Development for Mesurment System on Impact Fracture Toughness of Ceramic Material at Elevated Temperature

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A new instrumentation system has been developed for measutement of the impact fracture toughness of ceramic materials at the elebvated temperature up to 1200゜C by impact test with free ends bend specimenone-point-bend specimen). The specimen is of Charpy type(6mm widht, 8mm height and 50mm length) and hanged in an infrared image furnace by a couple of thin ceramic threads cemented onto the end surface of the specimen. Thus the heat counduction that usually take place through support structure can be avoided or kept to a minimum. The impact force id proveded by a falling steel cylinder of 6mm diameter and 1500mm length with a pair of semiconductor strain guages cemented onto a cylindrical surface to measure the stress wave history and hence to determine the impact force. Since the thin threads are thought to be broken at the moment of impact, the specimen is supposed to fracture with both ends free from constraint.A simple formula has been detived for determining the dynamic stress intensity factor from the measured impact force. A microcomputer is used for processing the experimental data. A series if impact tests has been performed with drop-height increased gradually and the impact fracture toughness was determined from the test data of the minimum drop-height that caused specimen fracture. The impact fracture toughness values of the ceramic specimens made of Silicon carbide(SiC), Silicon nitride(I_3n_4) or partially stabilized zirconia(ZrO_2) were measured and the usefulness of the present system has been demonstrated.