Ultrasensitive video extensometer using single-camera dual field-of-view telecentric imaging system

Video extensometer assesses mechanical properties of materials by measuring their length changes under different loadings with combined use of video recording and image processing. In this Letter, an ultrasensitive video extensometer implemented on a single-camera dual field-of-view (dual FOV) telecentric imaging system is proposed. The method integrates the idea of FOV separation and telecentric imaging, which can increase the strain resolution with an order of magnitude and enhance the strain accuracy significantly. Validation experiments indicate that the root mean square error of a video extensometer was effectively decreased from 25.2 to 4.4 microstrains after employing the proposed method. Time-varying thermal strains of Al alloy and alumina ceramic samples were also precisely measured by the established ultrasensitive video extensometer, confirming its accuracy and practicality.