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  • 1. Adlerborn, J
    et al.
    Björk, L
    Westman, Anna-Karin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Larker, H
    Particulate-reinforced ceramics densified by glass encapsulated HIP1991In: Hot isostatic pressing: Theory and applications / [ed] R J Schaefer; Melvin Linzer, Materials Park, Ohio: ASM International, 1991, p. 211-216Conference paper (Refereed)
  • 2.
    Ah Shenga, Pedro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. Luleå University of Technology.
    SAWING STRATEGIES FOR TROPICAL HARDWOOD SPECIES: Simulation studies based on industrial conditions of Mozambique2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The harvesting of Mozambique tropical hardwood species is considerable higher than the natural regrowth in the forest and the stock is decreasing drastically. Therefore, it is important to improve the material recovery when the wood is refined (i.e., in sawing and further refinement to products such as joineries, furniture etc.) to reduce the waste and to re-utilize efficiently the by-products to increase the added value. The wood processing industry is an important means to boost the industries in the rural areas and also to generate incomes for the local communities by creating jobs and business opportunities.

    The majority of the logging that can be used for sawmilling in Mozambique is exported as roundwood due to the inability of companies to meet the product standards set for export and to generate profit. The lack of capabilities of the local sawmills to generate profit, also foments the illegal logging because of the higher price of roundwood for export which contributes to increase the number of unlicensed individuals in harvesting. This threatens the law enforcement and thus the degradation of the local wood industry. An alternative to increase the profit and empower the local community could be to export more refined wood products such as sawn timber, parquet, and veneer instead of the roundwood.

    The objective of the work was to investigate alternative sawing strategies of tropical hardwood species that could increase the profitability of the Mozambique wood industry in general and at sawmill in particular. The subject was approached using a database of virtual logs and together with a sawing simulator. The thesis has two main focus areas: (1) creating the log database with the corresponding algorithms for sawing simulation, and (2) investigations of alternative sawing strategies.

    The first focus was to build the database of surface-scanned logs and develop the algorithm for the saw simulation. The results are a database of 15 logs models describing the logs outer shape in which 10 jambirre (Millettia stuhlmannii Taub.) and 5 umbila (Pterocarpus angolensis DC.), and the algorithm for the sawing simulation. The algorithm use “brute force” i.e., determines all volume yields of sawn timber from the combination of all settings of log-positioning parameters (offset, skew and rotation) and selects the maximum value of volume yield. From simulation, using three sawing patterns (cant-sawing, through-and-through sawing and square-sawing) combined with two positioning parameters (offset and rotation) it was found that the sawing pattern has great impact on volume yield and that the square-sawing gave higher yield followed by through-and-through sawing pattern.

    The second focus was on alternative sawing strategies; having in mind that the optimal volume yield is achieved by aid of computerized production systems and that these resources are not yet in use in Mozambique. Hence, the objective was to find the positioning parameters that can be set manually and improve the volume yield. The result have shown that the rotation is the most affecting parameter followed by offset and skew, and that the volume yield can decrease by between 7.7% and 12.5% from the optimal positioning when the logs are manually positioned with the knowledge about the optimal log position. In another study, using crook-up or horns-down positioning as alternative to the optimal positioning, the volume yield decreases by between 10% and 13% from the optimal positioning. By using bucked logs , the optimal volume yield increased by between 8% and 13% in relation to full lengths logs, and the volume yield of bucked logs when using crook up positioning decreases 2% in relation to optimal positioning of full length logs.

    It is concluded that there is an unexploited value potential in the wood chain which can be reached using alternative positioning and modern measurement techniques and that the grading of wood will facilitate and improve the sawing process.

  • 3.
    Ah Shenga, Pedro António
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Bomark, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    External Log Scanning for Optimizing Primary Breakdown of Tropical Hardwood Species2015Conference paper (Other academic)
    Abstract [en]

    The sawing of tropical hardwood species is a big challenge for sawmills in developing countries. In order to investigate sawing strategies and volume recovery of tropical hardwood species, a log shape database was created using a portable 3D laser scanner. The data were collected in Mozambique, where twelve Jambirre (Millettia stuhlmannii Taub.) and five Umbila (Pterocarpus angolensis DC) logs were scanned. The logs were selected among the most commercialized species and the crook was the main selection parameter. In addition, straight logs were incorporated as reference. A saw simulation Matlab algorithm that combines skew and rotation was developed. The results show that point cloud data from the 3D scanner provide detailed models of the external log geometry and accurately describe the log shapes and volumes. Preliminary results from breakdown simulation revealed that the through-and-through sawing pattern yields more than the cant saw pattern and that the increase in yield was almost the same for both species.

  • 4.
    Ah Shenga, Pedro António
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Bomark, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Simulated Breakdown of Two Tropical Hardwood Species2015In: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 11, no 4, p. 450-456Article in journal (Refereed)
    Abstract [en]

    A simulation study has been performed on a small log database of tropical hardwoods consisting of 10 Jambirre (Millettia stuhlmannii Taub.) and 5 Umbila (Pterocarpus angolensis D.C.) logs. The outer log shape was acquired by a 3D laser scanner before sawing and the heartwood content was estimated by measurement on images of the centre slabs after through-and-through sawing. Yield and value recovery using different sawing techniques and different sawing patterns, together with rotational and skew positioning errors, are presented. The results show that through-and-through sawing in the best rotation and skew positions tested improves the yield of Umbila logs by an average of 4.5 percentage points and Jambirre logs by 3.6 percentage points compared to cant sawing. It can be concluded that positioning and sawing patterns have a great influence on the yield and value recovery of these species and that log grade and species have an impact on the sawing pattern that should be used.

  • 5.
    Ah Shenga, Pedro António
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Bomark, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Simulation of Tropical Hardwood Processing: Sawing Methods, Log Positioning, and Outer Shape2015In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 10, no 4, p. 7640-7652Article in journal (Refereed)
    Abstract [en]

    To increase understanding of breakdown strategies for Mozambican timber, simulations were carried out using different sawing patterns that can be alternatives to the low degree of refinement performed for export today. For the simulations, 3D models of 10 Jambirre and 5 Umbila logs were used. The log shape was described as a point cloud and was acquired by 3D-laser scanning of real logs. Three sawing patterns (cant-sawing, through-and-through sawing, and square-sawing) were studied in combination with the log positioning variables skew and rotation. The results showed that both positioning and choice of sawing pattern had a great influence on the volume yield. The results also showed that the log grade had an impact on the sawing pattern that should be used for a high volume yield. The volume yield could be increased by 3 percentage points by choosing alternative sawing patterns for fairly straight logs and by 6 percentage points for crooked logs, compared to the worst choice of sawing pattern.

