A Six-Spot Grating Diffraction Strain Gauge and Its Application to Measuring High-Temperature Mechanical Behavior

A six-spot grating diffraction strain gauge (SS-GDSG) is presented. In the SS-GDSG, six light spots are focused on a screen and captured by one camera. Four spots (projected by diffraction beams) are used to determine the deformation of a specimen, while two spots (projected by reflected beams) are used to eliminate disturbance induced by out-of-plane displacement and rotation of the specimen. This paper details the principle, sensitivity and error analysis of the SS-GDSG. An SS-GDSG system is developed for convenient measurement, and the feasibility and reliability of the system are verified in a standard tensile test. Additionally, using a modified high-temperature loading system, the SS-GDSG is extended to the measurement of the mechanical behavior of a material at high temperatures up to 1000 °C for the first time. In our study, the SS-GDSG is demonstrated to possess advantages over the traditional grating diffraction strain gauge of no disturbance of the specimen’s out-of-plane displacement and rotation, a compact light path, high sensitivity, and a single camera for deformation measurement in two directions.