Effect of Dynamic Loading Rates on Cleavage Fracture Toughness Properties of Steels

Abstract

The effect of dynamic loading on cleavage fracture toughness of ferritic steels is an important factor in structural integrity assessments. To address this issue, statistical analyses were carried out on a cleavage fracture toughness database obtained for a range of loading rates for deeply cracked 10mm thick pre-cracked Charpy V notch specimens and nominally 25mm thick compact tension specimens. Additional analyses were performed on shallow cracked three point bend specimens, 25mm thick, to establish whether the effect of dynamic loading rates on cleavage fracture toughness varies with crack to width ratio. The statistical analyses employ a model in which logarithm of cleavage fracture toughness varies linearly with temperature. The logarithm of cleavage fracture toughness is initially modeled as being linearly dependent on the loading rate but the analyses show that a non linear dependence is more appropriate. The effect of specimen thickness on cleavage fracture toughness is found to be negligible at dynamic loading rates when displacement rate is used as a variable in the analyses. The displacement rates applied during testing were converted into stress intensity rates and statistical analyses were performed to establish the dependence of cleavage fracture toughness on stress intensity rate.