The Experimental And Theoretical Research On Ⅰ Type Fracture Of The Double Cantilever Beam Adhesive Structure

With the wide application of adhesives in industrial production, The fracture phenomenon in the service process of the adhesive structure is beginning to be concerned and studied. It is found that many structural fracture accidents occur in the case of lower than the strength of the material. The main reason is the defect or crack in the structure. This paper intends to be based on the double cantilever beam(DCB) adhesive structure to do experimental research and theoretical simulation research on the structure with defects and cracks.First, We carry out a large number of the single pull experiments of the double cantilever beam adhesive structure, and analyze the fracture failure characteristics of the adhesive structure. The fracture failure of the adhesive structure is pure brittle fracture mode,once the adhesive structure cracks and fails, the whole will quickly crack and damage, the tension will also drop close to 0,and the adhesive interface after cracking is usually that one of the interface is relatively smooth, another interface is attached to a complete glue adhesive layer.The average value of fracture toughness of the adhesive layer of the double cantilever beam adhesive structure can be calculated by the classical beam theory, it is GC=0.2536N·mm-1. It can be used as the reference value of the material parameters of the adhesive layer in the extended finite element method. The modified formula for calculating the fracture toughness of the adhesive interface is derived from the energy point of view,and it is used to do theoretical verification for the calculation of cohesive interface model.Secondly,We use the ABAQUS software platform to build the cohesive interface model of the double cantilever beam adhesive structure. The model considers only the strength of the adhesive interface, does not consider the strength of the adhesive layer, it is more convenient to simulate the I type fracture failure of the adhesive structure. We consider two aspects separately, one is the different strength of adhesive interface, one is the different loading displacement velocity. Simulation results show that the strength of the adhesive structure is seriously affected by the strength of the adhesive interface. The change of loading displacement velocity has weak influence on the strength of the adhesive structure,basically no influence, it can be considered that the strength of the adhesive structure is only related to the material parameters and the interface strength. The simulation results are consistent with the experimental results. It is shown that using cohesive interface model to calculating the strength of the bonding structure is reliable.Thirdly, using the extended finite element model to simulate the adhesive layer, and using the cohesive interface model to simulate the adhesive behavior of the interface. We consider the influence of the defect shape,the defect position in the adhesive layer and the local weak adhesive interface on the crack propagation in the adhesive structure and the structure strength. Simulation results show that the defect shape in the adhesive layer has a certain effect on the direction of the crack propagation path. The existence of circular defect makes the crack tip to turn when the crack tip extends to the defect nearby region. The square defect does to be same as the fracture failure of the defect free model. The defect position in the adhesive layer has great influence on the crack propagation and the strength of the adhesive structure. The existence of local weak adhesive interface has little effect on the crack propagation, but its effect on the strength of the adhesive structure conforms to the predetermined model, the tension-displacement curve appears accordingly fluctuation.