Examining Strain Propagation in the Lateral and Codominant Branch Attachment Using Digital Image Correlation

Static load testing of branches is a well-established method for examining attachment strength of trees. Information gathered from these experiments is used to better understand how branches fail, and predict how they are attached to their parent stem. Digital image correlation (DIC) is used to directly measure strain on the surface of materials during static load testing. By examining how strain moves through the branch attachment, a better understanding of how trees carry loads can also be attained. In these experiments, strain propagation in the branch connection zone of lateral and codominant stems was measured utilizing digital image correlation. In chapter 2, the lateral branch attachment of two oak species (Quercus alba L. & Quercus prinus L.) was examined and strain was mapped and analyzed. Little strain propagates into the main stem during branch failure exercise. In chapter 3, the codominant branch attachment of red maple (Acer rubrum L.) was examined, and differences between the two attachment types are compared. Strain was shown to propagate further into the surrounding stem wood in codominant branch unions. Change in angle to failure (Delta angle) was also examined in both chapters, and was a predictor of maximum compressive strain on the underside of branches during static loading. ? angle was also correlated with branch length and diameter. By qualitatively examining branch failures, a close relationship was found between aspect ratio and different failure types. This leads us to believe that from a mechanical perspective, a stem becomes codominant at an aspect ratio of around 0.8. Lateral branch attachments are more mechanically sound than codominant branches