Thermal Conductance of Delamination Cracks in a Fiber‐Reinforced Ceramic Composite

Abstract

The thermal conductance of delamination cracks in a unidirectionally reinforced ceramic composite is investigated. A phase-sensitive photothermal technique is used to measure the crack conductance in situ under load. Special emphasis is given to the effects of the local crack opening displacement (␦). A crack conductance model that considers the contributions from both the air and the fibers within the crack is developed and compared with the measurements. Despite considerable scatter in the experimental data, the model adequately predicts the increased conductance that is associated with fiber bridging, as well as the overall trend that is observed with ␦.

Effects of Matrix Cracks on the Thermal Diffusivity of a Fiber‐Reinforced Ceramic Composite

“…The average values obtained from several sets of measurements are ␣ L 0 ϭ 1.35 ϫ 10 Ϫ6 m 2 /s and ␣ T 0 ϭ 1.08 ϫ 10 Ϫ6 m 2 /s. The latter value is essentially the same as the one measured via the laser-flash method in the through-thickness direction on the same material (1.04 ϫ 10 Ϫ6 m 2 /s), 5 as expected from the transversely-isotropic symmetry of the composite.…”

“…Additionally, models for thermal diffusivity of composite materials are used to elucidate the origins of the degradation in both the longitudinal and transverse diffusivities with applied stress. A complementary study on the effects of delamination cracks on the through-thickness thermal behavior is presented by McDonald et al 5…”

“…In this way, the phase lag associated with the thermocouple is removed and the resultant measurements become a function of only the thermal properties and the geometry of the test specimen. The diffusivities are then obtained by fitting the experimental data with the theoretical analysis presented in McDonald et al 5 and summarized below. When necessary, the corresponding thermal conductivities (k) are calculated in accordance with…”

“…4,5 The technique utilizes periodic heating at one point on the specimen surface and measurement of the phase lag () of the temperature with respect to the heat input at some other point. The heat source comprises a focused 0.5 W diode laser that is mounted on a precision x-y-z translation stage and modulated sinusoidally using a lock-in amplifier.…”

The characterisation and modelling of manufacturing porosity of a 2-D carbon/carbon composite

“…Since carbon fibre has extremely high-longitudinal thermal conductivity compared to air, even a few bridging fibres will make a large difference to trans-tow crack thermal conductivity. 15 Hence, this feature should be taken into account in any thermal finite element (FE) modelling of C/C composites.…”