Full-field deformation measurement in wood using digital image processing

A digital image processing system was used to non-destructively measure the full-field deformation on aluminum and wood specimens loaded in compression and bending. The measurement technique consisted of creating a random speckle pattern on the specimen surface, recording images before deformation and after deformation, and computing the relative displacements of small image subsets. Two methods for producing speckle patterns on the specimens were studied: spray paint and adhesive-backed photographic film.

Baseline tests were conducted to evaluate the influence of signal noise on the measurement system. Uniform translation tests were conducted to evaluate the capability of the system for measuring finite motion. the technique was used to monitor the full-field deformation response of aluminum and wood specimens tested in bending and static compression. Moderate duration compression creep tests were conducted, on the wood specimens to investigate the suitability of the system for monitoring the creep response of materials. The results obtained from the two speckle techniques were also. compared. The results showed that for the magnification and speckle patterns tested displacement measurements smaller than 3.29x10-4 inch may be unreliable due to signal noise.