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  • 1.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    A study of contaminated lubricants concerning wear, rheological properties and sample withdrawal2001Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The wear of a machine, whether it is due to fatigue or abrasive wear, will add contaminants, in the form of particulates, to the system in question. Since a total breakdown of the machine can be rather costly, one wants to be able to foresee breakdowns and increase the machine life. Follow-up checks of machines are often performed to enable one to detect an increase in wear, and thereby replace the machine or remove it for service. This licentiate thesis mainly deals with the problems associated with contamination control and sample withdrawal. A survey of where and how to take a representative sample is performed using Stokes' law and the migration of spheres in a channel. Some different techniques to measure the contamination are also presented, together with their advantages and disadvantages. Sampling routines for proper sample withdrawal are included. The thesis also includes some field aspects concerning the influence of particles and the wear of grease-lubricated rolling element bearings.

  • 2.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A study of sample withdrawal for lubricated systems: Part 1: Influence of flow characteristics, sampling techniques and locations2001Inngår i: Industrial Lubrication and Tribology, ISSN 0036-8792, E-ISSN 1758-5775, Vol. 53, nr 1, s. 22-31Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The wear of a machine element, whether it is due to fatigue or abrasive wear, will add contaminants in the form of particulates to the system. If a machine element is starting to wear out it will produce a large amount of particles and it will finally break down. Since this can be very costly, one can establish the need to monitor the system so that one can foresee failure. There are many different ways to monitor a system, e.g. measurements of the temperature, pressure, vibrations and the degree of contamination. The purpose of contamination control is to extend the life of a component and thereby save money. When monitoring a system it is very important that the monitoring control instrument should give the right output. One important factor in achieving this is the withdrawal of a representative oil sample. In this paper an investigation of where and how to take a representative sample is performed using Stokes' law and the migration of spheres in a channel. A generalised sedimentation chart for diffe rent oils and particles is introduced. Sampling routines for proper sample withdrawal are also presented

  • 3.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A study of sample withdrawal for lubricated systems: Part 2: practical sample withdrawal and selection of proper sampling methods2001Inngår i: Industrial Lubrication and Tribology, ISSN 0036-8792, E-ISSN 1758-5775, Vol. 53, nr 3, s. 97-108Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Aims to use some of the sampling techniques and sampling routines, mentioned in Part 1 of the article, to perform practical tests to determine their differences in withdrawing samples. Uses two different types of systems, a hydraulic system and a gear system, together with some of the investigated sampling techniques. In order to find out the optimum sampling method for each of the two systems, uses a specification of requirements and a systematic approach, together with practical sample withdrawal from the two systems. For the hydraulic system, uses an on-line particle counter and bottle samples from valves, and for the gear system, applies drain-plug and vacuum pump sampling. It was found that for hydraulic systems on-line sampling is the most appropriate, if information on the elements is not required. If information on the elements is required, bottle sampling from a valve together with flushing of the valve should be performed. For the gear system no difference was seen between the samples taken with a vacuum pump and those taken from the drain-plug, and therefore an alternative method is suggested to improve the reliability of the sampling.

  • 4.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Ultra high-pressure compaction of powder2011Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Sintering at high-pressure improves the properties of the material, either through new sintering aids becoming available or through improving intergranular bonding. This gives the manufactured products potential advantages like faster cut rates, and more precise and cleaner production methods that add up to cost efficiency and competitive edge. The production of synthetic diamond products demands tooling that can achieve high pressures and deliver it with a high degree of certainty. The common denominator for almost all high-pressure systems is to use capsules where a powder material encloses the core material. Numerical analysis of manufacturing processes with working conditions that reach ultra high pressure (above 10 GPa) requires a constitutive model that can handle the specific behaviours of the powder from a low density to solid state. The work in this thesis deals with characterization and simulation of the material behaviour during high-pressure compaction in powder pressing. Some of the work was focused on investigating the material when used as compressible gasket in high-pressure systems. The aim was to increase the knowledge of the high-pressure pressing process. This includes a better understanding of how mean stress develops in the compact during pressing and an insight into the development material models concerning highpressure materials. Both experimental and numerical investigations were made to gain knowledge in these fields. The mechanical behaviour of a CaCO3 powder mix was investigated using the Brazilian disc test, uniaxial compression testing and closed die experiments. The aim of the experimental work was to provide a foundation for numerical simulation of CaCO3 powder compaction at higher pressures. Friction measurements of the powder were also conducted. From the experimental investigations, density dependent material parameters were found. An elasto-plastic Cap model was developed for ultra high-pressure powder pressing. To improve the material model, density dependent constitutive parameters were included. The model was implemented as a user-defined material subroutine in a nonlinear finite element program. The model was validated against pressure measurements using phase transitions of Bismuth. The measurements were conducted in a Bridgman anvil apparatus. The simulations showed that thin discs with small radial extrusion generate a plateau at a low-pressure level, while thick discs with large radial extrusion generate a pressure peak at a high-pressure level. The results showed that FE-results can be used to engineer pressure peaks needed to seal HPHT-systems. For compressible gaskets, it was found that diametral support increases the phase transformation load. Higher initial density of the powder compact and diametral support generate higher pressure per unit thickness. The results from the validation using pressure measurements showed that the simulation model was indeed capable of reproducing load–thickness curves and pressure profiles, up to 9 GPa, close to the experimental curves.

