Strain-Gage Reinforcement Effects on Orthotropic Materials

Abstract

There is both experimental and analytical evidence that the stiffness of a strain gage can produce a significant reinforcement error when it is installed on a low-modulus material such as a plastic.^1–4 This raises the question of errors due to the same effect when strain measurements are made on some types of orthotropic materials (e.g., unidirectionally reinforced plastics) which are characterized by a low elastic modulus in at least the minor principal material direction. Actually, as indicated by the goniometric distribution of mechanical properties plotted in Fig. 1, the elastic modulus of such a material is typically low in most directions, and not far from that of the plastic matrix, except for an angular range of about ± 30 deg from the major principal material axis.