Effects of Specimen thickness in tensile tests on elongation and deformation energy for industrially pure iron

Industrial pure iron specimens with a thickness that varied from 0.2 to 2.0 mm were investigated in tensile tests to examine the influence of specimen thickness on the percentage elongation and deformation energy. Conventionally, the total percentage elongation of a tensile specimen can be converted by Oliver's equation, 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 percentage elongation was influenced by the stress triaxiality. The FEM (Finite Element Method) analysis indicated 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's incompatibility. After completing the tensile test, the stress-strain curve can be obtained and categorized into the uniform and local deformation. The uniform deformation energy did not depend on the specimen thickness in contrast to duplex stainless steel, which was examined in our previous research. 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 percentage elongation.