The Mechanics Performance Experiments And Theoretical Research Of The Epoxy Bonding Structure

With the widely application of the adhesive technology, there are a series ofproblems in actual use. Under long-term loading, adhesive as polymer materialsgenerate creep strain, which is obvious in hygrothermal environment and eventuallylead bonding structures to slowly deform or even failure. At the same time, theproblem of brittle fracture in adhesive structure has took more and more attentionfrom researchers. Therefore, this paper focused on one of them-the creep behavior ofepoxy adhesive and brittle fracture and different forms of defectsin the adhesivestructure, the research contents and results are as follows:(1) Investigation on the creep behaviors of epoxy at differentenvironment.Reference to the specimen size standards (GB/T11546.1-2008, GB/T2008-6397), the experimental specimen were made by the teflon mold. The creep testsunder constant loading of epoxy adhesive were conducted in this paper, which stresseswere5MPa,10MPa,15MPa,17.5MPa, at ambient and hygrothermal environment.Comparing the creep deformation at ambient and hygrothermal environment, it wasfound that the hygrothermal environment had a significant effect on the creepproperties of epoxy, and this effect increased with the stress.Through consultingrelevant literature, it was found that time-hardening model is closer to experimentalresults than the Kelvin model. The creep behavior of epoxy adhesive under differentconditions were simulated by the software of ABAQUS, and the simulation resultswere consistent with experimental results. The error meet the requirements of theengineering practice, and this Investigation was beneficial to considering the effectsof the creep behavior of epoxy adhesive on the structure in engineering design.(2) Theresearch on fracture of cohesive structure with cohesive surfaces andcohesive material. The cohesive structure model with five layers consist of surfacesbased cohesive behaviors and material subroutine was established, and structuralfailure of docking and joinstructure were completed. Form simulation results, itwasfound that the tension-displacement curves consistent with characteristics of brittlefracture.When the bondinginterfacewasstronger or weaker than the adhesive layer,structural failure was consistent with the predicted location. When the bondingstrength of the interface layer was equal to the adhesive layer, the bonding interface of tensile docking structure was cracking, while the shear docking structureand lapstructure, both of the adhesive layer and the bonding interface appeared damaged.(3) The influence of different bubbles in the adhesive on strength of differentbonding structure. The influence of bubbles size,location and quantity on strength ofdifferent bonding structure were investigated. It was showed in the simulation resultsthat the strength of docking and lap structure was inversely proportional to the bubblesize. The location of bubbles has a less effect on the tensile and shear strength ofdocking joint.The bubble located on the upper edge of adhesive layer has an obviouseffect on the structural strength of lap joint, while the bubble located in the middleand the bias of adhesive layer has a less effect on the strength. Thestrength ofdockingstructure was inversely proportional to the total area of bubbles, and the influence ofbubble number on the strength is small.The strength of lap joint increased with thenumber of bubbles. The adhesive structure model can accurately describe the adhesivefailure of double cantilever beam.(4) The influence of the different forms weak bonding interface on the strengthof different adhesive structure. The influence of the size,location and quantity of weakbonding interface on strength of different bonding structure were investigated. It wasshowed in the simulation results that the strength of structure was inverselyproportional to the size of the weak bonding inteface.The larger the size of the weakbonding interface, the greater the fall. When the weak interface of the dockingstructruewas located in the edge, the structure of the tensile strength was reduced, andthe other positionswere the same. While the docking structure was shear tensile, thesituation was the opposite. When the weak interfacewas located at the edge of theadhesive layer, it had an obvious influence on the strength of the strcture. The strengthof lap joint was less affected by the weak interface when the weak interface waslocated in the other position of structure.Increasing the number of weak interface to acertain value, the shear and tension strength of the docking structure wereimproved.For the lap joint, when the number of weak interface was a certain value,the strength was the larger. While the number increased or reduced, the strength wasreduced. The tension-displacement curve of double cantilever beamwouldfluctuatebecause of the existence of bubbles, and the wave number was consistent with thebubble number. With the damage evolution, the fluctuations decrease.