Mechanism Study And Device Design Of Vibratory Stress Relief Using Coupled Lateral And Torsional Resonances

Residual stresses will produce during the process of metal material processing and the use of workpieces,especially in the condition of stress concentration and under the condition of irregular stress.The existence of residual stress will affect its size stability,stress corrosion and fatigue damage,resulting in economic loss or personal property safety.Therefore,it is necessary to reduce the residual stress inside the workpiece,eliminate the fatigue factors,make it safer and work within the range of life design.Rotating shaft parts are.widely used in mechanical and electrical equipment.Therefore,after the the processing of the shaft parts,the service life and dimensional stability of the rotating shaft can be improved by eliminated the residual stress,and the dynamic performance of mechanical equipment and electrical equipment when working can also be improved.Commonly used methods to reduce the residual stress are natural treatment,thermal treatment and vibration treatment and magnetic treatment.Natural treatment and heat treatment will consume a lot of time,space and fuel resources,affecting the environment;the mechanism of magnetic treatment is still need to study more in-depth and has not been widely used.After the vibratory stress relief process,the residual stress of the workpiece can be eliminated,and it takes only half an hour to complete the process.Compared with the annealing treatment,the time and cost of vibration treatment are reduced.However,for the shaft with high stiffness and complex residual stress distribution,there are less appropreiate methods to treat with the vibratory stress relief process.The excitation frequency of traditional eccentric motor is less than 200 Hz,which can not make high-stiffness parts resonance.For the high-frequency vibration treatment,to reduce the residual stress effectively,the enough dynamic stress also needs to be produced.The shear stress is the driving force to reduce the residual stress.The condition of vibratory stress relief proposed by Wozney is that only when the extral dynamic stress combined with the residual stress exceeds the yield strength and the residual stress can be reduced.According to the condition,the effect of the traditional vibrator on the high stiffness workpiece is not ideal.In this dissertation,the dynamic stress generated by bending and torsional coupling resonance is proposed to eliminate the residual stress.In order to apply the bending-torsional coupled resonance theory to the vibration aging process,it is necessary to determine the frequency and amplitude of the torsional vibration excitation,the rotation speed and the eccentricity of the shaft supported by the bearing.In this dissertation,the finite element method is used to establish the flexural-torsional coupling model of rotor-bearing system.The dynamic model is multi-degree of freedom.The eccentric mass is the coupling factor,which is considered as a single element to be added to the system equation.The model is taking into account of moment of inertia,shear deformation,gyroscopic moment effect,bearing stiffness damping and dynamic imbalance.The overall matrix is no longer symmetric and can not be regarded as a small damping system,and it is necessary to introduce the state variables and convert them into the state space for solving the influence of the gyroscopic torque and even the bearing anisotropic support parameters.The natural frequency and modes of the rotor-bearing system are obtained by numerical method.The relationship between bending stiffness,torsional stiffness,supporting property,eccentricity and external excitation is obtained.Because of the difference between the bending natural frequency and the torsional natural frequency is not necessarily small,if a bending-torsional coupling resonance is to be generated,a high rotational speed is required,so that structural adjustment is required in the process design.For example,adding cantilever flywheel or adding a cross bearing to support the extension shaft section with flywheels,in this way,we can try to adjust the difference between natural frequencies of bending and torsional.When the proper frequency equaled the difference of bending and torsional natural frequency is obtained,the speed of the motor is set according to the resonance condition.At this constant rotational speed,the dynamic eccentricity and periodic torque are applied to the rotating shaft according to the position that residual stress concentrated.Then,the transient dynamic analysis is carried out.To determine the various parameters of the coupled vibration,the lateral and torsional coupling vibration characteristics of the rotor-bearing system such as the displacement response and the dynamic response of each node are obtained by the MATALB program.Due to the dynamic equation of the bending-torsional coupling vibration,the mass matrix,the stiffness matrix,the damping matrix and the force vector matrix all change with time.It is a time-varying parameter excitation system.Stability analysis of lateral-torsional coupling is carried out by Fioquet theory.The stress state of the material under the lateral-torsional coupling resonance is in a complex stress state,which is different from the strength theory for uniaxial tension deformation.In this dissertation,the unified strength theory is introduced into the mechanism analysis of the vibratory stress relief via lateral and torsional vibration resonance.Considering the influence of the intermediate principal stress and the tensile and compressive strength of the material,the mechanism of the VSR using coupled lateral and torsional resonances is more reasonable than the traditional VSR mechanism.Through the above theoretical analysis,device and experiment with lateral and torsional coupling vibration is designed to obtain the dynamic response and verify the coupling between the lateral vibration and torsional vibration,which is helpful to produce enough dynamic stress to reduce residual stress and accumulate relevant experience and data for applying the theory of lateral and torsion coupling resonance to the field of vibratory stress relief.