Transverse fracture in thin-film coatings under spherical indentation

Indentation-induced subsurface tunneling cracks as a means for evaluating fracture toughness of brittle coatings

“…For this purpose we refer to previous experiments and FEM calculations pertaining to glass, alumina or Y-TZP coatings on polycarbonate, all undergoing only elastic deformations (Chai and Lawn 2004;Chai 2005). The results, which incorporate a wide range of coating thickness and indenter radius, may be expressed as reduced crack initiation load P* vs. reduced coating thickness d* as depicted in Fig.…”

“…The stress field in the undamaged coating provides valuable insight into the fracture behavior. For this purpose a commercial FEM code (Ansys, Inc.), specified to axisymmetric loading, elastic response and large deformation, is used Chai (2005). Load transfer between indenter and coating occurs via a built-in contact algorithm which, for simplicity, is specified to a frictionless contact.…”

“…Because of the diminishing nature of the contact stresses, these cracks proliferate and propagate stably in the radial direction with increasing load (Chai et al 1999). The onset of fracture is of interest in safety designs as well as a means for extracting critical failure stress in thin (Chai et al 1999;Chai 2005) or ultra thin (Kim et al 2006;Borrero-López et al 2008) coatings. The propagation phase of the subsurface radial cracks has been studied with the aid of 3D FEM analyses (Cao 2002;Rudas et al 2005) or analytic models which simplifies the damage to a semi-circular (Kim et al 2001) or semi-elliptical (Chai 2006) subsurface crack.…”

Mono- and multiple TiN(/Ti) coating adhesion mechanism on a Ti–13Nb–13Zr alloy

“…A spherical diamond indenter with a 5 m diameter was employed to test the fracture modes of the coatings. A spherical indenter utilized in the fracture study because it has been shown to produce a more uniform stress field beneath the contact area than pyramidal pointed indenters [15]. The tested loads were 360 mN.…”

Transverse fracture in multilayers from tension and line-wedge indentation

“…The effective flaw size c F introduced by this operation was determined via indentation experiments on bilayers as ≈20 µm (Chai 2006). (For comparison purpose, similar experiments on medium-grain alumina and fine-grain Y-TZP ceramics yielded the values 10 µm and 3.5 µm, respectively (Chai 2005) parameters. The toughness of the glass is taken as 0.6 MPa m 1/2 , consistent with a slow crack growth in a humid environment, while that for the adhesive is determined from the present indentation experiments (Sect.…”