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Visualization and quantification of aggregate and fiber in self-compacting concrete using computed tomography for wedge splitting test

100%

Rajeshwari B. R. , Sivakumar M. V. N. , Praneeth P. H.

tom Vol. 20, no. 4

617--632

Wedge splitting test gained popularity as a stable and simple method to predict the fracture mechanism properties of concrete specimens. The present research focuses on understanding the behavior of self-compacting concrete specimens made with and without steel fibers tested using wedge splitting test, later scanned under high resolution computed tomography. The contribution of hooked end steel fiber and coarse aggregates in fiber reinforced specimens was compared without steel fiber reinforced concrete specimens using high resolution computed tomography. As fracture takes place across the plane perpendicular to the splitting force, i.e. along the depth of specimens. High resolution computed tomography technique was adopted in visualizing the changes taking place across the matrix, coarse aggregate and steel fibers, along with the specimen’s depth. Datasets of the images, obtained from computed tomography, after images analysis and volume reconstruction, revealed a higher coarse aggregate and steel fiber participation in the failure region of without and with fibers specimens. Computed tomography investigation indicated a total of 23 coarse aggregate and 64 steel fibers participated in resisting the failure, during wedge splitting test of without and with fibers specimens. Therefore, high resolution computed tomography can be used in understanding, quantifying the participation of coarse aggregate and steel fiber in the failure plane, under fracture loads.

Microstructure characterization of 7055-T6, 6061-T6511 and 7A52-T6 Al alloys subjected to ballistic impact against heavy tungsten alloy projectile

100%

Khan M. A. , Wang Y. , Malik A. , Nazeer F. , Yasin G. , Khan W. Q. , Ahmad T. , Zhang H.

tom Vol. 19, no. 4

1484--1496

A spray formed 7055 Al alloy, and traditional formed 6061 Al and 7A52 Al alloy were subjected to extrusion. Later 7055Al and 7A52 treated with T6 and 6061 Al treated with T6511 heat treatment. To investigate the microstructure evolution by optical microscopy (OM), scanning electron microscopy (SEM), electron back scattering diffraction (EBSD) and X-rays diffraction pattern (XRD) analysis were employed to observe the variation in mechanical properties and damages patterns of single layered aluminum alloys impacted by heavy tungsten alloy (WHA) projectile. During impact a substantial increase in temperature inside the target material caused melting on crater wall. The hard metastable intermetallic compound and pores were produced on penetration path owing to diffusion of projectile particles and rapid melt re-solidification. These compounds enhance the hardness (600-650 HV0.1/10) in the middle deformed channels of 7055 Al alloy target. In addition, small size pores, whirl-pool and white adiabatic shear bands were observed in 7A52 and 6061 Al alloys, respectively. The variation in hardness and microstructure of Al alloys target was limited within the 2 mm area from the perforation path. 7055-T6 Al alloy has demonstrated better ballistic protection in terms of strength, mass efficiency (N), depth of penetration (DOP) and penetration path diameter in comparison of other Al alloys.