Study On The Degradation Of Mode-? Fracture Behaviour Of Structural Adhesive Under Hygrothermal Environment

With the concept of lightweight and the demand for dissimilar materials joining,structural adhesive technology has been widely applied in many industrial fields.Compared with the traditional connection methods,such as welding,bolt connection and riveting,adhesive bonding technology gains the advantages of keeping the integrity of the base material,uniform stress distribution in the overlap area and good fatigue resistance,etc.Meanwhile,due to the material properties of polymer,the mechanical properties of the adhesive will be degraded to certain extent under exposure to long-term humid,radiation,and acid and alkali,etc.Therefore,in order to improve the reliability and adaptability of structural bonding,it is necessary to study the degradation behavior of adhesive structure under long-term multi-physical coupled field as well as more complex environment.Due to the property degradation of adhesives caused by hygrothermal environment,the related crack propagation behaviour are different from those of unaged samples.Considering that relative few work has been done domestically studying the influence of hot-humid environment on cohesive properties of adhesive joints,it is reasonable to choose this subject in the research.The purpose of this study is to characterise the mode-I fracture performance of structural adhesives based on the degraded Cohesive Zone Model in hot and humid environment.First,the quasi-static mechanical parameters of the adhesive and the elastoplastic parameters of the base were obtained through preparation and testing of the dumbbell specimens of the adhesive and aluminum alloy.Then,the water absorption ageing test was designed and performed to determine the moisture diffusion and hygroscopic expansion characteristics,and the strength degradation behaviour caused by heat and heat was measured through quasi-static tensile test.The mode-I fracture loading test was subsequently carried out on the closed / open-face Double Cantilever Beam under ambient temperature and high temperature / high humidity environment,respectively,and the mode-I fracture properties before and after the environment ageing were obtained.Considering the experimental data of the closed double cantilever beam,the standard error estimation of the experimental and simulated load-displacement curves was defined as the objective function,while the material parameters of the adhesive and the substrate were selected as the design variables.The Multi-island Genetic Algorithm built in ISIGHT was used to identify the parameters,and in order to reduce the optimisation time,the Response Surface Method was adopted to construct the approximate models for optimization process.Based on the experimental data about the ageing mechanical properties of adhesives in the humid and hot environment,mode-I loading failure model for environmental degradation of adhesives based on the degraded Cohesive Zone Model was thus established.The obtained results were then compared with the corresponding mode-I loading fracture experimental results,and the validity and accuracy of the established FE model were thus verified.The numerical results showed that the fully-coupled modelling method and the research framework of the degradation cohesive zone model established in this paper can be used to predict the mode-I fracture performance of adhesive after ageing in hot and humid environment,and provide a reliable evaluation and prediction method for the design,application and service performance evaluation of the adhesive structure.