Interaction, instability, and simultaneity of debonding processes in flexure of masonry walls strengthened on two sides with FRP

This paper studies the interactive, simultaneous, and unstable multiple debonding mechanisms in masonry walls strengthened to resist out-of-plane flexure using composite materials bonded on their tensed and compressed faces. This structural form combines rigid blocks and brittle joints sandwiched between adhesively bonded composite layers. It characterizes masonry walls strengthened to resist dynamic and seismic out-of-plane loads, but also armor plates with ceramic tiles, electronic packaging, and sandwich panels with embedded inserts. The study focuses on the stability of the interactive debonding mechanisms and on the potential evolution of coupled and simultaneous debonding processes. It uses a cohesive interface approach and a geometrically nonlinear high order model. A numerical study that examines the coupled debonding processes in masonry wall samples strengthened with composite materials on the two outer faces is presented. The study examines the instabilities involved with the processes, the order in which the tension driven debonding and the buckling driven one nucleate, and the interaction between them. It also examines the impact of the properties of the cohesive interface, the presence of pre-existing debonded regions, the arching effect, and the accumulation of damage at the interfaces. This effort aims to gain insight into the debonding processes and their impact on the performance, functionality, and safety of the strengthened element.