Performance of strength grading methods based on fibre orientation and axial resonance frequency applied to Norway spruce (Picea abies L.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and European oak (Quercus petraea (Matt.) Liebl./Quercus robur L.)

Abstract

Performance of strength grading methods based on fibre orientation and axial resonance frequency applied to Norway spruce (Picea abies L.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and European oak (Quercus petraea (Matt.) Liebl./Quercus robur L.)Abstract & Key message Machine strength grading of sawn timber is an important value adding process for the sawmilling industry. By utilizing data of local fibre orientation on timber surfaces, obtained from laser scanning, more accurate prediction of bending strength can be obtained compared to if only axial vibratory measurements are performed. However, the degree of improvement depends on wood species and on board dimensions. It is shown that a model based on a combination of fibre orientation scanning and axial vibratory measurement is very effective for Norway spruce (Picea abies L.) and Douglas fir (Pseudotsuga menziesii (Mirb.) Franco). For European oak (Quercus petraea (Matt.) Liebl./Quercus robur L.) boards of narrow dimensions, axial vibratory measurements are ineffective whereas satisfactory results are achieved using a model based on fibre orientation. & Context Machine strength grading of sawn timber is an important value adding process for the sawmilling industry. & Aims The purpose of this paper has been to compare the accuracy of several indicating properties (IPs) to bending strength when applied to Norway spruce (Picea abies L.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco) and European oak (Quercus petraea (Matt.) Liebl./Quercus robur L.). & Methods The IPs were determined for a set of data comprising scanned high-resolution information of fibre orientation on board surfaces, axial resonance frequency, mass and board dimensions. & Results Whereas dynamic axial modulus of elasticity (MoE) gave good prediction of bending strength of Norway spruce (R 2 = 0.58) and Douglas fir (R 2 = 0.47), it did not for narrow dimension boards of oak (R 2 = 0.22). An IP based on fibre orientation gave, however, good prediction of bending strength for all three species and an IP considering both dynamic axial MoE and local fibre orientation for prediction of bending strength gave very good accuracy for all species (Norway spruce R 2 = 0.72, Douglas fir R 2 = 0.62, oak R 2 = 0.59). Comparisons of results also showed that scanning of fibre orientation on all four sides of boards resulted in more accurate grading compared to when only the two wide faces were scanned.

Contactless moisture content measurement on green veneer based on laser light scattering patterns

“…Each veneer sheet was characterized with an optical scanner initially designed to measure the local grain angle of wooden boards; the whole setup is described in Olsson et al (2018) and was used by Viguier et al (2018) to measure the local grain angle on veneer. For these experiments, a circular beam laser with a wavelength of 1064 nm was employed.…”

Variation and serial correlation of modulus of elasticity between and within European oak boards (Quercus robur and Q. petraea)

“…Although no local, namely cell-related, slope of grain data were sampled, it can be deduced from the results shown below that the local slope of grain should be an efficient indicating property for the variation in MOE and, hence, the tensile strength along the board length. The very promising potential of the local MOE prediction based on slope of grain, although denied by Schlotzhauer et al (2018) for oak, has recently been revealed by Olsson et al (2018) for narrow (100 mm) oak laminations, and will be investigated in a further study. Table 2 displays the statistical evaluation of the measured global and local densities, adjusted to MC = 12%.…”

Strength grading of hardwoods using transversal ultrasound

“…For the strength of wood and, particularly of hardwoods, visible local wood inhomogeneities are important. The same characteristics are more difficult to detect and measure with the available techniques compared to softwood (Olsson et al 2018;Schlotzhauer et al 2018).…”

“…For softwoods, the multisensory systems, able to detect the fibre deviation by means of laser scaning (tracheid effect), are available (Olsson et al 2013). More recent results show the potential of such measurements for hardwoods, particularly for oak (Olsson et al 2018). Application of other NDT techniques to hardwoods, such as thermal conductivity measurement (Daval et al 2015) and automated visual analysis of the spindle patterns (Ehrhart et al 2018) has been on the research agenda.…”