In a tensile test of mild steel, how does the fracture stress compare to the ultimate tensile stress_________________?
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Answer: B. less
Explanation
During a tensile test of mild steel, the actual fracture stress evaluated at the reduced neck area is lower than the nominal ultimate tensile stress calculated on the original area. Although true stress continues increasing up to the point of rupture, engineering stress uses the constant initial cross-sectional area. Localized necking drastically reduces the cross-sectional area, making the nominal engineering stress at fracture appear lower than the peak ultimate value. Engineering stress divides the applied load by the original cross-sectional area of the tensile test specimen. True stress divides the applied load by the instantaneous actual cross-sectional area at any given point during the test. Mild steel undergoes significant plastic deformation and localized necking after reaching its ultimate tensile strength.
The fracture stress in engineering terms is never more than the ultimate tensile stress because necking reduces the force required to break the sample. The fracture stress and ultimate tensile stress are clearly different values due to the progressive reduction of the cross-sectional area. The relationship between fracture stress and ultimate tensile stress remains consistently lower for mild steel under standard test conditions.
- Subject
- Engineering
- Category
- Mechanical Engineering
- Topic
- —
- Difficulty
- medium
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