Small high-elongation foil strain gages as fatigue-damage indicator

Small, high-elongation foil strain gages were employed to study cyclic loading of cylindrical specimens in closed-loop testing equipment. The strain gages were developed especially for the low-cycle loading conditions; annealed constantan foil was adopted for the tensometric grid, and highly deformable glues were used as backing and to attach the gages to specimens. Low-cycle loading was found to induce changes in tensometric sensitivity for high levels of initial strain and during the cyclic loading process. The strain gages failed after a certain number of cycles, the number being dependent on the strain range. Zero shifting of the strain gages was also noted during the low-cycle loading experiment.