Issue 19

P. K. Pradhan et alii, Frattura ed Integrità Strutturale, 19 (2012) 51-60; DOI: 10.3221/IGF-ESIS.19.05 57 strain (%) density of the material decreases due to increase of void density. It indicates that void nucleation and void growth is a continuous process during tensile deformation. Tensile Behavior of rectangular specimen with holes The tensile deformation behavior of the steel specimens containing holes were similar to that of the specimen without holes. However, the yield point (Y.P) and the Young’s modulus (E) of the material decreases due to the presence of holes. Mechanical Properties obtained from these tests are given in Tab. 2. Sl.No . Hole array inclination angle (degree) UTS (MPa) Strain at UTS ( %) Young’s Modulus E, (GPa) Yield point (MPa) Fracture Strain (%) 1 Without hole 366.07 22.3 203.9 244.5 42.4 2 0 0 (or 90 0 ) 232.4 11.5 145.6 174.7 17.4 3 30 0 234.9 12.3 149. 5 182. 6 22.9 4 40 0 238.9 13.8 154.8 184.5 23.8 5 45 0 244.8 15.0 165.4 188.2 25.1 6 50 0 238.0 12.9 153.2 186.0 23.1 7 60 0 239.5 12.1 148.3 179.7 22.8 Table 2 : Mechanical properties of rectangular specimen with hole. During deformation, the average width of the specimen is reduced. Due to stress concentration, the region adjacent to holes along the plane at mid section of the major axis showed large deformation. Shear band formation parallel to the array direction and passing through the holes is also observed (Fig. 11). The significant observations are obtained from the test results are: I. Mechanical properties of the specimen with holes decreases compared to specimen without holes. II. Among specimen with hole, with increase of angle of orientation to the tensile axis, the yield point, UTS, E, strain at UTS and fracture strain increases up to 45° and then decreases. III. For the specimens with hole array inclined at 90° (same as 0°) to the specimen edge, the fracture strain was least. Shear band formation is not observed in this sample. IV. Yield point phenomena is not found in specimen without hole. Figure 11 : Shear band formation during the tensile deformation of specimen (For Hole orientation (i) 60° and strain at 16%, (ii) 45° and strain at 18 % respectively). Macroscopic observation of the deformation of holes and fracture path From the observation (through the CCD camera) of the specimens with regular hole arrays during tensile testing, it was revealed that continuous deformation of holes takes place along the principal strain axis. Further, the major diameter of the holes increased continuously till the maximum load is reached. After the maximum load is reached, tensile instability occurs due to unstable deformation along localized region. On a macroscopic level, it appears that the failure process in these specimens is by shearing along the plane of intense shear band formation. The fractured path is found to be passing