Post on 21-Feb-2021
Interfacce e adesione
Alessandro Pegoretti Università degli Studi di Trento
Dipartimento di Ingegneria dei Materialivia Mesiano 77, 38050 Trento
ITALIA
5a Scuola AIMAT:I Materiali Compositi
Ischia Porto (NA) 15-19 Aprile 2002
Schema della lezione
- Introduzione
- Effetto dell’interfaccia sulle proprietà meccaniche dei compositi
- Micromeccanica all’interfaccia: meccanismi di trasferimento degli sforzi
- Misura dell’adesione fibra-matrice: metodi diretti ed indiretti
- Meccanica della frattura all’interfaccia fibra-matrice
- Come migliorare l’adesione fibra-matrice? Cenni sui trattamenti superficiali
An interface (2D) or interphase (3D)
is the region of significantly changed chemical composition thatconstitutes the bond between the matrix and reinforcement
(Metcalfe - 1974)
bulk matrix
bulk fiber
modified matrix
interphase
surface layer
adsorbed material
(after Drzal et al. 1983)
Why are interfaces in composites important? Surface area !
L = 1
Fibr filled
df = 10 µm Φf = 0.6
Vc = 1 m3 Vf = 0.6 m3
v d 7 10 mfiberf 4 f
2 x 113
= = −π .854
Nf = Vv
f
f = 7.639x109
Af = af Nf = π d (1) Nf f ≈ 240.000 mm
2
3
L = 1
Particulate filled
dp = 5 µm Φp = 0.4
Vc = 1 m3 Vp = 0.4 m3
v6
d 6.545 10 mpart.p p
3 x 173
= = −π
Np = Vv
p
p = 6.112x1015
Ap = ap Np = π d Np2
p ≈ 480.000 mm
2
3
Techniques for studying surface structures and composition
- Scanning electron microscopy (SEM)
- Transmission electron microscopy (TEM)
- Scanning tunneling microscopy (STM)
- Atomic force microscopy (AFM)
Microscopy
Spectroscopy
- Auger electron spectroscopy (AES)
- X-ray photoelectron spectroscopy (XPS)
- Secondary ion mass spectroscopy (SIMS)
- Ion scattering spectroscopy (ISS)
- Fourier transformed infrared (FTIR) spectroscopy
- Raman spectroscopy (RS)
- Nuclear magnetic resonance (NMR) spectroscopy
S.Incardona, C.Migliaresi, H.D.Wagner, A.H.Gilbert, G.Marom, Comp.Sci.&Techn. 47, (1993), 43
Photomicrographs of isothermal crystallization of J-Polymer® (DuPont) on a HM pitch based carbon fiber.
30µm
N.Klein, G.Marom, A.Pegoretti, and C.Migliaresi , Composites, 26(10) (1995) 707
Thermo-mechanical properties of transcrystalline layers in PA66 - Kevlar composites by dynamicmechanical thermal analysis (DMTA)
0
1000
2000
3000
4000
5000
6000
-150 -100 -50 0 50 100 150 200
stor
age
mod
ulus
(M
Pa)
temperature (°C)
quenched matrix
crystallized matrix
tc matrix
0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
-150 -100 -50 0 50 100 150 200
tanδ
temperature (°C)
quenched matrix crystallizedmatrix
tc matrix
Influence of fiber-matrix adhesion on mechanical properties: case of graphite/epoxy composites
M.S.Madhukar, L.T.Drzal,Fiber-matrix adhesion and its effect on composite mechanical properties:
I. Inplane and interlaminar shear behaviourof graphite/epoxy composites, J. Comp. Mater., 25 (1991) 932
II. Longitudinal (0°) and transverse (90°) tensile and flexurebehaviour of graphite/epoxy composites, Comp. Mater., 25(1991) 958
III. Longitudinal (0°) compressive properties of graphite/epoxy composites, J. Comp. Mater., 26 (1992) 310
