LECTURE 12.2

1. LECTURE 12.2

2. LECTURE OUTLINE • Lesson 12 Quiz Feedback • Ashby Maps

3. Q1. Table 1 shows some of the materials that were listed as Table 3.4 in the book. Use this information to answer the following question. The object is to design a scratch resistant countertop for the kitchen. Which material would be employed for maximum scratch resistance? <a> Soda-Lime Glass <b> HDPE <c> Tungsten <d+> Alumina <e> Mullite

4. Q2. Table 1 presents some property measurements for a series of materials, while Figure 1 plots the Young's moduli of these materials as a function of their specific gravities. The line P passes through the datum point for our benchmark material: aluminum. The datum point marked A on Figure 1 corresponds to _______. <a+> alumina <b> tungsten <c> copper <d> mullite <e> nylon

5. Q3. Table 2 presentsatomic numbers (At #), melting points (MP),specific gravities (SG), and Mohs Hardness values (H) for a series of metals and their corresponding oxides. The specific gravity of a metal oxide increases as the specific gravity of the metal increases. <a> Always true <b+> Sometimes false

6. Q4. Table 2 presents some properties of a variety of materials. Corundum is a ________. <a> metal <b+> ceramic <c> polymer <d> composite <F> Corundum is a compound; it is non-metallic and inorganic; it is an oxide-ceramic.

7. Q5. Table 2 presents some properties of a variety of materials. Corundum is an ore for which metal? <a> Magnesium <b+> Aluminum <c>Manganese <d> Iron <e> Copper

8. Q6. Figure 2 shows the variation in the specific strengths of a series of composites (also see Chapter 27) as a function of the percent of glass fiber in the composite. In order to attain a specific strength of approximately 105 MPa, the % fiber should be about _______. <a> 10 <b> 20 <c> 30 <d+> 40 <e> 50

9. Q7. Table 3 presents the specific gravities, Young's moduli, and yield strengths for a series of materials. The specific modulus of an alloy steel is approximately _______. <a+> 26 MPa <b> 13 GPa <c> 128 GPa <d> 260 GPa <e> 1280 GPa

10. Q8. Table 3 presents some property measurements for a series of materials, while Figure 3 plots the yield strengths of these materials as a function of their specific gravities. The line P passes through the datum point for our benchmark material: aluminum. The datum point marked A on Figure 3 corresponds to ______. <a+> CFRP <b> titanium alloys <c> alloy steel <d> alumina <e> GFRP

11. Q10. The semiconductor gallium arsenide (GaAs) has a specific gravity of about 5.5 and a Young's modulus of approximately 100 GPa. Is gallium arsenide a better or worse choice than aluminum (our benchmark material) for an aircraft wing—based on specific stiffness alone? <a> Better <b+> Worse

12. Q11. Table 1 presents some property measurements for a series of materials, while Figure 1 plots the Young's moduli of these materials as a function of their specific gravities. The line P passes through the datum point for our benchmark material: aluminum. Which of the following materials would have a superior performance index for application as an aircraft wing, for which a high value of Young's modulus and a low value of specific gravity are desirable? <a+> Alumina <b> Tungsten <c> Nylon <d> Copper

13. PERFORMANCE • Ashby Maps

14. THE MATERIALS SCIENCE TETRAHEDRON

15. A “PERFORMANCE INDEX” • Define a “performance index” as strength (hardness)/ unit weight, or • Specific Strength = Hardness Specific Gravity

16. SPECIFIC STRENGTH/SPECIFIC STIFFNESS • Weight-limited design! • Suppose that we have two materials, A and B, and that A has a yield strength of 200 MPa and B has a yield strength of 100 MPa. • Could I replace material A with material B for something such as the fuselage of a commercial aircraft? • I would need “struts”of material B that were twice as thick as “struts” of material A. Is this a problem?

17. SPECIFIC STRENGTH/SPECIFIC STIFFNESS II • Answer: It depends on the specific gravity of the two materials! • Case #1: Material B has a specific gravity ~ 0.33 x that of material A. Even though the struts must be twice as thick, they will still weigh less than the smaller struts of Material A. • Case #2: Material B has the same specific gravity as Material A. The struts of Material B will now weigh twice that of Material A.

18. SPECIFIC STRENGTH/SPECIFIC STIFFNESS III • Conclusion • A more important parameter than “strength” is “specific strength,” where: • Specific strength is the strength/unit weight, or: • Specific Strength = Yield Strength Specific Gravity Also: Specific Stiffness = Young’s Modulus Specific Gravity

19. SELECTED PROPERTIES OF SELECTED MATERIALS

20. SELECTED PROPERTIES OF SELECTED MATERIALS

21. SELECTED PROPERTIES OF SELECTED MATERIALS

22. TOWARD THE ASHBY MAP” • E/r = q • “q” is a “number” that can be used as a benchmark. Materials with a larger value of “q” will have a better “specific stiffness” than our benchmark, whereas materials with a lower value of “q” will be inferior. • We can plot the straight line:E = rq • Materials above this line are superior; those below are inferior.

23. A “PROPERTY MAP”

24. Reminder:E/r = q When values ofE/r varyover orders of magnitude, it is necessary to use a “log-log” plot and: logE = logr + logq y = mx + C TOWARD THE ASHBY MAP

25. LINEAR AND LOG-LOG PERFORMANCE MAPS

26. AN ASHBY MAP