| The remanufacturing project has become one of the most promising technologies,which provides a major solution to the current severe resource shortage and environmental pollution problems in China.As an important component of the engine,the crankshaft has become the main application object of remanufacturing due to its characteristics of high price,complicated structure and high added value.At present,the crankshaft remanufacturing method is mainly arc spraying 3Crl3,and according to research,the interface is the weakest part of the entire remanufactured part,and the bending fatigue failure is the main failure mode of the crankshaft.Therefore,it is of great significance to analyze the fatigue crack propagation of the crankshaft and study the failure mode of the remanufactured crankshaft under different interface characteristics.In this paper,the combination of numerical simulation and experiment is used to obtain the residual stress and roughness interface by shot peening.The relationship between shot peening parameters and roughness and residual stress is determined.The thickness and interface of thermal spray coating are studied.The relationship between the crack propagation and the crack propagation behavior of remanufactured parts was studied as a whole,and the internal cracking of the coating layer,the interfacial cracking of the coating-matrix interface,and the internal crack propagation behavior and its influencing factors were discussed.The main findings are as follows:(1)Numerical simulations and experiments show that different shot peening parameters have different effects on residual stress and roughness.The residual compressive stress increases with the increase of the projectile diameter,the projectile material,and the impact velocity of the projectile.With the increase of the coverage rate,the residual compressive stress increases.It gradually decreases,and the residual compressive stress on the surface of the material is more evenly distributed as the coverage increases,and the stability of the metal component during use increases.At the same time,with the increase of the projectile diameter,velocity and strength of the projectile,the energy of the projectile increases,and the roughness increases.The effect of coverage on the roughness increases first and then gently.(2)The mechanical properties and failure modes of the whole system are different with different coating thickness.For thin coatings,the crack mode is mainly vertical to the interface between coating and substrate,and the tensile failure is dominant.For thick coatings,interface crack is the main crack mode,and shear failure is dominant.It can be seen from the critical load of crack initiation that the thinner coating has better bending resistance.(3)The bending test of the specimen after shot peening shows that as the crack propagation progresses,the stress intensity factor at the crack tip increases continuously,at the same time,the greater the residual compressive stress,the harder the crack propagation The greater the roughness of the interface between the coating and the substrate,the higher the bond strength,but the roughness is too large,which causes stress concentration at the interface,resulting in large deformation and premature separation of the coating.When the coating is subjected to an axially symmetrical interface crack perpendicular to the interface load,the residual compressive stress causes the interface crack to accelerate,and the stress angle at the crack tip increases.With the increase of the residual tensile stress,the critical load of the interface crack propagation increases,the stress phase angle decreases,and the interface crack continues to expand;(4)Through the combination of numerical simulation and experiments,it is found that when the initial crack position is fixed,the vertical crack is more dangerous than the inclined crack,and when the crack morphology is certain,the crack is more dangerous near the centerline of the sample.The longer the initial length,the more cracks near the center of the specimen are prone to crack propagation and the more dangerous.When the crack morphology is constant,the critical load of crack propagation increases with the increase of crack burial depth,and when the burial depth reaches a certain level,there is no crack growth phenomenon.Through the finite element simulation of the tensile test,when the initial crack length is the same in the thickness direction of the coating,the critical cracking load of the vertical crack is smaller than the critical cracking load of the inclined crack;the initial pre-cracking crack parallel to the tensile stress direction is pulling.Cracks do not propagate under stress and such cracks are safe. |