  • 5.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Byheden, Åke
    Luleå tekniska universitet.
    A wear investigation in the FZG spur gear rig with particular matter contaminated oils2002Inngår i: Lubricants, materials and lubrication engineering : January 15 - 17, 2002: 13th International Colloquium Tribology. Technische Akademie Esslingen / [ed] Wilfried Bartz, Ostfildern: Techn. Akad. Esslingen , 2002, s. 1139-1143Konferansepaper (Fagfellevurdert)
  • 6.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    High-pressure compaction modelling of calcite (CaCO3) powder compact2011Inngår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 206, nr 3, s. 259-268Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Numerical simulation of manufacturing processes with working conditions at high pressure (above 1 GPa) requires constitutive data of the powder for the whole range of pressure and density. Most of the test apparatuses commonly used to obtain such data is only working in the lower pressure regions. Because of the absence of high-pressure data, many parameters have to be guessed or extrapolated. A material used in high-pressure applications is Calcite (CaCO3). The material can be used as an insulator in high-pressure capsules it is also a common material in the earth core. An apparatus often used to generate high pressure during compaction is the Bridgman anvil apparatus. In this work experimental tests with a Bridgman anvil set-up using Calcite powder discs with different thicknesses were done. A nonlinear elastic-plastic cap model was developed to model the behaviour of powder material from low pressure and loose state to high pressure and solid state. The constitutive model was implemented in a finite element code. The constitutive data were identified by optimization of experimental data. Validation was done by numerically reproduce the mechanical behaviour of uni-axially pressing Calcite to different pressure (up to 5 GPa) including unloading. The load-displacement curves, density distribution and the surface displacement were measured and compared to the finite element results. The results of the compaction simulations agree reasonably well with the experimental results.

  • 7. Berg, Sven
    et al.
    Jonsén, Pär
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Experimental characterisation of CaCO3 powder mix for high-pressure compaction modelling2010Inngår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 203, nr 2, s. 198-205Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The mechanical properties of powders at high pressures are difficult to measure and therefore such data are rarely reported in open literature. Available test equipment mainly operates in the low-pressure region, 0-200 MPa. Calcite (CaCO3) is a mineral suitable for high-pressure processes, e.g. sintering of diamond compacts. It is also a very common material in the earth core and therefore of interest for geoscientists. In order to model the processes in the high-pressure region (above 1 GPa), knowledge of the mechanical properties of the powder in the entire pressure range is needed. Experimental studies have been conducted to investigate the pressure-density relationship of a CaCO3 powder and also to correlate the relative density to elastic and strength properties using experimental results. Further, a methodology has been introduced to provide a foundation for an elastic-plastic constitutive model. The mechanical behaviour of a CaCO3 powder mix has been investigated using the Brazilian disc test, uniaxial compression testing and closed die experiments. The experiments showed increasing elastic modulus and strength with increasing density. An empirical expression of the dependence of the bulk modulus on density has also been introduced.

  • 8.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Experimental characterization of CaCO3powder for use in compressible gaskets up to ultra-high pressure2012Inngår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 215-216, s. 124-131Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The purpose of this study was to investigate the compaction properties for a CaCO3 powder mix up to ultra-high pressure (10GPa) and how these properties affect the gasket behaviour. Different parameters of the powder are investigated, i.e. initial density and internal moisture. A set-up, supporting the outer diameter of the compact, commonly used for gaskets in the belt apparatus was also investigated. The experimental results are in terms of pressure instrumentation in the Bridgman anvil apparatus together with load–displacement curves of the powder compacts. The instrumentation is done so that it can be used to calibrate constitutive models.

  • 9.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    High pressure characterization and modelling of CaCO3 powder mix in the Bridgman anvil apparatus2012Inngår i: High Pressure Research, ISSN 0895-7959, E-ISSN 1477-2299, Vol. 32, nr 4, s. 490-508Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    For investigating high pressure sintering processes, numerical models can be used. This will demand material models which give realistic mechanical response throughout the whole parameter space of the actual process. As the pressures become higher, the material density approaches its full theoretical value and the elastic part of the material properties becomes increasingly important. In this investigation, Poisson's ratio was determined using ultrasonic pulse-echo measurements. A new elastic model and an improved plasticity model were implemented into a user-defined material subroutine in a finite element (FE) code. To experimentally investigate the load displacement response and pressure distribution in powder compacts during pressing, a pressure instrumented Bridgman anvil apparatus was used. Validation of the FE model was conducted against experimental data from pressing experiments using two different start densities. The results show that the simulation model is indeed capable of reproducing load–thickness curves and pressure profiles reasonable close to the experimental curves.

  • 10.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jungmar, Ulf
    Bodycote Materials Testing AB, Linköping.
    Lundberg, Jan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Vähäoja, Pekka
    Department of Mechanical Engineering, University of Oulu.
    Investigation of the measurement precision of oil analysis instruments, using fully formulated oils: Part 1: Spectroscopic instruments2011Inngår i: Industrial Lubrication and Tribology, ISSN 0036-8792, E-ISSN 1758-5775, Vol. 63, nr 6, s. 404-411Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Purpose - The aim of this study is to determine the variation of the different oil analysis instruments in terms of standard deviation and CV-values, when measuring samples of fully formulated hydraulic and gear oils taken from working systems. Design/methodology/approach - In this investigation, two different spectrometric techniques, inductively coupled plasma-optical emission spectrometers (ICP-OES) and rotating disk electrode-optical emission spectrometers (RDE-OES), have been studied to determine the instruments' precision of measurement and ability to measure the absolute level of contamination. The study was based on a series of measurements using artificial contamination mixed with oil. Findings - The ICP has better precision of measurement of the two instruments, but cannot predict the absolute values of contamination when oil samples are only treated by organic solvent dilution if the samples include large or dense particles. It is therefore not too good, with the sample pre-treatment method used, at detecting wear processes that produce dense/large particles, such as pitting failure. For instance, microwave-assisted acid digestion could be used for sample pre-treating to obtain accurate results in that case. It should, however, be able to detect wear mechanisms that produce small particles such as abrasive wear in any case. The ICP has a repeatability value of r=3 percent and a reproducibility value of R=12 percent for contamination levels of between 50 and 400 ppm and r=0.6 and R=2 ppm, respectively, at values below 50 ppm. The RDE cannot predict the absolute value of contamination if this includes large or dense particles if proper sample pre-treatment is not used. It is therefore not good at detecting wear mechanisms that produces dense/large particles (if the oil samples are not pre-treated properly) such as pitting but should be able to detect abrasive wear and similar processes that produce small particles in any case. The RDE's precision of measurement is not as good as the ICP, with a reproducibility variation of R=r=25 percent for contamination levels between 20 and 500 ppm and R=r=6 ppm for contamination level below 20 ppm. Research limitations/implications - Only the effects from lubricating oils are studied. Practical implications - This study will significantly increase the industrial knowledge concerning measurement precision in particle contamination measurement systems. Originality/value - No similar study is found

