Hybrid PP/EPR/GF Composites I: Deformation Mechanisms

The modification of polypropylene (PP) with a combination of ethylene, propylene rubber (EPR) and glass fibres (GF) is a well known route to improving its mechanical properties. This is because the reductions in stiffness and strength due to the presence Of rubber particles are more than compensated by the addition of short glass fibres. This study has focused on the combined effects of glass fibres and rubber particles on the mechanical properties and mechanisms of deformation in PP-EPR-GF hybrid composites. Several composites with different amounts of rubber and short glass fibres were examined. To study possible synergistic effects, the total combined weight fraction of rubber and fibres was kept constant at 20%. The results of tensile tests show that the addition of glass fibres to PP EPR blends promotes yield strength and modulus while reducing elongation at break. Optical microscopy shows that, in the damage zones of all specimens, deformation bands. which appear similar to crazes, are visible after stretching. Scanning electron microscopy shows crazelike features including some voids, which tend to deviate from in plane propagation near the ends of glass fibres. The dominant mechanism of deformation in PP EPR GF observed in this work appears to be a crazelike type of damage, which is believed to be highly localised dilatational shear banding, propagating via repeated cavitation

Fabrication of AA356/SiCp Aluminum Composite Foam via In-Situ Foaming Route of Melt using CaCO3 Foaming Agent and an Investigation of its Compressive Properties

In this study, aluminium composite foams reinforced by different volume fractions of SiC particles as reinforcement and stabilizing agent were fabricated with the direct foaming route of melt using different contents of CaCO3 as foaming agent. The density of produced foams were measured to be from 0.38 to 0.68 g/cm3. The microstructural features and compressive properties of the AA356/SiCp composite foams were investigated. The relation between plateau stress, density and, weight percentage of CaCO3 and SiCp volume fraction with a given particle size was also investigated. The results showed that compressive stress-strain curves of the products were not smooth and exhibit some serrations. Also, it was shown that in the same density of composite foams, the plateau stress of the composite foams increases with increasing volume fraction of SiC particles and decreasing weight percentage of CaCO3

The Role of Multi-wall Carbon Nanotubes on Fracture Mechanism of Epoxy Nanocomposite

In order to investigate the role of multi-wall carbon nanotubes (MWCNTs) on fracture mechanism of epoxy nanocomposites, a series of tensile standard specimens reinforced with different carbon nanotube contents (0, 0.3, 0.6 and 1 wt%) were produced. The fracture surfaces of the produced nanocomposites were evaluated using scanning electron microscope (SEM). The results show that the surface fracture of epoxy nanocomposites comprised of three regions, i.e. mirror, transition and final propagation zones. The extension of all zones depends strongly on curing agent as well asMWCNTs content. The mirror zone is disappeared as curing agent and MWCNTs content increases, while the transition zone depends on the nucleation rate of secondary microcrack. The pattern of final propagation zone becomes coarser as MWCNTs are added to epoxy system