Compressibility of Elastomer Matrix Composites Filled With Hollow Thermoplastic Microspheres Under Low Hydrostatic Pressure

This paper investigates the pressure–volume response of elastomer matrix composites filled with hollow thermoplastic microspheres and subjected to low hydrostatic pressure. The hysteretic response of the material up to a pressure of 0.8 MPa is measured using an original experimental set‐up that combines hydrostatic pressure loading by nitrogen pressurisation and volume measurement thanks to digital image correlation. In terms of volume change vs. pressure, a detailed analysis of the pressurisation and depressurisation paths shows firstly that the macroscopic pressure which is emerging from the successive buckling of the microspheres does not depend on their concentration in the composite. Secondly, it is established that the unloading path, even if it does not change its slope steeply, admits a pressure inflection point that seems to depend on the volume fraction of the microspheres. In the future, these experimental observations will be useful for developing constitutive models for these composites and in particular for the strain energy density function dedicated to their spherical response.