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HYDROTHERMAL AGEING
OF AIRCRAFT COMPOSITES
Kolesnik Kirill
Junior researcher
The Central Aero-Hydrodynamic Institute
Postgraduate student
Moscow Institute of Physics and Technology
Russia
The Central Aerohydrodynamic Institute named after N.E. Zhukovsky (TsAGI)
Hydrothermal Ageing of Aircraft Composites Slide 2Kolesnik Kirill
─ theoretical and applied aerospace research facility
– primary carbon fiber composites
– secondary carbon fiber composites
– glass fiber composites
– FRP floor panels
– metals
• 34% composites
• 132 – 211 passengers
• up to 6 400 km range
Hydrothermal Ageing of Aircraft Composites Slide 3Kolesnik Kirill
Modern russian jet Irkut MC-21
A
B
D
Plan of the presentation
1. Hydrothermal effects
2. Qualification of composite structures
3. Maximum operating temperature
4. Operating moisture content
5. Realistic hydrothermal factors
Hydrothermal Ageing of Aircraft Composites Slide 4Kolesnik Kirill
Plan of the presentation
1. Hydrothermal effects
2. Qualification of composite structures
3. Maximum operating temperature
4. Operating moisture content
5. Realistic hydrothermal factors
Hydrothermal Ageing of Aircraft Composites Slide 5Kolesnik Kirill
Hydrothermal effects on composites
On the resin:• Plastification
• Swelling
• Destruction
• Secondary curing
On the lamina:
• Reduction of properties, mainly matrix governed
On the laminate:
• Internal hydrothermal stress
On the construction:
• Moisture affects bond-line (adhesive) - may lead to disbondings
• Moisture ingress in the honeycomb core
• Galvanic corrosion, mainly Al and carbon-epoxy
Hydrothermal Ageing of Aircraft Composites Slide 6Kolesnik Kirill
Structural materials handbook - Part 1: Overview and material properties and applications, ECSS‐E‐HB‐32‐20, 2011.
Longitudinal tensile strength Transverse tensile strength
Mechanical lamina properties as a function
of temperature and moisture content
Hydrothermal Ageing of Aircraft Composites Slide 7Kolesnik Kirill
Mechanical lamina properties as a function
of temperature and moisture content
Moisture content, %
Rel
ativ
e in
terl
amin
arsh
ear
stre
ng
th
Test temperature, ºCC
om
pre
ssiv
e st
ren
gth
, M
Pa
TürkmenD. Compressive behaviour of CFRP
laminates exposed in hot-wet environments – 1996.MardoianG.H., EzzoM.B. Flight service evaluation of
composite helicopter components – 1990.
Hydrothermal Ageing of Aircraft Composites Slide 8Kolesnik Kirill
Lamina properties degradation model
0
0 TT
TTg
g
g
−
−=
0
5.00
1212
5.00
22
04.00
11
=
=
=
=
gGG
gEE
gEE
Shan, Meijuan, et al. "A progressive fatigue damage model for composite structures
in hygrothermal environments." International Journal of Fatigue 111 (2018): 299-307.
5.00
1212
5.00
5.00
54.00
04.00
gSS
gYY
gYY
gXX
gXX
CC
TT
CC
TT
=
=
=
=
=
Tg – glass transition temperature
T – temperature
index 0 – reference data
A S Maxwell at. al. Review of accelerated ageing methods and lifetime prediction
techniques for polymeric materials, NPL Report DEPC MPR 016, 2005
Hydrothermal Ageing of Aircraft Composites Slide 9Kolesnik Kirill
Plan of the presentation
1. Hydrothermal effects
2. Qualification of composite structures
3. Maximum operating temperature
4. Operating moisture content
5. Realistic hydrothermal factors
Hydrothermal Ageing of Aircraft Composites Slide 10Kolesnik Kirill
Test conditions
for hydrothermal qualification of composite structures
High temperature
Moisture conditioning
High realism
Time consuming
Special equipment
High temperature
Dry
Time efficient
Building-block approach
Special equipment
Room temperature
Dry
Time efficient
Building-block approach
Hydrothermal Ageing of Aircraft Composites Slide 11Kolesnik Kirill
Test-bench
Hydraulic/Electric Ram
Lever-Loading System
Test Object
Dynamometer
Hydrothermal Ageing of Aircraft Composites Slide 12Kolesnik Kirill
Control surfaces test set up
Climatic cabinet
Hot-wet and cold conditions
Infrared heating
Hydrothermal Ageing of Aircraft Composites Slide 13Kolesnik Kirill
Building-block approach
Overload Factors:𝐾𝑊𝑇 , 𝐾𝑣𝑎𝑟 , 𝐾𝑑𝑎𝑚
Overload Factors assure
structural strength in all
operating conditions
Building-block approach
Hydrothermal Ageing of Aircraft Composites Slide 14Kolesnik Kirill
Test conditions for
hydrothermal qualificationTest elements
𝐾𝑊 =𝑋𝑊𝑋
𝐾𝑇 =𝑋𝑇𝑋
𝐾𝑊𝑇 =𝑋𝑊𝑇
𝑋
Environmental
compensation factor
Plan of the presentation
1. Hydrothermal effects
2. Qualification of composite structures
3. Maximum operating temperature
4. Operating moisture content
5. Realistic hydrothermal factors
Hydrothermal Ageing of Aircraft Composites Slide 15Kolesnik Kirill
Air flow velocity
for take off scenario
Maximum operation temperature
Rolfes, R., J. Tessmer, and K. Rohwer. "Models and tools for heat
transfer, thermal stresses, and stability of composite aerospace
structures." Journal of thermal stresses 26.6 (2003): 641-670.