IV. Mode I and mode II fracture toughness of graphite/epoxy composites, J. Comp. Mater., 26 (1992) 936
Material Tensile Modulus(GPa)
Tensile Strength(MPa)
Interfacial ShearStrength – ISS (MPa)[Fragmentation test]
Interfacial FailureMechanism
AU-4(untreated)
234 3585 37.2 Friction
Fibers(Hercules)
AS-4
(surface treated)
234 3585 68.3 Interfacial
AS-4C(epoxy coated AS-4)
234 3585 81.4 Matrix
Matrix Epon 828
(DGEBA + mPDA)
3.6 89.6 -- --
Effect of fiber-matrix adhesion on the longitudinaltensile behavior in graphite/epoxy composites fiber
matrix
σL σL
M.S.Madhukar, L.T.Drzal,J. Comp. Mater., 25 (1991) 958
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.6
0 1 2 3
Longitudinal Tensile Modulus
Longitudinal Tensile Strength
NO
RM
AL
IZE
D L
ON
GIT
UD
INA
L D
AT
A
NORMALIZED INTERFACIAL SHEAR STRENGTH
M.S.Madhukar, L.T.Drzal,J. Comp. Mater., 25 (1991) 932
fiber
matrix
τ
0.5
1.0
1.5
2.0
2.5
3.0
0 1 2 3
Data 1
Inplane Shear Modulus (45° Tension Test)Inplane Shear Modulus (Iosipescu Shear Test)Inplane Shear Strength (45° Tension Test)Inplane Shear Strength (Iosipescu Shear Test)Interlaminar Shear Strength (Short-Beam Shear Test)
NO
RM
AL
IZE
D S
HE
AR
DA
TA
NORMALIZED INTERFACIAL SHEAR STRENGTH
Effect of fiber-matrix adhesion on the inplane andinterlaminar shear behavior in graphite/epoxycomposites
fiber
matrix
σT
σT
Effect of fiber-matrix adhesion on the transversetensile and flexural behavior in graphite/epoxycomposites
M.S.Madhukar, L.T.Drzal,J. Comp. Mater., 25 (1991) 958
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0 1 2 3
Transverse Tensile ModulusTransverse Flexural ModulusTransverse Tensile StrengthTransverse Flexural Strength
NO
RM
AL
IZE
D T
RA
NSV
ER
SE D
AT
A
NORMALIZED INTERFACIAL SHEAR STRENGTH
starter crack
ENF specimen
Effect of fiber-matrix adhesion on Mode II fracturetoughness in graphite/epoxy composites
M.S.Madhukar, L.T.Drzal,J. Comp. Mater., 26 (1992) 936
0.5
1.0
1.5
2.0
2.5
3.0
0 1 2 3
NO
RM
AL
IZE
D G
IIC
NORMALIZED INTERFACIAL SHEAR STRENGTH
End Notched Flexure(Mode II Fracture Toughness)
Micromechanics of stress transfer across the interface
fibermatrix
unloaded case
loadload
loaded case
complex stress field oftendescribed by rough models, like
shear-lag model(Cox, 1952)
simplified physical model(Kelly-Tyson, 1965)
H.L.Cox “The elasticity and strength of paper and other fibrous materials” Br.J.Appl.Phys. 3, (1952) 72
hp:- linear elastic behavior for matrix and fiber;- perfect adhesion (no debonding).
σ ε ββf f c(x) E 1 cosh [ (L/2 x)]
cosh ( L/2)= − −
τ ε β β
βf (x) f cf = E
r
2 sinh [ (L/2 x)]
cosh ( L/2)
−
0
200
400
600
800
1000
0 200 400 600 800 1000
σ f (M
Pa)
x (µm)
-40
-20
0
20
40
0 200 400 600 800 1000
τ f (M
Pa)
x (µm)
x
2R0 2rf
L
fiber
matrix
σ
ε
A.Kelly, and W.R. Tyson, “Tensile properties of fiber-reinforced metals copper/tungsten andcopper/molybdenum” J. Mech. Phys. Solids 13, (1965) 329
hp:- linear elastic behavior for fiber;- elasto-plastic behavior for matrix;- debonding may occur.
