Metals such as titanium and stainless steel are frequently used for orthopedic implants such as artificial hip and knee joints. As with most metals, though, their elastic properties are significantly different from those of bone. Recently, metal "foams" made from aluminum and steel have been shown to have promising properties for use as implants.

(a) A 0.5-m-long piece of bone with a certain cross-sectional area shortens by 0.10 mm under a given compressive force. By how much does a piece of steel with the same length and cross-sectional area shorten if the same force is applied?

(b) In order to determine whether a material such as the aluminum-steel foam behaves similarly to bone, plots of measured stress (force per area) versus strain (ΔL/L0) such as the ones shown in FIGURE 17-40 may be used. Which one of these plots corresponds to a material with elastic properties equal to those of bone in compression?

(c) What is the value of Young's modulus for the material represented by curve D?

Figure 17-40,

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120 100 80 A 60 B. 40 D 20 0.001 0.002 0.003 0.004 0.005 0.006 Strain (m) Stress (MN/m?) ||||