  • 6.
    Ah Shenga, Pedro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Bomark, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hagman, Olle
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    3D Phase-shift Laser Scanning of Log Shape2014In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 9, no 4, p. 7593-7605Article in journal (Refereed)
    Abstract [en]

    In this paper, a portable scanner to determine the 3D shape of logs was evaluated and compared with the measurement result of a computer tomography scanner. Focus was on the accuracy of the shape geometry representation. The objective is to find a feasible method to use for future data collection in Mozambique in order to build up a database of logs of tropical species for sawing simulations. The method chosen here was a 3D phase-shift laser scanner. Two logs, a birch log with bark and a Scots pine log without bark, were scanned, resulting in 450 cross sectional “images” of the pine log and 300 of the birch log. The areas of each point cloud cross section were calculated and compared to that of the corresponding computer tomography cross section. The average area difference between the two methods was 2.23% and 3.73%, with standard deviations of 1.54 and 0.91, for the Scots pine and birch logs, respectively. The differences in results between the two logs are discussed and had mainly to do with presence of bark and mantle surface evenness. Results show that the shape measurements derived from these methods were well correlated, which indicates the applicability of a 3D phase-shift laser scanning technology for gathering log data.

  • 7.
    Ah Shenga, Pedro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Bomark, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Log sawing positioning optimization and log bucking of tropical hardwood species to increase the volume yield2017In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 12, no 4, p. 257-262Article in journal (Refereed)
    Abstract [en]

    The sawmill industry is a very important link in the Mozambique forest products value chain, but the industry is characterized by undeveloped processing technology and high-volume export of almost unrefined logs. The low volume yield of sawn timber has been identified as a critical gap in the technological development of the industry. To improve the profitability of the industry, there is thus a need to develop methods and techniques that improve the yield. In this paper, different positioning of logs prior to sawing and the possibility of increasing the volume yield of crooked logs by bucking the logs before sawing have been studied. A computer simulation was used to study the cant-sawing and through-and-through sawing of the logs to determine the volume yield of sawn timber from the jambirre (Millettia stuhlmannii Taub.) and umbila (Pterocarpus angolensis DC.) species. The optimal position, i.e. the position of the log before sawing that gives the highest volume yield of sawn timber for a given sawing pattern when the positioning parameters, offset, skew and rotation, are considered gave a considerable higher volume yield than the horns-down position. By bucking very crooked logs and using the horns-down positioning before sawing, the volume yield can be of the same magnitude as that obtained by optimal positioning on full-length (un-bucked) logs. The bucking reduces the crook of the logs and hence increases the volume yield of sawn timber.

  • 8.
    Ah Shenga, Pedro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Bomark, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sandberg, Dick
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    The Effect of Log Position Accuracy on the Volume Yield in Sawmilling of Tropical Hardwood2016In: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 11, no 4, p. 9560-9571Article in journal (Refereed)
    Abstract [en]

    This study investigated the effect of the positioning of the log before sawing on the volume yield of sawn timber from tropical hardwood species. Three positioning parameters were studied, the offset, skew, and rotation, combined with two sawing patterns of cant-sawing and through-and-through sawing. A database consisting of two tropical hardwood species with very different outer shapes, jambirre (Millettia stuhllmannii Taub.) and umbila (Pterocarpus angolensis DC.), was used to simulate the sawing process. The result of the simulation revealed that, according to the combined effect of offset, skew, and rotation positioning, the positioning of the log before sawing is extremely important to achieve a high volume yield of sawn timber. The positioning parameter that has the highest effect on the volume yield is the rotation, and the variation in the volume yield associated with a deviation in the positioning can reduce the volume yield of sawn timber by between 7.7% and 12.5%.

  • 9.
    Ah Shenga, Pedro
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Cristovao, Luis
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Broman, Olof
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    A review of Mozambican wood exploitation: map of the processing chain2013In: Proceedings of the 21th International Wood Machining Semina: August 4th – 7th, Tsukuba International Congress Center, Japan, 2013, p. 293-301Conference paper (Other academic)
  • 10.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Morén, Tom
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Distribution of preservatives in thermally modified Scots pine and Norway spruce sapwood2013In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 47, no 3, p. 499-513Article in journal (Refereed)
    Abstract [en]

    Studying the impregnation and distribution of oil-based preservative in dried wood is complicated as wood is a nonhomogeneous, hygroscopic and porous material, and especially of anisotropic nature. However, this study is important since it has influence on the durability of wood. To enhance the durability of thermally modified wood, a new method for preservative impregnation is introduced, avoiding the need for external pressure or vacuum. This article presents a study on preservative distribution in thermally treated Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) sapwood using computed tomography scanning, light microscopy, and scanning electron microscopy. Secondary treatment of thermally modified wood was performed on a laboratory scale by impregnation with two types of preservatives, viz. Elit Träskydd (Beckers) and pine tar (tar), to evaluate their distribution in the wood cells. Preservative solutions were impregnated in the wood using a simple and effective method. Samples were preheated to 170°C in a drying oven and immediately submerged in preservative solutions for simultaneous impregnation and cooling. Tar penetration was found higher than Beckers, and their distribution decreased with increasing sample length. Owing to some anatomical properties, uptake of preservatives was low in spruce. Besides, dry-induced interstitial spaces, which are proven important flow paths for seasoned wood, were not observed in this species.

  • 11.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Morén, Tom
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Moisture properties of heat-treated Scots pine and Norway spruce sapwood impregnated with wood preservatives2012In: Wood and Fiber Science, ISSN 0735-6161, Vol. 44, no 1, p. 85-93Article in journal (Refereed)
    Abstract [en]

    An experiment was conducted on commercially heat-treated (HT) Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies [L.] Karst.) sapwood collected from Ht Wood AB, Arvidsjaur, Sweden. Secondary treatment on HT wood was performed in laboratory scale by impregnating with water-repellent preservatives (a commercial one and pine tar) to evaluate their retention and different moisture-related properties. Preservative solutions were impregnated using a simple and effective method. Wood samples were heated at 170°C in a dry oven and were immediately immersed in preservative solutions. Considerable retention was observed in HT wood, particularly in pine. Moisture adsorption properties were measured after conditioning in a high-humidity environmental chamber (4°C and 84% RH). Experimental results showed that secondary treatment enhanced moisture excluding efficiencies by decreasing equilibrium moisture content, suggesting better hydrophobicity. Soaking test in water showed that antiswelling and water repellence efficiencies improved, especially in tar-treated wood. In addition, this type of treatment significantly decreased water absorption. It was also possible to decrease volumetric swellings. Thus, secondary treatment of HT wood with preservative, in particular with tar, improved dimensional stability and water repellency.