  • 11.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jungmar, Ulf
    Bodycote Materials Testing AB, Linköping.
    Lundberg, Jan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Vähäoja, Pekka
    Department of Mechanical Engineering, University of Oulu.
    Investigation of the measurement precision of oil analysis instruments, using fully formulated oils: Part 2: Contamination-measuring instruments2011Inngår i: Industrial Lubrication and Tribology, ISSN 0036-8792, E-ISSN 1758-5775, Vol. 63, nr 6, s. 412-419Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Purpose - The aim of this study is to determine the variation of the different oil analysis instruments in terms of standard deviation and CV-values, when measuring samples of fully formulated hydraulic and gear oils taken from working systems. Design/methodology/approach - In this investigation two different spectrometric techniques, ICP-OES and RDE-OES, have been studied to determine the instruments' precision of measurement and ability to measure the absolute level of contamination. Findings - The ICP has better precision of measurement of the two instruments, but cannot predict the absolute values of contamination when oil samples are only treated by organic solvent dilution if the samples include large or dense particles. It is therefore not too good, with the sample pre-treatment method used, at detecting wear processes that produce dense/large particles, such as pitting failure. For instance, microwave-assisted acid digestion could be used for sample pre-treating to obtain accurate results in that case. It should, however, be able to detect wear mechanisms that produce small particles such as abrasive wear in any case: the ICP has a repeatability value of ITr/IT=3 per cent and a reproducibility value of ITR/IT=12 per cent for contamination levels of between 50-400 PPM and ITr/IT=0.6 PPM and ITR/IT=2 PPM, respectively, at values below 50 PPM; the RDE cannot predict the absolute value of contamination if this includes large or dense particles if proper sample pre-treatment is not used. It is therefore not good at detecting wear mechanisms that produce dense/large particles (if the oil samples are not pre-treated properly) such as pitting but should be able to detect abrasive wear and similar processes that produce small particles in any case; the RDE's precision of measurement is not as good as the ICP, with a reproducibility variation of ITR/IT=ITr/IT=25 per cent for contamination levels between 20-500 PPM and ITR/IT=ITr/IT=6 PPM for contamination level below 20 PPM. Research limitations/implications - Measuring only on fully formulated oils from hydraulic and gear systems. Practical implications - The study will be of significant support regarding industrial interpretation of measurement results from the most common oil particle measurement methods. Originality/value - No other similar studies are known

  • 12.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lundberg, Jan
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Rheological properties of contaminated oil2000Inngår i: Proceedings of the International Tribology Conference: ITC Nagasaki 2000 ; October 29 - November 2, 2000, Tokyo: Japan Society of Tribologists , 2000, s. 1239-1243Konferansepaper (Fagfellevurdert)
  • 13.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Marklund, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Jonsén, Pär
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Frictional behaviour of CaCO3 powder compacts2012Inngår i: Powder Technology, ISSN 0032-5910, E-ISSN 1873-328X, Vol. 228, s. 429-434Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During powder compaction processes friction has an influence on the final shape and properties of components. It is therefore important to understand how the friction influences the compaction process. Since detailed friction measurements of the powder compact-tool interface are rare, simulation models of the powder compaction process often involve a more accurate description of the frictional behaviour. This limits the accuracy of the simulated results. More accurate numerical models can give improved results, especially in regards to the evolution of density and its distribution within the powder compacts.This study is as a step towards more advanced friction models for powder compaction simulations. A universal tribometer has been used to investigate the frictional behaviour of contact interfaces between a carbide counter surface and CaCO3 powder compacts with different densities. Both static and dynamic frictional properties were measured in a variety of conditions to build a fundamental foundation for friction modelling in powder compaction simulations.The results show that increasing the powder compact density decreases the dynamic friction coefficient but that the static friction coefficient remains fairly constant. The measured friction coefficient can be used to improve the simulation of a powder compact process. Also investigated is the change in friction coefficient that occurs in the compaction process when the surfaces are worn such that loose powder appears in the interface between the tool and the powder compact. This behaviour is important to take into account to accurately describe the compaction process.

  • 14.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Vaziri, Mojgan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Crack influence on load-bearing capacity of glued laminated timber using extended finite element modelling2015Inngår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 10, nr 4, s. 335-343Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Most of the cracks are caused by changes in temperature and relative humidity which lead to shrinkage and swelling of the wood and thereby induce stresses in the structure. How these cracks influence the strength of the wooden structure, especially the shear strength, is not well understood. However, it is reasonable to expect that cracks have an impact on the shear strength as they preferably run along the beams in the direction of grain and bond lines. The purpose of this study was to investigate the load-bearing capacity of cracked glulam beams and to find a model that could predict the failure load of the beams due to the cracks. Three-point bending tests were used on glulam beams of different sizes with pre-manufactured cracks. An orthotropic elastic model and extended finite element method was used to model the behaviour of the cracked beams and to estimate the load-bearing capacity. The conclusions were validated by numerical simulations of the mechanical behaviour of three-point bending of glulam beams with different crack locations. The crack initiation load was recorded as the failure load and compared to the experimental failure load. The results of the compaction simulations agree well with the experimental results

  • 15.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Turesson, Jonas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Björnfot, Anders
    Faculty of Engineering, Department of Manufacturing and Civil Engineering, Norwegian University of Science and Technology, Gjøvik, Norway.
    In-plane Shear Modulus of Cross-laminated Timber by Diagonal Compression Test2019Inngår i: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 14, nr 3, s. 5559-5572Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cross-laminated timber (CLT) is an engineered wood material that is used in the construction industry, e.g., for floors, walls, and beams. In cases where CLT-elements are used as shear walls, the in-plane-stiffness is an important property. For non-edge glued CLT, in-plane shear stiffness is lower than for edge-glued CLT. To evaluate the non-edge glued CLT panel’s in-plane shear modulus, the diagonal compression test and finite element (FE) simulation was used. FE-models with both isotropic and orthotropic material models were used to calculate the shear stiffness. The FE models using pure shear loads were used as a reference to determine the correct value of the shear modulus. To verify the FE simulations, diagonal compression tests were conducted on 30 CLT samples. A calibration formula was derived using the least square method for calculation of shear modulus. The formula gave accurate results. The results showed that FE simulations can reproduce the same shear stiffness as tests of non-edge glued 3-layer and 5-layer CLT panels.

