Issue 19

P. K. Pradhan et alii, Frattura ed Integrità Strutturale, 19 (2012) 51-60; DOI: 10.3221/IGF-ESIS.19.05 55 loading and unloading cycles of the tensile test is shown in Fig. 6. The variation of Young’s modulus (E) value due to the plastic deformation, during tensile loading after each unloading operation, is plotted in Fig. 7. It is evident that the value of E decreases with increase in strain (%).The decrease in E’s value with increase in strain may be due to the nucleation of voids in the matrix during the tensile deformation. In each successive deformation, the newer voids nucleate and earlier nucleated voids grow. Due to that, the void’s volume fraction in the material increases. Therefore, for the same amount of strain, lesser force required and the value of E decreases. Figure 6 : Stress-strain curve obtained during the loading and unloading operation for the flat tensile specimen. Figure 7 : Change of E (Young’s modulus) for corresponding strain (%) Microstructural study of specimen without holes Microscopic observation of the polished and etched undeformed specimen revealed the structure consisting of ferrite grains with small amount of pearlite colonies (black regions shown in Fig. 8) at the ferrite grain boundaries. The image analysis results revealed 13.10 % of pearlite indicating a carbon percentage of 0.15% for the steel. Figure 8 : Structure of undeformed specimen. Figure 9 : Void nucleation at grain boundary.