“…For contacts of complicated geometries or contacts under arbitrary loading, it is usually impossible to obtain an analytical solution for both elastically homogenous and nonhomogeneous materials, so that the numerical methods are widely developed for contact problems, e.g. finite element method (FEM) (Hyun, Pei, Molinari & Robbins, 2004;Abali, Völlmecke, Woodward, Kashtalyan, Guz & Müller, 2012), boundary element method (BEM) (Putignano, Afferrante, Carbone & Demelio, 2012;Paggi & Ciaveralla, 2010;Pohrt & Popov, 2012;Aleynikov, 2010) and molecular dynamics simulation (Yang & Persson, 2008;Campana & Muser, 2007). For contacts of linearly elastic or viscoelastic materials (Kusche, 2016).…”