Ultrasonic mechanical vibrations in solids are widely used in non-destructive testing, and high-power applications such as ultrasonic welding or soldering. The visualization of ultrasonic wave propagation in transparent solids is helpful for understanding the ultrasonic behaviours. The classical method of photoelasticity allows the visualization of the static stress distribution in birefringent materials. Utilizing recent high-power LEDs in the photoelasticity allows to capture dynamic stresses by high frequency stroboscopic light. High frequency stationary and transient oscillation processes in elastic solids can be visualized with this method. The designed LED array in this paper has a dimension of 210 mm_300 mm, and every LED has distance of 38mm to each other, and the light intensity has a homogeneity value. The temporal and spatial resolution of stress-optic systems depends mainly on the dynamic properties of the lighting technology used. The high speed synchronization of the stroboscopic light sources results in a high temporal resolution of the photoelasticity analyses. This enables the photoelastic investigation of highly dynamic load conditions, such as longitudinal waves and transverse waves.

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Jian Shi, Hendrik Ohrdes, Michael Weinstein, and Jens Twiefel, "Visualization of dynamic stress conditions in elastic solids utilizing high frequency stroboscopic LED arrays," Proc. SPIE 11105, Novel Optical Systems, Methods, and Applications XXII, 1110503 (Presented at SPIE Optical Engineering + Applications: August 13, 2019; Published: 9 September 2019); https://doi.org/10.1117/12.2529955.