Research on ballast breakage under tamping operation based on DEM–MBD coupling approach

•An API was developed to simulate ballast breaking.•Tamper-sleeper-ballast bed coupling model was established using DEM–MBD coupling approach.•Breaking behavior of ballasts while tamping was analyzed.•Optimal ballast properties were proposed. Tamping can effectively improve the service quality of ballast bed, but could cause ballast breakage. To mitigate the ballast damage caused by tamping, an application programming interface was innovatively developed to establish a ballast model that could actually simulate ballast breaking. This model was subsequently verified by a laboratory test. On this basis, a tamper-sleeper-ballast bed coupling model was constructed by the coupling of discrete element method and multibody dynamics. Finally, the coupling model was utilized to analyze the breaking behavior of ballasts in different sections and the influence of ballast properties on particle breakage. The results show that ballasts in the crib are the most probable to be broken in a tamping operation, whose breakage degree is 1.65%. Ballast properties can greatly influence particle breakage in a tamping operation. The recommended critical normal and tangential stresses of ballasts are 45 MPa and 15 MPa, respectively. Elongation and flakiness indexes are recommended to be limited in 20%. Wide gradation together with large size is recommended for ballast gradation. This study can provide critical insights for improving the service life of ballast bed.