Specimen Size and Measurement Error
The stress is calculated by dividing the tensile force by the cross-sectional area of the specimen. For circular specimens, the cross-sectional area is defined by the specimen diameter. Therefore, any uncertainty in diameter measurement directly affects the calculated stress.
In the JTE publication, the Gaussian error of stress calculation is discussed for a circular cross-section. The example shows that for a specimen with a diameter of 0.5 mm and a diameter uncertainty of 25 μm, an error of about 10 % of the ultimate tensile stress has to be considered. If the diameter uncertainty is reduced to 5 μm, the error is reduced to about 2 %.
This illustrates why precise diameter measurement and reproducible specimen geometry are essential for reliable micro tensile test data.