| High-speed maglev train is an important branch of the advanced rail transit equipment,with the support and guidance of the national policies,the high-speed maglev transit system develops rapidly in China.Currently,China has been the bellwether of high-speed maglev transit system with the maximum design speed of 600 km/h and even above.However,the design objective of high-speed maglev trains is developing to faster and better riding stability,safer and more reliable,more economical and comfortable,more energy-saving and environment friendly,more stringent requirements of the materials,design,manufacture,operation and maintenance of the critical load-bearing components such as maglev bogies are urgently needed,thus the new theories,new manufacturing techniques,new methods are urgently required to balance the design objective of lightweight,high durability,low-cost manufacture,economic operation and maintenance.In recent years,advanced technologies of the damage tolerance design and additive manufacturing have been developed rapidly and increasingly matured,both have driven a revolution for structural design methods and structural integrity assessment approaches in the aerospace,automotive and energy equipment industry,and then,some significant advantages of the realization of lightweight design,short and intelligent manufacturing,damage safety assessment,economic operation and maintenance have been achieved.However,few related research and application cases for rail transport have been reported at present,especially for critical load-bearing components such as railway bogies and maglev bogies.In this thesis,the operating environment of high-speed maglev trains,the service loads or load spectra and load-bearing characteristics of maglev bogies were considered comprehensively,and then,the time-domain stepwise structural integrity assessment method for maglev bogies and the optimization design method of maglev bogies based on the selective laser melting additive manufacturing technology were proposed,respectively.Then a lightweight,higher durability and damage insensitive maglev bogie with additive manufacturing aluminium alloys were developed by these two approaches for the application demonstration,the main research contents and conclusions are as follows:(1)Based on the detailed investigation of the Shanghai high-speed maglev line,the structural and load-bearing characteristics of high-speed maglev trains were concerned comprehensively for the operating environment research,and then,12 abnormal load conditions and nine fatigue load conditions were formulated.Based on the vehicle-bridge coupling system dynamics and a multiple physical coupling system dynamic model of a train,the vibration responses of vehicles and service loads of maglev bogies are first simulated,based on these,the ultimate design loads of maglev bogies were obtained and the abnormal load spectra and fatigue load spectra of maglev bogies were formulated.These loads and load spectra could provide theoretical basis and load input conditions for the subsequent structure design and structural integrity assessment of maglev bogies.(2)Based on the vehicle dynamics,fatigue damage mechanics,and fracture mechanics,the vehicle vibration responses of maglev bogies were first related with the structural fatigue damage evolution,then existing static or quasi-static structural integrity assessment methods could be extended as time-domain assessment methods.Based on these,the loads or load spectra in time-domain were taken as a principal outline for organization,the first level is the service loads analysis of maglev bogies based on vehicle system dynamics,the second level is the check analysis of structural strength based on the infinite life design principle,the third level is the fatigue life assessment based on the safe life design principle,and the fourth level is the residual life evaluation based on the damage tolerance design principle,finally,a time-domain stepwise structural integrity assessment method was established.(3)Based on the time-domain stepwise structural integrity assessment method,the structural strength check analysis,fatigue life assessment,and damage tolerance capability estimation of the maglev bogie were carried out successively.Analysis results of the structural strength check analysis and fatigue life assessment show the critical components with lower safety margin are bolsters and swing bars,while both are the key load-bearing components of the secondary suspension mechanism.The swing bars are identified as damage sensitive components with potential failure risk by the further damage tolerance capability estimation.This secondary suspension mechanism is determined as the component most in need of improvement for the existing maglev bogie from the perspective of structural integrity,and then,it was simplified in two aspects of the institution and structures.Finally,a modified design scheme of the maglev bogie was proposed.(4)Based on the comprehensive utilization of multiple material characterization and detection technologies and trail production tests,the composition and additive manufacturing parameters of selective laser melting Al Si10Mg-T6 alloy were first determined by the multi-schemes and multi-parameters comparison and optimization method.On this basis,the monotonic tensile tests,high-cycle fatigue tests and fatigue fracture tests of the additive manufacturing Al Si10Mg-T6 alloy were carried out.The ultimate tensile strength,yield strength,Young’s modulus and section shrinkage of the selective laser melting Al Si10Mg-T6 alloy were obtained,and then the material S-N curves,design S-N curves and design crack growth rate curves with the variable-amplitude loads were fitted.This selective laser melting Al Si10Mg-T6 alloy is demonstrated to be suitable for the design and development of maglev bogies from the perspective of the manufacturing capability and material properties.(5)A structural optimization design method based on the selective laser melting additive manufacturing technology was proposed by integrating the component integration optimization method,topology optimization method,and lattice structure optimization method of additive manufacturing structures into the time-domain stepwise structural integrity assessment framework of the maglev bogie.Based on this optimization design method,combined with the design scheme of the modified maglev bogie,a design scheme of the maglev bogie with additive manufacturing aluminium alloy was determined through by the iterative design process of the design scheme improvement,vehicle system dynamic model update,service loads analysis,structural integrity assessment,and design scheme improvement.Compared with the present scheme,the additive manufacturing scheme can achieve better lightweight design effect and higher fatigue durability,its critical safety components have better damage tolerance capabilities,and are less sensitive for the aspects of initial defects.In addition,high-speed maglev trains with additive manufacturing maglev bogies show better adaptability of plane curves and high-speed riding stability. |
