1. State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi’an Jiaotong University, No. 28, Xianning West Road, Xi’an, Shaanxi 710049, P. R. China
2. Department of Mechanics, Xi’an University of Science and Technology, No. 58, Yanta Road, Xi’an, Shaanxi 710054, P. R. China