Extrapolation of Fracture Mirror and Crack‐Branch Sizes to Large Dimensions in Biaxial Strength Tests of Glass

Abstract

Annealed glass disks were fractured in biaxial tension under a variety of conditions; crack lengths prior to branching and the sizes of the mirror and mist regions were measured. The experimental results indicated the expected correlation between fracture stress and these fracture features, except for an extrapolation to a consistent, clearly defined y‐intercept. Neither environment, surface preparation, nor the rate of applied stress was a factor in the fracture stress versus branch, mirror, or mist size relationships.

Fracture of a borosilicate glass under triaxial tension

“…where A, the ''mirror constant'' is characteristic of the material, independent of the test environment (Quinn, 1999) and, in the case of borosilicate glass, independent of temperature, at least in the range À150°C -85°C (Shi et al, 1989). Quinn (1999) used various test conditions to obtain a large range of mirror sizes in a crown borosilicate glass and observed that a modified version of Eq.…”

“…Quinn (1999) used various test conditions to obtain a large range of mirror sizes in a crown borosilicate glass and observed that a modified version of Eq. (12) with a threshold stress, r t , fits better the data:…”

“…Test The measurement of fracture mirror sizes is considered by Mecholsky (1995) and others (Shi et al, 1989;Quinn, 1999) as a reliable tool to evaluate the stress at fracture, r f , in a brittle material, since an empirical relationship between the latter and the radius of the mirror-mist boundary has been established based on a large number of experiments:…”

“…15 shows a plot of r f versus 1/ p R m . Like in the work ofQuinn (1999) the plot is linear, with a slope of 2.66 MPa p m, but does not intersect the origin. The y-intercept is 13.6 MPa, which thus corresponds to the threshold r t .…”

Spontaneous Fracture in Thermally Strengthened Glass - A Review and Outlook

“…It should be used in describing the relation between the fracture stress and the mirror radius [81]. K M is also called the mirror constant and sometimes denoted A M [23,82,83]. The fracture mechanics description of the relation of the fracture stress and the mirror radius should therefore be as described in Equation 1 [83] where σ f is the fracture stress, C M is the mirror radius and K M is in the range of 1.9 to 2.1 MPa•m ½ [23].…”