TEMPERATURE-DEPENDENCE OF THE MICROSCOPIC CLEAVAGE FRACTURE-STRESS

The microscopic cleavage fracture stress sigma(f)* which could be responsible for dramatic failure is commonly seen as a temperature independent material property. But a dependence on temperature was found in several former investigations. In this work new studies on cleavage fracture with low carbon steel C 10 were performed. The stress sigma(f)* = sigma(yy)(max) was determined with double-edge notched tensile (DENT) specimens at different temperatures and various crosshead speeds. In addition tests were made with four-point bend specimens (SENB4) according to Griffiths and Owen. A significant influence of temperature on the microscopic cleavage fracture stress was found. The explanation for this result is seen in terms of the thermal activation of dislocation movement, which is needed to produce the critical conditions for fracture. As temperature independence is proposed from the ''Local Approach'' a check up of this procedure is given and limitations of the ''Weakest Link-model'' are shown.