x
2R0 2rf
L
L < Lt L = Lt L > Lt
t t
fiber/matrix stress stress,
L < Lt L = L L > L
axial fiber stress, σf
(σf)max= Ef/Ec σc
τyτ
fiber
matrix
σ
ε
σ y( )
L
rf maxyσ
τ=
Stress transfer at fiber-matrix interface: Kelly-Tyson model
The “transfer length” Lt is given by: Ltr E
E f
y cc=
τσ
Lc/2 Lc/2
σc
(σf )max =σfb
and hence: τ σy fbr
Lc = =ISS
The “critical length” Lc is given by:
Lcr
y
fb=τ
σ
Quantitative measurement of fiber-matrix interfacial adhesion: state of the art
HISTORICALLY, TWO GENERAL METHODOLOGIES, BASED ON:
INDIRECT TESTING
of collective behaviour of fibers in a matrix (real composites)
- Interface strength interpreted via simplistic model
- Fast but questionable results are obtained
DIRECT TESTING
probes interfacial behavior of individual fibers in a matrix (microcomposites)
- More fundamental and accurate information
- Variability within and between techniques
- Issue of relevance to macrocomposites
INDIRECT TEST METHODS - (I)
[±45°] tensile test ASTM D 3518
τσ
12x
2=
0
[10°] off-axis tensile test
X
Y
fibre direction
F
45°45°
INDIRECT TEST METHODS - (II)Rail shear test ASTM D 4255
Two rails - tensionThree rails - compression
INDIRECT TEST METHODS - (III)
In-plane lap-shear test ASTM D 3518 Transverse tensile test ASTM D 3039
loading direction
fiber direction
INDIRECT TEST METHODS - (IV)
Short beam interlaminar shear test
ASTM D 2344
xy
y
z
B
h
L
x
y
x
y
σx
τxσx
3 F L
2 B hMAX 2=
τxy3 F
4 B hMAX=
τ
σxy
x
h
2 LMAX
MAX
=
F
F/2
fibre direction
F/2
Experimental problems with the short beam interlaminar shear test
Iosipescu shear test ASTM D 5379INDIRECT TEST METHODS - (V)
Matrix cracking in a 90° specimen
Matrix cracking in a 0° specimen
0° specimenfiber direction
F
F
90° specimenfiber direction
F
F
INDIRECT TEST METHODS - (VI):delamination tests
Modes of interlaminar crack propagation
a) Mode I opening modeb) Mode II sliding shear modec) Mode III tearing mode
a) b) c)
Mode I Interlaminar fracture toughnessDouble Cantilever Beam ASTM D 5528
GP
2B
dC
daIc
2
=
CP
= δ
C2 a3 E I
3
1
=
where
for the classical beamtheory:
INDIRECT TEST METHODS - (VII):delamination tests (cont.)
Mode II Interlaminar fracture toughness
End Notched Flexure specimen
End Loaded Split specimen
G9 a P
2 B (2 L 3 a )IIc
2
3 3=
+δ
G9 a P
2 B (L 3 a )IIc
2
3 3=
+δ
DIRECT TEST METHODS - (I)
load
displacement
Fp
Fiber microdebonding test
microvise
fiberdiam. (d)
matrixmicrodroplet
load, F
L
ISS F d L
p= π
Fiber pull-out test
load
displacement
Fp
matrixL
load, F
fiberdiam. (d)
ISS F d L
p= π
SEM micrograph of PCL droplet on Kevlar 149 fiber.
fiber microdebonding
a)
b)
SEM micrographs of PCL dropletbefore (a) and after (b) debonding.
