Numerical Analysis On Fracture-Splitting Process Of Rear Axle Reducer Shell Bearing Seat

The rear axle reducer shell bearing seat belongs to the typical box divided parts,which is mainly used to support the gear system and drive shaft in the main reducer.It is one of the most important parts of a car that can run safely.The fracture-splitting process can realize the three-dimensional meshing between the shell and the bearing cover,to greatly improve its bearing capacity and shear resistance.The material of shell bearing seat is QT450.The brittleness of cast iron itself increases the possibility for fracture-splitting process.The processing principle is to make use of the sensitivity of the groove to produce a high stress concentration.When the threshold value is reached,the shell bearing seat starts to crack and finally achieves quasi-brittle fracture under small applied load.For medium and heavy truck,the loss circle of bearing hole after fracture should be less than 0.2 mm,and good cross-section appearance is necessary to ensure the bearing capacity of shell bearing seat.It is obvious that the prefabricated groove is an important process.Based on the quasi-brittle fracture unstable once it begins to crack,the fracture is completed instantly.In paper,ABAQUS is used to simulate the initiation of shell bearing seat,and the stress and strain field during initiation is analyzed numerically.Besides,the fracture-splitting force,the starting time,the loss of circle,the cracking initiation node and reason are determined.Further more,by analyzing the influence of different cracking groove parameters on fracture-splitting force and loss of circle,the parameters of fracture-splitting groove are optimized and better cracking effect is obtained.Finally,the simulation results are verified by the experiment,and the effect of the material on fracture-splitting process is further discussed.The results of this paper will provides theoretical guidance for the practical production of shell bearing seat.The main contents and conclusions of this paper are as follows:(1)By analyzing the applicable range of various fracture criteria and the characteristics of stress and strain near the groove,the maximum tensile stress criterion is determined as the fracture criterion of shell bearing seat,which lays the theoretical foundation for initiation analysis.(2)QT450 with 50%pearlite in matrix was selected for fracture.According to the mechanical characteristics of shell bearing seat,simplified models including crack initiation model and rebound model were built.By analyzing the stress and strain field during the crack initiation,the characteristics of stress and strain distribution,the initiation position and the reason of shell bearing seat are determined.The displacement field after rebound is used to express the loss of circle caused by plastic deformation.The tensile test shows that QT450 material with 50%pearlite has high strength and low plasticity,which is beneficial to the fracture-splitting process.The results show that distribution of stress and strain is symmetric about fracture-splitting groove,the values of stress and strain increase from both ends to the center in thickness direction,and stress and strain values of arc end face are slightly larger than that of the plane.The initiation position of shell bearing seat is located at the 21.99 mm distance from the flat in the thickness direction,far away from the arc.In the cracking propagation direction,it is located on the sub-surface of the fracture-splitting groove root,which is due to the stress relaxation effect caused by local plastic deformation,causing the maximum tensile stress to deviate from the root of the fracture-splitting groove and form the maximum triaxial tensile stress state inside.The circle loss of shell bearing seat is mainly shown as follows:stretching along the direction of tensile stress and contracting perpendicular to the direction of tensile stress.However,due to the brittleness and groove effect of the material,the plastic strain and the circle loss of shell bearing seat are smaller.(3)The effects of fracture-splitting groove parameter on the stress and strain field,cracking initiation position,circle loss,fracture-splitting force and so on are studied by orthogonal experiment and control variable method.Finally,the range of optimal parameters is given.The curvature radius r has the most significant effect on the fracture,followed by the groove depth h,and the influence of the tension angle is not obvious.Combined with the processing,the circle loss,the maximum loading force of the equipment and the purpose to increase three-dimensional meshing area after cracked as much as possible,The fracture-splitting groove parameters of shell bearing seat of medium and heavy truck are determined as follows:the curvature radius is 0.1 mm~0.2 mm,the groove depth is 1.8mm~2.0 mm,the angle angle is0~o~60~o,and60~ois better.(4)The effectiveness of the simulation results is proved by experiments and the influence of the materials on the process was further analyzed.The cracking quality of shell bearing seat with optimized parameters is satisfying,which is consistent with the simulation results.The shell bearing seat failed to crack when the pearlite is reduced to25%.The experiments results show that the pearlite content of QT450 should be increased and the elongation and plasticity should be reduced so as to ensure the process.