  • 12.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Morén, Tom
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hagman, Olle
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Cloutier, Alain
    Wood Research Center (CRB), Department of Wood and Forest Sciences, Faculty of Forestry, Geography and Geomatics, Laval University, Quebec.
    Fang, Chang-Hua
    Wood Research Center (CRB), Department of Wood and Forest Sciences, Faculty of Forestry, Geography and Geomatics, Laval University, Quebec.
    Elustondo, Diego
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Anatomical properties and process parameters affecting blister/blow formation in densified European aspen and downy birch sapwood boards by thermo-hygro-mechanical compression2013In: Journal of Materials Science, ISSN 0022-2461, E-ISSN 1573-4803, Vol. 48, no 24, p. 8571-8579Article in journal (Refereed)
    Abstract [en]

    Approximately, 13.5 % of the standing volume of productive forest land in Sweden is covered by birch and aspen, which provides the vast potential to produce value-added products such as densified wood. This study shows whether it is possible to densify those species with a thermo-hygro-mechanical (THM) process using heat, steam, and pressure. In this process, transverse compression on thin European aspen (Populus tremula) and downy birch (Betula pubescens) boards was performed at 200 ºC with a maximum steam pressure of 550 kPa. To obtain a theoretical 50 % compression set, the press’s maximum hydraulic pressure ranged from 1.5 to 7.3 MPa. Preliminary tests showed that ~75 % of the birch boards produced defects (blisters/blows) while only 25 % of the aspen boards did. Mainly, radial delamination associated with internal checks in intrawall and transwall fractures caused small cracks (termed blisters) while blows are characterized by relatively larger areas of delamination visible as a bumpy surface on the panel. Anatomical investigations revealed that birch was more prone to those defects than aspen. However, those defects could be minimized by increasing the pre-treatment time during the THM processing.

  • 13.
    Ahmed, Sheikh Ali
    et al.
    Department of Forestry and Wood Technology, Faculty of Technology, Linnaeus University.
    Morén, Tom
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sehlstedt-Persson, Margot
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Blom, Åsa
    Department of Forestry and Wood Technology, Faculty of Technology, Linnaeus University.
    Effect of oil impregnation on water repellency, dimensional stability and mold susceptibility of thermally-modified European aspen and downy birch wood2017In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 63, no 1, p. 74-82Article in journal (Refereed)
    Abstract [en]

    Conventional chemical wood preservatives have been banned or restricted in some applications due to human and animal toxicity and their adverse impact on the surrounding environment. New, low-environmental-impact wood treatments that still provide effective protection systems are needed to protect wood. Thermal modification of wood could reduce hygroscopicity, improve dimensional stability and enhance resistance to mold attack. The aim of this study is to investigate if these properties enhanced in thermally-modified (TM) wood through treatments with oils. In this study, TM European aspen (Populus tremula) and downy birch (Betula pubescens) wood were impregnated with three different types of oil: water-miscible commercial Elit Träskydd (Beckers oil with propiconazole and 3-iodo-2-propynyl butylcarbamate, IPBC), a pine tar formulation and 100% tung oil. The properties of oil-impregnated wood investigated were water repellency, dimensional stability and mold susceptibility. The treated wood especially with pine tar and tung oil, showed an increase in water repellency and dimensional stability. However, Beckers oil which contains biocides like propiconazole and IPBC, showed better protection against mold compared with pine tar and tung oil. To enhance the dimensional stability of the wood, pine tar and tung oil can be used, but these oil treatments did not significantly improve mold resistance rather sometimes enhanced the mold growth. Whereas, a significant anti-mold effect was observed on Beckers oil treated samples.

  • 14.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sehlstedt-Persson, Margot
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Morén, Tom
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Evaluation of preservative distribution in thermally modified European aspen and birch boards using computed tomography and scanning electron microscopy2013In: Journal of Wood Science, ISSN 1435-0211, E-ISSN 1611-4663, Vol. 59, no 1, p. 57-66Article in journal (Refereed)
    Abstract [en]

    The aim of this experiment was to impregnate thermally modified wood using an easy and cost-effective method. Industrially processed thermally modified European aspen (Populus tremula L.) and birch (Betula pubescens Ehrh.) were collected and secondarily treated at the laboratory scale with the preservatives tung oil, pine tar and Elit Träskydd (Beckers) using a simple and effective method. Preservative uptake and distribution in sample boards were evaluated using computed tomography (CT) and scanning electron microscopy (SEM) techniques. Preservative uptake and treatability in terms of void volume filled were found the highest in Beckers and the lowest in tung oil-treated samples. Thermally modified samples had lower treatability than their counterpart control samples. More structural changes after thermal modification, especially in birch, significantly reduced the preservative uptake and distribution. The differences of preservatives uptake near the end grain were high and then decreased near the mid position of the samples length as compared with similar type of wood sample. Non-destructive evaluation by CT scanning provided a very useful method to locate the preservative gradients throughout the sample length. SEM analysis enabled the visualization of the preservative deposits in wood cells at the microstructural level.

  • 15. Ahmed, Sheikh Ali
    et al.
    Sehlstedt-Persson, Margot
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Karlsson, Olov
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Morén, Tom
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Uneven distribution of preservative in kiln-dried sapwood lumber of Scots pine: Impact of wood structure and resin allocation2012In: Holzforschung, ISSN 0018-3830, E-ISSN 1437-434X, Vol. 66, no 2, p. 251-258Article in journal (Refereed)
    Abstract [en]

    Scots pine (Pinus sylvestris L.) sapwood lumber was collected after kiln drying and preservative treatment with Celcure AC 800 (a copper-amine wood preservative). Distribution of the preservative throughout the lumber was visually examined. Not all, but some samples showed specific localized areas without any preservative distribution throughout their entire length. Those samples were assessed further for anatomical properties, specifically in impregnated and unimpregnated areas. Additional study was conducted on the morphological nature and redistribution of lipophilic extractives using three different histochemical staining methods. Intrinsic wood properties – especially the frequency of axial resin canals and the percentage of canals blocked – were found to be responsible for the irregular distribution of the preservative. Furthermore, the inability to create continuous and frequent interstitial spaces due to the collapse of thin-walled ray cells throughout the lumber resulted in uneven distribution of preservatives. Staining techniques were useful to localize places with more or less abundance of extractives (e.g., fats) in impregnated and unimpregnated wood, which varied considerably. Histochemical observations revealed information pertaining to the kiln dry specific distribution and redistribution of extractives between the areas. Moreover, resin reallocation and modification in ray parenchyma and resin canals induced by kiln drying would be another reason for the impregnation anomalies.

  • 16.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sehlstedt-Persson, Margot
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Morén, Tom
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Development of a new rapid method for mould testing in a climate chamber: Preliminary tests2013In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 71, no 4, p. 451-461Article in journal (Refereed)
    Abstract [en]

    The purpose of this study was to develop fast, simple and robust solid wood mould testing methods for the use in small-scale laboratory tests. The objective was to investigate mould susceptibility of different wood materials within the batches. The proposed method is based on natural contamination of non-sterile surfaces in climates conducive to mould growth. For this purpose, a climate chamber with regulated temperature and relative humidity was used. The conditioning chamber was divided into upper and lower chamber by a thin layer of stainless steel placed horizontally above the fan to minimise air circulation to the sample in the upper compartment. Mould-infected samples from outdoor tests were used as a source of mould inocula, and test trials were conducted on Scots pine (Pinus sylvestris L.) sapwood. Samples were suspended from the top of the upper chamber, and the chamber was exposed to different temperature and humidity levels. Severe mould infestation was observed after 12-14 days of incubation. Visual mould rating was then performed. Regardless of some constraints, this test method was very simple, fast, and effective. More importantly, unlike other test methods, it closely models mould infestation as it would occur under natural condition.

