Strain fields around knots in Norway spruce specimens exposed to tensile forces

Abstract

Two-dimensional strain fields around knots in two Norway spruce specimens subjected to tension loading were detected using a contact-free measuring technique based on white-light digital image correlation. The first specimen included a traversing Edge knot, and the second one, a Centric knot. The development of strain fields as a function of load level was measured by consecutive cyclic load tests where 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 a specimen and to analyse the strain distributions around the knots. The results show that the applied technique is useful for catching both overall and detailed information about the behaviour of knots in wood members exposed to loading. Clear wood defects that could not have been detected by neither visual inspection nor scanning were observed, and conclusions could be drawn regarding the release of internal stresses. The correlations between strain fields on different sides of the specimens were excellent, and the correspondence between measurement results and comparative finite element calculations was surprisingly good considering the fact that the employed FE models were fairly simple.

Strain Distribution of Dowel-Type Connections Reinforced with Self-Tapping Screws

“…DIC is a contact-free technique for strain measurement that has been used in the vehicle and aviation manufacturing industries (Oscarsson, et al, 2012). In timber engineering, Sjodin, et al (2006), Kunecky, et al (2015) and Milch, et al (2017) adopted DIC to monitor strain and displacement in timber joints for model verification.…”

“…Reynolds, et al (2016) used DIC to investigate the difference of material behaviour between bamboo and softwood with embedment tests. Studies on assessing the influence of knots on timber elements by Oscarsson, et al (2012) and Lukacevic, et al (2014) also used DIC technique. DIC assisted to validate numerical models that consider the existence of knots further improves the accuracy of simulation tools.…”

Modelling local bending stiffness based on fibre orientation in sawn timber

“…DIC systems are frequently used for understanding the mechanical behaviour of timber including knots (e.g. Sjödin et al 2006;Oscarsson et al 2012Oscarsson et al , 2014, and for verification of timber models established computationally by given algorithms (e.g. Hu et al 2015) or using FE method (Lukacevic and Füssl 2014).…”

Performance Assessment of a Numerical Simulation Tool for Wooden Boards with Knots by Means of Full‐Field Deformation Measurements

“…Oscarsson et al . used the DIC technique to detect strain fields around knots in tensile loaded Norway spruce specimens and compared them to results of linear‐elastic FE calculations. Dubois et al .…”

“…In 2006, Murata et al [10] investigated the strain distribution of wooden members subjected to four-point bending tests using the DIC method. Oscarsson et al [11] used the DIC technique to detect strain fields around knots in tensile loaded Norway spruce specimens and compared them to results of linear-elastic FE calculations. Dubois et al [12] studied the characterisation of timber fracture employing DIC and FE method.…”