<p class="Els-Abstract-text" style="line-height: 150%">Under conditions of Elastic-Plastic Fracture Mechanics (EPFM), less constrained fracture toughness test specimens show greater resistance to crack advancement due to high plastic deformation activity near and ahead of the crack-tip. From the study of crack-tip constraint effect, literature suggests that tri-axial stresses are highly active on the mid-plane of standard specimens and out of plane shear bands forms at 45̊ which lead ductile fracture. In J-R curve evaluation, after crack blunting line, generally steady crack growth is observed. There is chance of crack line inclination too which affects the test results. ASTM standard E1820 highly recommends the use of side grooves in fracture toughness specimens for the purpose of guiding the crack to grow parallel to the crack line, particularly when the compliance method of crack size prediction is used. From the literature, it is observed that the most commonly used fracture toughness test specimen types like Single Edge Bend (SE(B)) and Compact Tension (C(T)) are tested with the provision of side grooves on the both sides of the surface. It is also observed that significant amount of crack ligament area is lost due to provision of side grooves. This significantly affects the load Vs load line displacement plot and reduces the load as well as displacement at load line and CMOD. Though the maximum applied load is decreased, the load at the beginning of the crack tearing is almost same as the specimen without side grooves. In this work, fracture toughness tests are carried out on C(T) specimens with V- and U- side grooves and without side groove. J-R evaluation is done as per ASTM E1820 using compliance method. A thorough fractographic analysis is carried out on the broken specimens after J-R tests using Scanning Electron Microscope (SEM). High plasticity level is observed on the specimen without side grooves where as low plastic deformation is observed on the side groove specimens. It is due to the effect of high stress tri-axiality at the surface. Side groove specimen guides the crack in straight line with even surface so as to help the plane stress fracture specimens to fail in plane strain condition. It is observed that the ductile fracture phenomena of micro-void nucleation, accelerated void growth and coalescence of the voids leading to crack formation are localized in the fracture specimens. The size and the density of dimples on the fracture surface suggest that the ductile fracture was motivated clearly by the voids and in the side grooved specimen, the cluster of voids at the surface of the specimen is more compared to the mid-thickness regions of the specimen.</p>

Fractographic Analysis of the Effect of Side Grooves in C(t) Specimen

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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