Fracture characterization of asymmetric joints under pure mode I and mode II loading using the mixed-mode bending test

• Equivalence between the J -integral and the VCCT for small FPZs. • The MMB test, originally designed to obtain mixed-mode fractures in symmetric specimens, is applied to achieve pure mode fractures in asymmetric specimens. • Pure mode I and mode II fractures are obtained by varying the loading lever length across a wide range of thickness ratios. • An analytical approach is proposed to determine pure mode energy release rates (ERRs) in asymmetric specimens using MMB tests. The Mixed-Mode Bending configuration was proposed to characterize the interlaminar fracture of symmetric composite specimens in mixed-mode I/II. In the present study, that test configuration has been applied to obtain pure mode I and pure mode II test conditions in asymmetric specimens, constituted by one or more materials. In a first stage, the conditions for pure mode I and pure mode II have been formulated in a novel way by the J -integral, assuming a small fracture process zone. Those conditions have been applied to asymmetric specimens tested in mixed-mode bending, to obtain testing configurations of pure mode I and pure mode II. For a given asymmetric specimen, different pure mode configurations can be determined, by only varying the loading lever length. The admissible values of normalized loading lever lengths have been determined for three asymmetric systems. Then, a novel analytical approach has been developed to obtain the energy release rate in modes I and II. Several cases have been analysed by the finite element method, using the virtual crack closure technique. The agreement between numerical and analytical results is reasonable in terms of pure modes and energy release rate values.