Dynamic photoelastic study of flexure hinges produced by additive manufacturing technology

Abstract

There are many challenges in compliant mechanism redesign for additive manufacturing (AM) technologies, and in order to assess their applicability and propose adequate recommendations, the behavior of compliant elements has to be examined. Plastic materials are often used in AM technologies and are well suited for large volume compliant mechanisms due to their flexibility to strength ratio. However, they also have many disadvantages, notably a low fatigue strength and complex material behavior. Therefore, in this paper a photoelastic observations of corner-filleted flexure hinges manufactured from the transparent acrylic based photopolymer using the Digital Light Processing (DLP) AM technology subjected to the dynamic loading have been conducted in order to assess the fatigue strength and potentials of the photoelastic methods for the material behavior modeling. Three-point flexural tests on rectangular beam samples with the standardized dimensions printed in vertical and in horizontal orientation have been performed and the obtained data has been used for numerical simulations of corner-filleted flexure hinges. The specimens printed in different orientations exhibit significantly different anisotropic properties; the horizontally printed samples exhibit brittle behavior, while the samples printed vertically yields and consequently have much higher deformations, the calculated flexural moduli are also very different. Corner-filleted flexure hinges printed in vertical orientation and subjected to dynamic cantilever beam bending tests at relatively high stress amplitudes proved sufficient for the low dynamic compliant mechanisms applications. The qualitative photoelastic observations have shown that the photoelasticity is applicable in dynamic tests and useful in residual stress determination and stress concentration investigations.