| 1. |
- Berg, Jan-Erik, 1957-
(författare)
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Wood and fibre mechanics related to the thermomechanical pulping process
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of this thesis was to improve the understanding of some aspects on wood and fibre mechanics related to conditions in the thermomechanical pulping process. Another objective was to measure the power distribution between the rotating plates in a refiner. The thesis comprises the following parts: –A literature review aimed at describing fracture in wood and fibres as related to the thermomechanical pulping process –An experimental study of fracture in wood under compression, at conditions similar to those in feeding of chips into preheaters and chip refiners –An experimental study of the effect of impact velocity on the fracture of wood, related to conditions of fibre separation in the breaker bar zone in a chip refiner –A micromechanical model of the deterioration of wood fibres, related to the development of fibre properties during the intense treatment in the small gap in the refining zone –Measurements of the power distribution in a refiner. The fracture in wood under compression was investigated by use of acoustic emission monitoring. The wood was compressed in both lateral and longitudinal directions to predict preferred modes of deformation in order to achieve desired irreversible changes in the wood structure. It was concluded that the most efficient compression direction in this respect is longitudinal. Preferable temperature at which the compression should be carried out and specific energy input needed in order to achieve substantial changes in the wood structure were also given. The fibre separation step and specifically the effect of impact velocity on the fracture energy were studied by use of a falling weight impact tester. The fracture surfaces were also examined under a microscope. An increase in impact velocity resulted in an increase in fracture energy. In the thermomechanical pulping process the fibres are subjected to lateral compression, tension and shear which causes the creation of microcracks in the fibre wall. This damage reduces the fibre wall stiffness. A simplified analytical model is presented for the prediction of the stiffness degradation due to the damage state in a wood fibre, loaded in uni-axial tension or shear. The model was based on an assumed displacement field together with the minimum total potential energy theorem. For the damage development an energy criterion was employed. The model was applied to calculate the relevant stiffness coefficients as a function of the damage state. The energy consumption in order to achieve a certain damage state in a softwood fibre by uniaxial tension or shear load was also calculated. The energy consumption was found to be dependent on the microfibril angle in the middle secondary wall, the loading case, the thicknesses of the fibre cell wall layers, and conditions such as moisture content and temperature. At conditions, prevailing at the entrance of the gap between the plates in a refiner and at relative high damage states, more energy was needed to create cracks at higher microfibril angles. The energy consumption was lower for earlywood compared to latewood fibres. For low microfibril angles, the energy consumption was lower for loading in shear compared to tension for both earlywood and latewood fibres. Material parameters, such as initial damage state and specific fracture energy, were determined by fitting of input parameters to experimental data. Only a part of the electrical energy demand in the thermomechanical pulping process is considered to be effective in fibre separation and developing fibre properties. Therefore it is important to improve the understanding of how this energy is distributed along the refining zone. Investigations have been carried out in a laboratory single-disc refiner. It was found that a new developed force sensor is an effective way of measuring the power distribution within the refining zone. The collected data show that the tangential force per area and consequently also the power per unit area increased with radial position. The results in this thesis improve the understanding of the influence of some process parameters in thermomechanical pulping related wood and fibre mechanics such as loading rate, loading direction, moisture content and temperature to separate the fibres from the wood and to achieve desired irreversible changes in the fibre structure. Further, the thesis gives an insight of the spatial energy distribution in a refiner during thermomechanical pulping.
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| 2. |
- Engberg, Birgitta Anna, 1975-, et al.
(författare)
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On the importance of fatigue for the rheological properties of wood
- 2009
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Ingår i: Proceedings - 2009 International Mechanical Pulping Conference, IMPC 2009. ; , s. 239-244
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Konferensbidrag (refereegranskat)abstract
- In this study the rheological properties of both native and fatigued wood was quantified under conditions relevant to mechanical pulping. This work was part of a Nordic cooperation project on "Basic phenomena in mechanical pulping. The new knowledge is intended to give us guidance on process development in mechanical pulping. The recent EES-concept [1] is assumed to offer low specific energy consumption mostly because of wood fatigue. A modulated loading device (MLD) developed at KCL was here used to fatigue wood samples. The samples were then evaluated by impulsive loading experiments carried out in an encapsulated Split-Hopkinson device (ESHD) developed at Mid Sweden University. Impulsive loadings, which extended to the non-elastic deformation region, were performed at four temperatures: 20, 65, 100 and 135°C. A higher testing temperature softened the wood samples to a high extent as could be expected. The results show that the reference samples (that was not subjected to fatigue treatment) had the highest stiffness in the investigation. The stress-strain curves of the fatigued samples were less steep, which indicate a softer more loosened material. It was evident that the fatigue treatment had loosened or weakened the wood material considerably and the differences were most pronounced at the two lowest testing temperatures.