  • 17.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Sehlstedt-Persson, Margot
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Morén, Tom
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Mould susceptibility of Scots pine (Pinus sylvestris L.) sapwood: Impact of drying, thermal modification, and copper-based preservative2013In: International Biodeterioration & Biodegradation, ISSN 0964-8305, E-ISSN 1879-0208, Vol. 85, p. 284-288Article in journal (Refereed)
    Abstract [en]

    The development of mould on wood surfaces depends on several factors. Although mould does not affect the mechanical properties of wood, it greatly reduces the aesthetic value of wood like the sapwood of Scots pine (Pinus sylvestris L.), which is very prone to mould. In addition, adverse health effects of mould on humans are also a great concern. Different types of dried and treated wood were used to observe whether they had enhanced durability against mould following an accelerated laboratory test method in a climate chamber. Samples were green, air-dried, industrially thermally-modified, treated with copper-based preservative, and kiln-dried wood, which were tested within a single test run. The test produced the following main results: the thermal modification increased the durability of the wood, and the protective effectiveness of alternative treatments was comparable to that of commercially available copper-based treatment. However, the initial moisture content of the samples during mould exposure had a great influence on the onset of mould growth. The risk of mould susceptibility of industrial kiln-dried lumber can be reduced by drying using the double-layering technique which likely forced the nutrients to deposit near the evaporation surfaces followed by planing off the nutrient enriched edges.

  • 18.
    Ahmed, Sheikh Ali
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Yang, Qian
    Sehlstedt-Persson, Margot
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Morén, Tom
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Accelerated mold test on dried pine sapwood boards: Impact of contact heat treatment2013In: Journal of wood chemistry and technology, ISSN 0277-3813, E-ISSN 1532-2319, Vol. 33, no 3, p. 174-187Article in journal (Refereed)
    Abstract [en]

    We test the hypothesis that the combination of kiln drying of double-stacked boards and contact heat treatment will reduce the susceptibility of treated boards to colonization by mold fungi. Winter-felled Scots pine (Pinus sylvestris L.) sapwood boards were double-stacked in an industrial kiln in ‘‘sapwood out’’ and ‘‘sapwood in’’ positions. Dried samples were then contact heat-treated using a hot press at three different temperatures (140°C, 170°C, and 200°C) for three different periods (1, 3, and 10 min). Accelerated mold test was performed in a climate chamber where naturally mold infected samples were used as a source of mold inocula. Contact heat treatment degraded the saccharides which accumulated at dried surfaces, and reduced the mold growth. The threshold temperature and time for inhibiting mold growth was 170°C for 10 min. But, for industrial application, the most feasible combination of temperature and time would be 200°C for 3 min. We concluded that double stacking/contact heat treatment used is an environmentally friendly alternative to chemicals for reducing mold on Scots pine sapwood boards.

  • 19.
    Ananías, Rubén A.
    et al.
    Department of Wood Engineering, University of Bío-Bío, Concepción.
    Sepúlveda-Villarroel, Victor
    Departamento de Ingenieria en Maderas, Universidad del Bio Bio, Avenida Collao 1202, Casilla 5-C-CP: 4081112, Concepción.
    Perez-Peña, Natalia
    Departamento de Ingenieria en Maderas, Universidad del Bio Bio, Avenida Collao 1202, Casilla 5-C-CP: 4081112, Concepción.
    Leandro-Zuñiga, Laura
    Instituto Costarricense de la Madera, San Pedro, San José.
    Salvo-Sepúlveda, Linette
    Departamento de Ingenieria en Maderas, Universidad del Bio Bio, Avenida Collao 1202, Casilla 5-C-CP: 4081112, Concepción.
    Salinas-Lira, Carlos
    Departamento de Ingenieria en Maderas, Universidad del Bio Bio, Avenida Collao 1202, Casilla 5-C-CP: 4081112, Concepción.
    Cloutier, Alain
    Society of Wood Science & Technology Member, Centre de Recherche sur le Bois, Université Laval, Québec.
    Elustondo, Diego
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Collapse of Eucalyptus nitens Wood after Drying Depending on the Radial Location Within the Stem2014In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 32, no 14, p. 1699-1705Article in journal (Refereed)
    Abstract [en]

    Collapse is almost certain to occur in the industrial drying of Eucalyptus nitens, and as such this prevents the lumber manufacturing industry in Chile from producing commercial solid wood products from this species. This problem is still unsolved, and different studies to reduce collapse are currently underway. In this exploratory study, shrinkage and collapse after drying of Eucalyptus nitens was measured for boards cut from different radial locations within the stem (core, transition and outer wood from pith to bark) and having different annual ring orientation (flat-sawn and quarter-sawn). Even though exploratory, the results appear to confirm that pieces that were cut from the center of the trees were less susceptible to collapse than the pieces cut from the transition zone between the center and the periphery. On average, collapse in transition wood was approximately 50% higher than the collapse observed in wood cut from the central zone of the trees.

  • 20.
    Andersson, Håkan A.
    et al.
    Umeå universitet.
    Isaksson, Anders
    Umeå universitet.
    Lindbergh, Lars
    Umeå universitet.
    Nilsson, Henrik
    Umeå universitet.
    Peterson, Christer
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Företagets finanser2008Book (Other (popular science, discussion, etc.))
  • 21.
    Andersson, Jan-Erik
    et al.
    SP Sveriges Tekniska Forskningsinstitut, SP Trä.
    Nordman, Roger
    SP Sveriges Tekniska Forskningsinstitut, SP Energiteknik.
    Vikberg, Tommy
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Energy mapping in the sawmill industry with focus on drying kilns2013Conference paper (Refereed)
    Abstract [en]

