Research On Fatigue Reliability Of Hydraulic Excavator’s Manipulator

Hydraulic excavator’s working situation is complicated and some components of the mapulater have a huge bearing of alternating load. The greater the load and the higher the frequency, the easier fatigue failure occuring. The thesis regards a certain type of small-scaled hydraulic excavator as the object of research, and makes some in-depth study of the manipulator’s fatigue reliability.A 3-D model is built through field mapping, then ANSYS and ADAMS are used to establish a rigid-flexible coupling model. Kinematics simulation is done by applying function drivers on hydraulic cylinders, through which the limit movement trajectory of the bucket and 3 important parameters are obtained, which are compared with actual parameters The results show that the simulation error is quite small and the maximum error is less than 4%, so the simulation model can be approximately seen as the same with the physical model.To the bucket, lifting and digging resistance under digging working condition are calculated and the corresponding load functions are applied to run the dynamic simulation, through which the load-time curves of hinge joints are obtained, which can provide help to find the dangerous point. After that, some analysis is done based on the d-point’s stress-time curves. The results show that the d-point is near the hinge joint of bucket rod and bucket hydraulic cylinder, and the stress has a peak while the bucket tooth tip reaches to the deepest position.In order to reduce the risk of data error and research the accuracy of dynamic simulation results, a dynamic-stress acquisition experiment is then designed. The experiment results show that single stress cycle has the same discipline with dynamic simulation, and also is the position of dangerous point. The maximum stress of the d-point is 171.2 MPa, which is only 3.914% apart with simulation results.Using rain-flow counting method in NCodeDesignlife software, the fatigue load spectrum of dangerous point is constructed. Based on the CFD theory, the probability model of bucket rod’s reliability is built, from which the reliability value and fatigue life-reliability curve is obtained. In ANSYS the value is then verified using Monte-Carlo method and the sensitivity of random variables is analysed by tool of Six Sigma. The results show that the reliability of bucket rod is about 95% and it is almost the same between the sampled and calculated values. As the reliability index doesn’t meet the design requirement, it is necessary to do some reliability optimization on the bucket rod.Considering the thickness of U-sheet and fender as design variables, the total mass as objective function, and the reliability index being no less than the target value as constraint condition, the reliability-based optimization model of the bucket rod is set up, which is solved by using neural network toolbox in MATLAB. The results show that it occurs an optimal solution while two design variables be 8.6 mm and 8.2 mm respectively.