Experimental Technique to Estimate Interfacial Properties of Mechanoluminescent Particles in an Elastomer Matrix

Abstract

Mechanoluminescent-particulate filled composites have been gaining significant interest for light generation, stress visualization, health monitoring, damage sensing and pressure mapping applications. Previous works on stress-dependence of light emission have modeled emission intensity as a function of macroscopic composite stress. While this approach may suffice from an application point of view, the resulting model may not represent the mechanoluminescence phenomenon accurately. This is because in particulate filled elastomer composites, particulate stresses can be significantly different from matrix and macroscopic stresses, especially in composites with moderate and low filler volume fraction. Experimental difficulty in measuring stresses within micron-sized particles necessitate micromechanical models that can connect macroscale measurements to microscale parameters through material properties. Apart from the material properties of the matrix and the particles, the bonding between the two dissimilar materials at their interface influences the stress transfer significantly. Cohesive zone modeling (CZM) approach defines the interface between particles and matrix as a piecewise linear stiffness element with possible degradation of stiffness beyond a certain strain. CZM provides a convenient way to not only predict particulate stress from macroscopic stress, but also to track interface damage and debonding. In this paper, we demonstrate an experimental technique to obtain cohesive zone parameters for mechanoluminescent-particulate filled elastomer composites, utilizing optical microscopy and Digital Image Correlation (DIC). CZM thus obtained can help predict particulate stresses and aid better modeling of the mechanoluminescence phenomenon. The experimental technique can also be easily adopted for other particulate-filled composites.