Crack initiation determination for thee-point-bend specimens

The paper deals with the problematic of determination of the crack initiation for three point bend specimens during fracture toughness test of materials in the upper transition and upper shelf region. In the presented study various published methods as Double Clip Gauge Method, Strain Near to Crack Tip Measurement method, Double Displacement Method, Compliance Changing Rate Method, Stretch Width Zone measurement were applied together with the methods using the crack extension vs. crack mouth opening displacement and force vs. displacement for the crack initiation determination. Blunting line based evaluations were also performed and all results were compared. The investigation was carried out on five different steels.