Rw. Neu et al., CYCLIC BEHAVIOR OF UNIDIRECTIONAL AND CROSS-PLY TITANIUM MATRIX COMPOSITES, International journal of plasticity, 12(3), 1996, pp. 361-385
Relatively simple and efficient micromechanical models are used to obt
ain the uniaxial response of SCS-6/Timetal 21S with [0](4) and [0/90](
s) laminates when subjected to isothermal and thermomechanical fatigue
(TMF) loadings. Features of the modeling that are required to obtain
the accurate deformation behavior for this class of materials under th
ese loadings are highlighted. To this end, a comparison is made betwee
n the concentric cylinder model and the uniaxial stress model for repr
esenting the [0] laminate. The axial stresses from the two models are
very similar under mechanical loading. The greatest differences appear
under thermal loading alone. The differences on the composite respons
e between a lime-independent elastic-plastic and a viscoplastic matrix
constitutive model are also examined. The latter is based on the Bodn
er-Partom unified constitutive model. The [0/90] laminate is treated b
y adding a parallel element with smeared [90] ply properties to the [0
] model and invoking axial strain compatibility as well as stress equi
librium. The proposed constitutive law for the [90] ply includes both
matrix viscoplasticity and fiber/matrix separation damage and is based
on damage mechanics concepts. The effect of cyclic frequency on TMF b
ehavior is examined. The in-phase TMF life is shown to be very sensiti
ve to frequency due to the relaxation of matrix stress and the attenda
nt increase in fiber stress.