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| 3. |
- Moilanen, Carolina, et al.
(författare)
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Influence of strain rate, temperature and fatigue on the radial compression behaviour of Norway spruce
- 2017
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Ingår i: Holzforschung. - : Walter de Gruyter GmbH. - 0018-3830 .- 1437-434X. ; 71:6, s. 505-514
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Tidskriftsartikel (refereegranskat)abstract
- A dynamic elastoplastic compression model of Norway spruce for virtual computer optimization of mechanical pulping processes was developed. The empirical wood behaviour was fitted to a Voigt-Kelvin material model, which is based on quasi static compression and high strain rate compression tests (QSCT and HSRT, respectively) of wood at room temperature and at high temperature (80-100 degrees C). The effect of wood fatigue was also included in the model. Wood compression stress-strain curves have an initial linear elastic region, a plateau region and a densification region. The latter was not reached in the HSRT. Earlywood (EW) and latewood (LW) contributions were considered separately. In the radial direction, the wood structure is layered and can well be modelled by serially loaded layers. The EW model was a two part linear model and the LW was modelled by a linear model, both with a strain rate dependent term. The model corresponds well to the measured values and this is the first compression model for EW and LW that is based on experiments under conditions close to those used in mechanical pulping.
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| 4. |
- Moilanen, Carolina S., et al.
(författare)
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High strain rate radial compression of Norway spruce earlywood and latewood
- 2016
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Ingår i: Cellulose. - : Springer Science and Business Media LLC. - 0969-0239 .- 1572-882X. ; 23:1, s. 873-889
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical properties of Norway spruce were studied and a compression model for mechanical pulping was developed. The split-Hopkinson pressure bar technique was combined with high-speed photography to analyse local radial compression. Data analysis focussed on the differences between mechanical properties of earlywood and latewood. Measurements were conducted at both room temperature and 135 C. The effect of prefatigue treatment was also studied. A simple material model was defined linearly in parts and fitted to the measurement data to quantify the differences. New results were found on the differences in inelastic behaviour of earlywood and latewood at large deformations. In addition, other results were in line with previously published results.
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| 5. |
- Saari, Ulla A., et al.
(författare)
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Engaging students in cross-disciplinary research and education—A processual approach to educational development
- 2019
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Ingår i: Handbook of sustainability science and research. - Cham : Springer. - 9783319630069 - 9783319630076 ; , s. 353-363
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Bokkapitel (refereegranskat)abstract
- The creation of future sustainable and efficient energy systems requires a cross-disciplinary approach in engineering education. In order for energy-related engineering students to be prepared for real-world situations after their studies, it is important that, while they are still studying, they obtain the basic skills for handling different concepts, theoretical frameworks and solution types created in the various disciplines involved. At the Tampere University of Technology (TUT), a cross-disciplinary team was formed from four different departments in three different faculties to create a platform for research and education purposes on the university campus. The purpose was to coordinate research and provide students with a wider picture and a concrete implementation of the different layers and aspects that need to be taken into account when creating innovative solutions for future digital energy systems. The creation of the platform started from a successful student ideation competition that produced many viable solutions. This paper describes the bottom-up incremental process by which the cross-disciplinary platform was created. The innovative solutions created in the student ideation competition convinced the university organization that the cross-disciplinary collaboration should have a more permanent platform on the university campus, allowing researchers and students to incorporate more sustainability and systemic aspects into their work, and having a positive impact on the sustainable energy consumption on the campus.
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| 6. |
- Saari, Valtteri, et al.
