PSI - Issue 28

Nikolay Dolgov et al. / Procedia Structural Integrity 28 (2020) 1010–1017 Nikolay Dolgov & Tsanka Dikova / Structural Integrity Procedia 00 (2019) 000 – 000

1011

2

f (  ,  ) dimensionless function G c

shear modulus of the coating shear modulus of the substrate half thickness of the substrate thickness of the coating

G s

H

h

parameter

k n

length of the coating

l

load, applied to the substrate

P

p 1, p 2, q n , r n , s 1, s 2 – parameters  strain of the substrate  ,  n

dimensionless parameters Poisson's ratio of the coating Poisson's ratio of the substrate

 c  s

parameter, defining maximum normal stress σ x ( x , z ) in z =0

 max

 res residual stresses in the coating σ x ( x , z ) normal stresses in the x-direction σ z ( x , z ) normal stresses in the z-direction

 x (  ) normal stresses in the x-direction in accordance with the coordinate axis of Frank et al. (2009)  y (  ) normal stresses in the y-direction in accordance with the coordinate axis of Frank et al. (2009)  x (  ,  ) normal stress as a function of the dimensionless parameters  and  in the x -direction in accordance with the coordinate axis, given by Frank et al. (2009)  y (  ,  ) normal stress as a function of the dimensionless parameters  and  in the y -direction in accordance with the coordinate axis, given by Frank et al. (2009)

 xу ( x , z ) shear stresses in the coating-substrate interface  zу ( x , z ) shear stresses in the coating-substrate interface  max

parameter, defining maximum normal stress σ z ( x , z ) in x =0

 , 

dimensionless parameters

1. Introduction Co-Cr alloys are widely used in prosthetic dentistry because they possess good corrosion resistance and high mechanical properties. However, they are characterized with low esthetic by Al Jabbari et al. (2014), Lu et al. (2015), Kim et al. (2016), Wang et al. (2016), Han et al. (2018), Dikova (2018) and Dikova et al. (2019). They are mainly used in the production of fixed partial dentures (FPD). Taking into account that high esthetic is one of the main requirements for the dental restorations, usually the metal substructure is covered with a material having optical properties close to the natural teeth – polymers, composites, ceramic. Because of high mechanical and esthetic properties as well as high durability, the metal-ceramic FPDs are mostly used nowadays. The metal-ceramic FPD represents metal substructure, made of base Co-Cr, Ni-Cr or noble alloys, covered with porcelain coating. However, during chewing conditions, the ceramic coatings may crack or delaminate. These processes run due to the stresses that occur both in the coating and in the porcelain-alloy interface by Al Jabbari et al. (2014), Wang et al. (2016) Han et al. (2108) and Dikova et al. (2019). Tensile test of flat coated specimens is an universal method that allows studying the nature of the coatings fracture by Rehman et al. (2012) and Guo et al. (2018). Tensile stresses in the coatings can cause their cracking by Lyashenko et al. (1996) and Dolgov et al. (2015). Various approaches for determining the stress state in tensile samples exist, based on the shear-lag approximation methods by Cox (1952), Ting et al. (1985), Guo et al. (1990), Nair and Grosse (2005) and the Agrawal-Raj model by Agrawal and Raj (1989), Agrawal and Raj (1990). Experimental investigations of flat coated specimens make it possible to determine the interface shear strength and cohesive properties of the