Study On Damage Mechanics Of Sucker Rod Failure Of Pumped Well

Sucker rod is a power transmission component in rod pumping oil system, driving pump plunger up and down for reciprocating motion in oil Wells work, which carries alternating load. Sucker rod is damaged under the effect of alternating and results in failure of sucker rod. If sucker rod is fractured, oil-field operation of the sucker rod is needed to salvage and replace. So that it will not only affect the output of crude oil, but increase oil well operating costs, which means production costs rise.Most of the studies on the sucker rod failure are researched to get the extension of the crack sucker rod. However, fracture mechanics not only neglects damage stage before macroscopic crack forming stage, also ignores the damage around the macroscopic cracks. Combined crack formation with crack expansion, the theory of damage mechanics is applied into studying sucker rods fatigue damage, thereby the regular pattern of the sucker rod fatigue damage is researched.Derived from irreversible thermodynamics with internal variables and orthogonal flow rule, the sucker rod damage constitutive equation is built up in the use of principle of equivalent stress and strain, the fatigue damage evolution model of sucker rod by generalized stress and the corresponding damage driving force is presented. At the same time, in accordance with the characteristics of fatigue properties, the damage evolution equation for sucker rod high cycle fatigue is deduced. It is shown by the damage evolution equation that sucker rod damage is relevant to sucker rod stress and initial damage.The relationship between sucker rod fatigue damage and the load carried during the work process has been studied sucker rod suspended point load of the primary influencing factor is given, using the calculation of suspended point load. Sucker rod suspended point load predicting model is established on the basis of LMBP neural network algorithm. By taking data out of current site database as samples, the predicting model is repeated trained, moreover a higher training accuracy is obtained. Sucker rod suspended point can be predicted by the predicting model under different sections and different conditions.Sucker rod failure is a continuous damage process, which not only displays in sucker rod work stage, but also brings damage failure when the sucker rod is made. In this thesis, started from the structural characteristics of sucker rod, sucker rod upsetting forming process is analyzed and sucker rod forging process scheme is programed. In the use of 3D-DEFORM finite element simulation software for metal forming process and according to the rigid (viscous) plastic finite element theory, material gathered by three forming steps, performing forging process and forming forging process is respectively numerical simulation analyzed. Simultaneously stress distribution and damage parameter in sucker rod upsetting forming process is obtained, which provides the initial conditions For sucker rod fatigue damage simulation experiment.According to the principle of damage mechanics, it refers to two issues at the time of applying the damage mechanics into solve the fatigue problem. First, in the case of the damage having known, the component stress field, displacement field and strain field need to be taken the analysis. Second, in the case of the damage field and stress field having known, the damage evolution field need to analyze and the crack lifetime need to be estimated. In the paper, fatigue damage coupling theory is explained and focused on analysis of damage mechanics-finite element method. By used "additional load-finite element method" into the damage, crack formation is organic combined with extension of crack through damage mechanics.Using damage mechanics finite element method to study the sucker rod fatigue damage problem, the secondary development of ANSYS is developed and user subroutine is written with APDL language. In line with characteristics of sucker rods easy broken part, expressions of three-dimensional model of fatigue damage is derived for sucker rod's upsetting and threaded connection sections and the reasonable boundary condition is specified. By defining the reasonable sucker rod damage condition, sucker rod fatigue damage situation and Cycle number is stimulated under the condition of different initial stresses and different initial fatigue. An analysis of effect of different initial conditions for sucker rod fatigue cycle number is carried out, which provides a much more reliable method for estimation of sucker rod lifetime.