Study on High Temperature Impact Fracture Toughness of Toughened Ceramics

陶瓷材料与金属合金相比具有显著的特点，即高温强度、耐热腐蚀性和抗氧化性远高于金属合金。然而，有一个问题来自于它们的脆性或非延性。因此，我们需要了解高温下的冲击断裂韧性，才能使用陶瓷作为热截面部件。本课题的目的是探索一种测定陶瓷材料高温冲击断裂韧性的简单方法。研究工作总结如下：(1)研究了一种由车身冲击响应估算冲击载荷的反推方法。为了克服由于数据中包含的噪声而获得稳定数据的困难，提出了一种基于维纳滤波理论的方法。(2)研究了测量陶瓷材料高温冲击断裂韧性的方法，论证了一点弯曲试验的有效性。(3)通过对动应力强度因子公式进行塑性区修正，导出了一点弯曲试件的J积分的简单公式。(4)对氧化铝和氧化铝-氧化锆基复合材料进行了在1200ﾟ℃以下的冲击断裂韧性试验。结果表明，这两种材料的断裂韧性值都随着加载速度的增加而增加。氧化铝的断裂韧性在1200ﾟC以下基本不变，而氧化铝-氧化锆基复合材料的断裂韧性随试验温度的升高而降低。(5)对氧化铝-铝复合材料进行了冲击断裂韧性试验。结果表明，试验材料的断裂韧性值随试验温度的升高而减小，随加载速率的增加而增大。

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.