    The forest industry stands for approximately 11 % of Sweden’s total export. However, the forest industry is energy intensive. In 2008, sawmill industry alone consumed almost 8,7 TWh of energy, corresponding to 5 % of the Swedish industries total energy consumption. Out of their total consumption, 2200 GWh was electric power, 194 GWh heating oil , 4229 GWh bio-fuel, 574 GWh district heating, and other fuels such as diesel 1503 GWh [1].The project ”EESI- Energy Efficiency in the Sawmill Industry” was started in the spring of 2010 with the aim of demonstrating the possibilities to reduce the energy consumption in the sawmill industry with 20 % by 2020. 16 sawmill corporations and 14 equipment suppliers has joined the project which is carried out in two phases of which the first phase was carried out during 2010 and 2011. EESI has now reached half time and the first energy-saving implementations have been completed at the participating sawmills.This paper presents the energy-mapping, measurements and modelling performed by the participating sawmills during the first phase of the project [2, 3]. The average energy consumption per sawn cubic metre of boards varied between approximately 300 to 500 kWh/m3. Out of this, the electricity consumption was on average 85 kWh/m3, bio-fuel 290 kWh/m3 and diesel 1.8 l/m3.However, the main concern from sawmills regarding energy consumption was the wood drying process. The striking results from the preliminary measurements were the large variation in energy consumption even with similar drying kilns. This was especially apparent for the heat consumption in kiln dryers which could vary as much as 50 % for the same dimension of spruce planks.The results from the first phase of the project resulted in a large number of actions in order to reduce the energy consumption which are now being implemented or have already been completed. Examples of those actions are: simplified management system adapted to sawmills, weighing of packages for more accurate wood drying, reduced speed or intermittent operation of the air circulating fans in batch kilns and moisture content measurements of bio-fuel.References[1] Statistiska centralbyrån (SCB), 2013, Industrins årliga energianvändning 2011, Slutliga uppgifter, EN23SM1301, ISSN 1654-367X. (In Swedish). [2] Andersson, J-E., Lycken, A., Nordman, R., Olsson, M., Räftegård, O., and Wamming, T. State of the art – Energianvändning i den svenska sågverksindustrin. SP Rapport 2011:42, ISBN 978-91-86622-72-5. (In Swedish).[3] Andersson, J-E., Räftegård, O., Lycken, A., Olsson, M., Wamming, T., and Nordman, R. Sammanställning av energimätningar från EESI fas 1. SP Rapport 2011:41, ISBN 978-91-86622-71-8. (In Swedish).

  • 22.
    Andersson, Karl
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Lundahl, Carl-Gustav
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Lundmark, Martin
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science.
    Nordvik, Enar
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Pantze, Anna
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Förslag till handlingsplan för utveckling av LTU Skellefteå: Att synas med stolthet2008Report (Other academic)
  • 23.
    Andersson, Karl
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Computer Science.
    Lövf, Eva
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Studenters upplevelser av distansundervisning: en fallstudie2008Report (Other academic)
    Abstract [sv]

    Artikeln presenterar resultat från en studie av studenters upplevelser vid införande av modern videokonferensteknik i undervisningen. Studien omfattar 40 studenter vid fyra kurser. Resultaten indikerar att universitet och högskolor, förutom kostnadsbesparingar, lätt kan engagera specialistkompetens i kurser, erbjuda undervisning utanför campus och underlätta studentens självstudier. I sin bästa form uppnås både rums- och tidsoberoende. Samtidigt indikerar resultaten att det finns utrymme för förbättringar vid undervisning via videokonferenssändningar, främst i interaktionen mellan student och lärare. Oavsett lärarens pedagogik, ämnets inriktning och studenternas vana vid modern teknik så föredrog 39 av de 40 studenterna i undersökningen att ha en lärare på plats. Till viss del kan detta förklaras av teknikproblem, som delvis åtgärdats under kursernas genomförande, men även av att lärarna inte anpassat sin pedagogik fullt ut. Vår bedömning är att om rätt pedagogik används kan både kommunikation och interaktion fungera mycket bra och vara en utmärkt undervisningsform även om lärare och student inte befinner sig på samma plats.Vi föreslår att lärarna som sänder föreläsningarna ges tillfälle att interagera mer med studenterna, både synkront och asynkront, vilket kräver att kurserna planeras på annat sätt än vid traditionell campus-undervisning. Vidare föreslår vi att studenter på annan ort regelbundet erbjuds separata tillfällen för att diskutera och ställa frågor till läraren och gärna träffas fysiskt. Avslutningsvis föreslår vi att en särskild ämneskunnig producent, s.k. e-moderator, engageras parallellt med lärarens undervisning, för att stöda studenterna som följer föreläsningarna genom att besvara deras frågor. Alternativt kan en e-moderator uppmärksamma läraren på relevanta frågor som dyker upp, så att en utökad interaktion uppnås.

  • 24.
    Antti, Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Heating and drying wood using microwave power1999Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The potentials for moisture flux in wood during microwave heating have been investigated experimentally and theoretically. The experiments were performed in three different kinds of microwave applicators. A computer model based on the finite difference method was developed to describe and predict the heat and mass transfer. The main conclusions are that microwave energy of 2.45 GHz frequency makes it possible to heat and dry pine and spruce 20 - 30 times faster than with conventional methods without any deterioration in drying quality. Some hardwoods are dried in approximately half the time compared to the softwoods. The drying method evokes unique results either with diminishing colour changes or with possibilities to create such during drying. However, to avoid unevenness in the electromagnetic field distribution and considering the limitation in power penetration depth the drying should be performed on line where wood components continuously are fed through a microwave field.

  • 25.
    Antti, Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Microwave drying of hardwood: moisture measurements using CT-scanning1992In: Understanding the wood drying process: a synthesis of theory and practice : [proceedings of the] 3rd IUFRO conference on wood drying, August 18-21, 1992, Vienna, Austria, Wien: IUFRO , 1992Conference paper (Refereed)
  • 26.
    Antti, Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Microwave drying of hardwood: potentials for moisture flux1993Licentiate thesis, monograph (Other academic)
  • 27.
    Antti, Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Microwave drying of hardwood: Potentials for moisture flux1993In: Microwave and high frequency 1993: International congress : Papers, abstracts and programme., Göteborg: Institut für Volksmusikforschung und Ethnomusikologie, Universität für Musik und darstellende Kunst Wien, 1993, p. E2-Conference paper (Other academic)
  • 28.
    Antti, Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Microwave drying of hardwood: simultaneous measurements of pressure, temperature, and weight reduction1992In: Forest products journal, ISSN 0015-7473, Vol. 42, no 6, p. 49-54Article in journal (Refereed)
  • 29.
    Antti, Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Microwave drying of pine and spruce1995In: European Journal of Wood and Wood Products, ISSN 0018-3768, E-ISSN 1436-736X, Vol. 53, no 5, p. 333-338Article in journal (Refereed)
    Abstract [en]

    microwave energy consumption from 365 to 760 kWh/m 3. Internal wood temperatures up to 140°C were used. Internal vapour pressure in the wood could rise to about 20 kPa without checking. Maximal drying rates of 0.20 to 0.45% moisture content per minute are possible to obtain when drying above fiber saturation (fsp). Below fsp the feasible drying rates ranged from 0.10 to 0.20% moisture content per minute. Spruce dried approximately 1.6 times faster than pine. No conditioning of the wood was necessary since the wood was free of stresses. The wood was free of checks but colour changes occured in the interior of some specimens.

