C. Kaya et al. Joumal of the European Ceramic Sociery 29(2009)1631-1639 Fig 4.(a) An optical microscopy photo of the woven mullite fibre(Nextel 720)reinforced alumina matrix composite with NdPO4 interface and(b) SEM image of the same plate indicating the detailed microstructure. tic deformation, crack initiation and growth as well as fracture while burst type AE signals are characterised by high amplitude events result in AE signals. Depending on the nature of energy pulses. Continuous type signals are caused by plastic defor- release, two types of AE response are observed; continuous and mation, diffusion controlled phase transformations, while burst burst. Continuous AE signals are characterised by low amplitude type signals are caused by diffusionless phase transformations, crack initiation and propagation. However it is difficult to use a single all-encompassing parameter to describe an experimental result uniquely. Some of the parameters used for identifica tion of source are; amplitude, energy level, duration and rise time. 3 AE has been used extensively in composite materials characterisation in order to identify the possible mechanism of fracture.4, I5 It is reported that AE sources such as matrix crack ing, fibre/matrix interfacial separation and fibre failure could be evaluated simultaneously in both metallic and ceramic matrix composites. 4-19 The elastic wave generated by the propaga tion of a crack through the solid to the surface can be recorded by one or more sensors. The sensor is a transducer that con verts the mechanical wave into an electric signal. In this way information about the existence and location of a crack can be obtained. A variety of damage mechanisms including matrix cracking, fibre debonding and fibre fracture which are common events when a ceramic composite is subjected to loading, can be identified%As damage progresses, different forms of AE sig- Fig. 5. Images of (a)tensile test specimen, (b) jig used for alignment and (c) nals are detected depending on the type of fracture mechanism aligned test specimen. acting.1634 C. Kaya et al. / Journal of the European Ceramic Society 29 (2009) 1631–1639 Fig. 4. (a) An optical microscopy photo of the woven mullite fibre (Nextel 720TM) reinforced alumina matrix composite with NdPO4 interface and (b) SEM image of the same plate indicating the detailed microstructure. tic deformation, crack initiation and growth as well as fracture events result in AE signals. Depending on the nature of energy release, two types of AE response are observed; continuous and burst. Continuous AE signals are characterised by low amplitude Fig. 5. Images of (a) tensile test specimen, (b) jig used for alignment and (c) aligned test specimen. while burst type AE signals are characterised by high amplitude pulses. Continuous type signals are caused by plastic defor￾mation, diffusion controlled phase transformations, while burst type signals are caused by diffusionless phase transformations, crack initiation and propagation. However it is difficult to use a single all-encompassing parameter to describe an experimental result uniquely. Some of the parameters used for identifica￾tion of source are; amplitude, energy level, duration and rise time.13 AE has been used extensively in composite materials characterisation in order to identify the possible mechanism of fracture.14,15 It is reported that AE sources such as matrix crack￾ing, fibre/matrix interfacial separation and fibre failure could be evaluated simultaneously in both metallic and ceramic matrix composites.14–19 The elastic wave generated by the propaga￾tion of a crack through the solid to the surface can be recorded by one or more sensors. The sensor is a transducer that con￾verts the mechanical wave into an electric signal. In this way information about the existence and location of a crack can be obtained. A variety of damage mechanisms including matrix cracking, fibre debonding and fibre fracture, which are common events when a ceramic composite is subjected to loading, can be identified19 As damage progresses, different forms of AE sig￾nals are detected depending on the type of fracture mechanism acting