The thermomechanical fatigue (TMF) response of a unidirectional SCS-6/
Timetal 21S composite is determined using the unified inelastic-strain
model of Bodner and Partom for the matrix response. The Bodner-Partom
model captures the strain-rate sensitivity and time-dependent behavio
r of Timetal 21S for a wide range of temperatures (25-815-degrees-C) a
nd strain rates (10(-3)-10(-7) s-1). For nonisothermal conditions, spe
cial terms are added to the inelastic-strain-rate expressions that acc
ount for changes in the temperature-dependent material parameters with
changing temperatures. This viscoplastic model is implemented into th
e finite element package ADINA through user-defined subroutines. The u
nidirectional composite is represented by a concentric cylinder geomet
ry formulated from axisymmetric elements. Numerical simulations predic
t an increase in residual stresses as the cooling rate from consolidat
ion is increased. The composite response under in- and out-of-phase TM
F loading compares well with experimental measurements. Compared to ou
t-of-phase TMF, in-phase TMF shows considerably more ratchetting. For
in-phase TMF, both the response and fatigue lives are more sensitive t
o variations in fiber-volume fraction than the out-of-phase case. The
numerical model is consistent with the experimental observations in th
at the fibers control the in-phase TMF behavior, while the matrix cont
rols the out-of-phase TMF behavior.