Dynamic Response and Optimization Design of Fastening Systems
- What effects do dynamic train loads have on the fastening system?
Dynamic train loads cause high-frequency vibrations in the fastening system, leading to periodic changes in the clamping force of elastic clips, which can easily fatigue the elastic clips under long-term action. Bolts may loosen under vibration, reducing connection strength. Spikes are repeatedly impacted, and their anchoring force gradually attenuates, and may be pulled out in severe cases. Dynamic loads also cause elastic deformation and creep of under-rail pads, affecting their buffering performance and further aggravating the wear of other components.
- What parameters are mainly included in the dynamic response test of the fastening system?
Dynamic response tests mainly include vibration frequency, which needs to measure the vibration frequency of the fastening system at different train speeds, usually 10-50Hz. Amplitude is an important parameter, and the amplitude of elastic clips should be controlled within 0.5mm; excessive amplitude indicates poor system stability. Dynamic stress testing is also required, measuring the dynamic stress peaks of elastic clips, bolts and other components through strain gauges to ensure they do not exceed the fatigue limit of the material. In addition, dynamic displacement testing can understand the displacement of the rail under dynamic loads and evaluate the constraint effect of the system.
- How to reduce dynamic response by optimizing the elastic clip structure?
Optimize the bending angle of the elastic clip to make the stress distribution more uniform and reduce stress concentration under dynamic loads. Increase the elastic modulus of the elastic clip, select high-strength spring steel to improve its deformation resistance and reduce vibration amplitude. Add arc transitions at the contact part between the elastic clip and the rail to reduce local stress and improve dynamic stability. Finite element analysis can also be used to simulate the stress state of the elastic clip under dynamic loads, optimize structural details, and reduce resonance.
- How do the anti-loosening structures of bolts adapt to dynamic loads?
Use nuts with tooth patterns to increase friction with bolts, which are not easy to loosen under dynamic loads. Use anti-loosening washers, such as disc washers, which use their elastic deformation to generate continuous preload to offset preload loss caused by vibration. The threads of bolts and nuts adopt interference fit to increase friction between threads and improve anti-loosening effect. For high-frequency vibration parts, welding anti-loosening can be used, but attention should be paid to avoiding welding stress affecting bolt performance.
- What impact does the hardness of under-rail pads have on the dynamic response of the fastening system? How to choose?
When the hardness of the under-rail pad is moderate, it can effectively absorb the impact energy of dynamic loads and reduce vibration transmission, with the hardness generally being Shore hardness 60-70 degrees. Too high hardness makes the pad too rigid, with poor buffering effect, and dynamic loads are directly transmitted to other components, increasing stress; too low hardness makes the pad prone to excessive deformation and creep, leading to rail displacement and affecting system stability. Different lines should choose pads with different hardness; high-speed railways should choose pads with hardness 65-70 degrees, and ordinary railways can choose pads with hardness 60-65 degrees.