  • 30.
    Antti, Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Några inverkande faktorer vid mikrovågstorkning av lövträ1991Report (Other academic)
  • 31.
    Antti, Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Värmeövergång mellan trä och luft vid luftcirkulationstorkning: Klimat- och materialparametrars inverkan på värmeövergångstalet vid torkning av furu1989Report (Other academic)
  • 32.
    Antti, Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Finell, M.
    Arshadi, M.
    Lestander, T.
    Microwave drying of sawdust: effect on biofuel pellet2010In: Proceedings, 11th International IUFRO Wood Drying Conference: in Skellefteå, Sweden, January 18 - 22, 2010 ... the theme of the conference was "Recent Advances in the Field of Wood Drying" / [ed] Tom Morén; Lena Antti; Margot Sehlstedt-Persson, Luleå: Luleå tekniska universitet, 2010, p. 313-319Conference paper (Refereed)
  • 33.
    Antti, Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Finell, Michael
    Swedish University of Agricultural Sciences.
    Arshadi, Mehrdad
    Swedish University of Agricultural Sciences.
    Lestander, Torbjörn A.
    Swedish University of Agricultural Sciences.
    Effects of microwave drying on biomass fatty acid composition and fuel pellet quality2011In: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 6, no 1-2, p. 34-40Article in journal (Refereed)
  • 34.
    Antti, Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Equalization of moisture in pre-dried pinewood using microwave power2010In: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 6, no 2, p. 53-59Article in journal (Refereed)
    Abstract [en]

    Commonly, during air-circulation kiln drying moisture gradients within wood cross-sections are developed, i.e. the surfaces become drier than the interior. To minimize these gradients a conditioning step subsequent to the drying is needed. The aim with this study was to investigate the possibility to use microwave power for equalization of moisture within pinewood boards after air-circulation kiln drying to the average moisture content 0,14. Two dimensions of pinewood were tested; thickness 50 and 63 mm, in two different plants, generating 5 and 12 kW microwave power respectively. Results show that microwave energy give rise to a fast and advantageous moisture equalization within the wood. The higher microwave power density the faster heating and moisture redistribution in these wood dimensions. Required time for heating and redistribution of moisture was found to be as short as 3 minutes at the power density 500 kW/m3. In addition, split-tests indicate decreased or elimination of gap after microwave treatment in the investigated specimens.

  • 35.
    Antti, Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Microwave treatment of resinous wood2006In: Wood structure and properties '06: [proceedings of the 5th IUFRO Symposium Wood Structure and Properties '06 held on September 3-6, 2006 in Sliač - Sielnica, Slovakia] / [ed] R. Lagana; S. Kurjatko; J. Kudela, Zvolen, Slovakia: Arbora Publishers , 2006, p. 435-437Conference paper (Refereed)
    Abstract [en]

    The output from conventional air-circulation drying of wood is not always satisfying; some individual wood boards often contain somewhat higher moisture content (MC) than the target MC. Higher MC in some pine wood boards after conventional drying could origin from the fact that these contain higher amounts of resin, which may delay or to some extent prevent the moisture flux. It could be the reason to problems in further wood production processes, as for example in gluing processes. The aim of this study was to determine whether or not microwave (MW) heating could be a suitable method to condition these components. Another aim was to investigate if and how migration of resin appears during MW treatment. The study includes experimental tests where determination of both MC and resin content (RC) were carried out before and after MW treatment. Results from the tests show that the RC and the MC are interacting; it means that volumes with high RC also withhold increased amount of moisture; these volumes are often found within boards that origin from the root end of logs. It is possible to dry/condition these planks to reach the target MC within minutes or hours, depending on wood thickness, using MW power. By exposing resinous wood to microwaves, migration of resin takes place from the interior towards the wood surfaces, especially longitudinally through the wood towards the butt ends. It seems to be possible to redistribute RC and MC in wood by exposing only parts of a plank to microwaves.

  • 36.
    Antti, Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Hansson, Lars
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Redistribution of moisture in pre-dried pinewood using microwave power: a preliminary study2010In: Proceedings, 11th International IUFRO Wood Drying Conference: [... in Skellefteå, Sweden, January 18 - 22, 2010 ... the theme of the conference was "Recent Advances in the Field of Wood Drying"] / [ed] Tom Morén; Lena Antti; Margot Sehlstedt-Persson, Luleå: Luleå tekniska universitet, 2010, p. 234-238Conference paper (Refereed)
    Abstract [en]

    Commonly, during air-circulation kiln drying moisture gradients within wood cross-sections are developed, i.e. thesurfaces become drier than the interior. To minimize these gradients a conditioning step subsequent to the drying isneeded. The aim with this study was to investigate the possibility to use microwave power for redistribution ofmoisture within pinewood planks after air-circulation kiln drying to the average moisture content 0,14. Twodimensions of pinewood were tested; thickness 50 and 63 mm, in two different plants, generating 5 and 12 kWmicrowave power respectively. Results show that microwave energy give rise to a fast and advantageous moistureredistribution i.e. equalization of moisture content within the wood. The higher microwave power density the fasterheating and moisture equalization in these wood dimensions. Required time for heating and redistribution ofmoisture was found to be as short as 3 minutes at the power density 500 kW/m3. In addition, split-tests indicatedecreased or almost no gap in the investigated specimens.

  • 37.
    Antti, Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Jönsson, Anette
    LTU.
    Nilsson, Magnus
    LTU.
    The effect of drying method on the mechanical properties of wood: Comparisons between conventional kiln and microwave dried Scots pine2001In: Proceedings of the 3rd European Cost E15 Workshop on Wood Drying: with the theme Softwood drying to meets needs of further processing and specific end-uses : 11-13 June 2001 at Scandic Hotel Kalastajatorppa, Helsinki, Finland, Espoo: VTT Building and Transport , 2001, p. 21:1-21:9Conference paper (Refereed)
  • 38.
    Antti, Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Perre, P.
    ENGREF - Laboratory of Forest Sciences.
    A microwave applicator for on line wood drying: Temperature and moisture distribution in wood1999In: Wood Science and Technology, ISSN 0043-7719, E-ISSN 1432-5225, Vol. 33, no 2, p. 123-138Article in journal (Refereed)
    Abstract [en]

    An especially designed open microwave applicator was analysed using wood as the material to be heated and dried. The idea was to develop an on line microwave construction consisting of several small open applicators, each fed by a small standard magnetron (for example 1.4 kW main power). The process was analysed by measuring the wood temperature during heating using an IR-camera and detecting the moisture distribution during drying by CT-scanning. Pine and birch wood samples were used in the experiments, mainly 40 mm in thickness. The experiments show that the power distribution differs between dry wood and moist wood. The analysis of the temperature fields captured by the IR-camera during the first minutes allows a rather accurate determination of the MW power. Consequently, the drying proceeds unevenly in the wood specimens, especially in the longitudinal direction. The dimensions of the applicator and its relation to the wood dimension are very important. However, the wood was not destroyed, the temperature and moisture gradients did not affect the wood in terms of checks or deformations. The drying rate in different positions of the specimen varied between 0.30 and 0.80 percentage moisture content/min. The uneven energy, meaning temperature and field distribution, is to be compensated in the future by a moving wood load and by alternating the position of each applicator in a larger scale microwave pilot plant.

