| A fracture occurred on centrifugal compressor gears in a chemical plant,which caused serious equipment and production loss to the enterprise.It is of great significance to investigate the failure behavior and mechanism of the centrifugal compressor gears to find out the root causes of the damage and prevent the similar occurrences to promot production safety of the chemical enterprises.The main objective of this paper is the gears of the centrifugal compressor.Systematic test and analysis are carried out conducted to find out the fracture failure mechanism of the centrifugal compressor gears for corresponding prevention countermeasures.The test and analysis includes material physical and chemical properties,stress verification and finite element simulation analysis,material fatigue performance and crack propagation etc.The main contents of this dissertation are as per following:(1)The analysis of physical and chemical properties of materials is an important part of failure mechanism analysis.Through macro and micro fracture observation,material chemical composition analysis,mechanical property test and metallographic structure analysis,the gear failure form and material defects are investigated.The test results showed that a fatigue fracture failure occurred of the centrifugal compressor gear.Moreover,uneven grains in the metallographic structures has been observed and the plasticity and toughness of the gear materials are lower than the specified requirements by the standard.(2)The fatigue strength of gear is rechecked,including theoretical calculation and ANSYS transient dynamic simulation.Through strength recheck and finite element simulation,the stress distribution and the weak part of the structure of gears are pinpointed,which helped to determine whether the fracture failure of gears is caused by the high stress concentration.According to the stress recheck analysis,the contact stress and bending stress of the two gears are lower than the allowable stress,which meet the fatigue design requirements.The stress nephogram shows that the stress in the contact area and the fillet of the tooth root is the highest,which is consistent with the actual fracture position of the gear.Increasing tooth root fillet might reduce the stress concentration of the tooth root and increase the fatigue life of the gear.(3)With the combination of the fatigue test and finite element simulation of gear material,the fatigue performance of gear is investigated.By correlation of the fatigue test data,the fatigue strength limit and S-N curve expression of gear material are then obtained.It illustrated that the fatigue strength limit of gear material is 480.31 MPa with 10% failure probability and 95% confidence degree.The S-N curve is then introduced into ANSYS fatigue tool to simulate the fatigue life of the gears.The simulation results show that the fatigue life of the two gears is far below the design fatigue life.(4)With the consideration of the finite element simulation,the law of fatigue crack growth and the influence of crack on the fatigue life of gear are observed.The simulation results of gear crack growth show that the load has the greatest influence on the crack growth rate.When the crack size is fixed,the crack growth rate increases with the increase of load.The simulation results of the fatigue life of cracked gears show that the stress and the depth of crack are of greater influence on the fatigue life of cracked gears.(5)Based on the comprehensive analysis of material factors,stress factors,fatigue life and crack growth factors,the fracture failure mechanism of centrifugal compressor gear is summarized and the corresponding countermeasures are put forward.The analysis results may be used to prevent similar failure of the high speed and heavey duty gears.The research results of this paper provide important basis for the failure mechanism analysis and fatigue design of similar centrifugal compressor gears. |
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