Neal Gordon

Acoustic emission and electrical resistance were monitored for SiC-based laminate composites while
loaded in tension and correlated with damage sources. The ceramic matrix composites were composed of
Hi-Nicalon Type STM fibers, a boron-nitride interphase, and pre-impregnated (pre-preg) melt-infiltrated
silicon/SiC matrix. Tensile load-unload-reload or tensile monotonic tests were performed to failure or to
a predetermined strain condition. Some of the specimens were annealed which… Show more

Acoustic emission and electrical resistance were monitored for SiC-based laminate composites while
loaded in tension and correlated with damage sources. The ceramic matrix composites were composed of
Hi-Nicalon Type STM fibers, a boron-nitride interphase, and pre-impregnated (pre-preg) melt-infiltrated
silicon/SiC matrix. Tensile load-unload-reload or tensile monotonic tests were performed to failure or to
a predetermined strain condition. Some of the specimens were annealed which relieved some residual
matrix compressive stress and enabled higher strains to failure. Differences in location, acoustic frequency
and energy, and quantity of matrix cracking have been quantified for unidirectional and cross-ply type
architectures. Consistent relationships were found for strain and matrix crack density with acoustic emission
activity and the change in measured electrical resistance measured at either the peak stress or after
unloading to a zero-stress state. Fiber breakage in the vicinity of composite failure was associated with
high frequency, low energy acoustic events. Show less

Ceramic matrix composites (CMC) composed of Hi-Nicalon Type S™ fibers, a boron-nitride (BN) interphase, and pre-impregnated (pre-preg) melt-infiltrated silicon / silicon-carbide (SiC) matrix have been studied at room-temperature consisting of unidirectional and cross-ply laminates. Quasi-static, hysteretic and uniaxial tensile tests were done in conjunction with a variety of temporary, laboratory-based material health-monitoring techniques such as electrical resistance (ER) and acoustic… Show more

Ceramic matrix composites (CMC) composed of Hi-Nicalon Type S™ fibers, a boron-nitride (BN) interphase, and pre-impregnated (pre-preg) melt-infiltrated silicon / silicon-carbide (SiC) matrix have been studied at room-temperature consisting of unidirectional and cross-ply laminates. Quasi-static, hysteretic and uniaxial tensile tests were done in conjunction with a variety of temporary, laboratory-based material health-monitoring techniques such as electrical resistance (ER) and acoustic emission (AE). The mechanical stress-strain relationship paired with electrical and acoustic measurements were analyzed to expand upon current composite knowledge to develop a more fundamental understanding of the failure of brittle matrix laminates, their constituents, and interactions. In addition, a simple but effective method was developed to allow visual confirmation of post-test crack spacing via microscopy. To enhance fidelity of acquired data, some specimens were heat-treated (i.e. annealing) in order to alter the residual stress state. Differences in location, acoustic frequency, and magnitude of matrix cracking for different lay-ups have been quantified for unidirectional and [0/90] type architectures. Empirical results shows complex hysteretic mechanical and electrical behavior due to fiber debonding and frictional sliding of which no general model exists to capture the essence of this CMC system. The results of this work may be used in material research and development, stress analysis and design verification, manufacturing quality control, and in-situ system and component monitoring. Show less