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  • 3251.
    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.

  • 3252. 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.

  • 3253. 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.

  • 3254.
    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.  

  • 3255.
    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.

  • 3256.
    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.

  • 3257.
    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)
  • 3258.
    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.

  • 3259.
    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)
  • 3260.
    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.

  • 3261.
    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.

  • 3262.
    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.

  • 3263.
    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.

  • 3264.
    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.

  • 3265.
    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

  • 3266. 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

  • 3267.
    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)
  • 3268. 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.

  • 3269.
    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.

  • 3270. 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.

  • 3271. 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)
  • 3272. 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.

  • 3273.
    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)
  • 3274. 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)
  • 3275. 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.

  • 3276. 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.

  • 3277. 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.

  • 3278. 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.

  • 3279. 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.

  • 3280. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Analysis of dynamic properties of boring bars concerning different clamping conditions2009Inngår i: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 23, nr 8, s. 2629-2647Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Boring bars are frequently used in the manufacturing industry to turn deep cavities in workpieces and are usually associated with vibration problems. This paper focuses on the clamping properties’ influence on the dynamic properties of clamped boring bars. A standard clamping housing of the variety commonly used in industry today has been used. Both a standard boring bar and a modified boring bar have been considered. Two methods have been used: Euler–Bernoulli beam modeling and experimental modal analysis. It is demonstrated that the number of clamping screws, the clamping screw diameter sizes, the screw tightening torques, the order the screws are tightened has a significant influence on a clamped boring bars eigenfrequencies and its mode shapes orientation in the cutting speed—cutting depth plane. Also, the damping of the modes is influenced. The results indicate that multi-span Euler–Bernoulli beam models with pinned boundary condition or elastic boundary condition modeling the clamping are preferable as compared to a fixed-free Euler–Bernoulli beam for modeling dynamic properties of a clamped boring bar. It is also demonstrated that a standard clamping housing clamping a boring bar with clamping screws imposes non-linear dynamic boring bar behavior.

  • 3281. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Claesson, Ingvar
    Lagö, Thomas L
    Analog versus Digital Control of Boring Bar Vibration2005Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In workshops where metal cutting is performed, the machining processes frequently introduces productivity degrading vibration problems and annoying sound, sometimes almost at unbearable levels. Besides producing disturbing noise, the vibrations affect the surface finish of the workpiece and the tool life. Two different approaches based on feedback control are investigated, both applied for the control of an active boring bar. The first approach is based on a digital adaptive feedback controller; the feedback filtered-X LMS algorithm. The second approach is based on an analog controller; a feedback controller with gain and phase orthogonally adjustable, thus flexible for the control of systems with different dynamic properties. Based on open loop frequency response function estimates, robustness and stability of both the digital and the analog feedback control system are discussed. A comparison of the two controllers concerning their boring bar vibration attenuation performance shows that the analog controller attenuates the vibration in same order of magnitude as the digital controller which is approximately by up to 40 dB.

  • 3282. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Claesson, Ingvar
    Lagö, Thomas L
    Comparison between different controllers when having abrupt changes in a process2006Konferansepaper (Fagfellevurdert)
    Abstract [en]

    When metal cutting is performed, the machining processes introduce productivity degrading vibration. By applying an active control scheme, theses vibrations can be reduced significantly with the result of improved surface finish of the work piece and increased tool life. Due to the large difference of boundary conditions during the machining process, a controller fast enough to follow these changes is needed, for example from no cutting to cutting - the actual engagement of the cutting process. If the controller does not success to follow fast enough, the tool tip might break, as is the case without any active damping. Different approaches based on feedback control are investigated; all implemented using an active boring bar. The first approach is based on a digital adaptive feedback controller; the feedback filtered-X LMS algorithm. The two other controllers are analog; one is a lead controller and the other is lead-lag controller, both with gain and phase orthogonally adjustable. This paper focuses on robustness, stability and convergence of the digital and the analog feedback controllers. The analysis is based on open loop frequency response function estimates during different operating conditions.

