Fracture-strength studies on annealed and tempered glasses under dynamic conditions

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Abstract
Artificially induced surface flaws have been used to study the dependence of initial stress intensity factor on flaw size and loading rate for annealed soda lime and thermally toughened alumino-silicate glasses in water and silicone oil environments. Examination of the fracture surface has revealed that the ratio of the radius of the mirror region, rs, to the radius of the initial flaw size, c 1, on the tensile surface varied from 55 to 8, depending on the initial flaw size, the deflection rate and the ambient environment. Simple relationships between rs and r b, the radii of the mirror zone into the bulk of the sample, at the instant of ‘branching’, have been derived. These relationships, in good agreement with experimental observations, show that for annealed soda-lime glass ‘branching’ will only occur into the bulk for values of rs less than a tenth of the sample thickness; moreover, the ratio rb/rs lies between one and two. For toughened glasses the ratio rb,/rs is less than or equal to unity.

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