| With the development of diesel engines to high-strengthening,lightweighting and high efficiency,the higher temperature and higher explosion pressure demand higher requirements for the structural strength and fatigue reliability of components.Diesel engine components have different structures and installation forms,and their working loads are complex.Due to the low level of domestic processing and manufacturing,defects such as pores and inclusions are prone to be appeared in the components,reducing the fatigue life of components and affecting the reliability of diesel engine operation.Accurate life prediction of diesel engine components is not only of great significance for improving the safety,operational stability and economy of diesel engines,but also provides a basis for the design of components and the maintenance time.At present,a large number of studies on the life prediction of diesel engine components have been carried out on a domestic scale,but due to the diversity of damage mechanisms,it is difficult to form a unified theory and technical system for fatigue life prediction methods.On the other hand,in almost all studies,the correction of the asymmetric load of components is based on the Goodman model,and the accuracy and applicability of its predictions for the materials used in components has not been well proven.Besides,a small number of scholars have established a dedicated life prediction model for a certain component,which cannot be widely used in the life prediction of other components.Therefore,integrating the characteristics of life prediction models at home and abroad,establishing a life prediction model with a wide range of applications,and applying it to the life prediction research of diesel engine components is a problem that needs to be solved urgently.Focusing on this problem,this paper divides the fatigue life prediction of components into high-cycle fatigue and low-cycle fatigue in terms of load frequency.Based on the tensile test and fatigue test of the key components of the diesel engine,the mechanical properties and stress/strain-life curves of the high-pressure tubing and piston materials at their respective operating temperatures are mastered to provide data for subsequent life prediction.Combining the fatigue fracture analysis of the two materials,the damage mechanism of the materials under different load conditions is clarified,which provides a theoretical basis for the fatigue failure analysis of diesel engine components.Considering the asymmetry loading condition of diesel engine components,carry out research on the life prediction model with asymmetric loading,introduce variable parameters to modify the fatigue life,establish a high cycle fatigue life prediction model with wide material adaptability,and improve the accuracy of the high-cycle fatigue life prediction.Taking diesel engine vibration components as the research object,carry out research on the vibration fatigue damage mechanism and life prediction methods of diesel engine components.Based on the proposed high-cycle fatigue life prediction model,combined with the Dirlik frequency domain method and Miner damage accumulation criterion,a frequency domain-based vibration fatigue life prediction method for high-pressure tubing is proposed.Taking diesel engine high-pressure oil pipe as an example,the failure mechanism of high-pressure oil pipe is studied,and its life is predicted based on the proposed vibration fatigue life prediction method.Considering the low-cycle fatigue load characteristics of diesel engine hightemperature components under start-stop conditions and variable conditions,the mechanism of the influence of asymmetric loading on low-cycle fatigue life is studied.Considering the influence of fatigue characteristics such as average stress relaxation and ratchet effect on life in asymmetric loading,variable parameters and strain ratio are introduced to modify the model,and a low-cycle fatigue life prediction model with high accuracy and wide applicability is proposed.Aiming at the low-cycle fatigue failure of high-temperature components of diesel engines,research on its failure mechanism and life prediction methods is carried out.Taking the diesel engine piston as an example,considering the influence of the intake process on the gas temperature field distribution,and the strain distribution of the piston is calculated to determine the dangerous point.The load spectrum is compiled in the start-up and shutdown process,and the research of LCF life prediction is carried out based on the proposed LCF life prediction model. |
