I'm trying to answer a question regarding tensile testing and how the real tests may vary from theoretically. I'm thinking temperature but think I may be missing something more obvious?
Temperature effects are negligible within +/- 50 degrees F of ambient.
Most theoretical predictions of tensile strength do not include the effects of dislocation travel which is the primary source of ductility in engineering metals, and greatly reduces their strength from what one would calculate assuming perfect crystalline structure.
Furthermore, theoretical predictions of tensile strength cannot take into account the presence of manufacturing flaws in the test samples.