| Connecting rod is an important component and main moving parts of theengine,the structure and loading conditions of it are very complicated. Connecting rodeasily fatigue failure under periodic alternating load,however,there is no obviousdamage to the front of macroscopic phenomena in crack propagation.when connectingrod damage reaches a critical value,it can cause a sudden fatigue fracture which couldlead to the unproperly work or scrap of the engine. The reliability and life of the engineare directly decided by the reliability and life of the connecting rod.So there is a greatsignificance on that the analysis of mechanical properties and fatigue to improve thereliability and life of connecting rod.In this paper, do strength and dynamics analysis, calculation of fatigue reliabilityand life of engine to connecting rod of NC450engine of Zongshen motorcycle based onstructural dynamics, finite element techniques, multi-body dynamics, mechanicalfatigue reliability theory and other multi-disciplinary theory, at the same time combiningwith the finite element software, multi-body dynamics software and professional fatiguelife analysis software. Summarizes the calculation method of fatigue reliability and lifeof connecting rod. The concrete research contents include：(1) Analysis movement of the connecting rod and loding during the workingprocess by kinematics and structural dynamics, then to determine the typical workingconditions and the loading value. Combined with3D software Pro/e and based on2Ddrawings, established3D model and assembly model of the motor connecting rod end.(2) Focusing on the processing load of the connecting rod, inertia force anddisplacement constraints by the Finite Element software Ansys strength analysis on theconnecting rod, at the last, obtained the stress contours, stress concentration andmaximum stress values of the connecting rod in different typical working conditions.(3) Do the multi-body dynamics simulation of rigid-flexible coupling on theconnecting rod by combine the finite element software MSC.Patran/Nastran and thedynamics software MSC.Adams. focuse on the loading of piston and the model ofconnecting rod, obtained the force-time curve and fatigue load spectrum of the risk nodebased on the working process of simulation.(4) Do fatigue strength assessment of connecting rod by the data of strengthanalysis, and do the fatigue reliability calculation of the connecting rod based on the fatigue reliability theory, and combination of stress-time history curve in the workingprocess of connecting rod.(5) Based on S-N curve of the material20CrMo of connecting rod, considering thestress concentration factor, size factor and surface factor to obtaining the S-N curve ofthe connecting rod. Calculate the fatigue life of connecting rod by using MSC.Fatiguebased on the analysis of full life, and according the fatigue load spectrum and the S-Ncurve.The research results of the thesis include：(1) In the connecting rod strength finite element analysis process, using thefinite width journal of oil film pressure distribution processing loading, calculation ofarbitrary position element through the theory and practice of any force applide byAPDL, both of which can improve boundary conditions of strength finite elementanalysis of connecting rod closer to the actual work situation.Analysis results show thatthe stress is mainly concentrated on transition circle of the connecting rod small andbig end connecting with the rod body and the rod body, and the maximum stress value isfar less than the yield strength limit of the connecting rod material static strength, meetthe design requirements.(2) During the dynamic simulation, combination of Spline curve and theAKISPL function can be effectively applied in cylinder pressure data above the piston,the simulation results basically coincide with the finite element analysis. Obtained theload-force time curve of risk node in the work process and fatigue loading spectrum ofthe connecting rod.(3) Analysis of fatigue life and reliability of the connecting rod results show:Fatigue risk node link reliability were greater than the recommended value of reliabilitydesign of connecting rod, and the existence of certain safety margin, meet the designrequirements. The fatigue life of connecting rod shorter located mainly on the both sidesof the rod body,the lowest life cycle number of nodes can meet the requirementsof infinite life design. |
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