An experimental study of the large-strain tensile behavior of composite solid propellant using digital image correlation

This work aims to study the mechanical response of composite solid propellants undergoing large strain. In order to study the effect of displacement rate, uniaxial tensile tests were conducted at constant displacement rates of 1, 7, and 50 mm/min. The nominal strain from Universal Testing Machine and true strain obtained using digital image correlation (DIC) have been compared. It is observed that beyond a threshold strain, nominal strain is smaller than the true strain, and hence it is essential to measure the true strain using a full-field noncontact measurement technique like DIC. The tensile modulus in the linear region increases and failure strain decreases with an increase in the displacement rate. Nominal and true stress is determined by considering the initial and instantaneous cross-sectional area of the specimen. Poisson’s ratio is determined on the lateral and transverse surfaces of the specimen, and a similar variation is observed on both surfaces. Its value is close to 0.5 at the beginning of loading, which decreases with the increase in the applied longitudinal strain. It decreased to 70% of its initial value at a longitudinal strain of 50%. Dilatation is calculated using normal strains and divided into three regions by presuming it to be correlated to the development and growth of vacuoles based on the existing literature.