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  • 3401.
    Zachén, Esbjörn
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Extraction of tool reaction forces using LS-DYNA and its use in Autoform sheet metal forming simulation2019Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    In product development there is still potential to decrease lead times with faster and more accurate simulations. The objective of this thesis was to study whether Finite Element (FE) simulations using explicit LS-DYNA to extract reaction forces from sheet metal forming tools during forming, could be used to improve existing FE models in sheet metal forming software AutoForm.To begin with, the solid CAD-model of the stamping dies were meshed with tetrahedral elements in CATIA and imported into LS-DYNA. In combination with sheet mesh and milling surface meshes from AutoForm, an explicit model was realized. Contacts between sheet mesh and milling surface meshes used the so-called sheet forming contact. The resulting reaction forces were extracted and used in a simulation using the AutoForm software. Resulting simulation was compared to a scan of the physical sheet metal after forming.The direct transfer of reaction forces from LS-DYNA to AutoForm did however not result in the same pressure distribution in AutoForm. The AutoForm simulations using results from LS-DYNA were slightly worse than standard AutoForm simulations.Further work is needed to try and perhaps implement an implicit solution after an initial explicit solution.

  • 3402.
    Zakrisson, Björn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Numerical and experimental studies of blast loading2010Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In the past decade, there has been an increasing demand from governments for high level protections for military vehicles against explosives. However, designing and validation of protection is a time consuming and expensive process, where previous experience plays an important role. Development time and weight are the driving factors, where the weight influences vehicle performance. Numerical simulations are used as a tool in the design process, in order to reduce development time and optimise the protection. The explosive load acting on a structure is sometimes described with analytical functions, with limitations to shape and type of the explosive, confinement conditions etc. An alternative way to describe the blast load is to use numerical simulations based on continuum mechanics. The blast load is determined by modelling the actual type and shape of the explosive in air or sand, where the explosive force transfers to the structure of interest. However, accuracy of the solution must be considered, were methods and models should be validated against reliable experimental data. Within this work, tests with explosive placed in air, sand or a steel pot has been performed. For all tests, the dynamic and residual deformation of steel plates was measured, while the impulse transfer was measured for some tests. This thesis focuses on continuum based numerical simulations for describing the blast load, with validation against data from the experiments. The main conclusion of this work is that numerical simulations of air blast loading in the near-field can be described with sufficient accuracy.

  • 3403.
    Zakrisson, Björn
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Numerical simulations of blast loaded steel plates for improved vehicle protection2013Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In the past decade, there has been an increasing demand from governments for high level protections for military vehicles against explosives. However, the design and validation of protection is a time consuming and expensive process, where previous experience plays an important role. Development time and weight are the driving factors, where the weight influences vehicle performance. Numerical simulations are used as a tool in the design process, in order to reduce development time and successively improve the protection. The explosive load acting on a structure is sometimes described with analytical functions, with limitations to shape and type of the explosive, confinement conditions etc. An alternative way to describe the blast load is to use numerical simulations based on continuum mechanics. The blast load is determined by modelling the actual type and shape of the explosive in air or soil, where the explosive force transfers to the structure of interest. However, accuracy of the solution must be considered, where methods and models should be validated against experimental data. Within this work, tests with explosive placed in air, soil or a steel pot have been performed, where the blast load acts on steel target plates resulting in large deformations up to fracture. For the non-fractured target plates, the maximum dynamic and residual deformations of steel plates were measured, while the impulse transfer was measured in some tests. This thesis focuses on continuum based numerical simulations for describing the blast load, with validation against data from the experiments. The numerical and experimental results regarding structural deformation of blast loaded steel plates correlates relatively well against each other. Further, simulations regarding fracture of blast loaded steel plates show conservative results compared to experimental observations. However, more work needs to be undertaken regarding numerical methods to predict fracture on blast loaded structures. The main conclusion of this work is that numerical simulations of blast loading on steel plates, leading to large deformations up to fracture, can be described with sufficient accuracy for design purposes.

  • 3404.
    Zakrisson, Björn
    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.
    Modelling and simulation of explosions in sand2011Konferansepaper (Annet vitenskapelig)
  • 3405.
    Zakrisson, Björn
    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.
    Modelling and simulation of explosions in soil interacting with deformable structures2012Inngår i: Central European Journal of Engineering, ISSN 1896-1541, E-ISSN 2081-9927, Vol. 2, nr 4, s. 532-550Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A detonating explosive interacting with a deformable structure is a highly transient and non-linear event. In field blast trials of military vehicles, a standard procedure is often followed in order to reduce the uncertainties and increase the quality of the test. If the explosive is buried in the ground, the state of the soil must meet specific demands. In the present work, laboratory experiments have been performed to characterize the behaviour of a soil material. Soil may be considered a three-phase medium, consisting of solid grains, water and air. Variations between the amounts of these phases affect the mechanical properties of the soil. The experimental outcome has formed input data to represent the soil behaviour included in a three-phase elastic-plastic cap model. This unified constitutive model for soil has been used for numerical simulations representing field blast trials, where the explosive load is interacting with a deformable structure. The blast trials included explosive buried at different depths in wet or dry sand. A dependence of the soil initial conditions can be shown, both in the past field trials along with the numerical simulations. Even though some deviations exist, the simulations showed in general acceptable agreement with the experimental results.

  • 3406.
    Zakrisson, Björn
    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.
    Wikman, Bengt
    Numerical simulations of blast loads and structural deformation from near-field explosions in air2011Inngår i: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 38, nr 7, s. 597-612Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Numerical simulations of air blast loading in the near-field acting on deformable steel plates have been performed and compared to experiments. Two types of air blast setups have been used, cylindrical explosive placed either in free air or in a steel pot. A numerical finite element convergence study of the discretisation sensitivity for the gas dynamics has been performed, with use of mapping results from 2D to 3D in an Eulerian reference frame. The result from the convergence study served as a foundation for development of the simulation models. Considering both air blast setups, the numerical results under predicted the measured plate deformations with 9.4–11.1%. Regarding the impulse transfer, the corresponding under prediction was only 1.0–1.6%. An influence of the friction can be shown, both in experiments and the simulations, although other uncertainties are involved as well. A simplified blast model based on empirical blast loading data representing spherical and hemispherical explosive shapes has been tested as an alternative to the Eulerian model. The result for the simplified blast model deviates largely compared to the experiments and the Eulerian model. The CPU time for the simplified blast model is however considerably shorter, and may still be useful in time consuming concept studies. All together, reasonable numerical results using reasonable model sizes can be achieved from near-field explosions in air.

