Errors Due to Transverse Sensitivity

Errors in strain indication due to transverse sensitivity are generally quite small since the transverse sensitivity itself is small. However, in biaxial strain fields characterized by extreme ratios between principal strains, the percentage error in the smaller strain can be very great if not corrected for transverse sensitivity. On the other hand, in the particular case of uniaxial stress in a material with a Poisson's ratio of 0.285, the error is zero because the gage factor given by the manufacturer was measured in such a uniaxial stress field and already includes the effect of the Poisson strain. It is important to note that when a strain gage is used under any conditions other than those employed in the gage-factor calibration, there is always some degree of error due to transverse sensitivity. In other words, any gage which is: (a) installed on a material with a different Poisson's ratio; or (b) installed on steel, but subjected to other than a uniaxial stress state; or (c) even installed on steel with a uniaxial stress state, but aligned with other than the maximum principal stress, exhibits a transverse-sensitivity error which may require correction.

The historical practice of quoting gage factors which, in effect, mask the presence of transverse sensitivity, and which are correct in themselves for only a specific stress field in a specific material, is an unfortunate one. This approach has generally complicated the use of strain gages, while leading to errors and confusion. Although the uniaxial stress field is very common, it is not highly significant to the general field of experimental stress analysis. There is no particular merit, therefore, in combining the axial and transverse sensitivities for this case.

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