338 Appendix:Test 10.(4%)Polyvinyl chloride is stiffer than polyethylene.Explain the scientific origin of this observation.Note that the mer of polyethylene is HH -C-C— HH while the mer of polyvinyl chloride is the same as this except that one for the four hydrogen atoms has been replaced with a chlorine atom 11.(4%)What are the main problems with the method of self-healing involving microcapsules of a monomer? 12.(4%)Describe an effective method of improving the vibration damping ability of a continuous carbon fiber polymer-matrix composite. 13.(4%)Why does the time spent below the melting temperature prior to bonding affect the quality of the bond for polyphenylene sulfide(PPS)? 14.(4%)Why is aluminum foil sufficiently temperature resistant that it can be used in cooking? 15.(4%)Why does corrosion tend to occur in a fastened metal joint? 16.(4%)Why does sand blasting help to improve the corrosion resistance of steel rebars? Void content (Vol..‰%) 25 (a) (b) 15 00.05 0.10.150.2025030.35 Latex/cement ratio Figure A.2.Effect of the latex/cement ratio on the air void content of cement paste:a with 0.53 vol%carbon fibers;b with no fibers
338 Appendix: Test 10. (4%) Polyvinyl chloride is stiffer than polyethylene. Explain the scientific origin of this observation. Note that the mer of polyethylene is H H C C H H while the mer of polyvinyl chloride is the same as this except that one for the four hydrogen atoms has been replaced with a chlorine atom. 11. (4%) What are the main problems with the method of self-healing involving microcapsules of a monomer? 12. (4%) Describe an effective method of improving the vibration damping ability of a continuous carbon fiber polymer-matrix composite. 13. (4%) Why does the time spent below the melting temperature prior to bonding affect the quality of the bond for polyphenylene sulfide (PPS)? 14. (4%) Why is aluminum foil sufficiently temperature resistant that it can be used in cooking? 15. (4%) Why does corrosion tend to occur in a fastened metal joint? 16. (4%) Why does sand blasting help to improve the corrosion resistance of steel rebars? Figure A.2. Effect of the latex/cement ratio on the air void content of cement paste: awith 0.53vol% carbon fibers; bwith no fibers
A.0 Test Solutions 339 17.(4%)Figure A.2 shows the effect of the latex/cement ratio on the air void content of cement paste.Curve (a)is for the case with 0.53 vol%carbon fibers. Curve(b)is for the case without fiber.Explain the features of curve(a)in terms of their scientific origin. Test Solutions Part I(32%) The correct answers are: 1.d 2.e 3.c 4.c 5.e 6.b 7.c 8.d 9.a 10.e 11.b 12.a 13.d 14.c 15.b 16.e Part Il(68%) 1.Any two of the following answers are acceptable:higher modulus;higher ther- mal conductivity;higher electrical conductivity;higher oxidation resistance. 2.[(R-46)/46]/4.5%=22 (R-46)/46=0.99 R-46=45.54 R=91.52. 3.Modulus=(0.57)(3.4GPa)+(0.43)(0.12GPa)=2.0GPa. 4.Inhibition factor =9.9%/2.8%=3.5
A.0 Test Solutions 339 17. (4%) Figure A.2 shows the effect of the latex/cement ratio on the air void content of cement paste. Curve (a) is for the case with 0.53vol% carbon fibers. Curve (b) is for the case without fiber. Explain the features of curve (a) in terms of their scientific origin. Test Solutions Part I (32%) The correct answers are: 1. d 2. e 3. c 4. c 5. e 6. b 7. c 8. d 9. a 10. e 11. b 12. a 13. d 14. c 15. b 16. e Part II (68%) 1. Any two of the following answers are acceptable: higher modulus; higher thermal conductivity; higher electrical conductivity; higher oxidation resistance. 2. [(R − 46)/46]/4.5% = 22 (R − 46)/46 = 0.99 R − 46 = 45.54 R = 91.5Ω. 3. Modulus = (0.57) (3.4GPa) + (0.43) (0.12GPa) = 2.0GPa. 4. Inhibition factor = 9.9%/2.8% = 3.5