  • 3407.
    Zakrisson, Björn
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Wikman, Bengt
    BAE Systems Hägglunds.
    Johansson, Bo
    FOI, Totalförsvarets Forskningsinstitut.
    Half scale experiments with rig for measuring structural deformation and impulse transfer from land mines2008Inngår i: 24th International Symposium on Ballistics: proceedings, New Orleans, Louisiana, September 22-26, 2008 / [ed] Stephan Bless; James Walker, Lancaster, Penn: DEStech Publications, Inc. , 2008, s. 497-504Konferansepaper (Fagfellevurdert)
  • 3408.
    Zampogna, Giuseppe A.
    et al.
    Univ Genoa, Scuola Politecn, DICCA, Via Montallegro 1, I-16145 Genoa, Italy..
    Lacis, Ugis
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Bagheri, Shervin
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Bottaro, Alessandro
    Univ Genoa, Scuola Politecn, DICCA, Via Montallegro 1, I-16145 Genoa, Italy..
    Modeling waves in fluids flowing over and through poroelastic media2019Inngår i: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 110, s. 148-164Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Multiscale homogenization represents a powerful tool to treat certain fluid-structure interaction problems involving porous, elastic, fibrous media. This is shown here for the case of the interaction between a Newtonian fluid and a poroelastic, microstructured material. Microscopic problems are set up to determine effective tensorial properties (elasticity, permeability, porosity, bulk compliance of the solid skeleton) of the homogenized medium, both in the interior and at its boundary with the fluid domain, and an extensive description is provided of such properties for varying porosity. The macroscopic equations which are derived by homogenization theory employ such effective properties thus permitting the computation of velocities and displacements within the poroelastic mixture for two representative configurations of standing and travelling waves.

  • 3409. Zang, W.
    et al.
    Gudmundson, Peter
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Damage Evolution and Thermoelastic Properties of Composite Laminates1993Inngår i: International journal of damage mechanics, ISSN 1056-7895, E-ISSN 1530-7921, Vol. 2, s. 290-308Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An analytic model for the prediction of the thermoelastic properties of micro cracked composite laminates is presented. The expression for the calculation of en ergy release rates due to growth of micro cracks is also provided. Numerical results are presented that show that the present method, to a very good accuracy, can predict ther moelastic properties of micro cracked laminates at varying crack densities and layup con figurations. In addition, a resistance curve behavior of the energy release rate is observed for both carbon/epoxy and glass/epoxy composite laminates. The reasons for this R-curve behavior are discussed. Criteria that govern the initiation and growth of micro cracks in composite laminates are discussed and compared to experimental data.

  • 3410. Zang, W.L.
    et al.
    Gudmundson, Peter
    KTH, Tidigare Institutioner, Hållfasthetslära.
    An integral equation method based on resultant forces on a piece-wise smooth crack in a finite plate1989Inngår i: Proceedings of the 7th International Conference on Fracture (ICF7), Houston, Texas, 1989, s. 2127-2134Konferansepaper (Fagfellevurdert)
  • 3411.
    Zang, W.L.
    et al.
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Gudmundson, Peter
    KTH, Tidigare Institutioner, Hållfasthetslära.
    Kinked cracks in bonded half-planes modeled by an integral equation method1992Inngår i: International Journal of Fracture, ISSN 0376-9429, E-ISSN 1573-2673, Vol. 54, nr 1, s. 65-78Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Based on the integral equation for resultant forces along a crack, a boundary integral equation method for the solution of kinked cracks in bonded half-planes is presented. The equation only contains a weak logarithmic singularity and is valid for every point along the crack lines. Numerical results are presented to illustrate the efficiency and reliability of the method.

  • 3412. Zang, W.L.
    et al.
    Gudmundson, Peter
    KTH, Tidigare Institutioner, Hållfasthetslära.
    On integral equation methods for kinked cracks1990Konferansepaper (Fagfellevurdert)
  • 3413.
    Zenkert, Dan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Burman, Magnus
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Failure Mode Shifts in Fatigue of Sandwich Beams2009Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Sandwich beams are designed and tested in fatigue, and it is found that for high load and small number of cycles to failure, the beams fail by face tensile fracture. For lower loads, and large number of cycles to failure, the beams fail by core shear.

  • 3414.
    Zenkert, Dan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Burman, Magnus
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Tension, compression and shear fatigue of a closed cell polymer foam2009Inngår i: Composites Science And Technology, ISSN 0266-3538, E-ISSN 1879-1050, s. 785-792Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A closed cell foam of Polymetacrylimide (Rohacell) with three different densities is studied. The foam is tested quasistatically in tension, compression and shear. The tensile properties scale very well with the relative density of the foam, but the compression and shear properties do not. It is believed to be due to cell edge and cell wall buckling being the dominated deformation mechanism in compression and shear for lower densities that does not occur for higher densities. Fatigue testing is then performed in tension, compression and shear. It is seen that for all load cases and densities, the fatigue life can be plotted using Basquin’s law. The results also show that the different failure mechanisms found in the static tests are the same in fatigue. This means that the fatigue life for different load types exhibit different failure mechanisms. This shows not only as a clear difference in the stress levels for fatigue failure, but also on the slope in the fatigue life relation.

  • 3415.
    Zenkert, Dan
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Kazemahvazi, Sohrab
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Burman, Magnus
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Fatigue of foam core sandwich beams under localized loads2011Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Sandwich structures offer significant weight savings in many structural applications due to their high stiffness and bending strength to weight ratios. However, one Achilles heal of sandwich structures is their poor capability to carry localized loads. In this paper we investigate the fatigue behavior of sandwich beams subjected to localised loads.

  • 3416.
    Zetterkvist, Victor
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Industriell teknik.
    Analys av egenfrekvenser och laster för en vertikalaxlad, skruvad Savoniusturbin: slutsatser om möjliga materialval och geometrierför att undvika resonans2017Independent thesis Basic level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [sv]

