Visualization of principal strain direction by a mechanical device

Abstract Generally, the strains at a point must be measured at least in three directions simultaneously in order to find the principal strain. In this paper, a simple device is proposed to visualize the principal strain direction in structure in real-time. Different from the conventional methods, it is able to indicate the principal strain by detecting the largest deformation in the elliptical zone which is deformed from a circular zone. The mechanism and key structure of the device are introduced in detail. The main factors which influence the sensitivity and accuracy of the visualization are analyzed. The fundamental experiments including a uniaxial compression test and the simply supported beam experiment were conducted to verify the validity of the method. It is found that the device can work well to visualize the direction of principal strain.