Experimental studies on the energy absorption capacity of axially compressed metal tubes

Impact energy absorbers are expendable mechanical structural elements, which are brought into action to dissipate the kinetic energy in the event of an unwanted collision. These act as mechanical fuses to limit the loads, which may act on the main structure immediately after a collision. The use of aluminium tubes and tubular structures for use as impact energy absorbers in different engineering applications is encouraging. This is because of their ready availability in different cross sections and sizes, and also has high energy absorption capacity under quasi-static and dynamic loads. In this present study, experiments are conducted on circular aluminium tubes under quasi-static, axial compression. The different modes of deformation of these tubes are examined in two separate cases. Case 1: when the tubes compressed axially between a flat platen and shaped dies of different radii. Case 2: when the tubes compressed axially between two flat platens. Dies of different radii are used to evaluate the efficient mode of deformation. The energy absorption capacity under quasi-static loading conditions is evaluated in the above cases to evaluate the energy absorption capacity and to compare the energy absorption of aluminium tubes based on the different deformation modes. The results of the study are useful in the design of impact energy absorbers © IAEME Publicatio

Two Modular Equationsfor Squares of the Cubic-functions with Applications

In this paper, we derive two modular identities for cubic functions and are shown to be connected to the Ramanujan cubic continued fraction G(q). Also we have derived many theta function identities which play an important role in proving Ramanujan’s modular equations of degree 3

A modified restricted Euler equation for turbulent flows with mean velocity gradients

The restricted Euler equation captures many important features of the behavior of the velocity gradient tensor observed in direct numerical simulations (DNS) of isotropic turbulence. However, in slightly more complex flows the agreement is not good, especially in regions of low dissipation. In this paper, it is demonstrated that the Reynolds-averaged restricted Euler equation violates the balance of mean momentum for virtually all homogeneous turbulent flows with only two major exceptions: isotropic and homogeneously-sheared turbulence. A new model equation which overcomes this shortcoming and is more widely applicable is suggested. This modele is derived from the Navier-Stokes equation with a restricted Euler type approximation made on the fluctuating velocity gradient field. Analytical solutions of the proposed modified restricted Euler equation appear to be difficult to obtain. Hence, a strategy for numerically calculating the velocity gradient tensor is developed. Preliminary calculations tend to indicate that the modified restricted Euler equation captures many important aspects of the behavior of the fluctuating velocity gradients in anisotropic homogeneous turbulence

Enhanced Critical parameters of nano-Carbon doped MgB2 Superconductor

The high field magnetization and magneto transport measurements are carried out to determine the critical superconducting parameters of MgB2-xCx system. The synthesized samples are pure phase and the lattice parameters evaluation is carried out using the Rietveld refinement. The R-T(H) measurements are done up to a field of 140 kOe. The upper critical field values, Hc2 are obtained from this data based upon the criterion of 90% of normal resistivity i.e. Hc2=H at which Rho=90%Rho; where RhoN is the normal resistivity i.e., resistivity at about 40 K in our case. The Werthamer-Helfand-Hohenberg (WHH) prediction of Hc(0) underestimates the critical field value even below than the field up to which measurement is carried out. After this the model, the Ginzburg Landau theory (GL equation) is applied to the R-T(H) data which not only calculates the Hc2(0) value but also determines the dependence of Hc2 on temperature in the low temperature high field region. The estimated Hc(0)=157.2 kOe for pure MgB2 is profoundly enhanced to 297.5 kOe for the x=0.15 sample in MgB2-xCx series. Magnetization measurements are done up to 120 kOe at different temperatures and the other parameters like irreversibility field, Hirr and critical current density Jc(H) are also calculated. The nano carbon doping results in substantial enhancement of critical parameters like Hc2, Hirr and Jc(H) in comparison to the pure MgB2 sample.Comment: 25 pages with 9 Figs: comments/suggestions([email protected]

Microrheology of non mulberry silk varieties by optical tweezer and video microscopy based techniqueas

We have carried out a comparative study of the microrheol. properties of silk fibroin solns. formed from a variety of silks indigenous to the Indian subcontinent. We present the measured viscoelastic moduli of Tasar silk fibroin soln. using both a single and dual optical tweezer at 0.16​% and 0.25​% (w​/v)​. The bandwidth of the measurements carried out using optical tweezers is extended down to the lower frequency regime by a video microscopy measurement. Further, we have measured the viscoelastic moduli of Eri and Muga varieties of silk fibroin solns. at a higher concn. (1.00​% w​/v) limiting the tool of measurement to video microscopy, as the reduced optical transparencies of these solns. at higher concn. preclude an optical tweezer based investigation. The choice of a higher concn. of fibroin soln. of the latter silk varieties is so as to enable a comparison of the shear moduli obtained from optical methods with their corresponding fiber stiffness obtained from wide angle X-​ray scattering data. We report a correlation between the microstructure and microrheol. parameters of these silk varieties for the concn. of fibroin solns. studied

An Experimental Study On Load Carrying Capacity Of A Magnetic Bearing

The use of bearing is essential to all types of machines they provide the function of supporting heavier component in a desired position. These bearings have contact with the rotating part and causes surface wear which can be controlled by lubrication. The standards of performance for rotating equipment can be raised by providing robust, cost effective and easy to implement lsquoMagnetic bearingsrsquo. A radial magnetic bearing, consisting of two permanent magnets, is an attractive choice because of its zero wear, negligible friction, and low cost, but it suffers from low load capacity, low radial stiffness, lack of damping and high axial instability. To enhance the radial load and radial stiffness and reduce the axial thrust, a theoretical and experimental study of various radial configurations, including hydrodynamic lubrication to improve dynamic performance of the magnetic bearing is made