G. Gouadec et al., Raman study of Hi-Nicalon-fiber-reinforced celsian composites: II, residual stress in fibers, J AM CERAM, 84(5), 2001, pp. 1136-1142
Band shifts in Raman spectra were used to assess, on a microscopic scale, t
he residual strain existing in Hi-Nicalon silicon carbide fibers reinforcin
g celsian-matrix composites, Uncoated as well as p-BN/SiC-coated and p-B(Si
)N/SiC-coated Hi-Nicalon fibers were used as the reinforcements. We unambig
uously conclude that the fibers were in a state of compressive residual str
ess. Quantitative determination of the residual stress was made possible by
taking into account the heating induced by laser probing and by using a re
ference line, of fixed wavenumber, We found fiber compressive residual stre
ss values between 110 and 960 MPa, depending on the fiber/ matrix coating i
n the composite, A stress relaxation-like phenomenon was observed at the su
rface of p-BN/SiC-coated Hi-Nicalon fibers whereas the uncoated or p-B(Si)N
/SiC-coated Hi-Nicalon fibers did not show any stress relaxation in the cel
sian-matrix composites.