Effect of Machining Damage on the Strength of a Glass‐Ceramic

Abstract

A study has been made of the strength characteristics of machined glass‐ceramic surfaces using an indentation flaw technique. The strength is found to decline or increase with progressive removal of the machining damage layer by a polishing procedure, depending on whether the indentation is made after or before the polishing. The results are interpreted in terms of a residual compressive stress in the initial machined surface. It is argued that failure to allow for the contribution of this stress in the fracture mechanics description of flaw growth could lead to significant errors in the evaluation of crack propagation parameters.

Effect of sandblasting, grinding, polishing and glazing on the flexural strength of two pressable all-ceramic dental materials

“…Consequently, provided no significant median or lateral cracks formed, strength might be improved by grinding or machining. 47 Polishing with the diamond paste material produced the smoothest surface and the highest strength compared to all other groups for the two materials. The ability of polishing to eliminate various defects and flaws from the treated surface is considered responsible for such strength increment.…”

A review of indentation fracture theory: its development, principles and limitations

“…Other workers have also noted the influence of pre-existing stresses [56] resulting from surface grinding and tempering on the behaviour of materials subjected to sharp contact events [57][58][59].…”

Investigation of cutting-induced damage in CMC bend bars

“…It is well known that surface flaws induced by machining can reduce the strength of ceramics [6] and glass ceramics [7]. In these materials the flaws act as stress concentrators which can induce failure upon mechanical loading.…”