Abstract
This chapter discusses a technique for rapid and cost-effective determination of stress intensity factor (KI) and fracture toughness (KIC) using small circumferential notch tensile (CNT) specimens. Ahead of the notch of the CNT specimen, a uniform precrack is developed by subjecting the specimen to a controlled fatigue in a bending-rotating set-up. The precracked CNT specimen is then subjected to a constant load, until the specimen fails. KIC is determined by correlating the stress intensity factor KI with one of the crack propagation parameters such as crack-growth velocity or time-to-failure. One of the critical issues in determination of KIC by CNT method is the possible effect of the eccentric fatigue crack and the ligaments produced by the rotating bending fatigue crack machine of specimens. CNT is the smallest possible specimen that can produce valid plane strain crack loading conditions. KIC values determined using CNT specimens are claimed to be within –3% and +3% of the data generated using the ASTM compact tension (CT) specimen. In tests conducted earlier at Monash University, acceptable results have been achieved using 9.5 and 15 mm diameter CNT specimens, whereas for the same material, KIC determination, using standard CT specimens, requires widths up to 80 mm.
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