Visualization of Fresh Cut Timber Deformation by Photogrammetry

Abstract

Understanding the mechanical behaviour of fresh cut timber, in which the natural moisture content has been retained, has application in predicting the behaviour of living tree elements such as branch/stem joints, potentially inspiring structural designs through biomimicry. This project develops a process of strain imaging using particle image velocimetry to analyse behaviour of timber samples freshly cut from oak tree joints and tested in tension. The timber surface was not coated so the fibre response could be visualised directly. Load was applied in steps, and different methods for comparing images trialled, including a sequential method in which strain is accumulated progressively from image to image, and a first-to-last comparison. Sample flexibility caused significant deformation in the camera field of view, and so the analysis methodology was modified so that each image was compared sequentially with the first with the target area in the image for strain calculation expanded as the test proceeded.This resulted in strain contour plots able to show the impending failure of the component as the tension is applied.