Analysis of residual stresses and interface damage propagation in hybrid composite/metallic elements monitored through optical fiber sensors

The presence of residual stresses due to the manufacturing process may influence the development of damage in the interfaces of hybrid composite/metallic elements, thus complicating the structural integrity analysis. The paper presents an integrated experimental and numerical approach to develop sufficiently accurate models for the residual stress build-up and the interface damage propagation in hybrid structures. The experimental part focuses on the effect of residual thermal stress on mode I fracture behavior in three different interfaces of co-bonded composite/metallic hybrid specimens under the DCB test. The strain evolution is monitored by FBG sensors carried by optical fibers embedded in the specimens during the manufacturing and DCB test. Strain evolution during the curing cycle is used to calibrate a cooling simulation, followed by the simulation of the mechanical tests. The resulting multistep numerical approach obtains an appreciable correlation with experimental forces, strain evolution, and final residual strain in the DCB tests. Experimental and numerical analyses indicate that residual thermal stress can affect the evolution of strains during crack propagation, the development of permanent displacements, and the forces required to propagate the cracks.