Issue 19

P. K. Pradhan et alii, Frattura ed Integrità Strutturale, 19 (2012) 51-60; DOI: 10.3221/IGF-ESIS.19.05 53 plain (i.e.without any hole). III. Tensile deformation of rectangular plain specimen (without any hole). IV. Tensile deformation of rectangular specimen containing arrays of holes. V. Microstructural study of the above deformed specimen under Optical Microscope and Scanning Electron Microscope (SEM). VI. Preparation of flat square specimen of thickness 1mm. (as shown in Fig.2). VII. Arrays of hole (of size 0.5mm. diameter) have been made in such square specimen. VIII. Tensile deformation of those specimen under Optical Microscope. Figure 2 : Flat square specimen (thickness 1mm.) Figure 3 : Square specimen with array of hole. Preparation of Specimen Fifteen numbers of rectangular specimen of thickness 1mm were prepared from mild steel using surface grinding machine. Utmost care was taken to avoid overheating and undue deformation. Out of fifteen specimen, in six specimen (3×3) arrays of hole were made with different angle of inclination, i.e. 00, 30 0,400,450, 500 and 600 to the tensile load axis (as shown in Fig.1(b)-(g)) using drilling machine. The size of each hole was 1mm. In similar way, the square specimen of thickness 1mm. containing arrays of hole (of size 0.5 mm. diameter) with different inclination (as shown in Fig.3) were prepared. The 0.5 mm. holes were made by laser drilling machine and used for void coalescence studies (during straining) directly under optical microscope. These specimens were electro polished before testing to obtain a metalographically polished samples. Square specimen, except rectangular specimen have been taken for this test because these were tested under optical microscope directly and the attachment for this test does not permit other than this size. Experimental Procedure This experimental work mainly consists of: I. Tensile deformation of rectangular specimen without any holes; II. Tensile deformation of rectangular specimen containing 1 mm diameter holes; III. Tensile deformation of square specimen containing 0.5 mm diameter holes; IV. Microstructural studies of the above specimen. Tensile deformation of flat rectangular specimen without any holes Tensile deformation of all the rectangular specimens without any holes were carried out in a Universal Testing Machine (UTM, Make: INSTRON, Model: 8803, shown in Fig.4). Tensile tests were carried out with a crosshead speed of 2 mm/min. First, one specimen is tested till failure to get the mechanical properties of the material like Young’s modulus (E), yield point etc. Then another specimen is tested by repeated loading and unloading at different plastic strain to get the change of E for corresponding strain. Seven numbers of independent specimens were also loaded upto 8, 12, 16, 20, 25, 30, and 40% plastic strains and the tests were interrupted. These specimens were used to study the effect of strain on the void density by micro-structural observation using an optical microscope, SEM and Zeiss software. The observed void density (or void volume fraction) was measured by taking average of twenty subsequent adjacent area of the specimen and that is compared with actual void density. Actual void density is calculated relative to material density. The material density was determined by Density Kits. Also corresponding changes of grain size have been studied.