Study of the Uniform Corrosion Effects on Mechanical Properties of Tensile Plates by Experimental Tests and Scanning Electron Microscope (SEM)

摘要

The incidents due to the weakness of corroded steel members of structures, involves economic and human costs, to avoid the mentioned costs, an accurate estimation of the residual bearing capacity of corroded steel members is required. In this experimental study, uniform corrosion was applied on steel of types ST37, ST52 and Iracore with thicknesses of 4, 5, 6 and 8 mm by using salt spray machine. Two specimens from each thickness were tested by tensile test after times of 48, 96, 144 and 192 h and one specimen was also considered for corrosion penetration test. The reduction percentage of Ultimate Tensile Strength (UTS) obtained from force-displacement curve was compared to the expected reduction percentage of Ultimate Tensile Strength (EUTS_c). The results showed that in various specimens, the ultimate tensile strength obtained from exact measurement of the thickness of corroded steel plate could have a difference of 3-8% with the ultimate tensile strength obtained from the tensile test. Based on dimensional and weighted investigations and the Scanning Electron Microscopy (SEM) it was concluded that this difference is because of the creation of small-scale cavity corrosions despite applying uniform corrosion and also penetrating the corrosion in the depth of the plate. It seems that despite the direct relation that is considered between thickness parameter and tensile load in the calculations, applying a reduction factor for accurate estimation of the residual tensile strength capacity of corroded steel is required. It was shown that corrosion is not affected by the steel ductility and the speed of corrosion penetration in the Iracore specimens had a different process than the other specimens.