1. L.F. Ma, Q.X. Huang and J.J. Ji: Heavy Machinery, (2009) No. 4, p.4. (In Chinese).
2. R. Zhu: Jiang Su Metallurgy, Vol. 32 (2004) No. 6, p.32. (In Chinese).
3. Y.S. Zhang, Y.J. Huang: Southern Iron and Steel. (2000)No. 11, p.12. (In Chinese).
4. C. Xu,C. Zhang and H. Yang: Theory of Metal Plastic Forming (Metallurgical Industry published, China 2009). (In Chinese).
5. X.Y. Jiang, H. Gong: mechanics of materials (Xi'an Jiao Tong University Teaching and Research Group Mechanics of Materials Course published, China 2009). (In Chinese).