Characterizing environment‐dependent fracture mechanisms of ceramic matrix composites via digital image correlation

Abstract

Here, we unveil a methodology for a novel assessment of the fracture mechanics of SiC/SiC ceramic matrix composites enabled by in situ stereoscopic digital image correlation to quantify in-process flexural strain and crack opening displacement measurements. This technique isolates individual cracks on the composite surface as discontinuities in the spatial displacement field and correlates key fracture characteristics with the flexural strain of composite specimens during coupled four-point bend / hermeticity testing. Fracture was observed along the specimen length, originating at the tensile underside and propagating around the circumference of the tubular specimens with generally uniform spacing. Multiple specimens were also tested after heat treatments to 1200°C in open air, in vacuum, and in helium for 48 h to evaluate the environmental effects on the fracture mechanisms of SiC/SiC composites, which revealed degradation of flexural properties after treatment in open air resulting in brittle failure. Indentation-based fracture toughness measurements were performed, which confirmed a 25% reduction in toughness after open air heat treatment relative to the other heat treatments. This assessment indicated that significant oxidation may occur within the composites from these heat treatments and suggested that further protection of the composites may be necessary for high-temperature applications.

The Analysis of Stress Raisers Affecting the GFRP Strength at Quasi-Static and Cyclic Loads by the Theory of Critical Distances, Digital Image Correlation, and Acoustic Emission

“…A description of the types of damage to these materials using the optical CCI method is found in several other foreign works [41,42]. The work of Clifton H. Bumgardner et al [43] studies the failure mechanisms of composites with a ceramic matrix. The authors noted the influence of the correlation processing on the accuracy of the results obtained during the CCI tests.…”

Stress rupture of SiC/SiC composite tubes under high‐temperature steam

“…2,3 SiC-based materials, in particular continuous SiC-fiberreinforced-SiC matrix (SiC/SiC) composites, are among the candidate alternative materials for LWR fuel cladding and certain core structures, such as boiling water reactor channel boxes, to enable accident-tolerant fuel and accident-tolerant cores because of their inherent advantages of low neutron absorption, irradiation resistance, high-temperature capability, and slow kinetics of oxidation reactions. 1,3,4 Recent research and development of SiC ceramics and composites have advanced technologies for manufacturing small diameter thin-walled tubular structures, 5 understanding of the thermomechanical behavior of the component under normal and off-normal operating conditions, [6][7][8] and prediction of material performance by high-fidelity modeling. 9,10 Current SiC/SiC composite cladding designs include an outer monolithic SiC layer, in part, to maintain hermeticity and to increase resistance to coolant corrosion in normal operation and to steam oxidation in a loss-of-coolant accident (LOCA) scenario.…”