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  • 1.
    Aare, Magnus
    KTH, Tidigare Institutioner (före 2005), Flygteknik.
    Prevention of head injury by a new type of helmet system2002Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 2.
    Berggren, Daniel
    KTH, Tidigare Institutioner                               , Flygteknik.
    Investigation of limit cycle oscillations considering geometric nonlinearities2002Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 3.
    Berggren, Daniel
    KTH, Tidigare Institutioner, Flygteknik.
    Investigation of limit cycle oscillations for a wing section with nonlinear stiffness2004Inngår i: Aerospace Science and Technology, ISSN 1270-9638, E-ISSN 1626-3219, Vol. 8, nr 1, s. 27-34Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A wind tunnel experiment is designed with the objective to obtain well-behaved limit cycle oscillations for a wing section with two degrees of freedom, translation and rotation, in two-dimensional flow. This is accomplished using a setup of linear springs so that the resulting moment is a nonlinear function of the rotation angle. The experimental setup is designed so that the amplitudes of the limit cycle oscillations are sufficiently low to motivate the use of linear aerodynamics in the analysis. The experimental results are compared to analyses for two different configurations, and the agreement is fairly good.

  • 4.
    Borglund, Dan
    KTH, Tidigare Institutioner                               , Flygteknik.
    Active nozzle control and integrated design optimization of a beam subject to fluid-dynamic forces.1999Inngår i: Journal of Fluids and Structures, ISSN 0889-9746, E-ISSN 1095-8622, Vol. 13, nr 2, s. 269-287Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Active nozzle control is used to improve the stability of a beam subject to forces induced by fluid flow through attached pipes. The control system has a significant effect on the structural stability, making both flutter and divergence type of instabilities possible. The stability analysis is carried out using a state-variable approach based on a finite element formulation of the structural dynamics. The simultaneous design of the control system and the beam shape minimizing structural mass is performed using numerical optimization. The inclusion of the control system in the optimization gives a considerable reduction of the structural mass but results in an optimal design which is very sensitive to imperfections. Using a simple model of the control system uncertainties, a more robust design is obtained by solving a modified optimization problem. Throughout the study, the theoretical findings are verified by experiments.

  • 5.
    Borglund, Dan
    KTH, Tidigare Institutioner                               , Flygteknik.
    Aeroservoelastic design optimization with experimental verification2001Inngår i: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 38, nr 5, s. 958-961Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A demonstration of integrated design optimization of an aeroservoelastic system was presented. It was shown that the simultaneous design of structural and control system required a two-step procedure to result in a minimum weight design and a control law that is well-designed for all operating conditions. The essential dynamics was predicted using a aeroservoelastic model, and final design with 42% less weight penalty was obtained using the integrated approach.

  • 6.
    Borglund, Dan
    KTH, Tidigare Institutioner                               , Flygteknik.
    Control and optimization of pipes conveying fluid1998Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 7.
    Borglund, Dan
    KTH, Tidigare Institutioner                               , Flygteknik.
    Control and optimization of structures with fluid interaction2000Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Various problems on the optimal design of elastic structures subject to nonconservative fluid-dynamic forces are considered. The optimal design problem istypically posed as minimizing structural weight subject to constraints on structural stability. Traditionally, structural dimensions and orientations of fibercomposite materials are common design variables. It is demonstrated that the structural weight can be reduced further by including the design of a stabilizingcontrol system in the structural design optimization, giving an integrated optimization problem where both structural and control system parameters are used as design variables. The integrated approach may result in a design with significantly improved performance compared to traditional methods, both in terms of reduced structural weight and control system performance. Using optimization for design of mechanical systems with nonconservative external load tends to increase the likelihood of obtaining a design which is very sensitive to imperfections. As a result, the predicted performance of the optimal design may not be achieved in practice. The importance of this fundamental difficulty is emphasized throughout the thesis by comparing numerically obtained results to experiments.

    The first part of the thesis is concerned with the stability and optimal design of a beam subject to forces induced by fluid flow through attached pipes. A nozzle control system deflecting the fluid jet at the beam tip is used to improve the stability of the system. The simultaneous design of the control system and the beam shape minimizing structural mass is performed using numerical optimization. The inclusion of the control system in the optimization gives a considerable reduction of the beam weight but results in an optimal design which is very sensitive to imperfections. An optimal design with improved robustness is obtained by solving a modified optimization problem. The stability of a flexible wing structure with a controllable trailing edge flap is investigated. Due to uncertainties in the numerical stability analysis, the wing is predicted to become unstable at a significantly higher speed than what is observed in wind tunnel tests. Two different approaches to stabilize the wing in flutter is demonstrated. First, numerical optimization is used to design a controller which at each flow speed maximizes the damping of the flutter mode observed in the wind tunnel experiment. Second, an integrated approach is adopted, where a simultaneous mass balancing and control law design is performed. It is argued that a two-step procedure may be required to obtain a design with minimum weight and a control law that is well-defined for all operating conditions.

