Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : December 22, 2018 - December 24, 2018
It is well known that the elastic-plastic fracture toughness for a cyclic load was smaller than that for a monotonic load. This study was aimed at investigating reason for the reduction in the fracture toughness of carbon steel due to application of a cyclic load. First, fatigue crack growth tests were conducted using plate specimens for a fully-reversed load of various stress amplitudes. The crack growth equation, in which the effective strain intensity factor range was quoted as the crack driving force, was derived to predict the crack growth up to 0.5 mm/cycle. Then, using the same material, the fracture toughness tests were conducted for monotonic and cyclic loading conditions. The plate specimen were used to enable the nominal strain to be measured during the tests. It was shown that the J-R curve and J0.2 value were reduced due to application of the cyclic load. In order to investigate the reason why the fracture toughness reduction, it was assumed that the ductile crack extension was enhanced by the cyclic load. It was concluded that the reduction in the fracture toughness due to application of the cyclic load was attributed to the fatigue crack growth. The fatigue crack growth was brought about not only by the unloading cycles but also by the monotonic loading. The growth of the ductile crack extension was well predicted by considering the fatigue crack growth and crack tip blunting.
