Study On Distribution Of Stress And Strain In Interface Crack Of Polymer Glue Joint

In the glue processing, the design of the gluing joint is prerequisite and important. The stress and strain distributions in the gluing joint are considerably influenced by some factors such as the geometry of the adherend, the lap length and the adhesive thickness etc. The investigations on these factors are required for indicating the stress and strain distribution in the gluing joint, which is helpful for the material selection and the optimization of joint design. The overall mechanical properties of the gluing joint are highly dependent on the quality and the level of interfacial adhesion. The interfacial debonding inhibits the stress transfer and results in the stress concentration. The crack readily initiates in the interfacial debonding zone and then propagates, which leads to fracture eventually. Hence, in composite material design and interface engineering, some instructive suggestion are proposed on the basis of the interface effect on the fracture. The interface is called the heart of composite materials, especially for the fracture,damage and fatigue failure etc.Based on the above issues, the crack propagation direction and the redistribution of the stress and strain around the crack tip in the interface of (Polymethyl Methacrylate)PMMA gluing joint are investigated numerically and experimentally in the present work. The major research work and conclusions of this thesis are given as following:(1) The loading and failure patterns of gluing joint are reviewed. The corresponding gluing mechanisms are introduced. In light of the gluing processing, the types of gluing joint, the selection of the gluing components and the factors on the strength of gluing joint are discussed.(2) The unit of the fracture criterion in the ABAQUS HELPS is introduced, which is only applied as reference. Used three facture criterions (Critical stress criterion, Critical crack opening displacement criterion and Crack length versus time criterion)in the ABAQUS help, the problem of crack propagation path is simulated well, but this path is set in advance, which exists distant to the actual problem.(3) The stress and strain field around the interfacial crack tip of gluing joint is obtained numerically by means of the soft of ABAQUS. Some factors such as the crack length, the parallel distance between the crack and the gluing interface, the adhesive thickness and the geometrical asymmetries of adherend components are further investigated according to the relevant strain energy density factors.(4) By designed the load device self, the gluing processing is analyzed experimentally by collecting the pictures for representing the interfacial crack propagating process of PMMA gluing joint on the basis of CCD image analysis technique. The distribution of the stress and strain around the crack tip is demonstrated.