For the detection of problems like fastening failures and delamination in composites, the employment of embedded fiber Bragg grating (FBG) sensors is considered an effective tool to measure non-homogeneous internal strains near damage or interfaces of dissimilar materials which in turn can help identify the severity of fracture. In this work wavelength multiplexed FBGs are used to measure strains during gradual adhesive fastening failure in a single lap joint and delamination in a uniaxial composite, during monotonic and fatigue loads. It is shown that such measurements can be effectively used to determine the stresses near the joint and bridging tractions in delamination. The particular method can provide a significant tool in experimental mechanics and fatigue of composites as well as composite assemblies. Experimental measurements are in very good agreement with the numerical analysis concurrently used for the verification of the experimental procedure's feedback. (C) 2011 Elsevier Ltd. All rights reserved.