6-12. Composites have always occurred in nature. Wood consists of 6 fibers in a lignin because7. It breaks easily along the grain (along the direction of the fibers) because the break occurs only in the brokenacrossthegrain7. In this case the break is smooth. When broken across the grain, the break is rough. This is becanse Compositesarevere8. break, they also 19 . Unfortunately wood has a large UTS (ultimate tensile strength) in only one direction, the grain direction. In order to make a material which is strong in two directions we make plywood. But now the UTS measured along the sheet decreases because 10. Man-made composites using carbon fibers are used in sporting goods where they have a polymer 77, but for the high temperatures in rocket nozzles a 1111127 must be used. In many cases, conventional materials 6. (a) polyethylene (b) carbon (c) lignin (d) cellulose (e) polyester 7. (a) solution (b) mixture (c) concentration (d) matrix (e) gel 8. (a) fibers are broken (b) fibers do not all break in the same plane (c) some fibers do not break (d) both a and b (e) both b and c 9. (a) have a high Young's modulus (b) are very elastic (c) have to be pulled out of the surrounding material (d) are usually polymers ( e ) both a and d 10. (a) the glue between the plies makes it weak (b) oaly half the fibers give the strength (c) fibers are weakened by processing (d) both b \& c (e) strength does not decrease 11. (a) titanium (b) aluminum (c) boron (d) carbon (e) none of these 12. (a) are less flexible (b) are stiffer (c) are much heavier (d) have no durability