  • 16.
    Berg, Sven
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Turesson, Jonas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Huber, Johannes Albert Josef
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Finite element analysis of bending stiffness for cross-laminated timber with varying board width2019Inngår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 14, nr 6, s. 392-403Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    ross laminated timber (CLT) is a wood panelling building system that is used in construction, e.g. for floors, walls and beams. Because of the increased use of CLT, it is important to have accurate simulation models. CLT systems are simulated with one-dimensional and two-dimensional (2D) methods because they are fast and deliver practical results. However, because non-edge-glued panels cannot be modelled under 2D, these results may differ from more accurate calculations in three dimensions (3D). In this investigation, CLT panels with different width-to-thickness ratios for the boards have been simulated using the finite element method. The size of the CLT-panels was 3.0 m × 3.9 m and they had three and five laminate layers oriented 0°–90°–0° and 0°–90°–0°–90°–0°. The thicknesses of the boards were 33.33, 40.0, and 46.5 mm. The CLT panel deformation was compared by using a distributed out-of-plane load. Results showed that panels with narrow boards were less stiff than wide boards for the four-sided support setup. The results also showed that 2D models underestimate the displacement when compared to 3D models. By adjusting the stiffness factor k88, the 2D model displacement became more comparable to the 3D model.

  • 17.
    Blomqvist, Lars
    et al.
    Linnéuniversitetet.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Chipless machining: challanges in manufacture of laminated veneer products2015Inngår i: Proceedings of the 22nd International Wood Machining Seminar, IWMS 22. / [ed] Roger Hernández; Claudia B. Cáceres, Qubec City: Universite Laval , 2015, s. 155-164Konferansepaper (Fagfellevurdert)
  • 18.
    Blomqvist, Lars
    et al.
    Linnӕus University, Department of Building Technology, Växjö, Sweden. RISE, Research Institute of Sweden.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik. Department of Wood Processing and Biomaterials, Czech University of Life Sciences Prague, Prague, Czech Republic.
    Distortion in laminated veneer products exposed to relative-humidity variations: Experimental studies and finite-element modelling2019Inngår i: BioResources, ISSN 1930-2126, E-ISSN 1930-2126, Vol. 14, nr 2, s. 3768-3779Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A shortcoming of the laminated bending process is that the product may become distorted after moulding. This study focused on the influence of fibre orientation deviation for individual veneers on the distortion of a moulded shell. The distortion of 90 cross-laminated shells of the same geometrical shape, consisting of seven peeled birch veneers, were studied under relative humidity variation. All the veneers were straight-grained in the longitudinal-tangential plane, but to simulate a deviation in fibre orientation, some of the individual veneers were oriented at an angle of 7° relative to the main orientation of the other veneers in the laminate. A finite element model (FEM) was applied to study the possibility of predicting the results of a practical experiment. The study confirms the well-known fact that deviation in fibre orientation influences shape stability. The results also show how the placement of the abnormal veneer influences the degree of distortion. From this basic knowledge, some improvements in the industrial production were suggested. However, the FE model significantly underestimated the results, according to the empirical experiment, and it did not show full coherence. The survey shows the complexity of modelling the behaviour of laminated veneer products under changing climate conditions and that there is a great need to improve the material and process data to achieve accurate simulations. Examples of such parameters that may lead to distortion are density, annual ring orientation in the cross section of the veneer, the orientation of the loose and tight sides of the veneer, and parameters related to the design of the moulding tool.

  • 19.
    Ekevad, Mats
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Finite Element Models for Stress-Laminated Solid Wood Decks2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Stress laminated timber bridge decks consist of planks or glulam timber members that are put together side by side to form plates or solid volumes of wood to be used as bridge decks. The decks may also be used for other purposes than bridge decks. Load-carrying capacities of these decks are very high and friction alone carries load between individual members. Friction is achieved by using prestressed steel rods through the decks that give normal compressive forces between members, see Fig.1. Fig.1. Left: bridge deck in laboratory test situation. Right: FE modelThe load vs. displacement curve for a transversally loaded deck is normally nonlinear even for low load values but especially for high loads due to partial slip between members. FE simulations and laboratory tests for behaviour have been made earlier, see [1], [2], [3]. Two different approaches for FE-simulations have been used, one with an elastic-plastic material model without discrete member modeling and another with discrete member modeling and contact surfaces between members.In the presentation a summary of earlier results are shown and also some recent results due to additional features in the FE models. The additions are possibilities too simulate gaps between members for the elastic-plastic model and results from butt-end modeling with the contact model. Fig. 2 shows an example of a non-linear load vs. displacement curve for a model with butt-end joints in the deck.Fig.2. load vs. displacement curve for a model with butt-end joints in the deck.References[1] Ekevad M.; Jacobsson P.; Forsberg G. (2011). Slip between glulam beams in stress-laminated timber bridges: finite element model and full-scale destructive test. Journal of Bridge Engineering 16:188-196.[2] Ekholm K.; Ekevad M.; Kliger R. (2014). Modelling slip in stress-laminated timber bridges: comparison of two FEM approaches and test values. Journal of Bridge Engineering 19(9) 04014029.[3] Ekevad M.; Jacobsson P.; Kliger R. (2013). Stress-Laminated Timber Bridge Decks: Non-linear Effects in Ultimate and Serviceability Limit States. International Conference on Timber Bridges 2013 (ICTB2013). Arranged by USDA Forest Products Laboratory. Las Vegas, USA, September 30-October 2, 2013.

