Research Goal

Monitor crack growth along the interface region to uniquely establish rate dependent traction laws

Electrophoretic Deposition

PEI functionalized carbon nanotubes (CNTs) are dispersed in aqueous solution
Under DC electric field, charged CNTs migrate and deposit onto the surface of the fiber
Processing parameters to control coating thickness
• Electric field strength
• Deposition time
• CNT concentration
Prepare microdroplet specimen and measure resistance change along the fiber
Create non-intrusive nano-scale interface sensor for crack detection

Crack Monitoring in Microdroplet

Mixed mode crack initiation at the contact region between knife edges and droplet
Sharp increase in electrical resistance as the crack grows through the interface region
Unstable mode II crack growth along the interface as complete debonding occurs

Sensor Optimization Study

Thick coating of CNT increased the interfacial shear strength
Achieve thin uniform coating by manipulating processing parameters
Assess the uniformity of CNT coating through electrical resistance measurement and SEM

CNT as Non-Invasive Sensor

Crack Monitoring

Crack initiation occurs around 50 – 60 % of the maximum load
No change in failure mode
Crack initiation time can be correlated with the simulation to get more accurate traction laws

Conclusions

Methodology to monitor crack initiation in the microdroplet specimen developed
Conducted sensor optimization study to determine the best combination of processing parameters to create thin homogenous CNT coating, which acts as non-invasive sensor

Future Work

Monitor crack speed near failure load
Information on crack initiation and propagation will be used to uniquely establish the rate dependent traction separation law

Acknowledgements

This work is supported by the Army Research Laboratory through the Composite Materials Research program.