title: Study on torsional fretting wear behavior of a ball-on-socket contact configuration simulating an artificial cervical disk.
abstract: A ball-on-socket contact configuration was designed to simulate an artificial cervical disk in structure. UHMWPE (ultra high molecular weight polyethylene) hot pressed by powders and Ti6Al4V alloy were selected as the material combination of ball and socket. The socket surface was coated by a ~500 nm C-DLC (carbon ion implantation-diamond like carbon) mixed layer to improve its surface nano hardness and wear resistance. The torsional fretting wear behavior of the ball-on-socket model was tested at different angular displacements under 25% bovine serum lubrication with an axial force of 100 N to obtain more realistic results with that in vivo. The fretting running regimes and wear damage characteristics as well as wear mechanisms for both ball and socket were studied based on 2D (two dimension) optical microscope, SEM (scanning electron microscope) and 3D (three dimension) profiles. With the increase of angular displacement amplitude from 1° to 7°, three types of T-θ (Torsional torque-angular displacement amplitude) curves (i.e., linear, elliptical and parallelogram loops) corresponding to running regimes of PSR (partial slip regime), MR (mixed regime) and SR (slip regime) were observed and analyzed. Both the central region and the edge zone of the ball and socket were damaged. The worn surfaces were characterized by wear scratches and wear debris. In addition, more severe wear damage and more wear debris appeared on the central region of the socket at higher angular displacement amplitude. The dominant damage mechanism was a mix of surface scratch, adhesive wear and abrasive wear for the UHMWPE ball while that for the coated socket was abrasive wear by PE particles and some polishing and rolling process on the raised overgrown DLC grains. The frictional kinetic behavior, wear type, damage region and damage mechanism for the ball-on-socket model revealed significant differences with those of a ball-on-flat contact while showing better consistency with that of in vitro cervical prosthesis simulations according to the literature.
authors.affiliation: State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China; Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China.
authors.forename: Song
authors.initials: S
authors.lastname: Wang
authors.affiliation: School of Material Science and Engineering, China University of Mining and Technology, Xuzhou 221116, China.
authors.forename: Fei
authors.initials: F
authors.lastname: Wang
authors.affiliation: Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China; Biomechanics and Biotechnology Lab, Research Institute of Tsinghua University in Shenzhen, Shenzhen 518057, China.
authors.forename: Zhenhua
authors.initials: Z
authors.lastname: Liao
authors.affiliation: School of Material Science and Engineering, China University of Mining and Technology, Xuzhou 221116, China.
authors.forename: Qingliang
authors.initials: Q
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China; Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China.
authors.forename: Yuhong
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Biomechanics and Biotechnology Lab, Research Institute of Tsinghua University in Shenzhen, Shenzhen 518057, China; State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China. Electronic address: weiqliu@hotmail.com.
authors.forename: Weiqiang
authors.initials: W
authors.lastname: Liu
mesh_terms: D000497:Alloys; D000818:Animals; D002244:Carbon / Q000737:chemistry; D002417:Cattle; D002584:Cervix Uteri; D018130:Diamond / Q000737:chemistry; D005260:Female; D017276:Friction; D006244:Hardness; D008153:Lubrication / Q000379:methods; D008422:Materials Testing / Q000379:methods; D011095:Polyethylenes / Q000737:chemistry*; D019736:Prostheses and Implants; D044967:Serum / Q000737:chemistry; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry*
chemical_list: D000497:Alloys; D011095:Polyethylenes; C111601:ultra-high molecular weight polyethylene; C031462:titanium alloy (TiAl6V4); D002244:Carbon; D018130:Diamond; D014025:Titanium
keywords: Artificial cervical disk; Ball-on-socket; In vitro simulation; Surface modification; Torsional fretting wear