Acoustic Emission Informed Assessment of Damage In Sicf/Sic CMC Via In Situ X-Ray Computed Tomography Under Monotonic And Cyclic Loading Conditions

Abstract

The adoption of ceramic matrix composites (CMCs) in high performance engineering applications requires a comprehensive understanding of damage initiation and progression. Matrix crack onset and saturation are key damage states associated with continuous fibre-reinforced SiCf/SiC variants, and previous studies have successfully exploited acoustic emission (AE) monitoring to identify the corresponding stresses at which these occur. In this study, lab-based in situ X-ray computed tomography (XCT) was employed as a visual verification of the internal damage evolved at those established stress levels.

An initial specimen was inspected at five equally spaced stress conditions during an increasing monotonic loading ramp. A second specimen was subjected to ‘stepped’ fatigue loading, where the cyclic peak stress corresponded to the same five static stress levels. A third specimen experienced constant amplitude fatigue at the highest stress condition for the equivalent number of total cycles. The macro-scale specimens incorporated at least one unit cell of material, allowing the damage to interact with multiple 0/90° fibre tows and plies. Matrix crack density and spacing data were plotted against increasing stress and/or number of cycles, providing good agreement with the established AE onset and saturation stresses. The need for integrated XCT and AE experiments for damage correlation was highlighted.