    At the Division of Electricity at Uppsala university a project isconducted to develop a smaller wind turbine for conditions in theAntarctica. This is a part of a larger, international researchproject in the field of particle physics known as the Ariannaexperiment. The project consists of developing and installing avertical axle wind turbine of screwed Savonius type. A prototypeof this has been manufactured and installed 2016 in Antarctica forinitial testing and measurement.Wind turbines are subjected to complex and varied loads from windand rotation which gives rise to cyclical strain. The rotor bladesare particularly vulnerable, which imposes high material andconstruction requirements to avoid fatigue and failure, whichoften is caused by vibrations and oscillations. Vibrations can becharacterized in terms of the natural frequencies witch in shortmeans that the system, at specific frequencies, tend to oscillatewith increasing amplitude and at worst, resonate if these areexcited. How a complex design will behave by external periodicinterference is complicated to calculate analytically. Naturalfrequencies are therefore most often calculated using FEM-methodsand computer simulations.The aim of this thesis is to study how oscillating forces interactwith the natural frequencies and rotational loads for a specificSavonius wind turbine. How these are influenced by engineering,design and material selection. The goal is to draw conclusionsabout design and possible materials selection to avoid unnecessaryvibrations. Without this analysis, there is a risk of increasedwear and damage to the structure.The project includes such analysis of two different sizes of theSavonius turbine. A small 200x400 mm and a larger 1000x2000 mm.To understand the problem, a preliminary study of basic harmonicoscillation, strength of materials and of the existing prototypewas made. Following a requirement specification, somedelimitations were made so that the simulations would not be tooextensive. Subsequently, a minor design work was done to obtain 13different configurations of the turbine for simulation using FEM-methods.The result showed that none of the turbines rotational frequenciesis close to the turbine’s natural frequencies. However, accountmust be taken of cogging frequencies in the generator. These arewithin the range of the design's natural frequencies.All simulations of centrifugal force found that there isrelatively little tension at the selected maximum speed of 660 and132 revolutions per minute. However, as the results showed thatthe plates which are mounted between the rotor blades to providestability, creates greater stresses in the structure than thosewithout. Two proposals for the configuration of turbines have beenpresented in the report.  

  • 3417.
    Zhang, Defeng
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Kao-Walter, Sharon
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Development of Numerical  Research Tool  to Explore the Mechanism of Necking and Delamination in Packaging Materials2015Annet (Annet vitenskapelig)
    Abstract [en]

    Necking and delamination, appear due to loading in packaging materials, consisting of LDPE, Al-foil, adhesive layer, etc. These have significant negative influence on properties of packaging materials. However, how the mechanism influences is still unclear enough and there is no appropriate research tool available to study it.

    We are intend to develop an FEM model about it. It will work as a robust numerical analysis tool for further research.

  • 3418.
    Zhang, Defeng
    et al.
    College of Mech. Eng., Quzhou University, 324000 Quzhou, China.
    Mao, Kunming
    Dassault Systemes SIMULIA Corp, West Lafayette, Indiana, USA.
    Islam, Md. Shafiqul
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Andreasson, Eskil
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik. Tetra Pak Packaging Solutions AB.
    Kao-Walter, Sharon
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik. Fac. of Mech. & El. Eng., Shanghai Second Polytechnic Univ., 201209 Shanghai, China.
    Powerful Modelling Techniques in ABAQUS to Simulate Failure of Laminated composites2016Rapport (Fagfellevurdert)
    Abstract [en]

    In this study, laminated composites consisting of LDPE (Low Density Polyethylene), Al-foil (Aluminum foil)and an adhesive interface layer is focused. The defects like necking in LDPE, Al-foil layer and interfacial delaminationcan significantly impact the loading capacity of the laminated material. However, the influence mechanisms of thedefects are still unclear, and no appropriate research tool is available. Therefore, the FEM model based on alreadyavailable techniques in ABAQUS is developed in this work. The aim with the model is to create a robust numericalanalysis tool for further research work.In the modelling process, possibility of necking in substrates and interfacial delamination between material layers isconsidered. A coupled elasto-plasticity damage constitutive model, based on Hooke’s Law, the J2 yield criterion,isotropic hardening, associated flow-rule and ductile damage model, is formulated to demonstrate necking behaviorof substrates. In ABAQUS, three modelling techniques, namely VCCT, Cohesive Element, and XFEM, have been usedto simulate interfacial delamination. The simulation results are compared with the theoretical results.A uniaxial tension test consisting of a two material laminate is simulated by using these three modelling techniques.The special modelling skills for respective modelling techniques, element type, meshing technique of each model, arealso introduced. The comparison with the theoretical results shows necking in substrates and interfacial delaminationare also achieved in all three models as expected. Deformation results of the simulation are very close to that of thetheoretical analysis. Technique features of VCCT, Cohesive Element and XFEM in modelling of interfacialdelamination are analyzed and concluded. These three FEM models can all be utilized according to the requirementsof subsequent research.

  • 3419.
    Zhang, Defeng
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Mao, Kunming
    Dassault Systemes SIMULIA Corp.
    Islam, Md. Shafiqul
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Andreasson, Eskil
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Mehmood, Nasir
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Kao-Walter, Sharon
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Powerful Modelling Techniques in Abaqus to Simulate Necking and Delamination of Laminated Composites2015Annet (Annet vitenskapelig)
    Abstract [en]

    In this study, laminated composites consisting of LDPE (Low Density Polyethylene), Al-foil (Aluminum foil) and an adhesive interface layer is focused. The defects like necking in LDPE, Al-foil layer and interfacial delamination can significantly impact the loading capacity of the laminated material. However, the influence mechanisms of the defects are still unclear, and no appropriate research tool is available. Therefore, the FEM model based on already available techniques in ABAQUS is developed in this work. The aim with the model is to create a robust numerical analysis tool for further research work.

    In the modeling process, possibility of necking in substrates and interfacial delamination between material layers is considered. The constitutive material behaviour is elastic-plastic complemented with progressive damage, based on Hooke’s Law, the J2 yield criterion, isotropic hardening, associated flow-rule and ductile damage model are formulated to demonstrate necking behavior of substrates. In ABAQUS, three modeling techniques, namely VCCT, Cohesive Element, and XFEM, have been used to simulate interfacial delamination. The simulation results are compared with the theoretical results.

    A uniaxial tension test consisting of a two material laminate is simulated by using these three modeling techniques. The special modelling skills for respective modeling techniques, element type, meshing technique of each model, are also introduced. The comparison with the theoretical results shows necking in substrates and interfacial delamination are also achieved in all three models as expected. Deformation results of the simulation are very close to that of the theoretical analysis. Technique features of VCCT, Cohesive Element and XFEM in modelling of interfacial delamination are analyzed and concluded. These three FEM models can all be utilized according to the requirements of subsequent research.

  • 3420.
    Zhang, Xiaobo
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Influence of drying pressure on interfibre bond strength.2012Independent thesis Advanced level (degree of Master (One Year)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In this thesis the influence of the drying pressure on interfibre bond strength was investigated. Five different drying pressures, 0.7, 2.9, 4.5, 6.7, and 15 kPa, were applied during the preparation of fiber-fiber cross test pieces. The nominal overlap area of each fibre-fibre cross was measured in a transmission light microscope. A tensile tester was used to record the loaddeformation behavior of each fiber-fiber cross. The final results of the interfibre bond strength were defined by both the overlap area and the maximum force of each bond. The results showed that the influence of drying pressure to the average strength were very weak, although a maximum could be seen at 2.9 kPa of drying pressure. Moreover, the results suggested the overall trend of decreasing strengths at very high drying pressures. Finally, a statistical significance study of the results was presented. In addition, the influences of fiber type (spring wood vs. summer wood) and press type (steel vs. steel or steel vs. rubber) on interfibre bond strength were also discussed.

