Analysis Of Debonding Failure Mechanism For Interface Of AFRP-strengthened RC Beams

Aramid fiber-reinforced composites (AFRPs) have many advantages such as highstrength, light weight, corrosion resistance and non-magnetism. Due to their excellentcomprehensive performance, they are gradually used in the field of national defenseconstruction, automotive industry and so on. RC beam strengthened with AFRP sheets is oneof the most important aspects applied AFRP to structure reinforcement field. The debondingfailure at end interface is a main form of early failure for AFRP-strengthened RC beams underfour-point bending. The occurence of interfacial failure at the end of AFRP shows obviousfragility and it is one of the major factors of strengthening failure.In order to characterize the delamination failure form at end interface ofAFRP-to-concrete, the elastic-plastic peeling model of studying thin film, which does not takeinto account the microscale effect, and the three double-parameter criteria are introduced inthis paper. Based on a finite element software ABAQUS and the damage fracture principle inABAQUS, the damage and cracking behavior of a cohesive zone model is defined to simulatethe bonding interface properties. A2-D plane elastic-plastic model of describing interfacialdebonding failure at the end of AFRP-to-concrete under four-point bending is established tostudy the law of interfacial debonding failure at end in different AFRP reinforcement quantity.The results of characterizations used by three double-parameter criteria show that the energyrelease rate P is gradually increased as the increase of opening displacement and separationstress at the interfacial crack tip in the double-parameter criterion(Γ0,σ). As the thickness ofAFRP is increased, the opening displacement at crack tip is decreased but the separation stressis increased. In the double-parameter criterion(Γ,θ c0tip), the energy release rate P issharply increased as the increase of the critical slope angleθ ctipat crack tip, and the moreAFRP strengthening quantity is, the lessθ ctipbecomes. Because the thickness of AFRP hasexceeded the microscale range, the double-parameter criterion(Γ0,εc)can not be used.Extending2-D debonding failure model to3-D case and fully considering variousconstituent parts of RC beam, the mechanical properties of component parts with differentAFRP strengthening quantity are studied as the time of debonding failure happens at end ofRC beam. The results show that the concrete does not turn up the tensile or compressivefailure, but internal microcracks begin to grow and expand when the interfacial failure at end happens. The stress level of reinforcing steel framework is relatively low, that is, the steel bardoes not yet bring into play its high strength performance. AFRP sheets don’t step into aplastic deformation stage, but the end of AFRP sheets turns up the stress concentration withhigher tensile and shear stresses. The farther from the end region is, the gentler stressdistribution becomes. Simultaneously, the end of interfacial adhesive layer also turns up thestress concentration with the peak values of peeling stress and bonding shear stress. However,the level and distribution of bonding shear stress is obviously higher than the peeling stress.This illustrates that the bonding shear stress is a main cause induced by debonding failure.The2D and3D finite element simulation results are in good agreement with the experimentaldata, which shows the feasibility of simulating interfacial debonding behavior by ABAQUS.The present methods can provide a theoretical basis for studing the debonding failure ofFRP-reinforced concrete beam.