THE USE OF CHEVRON V-NOTCHED SPECIMENS IN FRACTURE TOUGHNESS DETERMINATION

Abstract

The relationship between the plane strain fracture toughness, KIC, obtained in accordance with the ASTM E399–78 testing standard and the maximum load, Pmax, determined from chevron–notched short bar specimens, 3–point bend rectangular specimens and 3–point bend round bar specimens expressed as KIC = A Pmax, where A is a geometric constant, has been investigated. High strengtn Assab 25X steel of 0.32% C was used. The specimens were tempered from the as–quenched state to 500°C. Although the values of A for a given specimen geometry were found to be roughly constant from 200°C to 400°C, its values at the other tempering temperatures were much larger. Notwithstanding the difference in the geometry of the chevron notch, A for a given heat treatment condition remained essentially invariant for both the 3–point bend specimen geometries throughout the entire range of tempering temperatures studied. However, no relationship could be discerned from the values of A obtained using the short bar and the rectangular bend specimens although both had identical notch geometry. Except at 500°C tempering condition, fracture toughness values calculated for the short bar specimens were found to be generally in good agreement with those obtained from the ASTM test standard when rising crack growth resistance curve was taken into consideration.