Comparison of shear properties of GFRP, determined using strain gauges and a video extensometer

Characterization of shear properties of fiber reinforced plastics requires measurement of shear strain. Strain gauges generally used for this purpose are prone to errors, especially due to the sensor application. Optical strain measurements based on digital image correlation or feature recognition therefore seem advantageous and very promising. In the present work, in-plane shear modulus and shear strength of a glass fiber reinforced plastic are determined according to ISO 14129. Shear strain is measured both using strain gauges and a video extensometer. Evaluation and comparison of the results show that there are negligible differences between the two strain measurement techniques in the beginning of the tests. Shear modulus values therefore differ by only 0.5 % on average. With increasing load, however, the video extensometer records larger strains than the strain gauges. This is attributed to the larger gauge length of the optical measurement, which includes local areas with larger strain. Nevertheless, shear strength values differ by only 1.4 % on average. The use of a video extensometer hence appears suitable for shear tests according to ISO 14129.