Primary suspension failure analysis in FIAT type LHB bogies and life estimation

Abstract

Multiple cases of failure in the primary suspension system of LHB coaches were reported in specific light-weight passenger coaches recently. Frequent failure in suspension systems led to increased downtime and maintenance costs. Failure was associated to fatigue in primary helical springs and was found to be preceded by failure of hydraulic dampers. We present a study on analysis of these failures and suggest design modifications for enhancing fatigue life. A flexible finite element model of the bogie, with suspension system involving flexible helical springs, is developed and simulated for typical load and vehicle speed parameters. Conditions of damper failure are incorporated and the exact location of failure and the observed fatigue life of spring are validated. Loading on the bogie involves tare weight and rail-wheel contact forces. Rail-wheel contact forces are computed through multibody dynamic model for typical track irregularity data. Linear static analysis is done to obtain stresses under steady loads. This is followed by pre-stressed modal analysis and harmonic response simulation of the flexible model of the bogie. Fatigue life computation under combined static and alternating load conditions is done by employing the Modified Goodman diagram. Iterative modifications in design of the primary suspension springs are carried out. Minimal changes, which do not require change in the designs of associated components or change in the manufacturing set-up, are suggested. Modifications are validated through comparative fatigue life estimation.