Analysis Of Bonding Behavior Of Adhesively Jointing Structures With Cohesive Zone Model

Fracture mechanics, a branch of solid mechanics, has been greatly developed during the last half of 20^th century. It has been applied in industry sectors, such as mechanical engineering, materials engineering and aerospace industry. CZM (Cohesive Zone Model), with appropriate choice of parameters, is a useful tool developed from nonlinear fracture mechanics, and is able to represent the properties of interface, such as elastic modulus, strength, and toughness. Introducing such a powerful tool into analysis of civil engineering materials and structures is a prospective work.First, the history of fracture mechanics is briefly reviewed. The concepts of stress intensity factor, energy release rate, fracture criteria and their relationship are introduced. Then, numerical implementation of CZM incorporated with commercial FEM (Finite Element Method) software ABAQUS is described.Interface toughness of adhesively jointing structures is an important parameter in adhesive structure design. Various tests of simple geometry have been developed to calculate interface toughness, such as DCB (Double Cantilever Beam) test for mode I and ELS (End Load Split) test for mode II. The LEFM (Linear Elastic Fracture Mechanics) assumption of point-wise crack tip is overly simplistic and errors in interpreting interface toughness are attributed to it. CZM is used as a benchmark to check the precision and applicability of beam-bending method, such as SBT (Simple Beam Theory), CBT (Corrected Beam Theory) and ECM (Experimental Compliance Method). Existence of the FPZ (Fracture Process Zone) ahead of crack tip is proposed as the reason for underestimating interface toughness. The formulation for estimating of FPZ size is proposed. CBT with the FPZ size as correction length will give better results, interpreting the essence of correction length.The single-shear test is recommended as the standard test to determine bond strength of FRP strengthened concrete structures. Conventional empirical bondstrength formulation is not consistent in dimensional consideration. As debonding is the main failure mode in application of FRP strengthening, new bond strength formulation based on fracture mechanics is proposed. New method is in good agreement with relevant test results and its validness is examined.In sum, CZM is a powerful tool to analyze nonlinear fracture problems, and is prospective to have wide application in civil engineering.