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Rayleigh damping co-efficients are the essential parameters to determine the damping matrix of a system in dynamic analysis. For the systems with multiple degrees of freedom, it is difficult to arrive for suitable Rayleigh damping co-efficients. This paper represents a simple and effective method for the determination of Rayleigh co-efficients α and β for the system with multiple degrees of freedom. An unrealistic constant damping ratio for all modes is assumed to get rational value of α and β, which leads the determination of progressively varying damping ratio for all modes. By comparing the damping ratio arrived from assumed α and β with assumed unrealistic damping ratio, the suitable and most precise values are determined. This method is implemented for different materials with different boundary conditions by considering different significant modes and the effect of above parameters on α and β values are also discussed.

This work investigates the effect of nanoclay in the mechanical and thermal characteristics of GFRP laminates. The Cloisite 15A nanoclay has added to the matrix with proportion of 1%, 2% and 3% by weight. The processed nanocomposites are characterized with X-Ray Diffraction to identify the inter layer spacing of clay in the matrix. The filler added epoxy, reinforced with the unidirectional glass fibre by hand layup technique and the specimens are tested for tension, hardness, flexural and fracture loadings. Dynamical mechanical analysis and thermo gravimetric tests are also conducted to understand the visco-elastic and thermal behaviour of the material. The addition of clay in the matrix generally increases the mechanical properties up to our consideration that is 3% clay loading. Thermal and visco-elastic behaviour found consistent up to 1% clay loading and reduces the performance after that in overall sense.

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This paper investigates carbon nano tube's (CNTs) effect in the mixed-mode inter-laminar fracture response of glass fibre reinforced epoxy laminates. Laminates are prepared by adding 1%, 2% and 3% of CNTs with matrix by weight. Modified arcan fixture has been employed to generate the data for Mode I, Mode II, and various mixed-mode ratios. Loading angle has varied from 0°to 90°in steps of 15°, and the generated data was reduced by applying correcting factors to get toughness value. Periodic function model was employed to estimate the elastic constants for data reduction. Loading angle, Proportion of Carbon Nano Tube, Crack length ratio, Stress intensity factor and Energy release rate are taken as the variables for discussion. Fractured surfaces are also captured with scanning electron microscopy to study the influence of Carbon Nano Tube in inter-laminar fracture. Genuineness of specimen and fixture on exhibiting mixed mode fracture load at crack tip, was verified before proceeding the characterization. Fracture resistance was enhanced from 2.95% to 5.24% and critical load at fracture was increased from 17.47% to 22.79% with Carbon Nano Tube addition compared to the neat GFRP specimens. Enhancement is high for 1% addition, and enhancement rate decreases after further reserves. Failure assessment study was also conducted on specimens and elliptical failure criteria was noted as the best one for defining mixed mode fracture of CNT filled glass epoxy specimens.