Three-point bending cyclic fatigue tests were conducted on base metal specimens with various edge rounding radii. Specimens were cut from 66 mm and 100 mm EH40 steel plate The steel was produced by a Japanese manufacturer. Fatigue curves for these specimen types were generated. It was concluded that increasing machined corner radius for plates of 66 and 100 mm thickness has no noticeable effect on fatigue life. It was observed that S-N curves as well as the thickness exponent were unusually high compared with known data for shipbuilding steels. An additional study was carried out to identify why this steel has higher fatigue strength and lower tolerance to plate thickness than conventional shipbuilding steel.
In Phase 1 (Polezhayeva, Badger, 2009) the effects of thickness and machining of the corners on fatigue strength were studied for base material and butt welded specimens. The corners of the specimens were machined to 3 mm radius independent of the thickness of the specimens. The machining of the corners had a pronounced effect on the fatigue resistance of 22 mm thick specimens but no effect for specimens of 66 and 100 mm thickness was identified. Therefore it was decided to carry out fatigue tests on base metal specimens cut from 66 mm and 100 mm EH40 steel plate with various edge rounding radii to find out whether radius of machining should increase with specimen thickness to produce a positive effect on fatigue life.
All the specimens were manufactured from EH40 steel plate supplied by a Japanese manufacturer and certified by Lloyd''s Register. Plates of two thicknesses, 66 mm and 100 mm, were used. All specimens were oxygen cut from the plate in the rolling direction. The main mechanical properties of the steel, as detailed in the Certificate, are presented in Table 1.(refer to the full paper)
