Progressive delamination in composite materials under static or fatigue loading condition are, in many structures, one of the predominant cause of failure. In the paper, an accurate study of quasi-static delamination growth under mode II loading condition is conducted. Several experimental tests are performed on composite laminates consisting of unidirectional carbon/epoxy layers. Four-point end-notched flexure (4ENF) test is employed in order to characterize the mode II interlaminar fracture toughness. The R-curve is obtained by means of optical and numerical determination of crack tip position. The energy release rate and the crack length are calculated through experimental determination of the compliance until unstable advance occurs. In order to confirm the experimental results, a cohesive-frictional model, implemented in the finite element program FEAP, allows to evaluate the influence of frictional phenomena in the Mode II delamination, when the compression of the two interfaces increases the energy dissipation due to the friction.
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