Fatigue Life Study Of Key Components Of Oil Machine

Pumping unit is a large, complex mechanical system constituted by a plurality of members. During the work process, fatigue damage of the key components of pumping unit occurs due to bear large amplitude, high frequency alternating load cycles for a long period of time. For the pumping member in terms, fatigue failure can occur with position that structures mutated or connections between components. Even if alternating load of these positions is less than the ultimate strength of the material, it will produce microscopic plastic deformation in localized high stress area for bearing alternating load for a long period of time, crack initiation and propagation, until it breaks, it will cause direct, serious economic losses and casualties. Currently use nominal stress method to predict fatigue life of pumping member, however, the method does not match the mechanism of fatigue, the prediction accuracy is not high and prediction has a large dispersion, can not provide reliable guidance for maintenance and replacement of pumping member. Therefore, it is necessary to study the approach that can accurately predict fatigue life of pumping component and reduce economic losses and casualties.Research work of this paper was mainly reflected in the following aspects:(1) Summarized the current fatigue life prediction method at home and abroad, detailed theoretical prediction and forecasting processes of each method. Judged the suitability of fatigue life prediction method in which the high-cycle fatigue and multiaxial stress state in the pumping unit, selected the Stress Field Itensity Approach which had high prediction accuracy and ability of sloving multiaxial and high-cycle fatigue problem as primary method of pumping components fatigue life prediction.(2) Launched a study of Stress Field Itensity Approach itself. Detailed physical meaning of each parameter in the mathematical model of Stress Field Itensity Approach and the determination of these various parameters. Stress field intensity numerical calculation must be done in finite element software, so first we studied the process of numerical calculation, its aslo mean to discrete the formula. Secondly, we studied how stress field intensity calculated in finite element calculation software. Used the fatigue test to verify the effect of field size and and weight function on fatigue life prediction results. Studied the interaction of field size and and weight function.(3) Improved the determination of some parameters in the mathematical model of Stress Field Itensity Approach. Improved the determination of field size, using theoretical calculations instead of experimentally determing. Saved the cost of prediction, and fatigue test result showed the Stress Field Itensity Approach had a better accuracy in the process of fatigue life prediction. Adopted a local stress gradient which represented local damage instead of calculated stress gradient of every point in local damage area.,overcame the shortcomings of the stress gradient of every point can not be calculated, and fatigue test result showed the Stress Field I tensity Approach which was improved can obtain a better accuracy in the process of fatigue life prediction.(4) Using commonly used Nominal Stress Approach and Stress Field Itensity Approach and Improved Stress Field Itensity Approach predicted the pumping unit components'fatigue life. First calculated the pumping rod load and load of each component suffered, used these three approachs to calculate the fatigue life, comparative analysis prediction and work life, got conclusion from error analysis, result showed the Improved Stress Field Itensity Approach well suited for fatigue life prediction of pumping unit component.