Study On Joint And Structural Performance Of Honeycomb Sandwich Structure On Car Body

Nowadays,the automobile industry in the world is booming,but global energy shortage and environmental degradation are becoming more and more serious.Automobile exhaust has become a major source of atmospheric pollution.For this reason,many countries have promulgated various laws and regulations to achieve the goal of energy saving and emission reduction.Lightweight technology of automobile is an important means to improve environmental problems.Due to the properties of low density,high strength and high modulus,using composite materials and honeycomb sandwich structures is the most direct and efficient way to achieve lightweight of automobile.However,the connection of composite materials is always a difficult problem in engineering and it is also an important factor that restricting the wide application of composite materials.In this paper,two types of typical connection of sandwich structure,namely external and embedded corner joint or L-joint,were comparatively investigated by experimental and finite element methods under Quasi-static compressive bending load.Firstly,the honeycomb sandwich structure specimens were prepared through molding process and a three-point bending test based on GB/T 1456-2005 was carried out to obtain the main mechanical properties of the structure.Then two types of typical connection of sandwich structure,namely external and embedded corner joints,were designed and manufactured,in which the embedded joint contained two types of specimens including adhesively bonded and hybrid rivet-bonded specimens.The mechanical properties of the specimens were measured under the compressive bending test and the stiffness,failure load and failure behavior of each kind of specimens were obtained.Furthermore,the test results of different connection forms were comparatively analyzed.The test results were used as a reference standard for subsequent finite element analysis.After getting the test data,the process of three-point bending test and the compressive bending test of the corner joint specimens were simulated by commercial finite element software ABAQUS.The two-dimensional Hashin criterion was used as the failure criterion of CFRP and Nomex.The cohesive element was combined with the maximum nominal stress criterion(Maxs criterion)and quadratic power-law criterion to evaluate the damage of the adhesive layer during the test.Then a comparative analysis with the test results was conducted to verify the accuracy of the finite element model.Finally,the analytical models of the external and embedded honeycomb sandwich structure corner joint specimens under compressive bending conditions were developed and mathematical formulas of stiffness under the same conditions were derived based on the theory in mechanics of materials and virtual work principle.The calculation results and test results were comparatively analyzed to verify the accuracy of the formulas.The results showed that the stiffness of the external joint is 30.4% higher than that of the embedded joint.It is suitable for engineering components with greater rigidity requirements.But it takes up more space,so the assembly flexibility is not as good as the embedded joint.Compared with the adhesively bonded specimen,the strength of the hybrid rivet-bonded specimen is increased by 2.2 times.Therefore,the structural strength can be improved by the hybrid connection.In addition,the finite element model established in this paper can accurately simulate the failure mode of the honeycomb sandwich structure.Finally,the analytical formulas derived in this paper could accurately calculate the stiffness of the structure and provide a reference for the design of honeycomb sandwich structure L-joint.