On the interpretation of microstrain measurements in iron
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and 175 ksi (1210 N / m s) on the hard side and soft side, experiments which employed both tension and compresrespectively. Previous tests have established the 0.2 sion testing and capacitance transducers or L V D T ' s to pct yield strength of the hard and soft side as 187 ksi measure displacements. The values of elastic limit (1290 N / m 2) and 159 ksi (1100 N/m2), respectively, so that at the notch root plastic delormation has been initi- measured at a strain sensitivity of 10 -e have spanned m o r e than an order of magnitude, as shown in Table I. ated. With the higher stress, the crack develops first In some recent experiments 6 we have used all the on the hard side. Tensile fracture origins have also above techniques on both polycrystalline and single been traced to hard side,2 probably for the same reacrystal specimens of iron, which had been either hyson. Associated with hard side is a lower value of drogen purified or doped with 0.15 pct Ti to remove fracture toughness so that it is not surprising that the the influences of interstitialimpurities, such as discrack becomes critical before reaching the soft side continuous yielding and strain aging. In this work we as shown in Fig. 2(b). have found that all of the techniques gave essentially 1. S. J. Manganello and K. H. Abbott: J. Mater., 1972, vol. 7, p. 23 I. equivalent results, as shown in Fig. 1. Here, for ex2. C. F. Hickey, Jr.: J. Mater., 1968, vol. 3, p. 3. 3. A. A. Anetil and E. B. Kula: Rept. No. AMMRC TR 69-26, Army Materials and ample, it can be seen that the r o o m temperature valMechanics Research Center, Watertown, Mass., 1969. ues lie between 2.9 and 6 ksi for all types of speci4. A. A. Anctil, R. Chait, and E. B. Kula: Rept. No. AMMRC TR 73-6, Army mens. In addition, the shape of the load-unload loops Materials and Mechanics Research Center, Watertown, Mass., 1973. was always found to be lenticular, regardless of the 5. R. Papirno and B. S. Parker: Amer. Soc. Test. Mater., Spec. Tech. Publ. 519, p. technique used. This is in contrast to the elastic limit 98, ASTM, Philadelphia, 1973. 6. R. Papimo: Exp. Mech., 1971, vol. 11, p. 446. of 0.7 ksi reported for iron s and the parallelogram7. R. Papimo: Rept. No. AMMRC TN 69-07, Army Materials and Mechanics Reshape loops reported for both iron s and tantalum search Center, Watertown, Mass., 1969. crystals.~ The latter experiments utilized compression tests
C)n the Interpretation of Microstrain Measurements in Iron D. S. TOMAT,TN, D. P. POPI~.,AND C. J. McMAHON, JR.
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10 y e a r s a n u m b e r of i n v e s t i g a t o r s have reported a range of values of the e l a s t i c limit and m i c r o y i e l d s t r e s s of iron obtained from m i c r o s t r a i n D. S. TOMALIN, formerly with the School of Metallurgy and Materials Science, University o f Pennsylvania, Philadelphia, Pa. 19174, is now Staff Scientist, General Electric Co., Vallecitos Nuclear Center, Pleasanton, Calif. D. P. POPE and C. J. McMAHON, JR. are Assistant Professor and and Associate Professor, respectively, S
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