surface against a rigid flat surface
Structures and Composite Materials Laboratory
Autohesion Phenomenon
Chain Like Molecules
Interface
Initial Contact
t=0
Partially
Diffused
t>0
Completely
Diffused
t=t∞
Structures and Composite Materials Laboratory
Autohesive Strength Measurements
Structures and Composite Materials Laboratory
Autohesive Strength Measurements
Structures and Composite Materials Laboratory
Isothermal Autohesion Model
GIC t 
R
 C (T )t 1 2
GIC
 1.604T  469
log aT 
11.26  T  469
1.94105 T
aT 
C T 
T is in °K
Structures and Composite Materials Laboratory
Modelling Void Fraction
• Voids form after heating during the consolidation
phase
Void
Resin
Fiber
Structures and Composite Materials Laboratory
Void Formation
Apply heat
Apply pressure
Structures and Composite Materials Laboratory
Void Fraction Content vs. Pressure
Structures and Composite Materials Laboratory
Work Plan
• Model development:
– Implement 1D heat transfer model
– Implement crystallinity kinetics model
– Tape machine heat source model
• Material characterization
– Crystallinity model
– Tape roughness measurement
• Validation experiments
– Get temperature-time data from AFP experiments (effect of
pressure, temperature, layup speed)
Structures and Composite Materials Laboratory
References
• “Automated Dynamics” http://www.automateddynamics.com/
• “Thermoplastic Composites: Module 6”
• S. Ranganathan, S.G. Advani, and M.A. Lamontia, “A NonIsothermal Process Model for Consolidation and Void Reduction
During In-Situ Tow Placement of Thermoplastic Composites”,
Journal of Composite Materials 29(8), 1995, pp. 1040-1062.
• J.M. Tang, W.I. Lee, G.S. Springer. “Effects of Cure Pressure on
Resin Flow, Voids, and Mechanical Properties”. Journal of
Composites 21, 1987, pp. 421-440.
Structures and Composite Materials Laboratory