  • 3283. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Claesson, Ingvar
    Lagö, Thomas L
    Dynamic Properties of Tooling Structure: Hydraulic Clamping versus Standard Screw Clamping in a Lathe Application2008Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    During turning, the metal deformation process excites the tooling structure and may result in high and degrading tool vibration levels. In internal turning the boring bar is generally the weakest link of the tooling structure. The boundary conditions imposed on the boring bar by the clamping housing influence the dynamic properties of a clamped boring bar. The dynamic properties of a clamped boring bar have been investigated for two different clamping housings; one that clamps the boring bar by means of hydraulic pressure and one that clamps the boring bar by means of clamping screws. Both experimental and analytical methods have been utilized in the investigation.

  • 3284. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Claesson, Ingvar
    Lagö, Thomas L
    Estimation and Simulation of the Nonlinear Dynamic Properties of a Boring Bar2011Inngår i: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 16, nr 1, s. 35-43Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper, an initial investigation of the nonlinear dynamic properties of clamped boring bars is carried out. Two nonlinear, single-degree-of-freedom models with different softening spring nonlinearities are introduced for modeling the nonlinear dynamic behavior of the fundamental bending mode in the cutting speed direction of a boring bar. Also, two different methods for the simulation of nonlinear models are used. The dynamic behavior in terms of frequency response function estimates for the nonlinear models and the experimental modal analysis of the clamped boring bar is compared. Similar resonance frequency shift behavior for varying excitation force levels is observed for both the nonlinear models and the actual boring bar.

  • 3285. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Claesson, Ingvar
    Lagö, Thomas L
    INVESTIGATION OF THE DYNAMIC PROPERTIES OF A BORING BAR CONCERNING DIFFERENT BOUNDARY CONDITIONS2007Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The boring bar is one of the most widely used types of tool holder in metal cutting operations. The turning process subjects the tool to vibration, and cutting in deep workpiece cavities is likely to result in high vibration levels. The consequences of such vibration levels are generally; reduced tool life, poor surface finishing and disturbing sound. Internal turning frequently requires a long and slender boring bar in order to machine inside a cavity, and the vibrations generally become highly correlated with the fundamental bending mode of the boring bar. Different methods can be applied to reduce the vibrations, the implementation of the most efficient and stable methods require in depth knowledge concerning the dynamic properties of the tooling system. Furthermore, the interface between the boring bar and the clamping house has a significant influence on the dynamic properties of the clamped boring bar. In this paper different cases of boundary condition of the boring bar are presented partly analytically but also experimentally. This paper focuses on dynamic properties of a boring bar that arise due to different clamping conditions of the boring bar introduced by a clamping house commonly used in the manufacturing industry.

  • 3286. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Claesson, Ingvar
    Sigfridsson, Andreas
    Svensson, Tobias
    Lagö, Thomas L
    A First Prototype of an Active Boring Bar Tested in Industry2006Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Metal cutting is a common process in the manufacturing industry. Vibration problem during metal cutting is a reality for these manufactures. The vibration level depends on many different parameters such as material type, dimensions of the workpiece and boring bar, cutting data and operation mode. Internal cutting is one of the most troublesome operation modes, without any continuous monitoring and control from an operator grave vibration levels quickly arises. From the industry point of view this is an expense in the production line. The reduced tool life and the coarse surface finishing caused by the large vibration will force the operator to stop the cutting process, either to change tool when it is broken or change cutting data like decreasing the cutting depth. Any interference like this increases the working time for each component tremendous. These problems have been located and examined in an industry producing and renovating components using a lathe. One lathe was chosen for further investigation by experimental modal analysis and analysis during operational mode. The examination was done in an environment with machining processes in full operation mode and also during non-working ours. After analyzing the problem different solution where scrutinized and a first prototype where constructed. The solution to the problem is an active boring bar. This paper will present the procedure from analyzing a problem in industry to the test of the first prototype of the solution.

