Effect of transverse cracking on stiffness reduction of cross-ply laminates

An analytical model based on the principle of minimum potential energy is developed and applied to study the effect of multiple cracks in cross-plies on the stiffness of a laminated composite. The transverse cracks are assumed to span the thickness of the cross-ply group only partially unlike in the previous studies in which they were assumed to span the entire thickness of the cross-ply group. This arrangement facilitates the study of competition between the self-similar extension of an inherent flaw within the cross-plies and the multiple parallel cracking. The numerical results for the axial stiffness as a function of both the crack density and the crack length are presented for three different composite material systems (glass/epoxy, graphite/epoxy and ceramic/ceramic) or which experimental results are available so as to validate the model.     

A maskless synthesis of TiO2-nanofiber-based hierarchical structures for solid-state dye-sensitized solar cells with improved performance

TiO₂ hierarchical nanostructures with secondary growth have been successfully synthesized on electrospun nanofibers via surfactant-free hydrothermal route. The effect of hydrothermal reaction time on the secondary nanostructures has been studied. The synthesized nanostructures comprise electrospun nanofibers which are polycrystalline with anatase phase and have single crystalline, rutile TiO₂ nanorod-like structures growing on them. These secondary nanostructures have a preferential growth direction [110]. UV–vis spectroscopy measurements point to better dye loading capability and incident photon to current conversion efficiency spectra show enhanced light harvesting of the synthesized hierarchical structures. Concomitantly, the dye molecules act as spacers between the conduction band electrons of TiO₂ and holes in the hole transporting medium, i.e., spiro-OMeTAD and thus enhance open circuit voltage. The charge transport and recombination effects are characterized by electrochemical impedance spectroscopy measurements. As a result of improved light harvesting, dye loading, and reduced recombination losses, the hierarchical nanofibers yield 2.14% electrochemical conversion efficiency which is 50% higher than the efficiency obtained by plain nanofibers.     

Effect of Shot Peening on Mechanical Properties and Ballistic Resistance of Magnesium Alloy AZ31B

Metal Science and Heat Treatment - The effect of shot peening on mechanical properties and ballistic resistance of plates from magnesium alloy AZ31B 25 × 300 × 300 mm in size to the...     

Flexural behavior of stepped graphite/epoxy laminates

Cross-ply tapered/stepped laminates with taper angles of 1 and 2° between the top and bottom surfaces were fabricated using T300/943 graphite/epoxy by compression molding. Ply terminations were done internally within the laminate and externally on the surface of the laminate at various cross-sections in order to obtain the taper. Equivalent cross-ply specimens with internal and external ply terminations, respectively, were tested in three point bending. The bending stiffness of the equivalent corss-ply are nearly equal, while the failure modes are significantly different. The tapered laminates with internal ply terminations failed due to a series of delaminations originating at the step corners of the 0° plies. Macroscopically, the specimens with internal ply term nations failed by tensile fracture of the outer plies at relatively higher loads.