  • 3421. Zhang, Yang-Fei
    et al.
    Bai, Shu-Lin
    Yang, Da-Yong
    Zhang, Zhong
    Kao-Walter, Sharon
    Study on the Viscoelastic Properties of the Epoxy Surface by means of Nano-Dynamic Mechanical Analysis2008Inngår i: Journal of Polymer Science Part B: Polymer Physics, ISSN 0887-6266, E-ISSN 1099-0488, Vol. 46, nr 3, s. 281-288Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The viscoelastic properties of the epoxy surface have been investigated by nano-dynamic mechanical analysis (nano-DMA). Both a Berkovich tip and a conospherical tip were used under the condition of different forces (i.e. different penetration depths) in the frequency range of 10–200 Hz. Loss tangent and storage modulus are characteristics that describe the viscoelastic properties. The effect of force frequency, penetration depth and tip shape on the viscoelastic properties is studied and discussed according to the features of microstructures and mobility of molecular chains. The experimental results show important variations when the penetration depth is shallow (<30 nm). As the depth becomes deeper, the results tend to be stable and become almost constant over 120nm. The two kinds of indenter tip can cause a slight difference of the storage modulus. A “master curve” of the storage modulus as a function of force frequency is established.

  • 3422. Zheng, Zhibo Pang
    et al.
    Zheng, Lirong
    Tian, Junzhe
    Kao-Walter, Sharon
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Dubrova, Elena
    Chen, Qian
    Design of a terminal solution for integration of in-home health care devices and services towards the Internet-of-Things2015Inngår i: Enterprise Information Systems, ISSN 1751-7575, E-ISSN 1751-7583, Vol. 9, nr 1, s. 86-116Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In-home health care services based on the Internet-of-Things are promising to resolve the challenges caused by the ageing of population. But the existing research is rather scattered and shows lack of interoperability. In this article, a business-technology codesign methodology is proposed for cross-boundary integration of in-home health care devices and services. In this framework, three key elements of a solution (business model, device and service integration architecture and information system integration architecture) are organically integrated and aligned. In particular, a cooperative Health-IoT ecosystem is formulated, and information systems of all stakeholders are integrated in a cooperative health cloud as well as extended to patients’ home through the inhome health care station (IHHS). Design principles of the IHHS includes the reuse of 3C platform, certification of the Health Extension, interoperability and extendibility, convenient and trusted software distribution, standardised and secured electrical health care record handling, effective service composition and efficient data fusion. These principles are applied to the design of an IHHS solution called iMedBox. Detailed device and service integration architecture and hardware and software architecture are presented and verified by an implemented prototype. The quantitative performance analysis and field trials have confirmed the feasibility of the proposed design methodology and solution.

  • 3423.
    Zhou, Lin
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strömningsakustik.
    Acoustic characterization of orifices and perforated liners with flow and high-level acoustic excitation2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis is motivated by the need for noise control in aircraft engine with orifices and perforated liner. The presence of high-level acoustic excitation, different flow situations either bias flow, grazing flow or any combination in the aircraft engine, makes the acoustic behavior complex due to the interaction between sound and flow over the lined wall. Both systematic acoustic prediction of aircraft engines and liner optimization necessitate progress in impedance measurement methods by including the effect of the complex flow situations. The aim of the present thesis is to experimentally study the change in acoustic properties of orifices and perforated liners under bias or grazing flow.

    In order to study the effect of different combinations of bias flow and high-level acoustic excitation, an in-duct orifice has been investigated with finely controlled acoustic excitation levels and bias flow speeds. This provides a detailed study of the transition from cases when high-level acoustic excitation causes flow reversal in the orifice to cases when the bias flow maintains the flow direction. Nonlinear impedance is measured and compared, and a scattering matrix and its eigenvalues are investigated to study the potentiality of acoustic energy dissipation or production. A harmonic method is proposed for modelling the impedance, especially the resistance, which captures the change in impedance results at low frequencies compared with experimental results.

    The presence of grazing flow can increase the resistance of acoustic liners and shift their resonator frequency. So-called impedance eduction technology has been widely studied during the past decades, but with a limited confidence due to the interaction of grazing flow and acoustic waves. A comparison has been performed with different test rigs and methods from the German Aerospace Center (DLR). Numerical work has been performed to investigate the effect of shear flow and viscosity. Our study indicates that the impedance eduction process should be consistent with that of the code of wave propagation computation, for example with the same assumption regarding shear flow and viscosity. A systematic analysis for measurement uncertainties is proposed in order to understand the essentials for data quality assessment and model validation. The idea of using different Mach numbers for wave dispersion and in the Ingard-Myers boundary condition has been tested regarding their effect on impedance eduction. In conclusion, a local Mach number based on friction velocity is introduced and validated using both our own experimental results and those of previous studies.  

  • 3424.
    Zhou, Yang
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Numerical instability investigations for thin membranes2017Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Membrane structures are commonly used in many fields. The studies of these structures are of increasing interest. The projects in this thesis focus on the evaluations of equilibrium states for pressurized membranes under different problem settings, using finite element methods, and the corresponding instability behaviors.

    The first part of the current work discusses the instability behavior of a thin, planar, circular and initially horizontal membrane subjected to downwards or upwards fluid pressure. The membrane structures exhibit large deformations under pressure. The method for evaluating fluid pressure from gravity was developed in finite element context, and used in numerical simulations. Limit and bifurcation points have been detected for different loading parameters and conditions. The effects on instabilities of parameters, the initial states of the membrane, and the chosen mesh are discussed.

    The second part of the current work discusses instability behavior of a thin, spherical and closed membrane containing gas and fluid, when placed on a horizontal rigid and non-friction plane. A multi-parametric loading is described. By adding practically relevant controlling equations, different classes of equilibrium paths were followed using a generalized path following algorithm. Stability conclusions were made, according to the considered load parameters and the constraints. A generalized eigenvalue analysis was used to evaluate the stability behavior including the constraint effects. Fold line evaluations were performed to analyze the parametric dependence. A solution surface approach is used to visualize the mechanical response under this multi-parametric setting.