  • 3287. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Claesson, Ingvar
    Sigfridsson, Andreas
    Svensson, Tobias
    Lagö, Thomas L
    Active Boring Bar Prototype Tested in Industry2006Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Metal cutting processes are common in the manufacturing industry. Vibration problems during metal cutting are a degrading reality in the manufacturing industry and have a negative impact on the productivity and increase’s the production costs. The vibration level depends on many different parameters such as material type, dimensions of the workpiece, tool, tooling structure, machine structure, the cutting data and operation mode. Internal turning is one of the most troublesome operation modes concerning vibration. It generally requires that extra care must be taken with pro-duction planning and in the preparations for the machining of a workpiece. Frequently, continuous monitoring and control by a skilled operator is required to avoid grave degrading vibration levels. The reduced tool life and the coarse surface finishing generally caused by large vibration levels will e.g. force the operator to stop the cutting process, either to change tool when it is broken or change cutting data like decreasing the cutting depth. Any interference like this increases the production time and cost for each component tremendously. In an industry producing and renovating compo-nents using different machine tools, a particular lathe used for internal turning of certain details with extensive vibration problem was chosen for further investigation by experimental modal analysis and vibration analysis during operation. The examination was done in an environment with ma-chine tools in full operation and also during non-working ours. After analyzing the problem different solutions for the reduction of the vibration problem was investigated and subsequently a first proto-type was constructed. The solution to the problem is active control of the tool vibration using an active boring bar. This paper will present the procedure from analyzing a problem in industry to the test of the first prototype of the solution.

  • 3288. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Håkansson, Lars
    Lagö, Thomas L
    Claesson, Ingvar
    Investigation of the Dynamic Properties of a Milling Tool Holder2009Rapport (Annet vitenskapelig)
    Abstract [en]

    Vibration problems during metal cutting occur frequently in the manufacturing industry. The vibration level depends on many different parameters such as the material type, the dimensions of the workpiece, the rigidity of tooling structure, the cutting data, and the operation mode. In milling, the cutting process subjects the tool to vibrations, and having a milling tool holder with a long overhang will most likely result in high vibration levels. As a consequence of these vibrations, the tool life is reduced, the surface finishing becomes poor, and disturbing sound appears. In this report, an investigation of the dynamic properties of a milling tool holder with moderate overhang has been carried out by means of experimental modal analysis and vibration analysis during the operating mode. Both the angular vibrations of the rotating tool and the vibrations of the machine tool structure were examined during milling. Also, vibration of the workpiece and the milling machine was examined during cutting. This re- port focuses on identifying the source/sources of the dominant milling vibration components and on determining which of these vibrations that are related to the structural dynamic properties of the milling tool holder.

  • 3289. Åkesson, Henrik
    et al.
    Smirnova, Tatiana
    Lagö, Thomas L
    Håkansson, Lars
    Analysis of Dynamic Properties of Boring Bars Concerning Different Clamping Conditions2007Rapport (Annet vitenskapelig)
    Abstract [en]

    The boring bar is one of the most widely used type of tool holders in metal cutting operations. The turning process subjects the tool to vibrations, and cutting in deep workpiece cavities is likely to result in high vibration levels. The consequences of such vibration levels generally results in: reduced tool life, poor surface finishing and disturbing sound. Internal turning frequently requires a long and slender boring bar in order to machine inside a cavity, and the vibrations generally become highly correlated with one of the fundamental bending modes of the boring bar. Different methods can be applied to reduce the vibrations, the implementation of the most efficient and stable methods require in depth knowledge concerning the dynamic properties of the tooling system. Furthermore, the interface between the boring bar and the clamping house has a significant influence on the dynamic properties of the clamped boring bar. This report focuses on the dynamic properties of a boring bar that arise under different clamping conditions of the boring bar and are introduced by a clamping house (commonly used in the manufacturing industry). The dynamic properties of a boring bar (for different cases of boundary condition of the boring bar) are presented partly analytically but also experimentally.

  • 3290. Åsa, Ericson
    et al.
    Tobias, Larsson
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för maskinteknik.
    Ola, Isaksson
    Andreas, Larsson
    Revisiting the Research Field of Product-Service Systems Development2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The research within the Product-Service Systems (PSS) field aims to support manufacturing industries’ ability to provide value in terms of a service offer to its customers, simultaneously taking a more holistic approach to eco- sustainability. The industrial idea of providing customer benefits in parallel with robust products is not new, yet equipping engineers to conduct innovation and applying a service perspective in the early design stages is noticed as fairly radical. The purpose in this paper is two-fold. First, to describe research efforts within the PSS field seen through our engineering design lenses, second, to explore and discuss plausible directions and by that identify “white spots” on the map, which may be seen as relevant directions for future research.

