Department of Mechanics and Engineering Science,Peking University,Beijing 100871,China;
College of Science,Shandong University of Science and Technology,Taian 271019,China;
Department of Mechanics and Engineering Science,Peking University,Beijing 100871,China;
Department of Mechanics and Engineering Science,Peking University,Beijing 100871,China;
oblique collision; energetic coefficient of restitution; tangential contact modes;