Deep-penetrating conical cracks in brittle layers from hydraulic cyclic contact

Yu Zhang, Jun Kwang Song, Brian R. Lawn

Research output: Contribution to journalArticlepeer-review

Abstract

A study is made of fracture from cyclic loading of WC spheres on the top surfaces of thick (1 mm) brittle layers on polymeric substrates, as representative of repetitive occlusal contact on dental crown structures. The advantage of glass layers is that internal cracks can be followed in situ during the entire cyclic loading process. The glass surfaces are first given a surface-abrasion treatment to control the flaw state, such that the strengths match those of dental porcelains. Cyclic contact tests are carried out at prescribed maximum loads and frequencies, in water. In addition to conventional cone cracks that form outside the contact circle, additional, inner cone cracks form within the contact in the water environment. These inner cones are observed only in cyclic loading in water and are accelerated at higher frequencies, indicating a strong mechanical driving force. They tend to initiate after the outer cones, but subsequently catch up and penetrate much more rapidly and deeply, ultimately intersecting the underlying coating/substrate interface. Comparative tests on glass/polymer bilayers versus monolithic glass, in cyclic versus static loading, in water versus air environment, on abraded versus etched surfaces, and with glass instead of WC indenters, confirm the existence of a dominant mechanical element in the inner-cone crack evolution. It is suggested that the source of the mechanical driving force is hydraulic pressure from intrusion and entrapment of liquid in surface fissures at the closing contact interface. This new type of cone cracking may limit dental crown veneer lifetimes under occlusal fatigue conditions, especially in thicker layers, where competing modes-such as undersurface radial cracks-are suppressed.

Original languageEnglish (US)
Pages (from-to)186-193
Number of pages8
JournalJournal of Biomedical Materials Research - Part B Applied Biomaterials
Volume73
Issue number1
DOIs
StatePublished - Apr 2005

Keywords

  • Biomechanical ceramics
  • Cone cracks
  • Contact damage
  • Cyclic fatigue
  • Fracture modes
  • Glass
  • Hydraulic fracture

ASJC Scopus subject areas

  • Biomaterials
  • Biomedical Engineering

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