    The third part of the current work focuses on instability response of a truncated sphere, containing gas and fluid, and in contact with two vertical rigid and non-friction planes. Different penalty formulations were used and compared. The effects of contact implementations on instability behaviors were investigated. Bifurcation points induced by contacts have been observed. Multi-parametric problems were defined, and generalized paths were followed. The multi-parametric stability was evaluated using generalized eigenvalue analysis, based on the mass and total differential matrices. The effects of augmenting equations on bifurcation points and limit points are discussed.

    The fourth part of the current work analyses the instability response of a truncated sphere, completely filled with fluid, placed on a horizontal plane and spinning around the vertical axis. The loads from fluid pressure and the constraints, e.g., fluid volume, were formulated to generate a symmetric differential matrix. Several mesh patterns with different symmetries were used to simulate the model, and the obtained results are compared. Various problem settings were considered, and generalized paths were followed. The effects of symmetry aspects of the chosen meshes on instability behaviors are discussed, as are the effects of parameters.

  • 3425.
    Zhou, Yang
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Parametric stability analyses for fluid-loaded thin membranes2015Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Membrane structures are commonly used in many elds. The studies of thesestructures are of increasing interest. The two projects focus on the evaluations ofequilibrium states for uid-pressurized membranes under dierent loading conditions,and the corresponding instability behavior.The rst part of the current work discusses the instability behavior of a thin,planar, circular and initially horizontal membrane subjected to downwards or upwards uid pressure. The membrane structures exhibit large deformations under uid pressure. Various instability behaviors have been observed for dierent loadingparameters. Limit and bifurcation points have been detected for dierent loadingconditions. Dierent loading parameters have been used to interpret the instabilitybehavior. The eects on instability of parameters, the initial states of the membrane,and the chosen mesh have been discussed.The second part of the current work discusses instability behavior of a thin,spherical and closed membrane containing gas and uid placed on a horizontal rigidand non-friction plane. A multi-parametric loading has been described. By addingthe practically relevant controlling equations, the complex equilibrium paths werefollowed using the generalized path following algorithm, and the stability conclusionswere made dierently, according to the considered load parameters and theconstraints. A generalized eigenvalue analysis was used to evaluate the stabilitybehavior including the constraint eects. Fold line evaluations were performed toanalyze the parametric dependence of the instability behavior. A solution surfaceapproach was used to visualize the mechanical response under this multi-parametricsetting.

  • 3426.
    Zhou, Yang
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Nordmark, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Instability investigation for rotating thin spherical membranesManuskript (preprint) (Annet vitenskapelig)
  • 3427.
    Zhou, Yang
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Nordmark, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Instability of thin circular membranes subjected to hydro-static loads2015Inngår i: International Journal of Non-Linear Mechanics, ISSN 0020-7462, E-ISSN 1878-5638, Vol. 76, s. 144-153Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Membrane structures subjected to hydrostatic load are prone to undergo large deformations and lose stability. This paper investigates different instability phenomena for a thin, circular and initially flat and horizontal membrane. The Mooney-Rivlin hyper-elastic model is used to provide the material description. An axisymmetric and a 3D model have been set up to show the large deformations and instability behavior with different parameter settings. Numerical examples show that the methods developed are capable to describe the deformation dependent loading conditions and the instability phenomena. The numerical simulations show fundamental differences in the response and instability behavior when the horizontal membrane is loaded from above or below. The parameters of fluids and membranes and the means for introducing the pressure are of essence for interpreting the instability behavior.

  • 3428.
    Zhou, Yang
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Nordmark, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Multi-parametric stability investigation for thin membranes with contactsManuskript (preprint) (Annet vitenskapelig)
  • 3429.
    Zhou, Yang
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Nordmark, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Multi-parametric stability investigation for thin spherical membranes filled with gas and fluid2016Inngår i: International Journal of Non-Linear Mechanics, ISSN 0020-7462, E-ISSN 1878-5638, Vol. 82, s. 37-48Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The instability behavior of spherical membranes completely or partially filled with fluid, also with internal gas over-pressure, placed on a friction-less rigid plane was investigated. The two-parameter Mooney-Rivlin model was used for material description. A third order penalty function was used to describe the rigid support. Different problem settings were considered, and different instability responses were observed. For the partially fluid-filled membrane, a multi-parametric problem was defined and analyzed. Augmenting equations were introduced to impose control constraints on variables chosen. These equations also affect the instability analysis. A generalized eigenvalue analysis was used for the stability conclusions. Numerical simulations showed that appropriate control constraints are of essence to interpret the instability conclusions. Fold line evaluations were performed to analyze the dependence of the instability behavior on the parameters. A solution surface algorithm was utilized to analyze and visualize the mechanical responses to multi-variable loading.

  • 3430.
    Zhou, Yang
    et al.
    KTH, Skolan för bioteknologi (BIO), Teoretisk kemi och biologi.
    Nordmark, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Multi-parametric stability investigation for thin spherical membranes with contacts2017Inngår i: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 131-132, s. 334-344Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The instability behavior for a thin truncated spherical membrane completely filled with fluid or containing both gas and fluid, fixed on a circular platform and in contact with two vertical planes was investigated. Different penalty functions for contacts, and symmetry aspects of the discretized model were studied, and gave effects on instability behavior. Stability conclusions for the multi-parametric problems were made using generalized eigenvalue analyses, showing limit points, bifurcation points and turning point. Contact conditions were shown to introduce bifurcations and secondary paths, dependent on the contact implementations and discretizations. Their effects on stability behaviors in connection with various controlling equations are discussed.

  • 3431.
    Zhou, Zhuohang
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Nilsson, Martin
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Design and Implementation of Angular Vibration Testing Equipment2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This thesis is done by two students from Blekinge Institute of Technology as an end of the master of engineering program with emphasis on applied mechanics. The thesis is done in cooperation with Axis Communications AB in Lund which develop surveillance cameras. The task was to design and implement an Angular Vibration Testing Equipment. Axis needs this to test their surveillance cameras for angular vibrations. These vibrations occur usually on cameras located on poles placed at roads and at train stations. The thesis has been carried out in three different phases where the first phase handled a deeper understanding of the problem, planning and investigating of related works. Axis has a solution for smaller cameras called Shakespeare MK I and this was used as an inspiration for us. The second phase included concept generation and concept evaluation. This has been done with brainstorming, workshop and concept scoring. At the last phase a prototype was built and tested and a detailed design was made. Two versions of the prototype were made and they showed that the concept works well. The project resulted in a working prototype that can transform linear motion to rotation around two axes. A drawing and a cost calculation were made for the final concept. The final construction is still not completely optimized and has improvement and adjustment possibilities that might be needed.

