Girraj K. Bansal

On fracture mirror formation in glass and polycrystalline ceramics

Abstract Specimens of one soda-lime silicate glass and three polycrystalline ceramics were fractured at room temperature and fracture-mirror radii (r) measured at the onset of crack branching or ‘hackle’. Measured radii and fracture stresses (σf) for each material obeyed the relation σf r l/2 = A, where A is a material constant. The ratio A/K ic, where K ic is the critical stress-intensity factor of a material, was, however, independent of material type. A criterion based on energy balance is presented to show that the hackles, which bound the fracture mirror, form at a fracture velocity approximately equal to one-third the elastic wave velocity in a brittle material.

Effects of moisture-assisted slow crack growth on ceramic strength

An investigation was made of strength degradation caused by moisture-assisted slow crack growth of surface flaws in two dense polycrystalline ceramics. Specimen sizes were varied. The observed strength degradation of each ceramic was predictable usingKIC as a material property in fracture-mechanics relations, suggesting that the only material variable involved was critical flaw size. The strength of one of the ceramics in water decreased significantly with increased specimen size, but its Weibull modulus was essentially unaffected by specimen size and slow crack growth.

Comments on ’’Griffith fracture equation—An experimental test’’

The Griffith equation was originally derived for relatively sharp cracks. The equation can also be applied to round cracks provided a characteristic fracture surface energy value associated with the particular crack‐tip radius is used.