lec22_ex_prob

# lec22_ex_prob - MASSACHUSETTS INSTITUTE OF TECHNOLOGY...

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MASSACHUSETTS INSTITUTE OF TECHNOLOGY DEPARTMENT OF MECHANICAL ENGINEERING CAMBRIDGE, MASSACHUSETTS 02139 2.002 MECHANICS AND MATERIALS II EXAMPLE PROBLEM Distributed : Wednesday, April 28, 2004 Two steels commonly used in the ground vehicle industry are SAE 1015 and SAE 1045. (SAE: Society of Automotive Engineers) Compositions include: Material C Mn S Si P Fe 1015 0 . 14% 0 . 47% 0 . 025% 0 . 037% 0 . 0004% bal. 1045 0 . 48% 0 . 71% 0 . 025% 0 . 20% 0 . 14% bal. The 1015 steel is normalized, leading to a Brinnel hardness of H B = 80, and the 1045 is quenched and tempered (at 500 o F ), leading to H B = 500. Monotonic stress-strain properties are: Material E ( σ y ) 0 . 2% UT S f σ f n ( ksi ) ( ksi ) ( ksi ) ( ksi ) 1015 1045 30 × 10 3 30 × 10 3 33 245 60 265 1 . 14 0 . 71 105 330 0 . 26 0 . 047 and cyclic properties include: Material ( σ y ) 0 . 2% ( ksi ) n K ( ksi ) σ f ( ksi ) f b c 1015 1045 35 185 0 . 22 0 . 12 137 120 330 0 . 95 0 . 25 0 . 11 0 . 64 0 . 08 0 . 68 (a) On an appropriate log-log plot, construct the strain amplitude/reversals to failure curves for each of the two steels. (b) Which material is “better” for low cycle fatigue?

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