  • 3432.
    Zhu, Lailai
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Lauga, Eric
    Dept. of Mechanical and Aerospace Engineering, University of California, San Diego, USA.
    Brandt, Luca
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Fysiokemisk strömningsmekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Self-propulsion in viscoelastic fluids: pushers vs. pullers2012Inngår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 24, nr 5, s. 051902-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We use numerical simulations to address locomotion at zero Reynolds number in viscoelastic (Giesekus) fluids. The swimmers are assumed to be spherical, to self-propel using tangential surface deformation, and the computations are implemented using a finite element method. The emphasis of the study is on the change of the swimming kinematics, energetics, and flow disturbance from Newtonian to viscoelastic, and on the distinction between pusher and puller swimmers. In all cases, the viscoelastic swimming speed is below the Newtonian one, with a minimum obtained for intermediate values of the Weissenberg number, We. An analysis of the flow field places the origin of this swimming degradation in non-Newtonian elongational stresses. The power required for swimming is also systematically below the Newtonian power, and always a decreasing function of We. A detail energetic balance of the swimming problem points at the polymeric part of the stress as the primary We-decreasing energetic contribution, while the contributions of the work done by the swimmer from the solvent remain essentially We-independent. In addition, we observe negative values of the polymeric power density in some flow regions, indicating positive elastic work by the polymers on the fluid. The hydrodynamic efficiency, defined as the ratio of the useful to total rate of work, is always above the Newtonian case, with a maximum relative value obtained at intermediate Weissenberg numbers. Finally, the presence of polymeric stresses leads to an increase of the rate of decay of the flow velocity in the fluid, and a decrease of the magnitude of the stresslet governing the magnitude of the effective bulk stress in the fluid.

  • 3433.
    Zipser, L.
    et al.
    HTW, Hochschule für Technik und Wirtschaft, Dresden.
    Franke, H.
    HTW, Hochschule für Technik und Wirtschaft, Dresden.
    Olsson, Erik
    Molin, Nils-Erik
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Ultrasound object fields in air reconstructed using digital phase conjugation2002Inngår i: Proceedings: 2002 IEEE Ultrasonics Symposium : October 8 - 11, 2002, Forum Hotel, Munich, Germany / [ed] Donald E. Yuhas, Piscataway, NJ: IEEE Communications Society, 2002, s. 765-768Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A scanning laser Doppler vibrometer is used to record 2D ultrasound fields in air. The laser light of the vibrometer traverses the sound field to and from a rigid reflector and determines the velocity field, a quantity proportional to the sound pressure rate, in each scanned point relative to the sound source. The object sound is the scattered field from objects outside the recording area. Digital reconstruction using phase conjugation (time reversal) of the object sound field is then performed and the original object field intensity and phase is reconstructed.

  • 3434.
    Zipser, Lothar
    et al.
    Hochschule für Technik/Wirtschaft, University of Applied Sciences, Friedrich-List-Platz.
    Franke, Heinz
    Hochschule für Technik/Wirtschaft, University of Applied Sciences, Friedrich-List-Platz.
    Olsson, Erik
    Molin, Nils-Erik
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Reconstructing two-dimensional acoustic object fields by use of digital phase conjugation of scanning laser vibrometry recordings2003Inngår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 42, nr 29, s. 5831-5838Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    scanning laser Doppler vibrometer is used to record two-dimensional ultrasound fields in air. The laser light of the vibrometer traverses the sound field to and from a rigid reflector and determines the velocity field, a quantity proportional to the sound pressure rate, in each scanned point relative to the sound source. The object sound is the scattered field from objects outside the recording area. Digital reconstruction by use of phase conjugation (time reversal) of the object sound field is then performed, and the original object field intensity and phase is reconstructed

  • 3435.
    Åberg, Mats
    et al.
    KTH, Tidigare Institutioner (före 2005), Hållfasthetslära.
    Gudmundson, Peter
    KTH, Tidigare Institutioner (före 2005), Hållfasthetslära.
    Acoustic emission in laminated beams due to fiber fractures1999Inngår i: Twelfth Int. Conf. on Composite Materials, ICCM-12, Paris, pap501, 1999, 1999Konferansepaper (Fagfellevurdert)
  • 3436. Åhrström, Bert-Olof
    et al.
    Lindqvist, S.
    Höglund, Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.
    Sundin, Karl-Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Modified split Hopkinson pressure bar method for determination of the dilatation-pressure relationship of lubricants used in elastohydrodynamic lubrication2002Inngår i: Proceedings of the Institution of mechanical engineers. Part J, journal of engineering tribology, ISSN 1350-6501, E-ISSN 2041-305X, Vol. 216, nr 2, s. 63-74Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In theoretical calculations of film thickness, pressure distribution and friction in an elastohydrodynamically lubricated (EHL) conjunction it is necessary to model the physical/mechanical behaviour of the lubricant. It is important to know, for example, the dilatation-pressure or the density-pressure relationship. In this paper a modified split Hopkinson pressure bar system for determination of the compressibility of oil is presented. It makes it possible to test oils under conditions similar to those found in real EHL contacts: loading duration in the range of 100-300 μs and pressures of almost 2 GPa. An empirical model has been suggested for mathematical description of the dilatation-pressure relation of the specific oils. A naphthenic mineral oil and a synthetic oil, 5P4E, have been tested under adiabatic conditions and at pressures up to 1.5 and 1.9 GPa respectively. The adiabatic results have been recalculated to isothermal conditions for comparison

  • 3437.
    Åkerlind, Kristina
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Danielsson, Rebecka
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Assessment of Life Extension for Welded Bridge Details Using HFMI2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 3438.
    Åkerström, Paul
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A Novel Tooling Technology for Hot Forming Processes2017Inngår i: 6th International Conference Hot Sheet Metal Forming of High-Performance Steel CHS2: June 4-7 2017, Atlanta, Georgia, USA : proceedings / [ed] Mats Oldenburg, Braham Prakash, Kurt Steinhoff, Warrendale, PA: Association for Iron & Steel Technology, AIST , 2017, s. 243-250Konferansepaper (Fagfellevurdert)
  • 3439. Åkerström, Paul
    Material characterisation for simulation of press hardening2004Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The growing effort to reduce vehicle weight and improve passive safety in the automotive industry has drastically increased the demand for ultra high strength steel components. There exist several production methods for such components, where the press hardening technique (hot stamping) is one of the most successful in producing complex components from boron steel. In order to accurately perform numerical Finite Element (FE) simulations of the actual thermo-mechanical forming, it is crucial to use correct material data and models. This work is focusing on two main aspects of the material characterisation as follows. The first is the flow stress of the austenite at elevated temperatures and different strain rates, relevant for the process, which is crucial for correctly predicting the strains in the component and the forming force. During a press hardening cycle, the actual forming is performed at high temperatures and the steel is in the austenitic state. The second, the austenite decomposition into daughter products such as ferrite, pearlite, bainite or martensite is a function of the thermal and mechanical history. To find the mechanical response (flow stress) for the austenite, a method based on multiple overlapping continuous cooling and compression tests (MOCCCT) in combination with inverse modelling has been developed. A validation test (in combination with the compression tests) shows good agreement with the simulated forming force, indicating that the estimated flow stress as a function of temperature, strain and strain rate is accurate in the actual application. The austenite decomposition model is developed and integrated as a material subroutine into the FE-code LS-DYNA. The model is based on the combined nucleation and growth rate equations proposed by Kirkaldy. A separate test to simulate different cooling histories along a boron alloyed steel sheet has been conducted.

