Study On The Mechanical Properties On Mode Ⅱ And Mode Ⅲ Fracture Of Aluminum Alloy Bonded Structure

Due to low price,complete structure,and simple preparation,aluminum alloy bonded structure is widely used in aerospace and transportation fields.In the aluminum alloy bonded structure,the interface mechanical properties of the adhesive are usually weaker than those of the matrix material,and the mechanical properties of the bonded structure under different fracture modes need to be evaluated.In the existing fracture research,mode III fracture is often replaced by mode II fracture,but there are essential differences between the two fracture methods.Therefore,this paper takes aluminum alloy bonded structure as the carrier to study the failure mode and fracture characteristics under mode II fracture and mode III fracture,and analyzes the difference between the two fracture mechanisms.The main research contents are as follows:Fracture theory and analysis of bonded structures.The theory of fracture mechanics and bonded theory were preliminarily discussed,and the basis for the analysis of fracture characteristics and adhesion mechanism of bonded structures were established.Based on the common traction-separation displacement relationship,a concise and efficient cohesive zone model was determined.According to the fracture characteristics of mode II and mode III,the starting criteria and evolution criteria in the damage process were clarified.It can provide a theoretical basis for the reasonable evaluation of interfacial adhesion strength and interlaminar fracture toughness of bonded structures.Study on the interface mechanical properties of aluminum alloy bonded structure under mode II fracture.The failure mode of end notched flexure of different bonded processes was studied,and the damage evolution process of adhesive under mode II fracture was analyzed.Based on the inversion method,the real mechanical properties of aluminum alloy bonded structure were analyzed,and the precise constitutive equation under mode II fracture was constructed.The peak load and critical strain energy release rate were further explored by the precise constitutive equation,so as to establish the cohesion zone model under mode II fracture of the bonded structure.The influence law of manufacturing processes such as adhesive type and adhesive thickness on the failure mode under mode II fracture was studied.Study on the interface mechanical properties of aluminum alloy bonded structure under mode III fracture.Based on the failure mode and the damage process of adhesive,The cohesive zone model of aluminum alloy bonded structure under mode Ⅲ fracture was derived.And the effect law of manufacturing processes such as adhesive type and adhesive thickness on the failure mode under mode Ⅲ fracture was determined.Based on the mechanical properties of the bonded structure under two different fracture modes,the different fracture mechanisms of mode II fracture and mode III fracture were revealed.In this paper,a method for measuring the toughness of mode III fracture is innovatively proposed,which can accurately evaluate the real mechanical properties of bonded structures under mode III fracture.Through the combination of simulations and experiments,the failure mode and mechanical properties of the bonded structure under mode II fracture and mode III fracture were compared and analyzed.The shortcomings of the traditional mode III fracture were substituted by mode II were pointed out.And different kinds of cohesive zone model considering the thickness effect under mode II fracture and mode III fracture were proposed,which can provide reference for the failure analysis and process design of bonded structures.