Constituent Materials: Micromechanical Aspects, Physical Properties… · 2017. 2. 23. · Matrix(resin) properties Processing aspects Capillarydriven flow Pressuredriven flow Chemical

||ETH Zurich, Laboratory of Composite Materials and Adaptive Structures 23.02.2017Manufacturing of Polymer Composites - Constitutent Materials 1

23 February 2017 14:00 – 15:00

Joanna Wong

Constituent Materials: Micromechanical Aspects,

Physical Properties, Processability

Spring Semester 2017

151-0548-00L Manufacturing of Polymer Composites

||ETH Zurich, Laboratory of Composite Materials and Adaptive Structures

Composite materials results from the combinationon a macroscopic scale of two or more materialsComposite materials results from the combination on a macroscopic scale of two or more materials

The advantage of composites is that they usually exhibit the best qualities of their consituents and often some qualities that neither constitutent possess (Jones).

R.M. Jones, Machanics of Composite Materials, Hemisphere Publishing Corp., 1975

Stiffness & strength Impact behavior, damage tolerance

and fatigue Thermomechanical behavior

Temperature resistance Environmental/chemical resistance Fire behavior ....Processability

Matrix

Fibre

Voids

viViV

v f vm vv 1

Physical properties

Mechanical properties

23.02.2017Manufacturing of Polymer Composites - Constitutent Materials 2


Micromechanical behavior

Stiffness E1 in fibre direction Stiffness E2 in transverse direction

0 1

Ef

Em

E1

vf

Kress, G., Mechanics of Composite Materials, ETH-Vorlesung Nr. 151-0353-00L

fmmf

mf

EvEvEE

E

2E1 vf Ef vmEm

R.M. Jones, Machanics of Composite Materials, Hemisphere Publishing Corp., 1975



Range of obtainable elastic moduli

Gutowski, T.G.: Advanced Composites Manufacturing; John Wiley & Sons, Inc. New York 1997

Continuous aligned

Short aligned

Random short

Random long

Woven fabric



Load transfer from matrix to fibre

Chawla, K. K., Composite Materials Science and Engineering, Sprinber Verlag, New York, 1987.

20

)2cosh(

)2(cosh1 lxfürlxl

eE ff

dxrdxdxdP

ff 2

( 4GmEf Af ln(

maxvf

))12

)2cosh(

)2(sinh

2 lxlerE ff

Normal stress in the fibre

Shear stress in matrix

with:



Strain amplification effects in the matrix

2/Fl

0l

Ml

l

2/Fl

MF0 lll

FF

Load directiond

)EE1(21

1f

f

m2

m



Tensile Strength in Fibre Direction

1

1max maxmax

f v f m

fv f

0 1vf

Faserfestigkeit

Matrixfestigkeit

Mat

rixko

ntro

lliert

Fase

rkon

trollie

rt

vkritischvminimum

Kress, G., Mechanics of Composite Materials, ETH-Vorlesung Nr. 151-0353-00L

1 1max max

min

maxmax

max maxmax

m v f

vm m

f

f m mf

1max max m

maxmax

maxmax

vkritisch

m mf

f mf



Compression strength

Failure takes place due to periodic buckling of the fibres

In-phase buckling involves shear deformation of the matrix:

Out-of-phase buckling involves transverse compressive and tensile strain:

Unbuckled fibrecomposite

In-phase buckling of

fibres

Out-of-phase buckling of

fibres

c Em

2(1m )Vm

c 2Vf (Vf EmEf3Vm

)1/2

c Gm

c (EmEf )1/2

Chawla, K. K., Composite Materials Science and Engineering, Sprinber Verlag, New York, 1987.



