Fatigue tests of notched and smooth specimens of alumina particulate filled epoxide composites were conducted and the effects of alumina dispersion on the fatigue strength, the fatigue limit, the fatigue fracture process, the final fracture condition in fatigue and the inherent flaw size were studied. The alumina volume fractions Vf used in this experiment were 13% and 37%. As a basis of comparison epoxy resin with no filler was also tested.
The results obtained are summarized as follows.
(1) Alumina dispersion had both (a) reinforcement effect and (b) flaw dispersion effect from the viewpoint of fatigue strength. The fatigue strength of the smooth specimens with 13% Vf reduced from the level of epoxy resin, and the strength recovered when Vf increased to 37%.
(2) The fatigue strength of the notched specimens was improved as alumina Vf was increased.
(3) The inherent flaw size became longer by the alumina dispersion and the composite became less sensitive to surface flaws than the epoxy resin.
(4) The fatigue limit of the composites seems to be determined by the condition that microdebond of particle/matrix interface in surface layer does not propagate. A model of fatigue limit was proposed based on the observation and the fatigue limit stress level vs. Vf relation was satisfactory explained.