Interlaminar fracture analysis of composite DCB specimens

Mode I interlaminar fracture was studies using double cantilever beam (DCB) specimens of unidirectional carbon fiber/epoxy composites. An improved analytical model was introduced to study the crack opening displacement (COD), compliance (C) and fracture toughness (G_I) as a function of the material stiffness ({left semidirect product}) ahead of the crack front. The COD expression was derived and compared with the COD profiles near the crack tip measured by moiré interferometry. Results showed that the COD expression can predict all the important qualitative features of the measured COD profiles; also, the quantitative agreement at the loading point was very good. It was found that {left semidirect product} plays an important role in evaluating the values of COD, C and GI.