Failure in Composites: Filling the knowledge gaps Giuliano Allegri - - PowerPoint PPT Presentation

Failure in Composites:

Filling the knowledge gaps

Giuliano Allegri ACCIS 2018 Conference November 22nd, 2018

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Failure of Composites

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• Scopus search - Title-Abs-Key ( composites AND failure AND ( delamination OR

interlaminar OR translaminar OR intralaminar ) )

• 7000 + papers!

22/11/2018

ACCIS 2018 Conference

Failure of Composites

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• Scopus search - Title-Abs-Key ( composites AND failure AND ( delamination OR

interlaminar OR translaminar OR intralaminar ) )

• 7000 + papers!

22/11/2018

ACCIS 2018 Conference Carbon fiber m arket volum e by region, 20 14 - 20 25 (Tons/ Tons @ 20 14)

x 2 x 3

No Growth Design Philosophy (CHM-17)

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• Substantiated by pyramid of testing
• Knockdowns dictated by uncertainty (A- or B-basis)
• Compound knockdowns for environmental effects (temperature & humidity)
• No growth implies no “lifing” – fatigue accounted for via static strength knockdowns

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ACCIS 2018 Conference

Coupons Generic features Specific features Sub-components Components Test Analysis

Current

Test backed up by Analysis

Probability Strength

B‐Basis A‐Basis

Beyond No Growth Design

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• Analysis backed up by testing (“virtual testing”)
• Data-rich approach to experimental testing (e.g. DIC + inverse FEM)
• Probabilistic assessment of structural integrity (e.g. stochastic FEM)
• Proper “lifing” of components (akin to ”damage tolerance” for metals)
• Structural health monitoring

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ACCIS 2018 Conference

Coupons Generic features Specific features Sub-components Components

Future

Test Analysis

Analysis backed up by Test

Test Analysis

Current

Test backed up by Analysis

Fatigue Damage Growth

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ACCIS 2018 Conference

• Delamination responsible for 60% of failure in

composite structures (US DoD)

• Delamination initiate at interlaminar stress risers

(e.g. free edges, ply drop-offs)

• Strongly dependent on environmental effects

(1) Micro‐Cracking (2) Delamination (3) Fibre‐Failure (1) (2) (3)

Fatigue Delamination Growth

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ACCIS 2018 Conference

• Usually described by semi-empirical equations (e.g. Paris law)
• C and b dependent on: stress-ratio, mode-mixity, frequency, temperature,

moisture, ageing…. Can such a problem be described using machine learning?

da dN  CGmax

b

Fatigue Delamination Growth

A Neural Network Approach

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ACCIS 2018 Conference

• 1. Buckingham  theorem (1914): similitude underlined by non-dimensional

governing parameters

• 2. Single Hidden-Layer Neural Network (SLHNN) trained via Extreme Learning

(Huang, 2006) – it can represent (semi-)monotonicity constraints (embedding previous physical knowledge)

+

c1 w

1 (1)

w

1 (2)

w

1 (3)

c2 cN wN

(3)

wN

(2)

wN

(1)

 f s Y

Hidden Layer

   Z

Allegri G., Modelling fatigue delamination growth in fibre‐reinforced composites: Power‐law equations or artificial neural networks?, Materials and Design; 155, 59‐70, 2018

Fatigue Delamination Growth

A Neural Network Approach

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ACCIS 2018 Conference

• Training performed in 0.1s on a standard desktop PC
• Application example to fatigue delamination growth in T800H/#3631
• G. Allegri., Modelling fatigue delamination growth in fibre‐reinforced composites: Power‐law equations or artificial neural networks?, Materials

and Design; 155, 59‐70, 2018

Delamination Suppression

Through-thickness Reinforcement (TTR)

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ACCIS 2018 Conference

• Strong enhancement of interlaminar fracture toughness (40x mode I; 4x mode II)
• Multi-scale modelling of delamination bridging via z-pins

10 20 30 40 0.0 0.2 0.4 0.6 0.8 1.0

G* 

 

(kJ/m2)



• G. Mohamed, G. Allegri, M. Yasaee, S.R. Hallett, Cohesive element formulation for z‐pin delamination bridging in fibre reinforced laminates,

International Journal of Solids and Structures; 132: 232‐44, 2018

Cartie’ (2000)

Structural Health Monitoring via TTR

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ACCIS 2018 Conference

• Through-thickness reinforcement (TTR) toughens the host material
• Multifunctionality: TTR (z-pins) can be employed for detecting delamination in-

situ!

Structural Health Monitoring via TTR

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22/11/2018

ACCIS 2018 Conference

• Through-thickness reinforcement (TTR) toughens the host material
• Multifunctionality: TTR (z-pins) can be employed for detecting delamination in-

situ!

• Demonstration on ASTM-standard coupons
• B. Zhang, G. Allegri, M. Yasaee, S.R. Hallett, I.K. Partridge, On the Delamination Self‐Sensing Function of Z‐Pinned Composite Laminates,

Composites Science & Technology; 128: 138‐46, 2016.

• B. Zhang, G. Allegri, S.R. Hallett, An Investigation into Multi‐Functional Z‐pinned Composite Laminates, Materials & Design; 108: 679‐88, 2016.

Structural Health Monitoring via TTR

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ACCIS 2018 Conference

• Through-thickness

reinforcement (TTR) toughens the host material

• Multifunctionality:

TTR (z-pins) can be employed for detecting delamination in-situ!

• Demonstration
• n

ASTM-standard DCB coupons

• B. Zhang, G. Allegri, M. Yasaee, S.R. Hallett, I.K. Partridge, On the Delamination Self‐Sensing Function of Z‐Pinned Composite Laminates,

Composites Science & Technology; 128: 138‐46, 2016.

• B. Zhang, G. Allegri, S.R. Hallett, An Investigation into Multi‐Functional Z‐pinned Composite Laminates, Materials & Design; 108: 679‐88, 2016.

Acknowledgements

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• The author would like to acknowledge Rolls-Royce plc for

their support

• f

this research through the Composites University Technology Centre at the University of Bristol, UK

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ACCIS 2018 Conference

Thank you for you attention!

giuliano.allegri@bristol.ac.uk

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