SIZE, THICKNESS AND GEOMETRY-EFFECTS ON TRANSITION FRACTURE

Transition fracture toughness was studied to look at the effect of siz e, thickness and geometry. Size effects were studied on six sets of da ta collected from the literature in which proportionally sized compact specimens of various steels were tested. Thickness effects were studi ed on tests of compact specimens of constant thickness and varying pla nar dimensions. Tests were conducted on a pressure vessel steel at a c onstant thickness of 20 mm where planar dimensions were increased so t hat thickness constraint was decreased. Geometry effects were studied on tests from a center cracked tension specimen geometry. Initially al l of the data from the tests were included in the study; none were eli minated due to a size or other validity requirement. Then two validity requirements, the K-kappa and the Anderson-Dodds size requirements, w ere imposed to study their effect on the data. The results showed that a smaller specimen size does not necessarily result in higher toughne ss. Rather, the smallest size often gave the lowest values of toughnes s. Loss of thickness constraint tended to increase toughness but not v ery much; it may not increase at all at the lower temperatures. The ce nter cracked tension geometry appeared to have a lower constraint. The se specimens showed an increase in toughness which is similar to that observed on a compact specimen for a change of temperature from -90 de grees C to -60 degrees C. Imposing a size validity requirement elimina ted much of the fracture toughness data in the transition and influenc ed the distribution of data. Validity size criteria should be avoided if possible, especially for a scientific study.