Theoretical And Experimental Study On Fatigue Behavior And Reliability Of Engine Crankshaft

The level of security and reliability is one of the most important performances to the quality of products of vichle and power machine. As a modern science and a system engineering technology, active reliability design for a scheduled service life and online intelligent prediction for failure are now widespread being thought much of. Under this frame, some concerned studies were made according to specially characteristes of the engine profession. Based on theories demonstration for the resonant fatigue test rig for crankshaft on hand, more experiment functions were developed, a fatigue behavior test methodology using spectrum scanning was constructed accordingly. Futhermore with this mothod, fatigue behavior characters and crack propagation pattern discovery of a kind of diesel engine's crankshaft was studied. In another branch of the study frame, study on statistical analysis of fatigue test data and service reliability estimation is also brought out.Contents of this thesis can be briefly listed as:1. By analysis of loading principle and measurement system, the mathematical model of the test rig was completely set up, according to which the data fitting algorithm for system input and the respound was derived. Necessary demonstrationes for the test system were made using FEA method, with this result, control reliance to achieve precision loading was formulated.2. Based on the above theory analysis, an experimental research method for crankshafts' fatigue behavior using spectrum scanning was constructed. The factor of stress indensity in different crack growth phase was calculated by using FEA method. The geometrical model/crack propagation rate curve and residual strength model of crankshaft fatigue test data are established. A three-section regular of the crack propagation was summarized according to test result.3. AR model and two kinds of anomaly detection algorithm based on hidden pattern/ε-machine and D-Markov were applied in prediction for crack propagation pattern change. Abnormal measure curves were plotted respectively with the initial status as the reference gross. Some regulars of crack propagation pattern's chopping round were deduced. The result shows that time series analysis method is suitable for this application.4. A comparison of accelerated life testing layout approaches for crankshaft are made including and their applicability were disscussed. An algorithm of Weibull-distribution based data regression for test data was set up using Nelder-Mead method. By comparing their fitting compatibility and the cumulative failure probability curve, the advantage of the Weibull-distribution based regression is concluded.5. To consider in fluence of the disparity of service loading asymmetric factor on reliability, a 2-dimensional stress strength interference model was constructed. Mento-Calo simulation method and stochastic finite-element method are applied to solve the model. The major influence factor on reliability of crankshaft was summarized.