Fracture Strength Analysis Of Bearing Steel With Different Notches Under Impact Load

The use of fracture design to separate materials is achieved by adding artificially created defects to the material and applying different forms of loading to it,resulting in a fast material separation process and less energy consumption.In the machining industry,bars are used in a wide range of applications as processing materials.The theory of fracture design is used to guide the blanking process of the bar in machining.Compared with the traditional machinery industry,the blanking method has high processing efficiency,low energy consumption,material saving and less wear on the tool.Especially suitable for the advantages of high strength raw materials.Based on this,this paper takes metal bar as the research object,analyzes the failure mechanism and the selection of main parameters in the process of bar blanking from two aspects of experiment and numerical simulation.The main work is as follows:(1)In this paper,the factors affecting the fracture of the bar during the blanking process of the factory are discussed.The influence of the V-notch size parameters of the bar,namely the opening angle,the corner radius and the groove depth on the fracture of the dynamic loading process,is discussed through experiments.(2)Comparative analysis of the three dimensional parameters to obtain the test results,the root radius has an impact on the impact force but the impact is limited.The opening angle has no effect on the impact force change.The groove depth has the greatest impact on the impact force.Through the analysis of the fracture of the test piece,it is known that the fracture surface of the test piece occurs in the radius of the corner.The fracture of the test piece is caused by the combination of normal stress and shear stress,and the shear stress on the flat and smooth fracture surface is strong.The stress is weaker.On the specimen with rough fracture surface,stepped fault or tearing edge,the shear stress is weakened,and the effect of normal stress is enhanced.(3)The numerical simulation analysis of the test process proves that the second peak of the impact force-time curve obtained by the test is caused by the fact that the bottom surface of the hammer head and the contact surface of the test piece are not parallel,which causes the test piece to be loaded by the asymmetric load during the test.It is verified that the numerical simulation model is reasonable and the numerical simulation results are accurate and reliable.The variation of normal stress and shear stress in the three points of the fracture of the numerical simulation specimen is analyzed.It is explained that the reason of the different shearing effects in the three regions on the SEM obtained by the test is due to the competition mechanism of shear stress and normal stress.And in the C1 region is tensile shear failure,the C2 region is pure shear failure and the C3 region is compression shear failure.(4)Based on the numerical simulation analysis method,the main parameters of the factory bar material cutting process are discussed.Considering the V-notch size parameter selection opening angle ?=30 °,root angle radius R = 0.25 mm,relative groove depth h = 0.4 is the most reasonable.The initial crack of the V-notch test piece based on the optimized selection appears at the foremost end and the last end perpendicular to the loading direction,and is pure shear failure.Based on the most reasonable V-notch parameters selected for optimization,it is considered that the hammer head with M30=30Kg is superior to the hammer head of other masses in the factory blanking process.With the rapid development of high-tech,the cutting process in the machining industry needs to process a large amount of raw materials.The efficiency and consumption of cutting is directly related to the production process and product processing cost.Therefore,the method of using this type of fracture design has a broad method.Application prospects.In this paper,some key problems of the fracture design blanking method are analyzed and analyzed,and the more reasonable key process parameters are given from the quantitative point of view,which provides guidance and reference for practical application.