Optical scanning and X-ray computed tomography (CT) scanning of sawn timber provide a large number of data points, on which data-driven numerical models can be based for simulations. These models require information about the deviations of the fibre orientations in the vicinity of knots. Optical scanning can be used to measure the in-plane fibre orientation on wood surfaces. In CT scans of sawn timber, the fibre orientation around knots can be estimated using a new fibre reconstruction algorithm based on the density gradient. The goal of this paper is to compare and synchronise optical and CT scanning data of sawn timber and then use the combined data set to evaluate fibre orientations derived from both representations. The material comprised sawn timber of Norway spruce, in which alignment holes were drilled. The timber was scanned in an industrial CT scanner and subsequently in an industrial optical scanner where scanning was repeated after successive planing of the sawn timber surface. The results show that a projective mapping in combination with a spline interpolation are required for synchronisation, and that the in-plane fibre orientations calculated from the density gradients are qualitatively similar to the orientations derived from the optical data.

Particleboards with different combinations of the adhesive material imidazole, citric acid, and sorbitol were produced. Softwood sawdust from a Swedish sawmill was mixed with an aqueous solution of the chemicals and then dried to 0% moisture content prior to pressing. The boards were pressed to a target density of 700 kg m−3 at either 200 °C or 220 °C for 10 min. The hygroscopic and mechanical properties of the boards were clearly better at 220 °C than 200 °C for all used chemical combinations. A combination of imidazole (14.4 wt%) and citric acid (11.3 wt%) led to the best results, where the thickness swelling after 24 h of water immersion was 6.3% and the internal bonding strength was 0.57 MPa. The modulus of rupture and modulus of elasticity were 3.3 MPa and 1.1 GPa, respectively. Cyclic accelerated weathering showed exceptional stability with a thickness change after boiling and drying of only 2.1% compared to the initial dry thickness. This study indicates that the presence of imidazole leads to greatly improved hygroscopic properties and good internal bonding strength when used in particleboards.

Drying green sawn timber to a specific moisture content is needed for further processing. Large batch kilns of approx. 100 cubic meters of timber loads are commonly used with heated air blowing across the packages. When the air reaches the end of the blow depth, it has considerably increased its relative humidity by the evaporation from the wet timber. To even out the climate at the beginning and end of the blow depth, the direction of air circulation is reversed periodically. This exposes timber at those locations to fluctuations in climate while the middle packages are exposed to a more even climate. This study aimed to find the influence of the location of timber along the blow depth in liquid-water-flow behavior during the initial stages of drying. A research drying kiln combined with a CT-scanner was used to mimic this environment across the load and obtain CT images simultaneously, which were used to study the moisture content evolution. The results found that the transition between the capillary and the diffusion regimes can be identified with this method. Additionally, the transition regime was entered earlier for specimens drying in the more even climate which modeled the middle of a drying kiln, but with larger water pockets nearer to the surface of the specimens.

A method is presented for reconstructing the geometry, the pith, the knots and the local fibre orientations in timber boards, based on X-ray computed tomography scans. The local fibre deviations around knots were found by a new algorithm, based on image analysis. The experimental data comprised tomography scans, eigenfrequency measurements and four-point bending tests of 20 Norway spruce boards. 3D and 1D finite element models of the pure bending zone of the bending tests were created, accounting for the exact board geometry and the reconstructed fibre deviations. A purely density based, a purely eigenfrequency based, and a mixed constitutive law were compared. Model estimations showed a high coefficient of determination (R²) for global modulus of elasticity (MoE) (R²⩽0.93), local MoE (R²⩽0.87), bending strength (R²⩽0.83), and the location of initial failure. Constitutive laws accounting for eigenfrequency showed the most accurate results. In the future, adapting the method for logs could enable analyses of boards before sawing.

Scots pine blister rust fungi (Cronartium pini) is expected to become an increasing problem for both forest owners and sawmills in the Nordic region, and there is great uncertainty about the economic consequences. There is also a lack of knowledge about the biology of Scots pine blister rust, as well as the tree's response and defence against ongoing infection. The tree is known to defend itself by enriching resin at the infected area, creating a damaged area of resin-wood. There is currently no reliable way to detect and assess the degree of damage in sawn timber, which leads to waste, as entire sawlogs are usually downgraded when parts or most of the timber could possibly be used. 

The objectives of this preliminary study were to: (1) investigate whether X-ray computed tomography (CT scanning) can detect blister rust damage in pine timber, in order to optimise sawing and save the value of the sawn timber; (2) to compare the 3-dimensional CT image description of the fungal attack with how the damage looks on the outside, to enable recommendations for external assessment of the damage attack, for example during felling; and (3) to assess the possibilities for describing the course of the damage and the tree's defence against the fungal attack.

