Time-aging time-stress superposition in soft glass under tensile deformation field

We have studied the tensile deformation behaviour of thin films of aging aqueous suspension of Laponite, a model soft glassy material, when subjected to a creep flow field generated by a constant engineering normal stress. Aqueous suspension of Laponite demonstrates aging behaviour wherein it undergoes time dependent enhancement of its elastic modulus as well as its characteristic relaxation time. However, under application of the normal stress, the rate of aging decreases and in the limit of high stress, the aging stops with the suspension now undergoing a plastic deformation. Overall, it is observed that the aging that occurs over short creep times at small normal stresses is same as the aging that occurs over long creep times at large normal stresses. This observation allows us to suggest an aging time - process time - normal stress superposition principle, which can predict rheological behaviour at longer times by carrying out short time tests.Comment: 26 pages, 7 figures, To appear in Rheologica Act

An experimental study of impulsively started turbulent axisymmetric jets

An impulsively started turbulent jet injected into quiescent surroundings with a constant inlet velocity has been studied experimentally. Results show that the jet length increases linearly with the square-root of time, over a wide range of Reynolds number calculated with respect to the jet diameter. The celerity factor, x f/t U, has been found to be nearly constant at 2.47 throughout with a 5% variance. Here, x f is the jet length, t is the time and U is the jet exit velocity. These results compare favourably with earlier results reported at lower Reynolds numbers. Finally, we present a simple model based on the integral energy balance of the turbulent boundary layer equation for an impulsively started turbulent axisymmetric jet. The model predicts a jet length that scales as, $(x_f/d)=\sqrt{(9B/10) (t U /d) }$ where d is the nozzle diameter and B(≈6.0) is the velocity-decay constant. This gives a celerity factor, $\alpha\equiv \sqrt{9B/10}=2.32$ in close agreement with the experiments. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 200847.27.wg Turbulent jets, 47.27.nb Boundary layer turbulence,