A.Gati, M. Sc.Thesis, The Weizmann Institute ofScience, Israel (1996
DIRECT TEST METHODS - (III)
Multi-fiber pull-out test
Y.Qiu and P.Schwartz, Comp.Sci.&Techn. 48 (1993) 5
Microindentation test
t < 3 ÷ 4 d
ISSFp d t
=π
DIRECT TEST METHODS - (IV): Fiber fragmentation test
load
load
matrix
fiber
load
load
Ls
ISSd (L )
2 Lfb c
c
= σ
σ αβ
fb0
1/
(L) = LL
1+ 1
−Γ
β
the “saturation length” Ls is related
to the critical length Lc:
Lc = 4/3 Ls
average fiber strength, depends on the fiber length
(generally this dependence follows the Weibull statistics),i.e.:
fb(L),σ
Fiber fragmentation: test apparatus
F
∆L
image analyser
video recorder monitor
video-camera
microscope
thermostatic chamber
load-cell
step-motor
control unity data acquisition
sample
Fiber fragmentation observed under polarized light
Glass fibersin PA6 matrix
Carbon fiber inepoxy matrix
Fiber fragmentation in carbon/epoxy composites: effect of temperature
For a “soft” epoxy matrix (Tg = 40°C)
0
10
20
30
40
0 10 20 30 40 50 60
ISS sized fibersISS desized fibersmatrix shear strength
shea
r st
ress
(M
Pa)
temperature (°C)
strain rate = 0.008min -1
M.Detassis, A.Pegoretti, and C.Migliaresi, Comp. Sci. & Techn., 53 (1995) 39.
Fiber fragmentation in carbon/epoxy composites: effect of temperature
For a stiff epoxy matrix (Tg = 150°C)
0
10
20
30
40
50
0 50 100 150 200
ISS sized fibersISS desized fibersmatrix shear strength
shea
r st
ress
(M
Pa)
temperature (°C)
strain rate = 0.008min -1
A.Pegoretti, C.DellaVolpe, M.Detassis, C.Migliaresi, and H.D.Wagner CompositesPartA, 27 (1996) 1067.
Fiber fragmentation in carbon/epoxy composites: effect of strain rate
For a “soft” epoxy matrix (Tg = 40°C)
0
10
20
30
40
50
0 0.005 0.01 0.015
ISS sized fibersISS desized fibersmatrix shear strength
shea
r st
ress
(M
Pa)
strain rate (min -1)
temperature = 20 °C
M.Detassis, A.Pegoretti, and C.Migliaresi, Comp. Sci. & Techn., 53 (1995) 39.
Fiber fragmentation in thermoplastic matrix composites: nylon6/glass fibers
aluminum plate
PTFE sheet
nylon-6 film
E-glass fibers
fiber 45 mm
4 mm
90 µm
Temperature = 300 °C Pressure = 10 kPa (under vacuum) Time = 50 min
load load
Fiber fragmentation in thermoplastic matrix composites: nylon6/glass fibers:effect of temperature
A.Pegoretti, L.Fambri and C.Migliaresi, Polymer Composites, 21 (2000) 466.
0
5
10
15
20
25
30
20 40 60 80 100 120 140 160 180
ISS unsizedISS polyamide sizedISS epoxy sizedmatrix shear strength
shea
r st
ress
(M
Pa)
temperature (°C)
strain rate = 0.008min-1
Fiber fragmentation in thermoplastic matrix composites: nylon6/glass fibers:effect of strain rate
A.Pegoretti, L.Fambri and C.Migliaresi, Polymer Composites, 21 (2000) 466.
0
5
10
15
20
25
30
35
40
10-3 10-2 10-1 100 101
ISS unsizedISS polyamide sizedISS epoxy sizedmatrix shear strength
shea
r st
ress
(M
Pa)
strain rate (min-1)
temperature = 25 °C
What is happening when afiber breaks in a polymer matrix ?
When a fiber filament breaks, cracks willpropagate from the broken fiber end either by:- interfacial debonding;- trasverse matrix cracks;- conical matrix cracks,or combinations of the three modes.
Example: fracture patterns at a broken fiber end depend on fiber/matrix adhesion.glass/epoxy system: a) interfacial debonding); b) radial matrix crack; c) conical matrix crack;d) mixed matrix crack.
