1. College of Mechanical and Electrical Engineering; Shandong University of Science and Technology; Qingdao 266510 Shandong Province P. R. China
2. School of Materials Science and Engineering; Beijing University of Technology; Beijing 100124 P. R. China
3. School of Electromechanical Engineering; Xi'an Polytechnic University; Xi'an 710048 Shaanxi Province P. R. China
4. State Key Laboratory for Mechanical Behaviour of Materials; Xi'an Jiaotong University; Xi'an 710049 Shaanxi Province P. R. China