Transverse behavior and acoustic-emission analysis of titanium metal-matrix composites under tensile loading

The transverse behavior of 1140+/Ti-6-4 and SCS-6/Ti-beta 21s composites has been investigated using conventional tensile testing in air. Acoustic emission (AE) has also been used to assess and to locate the position of damage. Few AE events can be detected in 1140+/Ti-6-4 composites below the stress of similar to 250 MPa, whereas for SCS-6/Ti-beta 21s composites, AE events are found almost immediately on loading. Many AE events of high energy were detected over a range of stresses, which appear to be associated with debonding. Continuous AE events are obtained with an increase of stress, and this suggests that debonding is an incremental process: a ring crack (formed by premature debonding at the surface) penetrates into the depth along interface "tubes." The peak energy of AE events obtained in SCS-6/Ti-beta 21s composites is similar to 650 arbitrary units, which is approximately 4 times that obtained in 1140+/Ti-6-4 composites. Distinct AE events have also been deduced to correspond to cracking of carbon coating layers and fiber/matrix reaction products. A change of fiber volume fraction from 8 to 21 pct for the 1140+/Ti-6-4 composites has no effect on the characteristics or distribution of AE events received.