A fatigue model based on cumulative damage is developed for predicting the
fatigue Life of fiber-reinforced polymeric composites. This model incorpora
tes applied maximum stress, stress amplitude, loading frequency, residual t
ensile modulus, and material constants as parameters. The model is verified
with experimental fatigue data on a glass fiber/vinyl ester composite. Whi
le the specimens are exposed to air, freshwater, or seawater at 30 degrees
C, they are subjected to tension-tension stress at four levels of applied m
aximum tensile stress in each of two frequencies. Both the residual mechani
cal properties at specified loading cycles and the number of cycles at whic
h the specimens fail are measured. The results show that, for the material
used in this study, the loss in residual tensile strength and modulus in sa
ltwater is approximately the same as that in freshwater and that the fatigu
e life in these aqueous environments is shorter than that in air. Numerical
analysis is carried out to determine the material constants of the composi
te. The fatigue model agrees well with the experimental data. The model can
be used to predict the fatigue life of the polymeric composites subjected
to an applied load in different environments and to predict the residual te
nsile modulus after a number of cycles of service at a given load.