Alessandro Pegoretti - UniTrento compositi/interfacce... · 2008. 3. 6. · Spectroscopy - Auger...

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


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


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


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


starter crack

ENF specimen

Effect of fiber-matrix adhesion on Mode II fracturetoughness in graphite/epoxy composites


0.5

1.0

1.5

2.0

2.5

3.0

0 1 2 3

NO

RM

AL

IZE

D G

IIC


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


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


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


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/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

Alessandro Pegoretti - UniTrento compositi/interfacce... · 2008. 3. 6. · Spectroscopy - Auger...

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Transcript of Alessandro Pegoretti - UniTrento compositi/interfacce... · 2008. 3. 6. · Spectroscopy - Auger...