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Articles by S.B. Tiwari
Total Records ( 6 ) for S.B. Tiwari
  K.G. Muthurajan , K. Sankaranarayanasamy , S.B. Tiwari and B. Nageswara Rao
  Studies are made to understand the delamination growth of general laminates with general loading conditions. Post-buckling solutions are obtained for a laminate with clamped ends applicable to thin film strip delamination in a base laminate under uniform membrane loads. The strain energy release rate at the crack-tip (G) is derived in terms of the critical equivalent base laminate strain at the onset of the buckling (ε*cr) and the applied equivalent strain (ε*). It is also expressed in terms of the maximum amplitude (Wmax) of the delaminated layer. A Griffith-type fracture criterion with constant specific fracture energy (Gc) of the material is used to govern the delamination growth. The stability characteristics of the delamination growth are discussed. The maximum amplitude (Wmax) of the delaminated layer increases with the applied load without enhancement in the length of the delamination for the values of G less than Gc. Initiation of the delamination growth can be expected when the value of G is very close to Gc.
  K.G. Muthurajan , K. Sankaranarayanasamy , S.B. Tiwari and B. Nageswara Rao
  Finite element analysis for adhesively bonded joints has been carried out by developing a special 6 node isoparametric element for the adhesive layer. The adhesive layer is assumed to be relatively thin and behaves elastically as simple tension-compression springs and shear spring connecting the adherends. The results of a metal-metal single lap joint are found to be in good agreement with the closed-form solution of Goland and Reissner. This adhesive element can be utilized for modeling adhesively bonded joints having shaped adherends for optimum joint efficiency.
  N.S. Babu , S.B. Tiwari and B. Nageswara Rao
  Studies are made on graphitised carbon fibres using wide-angle X-ray diffraction technique and Scanning/Transmission Electron Microscopy (SEM/TEM) to obtain structural parameters and morphological features of the fibres. Two important crystallite size structural parameters La and Lc can be generally obtained from X-ray diffraction technique. Lc values are evaluated by applying the necessary correction factors for the non-separation of Kα1 and Kα2 doublet and instrumental broadening. For simplicity empirical expressions are developed for these correction factors from the standard monograms. The surface features of pitch and PAN graphitised carbon fibres at high resolution are examined using SEM and orientation studies are made using TEM. Finally crystallite domain size parameters are related to the tensile modulus of the fibres. It is found that the crystallite domain size increases with the graphitisation temperature and stretching loads. This in turn leads to the enhancement in the tensile modulus of the fibre.
  K.G. Muthurajan , K. Sankaranarayanasamy , S.B. Tiwari and B. Nageswara Rao
  Delamination is one of the most commonly observed failure modes in laminated composites. The existence of a delamination in a structure can significantly reduce the stiffness and strength of the structure. Various types of cracked specimens were designed to quantify the effect of delaminations in composites. The growth of delamination in composite structures starts when the strain energy release rate (G) under service loads exceeds the fracture energy (Gc). The measurement of fracture toughness of a material relies strongly on the method of data interpretation. In the original form, the experimental fracture data normally consists of a load-displacement record for a cracked specimen. Data reduction requires the knowledge of the specimen crack length and dimensions and a suitable method for calculating the fracture parameters. This study presents a simple and reliable procedure for the evaluation of mode I and mode II delamination fracture toughness from the test data of Double Cantilever Beam (DCB) specimens and Cracked-Lap Shear (CLS) specimens made of carbon/epoxy. Critical load estimation of DCB specimens from the measured specific fracture energy (GIC) of the materials is found to be in good agreement with test results.
  Swamy N.S., , H.R. Nataraja , K.S. Sai , S.B. Tiwari and B. Nageswara Rao
  This study considers the Rivlin-Ericksen constitutive equation for the Cauchy stress in the equation of motion to examine the flow of an incompressible second-grade fluid with an oscillating rigid moving plate. Simple and reliable numerical procedures are used to obtain the parameters in the analytical expressions for the velocity field and the shearing stress on the moving plate. The Doppler effect is noticed from the increased frequency due to the motion of the plate. The thickness of the boundary layer reduces with an increase in the magnetic interaction parameter.
  Sai K.S., , N.S. Swamy , H.R. Nataraja , S.B. Tiwari and B. Nageswara Rao
  This study presents an exact solution for the flow of two immiscible fluids under a general oscillatory time-dependent pressure gradient in a channel with one porous floor. The oscillatory behavior of the time-dependent pressure gradient is expressed in terms of Fourier series. At the interface, continuity of velocities and shear stresses is assumed. Equations governing the flow are solved using the slip condition at the permeable interface whereas the generalized Darcy`s law in the porous region. The unsteady flow depends upon the Reynolds numbers of the fluids, slip parameter and porous parameter. Analytical expressions are provided for the mass flow rate and wall shearing stresses. Numerical results are presented considering water and mercury as the two immiscible fluids for the uniform pressure gradient as well as for the sinusoidal time-dependent pressure gradient. Since the formulation of the problem is general, it is possible to examine the unsteady flow of any two immiscible fluids under any specified oscillatory time-dependent pressure gradient. This study will be useful in learning how the pressure and viscous forces exert their influence to produce different flow patterns.
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