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I'm a few years out of school and out of practice on my Mechanics of Materials, so please pardon the fundamental question. Are there limitations on the use of the stress transformation equations in plane stress situations? For example I find the transformation equations don't yield the correct results when transforming the stress for a square plate, pulled in tension at it's corners (sectioned across it's diagonal) 45 degrees to get the stress when the plate is sectioned parallel to one pair of sides. Basically the transformation equations are yielding different results than if I were to just section the plate at 45 degrees and balance the internal forces.

Do the stress transformation equations assume your original stresses are found at the smallest cross sectional area? I can't find that limitation in any textbooks.

Thanks for the help.

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# Stress Transformation Question (Plane Stress)

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