Fig. 1. Principle of optical extensometer. (a) Arrangement of two rhombic prisms; (b) construction of optical extensometer; (c) captured image

Fig. 2. Diagram of gauge-length calibration

Fig. 3. Schematic diagram of segmented strain measurement in DIC

Fig. 4. Calculation flow chart of segmented strain superposition

Fig. 5. Tensile specimens. (a) Epoxy resin material; (b) glass fiber material

Fig. 6. Photos of field-of-view splitting device. (a) Front view; (b) side view

Fig. 7. Experimental setup

Fig. 8. Comparison of strain results before and after correction using strain gauge in the first group of tensile tests

Fig. 9. Speckle patterns obtained from the first specimen tensile test. (a) The first one; (b) the 300th one; (c) the 1000th one

Fig. 10. Strain results obtained by large strain optical extensometer and strain gauge in three tensile tests. (a) Specimen 1; (b) specimen 2; (c) specimen 3

Fig. 11. Strain results of tensile test for glass fiber specimen