Coupler force and fatigue assessments with stochasticdraft gear frictions

Train dynamics and component fatigue assessments are important steps towards successful operations of long heavy haul trains. Longitudinal train dynamics (LTD) simulation is an effective and efficient approach in this regard. Draft gear friction has been known to have a strong stochastic feature. However, relevant train dynamics simulations have not been reported in open literature. This paper uses experimental data to extract the stochastic feature of draft gear friction. The stochastic feature is then introduced into LTD simulations. Coupler force and fatigue damage assessments were conducted by simulating a heavy haul train that has 244 vehicles and weighs nearly 30,000 tonnes. The results show that average in-train force variations due to stochastic friction were 55 and 40 kN for the traction and air brake cases respectively; maximum force variations were 207 and 98 kN for the traction and air brake cases respectively. Coupler fatigue calculations are even more sensitive to stochastic draft gear friction; the largest variations can be up to 700 times different due to the strong nonlinearity of fatigue calculation procedures. Stochastic friction is an unavoidable nature in friction draft gears. Simulations using stochastic draft gear friction can deliver results that are more robust and reliable.