Study Of Remanufacturability Judgment Of Compressor Blade Based On Surface Notch

In the long-term service process,the compressor blade of aircraft engine is easy to produce fatigue cracks under alternating load.For the micro cracks on the blade,it can be directly remanufactured and repaired.While,for the macro cracks on the blade,it should be removed by crack grinding firstly.Thus,a surface notch on the blade is generated.At present,due to the lack of widely recognized methods and theories for the fatigue life prediction of remanufactured parts,the residual fatigue life prediction and remanufacturability judgment of blade core before remanufacturing are particularly important.In addition,only on the basis of judging the remanufacturability of blade core can subsequently remanufacturing repair be carried out.It can be seen that the research on residual fatigue life prediction and remanufacturability judgment of surface notched blade is the key of blade remanufacturing,which has important theoretical and practical guiding significance.Based on the classical fatigue theory,finite element technology and test method,the quantitative characterization of stress concentration,the residual fatigue life prediction and the remanufacturability judgment of surface notched blades are studied.The main work of this paper is as follows.The geometric properties of surface notched blade are qualitatively analyzed.The surface notch fatigue damage parameter D（d,w,t）highlighting the effect of notch depth,notch width and thickness is proposed.The local strain on surface notch root is measured to obtain the test value of stress concentration factor K_t.The rationality of the surface notch finite element modeling method is verified by the test value of stress concentration factor K_t.According to the blade structure and size,the simplified finite element model that suitable for the stress concentration analysis of surface notched blade is determined.Depending on the finite element results,the distribution law of surface notch fatigue damage parameter D（d,w,t）and stress concentration factor K_t is explored.Based on Inglis equation,the stress concentration factor equation of surface notched blade is proposed by introducing the thickness parameter,while the existing research only considering the geometric parameters of the notch.The stress concentration factor equation of surface notched blade can provide theoretical support for the evaluation of stress concentration after blade crack grinding.The nonlinear finite element analysis of surface notch is carried out to reveal the mapping law between surface notch fatigue damage parameter D（d,w,t）and local strain.The surface notch strain equation is proposed based on Neuber’s law,and the crack initiation life model of surface notched specimen is established.The expression of the stress intensity factor of the surface crack at the surface notch is clarified.The characterization method of the initial crack size of surface notch a₀ is proposed by using the surface notch fatigue strength modified equivalent initial defect theory.Then,the crack propagation life model of surface notched specimen is established.Taking the fatigue life model of surface notched specimen as basis model,the residual fatigue life model of surface notched blade is established by considering the effect of service damage and actual working condition parameters.This model can provide theoretical support for subsequent remanufacturability judgment.It is verified that the prediction results of the fatigue life model of surface notched specimen mainly fall into the scatter band of factor 1.5 by fatigue test.It is proved that the proposed model has a high prediction accuracy and can ensure the rationality of the residual fatigue life model of surface notched blades.The mapping relationship between surface notch size parameters and remanufacturability is studied.The surface notch residual thickness index,surface notch depth index and surface notch width index are constructed.Then,the characterization methods of surface notch residual thickness critical value,surface notch depth critical threshold and surface notch width critical threshold are established.The remanufacturability judgment based on surface notch for blade is proposed by constructing surface notch remanufacturability model.This method can provide theoretical guidance for the crack grinding size.