  • 20.
    Ekevad, Mats
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Finite Element Simulation of Nailed Glulam Timber Joints2015Inngår i: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 11, nr 4, s. 318-323Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    hispaper presents a finite element modeling method for a certain type of nailed jointbetween glulam beams. The joint in question is a traditional arrangement of a horizontal beam anda vertical pillar but herethere is also a nailed steel plate inserted on the two sides in order to strengthen the joint.Experimental results and a comparisonsof simulated and experimental results aremade. The model includes the elastic and plastic orthotropic behaviour of wood and the elastic and plastic behaviour of nails.The nail joint between the steel plate and the wood is modelled as an elastic-plastic surface to surface connection with elastic-plastic properties. Also the reinforcing effect of nails in the nail-affectedvolume of wood is taken into consideration by raising rolling shear yield limitin the affected wood volume.The comparisons showthat the model works well and give results that are comparable to experimental results.

  • 21.
    Ekevad, Mats
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Öhman, Micael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Guo, Xiaolei
    Nanjing Forestry University.
    Potential Yield Increase with Reduced Saw Kerf Deviations when Curve Sawing2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Curve sawing with circular saw blades introduces saw kerf deviations due to the combination of the flat sawblade and the curvature of the saw kerf in log or cant direction. Deviations for a double arbor resaw used for curve sawing, are that the saw kerf becomes wider at top and bottom and that the desired rectangular cross sections of the boards become distorted. The yield loss due to the saw kerf deviation in practice for a sawmill was of interest in this study. Earlier and very approximate guesses and simple estimates have been indicating that the loss of income for a sawmill in Sweden producing 200’ m3 of sawn timber may be about 2 MSEK/year (0.22 Meuro/year). In this study calculations were based on true log data and assumed sawing conditions for a sawmill. A true mixed input log assortment (78458 spruce and pine logs taken into the log yard of a sawmill in northern part of Sweden) was used as basis. Individual curvature of these logs was taken into consideration but the calculation was still approximate because not all facts about sawing patterns, log classes etc. for an actual sawmill were known. Instead one single sawing class was used for the calculation of saw kerf deviation.

     

    Results show that the direct yield loss given the assumed input data was 0.61 %-units. This corresponds roughly to the income loss 0.2 Meuro/year mentioned above. Besides from the yield increase there are other advantages gained if the saw kerf deviation can be reduced.

  • 22.
    Eliasson, Lars
    et al.
    Linneaus University.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Some aspects on the more efficient use of wood in the industrial manufacture of single-fammily timber houses2015Inngår i: Pro Ligno, ISSN 1841-4737, E-ISSN 2069-7430, Vol. 11, nr 4, s. 418-425Artikkel i tidsskrift (Fagfellevurdert)
  • 23.
    Huber, Johannes Albert Josef
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Girhammar, Ulf Arne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Assessment of Connections In Cross-Laminated Timberbuildings Regarding Structural Robustness2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Cross-laminated timber makes timber buildings with an increasing number of storeys achievable. Withmore storeys, structural robustness needs more attention to make a building survive unforeseen events (e.g. accidents,terrorism) and save lives. For steel and concrete buildings, design methods for robustness focus on connection details.The assessment of joints in cross-laminated timber buildings regarding robustness is rather limited in the literature. Theobjective of this paper is to conduct an initial assessment of the connectors after the removal of a wall in a platformcross-laminated timber building. We used the finite element method and the component method for the analysis of acase building. The results indicate that the wall-to-wall and the floor-to-floor connectors may fail at low deflectionlevels leading to high shear loads in the floor panel above the removed wall, which might induce cracking. The removalanalysis was only partially completed, but we identified an indication of the deformation behaviour of the case building.Testing and refined modelling of the connections is needed in the future to verify the results. This study may facilitatefuture investigations regarding robustness of multi-storey cross-laminated timber buildings.

  • 24.
    Huber, Johannes Albert Josef
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Girhammar, Ulf Arne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    A Review of Structural Robustness with Focus on Timber Buildings2018Inngår i: 40th IABSE Symposium: Tomorrow’s Megastructures, International Association for Bridge and Structural Engineering (IABSE) , 2018, artikkel-id S32-17Konferansepaper (Fagfellevurdert)
    Abstract [en]

    With an increasing number of storeys, timber buildings require closer attention to structuralrobustness. If a building can survive unforeseen events (e.g. accidents, terrorism), lives can be saved.The literature appears to be rather limited concerning robustness of timber buildings. This paperaims to give a brief review on robustness in general and design guidelines for timber in specific. Theresults indicate that connection design is a key aspect for robustness. Like in seismic design, by usingthe ductile capacity of connectors, the brittleness of timber can be controlled. For light timber-framebuildings, more guidelines exist than for posts and beams and cross-laminated timber, which bothseem to be similar to steel frames and precast concrete respectively regarding robustness.

  • 25.
    Huber, Johannes Albert Josef
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Girhammar, Ulf Arne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Simulation of Alternative Load Paths After a Wall Removal in a Platform-Framed Cross-Laminated Timber Building2019Inngår i: CompWood 2019 Book of Abstracts / [ed] Tomas K. Bader, Josef Füssl, Anders Olsson, 2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    An increasing number of multi-storey timber buildings use cross-laminated timber (CLT) for their bearing structure. Platform-framed CLT buildings consist of vertical repetitions of floors resting upon one-storey tall walls, squeezing-in the floor panels between the walls. Tall buildings need to be structurally robust because many lives would be at stake in case of a disproportionate collapse. Robustness is the ability of a system to survive the loss of components. For collapse resistance, it poses the last line of defence, after an unforeseen exposure (e.g. accident, terrorism) has already occurred and after the exposed components could not resist failure. A robust building offers alternative load paths (ALPs) which come into action when a part of the bearing structure has been removed [1].