Eight rust-infested and two non-infested trees (Scots pine) were collected from a thinning stand and a mature stand outside Bjurselet, Norsjö municipality in Västerbotten. The trees were felled in January 2022. After felling, the stems were visually inspected, and infected parts were marked with paint on the mantle surface. The stems were cut into logs of suitable length for transport and scanning. Cuts through fungal-infested regions were avoided. The wood was transported to LTU’s Wood Science and Engineering facility in Skellefteå for CT scanning.

The CT scan of the sample trees showed that damage due to pine blister rust can be detected in a way that enables further development of an industrial detection method and optimisation of the wood decomposition. However, one difficulty discovered was that fungal-infested sapwood areas have similar image intensity as non-infested heartwood. It could also be established that the distribution of damage inside the volume of the stem is greater than can be detected visually on the mantle, especially in the longitudinal direction. 

In this study the temporal development of the infection from the time of infestation to the time of CT scanning could not be analysed. However, annual rings could be distinguished in both damaged and undamaged wood, making it possible to monitor the evolution of the damage from year to year. DNA analysis detected the presence of blister rust fungus in the wood, both in and outside resin-rich areas. The highest amount of fungus-specific DNA was measured outside the resin-rich area in the outer parts of the sapwood.

Törskateangrepp på tall förväntas bli ett allt större problem för både skogsägare och sågverk i Norden. Det finns samtidigt stora kunskapsluckor om törskate generellt och om hur man ska hantera angripet timmer för att minska de ekonomiska konsekvenserna av angreppen. Det finns exempelvis inget tillförlitligt sätt att detektera och bedöma skadegraden hos sågtimmer, vilket leder till ökat spill vid sågning då hela stockar oftast nedklassas där man eventuellt skulle kunna använda delar eller merparten av timret. Osäkerheten om de ekonomiska konsekvenserna är stor. Det saknas även kunskaper kring törskatesvampens biologi, samt trädets respons och försvar mot pågående infektion. 

Syftet med denna förstudie var att (1) undersöka om röntgenbaserad datortomografi (CT-skanning) kan detektera törskateangrepp hos talltimmer, för att därmed kunna optimera sågningen och “rädda” det sågade virkets värde, (2) att jämföra CT-bildernas 3-dimensionella beskrivning av törskateangreppet med hur skadorna ser på utsidan, för att kunna ta fram rekommendationer för yttre bedömning av skadeangrepp till exempel vid avverkning, samt (3) att bedöma möjligheterna att beskriva skadeförloppet och trädets försvar mot svampangreppet. 

Åtta törskateangripna och två icke angripna träd (tall) insamlades från ett gallringsbestånd och ett slutavverkningsbestånd utanför Bjurselet, Norsjö kommun i Västerbotten. Träden avverkades under januari månad 2022. Efter fällningen gjordes en okulär besiktning av trädstammarna, där de törskateskadade delarna märktes med färg på mantelytan. Stammarna apterades i lämpliga längder för transport, samtidigt som det undveks att utföra apteringen i de törskateskadade områdena. Virket transporterades till LTU Träteknik i Skellefteå för CT-skanning.

CT-skanningen av provträden visade att törskate kan detekteras på ett sätt som möjliggör fortsatt utveckling av en industriell detektering av törskate och optimering av timrets sönderdelning. En svårighet som dock uppdagades var att törskateangripna områden i splintveden har snarlika bildanalystekniska egenskaper som icke angripen kärnved. Det kunde även konstateras att törskatens utbredning i stammens volym är större än vad som kan detekteras okulärt på stammens mantelyta, framför allt i stammens längdriktning. I de preliminära analyser som ligger till grund för denna rapport är det dock inte möjligt att urskilja svampens tidsmässiga utbredning från angrepp till tidpunkten då CT-skanningen genomfördes. Däremot kan det konstateras att årsringar går att urskilja både i skadad och oskadad ved vilket ger möjligheten att från år till år följa skadeutvecklingen. DNA-analys detekterade förekomst av törskatesvamp i veden, både i och utanför kådrika områden. Den högsta mängden av törskatespecifikt DNA uppmättes utanför det kådrika området i splintvedens yttre delar.

Sammanfattningsvis visar studien att de tekniska förutsättningarna för att detektera de inre skadorna av törskate med CT-skanning är goda och att utveckling av algoritmer för bildbehandling är ett viktigt nästa steg för automatiserad detektion av törskate i tall.

