A nonlinear finite element approach with cohesive-frictional interfaces for mode II Transverse Crak Tension test insight

In many circumstances structural failure modes are driven by the formation and propagation of fractures. For instance in composite laminate structures one of the most worrying condition is delamination, which is an interlaminar progressive fracture. Fracture toughness is the material mechanical parameters which ensure fracture safe condition and it is also an essential parameter for performing nonlinear structural analysis, no matter if based on Fracture Mechanics or by means of Interface Cohesive theories. It is then of paramount relevance to evaluate the critical fracture energy by means of simple and reliable laboratory tests. Several tests are available for the direct determination of mode I and mode II fracture energies. If for mode I, fracture energy determination is nowadays well defined and the Double Cantilever Beam (DCB) test is normed and universally adopted, it is not the same for mode II fracture energy. The tests based on bending beams theory such as End Notched Flexure (ENF), End Loaded Split (ELS) test and Four Point End Notched Flexure (4ENF) are all widely used tests, which however for different reasons have not been fully accepted.