In recent days, automobile and construction industries are focus on the light weight, environmental friendly materials with good mechanical properties. Glass fiber reinforced composites have excellent specific properties and are widely used because of reduced mass. However the manufacturing of glass fibers and end of life disposal are the major problem to the environment. To overcome these problems, natural fibers are used to manufacture composites. Flax is the one of the naturally available fiber having good mechanical properties than other natural fibers. It needs to be pointed out that most of research effort about the flax fiber reinforced composites focuses on the manufacturing techniques and primary mechanical properties and not on the secondary properties like sound absorption and vibration damping. In this paper, sound absorption and vibration damping properties of flax fiber reinforced composites were characterized and compared with the glass fiber reinforced composites. It was experimentally observed that the sound absorption coefficient of flax fiber reinforced composites has 21.42% & 25% higher than that of glass fiber reinforced composites at higher frequency level (2000Hz) and lower frequency level (100Hz). From the vibration study it was observed that the flax fiber reinforced composites have 51.03% higher vibration damping than the glass fiber reinforced composites. The specific flexural strength and specific flexural modulus for flax fiber reinforced composites also good. These results suggest that the flax fiber reinforced composites could be a viable candidate for applications which need good sound and vibration properties

Composites are used in conjunction with another material to form a multi-material stack-up, which results in greater strength to weight ratios. In a wide range of aerospace applications dissimilar material stack-ups of composites and aluminium and/or titanium are used. Drilling is probably the most common machining operation applied to composites since components made out of composite materials are usually near net shaped and require only holes for assembly integration. In this investigation, experiments were conducted by varying the drilling parameters and determining the optimum cutting conditions for drilling of CFRP/Ti stacks using Genetic Algorithm (GA) optimization technique. Tool wear study was performed by drilling 100 holes each with 118° and 130° point angle drills. Less progressive tool wear and better chip evacuation was achievable in 130° point angle drills when compared with 118°point angle drills