Flaws and cracks stability in strengthened glass by residual stress: Fid-Bau Portal

Flaws and cracks stability in strengthened glass by residual stress

Macrelli, Guglielmo

Strengthened glass is widely used in structural glazing applications in the building and transportation sectors. Surface flaws and cracks are the main glass strength limiting factors. In this theoretical study both thermally (TSG) and chemically (CSG) strengthened glass are considered. A general approach is proposed, based on the calculation of the stress intensity factor (K_I) resulting from the superposition of externally applied stresses, both mechanical and thermal, and residual stress introduced in the strengthening processes. In order to represent a severe design condition, an externally applied stress with a maximum tensile component of 50 MPa is introduced. The analysis is performed for soda‐lime glass for immediate breakage condition by comparing the stress intensity factor with the critical factor (K_IC) and for time delayed breakage activated by subcritical crack growth by comparing the stress intensity factor with the corresponding threshold value (K_Ith). The classical parabolic residual stress distribution is employed for thermally strengthened glass while a new approach is proposed for the evaluation of the residual stress profile of chemically strengthened glass. A crack growth stability analysis based on the concept of apparent fracture toughness is performed. The residual stress profiles analysed for thermally and chemically strengthened glass are the typical ones resulting from common technological processes. The crack growth stability for the analysed stress profiles do not match the criteria to be defined as flaws insensitive.