Abstract
An attempt to evaluate the fracture toughness of 5083 and 7075 alloys is made by observing the stretched zone (SZ) formed ahead of pre-crack in a Charpy test. The width and height of the stretched zone (SZW and SZH) analyzed stereographically from fracture toughness. Twice SZH corresponds to the critical crack tip opening displacement (CTODc). The plane strain fracture sunface. (K1c) estimated from CTODc measured is in good agreement with the valid K1c already informed. The fracture toughness is sufficiently appreciable by measuring SZ even in small size test pieces. A proportional relation is found between SZW and SZH. Plastic blunting of crack tip advances up to 60 to 70° in a particular direction.