A.Pegoretti, M.L.Accorsi and A.T.DiBenedetto, Journal of Materials Science, 31 (1996) 6145.
a) b)
c) d)
Recent trends in fiber/matrix load transfer:a fracture mechanics approach for fiber/matrix debonding.
E-glass fiber in nylon-6 matrix: debonding when fiber fails
load load
10 µm
fiber
debonding
T=25°C
matrix
load load
10 µm
T=100°C
fiber
matrix
debonding
Finite elements modeling of the fiber/matrix debonding
fiber
matrix
fiber fracture point
fiber/matrix debonding zone
Ld
fiber
matrix
fiber fracture point
FEM mesh
A B
C
DE
F
z
r
0
5
10
15
20
0 2 4 6 8 10 12 14 16 18 20
stra
in e
nerg
y re
leas
e ra
te (
J/m
2 )
debonding length, Ld (µm)
matrix = epoxy (E=2.9 GPa)fiber = S-glass (E=86.9 GPa)strain = 1%
A.Pegoretti, M.L.Accorsi and A.T.DiBenedetto, Journal of Materials Science, 31 (1996) 6145.
Strain energy release rate for the fiber/matrix debonding - I
fiber
matrix
fiber fracture point
fiber/matrix debonding
Ld
Strain energy release rate for the fiber/matrix debonding - II
0
100
200
300
400
500
0 1 2 3 4 5 6
G (J
/m2 )
strain (%)
elastic
elastic-plastic
0
20
40
60
80
100
0 1 2 3 4 5 6 7 8
stre
ss (
MPa
)
strain (%)
epoxy matrix
A.Pegoretti and A.T.DiBenedetto, Composites Part A, 29(9-10) (1998) 1063.
Strain energy release rate for the fiber/matrix debonding - III
A.Pegoretti, M.Fidanza, C.Migliaresi and A.T.DiBenedetto, Composites Part A, 29 (1998) 283.
0
50
100
150
200
250
300
350
unsized polyamide sized epoxy sized
T = 20°CT = 100 °C
Gar
rest (J
/m2 )
fiber surface treatment
Example: E-glass fibers in nylon-6 matrix
Can microcomposites (low volume fraction) be considered as representativefor interfaces in macrocomposites (high volume fraction) ?
Problem n° 1: thermal stresses H.D.Wagner, J.Adhesion, 52 (1995) 131.
Thermal stresses may induce fiber buckling in highmodulus fiber embedded in termosetting matrices
Carbon fiber in epoxy matrix
Thermal stresses may induce fiber fracture for highmodulus fiber embedded in termoplastic matrices
Carbon fiber in J-polymer
S.Incardona, C.Migliaresi, H.D.Wagner, A.H.Gilbert,G.Marom, Comp.Sci.&Techn. 47, (1993), 43
M.Detassis, A.Pegoretti, C.Migliaresi,H.D.Wagner, J.Mater.Sci, 31 (1996) 2385.
Experimental evaluation of thermal stresses
How can fiber-matrix adhesion be improved ?
Fracture surfaces of epoxy composites after 72 hr in boiling water
Matrix modifications
Surface treatments on fibers
Fibers surface treatments - (I):glass fibers
Typical component of a glass fiber size
• Film-forming resin ... 1-5 %wt
• Antistatic agent……. 0.1 - 0.2 %wt
• Lubricant ………….. 0.1 - 0.2 %wt
• Coupling agent……...0.1 - 0.5 %wt
- SILANE- TITANATE- ZIRCONATE
Fibers surface treatments - (II): silane coupling agents
R-SiX3 + H2O → R-Si(OH)3 + 3 HX
R is a group which can react with the resin
X is a group which can hydrolyze to form a silanol group in aqueous solution
a) Hydrogen bonding between hydroxyl groups of silanol and glass surface;b) polysiloxane bonded to glass surface;c) organofunctional R-group reacted with polymer
Fibers surface treatments -(III):
commercial coupling agents
Fibers surface treatments - (IV):effect of silane coupling agents on the mechanical properties of glass fiber composites
E.P.Plueddemann, H.A.Clark, L.F.Nelson, and K.R.Hofman Mod.Plast, 39 (1962) 136.
