Comparison of bulk modulus determined by transient bulk creep experiment and direct optical measurement of poisson’s ratio

This work presents a method to determine the bulk modulus and Poisson's ratio of an epoxy. Since either Poisson's ratio or bulk modulus is needed for a full description of the materials constitutive behaviour, both methods were compared to identify the more appropriate one. Poisson's ratio was obtained using an optical imaging system. The experimental setup consists of multiple cameras that measure the elongation and the lateral strain of a sample at tension load for different temperatures, ranging from -40degC up to 150degC. Bulk modulus was measured using transient bulk creep experiments. These were carried out using a pVT dilatometer. A pressure jump was applied to a constant level and pressure remained steady up to four days. Therefore, relaxation in the volume did occur. The pressure jump experiments were performed at different temperatures. The final pressure was 200 MPa and temperature ranges from 30degC to 150degC. The results indicate clearly, that there is a time and temperature dependency of the bulk modulus for the adhesive used. Poisson's ratio was computed and compared to the one from the direct optical measurement. Moreover, a time- temperature shift was done and data were fitted to Prony series. Viscoelastic data was implemented in a commercial finite element (FE) program.