Effects of tensile test specimen thickness on elongation and deformation energy for industrial pure iron

Industrial pure iron specimens with the thickness varied from 0.2 to 2.0 mm were investigated in tensile test to examine the influences of specimen thickness on elongation and deformation energy. Conventionally, the total elongation of tensile specimen can be converted by JIS 0202-1987 formula, which is related to the tensile test specimen thickness. However, in this experiment, it was noticed that there were number of factors which led to the inaccuracy in the result. The total elongation was influenced by the stress triaxiality. According to the FEM (Finite Element Method) analysis, it showed that the stress triaxiality increased significantly with the thinner specimen, this was due to the void growth behavior, observed by SEM (Scanning Electron Microscope) under low voltage. These results revealed that voids nucleation and growth behavior influenced by the stress triaxiality were the main cause for the formula incompatibility. After the tensile test, stress-strain curve can be obtained and categorized into the uniform and local deformation. The uniform deformation energy was not depended on the specimen thickness in contrast to duplex stainless steel of previous study. On the other hand, the local deformation energy lowered with the decrease in specimen thickness as with duplex stainless steel. These results indicated that the void nucleation and growth behavior had a significant impact on the total elongation.