Department of Mechanics, University of Science and Technology of China, Hefei 230026, China Department of Mechanics, University of Science and Technology of China, Hefei 230026, China Institute of Applied Mechanics, Hefei University of Technology, Hefei 230009, China Institute of Applied Mechanics, Hefei University of Technology, Hefei 230009, China;
BEM,; natural; BIE,; elasticity,; principal; value; integrals;