Diesel Engine Crankshaft Fatigue Life Prediction Method Study

The crankshaft as the most important moving parts of the engine interior, and plays avery important role in the engine. The crankshaft withstand the gas pressure of the cylinder aswell as the cyclical changes in the load caused by the inertial force of the reciprocating androtating masses in the working process, may also be exposed to torsional vibrations, bendingvibration and axial vibration, etc. Therefore an alternating torsional stress which the crankshaft generates may cause direct damage and fatigue failure of the crankshaft, fatal injuries onthe reliability and durability of the engine, causing machine damage and even personal injury.In order to solve this problem, the structure dynamic response analysis are conducted basedon finite element theory in this paper, stress state characteristics of high stress gradient parts isdetailedly researched, which provides support for the crankshaft fatigue life prediction.A single throw crankshaft bearing caps and other parts of the three-dimensionalgeometric entity model are established, and then import it into mesh of professional softwareANSA on materials, parts of attribute set, on the premise of guarantee calculation accuracy,according to the characteristics of the structure of the various parts of the reasonable selectionof unit type and the grid cell size, between crankshaft main journal and the bearing capdefined relations between the two to contact, and according to the actual condition ofcrankshaft and bearing cap imposed constraint boundary conditions of a cylindrical coordinatesystem, the complete composite structure finite element mesh model of crankshaft.Grid model is imported into finite element analysis software ANSYS, and changed thecoordinate system, by choosing the XYZ, determining the area of the node load imposed. Theradial force AVL boost obtained is discreted. Radial force is converted into pressure byempirical formula and written APDL command flow. The command stream loader cyclicalcrankpin pressure applied to the selected node in the form of a load step. Reasonable settingthe initial conditions, type of load, nonlinear options, integral method, etc., based on the Newmark implicit algorithm in the direct integral method. The complete method in ANSYSsoftware is adopted to improve the dynamic response analysis of a work cycle, get near thedetonation pressure and moments of crankshaft the overall displacement field and stress field.Areas of high stress analysis of the stress time history curves are easy to understand and graspthe crankshaft dynamic response characteristics, and it provides a theoretical basis. For theestablishment of load spectrum fatigue analysis.The transient dynamics analysis of the results of the stress are imported into fatigueanalysis software Design Life. Crankshaft load spectrum calibration conditions is prepared.Consider various fatigue factors on the SN curve correction, fitting a crankshaft SN curve, setthe material yield strength and elastic modulus, select the maximum principal stress,according to the linear cumulative damage theory to predict the fatigue life of the structure,and get the crankshaft in the radial force under the action of fatigue life prediction results.