Unraveling the nonlinear elastic response of materials with dynamic acousto-elastic testing

Abstract

Compared to standard nonlinear ultrasonic techniques based on harmonic generation or resonance tests that provide an average nonlinearity level, Dynamic Acousto-Elastic Testing (DAET) is a pump-probe approach that allows one to track the nonlinear elastic response at each phase of the dynamic cycle, and to quantify additional features such as transient softening/weakening and hysteresis. These so-called nonlinear signatures can help us unravel the origins of the nonlinear response at the micro/mesoscopic scale. In this talk, we first review some of the DAET results obtained by our group and others in a wide range of materials from cracked metals to rocks and unconsolidated granular media. Next, we present some of our most recent results where we investigate the effect of relative humidity (RH) on the nonlinear elastic response of granular media. We use DAET on samples of glass beads under dry (∼10%), ambient (∼60%) and humid (∼100%) conditions. We find that all extracted nonlinear parameters in humid samples increases by an order of magnitude compared to those in dry samples. This is consistent with the idea that water adsorption on the grains makes the contact junctions weaker. This has great relevance when trying to quantify the nonlinearity of porous materials.