Load And Void Damage Identification Method Of Ballastless Track Through Impact Vibration

Track structure is an important infrastructure to guide and support the smooth and safe operation of high-speed trains.Its good working state is an important guarantee for the safety of high-speed trains.With the rapid development of high-speed railway,the running speed and density of passenger train are increasing,and the interaction of wheel-rail system is intensifying and the dynamic problems of track structure are becoming more prominent.Once the state of rail deteriorates under train load,the occurrence and development of rail disease will be accelerated,and the track structure will be more prone to material failure,fatigue damage and even structural failure under high-frequency and large-value cyclic load.Therefore,it is of great significance to identify and predict the wheel-rail interaction and the damage status of the track structure in time and effectively.In order to realize the identification and prediction of the wheel-rail interaction and service state of track structure,and improve the theoretical work of the evaluation and prediction of the state of track structure,this paper,based on the principle of impact vibration test and dynamics,studies several problems of the identification of the service state of ballastless track by means of the combination of simulation analysis and test.The main research work and conclusions are as follows:1.Establishment of three-dimensional transient impact contact finite element modelWith the help of finite element method,a three-dimensional transient impact contact model is established to simulate the process and vibration response of impact vibration test.The wheel and rail are established as solid models to simulate the real structure force and vibration,and the interface impact contact is coupled with the structure vibration,and the transient impact contact behavior between wheel and rail is simulated numerically.The results show that the model is complete and can provide a refined numerical analysis method for the structural state evaluation.The characteristics of load input of falling-axle impact test and hammer impact test are analyzed in detail in this model.2.Research on applicability of ground test method for rail vertical stress stateThree-dimensional transient drop impact contact model is used to simulate the impact vibration test and calibrate and verify the ground test methods such as shear stress method,rail web compression method and bending moment method.The distribution characteristics of interior“equivalent strain”of rail in time and space zone under high-frequency load are explored.The feasibility and applicability of wheel-rail force measure method based on“equivalent strain”of rail is obtained.The simulation is also verified with the test results of indoor full-scale test.The results show that:（1）Methods based on the measurement of equivalent strain such as the shear stress method and rail web compression method can effectively identify high-frequency wheel–rail impact force,but the bending moment difference method provides an inferior performance in this respect.The calibration results obtained by quasi-static method are not applied for the measurement of high-frequency force,which needs dynamic verification.（2）The rail web compression method is relatively sensitive to“fixed point measurement”and can provide a more accurate value of the high-frequency wheel–rail force P₁.However,as the vertical compression strain in rail is only stable within a very small range near the load point,the stable range of measurement is quite small,and thus this method is not suitable for the measurement of moving loads in the field.Therefore it is recommended that the rail web compression method be used only for measurement of wheel–rail impact force in indoor wheelset load-drop tests.（3）The shear stress method can be used to measure the wheel–rail peak force caused by local irregularity within a certain area of 12cm,and therefore it is relatively suitable for field testing.However,the measured high-frequency wheel–rail impact force P₁is 10–15%lower than the actual wheel–rail impact force.In order to take stable measurements of the wheel–rail impact force for a moving contact area,it is recommended that the strain gauge interval be 24–32 cm.3.Research on the prediction of wheel-rail vertical impact stress state based on the principle of falling axle impactThe relationship between wheel-rail interaction force of ballastless track is studied by using the method of fine finite element simulation and theoretical derivation,and the calculation formula of impact load prediction which considers structural parameters and is suitable for the structural form of ballastless track in China is obtained.The research results show that:（1）Compared with ballasted track,there are different structural stiffness and layered distribution characteristics of mass in ballastless track.The existing dynamic load coefficient prediction formula based on ballasted track structure can not be fully applied to ballastless track structure.（2）The main influencing factors of high-frequency impact force P₁ are impact speed and rail mass.When the wheelset mass exceeds 800 kg,the increase of wheelset mass hardly changes the peak value of high-frequency impact force P₁.The main influencing factors of P₂ are impact speed,wheelset mass and fastener stiffness.（3）The prediction formula of wheel-rail impact load suitable for ballastless track is established.The wheel-rail impact load can be accurately predicted by this calculation formula.Meanwhile,it can predict the stress state of wheel and rail under different operating conditions,and provide a basis for the design,checking and maintenance of key track components that may have impact on non-standard rail sections such as turnouts and rail joints.4.Research on identification method of void damage state of ballastless track based on transient impact vibration responseAccording to the structural characteristics,damage modes,identification target and other factors of the unit slab ballastless track,a theoretical model of track slab substructure vibration under the condition of local void is established and a method for identification and evaluation of void damage state of ballastless track based on transient impact response is proposed.The results show that:（1）The main purpose of void damage identification of ballastless track is to provide basis for the decision of inspection,prepairation and maintenance plan of ballastless track structure.（2）Based on the vibration theory of slab,the local area of track slab to be measured is transformed into a thick slab substructure system with elastic support.Based on the classical slab theory,the modal theory of void substructure is analyzed,which provides a theoretical basis for the identification method of void damage of ballastless track based on transient impact response.Once the damage of track slab is formed,the plane size of void area and boundary support modes are the main factors of the deterioration of the track structure function.（3）According to the structural modal information of the local void state and the damage state of track slab,the identification method establishes the mapping relationship with the local characteristic frequency of track slab substructure as damage characteristic target,which can identify,locate and evaluate the hidden damage under slab without basic parameters.The target can also provide new research methods and solutions for the identification of void damage under track slab.But how to extract the characteristic frequency truly related to damage from multi-modal complex vibration response signals is the key to increase accuracy and speed of identification based on this method.5.Separation and extraction of damage characteristic frequency under multi-modal complex vibration responseIn this chapter,according to the theory of structural dynamics and the signal processing method in time and frequency domain,the damage characteristic index of modal parameters related to void damage is extracted from multi-modal complex vibration response signals by using EEMD signal decomposition method.Through the results of wavelet transform and HHT transform,the characteristics of vibration signal are analyzed in time-frequency domain.The research results show that the vibration response signal after signal processing not only improves the measurement accuracy,but also increases the recognizable distance,which realizes the rapid recognition of"multi-point excitation and single-point acquisition"in a certain area of track structure.Simulation and full-scale test show that the established damage identification method based on transient impact response has strong operability and application prospect.