Characterisation of acoustic emission signals during fracture and fatigue of SiC fibre reinforced titanium alloy composites

Acoustic emission (AE) signals generated during the fracture and fatigue of continuous SiC fibre reinforced titanium alloy composites (SCS-6/β21S, SCS-6/Ti–6Al–4V, and SM1240/Ti–6Al–4V) have been measured, and AE parameters have been correlated with microfracture processes. The amplitude distributions of AE signals in both fracture and fatigue were found to have distinct peaks at ∼90 dB with reference to 5 μV at the output of the sensor used. These high amplitude AE signals were confirmed to correspond to fibre fracture by direct optical observation, and deduced from sharp crack growth rate excursions measured by an electrical potential difference method. Although the distribution of lower amplitude signals (<70 dB)changed progressively during loading to fracture, it was difficult to distinguish microfracture processes precisely since several potential fracture modes overlap in the amplitude distribution. The ratio of the peak amplitude to the rise time of the AE signals could, however, be classified into several categories, and this method of analysis is most useful in discriminating between fibre/matrix debonding events and fibre sliding events. The present work suggests that the AE technique is useful for damage evaluation in these composites, in general, and in particular it can quantify fibre fracture.MST/3352