Fatigue Failure Analysis Of 50CrMnMoNbAT Plate Spring

As an important suspension component of trucks,leaf springs are subjected to various and complex forces in service,such as torsion,compression,tension and impact,and are prone to fatigue,which can cause fracture and pose a great threat to the safety of vehicles.The surface of the leaf spring is prone to decarburization during the production process,and due to the presence of decarburized layer,rolling defects will be generated during the rolling process,which will result in stress concentration on the surface when the leaf spring is in service,and cracks will sprout at the defects,thus triggering fatigue fracture.In this paper,the fatigue life of some products in a domestic plate spring plant is not qualified.Through finite element simulation and experimental analysis of50 CrMnMoNbAT steel plate spring,we study the influence of surface rolling defects on fatigue life caused by decarburization layer,clarify the weak area of fatigue life of steel plate spring,the influence of decarburization on fatigue life of plate spring and the trend of expansion of different defect forms inside the substrate.The aim is to obtain the factors affecting the fatigue life of plate springs in the plant and to provide guidance for the plant to improve the life of plate springs.The following conclusions were obtained:(1)Through macroscopic and microscopic analysis of the steel plate spring fracture and sampling on the surface of the plate spring,statistics on the morphology and distribution of defects on the inner and outer arcs and sides of the plate spring and microscopic analysis of the decarburization layer and defects,it is concluded that the fracture location is mainly concentrated at about 297 mm and 698 mm from the end face.The crack sources were all generated on the surface of the leaf spring,and the surface of the leaf spring was loose in texture due to severe decarburization of the surface,thus generating a large number of rolling defects during the rolling process,which resulted in multiple crack sources in the fatigue test.The fracture of the leaf spring is not related to internal defects but to surface defects.Therefore surface defects are the main cause of fatigue fracture of the leaf springs produced in this plant.(2)Using ANSYS software,the static performance analysis of the steel plate spring was performed by applying different loads according to the load-bearing characteristics of the heavy-duty truck itself,and the stress and displacement changes as well as the fatigue life clouds of the steel plate spring under no-load and full-load vehicle conditions were obtained.The results show that the most dangerous area of fatigue is mainly distributed in the curved area of the plate spring(180mm~300mm from the end face)and the area of the fixed ends of the gasket(650mm~700mm from the end face),and the fracture location of the fatigue test is consistent.(3)The results of the finite element analysis of the effect of decarburization on the fatigue life of the plate spring show that as the thickness of the decarburization layer increases to 300 um,the deformation of the substrate increases by 0.65%,but the growth rate of the deformation of the substrate gradually decreases.When the decarburized layer is 30,60,120,240 and 300 um,the fatigue life reduction rate is 0.88%,1.9.%,3.75%,7.43% and 9.0%,respectively.(4)Band defects,oblique defects,hook defects and radial defects were embedded in the inner and outer arcs of the leaf spring in different orientations,and the diffusion tendency of the four defects in different orientations and under different stresses was analyzed by stress intensity factors.The results show that when the four defects are radially embedded in the inner arc,the tendency of defect expansion is: oblique defect >band defect > hook defect > radial defect,and at this time the band defect has the tendency to expand in all directions,the radial defect expands inside the substrate,and the hook and oblique defects expand on both sides of the beginning and end.Defects in a radial manner within the outer arc,the four defects do not have a tendency to expand.Defects in the longitudinal way inside the arc,defect expansion trend: hook defects >oblique defects > band defects > radial defects,and the expansion trend of the four defects only in the direction of the tip of the defect.In the longitudinal way in the outer arc,the trend of defect expansion: band defects > oblique defects > hook defects > radial defects,so in terms of defect expansion rate,the fastest expansion of the radial inner arc of the defect,and the four defects in the oblique defect expansion is the fastest.