0
100
200
300
400
500
600
700
None Vynil silane Methacrylate silane
DryAfter 2-hr water boil
Flex
ure
stre
ngth
of
com
posi
te (
MPa
)
E-glass surface treatment
Fiberglass reinforced polyester composites
Fibers surface treatments - (V) carbon fibers
SURFACE TREATMENT forms chemical bonds to the carbon surface, to give abetter cohesion to the resin system of the composite
SIZING is a neutral finishing agent (usually epoxy) to protect the fibers during further processing (eg prepregging) and to act as an interface to the resin system of the composite
Fibers surface treatments - (VI) carbon fibers
Whiskerization Polymergrafting
Pyroliticcarbondeposition
OXIDATIVE NON-OXIDATIVE
Gaseousoxidation
Oxidationin air
Oxidationin oxygenand oxygencontaininggases (O3 , CO2)
Catalyticoxidation
Liquidphaseoxidation
Chemical(HNO3 , H2O2KMnO4, NaClOchromic acid)
Electrochemical(HNO3 , NaOH)
Fibers surface treatments - (VII) carbon fibers Chemical groups producedby surface treatments oncarbon fibers
J.C.Goan, T.W.Martin, R.Prescott 28th SPI Conf., (1973) Paper 21B.
Fibers surface treatments - (VIII) polymeric fibers
ARAMID FIBERS
- chemical etching/grafting (HCl, H2SO4, NaOH →→→→ reactive amino groupsfiber damage may occur!)
- plasma treatment (in ammonia or argon →→→→ 50-400% adhesion increase)
- application of coupling agent (not particularly successfull)
Ultra High ModulusPolyethylene Fibers(UHMPE)
- chemical etching (KMnO2, H2O2, K2Cr2O7 →→→→ 6-fold ISS increase in epoxy)
- plasma treatment (in oxygen or air)
M.S.Silverstein, O.Breuer J.Mater.Sci., 28 (1993) 4718.
Fibers surface treatments - (IX): plasma treatment of UHMWPE fibers
C.Della Volpe, L.Fambri, R.Fenner, C.Migliaresi, and A.Pegoretti, J. Mater. Sci., 29 (1994) 3919.
untreated UHMWPE fibers
plasma treated UHMWPE fibers(air, 20 W, 30 min, 10
-5 bar)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0 1 2 3 4 5
load
(N
)
displacement (mm)
untreated fiber
treated fiber
Fp
2 µm
2 µm
Fibers surface treatments - (X): plasma treatment of UHMWPE fibers
Fibers surface treatments - (XI): plasma treatment of UHMWPE fibers
Effect of time Effect of temperature
Stability of plasma treatments
C.Della Volpe, L.Fambri, R.Fenner, C.Migliaresi, and A.Pegoretti, J. Mater. Sci., 29 (1994) 3919.
Matrix modifications
Example: maleic anhydride or acrylic acid grafted onto polypropylene (Polybond™)
J.M.H.Daemen and J. den Besten, Eng. Plastics, 4 (1991) 82.
Books:
• J-K. Kim and Y-W. Mai “Engineered Interfaces in Fiber Reinforced Composites”, Elsevier Oxford (1998)
• E.P. Plueddemann “Silane Coupling Agents” Plenum Press NY 2nd Edition (1991)
• J-P.Donnet and R.C.Bansal “Carbon Fibers” Marcel Dekker NY 2nd Edition (1990)
Conferences:
• IPCM, Interfacial Phenomena in Composite Materials - biennal (next 2003)
• ECCM, European Conference on Composite Materials, biennal (next Brugge – Belgium June 3-7, 2002)
• IPC, Interfaces in Polymer Composites biennal (next, Orlando, FL; December 9-11, 2002)
• ICCI International Conference on Composite Interfaces
Journals:
• Composites Interfaces, VSP.
• Composites Science and Technology and Composites Part A,, Elsevier
• Polymer Composites, Society of Plastics Engineers SPE