MEASUREMENT OF FRACTURE TOUGHNESS AT HIGH LOADING RATE AND LOW TEMPERATURE

ABSTRACT The influences of loading rate and temperature on fracture initiation properties of a carbon steel (JIS-S45C) and an aluminum alloy (Al 7075-T651) were investigated at the rates of stress intensity factor from 4×10 -1 to 5×10 6 MPa√m/s over a range of temperatures between 4.2 and 300 K. For high rate fracture test, the dynamic fracture toughness was measured accurately by using the elastic response analysis, where the dynamic stress intensity factor and the transmitted stress through the precracked section of the specimen were predicted by superposing the step response function under the condition of no crack extension. For S45C, the fracture toughness decreased with increasing loading rate and decreasing temperature. On the other hand, for Al 7075-T651, the fracture toughness increased at extremely high loading rate or low temperature.