Effects of plastic relaxation on the semi-brittle fracture of 〈100〉 oriented tungsten single crystals

Electric spark discharge techniques developed by Hull, Beardmore and Valintine (1965) have been used in the study of 〈100〉 oriented tungsten single crystals at 77 K. Dislocation etch pitting techniques are used to assess the extent of plastic relaxation at the tip of stopped cracks as well as those that subsequently propagated under load. A model for the prediction of fracture stress values is proposed that incorporates the effects of crack tip plastic relaxation. Using this model, the value of fracture ‘surface energy’ for {100} planes in tungsten is found to be ∼3000 erg/cm2.