Composite Research Relevant to Aero Engine Applications
Dr. Giuliano Allegri
Key drivers in material developments for Aero Engines
1. Performance: stiffness, strength & operating temperatures
2. Reliability and durability: impact damage, containment, fatigue, creep
3. Cost: material selection, manufacturing technology, maintenance
4. Fuel consumption and emissions: high specific properties for lighter rotating parts, effective damping for noise reduction
Material potential in Aero Engine Applications
Materials in Aero Engine Applications: historical trends
Materials in Aero Engine Applications: historical trends
Materials in Aero Engine: polymer based composites
1 Electronic Control Unit Casing: Epoxy carbon Prepregs2 Acoustic Lining Panels: Carbon/glass Prepregs, high temperature adhesives, aluminum honeycomb 3 Fan Blades: Epoxy carbon Prepregs or Resin Transfer Molding (RTM) construction 4 Nose Cone: Epoxy glass Prepreg, or RTM 5 Nose Cowl: Epoxy glass Prepreg or RTM construction 6 Engine Access Doors: Woven and UD carbon/glass Prepregs, honeycomb and adhesives 7 Thrust Reverser Buckets: Epoxy woven carbon Prepregs or RTM materials, and adhesives 8 Compressor Fairing: BMI/epoxy carbon Prepreg. Honeycomb and adhesives 9 Bypass Duct: Epoxy carbon Prepreg, non-metallic honeycomb and adhesives 10 Guide Vanes: Epoxy carbon RFI/RTM construction 11 Fan Containment Ring: Woven aramid fabric12 Nacelle Cowling: Carbon/glass Prepregs and honeycomb
Materials in Aero Engine: CFRP fan blades
•Manufactured by RTM; final curing in high precision press followed by milling
•Leading edge, trailing edge and tips protected by Titanium cladding
•Extremely thick at the root: up to 4 inches in the GE90 engine fan
•Slender tips: typical thickness 0.25 inches
Materials in Aero Engine: MMC
•Titanium matrix composites are the most common choice (SiC/Ti-6Al-XX)
•Improved specific strength
•Improved fatigue life (crack bridging)
•Suitable for compressors disks and
secondary turbine stages
Materials in Aero Engine: CMC
•CMC (Si-Ti-C-/SiC) suitable for
applications in combustion liners, high
temperature turbine discs and nozzles
•Polytitanocarbosilane as ceramic fibre
precursor
•Woven fabric architecture used for 3D
reinforcement
Composite material expertise
1. FE simulation of delamination growth in composite structures comprising
TTR reinforcement (Z-pinning & Tufting)
2. Simulation of polymer composite curing
3. Aniso/iso-grid composite structures
4. Stochastic mechanics of composite materials & structures
5. Meshless-Galerkin simulation of crack growth in composites
6. Design for manufacturing
7. Aeroleastic tailoring of composite structures
1. Delamination growth modelling (with optional TTR)
FE model for delamination/debond: interface groups
• Interface elements represent the
adhesive layer between overlapping plies
• Interface element:
�Two rigid elements, to prevent
penetration under compressive
loading (RBE2)
�Three linear springs before failure
(CELAS2): one for peel (Z, yellow),
two for shear (X-Y, blue)
�Three nonlinear springs after
failure (CBUSH1D): Z-pins response
under mixed mode loading
Through the thickness reinforcement: constitutive equations
•Explicit constitutive laws: TTR modelled as a beam embedded in an elastic
foundation
•Mode I: pre-debonding ; pull-out
•Mode II: pre-debonding ; pull-out
where and
1. Delamination growth modelling (with optional TTR)
Through the thickness reinforcement: constitutive equations
1. Delamination growth modelling (with optional TTR)
Through the thickness reinforcement: constitutive equations
1. Delamination growth modelling (with optional TTR)
Initiation FailureLoad
Delamination growth modelling in Z-pinned T-joints
1. Delamination growth modelling (with optional TTR)
•T-joint: FE analysis - pinned configuration - 0.28 mm diameter, 4% density
0
400
800
1200
1600
0 2 4 6
Displacement (mm)
Lo
ad
(K
N)
Control Case
Experimental 1
Experimental 2
FEM t = 30 MPa
Delamination growth modelling in Z-pinned T-joints
1. Delamination growth modelling (with optional TTR)
Engine nacelle composite joints with TTR
•Cross-Joint configuration: 2 (x) : 1 (y) displacement ratio
