The brittle fracture of [100] axis tungsten single crystals

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Abstract
Cleavage cracks have been introduced into 〈100〉 axis single crystals of tungsten by a modification of the spark discharge technique used by Hull, Beardmore and Valintine (1965). It has been possible to insert cracks in specimens at 77°K and to subsequently test these specimens in tension at 77°K without an intermediate rise in temperature. Various other test conditions have also been used. From the values of fracture stress and crack length obtained, values of the effective surface energy, γ, have been determined. In analysing the results, account has been taken of the shape of the spark crack and specimen geometry and dimensions using theoretical analyses of the stress concentrations associated with cracks. Both the temperature of crack initiation and the temperature of crack propagation were found to affect γ. For specimens in which both initiation and propagation of the cracks took place at 77°K, a value of γ = 1700 ± 300 ergs/cm2 was obtained.

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