X-ray computed tomography (CT) of wood delivers internal density data of a scanned object, where, depending on the resolution, internal features like the pith, annual rings and knots can be identified. Some sawmills use CT scanners in front of the saw line to determine the optimal positioning of the log in the saw, to maximise the value yield of the sawn products. We envision that the gathered CT data also could be used for mechanical evaluations of the timber using numerical models of boards prior to sawing. In a recent study by the authors, a method was developed to create 3D and 1D finite element (FE) models based on CT scans of dried sawn timber, which could predict bending stiffness and strength in bending simulations with high accuracy. The objective of the present study is to explore how the method can be adapted to CT scans of logs before sawing. Our preliminary study was based on CT data of green Norway Spruce logs and the corresponding scans of dried sawn timber. The stiffness and strength were evaluated using four-point bending tests. Additionally, the resonance frequency of the logs was recorded. The corresponding volume of each piece of sawn timber was extracted from the log data and an FE model was created. The model accounted for the pith, the annual rings, the knots, and the local fibre deviations around knots. Various laws for local stiffness and different failure criteria were tested. The study showed how FE models of virtual pieces of sawn timber can be created from CT data and what obstacles need to be overcome for further development of the presented method. The results indicated that more detailed evaluations of the relationship between local stiffness and density may be required, in specific for knots and for wood in green state.

Engineered wood products of today's construction industry require predictable mechanical properties of the used structural timber. At sawmills, automated strength grading is used to assess the stiffness and strength of sawn and dried timber boards. This process can be based on various technologies, e.g. surface scanning, dynamic excitation, flat-wise bending, which are used to derive so-called indicating properties, i.e. simplified numerical values. Heuristically derived statistical models can then be used to predict the stiffness and strength based on indicating properties. However, statistical strength grading can only exploit a small fraction of the potential strength of a single board, since it assesses the properties of a board in relation to its population. 

A growing number of sawmills in Sweden use computed tomography (CT) scanners to assess the incoming logs to optimise their positioning prior to sawing. CT scans provide high-quality data of the cross-sectional density distribution along the length of a log, which could also be used to derive continuum mechanical models of the yet unsawn boards and with that assess their mechanical properties. If the stiffness and strength of a virtual board can be predicted before it is sawn, then it could be pre-classified into a strength class or its specific use as a specific construction part could be predetermined already at the log stage, which would lead to a more efficient material usage. Additionally, the predictive power of the existing statistical strength grading processes could be improved for the final boards.

The goals of this study were to i) derive 3D quasi-continuum and finite element (FE) models of CT scanned timber boards using different material laws for local stiffness based on measured density and ii) compare their capabilities for predicting stiffness and strength of the boards.

The experimental material consisted of dried softwood boards (12% moisture content) of nominal cross-sectional dimensions 50x100mm with different lengths, scanned with a medical high-resolution CT scanner. The boards underwent an eigenfrequency measurement by dynamic excitation and were tested until failure in a four-point bending test, where both the local and global displacement were recorded.

A previously developed algorithm was used to derive 3D quasi-continuum reconstructions from the CT scans and subsequently finite element (FE) models. The algorithm reconstructed the board geometry, pith, knots and local fibre directions (material coordinate system) on a volume grid of material points spaced 0.68mm apart. The stiffness tensor in each material point was made locally dependent on the measured density by different mathematical laws, e.g. constant, linear or power laws. Furthermore, material laws which scaled the stiffness tensor based on the ratio between the simulated and measured eigenfrequency were tested for comparison. The bending stiffness profile was calculated for each board along its length and different indicating properties for predicting stiffness and strength were derived and compared with respect to the experimental results. With the FE model, strain distributions in the cross-sections were studied and local stress states around the experimentally observed points of initial failure were investigated to determine whether similar dominant failure stress states existed among boards.

The results showed high coefficients of determination between predicted stiffness and strength for material laws based on power laws and low values for linear laws. Nevertheless, the four-point bending tests only provided point-wise data (mid points) that could be used to validate the numerical model. It is therefore recommended to use field-based evaluations in the future, e.g. the surface strain obtained with DIC under four-point testing.

Timber utilisation and wood construction are fundamental components of Europe's strategy on progressing towards a sustainable bio-based economy. Both components require optimised strength grading procedures in Europe's sawmills. To further improve the current procedures, quality assessment and segregation of the raw material need to start already at the roundwood stage. Furthermore, the quality information should be made accessible throughout the production process to leverage the full potential for optimisation. This paper discusses the current state of research on combined log and board strength grading with a focus on the situation in Europe. It highlights limitations due to technology and current standardisation and identifies knowledge gaps and research opportunities. The European research project READiStrength (resource-efficient and data-driven integrated log and board strength grading) has been initiated to address these issues.