  • 3291. Åslund, P.
    et al.
    Hägglund, R.Carlsson, L.Isaksson, PerUppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    Modeling of global and local buckling of corrugatedboard panels loaded in edgewise compression2012Konferanseproceedings (Fagfellevurdert)
  • 3292.
    Åslund, Pär
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    On failure mechanisms and strength predictions in corrugated board structures2014Doktoravhandling, med artikler (Annet vitenskapelig)
  • 3293. Åslund, Pär E.
    et al.
    Hägglund, Rickard
    Carlsson, Leif A.
    Isaksson, Per
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad mekanik.
    An analysis of strain localization and formation of face wrinkles in edge-wise loaded corrugated sandwich panels using a continuum damage model2015Inngår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 56-57, s. 248-257Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper examines the compressive failure mechanism in edge-to-edge loaded corrugated sandwich panels. The formation of face wrinkles is specifically considered. A detailed finite element model of face sheets and web core of a sandwich panel was developed to provide insight on the failure mechanism. A gradient enhanced continuum damage theory was implemented to capture length effects caused by the material microstructure including formation of damage in the face sheets and core. Distributions of strains in the face sheets determined from finite element analysis (FEA) are compared to experimentally measured strains. The predicted location and orientation of the face wrinkle, as indicated by high values of the second principal strain, agrees well with experimental observations. Load vs. out-of-plane deflection curves obtained from FEA with the gradient enhanced damage material model are compared to those obtained from a linear-elastic material model and experimentally determined curves. The gradient enhanced solution gives qualitatively better agreement with experimental results, although the magnitudes of strains are less than those determined experimentally. 

  • 3294.
    Åslund, Pär
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Hernández-Pérez, Adrián
    Hägglund, Rickard
    Isaksson, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    In situ XCT study of failure mechanisms in corrugated boards subjected to out-ofplane compressionManuskript (preprint) (Annet vitenskapelig)
  • 3295.
    Åslund, Pär
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Hägglund, Rickard
    SCA R and D Centre, Box 716, SE-851 21 Sundsvall, Sweden.
    Carlsson, Leif
    Department of Mechanical Engineering, Florida Atlantic University, Boca Raton, FL 33431, USA .
    Isaksson, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap. Applied Mechanics, The Ångström Laboratory, Uppsala University, Box 534, SE-751 21 Uppsala, Sweden .
    An analysis of strain localization and formation of face wrinkles in edge-wise loaded corrugated sandwich panels using a continuum damage model2015Inngår i: International Journal of Solids and Structures, ISSN 0020-7683, E-ISSN 1879-2146, Vol. 56-57, s. 248-257Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper examines the compressive failure mechanism in edge-to-edge loaded corrugated sandwich panels. The formation of face wrinkles is specifically considered. A detailed finite element model of face sheets and web core of a sandwich panel was developed to provide insight on the failure mechanism. A gradient enhanced continuum damage theory was implemented to capture length effects caused by the material microstructure including formation of damage in the face sheets and core. Distributions of strains in the face sheets determined from finite element analysis (FEA) are compared to experimentally measured strains. The predicted location and orientation of the face wrinkle, as indicated by high values of the second principal strain, agrees well with experimental observations.Load vs. out-of-plane deflection curves obtained from FEA with the gradient enhanced damage material model are compared to those obtained from a linear-elastic material model and experimentally determined curves. The gradient enhanced solution gives qualitatively better agreement with experimental results, although the magnitudes of strains are less than those determined experimentally.

