Conductive Composites such as carbon fiber reinforced composites are increasingly used in safety critical aerospace applications. The catastrophic macro structural failure of composite structures initiates from a micro level failure event such as fiber breaks. The ability to detect damage early on can improve the safety level and reliability of composite structures. A multilevel self-sensing damage detection techniques ability to detect damage at various length scales are numerically explored using COMSOL multiphysics software. The simulation methodology and results are reported highlighting the multilevel damage detection capability. The electrode configuration and detection sensitivity is also reported.

1. Multiscale Damage Detection in
Conductive Composites
Raj C Thiagarajan, PhD
ATOA Scientific Technologies Pvt Ltd
ATOA Scientific Technologies
Engineering Simulation For Innovation

2. ATOAST
• We Provide Multiphysics
Engineering Design Solutions
• Driven by Material Unity Vision
• We are the first COMSOL
Certified Consultant from India
• ATOAST JOTHI foundation
• www.atoastech.com
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3. Multiscale Damage Detection in
Conductive Composites
• Multiscale nature of damage
• Damage Modes in composites
• Damage detection techniques
• Self sensing Carbon fiber Composites
• Numerical model
– Implementation
– Results and discussion
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4. Multiscale
damage mechanism
 Structure
 Part
Laminate
Fiber
Matrix
Molecular c
0.142 nm
0.3345 nm
0.669 nm
a b
 ATOMIC bond breakage
ATOA Scientific Technologies Pvt Ltd | www.atoastech.com | COMSOL Conference 2011 | SM Composites 4

5. Why
Potential Safety Risk
without diagnostics
(SAFETY)
• Increase use of
composites in safety
critical application. Design life
Severe
usage
• Increase reliability and Designed
usage
safety levels Service
Mild Limit
usage
• Reduce cost and cycle Time in Operation
time
Additional use may be
gained through
• Focus on carbon fiber
diagnostics
(COST)
composites
ATOA Scientific Technologies Pvt Ltd | www.atoastech.com | COMSOL Conference 2011 | SM Composites 5

6. Damage Mechanisms
• Fiber
– Fiber breaks
(a)
• Matrix
– Matrix crack (b)
• Interface (c)
– Delamination
– Longitudinal (d)
cracks
ATOA Scientific Technologies Pvt Ltd | www.atoastech.com | COMSOL Conference 2011 | SM Composites 6

7. Structural Health monitoring
Existing Techniques
• ultrasonic, acoustic emission, X-ray and eddy current Piezo
sensors with ultrasonic tomography, Embedded Optical
fibers (FBGs)
Limitations
• Based on external or embedded sensors.
• Embedded sensors/electrodes/FBGs lead to initiation of
damage in composites.
Self sensing of Carbon fiber composites
ATOA Scientific Technologies Pvt Ltd | www.atoastech.com | COMSOL Conference 2011 | SM Composites 7

8. Numerical investigation
• The electrical conduction
mechanism and the
effect of damage in CFRP
composites were
simulated in COMSOL
using AC/DC Electric
Currents Interface.
• Homogeneous composite
model with effective
properties
• Micromechanical model
with constituent
properties
ATOA Scientific Technologies Pvt Ltd | www.atoastech.com | COMSOL Conference 2011 | SM Composites 8

9. Results : Fiber breaks
• UD composites
• Electrode on edge
• Resistance change vs
fiber breaks
• Parallel resistance
model behavior
• Very sensitive to fiber
breaks.
ATOA Scientific Technologies Pvt Ltd | www.atoastech.com | COMSOL Conference 2011 | SM Composites 9

10. Results: Matrix Cracks
• Matrix crack
density vs
change in
resistance
• Can detect
matrix cracks
also
ATOA Scientific Technologies Pvt Ltd | www.atoastech.com | COMSOL Conference 2011 | SM Composites 10

11. Results : Delamination
• Delamination
length vs
resistance
change.
• Delamination
growth
between
fibres
ATOA Scientific Technologies Pvt Ltd | www.atoastech.com | COMSOL Conference 2011 | SM Composites 11

12. Conclusions
• The COMSOL model results show that the electrical
resistance change is sensitive to fiber breaks and
delamination.
• The homogenized and micromechanical model
demonstrated the changes in resistance as function of
damage.
• The methodology developed can be used to improve the
damage detection capability and reliability of composite
structures by Virtual optimisation.
ATOA Scientific Technologies Pvt Ltd | www.atoastech.com | COMSOL Conference 2011 | SM Composites 12