Abstract: Tubular bar will produce stress and strain when bearing shear force and bending moment. Strain of bar is usually measured by strain gauge. Strain gauge will deviate and deflect inevitably when pasted to the tubular bar, resulting in strain measurement errors. According to stress state and elastic theory of stress-strain, the stress, strain and their errors at different positions of tubular bars with diameters of 14-20 mm were analyzed. Example analysis indicates that the strain error is not more than 5% when the deviation is not more than 4 mm and the deflection is not more than 4°. The influence of Poisson ratios of tubular bar on strain error can be basically neglected.

Key words: tubular bar, strain gauge, strain measurement, error analysis, elastic theory