In the case of composite materials, failure can occur due to delamination between the fibers and the matrix, prior to complete specimen failure. While this can sometimes be seen in the stress-strain curve data, it can also be detected using an acoustic emission (AE) sensor, and with much higher sensitivity. Failure criteria thus can be defined as the first indication of fiber delamination or breakage, the onset of significant AE signal, or the rise to a specific pre-defined level of AE, as shown in Figure 2.
3-point bend data showing internal failure, identified by Acoustic Emission signal, prior to sample fracture.
The optional AE sensor can be used to assess a number of composite research areas, including surface activation of the fibers, wetting chemistry of the matrix, and fiber surface roughness characteristics.