    Fulltekst (pdf)
    FULLTEXT01
  • 8.
    Borglund, Dan
    KTH, Tidigare Institutioner                               , Flygteknik.
    On the optimal design of pipes conveying fluid.1998Inngår i: Journal of Fluids and Structures, ISSN 0889-9746, E-ISSN 1095-8622, Vol. 12, nr 3, s. 353-365Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The stability and optimal design of a beam subject to forces induced by fluid flow through attached pipes is investigated. The structure is assumed to have the same dynamics as a fluid-conveying pipe, and the dynamic stability is analysed using a finite element formulation of the linear equation of motion. The optimal design problem of minimizing the structural mass at fixed critical flow speed is solved. The numerical results are compared to experiments with satisfactory agreement, provided that the lower bounds of the beam dimensions are properly chosen. The influence of structural damping on the critical flow speed is significant, and is found to be strongly design-dependent.

  • 9.
    Borglund, Dan
    et al.
    KTH, Tidigare Institutioner                               , Flygteknik.
    Kuttenkeuler, Jakob
    KTH, Tidigare Institutioner                               , Flygteknik.
    Active wing flutter suppression using a trailing edge flap2002Inngår i: Journal of Fluids and Structures, ISSN 0889-9746, E-ISSN 1095-8622, Vol. 16, nr 3, s. 271-294Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aeroservoelastic behaviour of a thin rectangular wing with a controllable trailing edge flap is investigated. A rather high aspect ratio motivates a numerical model based on linear beam theory for the structural dynamics and strip theory for the unsteady aerodynamic loads. Experimental flutter testing shows good agreement with the numerical stability analysis, and the impact of the trailing edge flap on the dynamics is verified by open-loop testing. The problem of stabilizing the wing utilizing the trailing edge flap is posed, and the design of a fixed-structure feedback controller is performed using numerical optimization. The problem of maximizing closed-loop modal damping with constraints on actuator performance is solved for a sequence of flow speeds and the obtained controller is synthesized using gain scheduling. The fairly large predicted increase in critical speed is experimentally verified with satisfactory accuracy.

  • 10.
    Brolin, Karin
    KTH, Tidigare Institutioner                               , Flygteknik.
    Cervical Spine Injuries - Numerical Analyses and Statistical Survey2002Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Injuries to the neck, or cervical region, are very importantsince there is a potential risk of damage to the spinal cord.Any neck injury can have devastating if not life threateningconsequences. High-speed transportation as well as leisure-timeadventures have increased the number of serious neck injuriesand made us increasingly aware of its consequences.Surveillance systems and epidemiological studies are importantprerequisites in defining the scope of the problem. Thedevelopment of mechanical and clinical tools is important forprimary prevention of neck injuries.

    Thus, the main objectives of the present doctoral thesisare:- To illustrate the dimension of cervical injuries inSweden,- To develop a Finite Element (FE) model of the uppercervical spine, and- To study spinal stability for cervical injuries.

    The incidence studies were undertaken with data from theinjury surveillance program at the Swedish National Board ofHealth and Welfare. All in-patient data from Swedish hospitals,ranging over thirteen years from 1987 to 1999, were analyzed.During this period 14,310 nonfatal and 782 fatal cervicalinjuries occurred. The lower cervical spine is the mostfrequent location for spinal trauma, although, this changeswith age so that the upper cervical spine is the most frequentlocation for the population over 65 years of age. The incidencefor cervical fractures for the Swedish population decreased forall age groups, except for those older than 65 years of age.The male population, in all age groups, has a higher incidencefor neck fractures than females. Transportation relatedcervical fractures have dropped since 1991, leaving fallaccidents as the sole largest cause of cervical trauma.

    An anatomically detailed FE model of the human uppercervical spine was developed. The model was validated to ensurerealistic motions of the joints, with significant correlationfor flexion, extension, lateral bending, axial rotation, andtension. It was shown that an FE-model could simulate thecomplex anatomy and mechanism of the upper cervical spine withgood correlation to experimental data. Three studies wereconducted with the FE model. Firstly, the model of the uppercervical spine was combined with an FE model of the lowercervical spine and a head model. The complete model was used toinvestigate a new car roof structure. Secondly, the FE modelwas used for a parameter study of the ligament materialcharacteristics. The kinematics of the upper cervical spine iscontrolled by the ligamentous structures. The ligaments have tomaintain spinal stability while enabling for large rotations ofthe joints. Thirdly, the FE-model was used to study spinalinjuries and their effect on cervical spinal stability inflexion, extension, and lateral bending. To do this, the intactupper cervical spine FE model was modified to implementruptures of the various spinal ligaments. Transection of theposterior atlantooccipital membrane, the ligametum flavum andthe capsular ligament had the most impact on flexion, while theanterior longitudinal ligament and the apical ligamentinfluenced extension.