  • 3296.
    Åslund, Pär
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Avdelningen för naturvetenskap.
    Hägglund, Rickard
    SCA R&D Centre, Sundsvall, Sweden.
    Carlsson, Leif
    Department of Mechanical Engineering, Florida Atlantic University, Boca Raton, FL, United States .
    Isaksson, Per
    Applied Mechanics, The Ångström Laboratory, Uppsala University, Uppsala, Sweden .
    Modeling of global and local buckling of corrugated board panels loaded in edge-to-edge compression2014Inngår i: Journal of Sandwich Structures and Materials, ISSN 1099-6362, E-ISSN 1530-7972, Vol. 16, nr 3, s. 272-292Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Detailed structural nonlinear finite element modeling of a sandwich panel with corrugated core is performed in this study. A simply supported panel is loaded in uniaxial compression well into the regimes of global panel buckling and local face sheet buckling. The highly nonlinear load versus in-plane and out-of-plane displacement responses obtained from finite element analysis agree reasonably well with experimental results, but the model slightly overpredicts the maximum load. The difference between experiments and predictions is attributed to damage of the corrugated paper web introduced during manufacture of the core and corrugated board. Computations of the buckling also results in a slight thickness reduction of the panel for a large range of face and web thicknesses identify lower thickness limits when the web loses its ability to contribute to the compressive strength of the panel. The highly nonlinear response associated with local and global buckling also results in thickness reduction of the panel.

  • 3297.
    Åslund, Pär
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    Isaksson, Per
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap, teknik och matematik.
    A note on the nonlinear mechanical behavior of planar random network structures subjected to in-plane compression2011Inngår i: Journal of composite materials, ISSN 0021-9983, E-ISSN 1530-793X, Vol. 45, nr 25, s. 2697-2703Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The microstructural effect on the mechanical behavior of idealized two-dimensional random fiber networks subjected to in-plane compression is studied. A finite element model utilizing nonlinear beam elements assuming a linearly elastic material is developed. On a macroscopic level, random fiber networks often display an asymmetric material behavior when loaded in tension and compression. In mechanical models, this nonlinearity is traditionally described using continuum elastic-inelastic and/or damage models even though using a continuum approach risks overlooking microstructural effects. It is found that even though a linear elastic material model is used for the individual fibers, the network gives a nonlinear response in compression. The nonlinearity is found to be caused by buckling of individual fibers. This reversible nonlinear mechanism is limited in tensile loading and hence offers an alternative explanation to the global asymmetry of random fiber networks.

  • 3298.
    Åstrand, Anders P.
    et al.
    Umeå University. Department of Applied Physics and Electronics.
    Jalkanen, Ville
    Umeå University. Department of Applied Physics and Electronics.
    Andersson, Britt M.
    Umeå University. Department of Applied Physics and Electronics.
    Lindahl, Olof
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Detection of stiff nodules embedded in soft tissue phantoms, mimicking cancer tumours, using a tactile resonance sensor2014Inngår i: Journal of Biomedical Science and Engineering, ISSN 1937-6871, E-ISSN 1937-688X, Vol. 7, nr 4, s. 181-193Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: Prostate cancer (PCa) is the most common form of cancer among males in Europe and in the USA and the most common curative treatment is removal of the prostate, i.e. prostatectomy. After the removal, the prostate is histopathologically analysed. One area of interest is to examine the perifery of the prostate, as tumours on and near the surface can indicate that the PCa has spread to other parts of the body. There are no current methods to examine the surface of the prostate at the time of surgery. Tactile resonance sensors can be used for detecting areas of different stiffness in soft tissue. Human prostate tissue affected by cancer is usually stiffer than healthy tissue, and for this purpose, a tactile resonance sensor was developed. The aim of this study was to investigate the depth at which embedded stiffer volumes could be detected, using soft tissue phantoms. Methods: With the tactile resonance sensor used in this study, the shift of the resonance frequency and the force at contact with tissue can be measured, and combined into a tissue stiffness parameter. The detection sensitivity of the sensor at impression depths, 0.4 and 0.8 mm, was measured for detection of inserted nodules of stiff silicone in softer silicone and in chicken muscle tissue, mimicking prostate tissue with cancer tumours. Results: Measurements on the silicone samples detected the hidden stiffer object at a depth of 1 - 4 mm with a difference in the stiffness parameter of 80 - 900 mN/kHz (p < 0.028, n = 48). At the depth 5 - 6 mm the difference was smaller but still significant < 30 mN/kHz (p < 0.05, n = 24). For the measurements on chicken muscle, the detectable depth was 4 mm (p < 0.05, n = 24). Conclusion: This model study suggests that, with only a small impression depth of ≤1 mm, the resonance sensor system described here can detect stiffness variations located at least 4 mm in silicone and chicken muscle, mimicking tumours in prostate tissue.

