An experimental study on fracture process zone in high strength concrete beams

An attempt has been made to experimentally investigate the fracture process zone (FPZ) using Acoustic Emission (AE) method in High Strength Concrete (HSC) beams subjected to monotonically increasing load. Stress waves are released during the fracture process in materials, which cause acoustic emissions. AE energy released during the fracture of notched HSC beam specimens during Three Point Bend (TPB) tests is measured and is used to investigate the FPZ in the notched HSC beams having 28-day compressive strength of 78.0 MPa. The specimens are tested by Material Testing System (MTS) of 1200 KN capacity employing Crack Mouth Opening Displacement (CMOD) control at the rate of 0.0004 mmlsec in accordance with RILEM recommendations. A brief review on AE technique applied to concrete fracture is presented. The fracture process zone developed and the AE energy released during the fracture process in high strength concrete beam specimens are presented and discussed. It was observed that AE events containing higher energy are located around the notch tip. It may be possible to relate AE energy to fracture energy of concrete.

Computational and experimental studies of fluid flow and heat transfer in a Calandria based reactor

CFD investigations are carried out to study the heat flux and temperature distribution in the calandria using a 3–Dimensional RANS code. Internal flow computations and experimental studies are carried out for a calandria embedded with a matrix of tubes working together as a reactor. Numerical investigations are carried on the Calandria reactor vessel with horizontal inlets and outlets located on top and the bottom to study the flow pattern and the associated temperature distribution. The computations have been carried out to simulate fluid flow and convective heat transfer for assigned near–to working conditions with different moderator injection rates and reacting heat fluxes. The results of computations provide an estimate of the tolerance bands for safe working limits for the heat dissipation at different working conditions by virtue of prediction of the hot spots in the calandria. The isothermal CFD results are validated by a set of experiments on a specially designed scaled model conducted over a range of flows and simulation parameters. The comparison of CFD results with experiments show good agreement.

Spin Probe Signature of Freezing in Water Slow Cooling Experiment: Our Observation is Global or Local?

First systematic spin probe ESR study of water freezing has been conducted using TEMPOL and TEMPO as the probes. The spin probe signature of the water freezing has been described in terms of the collapse of narrow triplet spectrum into a single broad line. This spin probe signature of freezing has been observed at an anomalously low temperature when a milimoler solution of TEMPOL is slowly cooled from room temperature. A systematic observation has revealed a spin probe concentration dependence of these freezing and respective melting points. These results can be explained in terms of localization of spin probe and liquid water,most probably in the interstices of ice grains, in an ice matrix. The lowering of spin probe freezing point, along with the secondary evidences, like spin probe concentration dependence of peak-to-peak width in frozen limit signal, indicates a possible size dependence of these localizations/entrapments with spin probe concentration. A weak concentration dependence of spin probe assisted freezing and melting points, which has been observed for TEMPO in comparison to TEMPOL, indicates different natures of interactions with water of these two probes. This view is also supported by the relaxation behavior of the two probes.