    It is concluded that neck injuries in Sweden is a problemthat needs to be address with new preventive strategies. It isespecially important that results from the research on fallaccidents among the elderly are implemented in preventiveprograms. Secondly, it is concluded that an FE model of thecervical region is a powerful tool for development andevaluation of preventive systems. Such models will be importantin defining preventive strategies for the future. Lastly, it isconcluded that the FE model of the cervical spine can increasethe biomechanical understanding of the spine and contribute inanalyses of spinal stability.

    Fulltekst (pdf)
    FULLTEXT01
  • 11.
    Bull, Peter H.
    KTH, Tidigare Institutioner                               , Flygteknik.
    Structural integrity of sandwich elements with localized damage2001Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 12.
    Burman, Magnus
    KTH, Tidigare Institutioner                               , Flygteknik.
    Fatigue crack initiation and propagation in sandwich structures1998Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    The focus throughout this thesis is on the fatigue characteristics of core materials used insandwich structures. Three sandwich configurations are investigated, two with cellular foamsand one with honeycomb core material These corresponds to typical materials and dimensionsused in the marine and aeronautical industry.A modified four-point bending rig, which enables reversed loading, is successfully used forconstant amplitude fatigue tests of all material configurations. The core materials are tested asused in composite sandwich beams and through the design of the specimens the desiredfailure is in shear of the core. Analyses and inspections during and after the tests supports thetheory that the fracture initiation and fatigue failure occurs in a large zone of the core withwell distributed micro cracks rather than a single propagating crack. The fatigue test resultsare plotted in stress life diagrams including a Weibull type function which provides a goodaccuracy curve fit to the results. The fatigue life of the core materials is found to be reducedwith a increased load ratio, R.The influence on the strength and fatigue performance on sandwich beams with two types ofcore damages, an interfacial disbond and a flawed butt-joint, are experimentally investigated.The fatigue failure initiates at the stress intensity locations which are present due to the predamage.The specimens with flawed butt-joints display a fatigue crack propagation in theinterface between the core and face of the sandwich while the crack propagates through thethickness of the beams where an initial interface flaw is present. A fatigue failure predictionmodel is suggested which utilises the fatigue performance of undamaged beams and thestrength reduction due to the damages. The approach is correlated with results from fatiguetesting and satisfactory correlation is found.A uni-axial fatigue tests method is developed which simplifies the rig and specimenscompared to the four point bend method. A comparison between the results from uni-axialtension/compression fatigue tests and shear fatigue tests shows good correlation, although theR-dependency differs in some cases.The fatigue crack propagation rates are investigated for two configurations: crackspropagating in pure foam core material and cracks propagating in the core material near andalong a sandwich face/core interface. The rate at which a crack propagates stable in the socalled Paris’ regime is extracted for both Mode I and Mode II loading. The agreement betweenthe Mode I crack propagation rate in the pure foam and in the core/face sandwich interfacelayer supports the theory that the crack actually propagates in the sandwich core beneath astiffened resin rich layer present in the face/core interface. The stress intensity thresholds andthe limits at which the crack growth becomes unstable are further established.Acoustic Emission (AE) is used to monitor crack initiation and growth in the core, duringboth static and fatigue loading. It is found that the approximate location of AE-hits can bedetermined which demonstrates that AE has a potential both as an non destructive testing tooland to study the failure process of non-visible sub-surface damages in sandwich structures.

    Fulltekst (pdf)
    FULLTEXT01
  • 13.
    Burman, Magnus
    et al.
    KTH, Tidigare Institutioner (före 2005), Flygteknik.
    Stig, Fredrik
    Zenkert, Dan
    KTH, Tidigare Institutioner (före 2005), Farkost- och flygteknik.
    Blister propagation in sandwich panels2019Inngår i: Journal of Sandwich Structures and Materials, ISSN 1099-6362, E-ISSN 1530-7972, Vol. 21, nr 5, s. 1683-1699Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper deals with the problem of face/core interfacial disbonds in sandwich panels that are pressurised, i.e. the disbond has an initial fluid pressure that causes the disbond to deform. The problem is often referred to as a blister. The panel with a blister is then subjected to an in-plane compressive load. Four different panels are analysed and tested, having different size disbonds and different initial internal pressure. The cases are analysed using a finite element approach where the blister is modelled using fluid elements enabling the pressure inside the blister to vary as the in-plane load is applied. The analysis uses non-linear kinematics, and in each load step, the energy release rate is calculated along the disbond crack front. This model is used for failure load predictions. The four cases are then tested experimentally by filling a pre-manufactured disbond cavity with a prescribed volume of air. This air volume is then entrapped, and the panel is subjected to an in-plane compressive load. The load and blister pressures are measured throughout the test and compared with the finite element analysis. Surface strains and blister deformations are also measured using digital correlation measurements. The predicted failure loads compare well with the experimental results, and so does the blister pressures, the latter at least qualitatively.

