Optical 3D Deformation and Strain Measurement

Abstract

3D Image correlation technology has been widely used for the analysis of a broad range of materials ranging from biomechanics measurements of tissues, organs, ligaments and bones to microelectronics, automotive and aerospace applications. Manufacturing optical measurement systems for digitizing, forming analysis and materials analysis has become a part of advanced process chains for the development of products and production processes allowing data to be linked and automatically uploaded to quality control systems for precision lean operations.

ExxonMobil was an early adopter of the 3D Image Correlation technology for full-field deformation and strain studies of their piping systems and pipeline welding. This same technology has been widely used for the analysis of a broad range of materials ranging from biomechanics measurements of tissues, organs, ligaments and bones to microelectronics, automotive and aerospace applications. Because of its accurate and full-field nature, it is the best tool for computer model validation and iteration. As an example, the high speed ARAMIS 3D Image Correlation ­system was chosen by NASA for the Return-to-Flight of the Space Shuttle LS-DYNA model validations (Tyson et al. Performance verification of 3D image correlation using digital high-speed cameras. Proceedings of 2005 SEM Annual Conference and Exposition; 2005 June 7–9, Portland, OR, 2005). A related system monitors quality at Ford stamping plants and automatically downloads comparisons to finite element model (FEM) data of real line parts directly into the Ford Quality Control System (Tyson and Psilopoulos, Automated quality control of stamping with optical methods. International auto body congress, Troy, MI, 2009).

Image Correlation (DIC) has greatly benefited from the explosive growth of computer power and digital camera technology. We used to perform full-field optical measurements with laser holography (ESPI). ARAMIS has replaced most of this technology with its simple method of stereo imaging, which uses a pair of video cameras, like our eyes, to measure materials and structures in 3D space, but quantitatively down to the micron-scale world (Tyson et al. 3D Image correlation for dynamic and extreme environment materials measurements holistic structure measurements from the ­laboratory to the field. SEM 2005 Conference Proceedings, Portland, OR, 2005). The materials that this measures are any solid materials. Deformation and strain are material independent, so it works well for ceramics to thin films. Fields-of-view are solely optics dependant, so the technology is capable of performing measurements from 100 m (wind turbines & bridges) (Schmidt Paulsen et al. 2009) to sub-micron volumes (crystalline structures) (Kang J. 2007 Microscopic strain mapping based on digital image correlation). Since ARAMIS measures with 10,000 measurement points, it’s like having a finite element program for real testing, which compares directly to finite element analysis (FEA) models. Advances in high-speed cameras have allowed the technology to measure high-speed events from impact, ballistic and blast to split-Hopkinson bar and shock, up to 1 M frames/s (fps) (Tyson et al. 3D image correlation studies of geometry and material property effects during split hopkinson bar experiments. SEM 2008 Conference, 2008).