"Static Strength Substantiation of Composite
Airplane Structure"
PS-ACE100-2001-006, December 2001
For most paint colorsa default critical structural
temperature is 82°C (180°F)
Hydrothermal Ageing of Aircraft Composites Slide 16Kolesnik Kirill
40
45
50
55
60
65
70
75
80
85
-300 -200 -100 0 100 200 300
Surface temperature, ºC
верх. обш. снаружи
верх. обш. внутри
нижн. обш. внутри
нижн. обш. снаружи
Taxi Start phaseStop
Transient cooling of wing box during take off scenario
16°C
Hydrothermal Ageing of Aircraft Composites Slide 17Kolesnik Kirill
t, s
l1 = l2 = 8 mm, qс = 1082 W·m–2,
A = 0.45, Tair = 56 ºС,
h0 = 8.5 W·m–2°K–1, Ag = 0.73,
Tg = 75 ºС, q12 ≠ 0, h12 = 0
Top skin outside
Top skin inside
Bottom skin inside
Bottom skin outside
Ultimate load
0
20
40
60
80
100
0 5 10 15 20
Su
rfac
e te
mp
erat
ure
, ºC
l, mm
t = –300 сек.
t = 120 сек.
Hydrothermal Ageing of Aircraft Composites Slide 18Kolesnik Kirill
A = 0,2 (white)
A = 0,45 (gray)
A = 0,9 (black)
Composite skin temperatures
due to solar heating and takeoff cooling
Takeoff cooling reduces
the maximum operating temperature of thin components
Before take of
Ultimate load
Plan of the presentation
1. Hydrothermal effects
2. Qualification of composite structures
3. Maximum operating temperature
4. Operating moisture content
5. Realistic hydrothermal factors
Hydrothermal Ageing of Aircraft Composites Slide 19Kolesnik Kirill
0
0.2
0.4
0.6
0.8
1
0 10 20 30 40 50
Relative
moisture
content
t, years
l = 2
l = 8
l = 12
l = 20
Hydrothermal Ageing of Aircraft Composites Slide 20Kolesnik Kirill
0.00
0.04
0.08
0.12
0.16
0 100 200 300
Moisture content, %
t, days
образец
численное моделирование
Calculated and experimental moisture contents
Experimental data
Numerical calculation
6 mm laminate
Moisture absorption modeling for diff. thicknesses
Moisture absorption in hot-wet climate (Sochi, Russia)
Moisture diffusion obeys the Fick’s law
0
0.2
0.4
0.6
0.8
1
0 5 10 15 20
Relative moisture content
l, mm
Порт-Харкорт, Нигерия
Гуам
Сингапур
Мухаррак, Бахрейн
Сочи
Вудбридж, Англия
Шлезвиг-Гольштейн, Германия
Владивосток
Москва
Магадан
Hydrothermal Ageing of Aircraft Composites Slide 21Kolesnik Kirill
Port Harcourt, Nigeria
Guam
Singapore
Bahrain
Sochi, Russia
Woodbridge, UK
Schleswig, Germany
Vladivostok, Russia
Moscow, Russia
Magadan, Russia
Moisture content resulting 30 years of operation
Equivalent to RH = 85%
More than 10 mm thick laminates does not reach the equilibrium moisture level
The effect of stiffener
on moisture distribution
Stiffener
Stiffener core has lower
moisture concentration
Relative
moisture
content
Hydrothermal Ageing of Aircraft Composites Slide 22Kolesnik Kirill
(Port Harcourt, Nigeria)
a bc
Pure resin
filler
The effect of fiber fraction V f
and radius of the stiffener
on total moisture content
0
0.2
0.4
0.6
0.8
1
0 5 10 15 20 25 30
Rel
ativ
e m
ois
ture
conte
nt
Radius, mm
Vf = 0.6
Vf = 0
0
0.2
