A Non-Destructive Method for Evaluation of the Out of Plane Elastic Modulus of Porous and Composite Materials

This paper presents an effective and reliable non-destructive method to measure the Young Modulus of porous and out of plane Young Modulus of composite materials using sound waves. First, a Finite Element Model based on Representative Volume Element (RVE) is developed to demonstrate how the elastic properties of composite material can be estimated by acoustic measurements using an impedance tube test rig. Second, the results of the experimental measurement campaign was carried out to validate the proposed method. In particular, two soft elastic foams with different density, an epoxy-carbon fibre composite and vynilester-glass fibre composite were tested. In the proposed method, a two-microphone impedance tube setup was used where the measured acoustic pressures at two upstream locations allowed the estimation of the reflection coefficient and the acoustic impedance of the tested materials. Since the acoustic impedance can be expressed as a function of the longitudinal speed of sound (assuming a plane standing wave excitation), the elastic modulus can be estimated which is associated with the speed of sound. The elastic modulus measured using the proposed method were in good agreement with the values obtained by the standard methods such as tensile tests and ultrasound time of flight measurements. The proposed method would allow in an accurate and fast manner the non-destructive evaluation of Young Modulus of porous materials and for the first time the proposed approach is applied successfully to the measurement of out of plane Young modulus of composite materials.