Improved Model For Interfacial Stress In Adhesively Bonded Joints Of Bi-material Beam

Adhesive bonding is a binding technique with a broad use.It has many advantages such as simple process,fatigue resistance and light quality.The bonded interface of adhesive joint is more ‘trim’ so that the degree of stress concentration is reduced and the residual stress is lower relative to traditional riveting,bolts,and welding technology.Therefore,Adhesive bonding has been widely used in aviation and aerospace,automobile manufacturing and civil engineering,etc.Usually,the strengthened structure is fulfilled by bonding the FRP composite plate or sheet to conventional material using a thin or moderately-thick adhesive layer.Thus,the adhesively-bonded interface plays a crucial role in providing effective stress transfer from the strengthened structures(e.g.,concrete beams)to the FRP plates as well as securing the integrity and durability of the plate-strengthened structures.Due to high stress concentrations in the adhesive layer,especially at the locations near the plate ends,the interface debonding or peeling of the adhesively-bonded interface often occurs,leading to premature failure of the designed structures.Therefore,accurate prediction and characterization of the interface stresses and bond strength are essential for design of structures externally bonded with FRP composites.The existing theoretical models of adhesive joints analyze the adhesive layer as a beam without considering the Poisson’s effect,which violates the Hooke’s law and cannot satisfy the compatibility condition of the adhesive layer;furthermore,the bending moment of the adhesive layer is neglected by assuming the thin thickness of adhesive layer.To eliminate these flaws,the present study models the adhesive layer as a 2-D elastic continuum in which both the Hooke’s law and equilibrium equations are fully satisfied.The longitudinal strain caused by the transverse stress is also considered,and it is proved to have a significant effect on the interface stress distributions.The present model regains the missing bending moment of the adhesive layer which is absent in the existing models,and it satisfies all the boundary conditions.The validity of the new model is demonstrated by its excellent agreements with the results from the numerical finite element analysis when predicting the interface stress distributions for the single-lap joints and CFRP-strengthened reinforced concrete beams,and the broader applicability of the present model can be expected.The new model developed presents explicit closed-form solutions for the interface stresses and beam forces,and it provides an accurate tool for design analysis of adhesively bonded joints or interfaces.