  • 39.
    Antti, Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Torgovnikov, Grigori
    Microwave heating of wood1995In: Fifth international conference on microwave and high frequency heating, 17-21 September 1995, Cambridge: Cambridge University Press, 1995, p. E3.1-3.4Conference paper (Refereed)
  • 40.
    Antti, Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Zhao, H.
    Turner, I.
    An Investigation of the Heating of Wood in an Industrial Microwave Applicator: Theory and Practice2000In: 6th international IUFRO wood drying conference on wood drying research and technology for sustainable forestry beyond 2000, Marcel Dekker Incorporated , 2000Conference paper (Refereed)
  • 41.
    Antti, Lena
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Zhao, H.
    Turner, I.
    Investigation of the heating of wood in an industrial microwave applicator: theory and practice2000In: Drying Technology, ISSN 0737-3937, E-ISSN 1532-2300, Vol. 18, no 8, p. 1665-1676Article in journal (Refereed)
    Abstract [en]

    In this work a comprehensive set of experimental results are used as an excellent means to understand the coupling that exists between the material and the electromagnetic fields in a specific industrial microwave applicator. The analysis of the infrared images allows an accurate map of the power and temperature distributions within the wood sample to be determined. This map, together with the simulation results of a previously developed computational electromagnetic model, can provide a detailed understanding of the design features of the microwave applicator. In particular, it is possible to locate the occurrence of localised hot spots and to examine the uniformity of the heat distribution throughout the sample. The simulation results provide the evolution of the electromagnetic fields inside the entire applicator and the sample. The coupling of theory and practice is the best way to proceed in optimising the design and for proposing new applicator geometry that can heat the material more effectively.

  • 42. Arfvidsson, J.
    et al.
    Lindgren, Owe
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Wiberg, P.
    Luleå tekniska universitet.
    The development of a moisure sorption model to predict moisture within solid wood based on non-destructive moisture gradient measurements using CT-scanning and digital ...1997In: International Conference on Wood-Water Relations, 16 - 17 June 1997, Copenhagen, Denmark: [COST Action E8, Mechanical Performance of Wood and Wood Products] / [ed] Preben Hoffmeyer, Copenhagen: Technical University of Denmark , 1997Conference paper (Refereed)
  • 43.
    Atashipour, Seyed Rasoul
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. Department of Civil and Environmental Engineering, Division of Structural Engineering, Chalmers University of Technology.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Influence of Grain Inclination Angle on Shear Buckling of Laminated Timber Sheathing Products2018In: Structures, ISSN 2352-0124, Vol. 13, p. 36-46Article in journal (Refereed)
    Abstract [en]

    Recent advances in timber production industries have enabled production of new innovative laminated timber products having layers with grain inclination angle. This paper is aimed to study influence of grain inclination angle in the laminated veneer lumber (LVL) and plywood sheathings on their shear buckling loads. Two extreme edge conditions of simply supported and clamped edges are considered. First, an accurate differential quadrature (DQ) computational code is developed using MAPLE programming software to obtain eigen buckling values and their corresponding eigen mode shapes. Next, for convenience of engineering calculations, approximate algebraic formulae are presented to predict critical shear buckling loads and mode shapes of LVL and plywood panels having layers with grain inclination angle, with adequate accuracy. Furthermore, finite element (FE) modelling is conducted for several cases using ANSYS software to show validity and accuracy of the predicted results for the problem. It is shown that the highest shear buckling loads of LVL sheathings is achievable when the inclination angle of about 30° with respect to the shorter edges is considered for production of LVL panels, whereas the same angle with respect to the long edges of the LVL sheathings results in a relatively lower buckling load. Considering similar inclination angle with respect to any edges of a plywood sheathings will also results in its highest pre-buckling capacity. It is also demonstrated that, under optimal design and certain loading circumstances, LVL shows a higher shear buckling capacity compared to a similar plywood sheathing.

  • 44.
    Atashipour, Seyed Rasoul
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    On the Shear Buckling of Clamped Narrow Rectangular Orthotropic Plates2015In: Mathematical problems in engineering (Print), ISSN 1024-123X, E-ISSN 1563-5147, Vol. 2015, article id 569356Article in journal (Refereed)
    Abstract [en]

    This paper deals with stability analysis of clamped rectangular orthotropic thin plates subjected to uniformly distributed shear load around the edges. Due to the nature of this problem, it is impossible to present mathematically exact analytical solution for the governing differential equations. Consequently, all existing studies in the literature have been performed by means of different numerical approaches. Here, a closed-form approach is presented for simple and fast prediction of the critical buckling load of clamped narrow rectangular orthotropic thin plates. Next, a practical modification factor is proposed to extend the validity of the obtained results for a wide range of plate aspect ratios. To demonstrate the efficiency and reliability of the proposed closed-form formulas, an accurate computational code is developed based on the classical plate theory (CPT) by means of differential quadrature method (DQM) for comparison purposes. Moreover, several finite element (FE) simulations are performed via ANSYS software. It is shown that simplicity, high accuracy, and rapid prediction of the critical load for different values of the plate aspect ratio and for a wide range of effective geometric and mechanical parameters are the main advantages of the proposed closed-form formulas over other existing studies in the literature for the same problem.

  • 45.
    Atashipour, Seyed Rasoul
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Al-Emrani, Mohammad
    Chalmers tekniska högskola .
    Exact Lévy-type solutions for bending of thick laminated orthotropic plates based on 3-D elasticity and shear deformation theories2017In: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243, Vol. 163, p. 129-151Article in journal (Refereed)
    Abstract [en]

    Exact solutions for static bending of symmetric laminated orthotropic plates with different Lévy-type boundary conditions are developed. The shear deformation plate theories of Mindlin-Reissner and Reddy as well as the three-dimensional elasticity theory are employed. Using the minimum total potential energy principle, governing equilibrium equations of laminated orthotropic plates and pertaining boundary conditions are derived. Closed-form Lévy-type solutions are obtained for the governing equations of both theories using separation of variables method and different types of classical boundary conditions, namely simply-supported, clamped and free edge, are exactly satisfied. Thereafter, 3-D elasto-static equations for orthotropic materials are solved for bending analysis of laminated plates using two different approaches. First, the method of separation of variables is utilized and an exact closed-from solution is achieved for simply-supported laminated orthotropic plates. Next, a combined Fourier-Differential Quadrature (DQ) approach is employed to present a semi-numerical solution for bending of laminated orthotropic plates with Lévy-type boundary conditions based on the three-dimensional elasticity theory. High accuracy of the presented solutions are proven and comprehensive comparative numerical results are provided and discussed. Presented comparative numerical results can serve as benchmark for investigating the correctness of new solution methods which may be established in the future.

