Assessment of the stress-strain state of an elastic rail fastening clip as a function of the fastener tightening force

The reliability of intermediate rail fastenings acquires particular importance under conditions of increasing traffic density and axle loads of rolling stock. The serviceability of the fastening assembly is largely determined by the rail clamping force exerted by the elastic clip, which in operational practice is not measured directly but is monitored indirectly – by the tightening torque of the fastener. Due to the significant expenditure of the applied torque on overcoming friction forces, the actual axial force in the fastener is characterized by considerable statistical scatter, which leads to both insufficient and excessive loading of the clip. Analysis of inservice failures shows that about 99 % of cases of ZhBR clip failure are associated with crack formation and fractures, which necessitates a quantitative assessment of the stress state of the clip over the entire range of attainable tightening forces.

In this study, the finite element method in the APM FEM environment was used to model the stress-strain state of the CP369.102 spring clip of the ZhBR fastening within the ‘clip – rail – thrust bracket’ assembly. The location of the most heavily loaded zones was established, analytical dependences of stresses at the control points on the axial tightening force were obtained, and the critical force values were determined at which stresses in the dangerous section reach the yield strength (about 35.4 kN) and the ultimate strength (about 39.5 kN) of 60S2A steel. Based on statistical data on the scatter of the tightening force, a probabilistic assessment of the risk of reaching limit states was performed for various conditions of the threaded surfaces. It is shown that for new and lubricated screws the probability of exceeding the yield strength reaches significant values.

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