  • 3440.
    Åkerström, Paul
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Modelling and simulation of hot stamping2006Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The growing effort to reduce vehicle weight and improve passive safety in the automotive industry has drastically increased the demand for ultra high strength steel components. There are several production technologies for such components. The hot stamping technology (press hardening) is one of the most successful in producing complex components with superior mechanical properties. The hot stamping process can be described by the following steps; punching of blanks, heating to 900C in a furnace to austenitization followed by simultaneous forming and quenching in forming tools. In order to obtain accurate numerical Finite Element (FE) simulations of the actual thermo-mechanical forming, correct material data and models are crucial and mandatory. This work is focusing on three main aspects described below for the numerical simulation of the thermo-mechanical forming of thin boron steel sheets into ultra high strength components. The objective is to predict the shape accuracy, thickness distribution and hardness distribution of the final component with high accuracy. The first aspect is the flow stress of the austenite at elevated temperatures and different strain rates, which is crucial for correctly predicting the strains in the component and the forming force. During a hot stamping cycle, the actual forming is performed at high temperatures and the steel is mainly in the austenitic state. The second aspect is the austenite decomposition into daughter products such as ferrite, pearlite, bainite or martensite that is a function of the thermal and mechanical history. The third aspect is the mechanical material model used, which determine the stress state and consequently the component distortion. To find the mechanical response (flow stress) for the austenite, a method based on multiple overlapping continuous cooling and compression experiments (MOCCCT) in combination with inverse modelling has been developed. A validation test (in combination with the compression tests) shows good agreement with the simulated forming force, indicating that the estimated flow stress as a function of temperature, strain and strain rate is accurate in the actual application. The austenite decomposition model is developed and integrated as a material subroutine into the FE-code LS-DYNA. The model is based on the combined nucleation and growth rate equations proposed by Kirkaldy. A separate test to simulate different cooling histories along a boron alloyed steel sheet has been conducted. Different mixtures of daughter products are formed along the sheet and the corresponding simulation show acceptable good agreement with the experimentally determined temperature histories, hardness profile and volume fractions of the different microconstituents formed in the process. For the mechanical response, a mechanical constitutive model based on the original model proposed by Leblond has been implemented into LS-DYNA. The implemented model account for transformation induced plasticity (local plastic flow in austenite) according to the Greenwood-Johnson mechanism as well as classical plasticity during global yield. Finally, a FE-simulation using the implemented models of the thermo-mechanical forming of a component is compared to the corresponding experiment, including forming force, thickness distribution, hardness distribution and shape accuracy/springback.

  • 3441. Åkerström, Paul
    et al.
    Bergman, Greger
    SSAB HardTech.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Numerical implementation of a constitutive model for simulation of hot stamping2007Inngår i: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 15, nr 2, s. 105-119Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In order to increase the accuracy of numerical simulations of the hot stamping process, an accurate and robust constitutive model is crucial. During the process, a hot blank is inserted into a tool where it is continuously formed and cooled. For the steel grades often used for this purpose, the initially austenitized blank will decompose into different product phases depending on the cooling and mechanical history. As a consequence, the phase proportions change will affect both the thermal and mechanical properties of the continuously formed and cooled blank. A thermo-elastic-plastic constitutive model based on the von Mises yield criterion with associated plastic flow is implemented into the LS-Dyna finite element code. Models accounting for the austenite decomposition and transformation induced plasticity are included in the constitutive model. The implemented model results are compared with experimental dilatation results with and without externally applied forces. Further, the calculated isothermal mechanical response during the formation of a new phase is compared with the corresponding experimental response for two different temperatures.

  • 3442. Åkerström, Paul
    et al.
    Bergman, Greger
    Gestamp R&D.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Salomonsson, Per
    Utveckling av mikrostruktur och mekanisk respons vid presshärdning2007Inngår i: Svenska Mekanikdagar 2007: Program och abstracts / [ed] Niklas Davidsson; Elianne Wassvik, Luleå: Luleå tekniska universitet, 2007, s. 98-Konferansepaper (Annet vitenskapelig)
  • 3443. Åkerström, Paul
    et al.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Austenite decomposition during press hardening of a boron steel: computer simulation and test2006Inngår i: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 174, nr 1-3, s. 399-406Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this work a model to predict the austenite decomposition into ferrite, pearlite, bainite and martensite during arbitrary cooling paths for thin sheet boron steel is used. The model is based on Kirkaldy's rate equations. The basic rate equations has been modified to account for the austenite stabilization effect from the added boron. The model is implemented as part of a material subroutine in the Finite Element Program LS-DYNA 970. Both the obtained simulated volume fractions microconstituents and hardness profiles shows promising agreement to the corresponding experimental observations.

  • 3444.
    Åkerström, Paul
    et al.
    Gestamp Hardtech AB, Luleå.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Numerical simulation of a thermo-mechanical sheet metal forming experiment2008Inngår i: Numisheet 2008: Proceedings of the 7th international conference and workshop on numerical simulation of 3D sheet metal forming processes, September 1-5, 2008, Interlaken, Switzerland / [ed] Pavel Hora, Zurich: Institute of Virtual manufacturing, ETH Zurich , 2008, s. 569-574Konferansepaper (Fagfellevurdert)
  • 3445. Åkerström, Paul
    et al.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Studies of the thermo-mechanical material response of a boron steel by inverse modelling2004Inngår i: Proceedings: 2nd International Conference on Thermal Process Modelling and Computer Simulation : Nancy, France, March 31 - April 2, 2003 / [ed] S. Denis, Les Ulis: EDP Sciences, 2004Konferansepaper (Fagfellevurdert)
  • 3446. Åkerström, Paul
    et al.
    Wikman, Bengt
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Material parameter estimation for boron steel from simultaneous cooling and compression experiments2005Inngår i: Modelling and Simulation in Materials Science and Engineering, ISSN 0965-0393, E-ISSN 1361-651X, Vol. 13, nr 8, s. 1291-1308Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In order to increase the accuracy of numerical simulations of the hot stamping process, reliable material data is crucial. Traditionally, the material is characterized by several isothermal compression or tension tests performed at elevated temperatures and different strain rates. The drawback of the traditional methods is the appearance of unwanted phases for some test temperatures and durations. Such an approach is also both time consuming and expensive. In the present work an alternative approach is proposed, which reduces unwanted phase changes and the number of experiments. The isothermal mechanical response is established through inverse modelling of simultaneous cooling and compression experiments. The estimated material parameters are validated by comparison with data from a separate forming experiment. The computed global response is shown to be in good agreement with the experiments.

