Digital image correlation techniques for strain measurement in a variety of biomechanical test models.

PURPOSE Previous biomechanical studies have estimated the strains of bone and bone substitutes using strain gages. However, applying strain gages to biological samples can be difficult, and data collection is limited to a small area under the strain gage. The purpose of this study was to compare digital image correlation (DIC) strain measurements to those obtained from strain gages in order to assess the applicability of DIC technology to common biomechanical testing scenarios. METHODS Compression and bending tests were conducted on aluminum alloy, polyurethane foam, and laminated polyurethane foam specimens. Simplified single-legged stance loads were applied to composite and cadaveric femurs. RESULTS Results showed no significant differences in principal strain values (or variances) between strain gage and DIC measurements on the aluminum alloy and laminated polyurethane foam specimens. There were significant differences between the principal strain measurements of the non-laminated polyurethane foam specimens, but the deviation from theoretical results was similar for both measurement techniques. DIC and strain gage data matched well in 83.3% of all measurements in composite femur models and in 58.3% of data points in cadaveric specimens. Increased variation in cadaveric data was expected, and is associated with the well-documented variability of strain gage analysis on hard tissues as a function of bone temperature, hydration, gage protection, and other factors specific to cadaveric biomechanical testing. CONCLUSIONS DIC techniques provide similar results to those obtained from strain gages across standard and anatomical specimens while providing the advantages of reduced specimen preparation time and full-field data analysis.