Mapping of failure process in whisker-ceramics composites using acoustic emission parameters

Abstract

Concerning the strengthening mechanism of brittle materials, the incorporation of whiskers to brittle monolithic materials has been considered to be one of the promising ways of improving the mechanical properties of the materials. Recently studies on the failure process of whisker-reinforced glass, glass ceramics and ceramics revealed that the strength and toughness of these materials increased significntly when an adequate amount of whisker was incorporated into the monolithic brittle materials [1-4]. Such an improvement of the mechanical properties arises from various microscale toughening mechanisms, such as microcracking, crack branching, constraining effects of the whisker, etc. Macroscopically, the toughening mechanisms often appeared as a form of non-linearity in the load-displacement records. To understand microcrack-related toughening mechanisms of whisker-reinforced brittle materials, a clear understanding of microcrack-related macroscale nonlinear behaviour is very important. The acoustic emission (AE) technique provided very useful tools to determine microscale failure mechanisms of ceramics [5] and ceramics matrix composites [6]. However, to use the full potential of AE results, some modifications of the data obtained would be required. This letter reports preliminary experimental results of the mapping of the microfailure process of the composites using an AE parameter-mapping technique. SiC whisker-reinforced sodium borosilicate glass (Corning Glass Works 7740) (SiCw/glass), SiC whisker-reinforced A1zO3 (SiCw/A1203), and unreinforced sodium borosilicate glass were selected at test materials. The composite materials were obtained by hot-pressing a mixture of SiC whisker (Tateho Chemical Industries Co. Ltd, Japan) and powder of the matrix material. The volume fraction of the both composites was fixed at 0.2 and the whisker was nearly three-dimensionally randomly oriented in the matrices. The processing method of the composites was the same as in [6]. The three-point bend strength (orB) and critical stress intensity factor (Krc) of the materials used were