Unidirectional Non-Crimp Glass-Carbon Hybrid Composite Laminates For Automobiles

This thesis focuses in details on the processes of hybridization, effect of relative proportions of the fibers, effect of different types of laminate geometries and effect of dispersions on four basic mechanical properties of non-crimp unidirectional laminated composites including tensile, compression, flexural and shear characteristics. These characteristics have also been predicted by using a commercial software package ABAQUS/STANDARD. The damage mechanics and morphology under each loading conditions have been investigated visually at macro-level and by using Optical Microscope and Scanning Electron Microscope at micro-level. Unidirectional laminated composites were manufactured by impregnating the plain glass, plain carbon and glass-carbon hybrid preforms with epoxy resin using Vacuum Assisted Resin Infusion process.Test results reveals some interesting consequences of the process of hybridization. Tensile, compressive, flexural and shear performances of hybrid specimens show the anticipated trend of increase and/or decrease with increasing hybrid ratio and are lying in between those of GFRP and CFRP composites. In some cases the trends appear to be uniform while in some other cases the effects are erratic and do not have any clear trend. Meaning that hybridization appears to have an adverse effect on these mechanical properties. Laminate geometry and higher dispersion further optimize these mechanical performances and undeniably have noteworthy effects on failure modes of the composites which could be realized from the stress-strain relationships. The last part of the curves are not linear anymore (have some sort of plateau, more gradual failure), meaning that the catastrophic failure of the composites is avoided through hybridization. When the material is subjected to tension and compression the carbon fibers fail when their rupture strain is reached transferring all the load to the glass fibers. This then fail catastrophically if the relative proportion of glass fibers is small, or carry the additional load if the glass fiber content is substantial. Percentage gain in mechanical strengths and stiffness for hybrid laminates is significant when compared to composites entirely reinforced with glass fibers. The opposite is true when compared to composites utterly reinforced with carbon fibers. Hybridization results in significant percentage gain in rupture strain/strain-to-failure when compared to composites entirely reinforced with carbon fibers. Meaning that, hybridization is a trade-off between loss in strength and stiffness and gain in strain-to-failure, thereby, making the composite materials more damage tolerant. All mechanical properties such as tensile/compressive/flexural strengths, rupture strains exhibited what is often termed the synergistic effect-for both strengths and moduli the effect is negative. For rupture strains, the effects are both positive and negative. Therefore, hybrid ratio, laminate geometry and dispersions should be considered as the most crucial parameter while assessing these mechanical characteristics as well as the synergistic effects. The interlaminar shear characteristics have also been investigated and improved performances have been noticed with intra-layer hybrid laminates having the glass and carbon fibers being intimately mixed, i.e., highly dispersed.Light-weight structure utilizing novel design and advanced materials is one of the keys to improving the fuel energy efficiency and reducing the environmental burden of automotive vehicles. To ensure the low cost of applying fiber-reinforced materials in automotive vehicles and improve the strain-to-failure of CFRP composite, it is proposed to selectively intermingle the glass and carbon fibers through intra-layer hybridization technique. It is also proposed to mix the fibers as intimately as possible.