Artificial healing of cone cracks in glass

Abstract

Hertzian cone cracks formed by indenting brittle solids with a hard sphere have previously been shown to close imperfectly as the indenter load is released; accordingly, there is little tendency for air-formed cone cracks to heal naturally. I n the present instance partial healing has been achieved artificially by subjecting residual cone cracks in glass to closureenhancing treatments. Observations of the crack geometry both during and after loading suggest that healing occurs only a t localised regions of intimate contact across the crack interface. Possible mechanisms for the healing process are discussed. Es wurde schon friiher gezeigt, daB Hertzsche Kegelspriinge, die durch Driicken eines sproden Festkorpers mit einer harten Kugel entstehen, sich nur unvollstiindig schlieBen, wenn die Stempellast gelost wird; demgemaB besteht nur eine geringe natiirliche Ansheiltendenz fur an Luft gebildete Kegelspriinge. I m vorliegenden Falle wurde partielle, kunstliche Ausheilung verbliebener Kegelspriinge in Glas durch eine den VerschluB fordernde Behandlung erreicht. Beobachtungen der Sprunggeometrie wahrend und nach der Belastung weisen darauf hin, dal3 Ausheilung nur in lokalisierten Bereichen mit unrnitt.elbarem Kontakt iiber die Sprungzwischenflache stattfindet. Mogliche Mechanismen fur den Aus-hcilprozeB werden diskutiert.

Experimental and numerical study of crack healing in a nuclear glass

“…Literature on low-temperature crack healing in glasses Cheeseman and Lawn (1970) achieved partial healing of Hertzian cone cracks in an unspecified type of glass, by low temperature annealing (200°C) in nitrogen and even at room temperature, under the mere effect of a compressive stress. Widerhorn and Townsend (1970) reported a more complete room temperature healing of cracks induced in sodalime-silica glass by mechanical shock in a superdry nitrogen atmosphere than that of cracks grown in air.…”

Viscous healing of Vickers indentation–induced cracks in glass

“…Studies on crack healing are therefore of continuous interest. [13][14][15] Most studies have been based on the Vickers indentation technique, which allows radial cracks of limited size to be easily reproduced and readily described in terms of their length, L, width, W, and depth, D. [16][17][18] The viscous healing process of radial cracks was observed to include several stages: crack tip blunting, 19 rounding of the crack edges, widening 20 or grooving of radial cracks to form oval cavities or rounded open valleys, and their smoothing and filling. 21 Such phenomena have been reported for borosilicate, 22 magnesium-calcium silicate, 23 and soda lime silicate glasses.…”

“…Studies on crack healing are therefore of continuous interest 13–15 . Most studies have been based on the Vickers indentation technique, which allows radial cracks of limited size to be easily reproduced and readily described in terms of their length, L , width, W , and depth, D 16–18 .…”