Study Of Nonlinear Mechanical Behavior Of Assembly Structure With Bolted Joints In Diesel Engine Design

Due to the influence of multiple nonlinear characteristics of the contact nonlinear and the sealing gasket material nonlinear, the mechanical behavior of assembly structure with bolted joints becomes more complex. In order to study the mechanical behavior of the assembly structure with bolted joints, in this paper, the bolted flange joints with gasketnonlinear static and dynamic modeling methods, the sealing performance under the quasi-static and the dynamic response mechanism are studied. The main contents of this articleare as below:1) Considering the gasket material nonlinear and the contact nonlinear, nonlinear static mechanical finite element model was established. The residual preload bolt and gasket contact pressure simulation results under different connection assembly processes was acquired. The simulation results and experimental test results were compared to verify the simulation model and calculation results, the optimal connection assembly processes satisfied the sealing characteristics of was acquired.2) Consider the gasket material nonlinearity and the contact nonlinear, the nonlinear static finite element model of diesel engine assembly structures was established. Studied the effects of different connection assembly process on the sealing characteristics of cylinder diesel engine assembly structures, the best assembly connection process for the requirements seal performance was acquired, it was provided guidance for modern design of diesel engine sealing characteristics.3) Presented the assemble structures without gasket and with different material gasket,and calculate the pre-stressed modal frequency response and modes of the three kinds of different assemble structures By comparing with the corresponding modal test results,determine the accuracy of modal simulation results. The results also show that: compared with the assemble structure use of linear elastic material of aluminum gasket, the assemble structure with the graphite filled spiral wound gasket, the first two bending mode frequency decreased by 13.5% and 13.7%. The assemble structurewith different axial tension and compression modes.4) Founded that the assemble structure in axial has obvious nonlinear stiffness characteristics on the tension and compression states; put forward combined parts of the bolted flange joints with gasket equivalent to axial Double springs-bending beam analytic model, found that the connecting parts in the axial tensile and compressive nonlinearstiffness characteristics is similar to the whole assemble structure; discovery when the assemble structures using linear elastic material aluminum gasket, its axial tensile and compressive stiffness were bilinear relations; when using nonlinear material graphite filled spiral wound gasket, the axial tension and compression stiffness were nonlinear relations.5) The assemble structure is simplified as a spring-mass system, the vibration control equation of the system was established, to solve the vibration equation: under the axial loading, the assemble structure excited only axial vibration. Under the transverse load,when the axial stiffness of the spring are respectively for constant or the relationship between axial stiffness and displacement can be approximated as a linear function and the mass matrix of the vibration control equations is coupled, the assemble structure produced only transverse vibration. When the relationship between axial stiffness and displacement can be approximated as a linear function and the mass matrix of the vibration control equations is not coupled, bilinear and cubic functions, respectively, the assemble structure excited the coupling vibration of axial vibration and transverse vibration. Under the effect of axial and transverse coupling impact, the assemble structure also excited the coupling vibration of axial vibration and transverse vibration.6) Converted the gasket material nonlinearity and the contact nonlinear to the spring axial stiffness nonlinear, the simplified nonlinear dynamic finite element model was established. Under the axial and transverse impact respectively, the assemble structure of the axial and transverse vibration characteristics was acquired. The results show that: the simplified nonlinear dynamic finite element model calculation results and the mechanism analysis results have good consistency. The assemble structure dynamic impact tests verified the proposed simplified nonlinear dynamic model and mechanism analysis model,and validated on the phenomenon of dynamical mechanism model predictions.7) Using the nonlinear spring element, the connection parts of the cylinder head bolts were re modeling, incorporate the nonlinear axial stiffness of spring element to the whole dynamic analysis of the diesel engine assemble structure; the dynamic performance of the diesel engine assemble structure were simulated. The resultsfirst to predict: under the axial impact the assemble structure only excited the axial displacement; under the transverse impact, the assemble structure also excited the coupling vibration of axial vibration and transverse vibration.