Study on High Temperature Impact Fracture Toughness of Toughened Ceramics

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Ceramic Materials have significant features as compared with metallic alloys, i. e., high temperature strength, hot-corrosion resistance and oxidation resistance much greater than those of metallic alloys. However, there is problem which is come from their brittle or non-ductile nature. Therefore, we need a knowledge of impact fracture toughness at elevated temperatures to use ceramics as hot-section components. The purpose of the present project is to investigate a simple method to determine the impact fracture toughness of ceramics materials at high temperatures. The research works are summarized as follows :(1) An inverse method in which the impact load was estimated from the impact response of the body was studied. in order to overcome the difficulties in obtaining the stable data due to noise contained in data, a method based on the Wiener filtering theory was presented.(2) methods to measure the impact fracture toughness of ceramic materials at elevated temperature were examined and the usefulness of the one-point-bend test was demonstrated.(3) Simple formulae of the J-integral for the one-point bend specimens has been derived by applying a plastic zone correction to the formulae of the dynamic stress intensity factors.(4) Impact fracture toughness tests were carried out on an alumina and alumina-zirconia composite at temperatures up to 1200ﾟC. It was found that the fracture toughness values of both materials increased with the loading rate, and that of alumina was almost constant at temperature up to 1200ﾟC, while that of alumina-zirconia composite decreased with test temperature.(5) Impact fracture toughness tests were performed on alumina-aluminum composite materials. It was found that the fracture toughness values of the tested materials decreased with testing temperature while increased with the loading rate.