Coupling Research On Dynamics And Fracture Mechanics In The Cracked Crankshaft-Bearing System Of Internal Combustion Engine

With the development trend of high power and fast velocity, the better performance of I.C.E have been demanded in industry and the working condition of crankshaft in I.C.E is more rigorous. So it is highly indispensable to develop the research of the crankshaft. Due to the crankshaft is applied by the periodic vibration and impact load, the endurance crack is apt to be produced in the position of the maximum stress points. Once the crack has generated, the strength and carrying capacity of the crankshaft will be reduced, or even fracture. It is one of the familiar failure mode of crankshaft. According to the Classic Fatigue Strength Theory, the crankshaft has to be replaced immediately when the crack has generated. But there is a certain fatigue residual life in the crankshaft for some stress cycle times existing from crack initiation to fracture. So it is very significant to calculate the crack propagation residual life of the crankshaft. However, the analysis on the Dynamics and Fracture Mechanics for the crankshaft have been researched independently in the respective disciplines. The multidisciplinary performances of the system happen simultaneously and affect each other as engine works. The coupling study on dynamics and fractures is very important both in theoretical and practice sense. The research subject is originated from the Natural science fund for colleges and universities in Anhui Province——Coupling Analysises and Application Researches on Multidisciplinary Performances in the Crankshaft-Bearing system of I.C.E(KJ2010A042). The professor He Zhixian had done the coupling researches on dynamics tribology stiffness and strength in the crankshaft-bearing system of I.C.E. The main work in this thesis is to do the coupling researches on dynamics and fracture in the crankshaft-bearing system of I.C.E.Two aspects of the present research status are reviewed, one is the dynamics in the cracked rotor system, and the other is fractures in the cracked crankshaft. So it is obvious that the coupling research on dynamics and fractures in the crankshaft-bearing system of I.C.E is of great significance. And the decoupling method is suggested.The crankshaft bearing system of N4105 I.C.E is selected as the research object. The multi-body dynamics model of the crankshaft bearing system is built in ADAMS with a flexible crankshaft. The dynamic calculation is done in the speed (3200r/min) and rated working loads. And meanwhile, it becomes the basis of the study on dynamics in the cracked crankshaft bearing system of I.C.EThe dynamic pressures of oil film in the bearings, which can be calculated by the dynamical parameter of journal center or by the applied load on bearings, are converted to the dynamic node forces. A finite element model is set up to calculate the dynamic stress on journal surface. Calculating program is developed by the ANSYS parameter program language (APDL) to put on the boundary condition dynamically, solve and record the stress on the designated nodes automatically. Theφ=180°point in the left section of the 2th link is identified as the position of crack initiation by comparing with the dynamic stress in the different nodes.According to the proposed decoupling method, the coupling study on dynamics and fractures of the cracked crankshaft-bearing system with the different depth crack is done to calculate the dynamic response, stress intensity factors based on the dynamics analysis results and crack propagation residual life of crack by the Paris formula.Finally, the prime task and the innovation in this article are summarized, and some views for the further research are proposed.