表面形状の再現加工による腐食鋼板の引張強度と変形能の解明

抄録

The strength and deformability of corroded steel plates are of great interest for the proper evaluation of structural integrity of aged marine structures. In the present paper, the authors use a CAM system which numerically controls a desktop milling machine to reproduce the surface geometry of a corroded surface. Surface data may be generated by a CAD system by the assembly of simulated pits of certain shapes such as cone or partial spherical shapes, or by numerically simulated arbitrary surfaces. Also, corroded surfaces may be measured by scanned the plate by a laser displacement sensor, so that the surface data are stored in the CAD system to generate the input for the CAM system. In order to investigate the effects of surface pits, three kinds of periodically distributed surface pits are machined on the both sides of specimens, where geometrically similar specimens, whose sizes are a half and a quarter of the original ones, respectively, are also used to investigate the size effect to the strength and deformability of the specimens. It will be seen that the size effect can be disregarded so that valid data can be obtained by scaled model experiments. As a typical example of plates with general corrosion, surface geometries of a sample specimen taken from the bottom plate of MS Nakhodka are reproduced, and the corresponding tensile test are carried out. The results show a slight reduction of the tensile strength, while the plastic deformation is reduced considerably. In order to examine the extent of the corroded surface, test specimens having different size but the same thickness are tested, where the surface undulation is machined in the original scale.