MTL Annual Research Report 2011

Catastrophic structural failures are the cause of many physical and personal losses, with prevention estimated at billions of dollars in savings each year. Non-destructive evaluation (NDE) techniques have been pursued and employed for damage detection of such structures to detect cracks and other damage at pre-critical levels for remediation ^{[1] [2]} . Here, a novel multi-physics approach is reported that addresses drawbacks in existing techniques by taking advantage of the effects that damage, such as a crack, has on the electric and thermal transport in a material containing a CNT network distributed in the bulk material. When a potential is applied to a nano-engineered structure (Figure 1), electric field lines concentrate in the vicinity of cracks as electrons flow around damage, causing field concentrations and “hot spots” via Joule heating, an effect which is amplified because the heat flow is also impeded in areas of damage (e.g., across a crackface). These changes of temperature can be localized through a conventional infrared thermal camera. Low power operation (a 9-V standard battery is exemplary, providing a 15C rise at 1 Watt as in Figure 2), and high spatial resolution is demonstrated that is beyond state-of-the-art in non-destructive evaluation.

Using this technique, multiple applications have been identified such as crack detection in composite components that are joined by metallic fasteners, structures having internal nonvisible damage due to impact, and in situ progressive damage monitoring during a tensile strength test.  The thermal nano-engineered NDE technique demonstrated here can provide a new and effective inspection route for monitoring next-generations of safer infrastructure ^{[3] [4]} .