Study On Residual Fatigue Life Prediction Methods Of Remanufacturing Parts And Assessment Of Remanufacturability

With the rapid economic and population growth at present, the lack of water, land, energy, and mineral resources will become more and more striking, and it becomes more and more urgent for ecological construction and environmental protections. In such context, to vigorously develop recycling economy and speed up the construction of resources saving society are becoming more important and urgent.Green remanufacturing engineering is generic terms of repair, rebuilding and a series technical measures and engineering activities, using advance technology and industrializing methods, whose aim is environmental protection. It is one of important paths of developing recycling economy and constructing saving society.Whether the products are worthy to be remanufactured determined by whether the key parts of the products, which are of high added value in the form of labor power, energy and so on, are need to be replaced. Broken, wear, corrosion and deforming are the main failure forms of parts, among which only fatigue broken is uneasy to be detected and other forms are visual and easy to be measured. How to determine whether the residual fatigue life is adequate to sustain another life cycle is a problem to be facing in remanufacture. And the remanufacturability of products is a primary problem to be facing in remanufacture. So it is of sense to study the two problems.The paper studies on the above stated two problems and uses crankshaft as fatigue life prediction study case and automobile engine as remanufacturability study case, including following works:1. Study on the redisual fatigue life prediction methods of remanufacturing parts, which first calculates fatigue life of parts under maximum loadings using the model of fatigue life prediction based on FE (Finite Element), then minus enquivalent fatigue life based on known active damage accumulation.2. Simulating the crankshaft system and the dynamic simulation was carried out. This model allows not only for the interaction of the bending moment and torque and the flexibility of the supports, but also for the effects of continuous ignition among multi-cylinder.3. Spring elements were taken to model the constraints on the main bearings and the end of the flywheel was fixed. According to the fire order of the engine, 6 cases of loads were picked from the dynamic computation results and exerted on the nodes. The multi-conditional stress of the crankshaft was obtained.4. Study on the fatigue behavior of crankshaft material 48MnV and 48MnV with 3Cr13 arc spray coatings of different thickness. And put off a modify coefficient of fatigue prediction after crankshaft repaired by arc spray.5. Predicting the residual fatigue life of crankshaft before and after repaired by arc spray using monoaxial model: S-N and multiaxial model: normal strain method, SWT–Bannantine, shear strain method, Fatemi-Socie respectively.6. The effective and directly method to verify whether remainder fatigue life of crankshaft adequate is to do fatigue test of crankshaft. Firstly, the paper uses new crankshaft to respectively carry out 500, 1000 and 3000 hours accelerated bench fatigue test of engine. Then, the crankshafts after accelerated test are cut into one-throw crankshaft and do one-throw crankshaft fatigue test. Finally, the test results are analyzed.7. The paper developed an assessing model of remanufacturability. It consists three modular: technological modular, economical modular and environmental modular. Technological modular involves the feasibility of remanufacturing on technological view. Economical modular involves that of remanufacturing on economical view. The economical or environmental index only get 0 or 1, which represents feasibility or infeasibility on economical or environmental view. Then the index of remanufacturability is gained by multiplying technical index, environmental index and economical index. The remanufacturability of a certain automobile motor based on the model and collected data was assessed and the result indicates that the model is effective and practical.Finally, the following conclusions were obtained:1.The method and model using to predict remanufacturing parts is of sense for preliminary determine whether the residual fatigue life is adequate to sustain another life cycle.2. Comparison of the results to the results when the constraints of the main bearings are taken as rigid support, it is found that the results have very large differences and that using flexible supports simulating the constraints of the main bearings be more practical. A computational comparison of rigid support and flexible one of the crankshaft is also followed.3. It came from the results that stress concentration of the crankshaft occurred both around the oil holes and fillets, maximum of which is 205MPa, half of the 1/2 throw finite element model, located around the oil hole of the 3rd throw. This is mainly because the accurate dynamic computation of the constrained force and high quality mesh.4. The fatigue behaviors of 48MnV steel, both uncoated and coated with different thickness of 3Cr13 deposits using twin arc spraying, have been investigated. The fatigue properties of the 48MnV steel, determined under axial loading conditions, can be substantially decreased by coating 3Cr13 films, deposited by twin arc spraying. And the fatigue behavior of the thinner coatings was found to be better than the thicker ones, which the fatigue limits decrease by 9-14%. The decrease in fatigue life has been attributed to the less mechanical properties of the coatings in comparison with those of the substrate, their relative bad bonding strength and trapped oxide or AL2O3 particles retained in the matrix after blasting responsible for the initiation of fatigue cracks.5.The results of fatigue life of crankshaft before or after remanufacturing indicate not only that the traditional calculation is conservative, which is of certain significant to crankshaft design and optimization, but also that the life of crankshaft whether using"minus materials"or"add materials"by arc spraying 3Cr13 to recovery repaired is sufficient to maintain another life cycle.6. The samples of fatigue test are after 500, 1000 and 3000 hours bench fatigue tests are relatively small, so the tested results probably have deviation. But the varying trend is obvious, which the limit moment of flexion and safe coefficient become smaller and smaller. Fatigue tests t of new crankshaft and used crankshafts, which are after 500, 1000 and 3000 hours bench fatigue tests indicate crankshafts can be remanufactured for three times theoretically and the calculation of the paper is correct.7. The assessing model of remanufacturability has following limits:(1) It is only suitable for the products, whose design are specified, i.e. the number of the parts are known, and(2) The model was developed under normal remanufacturing conditions and not suitable for the remanufacturing conditions largely different.