Study On Flatigue Reliability Based On Simulation Experiment Of Engine-block

Fatigue reliability is one of the most important performances of critical automobile parts, and it is the principal element that restricts our automobile industry to achieve international level. In the paper fatigue properties of engine-block were lucubrated by means of CAE (Computer Aided Engineering) and strengthened fatigue test. The main contents are as follows:1) Simulation experiment system was modeled based on FE (Finite Element) analysis, and the relationship between shaft style (half-shaft, whole-shaft), assembly parameters of bearing (clearance, interference) and stress of engine-block was studied. The results show that compared with acting by half-shaft, the contact pressure of bearing, stress of main bearing wall and deformation of bearing hole acting by whole-shaft are greater.. Stress with the bearing assembly interference increases, but relationship between bearing clearance and stress is relatively complex.2) In order to realize automation and intelligentialize for fatigue crack diagnosis of engine-block fatigue test system, classical time-series analysis was applied to dynamic strain data acquired in fatigue test, and parameters of AR model were estimated. Residual variance of AR model is very sensitive to occurrence of crack, and the sbutle difference of strain lead to abrupt change of residual variance of AR model. Residual variance of AR model can diagnose the occurence of crack qualitatively in engine-block fatigue test. Engine-block with prefabricated crack was modeled by FE, and relative variation of strain was analysed, and damage index was applied to diagnose the position of crack. Damage index made full use of the relationship between all strain points, so it has high-accuracy for diagnosing position of crack, and position error is approximately2.25%.3) Engine-block has complex geometry, and thouth it was acted by simple load, the stress status can take on multiaxiality. For example, the position of intercrossing between camshaft hole and main oil hole is that. Fatigue life of these positons should be estimated by multiaxial fatigue damage model. On the basis of popular multiaxial damge model which had applied to the standard notched specimens generally, a new multiaxial damage model was proposed based on cirtial plane, which was made by nolinear combination of shear and normal strain on critical plane. Finally, the new damage model was verified by experiment.4) Considering high costs and large test period for the engine-block, a small number of specimens were used to predict fatigue limit of the engine-block. The load of low cycle life was estimated using least-squares method from test data. Fatigue limit was estimated by SAFL which was modified by load of low cycle life. Fatigue reliability was studied using Gauss and Weibull distribution respectively. The result of regression analysis on fatigue test data shows that mean and variance estimated by Gauss distribution were little different from that estimated by Weibull distribution, But the quality of test data affects fitting accuracy directly.5) Model of crack and notch was built by stress field of crack equivalent to camshaft hole, and fracture mechanics was applied to prediction of fagitue limit of engine-block. The threshold of stress intensity factor was estimated by comparing between test datum and crack model. Fatigue limit of other components with the same material, the same production process were estimated by threshold of stress intensity factor and the stress status.