Experimental Study on Statical Strength of Corrosive Mild Steel

Abstract

It is said that most of hull damages in old ships are caused by corrosion /wear because ships are closely related with corrosion in the sea condition. Accordingly, in assessing the remaining lives of those ships, it is important how to estimate the strength of corrosive members.On the other hand it has ever been said that corrosive members often indicate the characteristics of brittleness even if they are mild steel in the room temperature. So the authors confirmed that corrosive members of mild steel, in some cases, shows the decrease in ductility, that is, elongation by the experiment. Furthermore, it has been examined that this phenomenon has been brought about by corrosive pits formed on their surfaces. And the effect of corrosive pits on static strength have been studied parametrically by the simulation test in which artificial pits are formed on the surfaces of the test specimens. Obtained main conclusions are as follows ;(1) The characteristics of tensile strength in corrosive members are very similar with that of members with artificial pits on their surfaces. Then the tensile strength of corrosive members can be substituted by that of those with artificial pits.(2) Elongation of members with pits varies with the density and depth of pits. That is, as the density becomes high and the depth ratio (d/t) becomes large, the value of elongation decreases.(3) Ductile fracture of members with pits starts at the pits in the tensile test. And introducing the volume ratio Vp, the elongation can be represented as the following equation;εe/εe0=1/1+kpVp (kp : constant) where k corresponds with the density of pits.(4) Absorbed plastic energy of members with pits is the function of Vp as well as the case of elongation and can be represented as the hyperbolic relation;W/W0=1/1+kpVp (kp : constant)