Research in Composites for Aero Engine Applications

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: 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


Through the thickness reinforcement: constitutive equations


Initiation FailureLoad

Delamination growth modelling in Z-pinned T-joints


•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


Engine nacelle composite joints with TTR

•Cross-Joint configuration: 2 (x) : 1 (y) displacement ratio

Top View Bottom View



Cross-Joint: X radiography vs. FE at failure – Unpinned – 17 KN

FE: survived bonded regions

are white shadedX Rays


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)



0.51 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


•An example of anisogrid cylinder (300 mm diameter x 400 mm height); wet filament

winding and oven polymerization


•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


•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


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

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

Research in Composites for Aero Engine Applications

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