Page 254 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

Synthesis, Design, and Projects 233

9.25. Do metal-matrix composites have any advantages 9.30. Describe situations in which a glass could be used as a
over reinforced plastics? Explain. matrix material.
9.26. Give reasons for the development of ceramic-matrix 9.3 I. When the American Plains states were settled, no trees
composites. Name some applications and explain why they existed for the construction of housing. Pioneers cut bricks
should be effective. from sod-basically, prairie soil as a matrix and grass and
its root system as reinforcement. Explain why this approach
9.27. Explain how you would go about determining the
hardness of reinforced plastics and of composite materials. was successful. Also, if you were a pioneer, would you stack
Are hardness measurements on these types of materials mean- the bricks with the grass horizontally or vertically? Explain.
ingful? Does the size of the indentation make any difference? 9.32. By incorporating small amounts of a blowing agent, it
Explain. is possible to manufacture hollow polymer fibers with gas
9.28. How would you go about trying to determine the cores. List possible applications for such fibers.
strength of a fiber?
9.29. Glass fibers are said to be much stronger than bulk
glass. Why is this so?

QUANTITATIVE PROBLEMS

|]9.33. Calculate the average increase in the properties of u9.38. Repeat the calculations in Example 9.1 (a) if
the plastics given in Table 7.1 as a result of their reinforce- Nextel 610 fiber is used and (b) if Spectra 2000 is used.
ment, and describe your observations. 9.39. Refer to the properties listed in Table 7.1. If acetal is
9.34. In Example 9.1, what would be the percentage of the reinforced with E-type glass fibers, what is the range of fiber
load supported by the fibers if their strength were 1000 MPa content in glass-reinforced acetal?
and the matrix strength were 200 MPa? What would be the |]9.40. Plot the elastic modulus and strength of an alu-
answer if the fiber stiffness were doubled and the matrix stiff- minum metal-matrix composite with high-modulus carbon
ness were halved? fibers as a function of fiber content.
|]9.35. Calculate the percent increase in the mechanical 9.4l. For the data in Example 9.1, what should be the fiber
properties of reinforced nylon from the data shown in Fig. 9.5. content so that the fibers and the matrix fail simultaneously?
|]9.36. Plot E/p and E/p0'5 for the composite materials Use an allowable fiber stress of 200 MPa and a matrix
listed in Table 9.1, and compare your results with the proper- strength of 30 MPa.
ties of the materials described in Chapters 4 through 8. (See
also Table 9.2.)
u9.37. Calculate the stress in the fibers and in the matrix
in Example 9.1. Assume that the cross-sectional area is 150
mm; and PC = 220 kg.

SYNTHESIS, DESIGN, AND PROJECTS

9.42. What applications for composite materials can you 9.48. What applications for composite materials can you
think of other than those given in Section 9.4? Why do you think of in which high thermal conductivity would be desir-
think your applications would be suitable for these materials? able? Explain.
9.43. Using the information given in this chapter, develop 9.49. As with other materials, the mechanical properties of
special designs and shapes for possible new applications of composites are obtained by preparing appropriate specimens
composite materials. and then testing them. Explain what problems you might en-
9.44. Would a composite material with a strong and stiff counter in preparing specimens for testing in tension. Suggest
matrix and a soft and flexible reinforcement have any practi- methods for making appropriate specimens, including fash-
cal uses? Explain. ioning their shape and how they would be clamped into the
jaws of testing machines.
9.45. Make a list of products for which the use of compos-
ite materials could be advantageous because of their 9.50. Developments are taking place in techniques for
anisotropic properties. three-dimensional reinforcement of composites. Describe (a)
applications in which strength in the thickness direction of
9.46. Inspect Fig. 9.1 and explain what other components of
the composite is important and (b) your ideas on how to
an aircraft, including the cabin, could be made of composites.
achieve this strength. Include simple sketches of the structure
9.47. Name applications in which both specific strength and utilizing such reinforced plastics.
specific stiffness are important.