Reason of Fatigue Strength Improving Effect of Epoxy Resin Coating Steels

Abstract

Gilde1) has reported on the effect of epoxy-resin coating over the weld reinforcement in improving the fatifue strength of welded joints. But the reason of this effect has not been explained clearly. Authors) have experimentally showed the influence of atmospheres on the fatigue strength of steels. And it is considered that the fatigue strength improving effect of epoxy-resin coating may be attributed to the protective effect of its coating against air. Then the improving effect of coating may depend on the coating conditions and the kinds of coatings and metals. These points are experimentally studied in this report by a plate bending fatigue tests in the controlled atmosphere tank and rotating bending fatigue tests, using mild steel, 60 kg/mm² and 80 kg/mm² high strength steels.
The reslts obtained are as follows.
1) Improvement of fatigue strength of notched steel specimens by epoxy-resin coating is attributed to its protective effect against oxygen and/or humidity in air.
2) The most effective coating was epoxy-resin cured by poly-amid and another coatings, synthetic rubber, vinyle chloride and acrylicemulsion has little effect on improving fatigue strength.
3) An effective epoxy-resin coating has poor air peremeability, flexibility and a good adhesion for metals.
4) The coating effect by epoxy-resin is more predominant in the notched specimen than in the plain specmen. This shows that the coating delay a fatigue crack propagation rate as the same as the no oxygen atmosphere.