  • 46.
    Atashipour, Seyed Rasoul
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering. Department of Architecture and Civil Engineering, Division of Structural Engineering, Chalmers University of Technology.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Challamel, Noël
    Université de Bretagne Sud, UBS – Institut Dupuy de Lôme, Centre de Recherche.
    A weak shear web model for deflection analysis of deep composite box-type beams2018In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 155, p. 36-49Article in journal (Refereed)
    Abstract [en]

    Deep box-type beams, consisting of framing members and sheathings, are sensitive to shear deformations and hence appropriate refined theories or complicated magnification factors are needed to be used to obtain accurate results. For sheathings or webs between the framing members that are weak in shear, additional shear deformations occur corresponding to the relative axial displacement between the framing members. These sandwich-type or partial interaction-type of in-plane shear behaviour between the framing members, needs to be taken into account, especially when the web shear stiffness is very low. The composite box-type beam treated here is composed of three framing members with sheathings on both sides. To incorporate effects of the sheathings shear deformations between the framing members on the deflection, the sheathings, here called web interlayers, are modelled as shear media with equivalent slip moduli corresponding to a partially interacting composite beam model. Governing equilibrium equations of the model are obtained using the minimum total potential energy principle and solved explicitly. The obtained results are compared with those based on different conventional beam theories and 3-D finite element (FE) simulations. It is shown that the model is capable of predicting accurately the deflection for a wide range of geometry and property parameters. It is demonstrated that the deflection of such deep box-type beams can be expressed as the summation of three different effects, namely bending deformations, conventional shear deformations in the framing members and sheathings, and additional in-plane shear deformations or shear slips of the weak web causing relative axial displacements between the framing members.

  • 47.
    Atashipour, Seyed Rasoul
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Challamel, Noël
    Université de Bretagne Sud, UBS – Institut Dupuy de Lôme, Centre de Recherche.
    Stability analysis of three-layer shear deformable partial composite columns2017In: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 106-107, p. 213-228Article in journal (Refereed)
    Abstract [en]

    This paper is focused on the effect of imperfect bonding and partial composite interaction between the sub-elements of a box-type column on the critical buckling loads. The box column is modelled as a symmetric three-layer composite structure with interlayer slips at the interfaces, based on the Engesser-Timoshenko theory with uniform shear deformation assumptions. Linear shear springs or slip modulus is considered at the interfaces to model the partial interaction between the sub-elements of the structure. The minimum total potential energy principle is utilized to obtain governing equations and boundary conditions. A direct analytical solution of the original governing equations is presented for obtaining exact buckling characteristic equation of the three-layer partial composite column with different end conditions including clamped-pinned end conditions. Also, the coupled equations are recast into an efficient uncoupled form and shown that there is a strong similarity with those for the two layer element. It is shown that the obtained formulae are converted to the known Euler column formulae when the slip modulus approaches infinity (i.e. perfect bonding) and no shear deformations in the sub-elements are considered. A differential shear Engesser-Timoshenko partial composite model is also employed and critical buckling loads, obtained from an inverse solution method, are compared to examine the validity and accuracy level of the uniform shear model. Comprehensive dimensionless numerical results are presented and discussed

  • 48.
    Atashipour, Seyed Rasoul
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Girhammar, Ulf Arne
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Challamel, Noël
    University of Europeenne Bretagne, Laboratory Genie Civil & Genie Mecan, Université Européenne de Bretagne, Mechanics Division, Department of Mathematics, University of Oslo, LIMATB, Université Européenne de Bretagne, University of South Brittany, Lorient.
    The effect of weak shear webs on the deformations of timber box type beams2015In: Proceedings of the Fifteenth International Conference on Civil, Structural and Environmental Engineering Computing / [ed] J. Kruis; Y. Tsompanakis; B.H.V. Topping, Stirlingshire: Civil-Comp Press , 2015, article id 259Conference paper (Refereed)
    Abstract [en]

    This paper deals with deflection analysis of a deep composite box beam due to inplane shear deformations, especially the modelling of the shear deformations in the webs is considered. The beam is composed of three framing members with sheathings on both sides. The sheathings or webs between the framing members are modelled as shear media with equivalent slip moduli corresponding to the partially composite beam model with three separated layers and two interlayer slip areas. The minimum total potential energy principle is employed to obtain the governing equilibrium equations and corresponding boundary conditions. The coupled set of governing equations is recast into an uncoupled form and solved explicitly together with the corresponding boundary conditions. The closed-form solutions obtained are compared to those based on the conventional beam theories. It is shown that the model is capable of predicting accurately the deflections for a wide range of geometry and property parameters, especially for small shear stiffness (slip modulus) values for the webs. The formula for the deflection is reduced to the Timoshenko formula for full composite interaction when the shear slip modulus of the web approaches infinity. Comparative numerical results are presented to show the influence of bending deformations, shear deformations in the framing layers and the in-plane shear deformations in the sheathings

  • 49.
    Awoyemi, Lawrence
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Influence of prefreezing on the fibre saturation point, sorption and swelling properties of birch (Betula pubescens) wood2006In: International Wood Products Journal, ISSN 0020-3203, Vol. 17, no 4, p. 225-227Article in journal (Refereed)
    Abstract [en]

    Matched samples were obtained from green birch (Betula pubescens) wood. Prefreezing was done at -20°C for 72hours. Both the prefrozen and unfrozen samples were dried and soaked in water for the determination of sorption behavior, swelling properties and fibre saturation point. Prefreezing resulted in 6.7 to 666.7% increase in rate of adsorption, 0 to 13.3% decrease in the rate of desorption, 2.2% decrease in volumetric swelling coefficient and 0.8% decrease in fibre saturation point. However only the change in the rate of water adsorption is statistically significant at 95% confidence level. Since these results were obtained from samples taken from a typical board, more results are required in order to characterise the effects of prefreezing on available stock of Birch wood

  • 50.
    Awoyemi, Lawrence
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Wood Science and Engineering.
    Mechanical behaviour of birch (Betula Pubescens) wood under high temperature drying2009In: International Wood Products Journal, ISSN 0020-3203, Vol. 19, no 1, p. 27-30Article in journal (Refereed)
    Abstract [en]

    High temperature drying is employed to reduce the drying time of sawn wood. However the deterioration in mechanical properties associated with it seems to be a major limitation of its use in the seasoning of some wood species. As in conventional drying, both the modulus of elasticity and modulus of rupture increase with decreasing moisture content. High temperature drying does not seem to constitute a meaningful threat to the mechanical properties of this species and hence its use is strongly recommended. The low effect of high temperature drying on this species strongly reinforces the results of the previous studies on other species that the effect of this technique is both species and property dependent.

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