Top View Bottom View
1. Delamination growth modelling (with optional TTR)
Engine nacelle composite joints with TTR
Cross-Joint: X radiography vs. FE at failure – Unpinned – 17 KN
FE: survived bonded regions
are white shadedX Rays
Engine nacelle composite joints with TTR
Cross-Joint: FE Analysis – Effects of Z-fibre insertion
0
5
10
15
20
25
0 0.1 0.2 0.3 0.4 0.5 0.6
D isplacement X (mm)
Unpinned Load X (kN)
Unpinned Load Y (kN)
0.28 mm 4% Load X (kN)
0.28 mm 4% Load X (kN)
0.51 mm 4% Load X (kN)
0.51 mm 4% Load Y (kN)X
o+
Experimental Load vs displacement @ failure: “x” un-reinforced; “o” 0.28 4%; “+” 0.51 4%
2. Cure monitoring via optical fibres
•Non linear thermo-elasto-kinetic model for a representative material unit cell
•Strain compatibility imposed starting from the resin gelation point
•Representative experimental results
2. Cure monitoring via optical fibres
•Simulation for an high temperature curing case: finite difference time integration
3. Iso/anisogrid composite structures
•A structural concept widely employed in the former USSR
•It provides the highest specific stiffness within prescribed mass and volumetric constraints
3. Iso/anisogrid composite structures
•An example of anisogrid cylinder (300 mm diameter x 400 mm height); wet filament
winding and oven polymerization
3. Iso/anisogrid composite structures
•Preliminary design: analytical methods
+ geometric programming
•Detail design and topological
optimization: FE + genetic algorithms
•Testing for verifying the buckling
strength after manufacturing
4. Stochastic Analysis of Composite Structures
•Stochastic FE allows modelling the effect of uncertainties on the mechanical
response of composite materials and structures
•Material/geometrical uncertainties can play a very significant role in the
dynamic behaviour of fast rotating machinery
•Example: multi-layered composite beam
∑=
=s
i
iitR
1
2πρµ
( )∑=
=s
i
iiizztRC
1
3απχ
i
s
i
ii
s
i
iitRtR ξπρµπρµ ∑∑
==
=∆=11
2,2
( ) ∑∑==
+
∂
∂=∆=
s
i
iiizziiii
i
zz
s
i
iiizztRCtR
CtRC
i1
33
1
3
, ξηαα
πχαπχα
χχχµµµ ∆+=∆+= ,
4. Stochastic Analysis of Composite Structures
•Weighted Integral stochastic finite element method: the random field properties are projected on the shape functions
•Example random vibration of an uncertain composite truss
5. Meshless-Galerkin simulation of crack growth in composites
•An efficient technique for simulating crack growth along arbitrary patterns and in mixed mode conditions without the need of re-meshing
0.304 x 10-81.102 x 10-60.01
0.118 x 10-81.098 x 10-60.3
0.247 x 10-81.101 x 10-60.4
J2(J/m2)J1 (J/m2)b/a
-0 ,5
0
0,5
1
1,5
2
2,5
3
3,5
0 15 30 45 60 75 90
Ply Angle ±θθθθ
No
rma
lis
ed
SIF
KI
KII
Bow ie & Freeze
5. Meshless-Galerkin simulation of crack growth in composites
0,0
1,0
2,0
3,0
4,0
5,0
6,0
7,0
8,0
9,0
10,0
0 15 30 45 60 75 90
Ply Angles ±θθθθ
No
rmalised
SIF KI
KII
KI Chu & Hong
KII Chu & Hong
•Single edge notched specimen under pure shear
6. Design for manufacturing: composite structures
•Adapting the structural concept to the manufacturing process in order to
deliver the target performance while reducing the costs
•Alternative solution compared via extensive FE analysis
7. Aeroelastic tailoring of composite structures
0.00
1.00
2.00
3.00
4.00
5.00
0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 100.00
EAS (m/s)
Fre
qu
en
cy
(H
z)
-2.00
-1.00
0.00
1.00
2.00
Da
mp
ing
Frequency Damping
•Optimization of laminate layout for prescribed flutter/divergence constraints
•MSC/NASTRAN as simulation engine
•Interface for external aerodynamic codes (“in house” 3D panel method)
•Approach suitable for applications to fan/compressor/turbine blades and
cascades
Design of Fluidic Thrust Vectoring nozzles
Design of Fluidic Thrust Vectoring nozzles
Design of Fluidic Thrust Vectoring nozzles
FTV Angle = -0.0261MFR2 + 1.4135MFR - 0.3392
R2 = 0.9625
0.00
5.00
10.00
15.00
20.00
25.00
0.00 5.00 10.00 15.00 20.00 25.00 30.00
Mass flow ratio (%)
Th
rust
Defl
ecti
on
An
gle
(d
eg
)
RPM = 40000 RPM = 78000 RPM = 88000 RPM = 98000 RPM = 110000
•Rectangular nozzle
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