北京化工大学2006—2007学年第二学期 《材料导论》期末考试试卷标准答案 出卷人：耿海萍；审阅人：于运花、刘莲英 I.Choose the BEST TERM to match the definition and translate the selected term into Chinese(10pts). 1C粘合剂2A被粘物3F孀变4D应力松驰5H粘弹性 6J滞后7Q异构体8M预浸坯料9P层状复合材料10N混杂复合材料 ll.Choose the correct answers to the following questions(35points) 1-5 ABECC,6-10 BBDAC 11-15 CBBAC,16-20 AABAC 21-25 BDCCD,26-30 DCBCD 31-35 DAABA Ill.Choose a correct word or phrase according to the basic concepts and write it in the space provided.(15 points) 1.Copolymers are classified into four sub group s:1)Random copoly mer.2) Block- 3)Alternative 4)Graft according to the ordered degree of molecular arrangement. 2.According to mechanism,polymerization can be classified into 5)Chain reaction (addition)polymerization,and 6)Step reaction (condensation) polymerization. 3.According to the matrix materials,composites are classified into 7)Metal Matrix Composite 8)Ceramic ~9)Polymer~ 4.10)Specific tensile strength is the ratio of the tensile strength of a fiber material to its weight density. 5.The ratio of length (L)to diameter(D)of a reinforcing fiber is know as 11) aspect ratio 6. The four basic types of hybrid composites are 12)Interply Hybrid,13) Intraply Hybrid,14)Interply/Intraply Hybrid,and superhybrid. 7.The term used to describe the crystallinity of polymers is 15)_Degree of Crystallinity. PDF文件使用"pdfFactory Pro”试用版本创建，fineprint,com,cn
1 北京化工大学 2006—2007 学年第二学期 《材料导论 II》期末考试试卷标准答案 出卷人：耿海萍；审阅人：于运花、刘莲英 I. Choose the BEST TERM to match the definition and translate the selected term into Chinese (10pts). 1 C 粘合剂 2 A 被粘物 3 F 蠕变 4 D 应力松弛 5 H 粘弹性 6 J 滞后 7 Q 异构体 8 M 预浸坯料 9 P 层状复合材料 10 N 混杂复合材料 II. Choose the correct answers to the following questions (35points) 1-5 ABECC, 6-10 BBDAC 11-15 CBBAC, 16-20 AABAC 21-25 BDCCD, 26-30 DCBCD 31-35 DAABA III. Choose a correct word or phrase according to the basic concepts and write it in the space provided. (15 points) 1. Copolymers are classified into four subgroups: 1) Random copolymer, 2) Block ~ 3) Alternative ~ , 4) Graft ~ according to the ordered degree of molecular arrangement. 2. According to mechanism, polymerization can be classified into 5) Chain reaction (addition) polymerization , and 6) Step reaction (condensation) polymerization. 3. According to the matrix materials, composites are classified into 7) Metal Matrix Composite ; 8) Ceramic ~ ; 9) Polymer ~ . 4. 10) Specific tensile strength is the ratio of the tensile strength of a fiber material to its weight density. 5. The ratio of length (L) to diameter (D) of a reinforcing fiber is know as 11) aspect ratio . 6. The four basic types of hybrid composites are 12) Interply Hybrid , 13) Intraply Hybrid , 14) Interply/Intraply Hybrid , and superhybrid. 7. The term used to describe the crystallinity of polymers is 15) Degree of Crystallinity. PDF 文件使用 "pdfFactory Pro" 试用版本创建 www.fineprint.com.cn
IV.True or false questions.If you think the statement is true,write the letter"T"; otherwise,write the letter"F"(10points) 1-5T F TT F,6-10 FFTTF,11-15 TTTFF,16-20 TFTTT PDF文件使用”pdfFactory Pro”试用版本创建w,fineprint.con.cn
2 IV. True or false questions. If you think the statement is true, write the letter “T”; otherwise, write the letter “F” (10points) 1-5 T F TT F, 6-10 FFTTF, 11-15 TTTFF, 16-20 TFTTT PDF 文件使用 "pdfFactory Pro" 试用版本创建 www.fineprint.com.cn
V.Give a simple answer to the following questions(10points) 1.(3 pt)What are polymers,homopolymers and copolymers?And another name for polymer is Macromolecules A polymer is a chain like molecule made up of smaller units"monomers".The monomers",made up of atoms,bond together covalently to form a polymer that usually has a carbon backbone. When a polymer is made by linking only one type of monomer together,it is called a homopolymer. When two different types of monomers are joined in the same polymer chain, the polymer is called a copolymer 2.(4 pt)Figure 1 is Graphical plot of the tensile modulus of a unidirectional composite material loaded under iso-strain iso-stress conditions as a function of volume fraction of reinforcing fiber. (1)Which curve is the tensile modul s curve under iso-strain loading condition? (2)Draw a sketch to show iso-strain loading. (3)Under iso-strain loading,the modulus of elasticity can be calculated by equation (4)Under iso-stress loading,the modulus of elasticity can be calculated by equation 边E Figure 1 Em 0.25 0.50 0.75 1.0 Volume fraction of fiber (1)A:iso-strain loading,B:iso-stress loading 2 iso-strain loading PDF文件使用“pdfFactory Pro”试用版本创建，fineprint,con,cn