    Many alternative load path analyses (ALPA) have been conducted for tall concrete and steel buildings using the finite element method (FEM), but for timber, ALPA are still scarce. ALPs depend on the behaviour of the connections after a loss [1]. Studies on timber so far have accounted for connections in a simplified manner by lumping their aggregate behaviour into single points. Our goal is to elicit the ALPs after a wall removal in a platform-framed CLT building, study their development and quantify their capacity, to determine whether they can prevent a collapse.

    We investigated a corner bay of an 8-storey platform-framed CLT building (see Figure 1) and removed a wall at the bottom storey. We studied the ALPs of each storey by pushing down the walls above the gap in a non-linear quasi-static analysis in the FE software Abaqus. We accounted for contact and friction, considered plastic timber crushing, and accounted for brittle cracking in the panels. We modelled single fasteners with connector elements which simulated the elastic, plastic, damage and rupture behaviour. We recorded the force-displacement curves, i.e. pushdown curves, for each storey and used them to conduct a dynamic analysis of the entire bay in a simplified model, as suggested by [2].

    The results show that the structure could engage the following ALPs after a wall removal: I) arching action in the outer floor panels, II) arching action of the walls, III) quasi-catenary action in the floor panels, and IV) hanging action from the roof panels. The ALPs were limited by various parameters, but they sufficed to resist a collapse of the bay. We observed that the inter-storey stiffness influenced the load-sharing among storeys, which affected the structural robustness. In the compressed connections, friction, and not the fasteners, transferred most of the horizontal loads. Future research should test the squeezed-in platform joint experimentally, to quantify its capacity for transverse shear loads. We also advise to assess the inter-storey stiffness to estimate the capacity for load-sharing among storeys.

  • 26.
    Huber, Johannes Albert Josef
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Girhammar, Ulf Arne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Structural robustness and timber buildings: a review2019Inngår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 14, nr 2, s. 107-128Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Timber buildings are increasing in their dimensions. Structural robustness is imperative for all buildings and specifically important for tall buildings. Lives can be saved if disproportionate collapse can be avoided after a catastrophic event (e.g. accident, terrorism). The literature about robustness is comprehensive concerning concrete and steel buildings, but is rather limited regarding timber. This paper reviews robustness in general and robustness of timber buildings in particular. Robustness is an intrinsic structural property, enhancing global tolerance to local failures, regardless of the cause. A deterministic approach to assess robustness is to remove certain load-bearing elements from the structure and compare the consequences to given limits. Design methods for robustness may be direct by assessing effects of local failure, or indirect by following guidelines. For robust timber buildings, the connections are the key aspects. Usually, metal connectors may provide the required joint ductility. For robust light timber-frame construction, rim beams may be designed. For timber posts and beams and cross laminated timber, guidance regarding robustness is scarce, but in some aspects they seem to be similar to steel frames and precast concrete. Future research should assess the capacity of connections, and evaluate the adequacy of seismic connectors for robust timber buildings.

  • 27.
    Huber, Johannes Albert Josef
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Girhammar, Ulf Arne
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Structural Robustness of Timber Buildings2018Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The number of storeys in timber buildings are increasing. With more storeys, structural robustness needsmore attention, to make a building survive unforeseen events (e.g. accidents, terrorism) and save lives. The state of theart regarding robustness of concrete and steel buildings seems to be rather refined, but for timber buildings, theliterature appears to be quite limited. This study aims to review the design methods for robustness of timber buildings.First, the terminology and definitions are introduced. Then, the state of the art for design methods for robustness ingeneral are presented. Finally, the design methods for timber buildings are discussed and compared to those from otherbuilding materials. The results indicate that the guidelines for light timber-frame buildings are more refined than thosefor post and beam and cross-laminated timber buildings. Regarding robustness, the latter two construction types exhibitcertain similarities to steel frames and precast concrete buildings respectively. For timber, ductile connections can beused to avoid brittle timber failure after local damages, which resembles the approach of seismic design. Future researchin robustness should focus on the connection details in multi-storey timber buildings.

  • 28.
    Jonsén, Pär
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Häggblad, Hans-Åke
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Modelling ultra high pressure compaction of powder2012Inngår i: Technische Mechanik, ISSN 0232-3869, Vol. 32, nr 2-5, s. 287-302Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The use of high pressure high temperature (HPHT) equipment varies; in mineral physics research the equipment is used for investigation of the earth’s interior and in industry it is used for commercially produced synthetic diamonds and other polycrystalline products. The common denominator for almost all high pressure systems is to use capsules where a powder material encloses the core material. Numerical analysis of the manufacturing processes with working conditions which reaches ultra high pressure (above 10 GPa) requires a constitutive model which can handle the specific behaviours of the powder from a low density to solid state. Calcium carbonate (CaCO3) is a mineral that can be used in high pressure processes and is very common in the earth core. A constitutive model for calcium carbonate applied to high pressure compaction is presented. The plastic response of powder is non-linear and described in a rate-independent cap plasticity model. The cap model has been developed to capture the behaviour of minerals in high pressure applications. The yield function consists of a failure envelope fitted to a strain-hardening cap. Experimental tests with a Bridgman anvil set-up using calcium carbonate powder discs are performed. Numerical analysis using the finite element method is done to virtually reproduce the experiments Results from the analysis are compared to measured experimental results. The numerical analyses agree reasonably well with the experimental results.

