Variable Strain Rate In Situ Piezospectroscopic Studies Of Alumina Nanocomposites

Alumina nanoparticles embedded in an epoxy matrix both strengthen the host material and act as nano stress sensors for the purpose of tracking changes in localized stress concentrations of the nanocomposite. At variable strain rates, in situ photo-stimulated luminescence measurements can provide dynamic stresssensitive information using the nanoparticle\u27s piezospectroscopic (PS) behavior. For these tests, cylindrical specimens with 4.5, 13.7, and 29.7 % volume fraction of particulate modifiers were fabricated and loaded under variable compressive strain rates on the order of 10-4to 10-2s-1. Mechanical results show an increasing compressive strength with increasing strain rate and volume fraction. By using alumina nanoparticles as a diagnostic mechanism, the stress-induced shifts of the spectral R-line peaks were measured and quasi-static results show an increase in sensitivity of the PS coefficients when compared to similar materials under static conditions. Upshifts of the PS coefficients near the maximum stress reveal the potential of alumina particulate composites to monitor the early onset of failure likely caused from matrix micro-cracking. Additionally, the relationship between PS coefficient sensitivity and strain rate reveals trends that could be used to optimize the material particulate concentration and loading rate. The use of piezospectroscopy in these dynamic tests provides the potential for monitoring in situ material behavior with respect to time and paves the way for the integration of these materials in stress sensitive applications