Determination of dynamic elastic-plastic fracture toughness by a drop-weight impact testing machine.

Abstract

A drop-weight type tensile testing machine has been designed and built. The testing machine elementally consists of a drop weight, a loading rod, and a stopper. A test is performed by dropping the weight on the stopper. The use of the stopper which has an oil damper within results in dampening the initial shock waves, and tensile speed as high as a quarter of falling speed of drop weight is obtained. Using this stopper, the measured data can be similarly analyzed as those in a static test.Load-line displacement is estimated from the crack opening displacement on the front surface of the specimen. The estimated load-line displacement was confirmed to be in good agreement with the load-line displacement measured directly in a static test. Furthermore, the onset of crack propagation can be detected by an ultrasonic method. Using these methods, dynamic elastic-plastic fracture toughness JId of a nodular cast iron was determined at the stress intensity rate KI of less than 1.9×105 MNm–3/2 s–1. The specimens used were 25 mm-thick CT specimens. In the upper-shelf fracture toughness region, JId of nodular cast iron increases with increasing KI.