Monitoring of Matrix Breaking in Composite
Ultrasonic guided wave propagation in composite materials has been investigated theoretically and experimentally for many years.
It was found that symmetric (S0) Lamb wave has much lower attenuation than asymmetric (A0) Lamb wave in composite material.
Much research was performed to make a transducer generate SO-mode wave. However, the piezoelectric and PVDF transducers can
efficiently generate AO-mode wave in composite, but they are not good for generating S0 Lamb wave.
Recently, Southwest Research Institute® (SwRI®) scientists successfully applied magnetostrictive sensor (MsS) system to generate
and detect 80-kHz symmetric (S0-mode) Lamb wave in composite plate of 0.08-inch-thick, 1- by 2-foot IM7-6K plain weave carbon fabric.
The layup of the composite is [(0,90)/(90,0)/(0,90)/ (90,0)/(0,90)/(90,0)], and its resin is Hexcel's Hexflow RTM 6 that is a mono-component
resin already degassed, specially developed for use of the aerospace and space industries.
The photograph shows the MsS system installed to monitor a composite plate with notch defect and matrix breaking defect. The notch defect growth
was monitored, and the matrix breaking data were plotted in the below. The left, middle, and right plots show the periodically
acquired RF, the RF-differential, and video-differential waveforms, respectively. The RF- and video-differential waveforms were obtained by
subtracting the periodically acquired waveforms from the baseline waveform. The first trace is data acquired before matrix breaking, the second
trace is acquired after 1-by-1 inch matrix breaking, and the third trace is acquired after 1-by-2 inch rectangular matrix breaking. The RF- and
video-differential data showed the matrix breaking signal, and their amplitudes were increased with increment of matrix breaking area. Even though
this test was performed on a small sample, it showed the potential of structural health monitoring for detecting matrix breaking in composite material
or composite aircraft structure.