A prediction method of fatigue strength of polymer composites for an arbitrary frequency, stress ratio, and temperature has been already proposed. The method is based upon the four hypotheses, (A) failure mechanism for CSR (constant strain-rate), creep, and fatigue failure is the same, (B) the same time-temperature superposition principle is valid for all failure strengths, (C) linear cumulative damage law is applicable for specimen failure under monotonic loading, and (D) fatigue strength shows linear dependence on stress ratio. In this paper, tensile CSR, creep, and fatigue strengths in the longitudinal direction of unidirectional CFRP at various loading rates and temperatures were measured by the NOL ring tests. The validity of hypotheses B, C, D, and the applicability of this prediction method were confirmed by creep tests and fatigue tests of different conditions of loading rate and temperature. It was also confirmed that the hypothesis A is not always necessarily for this prediction method through discussions.

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CFRP specimens have been tested under accelerated exposure experiments. The specimens were made of epoxy resin and unidirectional carbon fiber prepreg to the fiber orientation angles of 0, 45 and 90 degrees. In order to clarify the dependence of the exposure period on the weatherability strength, the accelerated exposure of complex testing is continued through 20 cycles and the relation of thier flexural strengths and moduli, etc. to the number of cycle are examined. The variations of flexural strengths, flexural moduli, matrix volume fractions, hardnesses, hydrolytic decomposition of polymer chains and absorbance peak of infrared spectrums with the exposure period are reported in this paper. Furthermore, the non-destructive estimation for weatherability of flexural strengths have reached the estimated values by making full use of the flexural modulus and cycle number data. It has been confirmed that the estimated results are in good agreement with the experimental ones of accelerated exposure for CFRP.

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