  • 29.
    Kováciková, Janka
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ivankova, Olga
    Slovak University of Technology in Bratislava.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Finite element analysis of timber beams with flaws2016Inngår i: ECCOMAS Congress 2016: Proceedings of the 7th European Congress on Computational Methods in Applied Sciences and Engineering / [ed] M. Papadrakakis; V. Papadopoulos; G. Stefanou; V. Plevris, Athens: National Technical University of Athens , 2016, Vol. 4, s. 8606-8611Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The work was focused on modelling of cracks and simulations of their propagationin timber beams. The aim was to find out the influence of flaws on load-carrying capacity. Inbeam design and beam inspection, it is necessary to determine the load-carrying capacity of abeam with flaws. There is not much information in literature about the influence of flaws onbending and shear strength of timber beams. Standards for fracture mechanics design approachfor timber structures are not easily available.The results from simulations of loaded timber beams with flaws are discussed in this paper.Two different types of timber beams were analysed. First type was a sawn timber beam andfor that four different models were analysed: first model was a beam without flaw; secondmodel was a beam with a straight central flaw; next was a beam with an oblique crack andfourth beam had a round hole in the middle of the span. Second type of beam was a gluedlaminated timber beam (glulam). For this type, five different models were analysed. First fourvariants were the same as for the solid timber beam and the fifth variant had an initial crackalong a glue line. We analysed these types of flaws, since they are the most common flaws inwood.Simulations were conducted in ABAQUS. Material properties of wood used in the modelswere retrieved from standards; C24 for solid timber and GL24c for glulam timber beams.Dimensions of beams were the same for all variants and beams were considered simply supported.For an analysis of crack propagation, linear elastic fracture mechanics was considered.Modelling fracture was conducted using the extended finite element method (XFEM).The energy approach was used for the analysis of crack propagation. Comparing results forsolid and glulam beams with and without cracks gave us an overview how different flaws influenceload-carrying capacity of the beams and under which loading failure occurs. Simulatingtimber beams is more complicated compering to steel or plastic. By understanding how tosimulate flaws in wood material it is possible to obtain reliable results with finite elementanalysis

  • 30. Lundberg, Jan
    et al.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Grease-lubrication of roller bearings in railway waggons. Part 2: Laboratory tests and selection of proper test methods2000Inngår i: Industrial Lubrication and Tribology, ISSN 0036-8792, E-ISSN 1758-5775, Vol. 52, nr 2, s. 76-86Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    New, undestroyed greases of the same brands as those used in a field test, described in Part 1, were examined using conventional methods, such as the SKF V2F test, the roll stability test (ASTM D-1831), the Grease Worker (ASTM D-217), the torque test (ASTM 1478-91), bleeding measurements ( IP 121), yield stress measurements, the 4-ball test (ASTM D 2266-86), base oil viscosity measurements, thickener content and the cone penetration test (ASTM D217-88). The greases have also been tested with several new test methods developed at the University. A specification for relevant testing methods was drawn up and the connections between the tested parameters were investigated. It was found that the mechanical stability could be predicted with a combination of ASTM D-1831 and the limiting shear stress coefficient ?. This coefficient is capable of predicting wear. It was found that the bearing temperature could be predicted by using the base oil viscosity.

  • 31. Lundberg, Jan
    et al.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Handbook for grease applications2000Inngår i: Industrial Lubrication and Tribology, ISSN 0036-8792, E-ISSN 1758-5775, Vol. 52, nr 5, s. 221-232Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The process of finding the ultimate grease is described in this report using an example from railway applications. This example includes steps such as a requirement list, field tests, laboratory tests and an evaluation method. The example deals with the problems discovered in a field test performed to determine the best grease for tapered roller bearings in railway wagon wheels and to increase the knowledge of grease lubrication. Seven different fully formulated commercial greases were examined in the wheel bearings of one ore wagon, used for transporting ore commercially by railway from the Kiruna Mine in northern Sweden to Narvik in northern Norway for shipping to foreign markets. The steps performed in this study are recommended in all problems associated.

  • 32.
    Nilsson, Daniel
    et al.
    Hägglunds drives, Mellansel.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Wear and life of roller bearings under low speed and clean environment, a comparison of ME-C: H coated and uncoated rollers2002Inngår i: 10th Nordic Symposium on Tribology: NORDTRIB 2000 : Hotel Foresta and KTH, Stockholm, Sweden, June 9-12, 2002, Stockholm: Kungl. Tekniska Högskolan , 2002, s. 135-Konferansepaper (Annet vitenskapelig)
  • 33. Tuomas, Roger
    et al.
    Almqvist, Torbjörn
    Åhrström, Bert-Olof
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Influence of molecular structure on the lubrication properties of four different esters2000Inngår i: Tribologia, ISSN 0780-2285, Vol. 19, nr 4, s. 3-8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The lack of published data on the chemical structures of lubricants makes it almost impossible to investigate the influence of structure on lubrication properties. In this investigation, the lubricating properties of three esters with known chemical structure have been investigated and compared with a commercial ester. The lubrication properties that were expected to be dependent on chemical structure such as film thickness and traction, viscosity and friction coefficients were compared by experiment. To measure the film thickness a Ball and Disc Apparatus was used, the traction coefficient was measured in a Jumping Ball Apparatus, the viscosity in a rotational cylindrical viscometer and the friction coefficient in a reciprocating friction and wear test apparatus. The results showed that molecular length has a significant influence on lubrication properties, with longer molecules giving the highest viscosity and greatest film thickness. The length of the molecule did not influence the coefficients of friction, but the traction coefficient, Υ, decreased with increasing molecular length.

  • 34.
    Turesson, Jonas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Impact of board width on in-plane shear stiffness of cross-laminated timber2019Inngår i: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 196, artikkel-id 109249Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Board width-to-thickness ratios in non-edge-glued cross laminated timber (CLT) panels influence the in-plane shear stiffness of the panel. The objective is to show the impact of board width-to-thickness ratios for 3- and 5-layer CLT panels. Shear stiffnesses were calculated using finite element analysis and are shown as reduction factors relative to the shear stiffnesses of edge-glued CLT panels. Board width-to-thickness ratios were independently varied for outer and inner layers. Results show that the reduction factor lies in the interval of 0.6 to 0.9 for most width-to-thickness ratios. Results show also that using boards with low width-to-thickness ratios give low reduction factors. The calculated result differed by 2.9% compared to existing experimental data.

