Research On Fatigue Strength Similarity Theory Based On Scaled Model Of Key Components Of Marine Low Speed Machine

Connecting rod and crankshaft are the key parts of diesel engine which require high fatigue reliability.For the design process of key components,various fatigue strength tests and simulations are often needed to know whether it meets the requirements.But for marine low-speed diesel engine,this repeated production and research process will seriously increase costs,waste time and manpower,and waste material resources.Therefore,it is necessary to study a method of using scaled small model to replace the original model.Because of the economy and practicability of this method,it will inevitably become an important method for the research of low-speed diesel engine structural parts at present and in the future.The specific research contents of this paper are as follows:(1)Firstly,Finite element software is used to simulate the static fatigue of the original model and scaled model of the key parts of the low-speed machine.Then the static calculation results are analyzed by Goodman curve,working life nephogram and fatigue safety factor nephogram respectively,and the reliability of fatigue strength under static conditions is verified.Finally,according to the strength relationship between the original model and the scaled model,it is concluded that the similarity theory of static fatigue strength is related to the size of the model and the ratio of applied load to original load n.And according to the similarity relation,fitting the similar theoretical empirical formula of static fatigue strength.(2)Firstly,Finite element software is used to simulate and analyze the original model and scale model of crank-connecting rod.Through the dynamic calculation,the fatigue strength changes under dynamic conditions are obtained.Then the dynamic calculation results are analyzed by Goodman curve,working life nephogram and fatigue safety factor nephogram.And comparing the dynamic results with the static results.Finally,according to the strength relationship between the original model and the scaled model,it is concluded that the similarity theory of dynamic fatigue strength is not only related to the size of the model,the ratio of applied load to original load n,but also to the correction factor b,and the value of correction coefficient b varies with the location of the feature.And according to the similarity relation,we fit the empirical formula of dynamic fatigue strength similarity theory.(3)We use the WAW-2000 Microcomputer Controlled Electro-hydraulic Servo Universal Test Bench to perform static fatigue strength test on the 1/4 scale reduction model of the crankshaft and the connecting rod.And the experimental results are compared with the simulation results.We verify the correctness of fatigue strength simulation analysis and fatigue strength similarity theory.