Estimation of Corrosion Fatigue Strength by Corrosion Resistance and Notch Sensitivity of Materials

Abstract

Corrosion fatigue tests of various materials have been carried out in 1% saline and in 0.3N hydrochloric acid, accompanied with the measurements of corrosion current and notch sensitivity. In corrosion fatigue the critical depth of pits from which fatigue cracks initiate is determined by the stress concentration of pits depending on the corrosion resistance of materials and by the notch sensitivity. Corrosion effects κ (the ratio of fatigue strength in air σ to that in corrosive media σc) are referred to the static and the dynamic corrosion resistance, which are indicated by the corrosion current density ic0 at the beginning of the tests and by the inclination s of the corrosion current-testing time curve respectively, and to the notch sensitivity which is obtained by fatigue tests in air with notched specimens. Finally Eq. (14), (κ-1)/η=K3K4√((e<SUP)<K1K2>-1)/K1>√(i<SUB)c0τT> is obtained. (κ-1)/η is proportional to K3K4√(i<SUB)c0τT> for the same corrosive media irrespective of materials and of testing conditions. Test results show a linear relation between (κ-1)/η and √(i<SUB)c0τT> for the variety of materials, K3 and K4 being constant for the materials used in the present experiment. Thus, the meaning of the corrosion effect κ proposed by one of the authors is made clear. Besides sτT=K1 is obtained between the corrosion fatigue life τT and the dynamic corrosion resistance s, where the value of K1 is 4 in 1% saline and 2 in 0.3N hydrochroric acid.