Analytical, numerical and experimental study of the thermal influence in strain measurements of structural elements

Abstract

Strain measuring on structural el ements requires to take necessary precautions during the design and as- sembly of the strain gage element, as well as during th e measurement interpretation process. In general, the ele- ments that make up a structure are designe d so that they are able to withstand the applied load, and so that the con- sequent distortion does not affect its nor mal function. The distortion raises an important issue related to the strain measurement, as due to design principles it should be minor . Thereby, the distortions to be evaluated are in the same order of magnitude as those due to external factors, such as thermal expansion. In this work, we study how thermal expansion affects the strain gauging on a beam when a specific device is used. We show different alternatives to compensate the measured deformation, so that the final measurement reflects the intended information. The system we consider has a large beam where a parallel strain gage device is applied and a thermometer is used to measure ambient temperature. The masses of each element of the system yield different thermal variation rates, and hence their thermal expansion variation rates are also different. In order to compensate this fact, we present the analysis of the physical phenomenon that relates the heat contributed to the system and th e masses of the elements. The results are compared to empirical measurements. Finally, the analysis of the experimental measurements is studied, and we propose a computational model based on artificial neur al networks to estimate the thermal expansion.