Experimental study on effects of asymmetrical stacking sequence on carbon fiber/epoxy filament wound specimens in DCB, ENF, and MMB tests

This study focused on the delamination fracture behavior of asymmetrical stacking sequences of CFRP laminates subjected to different loading directions in double cantilever beam (DCB), end-notched flexure (ENF), and mixed-mode bending (MMB) tests. CFRP laminates with three different stacking sequences mimicking the winding angles of filament wound structures were considered. As the stacking sequences were asymmetrical, flipped and non-flipped specimens were tested to examine the effects on different test loading conditions. According to the results, each stacking sequence provided a different load–displacement response and fracture toughness. The flipped and non-flipped specimens did not appear to affect the fracture toughness in the DCB test . However, significant effects were observed in the ENF and MMB tests. Observations at the edges of the specimens indicated the dependency of the delamination behavior on the specimen stacking sequence. The delamination surfaces were further analyzed using a scanning electron microscope (SEM). SEM images revealed several delamination mechanisms that contributed to the load–displacement response and fracture toughness of the laminates.