טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentMulian Gilad
SubjectDynamic Interfacial Failure in Beams Strengthened with
Composite Materials
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Oded Rabinovitch


Abstract

The use of composite materials for strengthening structural components has become widely accepted in the past three decades. Extending the service life of existing buildings, handling cases where there are access limitations or geometrical constraints, or reducing installation and downtime costs are only few examples where this method becomes relevant. Yet, along with the vast advantages of using the lightweight high performance materials, the evolution of new modes of failure and their tendency to dictate the structural behavior, strength, and stability play a critical role. One of the common and, in most cases, catastrophic failure mode in FRP plated beams involves debonding of the strengthening layer. This failure mechanism is commonly a dynamic process that rapidly propagates along the interface of two materials.

This work presents an analytical and experimental study of the dynamic debonding failure mechanism in FRP plated beams. The first is addressed by formulating a special finite element for the dynamic analysis of the layered beam and looking into the parameters that govern the dynamic phenomenon. The finite element is based on an extended high order theory that incorporates a rich 2D elasticity based stress and displacement fields in the adhesive layer and allows to consider debonding at the two physical interfaces of that layer through cohesive interfaces. The computational framework is then used to study the dynamic debonding process and to examine the impact of a series of geometrical, elastic, mechanical, and physical parameters.

The experimental study is based on four point bending tests of FRP plated beam specimens. The main monitoring technique uses high-speed digital photography. The movement of the crack front in time is quantified by means of the digital image processing in terms of the location of the interfacial debonding front in time and its velocity. The results reveal the dynamic nature of the failure process and provide an experimental benchmark for its consideration. They also provide direct experimental data that supports and validates the theory. With that, the combined experimental and theoretical study further explores the dynamic features of the failure mechanism.