第4项共6页 2.Give examples to explain how the properties of polymers are influenced by the structure or processing methods of polymers.(4pts) Polypropylene (PP)is a good example to explain the relationship between the structur and properties of polymers.For instance.if PP is isotactic.then it has a high degree of crystallinity,PP in turn becomes useful materials for refrigerators,washing machines. bumpers.However,if PP is atactic.it then has amorphous structure.and the corresponding materials are sticky liquid,and they are useless. 3.Discuss the factors influencing the properties of fiber-reinforced composites.(6pts) The properties of fiber-reinforced composites depend on the fiber,the matrix and processing methods.The fiber influence the properties of fiber-reinforced composites through its loading aspect ratio,(inluding straightness.degree of knitting interlacing).and defects in atomic structure or macrodefects on the surfaces of the fibers The matrix's ability to adhere to the fibers,as well as its inherent toughness,also makes a contribution.The processing method that affects performance of composite is the degree to which the fibers are saturated with wet matrix,leaving few or no voids. 4.Define the term of"wind angle"for filament winding.How do the hoop tensile strength and axial tensile strength change with wind angle?(4pts) The properties of composites are influenced by A:The"wind angle"is measured between the axis of the mandrel and the lay of the filaments.The tangent of this angle is the ratio of the circumference of the mandrel and the pitch of the filaments.The hoop tensile strength increases with wind angle,while the axial tensile strength decreases with wind angle 第 4 页 共 6 页 4 2. Give examples to explain how the properties of polymers are influenced by the structure or processing methods of polymers. (4pts) Polypropylene (PP) is a good example to explain the relationship between the structure and properties of polymers. For instance, if PP is isotactic, then it has a high degree of crystallinity, PP in turn becomes useful materials for refrigerators, washing machines, bumpers. However, if PP is atactic, it then has amorphous structure, and the corresponding materials are sticky liquid, and they are useless. 3. Discuss the factors influencing the properties of fiber-reinforced composites. (6pts) The properties of fiber-reinforced composites depend on the fiber, the matrix and processing methods. The fiber influence the properties of fiber-reinforced composites through its loading, aspect ratio, orientation (including straightness, degree of knitting, interlacing), and defects in atomic structure or macrodefects on the surfaces of the fibers. The matrix’s ability to adhere to the fibers, as well as its inherent toughness, also makes a contribution. The processing method that affects performance of composite is the degree to which the fibers are saturated with wet matrix, leaving few or no voids. 4. Define the term of “wind angle” for filament winding. How do the hoop tensile strength and axial tensile strength change with wind angle? (4pts) The properties of composites are influenced by A: The “wind angle” is measured between the axis of the mandrel and the lay of the filaments. The tangent of this angle is the ratio of the circumference of the mandrel and the pitch of the filaments. The hoop tensile strength increases with wind angle, while the axial tensile strength decreases with wind angle