Inadequate management of large in-train forces transferred through coupler systems of a railway train leads to running and structural failures of vehicles.Understanding these phenomena and their mitigation requires ac...Inadequate management of large in-train forces transferred through coupler systems of a railway train leads to running and structural failures of vehicles.Understanding these phenomena and their mitigation requires accurate estimation of relative motions and in-train forces between vehicle bodies.Previous numerical studies have ignored inertia of coupling elements and the impacts between couplers.Thus,existing models underestimate the additional dynamic variations in in-train forces.Detailed multi-body dynamic models of two AAR(Association of American Railroads)coupler systems used in passenger and freight trains are developed,incorporating coupler inertia and various slacks.Due to the modeling and simulation com-plexities involved in a full train model,with such details of coupler system,actual longitudinal train dynamics is not studied.A system comprising only two coupling units,inter-connecting two consecutive vehicles,is modeled.Considered system has been fixed at one end and an excitation force is applied at the other end,to mimic a relative force transmission through combined coupler system.Simulation results obtained from this representative system show that,noticeable influence in in-train forces are expected due to the combined effect of inertia of couplers and intermittent impacts between couplers in the slack regime.Maximum amplitude of longitudinal reaction force,transferred from draft gear housing to vehicle body,is expected to be significantly higher than that predicted using existing models of coupler system.It is also observed that the couplers and knuckles are subjected to significant longitudinal and lateral contact forces,due to the intermittent impacts between couplers.Thus,accurate estimation of draft gear reaction force and impact forces between couplers are essential to design vehicle and coupler components,respectively.展开更多
Purpose-Association of American railroads(AAR)standard automatic couplers are designed for much higher capacity than the normal operating loads.However,failure of knuckles and coupler bodies is still a common occurren...Purpose-Association of American railroads(AAR)standard automatic couplers are designed for much higher capacity than the normal operating loads.However,failure of knuckles and coupler bodies is still a common occurrence.Recent studies have shown that fatigue is the main reason behind such failures below the expected load.Moreover,knuckle failures occur more frequently than coupler body failures,which cause operational disruptions and also influence overall coupler life because of nonconforming contact between a new knuckle and an old coupler.In addition to new and old counterparts,undesired contact conditions are often the case with the new assembly due to casting-based manufacturing inaccuracies.Design/methodology/approach-A study is thus carried out in this paper to understand the variation of load transfer paths and its consequences caused by dimensional variability.A finite element model of an E-type coupler’s knuckle is developed and different possible contact conditions of the knuckle with the coupler head are simulated.Knuckles generally fail in pulling mode,during which the possible contacting elements of knuckle are pulling lugs,pin protector regions and pinholes.Due to dimensional variability,contact conditions may exist where an individual or a combination of these elements are in contact.Findings-Simulation results indicate that under regular operational conditions,having only the pulling lugs in contact reduces the risk of knuckle failure and maintains assembly integrity even if the knuckle fails.However,under extreme loading conditions,the safest scenario is when both pulling lugs and pin protector regions are in contact.Originality/value-These findings are believed to assist in defining the dimensional variability limits to ensure the desired contacts between the mating surfaces of the knuckle and coupler body of railway couplers of AAR type.This work contributes to understanding implications of dimensional variability in the railway couplers.The insight presented are useful in design,manufacturing and maintenance of railway coupler’s knuckle.展开更多
文摘Inadequate management of large in-train forces transferred through coupler systems of a railway train leads to running and structural failures of vehicles.Understanding these phenomena and their mitigation requires accurate estimation of relative motions and in-train forces between vehicle bodies.Previous numerical studies have ignored inertia of coupling elements and the impacts between couplers.Thus,existing models underestimate the additional dynamic variations in in-train forces.Detailed multi-body dynamic models of two AAR(Association of American Railroads)coupler systems used in passenger and freight trains are developed,incorporating coupler inertia and various slacks.Due to the modeling and simulation com-plexities involved in a full train model,with such details of coupler system,actual longitudinal train dynamics is not studied.A system comprising only two coupling units,inter-connecting two consecutive vehicles,is modeled.Considered system has been fixed at one end and an excitation force is applied at the other end,to mimic a relative force transmission through combined coupler system.Simulation results obtained from this representative system show that,noticeable influence in in-train forces are expected due to the combined effect of inertia of couplers and intermittent impacts between couplers in the slack regime.Maximum amplitude of longitudinal reaction force,transferred from draft gear housing to vehicle body,is expected to be significantly higher than that predicted using existing models of coupler system.It is also observed that the couplers and knuckles are subjected to significant longitudinal and lateral contact forces,due to the intermittent impacts between couplers.Thus,accurate estimation of draft gear reaction force and impact forces between couplers are essential to design vehicle and coupler components,respectively.
文摘Purpose-Association of American railroads(AAR)standard automatic couplers are designed for much higher capacity than the normal operating loads.However,failure of knuckles and coupler bodies is still a common occurrence.Recent studies have shown that fatigue is the main reason behind such failures below the expected load.Moreover,knuckle failures occur more frequently than coupler body failures,which cause operational disruptions and also influence overall coupler life because of nonconforming contact between a new knuckle and an old coupler.In addition to new and old counterparts,undesired contact conditions are often the case with the new assembly due to casting-based manufacturing inaccuracies.Design/methodology/approach-A study is thus carried out in this paper to understand the variation of load transfer paths and its consequences caused by dimensional variability.A finite element model of an E-type coupler’s knuckle is developed and different possible contact conditions of the knuckle with the coupler head are simulated.Knuckles generally fail in pulling mode,during which the possible contacting elements of knuckle are pulling lugs,pin protector regions and pinholes.Due to dimensional variability,contact conditions may exist where an individual or a combination of these elements are in contact.Findings-Simulation results indicate that under regular operational conditions,having only the pulling lugs in contact reduces the risk of knuckle failure and maintains assembly integrity even if the knuckle fails.However,under extreme loading conditions,the safest scenario is when both pulling lugs and pin protector regions are in contact.Originality/value-These findings are believed to assist in defining the dimensional variability limits to ensure the desired contacts between the mating surfaces of the knuckle and coupler body of railway couplers of AAR type.This work contributes to understanding implications of dimensional variability in the railway couplers.The insight presented are useful in design,manufacturing and maintenance of railway coupler’s knuckle.