0.4
0.6
0.8
1
0 0.1 0.2 0.3 0.4 0.5 0.6
Rel
ativ
e m
ois
ture
conte
nt
V f
Radius = 10 mm
Radius = 30 mm
Hydrothermal Ageing of Aircraft Composites Slide 23Kolesnik Kirill
(Port Harcourt, Nigeria)
0
20
40
60
80
0 4 8 12 16 20 24
Surf
ace
tem
per
atu
re,ᵒ
C
t, hour
White paint
No heating
Black paint
0
20
40
60
80
100
0 4 8 12 16 20 24
Rel
ativ
e h
um
idit
y, %
t, hour
White paint
No heating
Black paint
Typical daily surface temperatures
Corresponding relative humidity
0
0.2
0.4
0.6
0.8
1
0 5 10 15 20
Rel
ativ
em
ois
ture
conte
nt
l, mm
Black paint
White paint
No heating
The effect of color on the moisture content
of a horizontal panel
The effect of solar heating
on total moisture content
Hydrothermal Ageing of Aircraft Composites Slide 24Kolesnik Kirill
(Port Harcourt, Nigeria)
Exposure to the sun reduces final moisture content
The effect of operation
on total moisture content
0
0.2
0.4
0.6
0.8
1
0 5 10 15 20
Rel
ativ
e m
ois
ture
conte
nt
l, mm
Day 8 hour flights, without solar heating
Two 4 hour day flights, white paint
Night 8 hours flights, black paint
Hydrothermal Ageing of Aircraft Composites Slide 25Kolesnik Kirill
(Port Harcourt, Nigeria)
Flight exposure disperses the total moisture content
Plan of the presentation
1. Hydrothermal effects
2. Qualification of composite structures
3. Maximum operating temperature
4. Operating moisture content
5. Realistic hydrothermal factors
Hydrothermal Ageing of Aircraft Composites Slide 26Kolesnik Kirill
Application of operational temperature and moisture content
Hydrothermal Ageing of Aircraft Composites Slide 27Kolesnik Kirill
Numerical method: Laminated theory
Material: CYCOM 977
Lay-up configuration: {–45/0/45/0/0/90/0/0/45/0/–45}n
Failure criterion: Tsai-Hill
Thickness, mm Temperature °C Moisture content
2 54 0.84
8 60 0.83
20 65 0.70
-100
-50
0
50
100
150
0 10 20 30 40
σ11
τ12
Hydrothermal Ageing of Aircraft Composites Slide 28Kolesnik Kirill
Initial failure
-100
-50
0
50
100
150
0 10 20 30 40
σ11
τ12
normal conditions
high temperature and moisture content
realistic temperature and moisture for top surface
realistic temperature and moisture for bottom surface
Failure envelopes for 2 mm laminate
Ultimate failure
Application of operational temperature and moisture content
Hydrothermal Ageing of Aircraft Composites Slide 29Kolesnik Kirill
Thickness, mm Temperature °CMoisture
content
𝐾𝑊𝑇 Average
degradation𝜎11𝑇 𝜏12 𝜎11𝐶
2 54 0.84 0.93 0.78 0.76 17%
8 60 0.83 0.93 0.73 0.72 21%
20 65 0.70 0.90 0.69 0.68 24%
Standard case 82 0.85 0.85 0.63 0.63 30%
Hydrothermal Ageing of Aircraft Composites Slide 30Kolesnik Kirill
Summary
• Takeoff cooling reduces the maximum
operating temperature of thin components
• Thick laminates does not reach the equilibrium
moisture level over the operational lifetime
• Realistic temperature and moisture content
may reduce structural test’s overload factors
Thank you for your attention!