Fracture toughness is characterizing the ability of a material containing imperfections to withstand an applied load*

*D.R. Askeland, P.P. Phulé, The Science and Engineering of Materials, fourth Edition, Thomson Brooks/Cole, 200323.02.2017Manufacturing of Polymer Composites - Constitutent Materials 9


Relationship between matrix mechanical properties to composites delamination fracture toughness

Effect of resin elongation on resin toughness

Effect of resin toughness on composite delamination toughness

W.M. Jordan, W.L. Bradley, R.J. Moulton, Relating Resin Mechanical Properties to Composite Delamination Fracture Toughness, Journal of Composites Materials, Vol. 23, 1989

toughness is a critical issue, especially in case of thermosets resin systems. Due The poor matrx toughness is a critical issue, especially in case of thermosets resin systems. Due to their brittle nature thermoset resins often require application of toughening techniques for

structural applications.



Compression after Impact (CAI)

Arendts, F.J., Aktuelle Entwicklungen in der Strukturtechnik, Z. Flugwiss. Weltraumforschung, 16 (1992) 231-24623.02.2017Manufacturing of Polymer Composites - Constitutent Materials 11


Temperature resistance

Metals

Intermetallic compounds

Polymer composites

Metal composites

Ceramic composites

Arendts, F.J.: “Aktuelle Entwicklungen in der Strukturtechnik“ in Zeitschrift für Flugwissenschaften und Weltraumforschung 16/1992, S. 243, Springer 1992



Thermomechanical Behaviour





Thermal gradient:

∆1

Thermal stresses:



Viscoelastics Effects

Creep

Stress relaxation

Will be discussed in more detail in lecture “Introduction to Polymer Materials”



Chemical Resistance


Galvanic corrosion

NaCl and NaOH etching of polyester, S. P. Sonawala, R. J. Spontak (1996)

E Glass in H2SO4, Owens Corning (2010)


Fire Resistance


• Matrix systems tend to degrade at lower temperatures than reinforcement fibres

• Flame retardants may be added to matrix systems


Operating Temperatures


Too hot:Reduced stiffness, strength

Too cold:Reduced ductility


Fabrication route

Physical and chemical processes

Matrix(resin) properties

Processing aspects

Capillary drivenflow

Pressure drivenflow

Chemical reaction

Matrix viscosity


Final part & material

properties

Manufacturing process

CuringFormingImpregnation

Reaction kinetics

Layup,Preform

Constituent materials


Matrix viscosity as function of time for a typical thermosets matrix system (EP-resin)

0,000

0,100

0,200

0,300

0,400

0,500

0,600

0,700

0 60 120 180 240 300

Zeit / s

Visk

ositä

t / Pa *s isotherm bei 50°C

isotherm bei 90°C



Curing reaction as function of time for a typical thermosets matrix system (EP-resin)



Matrix requirements: Summary (I)

High Matrix ductility: Matrix ductility must be much higher (at least 2-3 times higher) compared to the one of the fibres because of:

– Strain amplification effects– Thermal induced strains due to mismatch in thermal elongation

coefficent between fibre and matrix

High tension strength, because the strength of multi-layers laminates in tranverse direction is determined by the strength and ductility of the resin

High Shear modulus and strength: Those properties are significantly influencing the Inter-Laminar Shear Strength of the composite

High shear and Young’s modulus: Those properties are determining the compression strength of the composite



Matrix requirements: Summary (II)

Softening temperature of the matrix is responsible for the temperature behavior of the composite and should thus be higher then the service temperature of the part. The glass transition temperature of the matrix should therefore be much higher than the maximum expected service temperature (50°C +).

Processing properties:– Matrix systems should possess low viscosity (< 1Pa.s) at adequate

temperatures– In case of thermosets resins, the processing time is limited by the

curing reaction. – Health aspects are critical!

• Exposure to resin vapour and contact with the uncured components can result in irritations and the development of allergies and asthma.

• Some epoxy resin systems have even worth health effects.



Influence of Voids


J. Wong, J. Molina Blanca, Ermanni (2016)

Documents

Constituent Materials: Micromechanical Aspects, Physical Properties… · 2017. 2. 23. · Matrix(resin) properties Processing aspects Capillarydriven flow Pressuredriven flow Chemical