A Nicalon-fiber-reinforced hybrid composite with a matrix of barium magnesi
um aluminosilicate (BMAS) glass with silicon carbide whiskers was subjected
to thermal shock from elevated to ambient temperatures. The combination of
SiC whisker and BMAS glass resulted in a hybrid matrix with a lower therma
l expansion than that of the fibers, inducing tensile stresses in the fiber
upon thermal shock. This stress state resulted in microstructural damage i
n the form of fiber cracking and cracking along the fiber/matrix interface,
as opposed to the conventional matrix cracking which is typically observed
in ceramic-matrix composites. Significant damage in the composite was only
observed after three thermal shock cycles. Flexural resonance measurements
, used to evaluate thermal shock-induced changes in Young's modulus, showed
a reduction in modulus that correlated well with the onset of microstructu
ral damage. Finally, fiber push-out tests, performed to evaluate changes in
fiber/matrix interface strength after thermal cycling, indicated a slight
decrease in interfacial strength, which was attributed to recession of the
carbon-rich fiber surface during thermal shock. (C) 2001 Elsevier Science L
td. All rights reserved.