Experimental and numerical investigation of the effect of the assembled state on the static-dynamic characteristics and fatigue performance of railway fastening clips

To study the effects of the assembled state on the static-dynamic characteristics and fatigue performance of railway fastening clips, the clamping-force and modal characteristics of the clip with different assembled states are obtained with field experiments, and a refined finite element model of the fastening system is established and verified. The static-dynamic mechanical properties and evolution law with different assembled states of the clip are comprehensively investigated based on the numerical model. Combined with the measured S-N fatigue life curve of the clip, the time domain method of vibration fatigue damage of fastening clips is further established, and the effects of the assembled state on the clip's fatigue failure mechanism and the distribution characteristics of clip fatigue damage peril points (CFDPPs) are investigated. Eventually, the recommended value for the assembled state of the clips is proposed. The results show that the first two natural frequencies in standard assembled state are the largest, with increasing separation gap or degree of over-screwing, which gradually decrease. The fatigue life of a clip is significantly affected by the assembled state and excitation frequency, the resonance at the 2nd natural frequency is important for fatigue failure of the fastening clips, and with increasing assembly tightness, the resonance effect is more significant. The distribution of CFDPPs is not affected by the assembled state, but it gradually develops from the inner arc surface of the clip heel near the mid-leg to the position near the lateral leg with increasing excitation frequency. By considering the high-frequency excitation of the wheel-rail system and clamping force requirements, as well as the field assembly operability, it is recommended that the assembled state of the clip for railway fastening systems should be controlled within a 0 similar to 0.5 mm separation gap.