  • 3447. Åkesson, Henrik
    Active control of vibration and analysis of dynamic properties concerning machine tools2007Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Vibration in internal turning is a problem in the manufacturing industry. Vibrations appear under the excitation applied by the material deformation process during the machining of a workpiece. In order for a lathe to perform an internal turning or boring operation, for example, in a pre-drilled hole in a workpiece, it is generally required that the boring bar should be long and slender; therefore extra sensitive to vibrations. These vibrations will affect the result of machining, in particular the surface finish, also the tool life may be reduced. As a result of tool vibration, severe acoustic noise frequently occurs in the working environment. This thesis comprises three parts and the first part presents a method for active control of boring bar vibration. This method consists of an active boring bar controlled by, for example, an analog controller. The focus lies on the analog controller and the advantages that may be obtained from working in the analog domain. The controller is a lead-lag compensator with digitally controlled parameters, such as gain and phase. However, signals remain in the analog domain. In addition, the analog controller is compared with a digital adaptive controller and it is found that both controllers yield an attenuation of the vibration by up to 50 dB. The second part of this thesis concerns the dynamic properties of a clamped boring bar used by the industry. In order to design a robust controller for a certain system, knowledge about the system's dynamic properties is required. On the workshop floor, a boring bar is dismounted and remounted, and reconfiguration of boring bars will alter the dynamic properties of the clamped boring bar. The dynamic properties of a standard boring bar and an active boring bar for a number of possible clamping conditions, as well as for a linearized clamping have been investigated based on an experimental approach. Also simple Euler-Bernoulli modeling of clamped boring bars incorporating simple non-rigid models of the boring bar clamping are investigated. Initial simulations of nonlinear SDOF systems have been carried out: one with a signed squared stiffness and one with a cubic stiffness. The purpose of these simulations was to identify a nonlinearity that introduces a similar behavior in the SDOF system dynamics as the nonlinear behavior observed in the dynamic properties of a clamped boring bar. The third and final part of this thesis focuses on vibration analysis methods in engineering education. A signal analyzer (which is a commonly used instrument in signal processing and vibration analysis) was made accessible via the Internet. Assignments were developed for students to learn and practice vibration analysis on real signals from a real setup of a relevant structure; a clamped boring bar. Whilst the experimental setup was fixed, the instrument and sensor configuration nonetheless enable a variety of experiment, for example: excitation signal analysis, spectrum analysis and experimental modal analysis.

  • 3448. Åkesson, Henrik
    Investigation of the Dynamic Properties of a Milling Structure; Using a Tool Holder with Moderate Overhang2009Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Vibration problem during metal cutting occurs frequently in the manufacturing industry. The vibration level depends on many different parameters such as material type, dimensions of the workpiece, rigidity of tooling structure, cutting data and operation mode. In milling the cutting process subject the tool to vibrations and having a milling tool holder with long overhang, will most likely results in high vibration levels. These vibrations have a consequence of reduced tool life, poor surface finishing and disturbing sound. An investigation of dynamic properties of a milling tool holder with moderate overhang has been carried out by means of experimental modal analysis and vibration analysis during operating mode. Both angular vibrations of the rotating tool and vibrations of the machine tool structure were examined during milling. Also, bending motion of the rotating milling tool holder was examined during cutting. This paper focuses on identifying the source/sources of the dominating milling vibration components and to identify that of these vibrations which may be related to the structural dynamic properties of the milling tool holder.

  • 3449. Åkesson, Henrik
    et al.
    Brandt, Anders
    Håkansson, Lars
    Lagö, Thomas L
    Claesson, Ingvar
    Operational Modal Analysis of a Boring Bar During Cutting2005Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Internal turning or boring operation is a common metal working process that is usually associated with vibration problems. Vibration problems in internal turning considerably influence important factors such as surface quality, productivity, production costs, etc. In this paper we report analysis results from an operational modal analysis of a boring bar during cutting operation. The results are compared with operating deflection shape results and traditional modal analysis results of the same boring bar. Results show that the first bending modes in the directions of cutting speed and cutting depth are active in the operating vibrations. The three analysis methods result in similar conclusions.

  • 3450. Åkesson, Henrik
    et al.
    Håkansson, Lars
    Gustavsson, Ingvar
    Zackrisson, Johan
    Claesson, Ingvar
    Lagö, Thomas L
    Vibration Analysis of Mechanical Structures over the Internet Integrated into Engineering Education2006Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Experimental vibration analysis is one of the most important tools for analyzing dynamic properties of mechanical structures. The information from experimental vibration analysis is used in the development of products to obtain a required dynamic behavior, or for instance classify vibration problems in different public, industrial environments etc. In order to carry out such experiments with high quality, knowledge about different analysis methods is of great importance. Also a large experimental experience is required to obtain reliable results as in any field. In engineering education experiment using real mechanical structures and equipment is of significance for the learning process. In traditional university laboratories students conduct experiments under the supervision of an instructor. However, a trend towards decreasing investments to maintain these laboratories can be seen all over the world and instead an increase of simulations or theoretical experiments is replacing these hands on experiments due to cost. Blekinge Institute of Technology (BTH), Sweden provide the opportunity for engineering students to remotely access the practical and theoretical knowledge advancement in experimental vibration analysis that is highly attractive for the industry. Remote laboratory exercises are to day a reality at BTH and are a complement to on-campus laboratory experiments, increasing the availability of the instruments. Previously vibration experiments have been conducted over the Internet at BTH, using experimental hardware located in a small closed laboratory. A further step towards a more user-friendly interface has been developed, increasing the feeling of being in front of a real instrument instead of a virtual front panel. This paper presents a new remote vibration laboratory and how remote experimental vibration analysis has been integrated in the engineering education as a complement to ordinary lessons and experiments in traditional laboratories.

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