Tensile strain fields around an edge knot in a spruce specimen

Strain fields around a traversing edge knot in a spruce specimen subjected to tensile loading were measured using a contact-free measuring technique based on digital image correlation. The strain fields were measured by consecutive load tests in which one side of the specimen was studied during each test. The objectives were to examine 1. to what extent the strain fields could be detected, 2. the correlation between strain fields on different sides of the specimen, and 3. the strain distribution around the knot. It was shown that the applied technique is very useful for catching both overall and detailed information about the behaviour of knots in wood members exposed to loading. Both clear wood defects that could not have been detected by visual inspection or scanning and the release of internal stresses were identified. The correlation between strain fields on different sides of the specimen was very good. The correspondence between measurement results and comparative finite element calculations was surprisingly good, considering the fact that the used model was fairly simple