Splitting Mechanism And Fracture Analysis Of Connecting Rod Material Under High Frequency Vibration

Fracture splitting of connecting rod is based on fracture mechanics and stress concentration theory.The separation of the connecting rod body and the cover is realized by the artificial stress concentration source and the rapid expansion.The obtained three-dimensional fracture surface realizes the precise engagement between the body and the cover.This technology has higher requirements on materials.It not only requires good mechanical properties of the material in service,but also requires brittle fracture and post-fracture assembly in cracking process.In order to break through the limitations of materials and solve the existing processing defects,this paper proposes a method of adding ultrasonic vibration to assist in the traditional splitting of connecting rods.In this paper,45 steel is used as experimental material,and the effects of ultrasonic amplitude,frequency,loading speed and groove depth on cracking force,deformation and stress cloud are analyzed by simulation.The mechanism of the influence of ultrasonic amplitude on cracking force,deformation of large hole,fracture line offset and fracture was studied experimentally.And the primary research results and contents are found that:(1)Based on the theory of cracking and high frequency vibration,the design of the device was carried out.The ultrasonic generator is selected by combining theoretical calculation with empirical optimization.Piezoelectric ceramic transducer and stepped horn are designed.The wedge tool was designed by half-wavelength method and its natural frequency was verified by simulation.Finally,an experimental device for high frequency vibration-assisted splitting in non-resonant state was set up.(2)Based on ABAQUS,the finite element model of high frequency vibration assisted connecting rod splitting was established.The effects of amplitude,frequency,velocity and groove depth on splitting force were analyzed.It is found that high-frequency vibration-assisted splitting can reduce the splitting force and the deformation of the big head hole compared with conventional splitting.The amplitude has a great influence on the splitting force and the deformation of the big head hole.There is an optimal amplitude value to minimize the splitting force.The change in frequency affects the amount of splitting force and deformation.Lower ultrasonic frequency improves better.The splitting speed and the depth of the groove have a great influence on the stress distribution.The greater the velocity or groove depth,the more obvious the stress concentration.The smaller the cracking force,the smaller the plastic deformation during the splitting,which is more conducive to the splitting of the connecting rod.(3)The effect of amplitude on the splitting force,the deformation of the big hole and the offset of the fracture line were analyzed by the splitting experiment assisted with high frequency vibration.The results show that the amplitude has a great influence on the cracking force.The high frequency vibration can reduce the splitting force,the splitting stroke and the offset of the fracture line.When the amplitude is lower or higher,the deformation of the big head hole is significantly higher than conventional splitting.There is an optimum amplitude in the middle of the interval,and the splitting force,the splitting stroke,the deformation of the big hole and the offset of the fracture line are the smallest under this condition.(4)Observing the fracture of the sample,it was found that the high frequency vibration can increase the brittleness of the root region of the groove,so that the crack appears and expands at the bottom of the tank earlier.When the amplitude is low,the high-frequency vibration will increase the plasticity of the material,and the fracture is ductile.When the amplitude is centered,more cracking edges and steps appear in the crack propagation zone and the rapid fracture zone,which improves the brittleness of the fracture;When the amplitude is high,the pressing force between the expansion sleeve and the big hole limits and weakens the effect of high-frequency vibration,which converts the ultrasonic energy into heat energy and is transmitted to the sample,which improves the plasticity of the material and is not conducive to the splitting of the connecting rod.Through the research on high-frequency vibration-assisted splitting of connecting rod,it is found that the changes of amplitude,frequency,speed and the depth of groove will affect the splitting.The addition of high-frequency vibration isnot necessarily beneficial to splitting.There is an optimal amplitude in the middle of the range which has the minimum splitting force,the big head hole deformation is the smallest,the brittleness of the fracture is enhanced,and it is more suitable for the splitting of the connecting rod.