3 Ef Em Te n sile M o d ulu s (E c) 0.5 Volume Fraction of fiber (Vf) Isotrain conditions Isostress conditions Volume fraction of fiber Em Ef A B C o m p osite M o dulus Figure 1 V. Give a simple answer to the following questions (10points) 1. (3 pt) What are polymers, homopolymers and copolymers? And another name for polymer is Macromolecules ? A polymer is a chain like molecule made up of smaller units "monomers". The "monomers", made up of atoms, bond together covalently to form a polymer that usually has a carbon backbone. When a polymer is made by linking only one type of monomer together, it is called a homopolymer. When two different types of monomers are joined in the same polymer chain, the polymer is called a copolymer. 2. (4 pt) Figure 1 is Graphical plot of the tensile modulus of a unidirectional composite material loaded under iso-strain & iso-stress conditions as a function of volume fraction of reinforcing fiber. (1) Which curve is the tensile modulus curve under iso-strain loading condition? (2) Draw a sketch to show iso-strain loading. (3) Under iso-strain loading, the modulus of elasticity can be calculated by equation . (4) Under iso-stress loading, the modulus of elasticity can be calculated by equation . (1) A: iso-strain loading, B: iso-stress loading (2) iso-strain loading PDF 文件使用 "pdfFactory Pro" 试用版本创建 www.fineprint.com.cn
(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)LDPENylon 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)]nisotactic(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,cn
4 (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 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 (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
align. 2.What is a fiber-reinforced composite primary composed of?Discuss the major functions of each component in a composite?Discuss the factors which affect the properties of fiber-reinforced composites.(8) A fiber-reinforced composite (FRC)is primary composed of matrix,fiber and coupling agent. In FRC,fibers are used as the principal load-carrying agent.The reinforcement in FRC is mostly realized by fibers. In FRC,the major functions of matrix are to support and protect the fibers, distribute the load among fibers,and transfer of loads to fibers. In FRC,coupling agents are used to treat the surface of fibers in order to form a flexible layer at the interface between fiber and matrix,improve their adhesion and reduce the number of voids trapped in the material. The factors which affect the properties of FRC include: 1 Characteristics of Fiber:including types of fiber used,fiber loading,fiber aspect ratios,fiber Orientation.For example:(1)In FRCs,the strength and stiffness may be controlled by specifying the fiber orientation.The highest levels of properties are achieved when all fibers are aligned along the primary loading direction within the composite.(2)A higher volume fraction of fibers in the resin matrix improves the mechanical properties of composites. 2 Properties of Matrix:The matrix's ability to adhere to the fibers,as well as its inherent toughness,make a contribution to the properties of composites. 3 Adhesion between fibers and matrix:Without adequate adhesion the fiber acts as an inclusion in the resin matrix,which actually weakens the composite. 4 Mode of Fabrication:For example:A significant processing aspect that affects performance is the degree to which the fibers are saturated with wet matrix, leaving few or no voids. 5 PDF文件使用"pdfFactory Pro”试用版本创建ww,fineprint..com,cn
5 align. 2. What is a fiber-reinforced composite primary composed of? Discuss the major functions of each component in a composite? Discuss the factors which affect the properties of fiber-reinforced composites. (8) A fiber-reinforced composite (FRC) is primary composed of matrix, fiber and coupling agent. In FRC, fibers are used as the principal load-carrying agent. The reinforcement in FRC is mostly realized by fibers. In FRC, the major functions of matrix are to support and protect the fibers, distribute the load among fibers, and transfer of loads to fibers. In FRC, coupling agents are used to treat the surface of fibers in order to form a flexible layer at the interface between fiber and matrix, improve their adhesion and reduce the number of voids trapped in the material. The factors which affect the properties of FRC include: 1 Characteristics of Fiber: including types of fiber used, fiber loading, fiber aspect ratios, fiber Orientation. For example: (1) In FRCs, the strength and stiffness may be controlled by specifying the fiber orientation. The highest levels of properties are achieved when all fibers are aligned along the primary loading direction within the composite. (2) A higher volume fraction of fibers in the resin matrix improves the mechanical properties of composites. 2 Properties of Matrix: The matrix's ability to adhere to the fibers, as well as its inherent toughness, make a contribution to the properties of composites. 3 Adhesion between fibers and matrix: Without adequate adhesion the fiber acts as an inclusion in the resin matrix, which actually weakens the composite. 4 Mode of Fabrication: For example: A significant processing aspect that affects performance is the degree to which the fibers are saturated with wet matrix, leaving few or no voids. PDF 文件使用 "pdfFactory Pro" 试用版本创建 www.fineprint.com.cn