  • 35.
    Turesson, Jonas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Björnfot, Anders
    Department of Manufacturing and Civil Engineering, Faculty of EngineeringNorwegian University of Science and TechnologyGjøvikNorway.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Tomasi, Roberto
    Faculty of Science and Technology, Division of Buildings, Architecture, and Environmental EngineeringNorwegian University of Life SciencesÅsNorway.
    Picture frame and diagonal compression testing of cross-laminated timber2019Inngår i: Materials and Structures, ISSN 1359-5997, E-ISSN 1871-6873, Vol. 52, nr 4, artikkel-id 66Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Currently, no appropriate standard exists that describes how to determine the in-plane shear stiffness for cross-laminated timber (CLT) panels, meaning that, there is a lack of appropriate and reliable test methods. In this paper, two gross shear test methods are evaluated: a picture frame test and a diagonal compression test, which are intended to measure the shear stiffness of a whole CLT panel. This evaluation aimed to compare the shear modulus, the amount of compression/tension in the diagonal directions of the panels and the deformations of both sides of the panels. The picture frame test and diagonal compression test provides a bi- and uniaxial pre-stress, respectively. A total of 30 non-edge glued CLT panels were tested, 17 3-layer and 13 5-layer panels. The shear modulus for the 3- and 5-layer non-edge-glued panels were measured as 418 and 466 MPa, respectively, in the picture frame test. In the diagonal compression test, the shear modulus was measured to substantially higher values of 530 and 626 MPa for the 3- and 5-layer panels, respectively. In the picture frame test, panels were equally stretched along one of the diagonals as they were compressed along the other diagonal, which was not the case for panels in the diagonal compression test. The test results also showed that measuring only one side incurs a risk of over- or under-estimating the in-plane shear modulus. Compared with results from the literature, the picture frame test seems to be a more reliable test method than the diagonal compression test.

  • 36.
    Turesson, Jonas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Ekevad, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Comparison of Cross- and Stress-Laminated Timber Bridge Decks2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Simply supported bridge decks made of cross-laminated timber (CLT) and stress-laminated timber (SLT) are compared. The decks have a constant axle load and varying span and thickness. CLT in the form of a plate is built up from an uneven number of layers of boards with crosswise varying fibre directions. SLT is built up from glulam beams with the same fibre direction placed side by side to form a plate. Both CLT and SLT have homogenised mechanical and physical properties and can be produced as large elements. This study was conducted by comparing results from finite element simulations of bridge decks made up from SLT and CLT for various bridge spans. The ratio of timber volume needed to fulfil deflection limits for CLT and SLT increased as the bridge span increased. The ratio was 1.3 for 24 m span and width 3.2 m. The transverse displacement curve was flatter for CLT compared to SLT. Longitudinal displacement curves were similar for CLT and SLT.

  • 37.
    Vaziri, Mojgan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Three-dimensional finite element modelling of heat transfer for linear friction welding of Scots pine2014Inngår i: Final Cost Action FP0904 Conference: “Recent Advances in the Field of TH and THM Wood Treatment” : May 19-21, 2014, Skellefteå, Sweden : book of abstracts / [ed] Mojgan Vaziri; Dick Sandberg, Skellefteå: Luleå tekniska universitet, 2014, s. 45-46Konferansepaper (Fagfellevurdert)
  • 38.
    Vaziri, Mojgan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Gheinani, Iman Tavakoli
    Department of Mechanical Engineering, ENSTIB-LERMAB, University of Lorraine.
    Three-dimensional finite element modelling of heat transfer for linear friction welding of Scots pine2014Inngår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 9, nr 2, s. 102-109Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Finite element numerical analyses were performed to determine three-dimensional heat flux generated by friction to wood pieces during linear friction welding. The objective was to develop a computational model to explain the thermal behaviour of welded wood material rather than experimental methods, which are usually expensive and time consuming. This model serves as a prediction tool for welding parameters, leading to optimal thermo-mechanical performance of welded joints. The energy produced by the friction welding of small wood specimens of Scots pine (Pinus sylvestris L.) was determined by thermocouples and used as input data in the model. The model is based on anisotropic elasticity and the thermal properties were modelled as isotropic. This numerical simulation gave information on the distribution of the temperature in the welding interface during the entire welding process. A good agreement between the simulation and experimental results showed the appropriateness of the model for planning welded wood manufacture and prediction of thermal behaviour of wood during other mechanically induced vibration processes. The specimens presented in this model required a heat flux of 11 kW/m2 to achieve a satisfactory welding joint

  • 39.
    Vaziri, Mojgan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknologi.
    Gheinani, Iman Tavakoli
    ENSTIB-LERMAB, University of Lorraine.
    Wood modification through mechanically induced wood fusion welding: 3-D finite element modelling of heat transfer.2014Inngår i: The seventh European Conference on Wood Modification (ECWM7: Book of Abstracts / [ed] Lina Nunes; Dennis Jones; Callum Hill; Holger Militz, Lissabon, 2014, s. 43-44Konferansepaper (Fagfellevurdert)
  • 40.
    Vaziri, Mojgan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Plessis, Anton du
    University of Stellenbosch.
    Sandberg, Dick
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Berg, Sven
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Träteknik.
    Nano X-ray tomography analysis of the cell-wall density of welded beech joints.2015Inngår i: Wood Material Science & Engineering, ISSN 1748-0272, E-ISSN 1748-0280, Vol. 10, nr 4, s. 368-372Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper reports the results of a novel approach using nano X-ray computed tomography (CT) for the non-invasive determination of the weld-line density profile of welded wood joints. As a case study, wood samples with a dimension of 2 mm × 2 mm × 20 mm were cut from a board of welded beech (Fagus sylvatica L.). The spatial resolution of the X-ray scan was 500 nm. Densitometry results showed that welding was accompanied by a considerable increase in the bulk density and a decrease in the cell-wall density at the weld-line. The cell-wall density in the weld-line was almost 33% less than that of the unaffected wood. As an additional application of nano computed tomography, the 3D imaging also revealed details of the internal structure of the welded sample. This study showed that nano-CT is a powerful tool for the descriptive and quantitative study of welded wood

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