Non-destructive technology associating PIV and Sunset laser to create wood deformation maps and predict failure

Abstract

Mechanical tests on wood specimens are usually made using a Universal Testing Machine (UTM) which allows the monitoring both of deformation and the moment of failure. However, besides the destruction of the samples, it is not possible to evaluate through these tests the distribution of deformations and the intensity of the forces involved throughout the sample, particularly in heterogeneous materials such as wood. Among the non-destructive techniques, optical approaches are available associated with image analysis that can overcome the destruction of samples and can even be used when one cannot remove a piece of wood installed in a building structure. This study presents an optical approach using particle image velocimetry (PIV) to create deformation maps of wood specimens under loading, without contact. A laser beam was placed parallel to the wood surface emphasising the irregularities, which are used as particles in the PIV method, and are monitored during the deformation of three different wood species during tests in the UTM. The results showed that the optical approach, using a Sunset laser in conjunction with the PIV method, could monitor the deformation of the samples in a non-destructive way, mainly in the elastic region. It was possible to predict the failure of the specimen earlier than by the UTM. In addition, the method presented a deformation map of the wood specimens allowing additional understanding of the phenomena.