I have this real graphic from a tensile test

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SUMMARY

The discussion centers on calculating the ultimate stress from a tensile test graphic, specifically focusing on the stress indicated in the green rectangle. The user presents two deformation tests from the same material, with the orange curve representing stress versus unit deformation for the first test and the gray curve for the second. The blue curve is claimed to be the average of the two tests, although some participants challenge this interpretation, suggesting that the red rectangles do not accurately represent fracture stresses due to potential machine calibration issues affecting displacement readings.

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Queren Suriano
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Homework Statement


How can I calculate the ultimate stress? (I refere to the stress that it's in the green rectangle). I have a real graphic, I have two deformations, (it was 2 test, from the same material) and only one stress. The orange curve is Stress versus unit deformation 1, and the gray one is stress vs. deformation 2 . The blue one is the average between the deformation 1 and 2 vs Stress. The REAL graphic from I want calculate this, it's in the last part of the post

upload_2015-4-29_9-34-26.png


Homework Equations



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The Attempt at a Solution



I know that fracture stress is in the red rectangle. I know that the graphic in the last part of the curves, it's illogic (because the deformation "decrease") but the stress is ok, because is the real fracture stress

upload_2015-4-29_9-36-9.png
[/B]
 
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I don't think the red rectangles are the fracture stresses. When the specimens failed the testing machine probably rebounded and since the machine is most likely calibrated using a strain gauge it gave you some negative displacement values. Not sure why an increased load was measured but I would be attempted to ignore these values.

Also the blue curve does not look like the average of the two curves to me.
 
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