An experimental apparatus to evaluate the non-linearity of the acoustoelastic effect in rubber-like materials

In this paper, the non-linearity of the propagation velocity of ultrasound longitudinal waves in a filled elastomer as a function of quasi-static deformation was investigated. A theoretical-experimental approach to determine the trend of the ultrasonic velocity, considering the variations of the tangential compression modulus and the density as functions of the imposed deformation, was proposed by authors. This new methodology has required both the modification of an experimental apparatus designed by Lo Savio and Bonfanti in a previous work, and the realization of a temperature-controlled compressive testing machine. Through the Digital Image Correlation and laser scanning during a uniaxial tensile test, the first apparatus allowed to evaluate the specimen volume change and the consequent density change. The second device was used to measure the compressive tangent modulus variations. The approach validity was confirmed by the best fitting with the experimental trend from ultrasound immersion technique compared to energy-type methodologies.