The tensile fatigue characteristics of graphite/glass/epoxy hybrid composites were investigated before and after exposure to various high humidity environments. Accelerated aging treatments of 98 percent RH and 120°F were applied both continuously for 500 and 1000 h and coupled with a 350°F thermal shock after −67°F low temperature exposure. This latter thermohumidity cycle was applied for 500 h total exposure time. Cyclic loading tests showed that degradation due to the moisture and thermohumidity conditioning treatments was in‐most cases small. Some bereficial behavior of the humidity exposure was also noted. The hybrid fatigue characteristics both before and after exposure were a blend of the nearly flat advanced fiber composite S‐N behavior and the highly curved glass fiber composite S‐N behavior. This was attributed to a mixture of failure modes for the hybrid system.

Fiber reinforced resin composites have been extensively used in marine applications. These materials offer both weight savings and improved performance over conventional structural materials. There exists an area of concern in the incorporation of these materials into marine construction programs relative to their fatigue resistance. Cyclic stressing has always been an ever-present part of the marine environment.A coordinated mechanical fatigue testing program and microscopic analysis is described which includes the effect of moisture on fatigue performance. This is supplemented with a step by step description of the fatigue crack penetration into the composite.

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The static mechanical properties of S-glass/high-strength graphite/ epoxy hybrid composites were investigated before and after exposure to high humidity for 1000 h. Graphite-to-glass ratios of 0, ∞, 1, and 2 were studied. Both unidirectional (0 deg) and quasi-isotropic fiber orientations were studied. In general, the stress cycling caused a decline in the static tensile strength, an increase in the Poisson's ratio, and no change whatever in the elastic modulus of the base and hybrid composites. The addition of moisture did not result in a basic alteration in the behavior of the hybrid or base composites after stress cycling.

This paper deals with the determination of the stress distribution at the fillet of a flange attached internally to a hollow cylinder. A load parallel to the axis of the cylinder and of variable eccentricity acts on a bearing plate which rests on the flange. The strains are measured by means of electrical resistance wire strain gages. The ratios of the mean cylinder diameter to the cylinder wall thickness and of the mean cylinder diameter to the flange thickness are varied. The principal stresses at the fillet are given as functions of these parameters. The experimental results are compared with the stresses calculated on the basis of an approximate theoretical solution for both an axial and an eccentric load.