Michael R. Wisnom

High Performance

Ductile Composites

Programme Grant

Current high performance composites

Stiff, strong, light, but fail suddenly and catastrophically

HiPerDuCT programme

High Performance Ductile Composites Technology

• Challenge is to create composites that fail more gradually

• Overcome a key limitation of conventional materials: their inherent lack of ductility

• Retain high strength and stiffness

• Potential benefits:

– Increased damage tolerance

– Less notch sensitivity

– Greater work of fracture

– Benign failure

– Warning of overloading

Mechanisms for creating gradual failure

0

200

400

600

800

1000

1200

1400

0 0.5 1 1.5 2 2.5 3 3.5

Strain [%]

Str

ess [

MP

a]

0

200

400

600

800

1000

1200

0.0 0.2 0.4 0.6 0.8 1.0

Strain [%]

Str

es

s [

MP

a]

• Fibre reorientation -using excess length e.g. angle plies

• Strength dispersion e.g. fragmentation in thin ply hybrid laminates

• Aligned discontinuous composites – slip at interfaces

• Ductile fibres

θ

θ’

Mean Max Shear Stress, τ12 = 150 MPa

Mean Shear Modulus, G12 = 2.4 GPa

Mean Failure Axial Strain, εX = 20.3 %

Mean Failure Shear Strain, γ12 = 35 %

Thin Angle Plies – [±45]5S

Skyflex 0.03 mm carbon/epoxy

J. D. Fuller

Thin ±26° laminates

Investigate the influence of resin plasticity using a range of 6 values for n.

β is constant.

3 values of resin modulus, Em:2.5 GPa, 3.5 GPa, 4.5 GPa.

Leads to 18 ‘material’ input files for one-parameter plasticity model.

Each ‘material’ has unique plasticity constants (a66, α and r).

Range of 6 laminate ±θ from ±25° - ±30°in 1° increments.

Vf increased to 50%

εpMeff = β(σM

eff)n

Yields results of size 6x6x3 for each of:

Strength“Yield” StressPseudo-Ductile StrainFailure Strain

“Yield” Point

Pseudo-Ductile Strain

Thin ply hybrid failure modes

Possible failure modes of a ply-by-ply hybrid laminate in tension

Thin ply hybrid behaviour

(multiple cracks+stablelocalised pull-out if any)

Conventional hybrid behaviour 2(single crack+instant unstable delamination)

FF

FF

FF

Conventional hybrid behaviour 1(single crack through the whole thickness)

Low modulus, high strain

High modulus, low strain

Low modulus, high strain

Failure mechanism map

M. Jalavand

0

200

400

600

800

1000

1200

1400

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

Strain [%]

Str

es

s [

MP

a]

Stacking sequence: [190GSM S-Glass1/50GSM MR401/190GSM S-Glass1]

High modulus carbon / S-glass hybrid

1.44% pseudo-ductile strain

G. Czel

High modulus / high strength thin carbon/carbon

Lay-up sequence: [28 GSM T10002/50 GSM XN802/28 GSM T10002]

260 GPa modulus0.97% pseudo-ductile strain

Combining mechanisms - [±265/0]S

εd = 2.22%σy = 691 MPa

High Performance Discontinuous Fibres

0

400

800

1200

1600

2000

0 0.4 0.8 1.2 1.6 2S

tress

(M

Pa

)Strain (%)

High performance Carbon/epoxy composites (3 mm of fibre length, 55vf%) E≈115 GPa, σT≈ 1500 MPa

Tape type preform

y

z

xConveyor belt

Fibre suspension jets

Thin parallel plates

Fibre orientation head

50 μm

• Newly developed discontinuous fibre alignment method using water

• Enables high volume fraction and high degree of alignment

• Flexibility to combine different fibre types, lengths…

H. Yu, M. Longana, K.Potter

0

200

400

600

800

1000

0 0.5 1 1.5 2 2.5

Str

ess(

MP

a)

Strain(%)

• HM Carbon/E-Glass epoxy composites

C:G = 1:9

50 µm

C:G = 1:2

50 µm

vf≈55%

Pseudo-ductility obtained from the intermingled-hybrid composites by the fragmentation process in the carbon phase

Carbon ratio

0.10

0.20

0.25

0.33

0.40

0.50

Hana.Yu@bristol.ac.ukm.l.longana@bristol.ac.uk

Intermingled discontinuous hybrids

Conclusions

• A number of approaches to creating more gradual failure demonstrated

• Possible to suppress delamination and cracking using thin plies

• Fibre reorientation in angle plies can create additional strain

• Ply fragmentation in thin hybrids creates a pseudo-ductile response

• Mechanisms can be combined

• Analysis can predict behaviour and produce failure mechanism maps

• Opens up new possibilities for composites which fail more gradually

Thank you for your attention!

Programme Grant

This work was funded under the EPSRC Programme Grant EP/I02946X/1 onHigh Performance Ductile Composite Technology, a collaboration betweenBristol University and Imperial College, London

Acknowledgement