Fracture toughness tests on an aluminium alloy using a chevron notch bend specimen

Three types of Al--4Cu specimens were tested: the standard precracked three-point bend specimens of ASTM 399 and BS 5447 standards; precracked specimens of half-standard width; and the half-width specimens having a chevron notch. For the standard 50 x 25 mm precracked specimens, the K sub Q values calculated from the max. load are approx 4% over K sub IC . For the 50 x 12.5 mm precracked specimens, the K sub Q values are very close to K sub IC , but those from the max. load are approx 23% higher. For the chevron notch specimens, the load vs. clip gage displacement curves all had a double peak, as shown; consequently, for a material with a rising crack growth resistance curve, K sub IC could not be measured using chevron notch specimens.--J.J.P.