• 4ENF test
• bridging
• carbon composite
• crack monitoring
• ERR
• Fracture toughness
• friction
• Mixed Mode I-II
• Mode II
• optical fiber
• R-curve

An experimental evaluation of the parameters characterizing the delamination process for an unidirectional carbon fiber reinforced epoxy composite laminate, under different I and II opening modes is presented, followed by a statistical analysis of the experimental data for each loading condition with the final aim of evaluating the critical fracture toughness and the propagation values for each mode mixity. Special attention is given to the influence of bridging fibers on Mixed Mode I-II tests.
Optical fiber sensors are embedded in a carbon fiber reinforced epoxy composite to obtain strain measurements along the crack path at different crack lengths. A comparison of the experimental strains with numerical models to quantify the influence of fiber bridging upon the sample stiffness is done.
Subsequently it is studied the influence of friction coefficients on Mode II (4ENF) pure tests and finally an empirical method is developed for crack front identification in 4ENF tests by means of an embedded optical fiber sensor placed far away from the fracture surfaces.