Research On Improvement Of Fracture Failure Criterion Of Body Adhesion

With the increasingly strict requirements for automotive fuel economy and emission performance,in addition to the development of new energy vehicles and high-efficiency engines,reducing the weight of the body structure is also an important technical approach of energy saving and emission reduction.Multi-material body can not only significantly reduce the weight of the body but also improve the performance of the body.Multi-material body will be the future development trend of body structure.The connection of heterogeneous materials in multi-material body has become one of the key technologies to be solved urgently.As a new type of connection,adhesive technology can realize the connection of heterogeneous materials without destroyed,and the adhesive structure also has the advantages of large bearing area and uniform stress distribution on the bonding surface.Its application is mainly confined to the non-bearing structural parts with little force in the body.And the reason why its application can't be popularized is that there is no specific evaluation criterion for the strength of adhesive structure under the condition of complex stress,which leads to the lack of effective failure criterion in the early engineering design stage by finite element simulation analysis.In engineering field,fracture failure often lead to more serious consequences,so it is important to predict and prevent the failure of adhesive structure.This paper mainly focuses on the problems that the description of the existing failure criterion is not in good agreement with the real failure of the adhesive structure.A fracture failure criterion based on stress by combining experiment and simulation is established with the main research object of ISR-7008/aluminum alloy adhesive joints.The specific research contents of this paper include the following aspects:(1)Design the adhesive joints of five sets typical pull-shear ratio with the research object of bearing the pull-shear load of the bonding joint.Adhesive joints consist of polyurethane adhesive ISR-7008 and adhesive substrate 6005A aluminum alloy composition.The dumbbell type specimen of the adhesive was made to obtain the basic mechanical parameters of the adhesive.The quasi-static tensile test of five groups of adhesive joints with different pull-shear ratios was carried out by using the method of electronic tensile tester combined with DIC-3D to obtain the initial fracture load and the maximum fracture load during the tensile process when the adhesive joint layer was first cracked.The failure process of the adhesive layer of different pull-shear ratio joints in the course of test and test is analyzed and the initial failure position of the adhesive layer is determined.Designs the verification test of the crack generation of the adhesive layer,and proves that the cracking position of the adhesive joint occurs at the corner edge of the rubber layer with the existing adhesive substrate reprocessed.(2)The simulation model of the adhesive joint of the same size in the test is established.The initial fracture load is applied to the model.The failure area in the simulation model is determined based on the crack generation position in the test.The stress is extracted from the initial fracture point in the failure area of adhesive joints of five groups of typical pull shear ratio.On the basis of the inference that the true strength of the adhesive joints is independent of the stress state of the adhesive layer,the formula for calculating the equivalent stress is obtained by the ratio method and the linear combinatorial method.And the initial failure criterion is established based on the equivalent stress calculation formula.This paper analyzes the possibility and necessity of using stress-based failure criterion in the process of subsequent failure,and establishes the same follow-up failure criterion based on stress on the basis of initial failure criterion.(3)The validation of the established failure criterion.The failure criterion is written into the VUMAT subroutine and embedded in the ABAQUS~?in accordance with certain specifications and formats with FORTRAN.Through comparison the cracking process and failure load of the rubber layer during the score simulation and test,the feasibility of predicting the failure of the adhesive joint is proved.The accuracy of the failure criterion established in this paper is verified by the test of other pull-shear ratio adhesive joints.In order to better compare the crack propagation in the adhesive plane,the simulation method on the basis of the failure criterion and the simulation method using the cohesive zone model are used to simulate the adhesive joint of the Araldite~?2015 respectively.It is found that the crack propagation path of the adhesive layer is consistent in the two simulation results.The accuracy of failure load prediction is close to and can meet the engineering needs,which proves the effectiveness of the failure criterion for the failure prediction of structural adhesive joints.