Abstract
The fatigue strength of unsaturated polyester has been studied with respect to the effect of temperature, humidity, water absorption and its exposure to ultraviolet ray, and the following facts have been made clear.
(1) The fatigue strength of unsaturated polyester has been much affected by temperature, but hardly affected by humidity.
(2) When the relation between the work of internal friction per cycle ΔW and the number of cycles to failure N is presumed as (ΔW)a·N=K, the fatigue Strength σa is presented by
σaNα=k(E/δ)1/2,
where δ and E denote respectively the logarithmic decrement and the modulus of elasticity.
The relation shows good coincidences with the experimental results. It is explained by the decrease of E/δ that the fatigue strength is lower under higher temperature, While ΔW is independent of temperature.
(3) The fatigue strength of unsaturated polyester is reduced by exposure to the ultraviolet ray. The reduction of fatigue strength may be mainly attributed to the roughening of the surface.
