Full-field 3D displacement and strain analysis during low energy impact tests employing a single-camera system

Abstract

Characterising materials behaviour during dynamics events such as impact require several features related to monitoring and instrumentation which find in full-field techniques one of the main responses due to high spatial and, nowadays, also temporal resolution. 3D-Digital Image Correlation has provided an interesting tool to evaluate the material response during impact testing. It contributes with displacement and strain fields at high frame rates, which represents enormous potential for subsequent analysis. However, 3D-DIC also presents some issues which may condition the experimentation. The first of them is the requirement of a stereoscopic optical system, which lead to important economic issues if high speed cameras are required. Secondly, certain impact arrangements have limited space which make complicated to dispose of a proper stereoscopic system observing an area of interest with a suitable angle that makes it possible r a successful processing. In this work, a recent procedure combining Fringe projection and 2D-DIC is presented as an alternative for impact testing analysis. As main characteristic, the optical arrangement is simplified to only one high speed camera and an additional simple LCD projector which makes it easier the experimentation, reducing significantly the setup cost. To demonstrate that capabilities of FP+2D-DIC as a simpler approach with results comparable to those obtained with 3D-DIC, in this work it was analysed 2, 3, 4, and 5 mm thickness aluminium plates under low speed impacts with different energy levels. Impacts were performed employing an impact tower with a hemispherical impactor, connected to a load cell. During the impact, displacement and strain maps were measured at the non-impacted face of the specimen, using a single camera system implementing the combination of FP and 2D-DIC techniques. Permanent displacement and strain maps were validated with those obtained with a 3D-DIC system, supporting the potential of this FP+2D-DIC approach for impact testing.