Slow Crack Growth during Static and Dynamic Loading in Silicate Glasses

Abstract

Analytical solutions for stable crack growth in silicate glasses are provided in this paper for two important cases of loading, namely (i) constant stress and (ii) constant stress rate. The former simulates real life glass components subjected to uniform tensile stress while the latter represents strength measurement test for glass specimens. In both cases it is desirable to envision the onset and progression of slow crack growth over time. In this manner the state of initial crack and associated strength can be monitored as a function of applied stress and stress duration. In addition, the progressive crack history provided by analytical solutions helps estimate both the threshold and residual strengths of glass articles which, in turn, are needed to quantify their long term mechanical reliability.

The analytical solutions obtained by integration of the power law model involve two system constants which are readily evaluated by imposing certain conditions on crack length at threshold stress. These solutions show that the initial crack velocity is extremely small but increases exponentially with crack length. Hence the onset of fast fracture can be predicted from crack kinetics in the stable region. Thereafter, the crack growth is extremely rapid, unstable, difficult to model, and not of practical interest.

The analytical solutions can also be used to design proof test conditions which will ensure both the initial quality and long term integrity of glass articles under specified loading and environment.

Keywords:

• Silicate glasses
• Crack growth
• Static fatigue
• Dynamic fatigue