(3)Ec=Vt Ef+Vm Em (4)Inverse rule of mixture or E1=VmE+VE1 modulus),Vi s volume fraction,(c)refers to the composite material,(f)refers to fibers,and(m)refers to matrix 3.(3pt)Explain why carbon fiber reinforced composites are widely used in manufacturing airplane. Carbon fibe are light weight,and have high strength,toughness,specific modulus,high dimensional stability,low coefficient of thermal expansion,and low abrasion,which ensure carbon fiber reinforced composites as an ideal material in airplane industry. VI.Complex questions.(20points) 1.Predict which polymer in each pair listed can have higher degree of crystallinity,and justify your answer.(12) (1)PE>Polystyrene(PS) Polymers with large,bulky side groups cannot be packed efficiently,and therefore have difficulty forming crystals (2)LDPE<HDPE Polymers with branched chains cannot be packed efficiently,and hence it is far more difficult to form crystals (3)PE>Nylon Polymers with long repeat units require more extensive chain segment motion to establish Long range order,and hence it will crystallize slowly, and can be easily formed into glasses using modest quench rates. (4)Atactic [C2Hs(CH3)]n<isotactic [C2H3(CH3ln Symmetrical structures that permit close packing of chains favour crystallinity. (5)isotactic(C2H3CDn,>isotactic(C2H3CH3)n Stronger secondary forces allow greater compacting forn tion of Polymers are long chain structures.The movement of polymer chains needs time.Slow cooling means giving Polymer chains more time to allow them to 4 PDF文件使用"pdfFactory Pro”试用版本创建ww,fineprint,con,cn4 (3) Ec = Vf E f + Vm Em (4) Inverse rule of mixture or Ec -1=VmEm -1+VfEf -1 where E is the modulus of elasticity (elastic modulus), V is volume fraction, (c) refers to the composite material, (f ) refers to fibers, and (m) refers to matrix 3. (3pt) Explain why carbon fiber reinforced composites are widely used in manufacturing airplane. Carbon fibers are light weight, and have high strength, toughness, specific modulus, high dimensional stability, low coefficient of thermal expansion, and low abrasion, which ensure carbon fiber reinforced composites as an ideal material in airplane industry. VI. Complex questions. (20points) 1. Predict which polymer in each pair listed can have higher degree of crystallinity, and justify your answer. (12) (1) PE > Polystyrene (PS) Polymers with large, bulky side groups cannot be packed efficiently, and therefore have difficulty forming crystals (2) LDPE < HDPE Polymers with branched chains cannot be packed efficiently, and hence it is far more difficult to form crystals (3) PE > Nylon Polymers with long repeat units require more extensive chain segment motion to establish Long range order, and hence it will crystallize slowly, and can be easily formed into glasses using modest quench rates. (4) Atactic [C2H3(CH3)]n < isotactic [C2H3(CH3]n Symmetrical structures that permit close packing of chains favour crystallinity. (5) isotactic (C2H3Cl)n , > isotactic (C2H3CH3 )n Stronger secondary forces allow greater compacting. The existence of small, regularly spaced polar side groups can aid in the formation of polymer crystals by providing a driving force for the necessary alignment of adjacent chain segments. (6) Cooling molten PP to form solid PP under high cooling rate or under low cooling rate Polymers are long chain structures. The movement of polymer chains needs time. Slow cooling means giving Polymer chains more time to allow them to PDF 文件使用 "pdfFactory Pro" 试用版本创建 www.fineprint.com.cn