  • 3299.
    Åstrand, Erik
    et al.
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Forskningsmiljön produktionsteknik(PTW). Volvo Construction Equipment AB, Braås, Sweden .
    Stenberg, T.
    Royal Institute of Technology (KTH), Department of Aeronautical and Vehicle Engineering, Division of Lightweight Structures, Stockholm, Sweden .
    Jonsson, B.
    Volvo Construction Equipment AB, Braås, Sweden .
    Barsoum, Z.
    Royal Institute of Technology (KTH), Department of Aeronautical and Vehicle Engineering, Division of Lightweight Structures, Stockholm, Sweden .
    Welding procedures for fatigue life improvement of the weld toe2016Inngår i: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 60, nr 3, s. 573-580Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents the results of an experimental study of gas metal arc welded, GMAW, cruciform joints made of common construction steel S355. The hypothesis is that smooth undercuts in as welded conditions can give enhanced fatigue properties similarly as post treated welds. Undercuts are generally seen as a defect or imperfection. Welders try to avoid these and repair them when they occur, which result in increased production lead time. Post weld improvement methods i.e. grinding or high-frequency-impact treatment (HFMI) as fatigue-enhancing post-treatment methods enforce amongst other effects a certain smooth undercut-shaped groove in the treated weld toe region. The obtained shallower weld toe transition reduces the geometrical notch effect and increases fatigue strength. This paper presents a study whereas welded specimens with a weld toe geometry similar to what is obtained by weld toe grinding or HFMI-treatment, has been produced, fatigue tested and analyzed. The improvement of the fatigue strength is comparable to post-weld treated specimens. It has proven to be an efficient way to achieve high-quality welds without introducing any additional operations in production, thus enabling weight reduction using cost-effective methods.

  • 3300.
    Åström, E.
    et al.
    LKAB R&D, Luleå.
    Bonomi, Germano
    Department of Mechanical and Industrial Engineering, University of Brescia.
    Calliari, Irene
    Department of Industrial Engineering, University of Padova.
    Calvini, Piero
    Department of Physics, University of Genova and Sezione INFN di Genova.
    Checchia, Paolo
    INFN Sezione di Padova.
    Donzella, Antonietta
    Department of Mechanical and Industrial Engineering, University of Brescia.
    Faraci, E.
    Centro Sviluppo Materiali SPA, Rome.
    Forsberg, Fredrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gonella, F.
    INFN Sezione di Padova.
    Hu, X.
    Swerea MEFOS AB, Luleå.
    Klinger, Joel A.
    INFN Sezione di Padova.
    Sundqvist Ökvist, Lena
    Swerea MEFOS AB, Luleå.
    Pagano, Davide
    Department of Mechanical and Industrial Engineering, University of Brescia.
    Rigoni, Andrea
    Department of Physics and Astronomy, University of Padova.
    Ramous, Emilio
    Department of Industrial Engineering, University of Padova.
    Urbani, M.
    Department of Physics and Astronomy, University of Padova.
    Vanini, Sara
    Department of Physics and Astronomy, University of Padova.
    Zenoni, Aldo
    Department of Mechanical and Industrial Engineering, University of Brescia.
    Zumerle, Gianni
    Department of Physics and Astronomy, University of Padova.
    Precision measurements of linear scattering density using muon tomography2016Inngår i: Journal of Instrumentation, ISSN 1748-0221, E-ISSN 1748-0221, Vol. 11, nr P7010Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We demonstrate that muon tomography can be used to precisely measure the properties of various materials. The materials which have been considered have been extracted from an experimental blast furnace, including carbon (coke) and iron oxides, for which measurements of the linear scattering density relative to the mass density have been performed with an absolute precision of 10%. We report the procedures that are used in order to obtain such precision, and a discussion is presented to address the expected performance of the technique when applied to heavier materials. The results we obtain do not depend on the specific type of material considered and therefore they can be extended to any application

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