STRAIN FIELDS AROUND A TRAVERSING EDGE KNOT IN A SPRUCE SPECIMEN EXPOSED TO TENSILE FORCES

摘要

Two-dimensional 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 to what extent the strain fields could be detected, to investigate the correlation between strain fields measured on different sides of the specimen and to analyse the strain distribution around the knot. The results show 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 identified by neither visual inspection nor scanning and the release of internal stresses were identified. The correlation between strain fields on different sides of the specimen was very good. The measurement results were compared with finite element calculations and the degree of correspondence was surprisingly good, considering the fact that the used model was fairly simple.