1. Ph.D. Student, College of Mechanics and Materials, Hohai Univ., No. 8 Fochengxi Rd., Nanjing, Jiangsu 211100, PR China.
2. Professor, College of Mechanics and Materials, Hohai Univ., No. 8 Fochengxi Rd., Nanjing, Jiangsu 211100, PR China (corresponding author).