(författare)
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Strain distribution in annual rings under compression by high speed photography
- 2009
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Ingår i: Proceedings - 2009 International Mechanical Pulping Conference, IMPC 2009. ; , s. 245-251
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Konferensbidrag (refereegranskat)abstract
- Fatigue is essential in mechanical pulping when producing flexible paper fibers energy efficiently from stiff wood fibers. Fatigue propagation depends mainly on strain variation. The objective of the study is to determine how compressive strain is distributed between earlywood and latewood. Uneven distribution of local strain variation is likely to cause different amount of fatigue for earlywood and latewood and thus affects the usability of these fibers in the paper products. To characterize the material's response to mechanical defibration at high strain rates a unique testing equipment was utilized. The ESHD (Encapsulated Split-Hopkinson Device) at Mid Sweden University allows generation of such high strain rate pulses. Combining this with high speed photography at 50 000 fps offered the possibility of quantitative strain field mapping by image analysis. Since both wood temperature and moisture content affect strain behavior, moisture content was in this study kept constant at 45 %. Testing temperature was varied between 20°C and 135°C. Additionally, four levels of compressive fatigue treatment in the radial direction, prior to the high strain rate tests, were used to investigate how different parts of the annual rings were changed due to the fatigue treatment. In the measurements, it was noted that the strain was concentrated in the softer earlywood layers and there were unexpectedly little strain in the latewood layers. The temperature and the fatigue level clearly affected the magnitude of the strains. Higher temperature and fatigue level increased the strain difference between earlywood and latewood in the sample.
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| 7. |
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| 8. |
- Salminen, Lauri, et al.
(författare)
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Cyclic loading and fatigue of wood
- 2011
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Ingår i: Progress in Paper Physics Seminar2011. - 9783851251630 ; , s. 243-245
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 9. |
- Soylu Kucharz, Rana, et al.
(författare)
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Mutant huntingtin expression in the hypothalamus promotes ventral striatal neuropathology
- 2023
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Huntington’s disease is a fatal neurodegenerative disorder caused by an expanded CAG triplet repeat in the huntingtin (HTT) gene. Previous research focused on neuropathology in the striatum and its association with a typical movement disorder. Direct effects of mutant HTT (mHTT) in the striatum may cause neuropathology, although non-cell autonomous effects have also been suggested. Important non-motor features of HD include psychiatric symptoms and metabolic dysfunction, which may be linked to hypothalamic neuropathology. As hypothalamic neurons project to the ventral striatum, we hypothesized that expression of mHTT in the hypothalamus leads to disrupted neurotransmission in the ventral striatum and causes pathology. The overall aim of this study was to investigate the impact of mHTT expression in the hypothalamus on ventral striatal neuropathology and its contribution to non-HD motor symptoms. We demonstrate that selective expression of mHTT in the hypothalamus leads to the loss of dopamine and cAMP-regulated phosphoprotein (DARPP-32) immunopositive neurons in the ventral striatum in mice. Contrary to the effects of direct expression of mHTT in the hypothalamus, selective overexpression of mHTT in the ventral striatum does not affect body weight. Selective expression of mHTT in the ventral striatum leads to mHTT inclusion formation and loss of DARPP-32 neurons without affecting motor activity or anxiety-like behavior. We show that DARPP-32 neuron loss in the ventral striatum is recapitulated in the R6/2 mouse model of HD. Chemogenetic activation of hypothalamic neurons projecting to the ventral striatum had a blunted response in the R6/2 mice compared to wild-type mice, indicating a disrupted hypothalamus-ventral striatal circuitry. In summary, the expression of mHTT in the hypothalamus may impact the development of ventral striatal pathology in mice. This opens the possibility that non-cell-autonomous effects in the reward circuitry play a role in HD.
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| 10. |
- van der Burg, Jorien m, et al.
(författare)
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Increased metabolism in the R6/2 mouse model of Huntington's disease.
- 2008
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Ingår i: Neurobiology of Disease. - : Elsevier BV. - 0969-9961. ; 29:1, s. 41-51
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Tidskriftsartikel (refereegranskat)abstract
- Huntington’s disease (HD) is a hereditary disorder characterized by personality changes, chorea, dementia and weight loss. The cause of this weight loss is unknown. The aim of this study was to examine body weight changes and weight-regulating factors in HD using the R6/2 mouse model as a tool. We found that R6/2 mice started losing weight at 9 weeks of age. Total locomotor activity was unaltered and caloric intake was not decreased until 11 weeks of age, which led us to hypothesize that increased metabolism might underlie the weight loss. Indeed, oxygen consumption in R6/2 mice was elevated from 6 weeks of age, indicative of an increased metabolism. Several organ systems that regulate weight and metabolism, including the hypothalamus, the stomach and adipose tissue displayed abnormalities in R6/2 mice. Together, these data demonstrate that weight loss in R6/2 mice is associated with increased metabolism and changes in several weight-regulating factors.
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