Evaluating the loading rate dependency of mode I delamination for composite laminates at different temperatures

This study presents an investigation on the influence of loading rate and temperature on mode I interlaminar fracture toughness of unidirectional composite laminates. An analytical model was developed to describe the temperature- and loading rate-dependent fracture toughness, and a loading rate coefficient m was defined to evaluate the rate dependency. Quasi-static and dynamic double cantilever beam (DCB) tests were conducted at various temperatures from -20 to 110 degrees C. A dual electromagnetic Hopkinson bar was employed to perform dynamic tests under loading rates of 15 and 24 m/s to achieve pure mode I delamination. The experimental results show that the fracture toughness exhibits an obvious positive loading rate sensitivity at all temperatures, whereas the loading rate coefficient m shows two different trends with temperature indicating different loading rate dependency. Fractography observations reveal an obvious transition in the dominant failure mechanism at low temperatures from fiber/matrix interface debonding under quasi-static conditions to brittle fracture of matrix under dynamic conditions. However, both the quasi-static and dynamic delamination surfaces exhibit multiple failure modes at high temperatures. It is reasonable to deduce that the effect of temperature and loading rate can be attributed to the nature of matrix, the bonding between fiber and matrix.