2.13, 4749, 51, Gd. 5961
2.1 Can you calculate the percent elongation of materials based only on the information given in Fig. 2.6? Explain.
Recall that the percent elongation is defined by Eq. (2.6) on p. 33 and depends on the original gage length (l
o
) of the
specimen. From Fig. 2.6 on p. 37 only the necking strain (true and engineering)
and true fracture strain can be determined. Thus, we cannot calculate the percent elongation of the specimen; also,
note that the elongation is a function of gage length and increases with gage length.
2.2 Explain if it is possible for the curves in Fig. 2.4 to reach 0% elongation as the gage length is
increased further.
The percent elongation of the specimen is a function of the initial and final gage lengths. When the specimen is
being pulled, regardless of the original gage length, it will elongate uniformly (and permanently) until necking
begins. Therefore, the specimen will always have a certain finite elongation. However, note that as the specimen’s
gage length is increased, the contribution of localized elongation (that is, necking) will decrease, but the total
elongation will not approach zero.
2.3 Explain why the difference between engineering strain and true strain becomes larger as strain increases. Is this
phenomenon true for both tensile and compressive strains? Explain.
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 Spring '08
 RHSturges
 Materials Science, Tensile strength, percent elongation, gage length

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