Strain and damage sensing of polymer bonded mock energetics via piezoresistivity from carbon nanotube networks

The strain and damage sensing abilities of randomly oriented multi-walled carbon nanotube (MWCNT) networks dispersed in the polymer binder of polymer bonded energetics are experimentally investigated. Monoclinic sugar crystals acting as mock energetics and aluminum powder acting as metallic fuel were added to simulate a fuel-oxidizer combination commonly used in the aerospace industry. MWCNTs were added to polydimethylsiloxane (PDMS), an elastomeric polymer binder, and hybrid mock energetics were fabricated. Four different material compositions were characterized based on the stress-strain response under monotonic uniaxial tension and compression to failure tests, allowing for the assessment of the effects of MWCNTs and aluminum powder on the average bulk elastic modulus, peak stress, and strain to failure. Along with mechanical loading, the piezoresistive response i.e. the change in resistance and reactance as a function of applied strain, was measured in both the elastic and failure regimes of the mechanical response for each material system. Gauge factors were calculated in three distinct regions of elastic behavior, microscale, and macroscale damage demonstrating the MWCNT network's ability to sense strain, microscale damage, and macroscale fracture of mock energetic materials. Results observed herein demonstrate valid structural health monitoring applications for embedded carbon nanotube sensing networks in elastomer-based energetics experiencing significantly higher strain levels than prior proofs of concept with epoxy-based material systems.