1. Indicate whether statements are true or false ① All natural fibers are organic and all synthetic fibers inorganic. ② Polyethylene has the lowest density of any readily available synthetic fibers. ③ Glass fibers are crystalline and the crystal size is about 20  m. ④ Alumina fibers always have the  -alumina structure ⑤ Boron fibers are produced by vapour deposition from boron trichloride (BCl 3 ) on to a heated substrate. ⑥ The elastic properties of graphite are anisotropic. ⑦ All interfaces between the matrix and the reinforcement are stable and will never change during service even at high temperature.

2. For each of the statements of following questions, one or more of the completions given are correct. Choose the correct completions. ① Aramid fibres a)are stretched and drawn to align the structure b)maintain their properties to temperatures in excess of C c)are produced by chemical vapour deposition from nylon. ② Glass fibres a)are made from silica glass, b)have the highest specific modulus of any fibres c)are produced by vapour deposition d)have an amorphous structure e)may be chopped to make a chopped strand mat. ③ Alumina fibres a)are produced form an organic precursor b)are produced via a slurry c)have extremely high values for the specific strength d)may be predominately  -phase

④ Graphite a)is a non-crystalline form of carbon b)has covalent bonding in the basal planes c)has weak bonds in the basal plane d)starts to oxidize in air at about C ⑤ SiC fibres a)are produced by melt spinning b)are produced by chemical vapour deposition c)are produced by decomposition of a precursor, d)sometimes have a tungsten core, e)usually contain a significant amount of Al 2 O 3. ⑥ Wetting a)does not occur if the contact angle  =0 b)does not occur is the contact angle  =180 c)Is the spreading of a liquid over a solid d)Is the flow of a liquid under gravity through a porous medium.

⑦ The specific modulus a)is given by 1/E where E is Young’s modulus b)is given by E  where  is density c)is given by E/  d)Is generally low for polymer matrix composites, e)Is generally low for metallic materials.