  • 14.
    Carlsson, Martin
    KTH, Tidigare Institutioner                               , Flygteknik.
    On the design and testing of aeroelastic wind tunnel models2002Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 15.
    Croander, Carin
    KTH, Tidigare Institutioner                               , Flygteknik.
    Control applications in aeronautics1999Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 16.
    Dahle, Tormod
    KTH, Tidigare Institutioner                               , Flygteknik.
    Spectrum fatique of welded components2001Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 17.
    de Try, Fredrik
    KTH, Tidigare Institutioner, Flygteknik.
    Flight-path reconstruction using numerical optimization2004Inngår i: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 41, nr 4, s. 959-962Artikkel i tidsskrift (Fagfellevurdert)
  • 18.
    Dozolme, Antoine
    KTH, Tidigare Institutioner                               , Flygteknik.
    Simulation of water flow in a centrifugal pump: the N-PUMP2001Licentiatavhandling, monografi (Annet vitenskapelig)
  • 19.
    Fagerberg, Linus
    KTH, Tidigare Institutioner                               , Flygteknik.
    Wrinkling in sandwich panels for marine applications2001Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 20.
    Fredriksson, Mats H.
    et al.
    KTH, Tidigare Institutioner                               , Mekanik.
    Borglund, Dan
    KTH, Tidigare Institutioner                               , Flygteknik.
    Nordmark, Arne B.
    KTH, Tidigare Institutioner                               , Mekanik.
    Experiments on the Onset of Impacting Motion Using a Pipe Conveying Fluid1999Inngår i: Nonlinear dynamics, ISSN 0924-090X, E-ISSN 1573-269X, Vol. 19, nr 3, s. 261-271Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The transition from stable periodic nonimpacting motion to impacting motion, due to variations of parameters, is observable in a wide range of vibro-impact systems. Recent theoretical studies suggest a possible scenario for this type of transition. A key element in the proposed scenario is fulfilled if the oscillatory motion involved in the transition is born in a supercritical Hopf bifurcation. If the onset of impacting motion is close to the Hopf bifurcation, the impacting motion is likely to be chaotic. A numerical simulation of a system of articulated pipes conveying fluid is used to illuminate the theory. An experimental setup is presented, where a cantilevered pipe conveying fluid is unilaterally constrained. Results from experiments are found to be in good qualitative agreement with the theory.

  • 21.
    Friberg, Magnus
    KTH, Tidigare Institutioner                               , Flygteknik.
    Fastener load distribution and interlaminar stresses in composite laminates2000Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 22.
    Gustavsson, Anders
    KTH, Tidigare Institutioner                               , Flygteknik.
    Fatique behaviour of press formed sheet steels1997Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 23.
    Halldin, Peter
    KTH, Tidigare Institutioner                               , Flygteknik.
    Prevention and prediction of head and neck injury in traffic accidents - using experimental and numerical methods2001Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Injuries to the head and neck system are potentially amongthe most serious injuries in humans, since they may damage thespinal cord. It is therefore important to develop safetysystems that can prevent injuries to the neuro- system, therebyreducing human suffering and costs to society. In thedevelopment of new and improved systems for injury preventionin car accidents, accurate criteria for predicting injury dueto mechanical forces in different impact loading situations areneeded to guide the development of improved safety systems.

    This thesis deals with three aspects related to theprevention of injury to the head and neck. First anexperimental and numerical study investigated how to reduce theforces on the head and neck in frontal car crashes. Secondly, afinite element model of the human neck was developed. Finally,head protection in oblique motorcycle crashes wasexperimentally and numerically studied.

    Specifically, the first study is focused on a headprotection system for reducing the forces to the head and neckduring frontal car accidents. An Experimental Head RestraintConcept (EHRC), a safety belt for the head, was designed to actas a complement or alternative to the conventional airbag. TheEHRC was evaluated experimentally in frontal collision for acrash severity of 11 m/s, and numerically in frontal collisionfor crash severities of 11 and 15 m/s. Experimental dataobtained from a frontal barrier test (11 m/s) showed a 67%reduction in the HIC value from 411 (without EHRC) to 136 (withEHRC). The EHRC clearly has a potential role in the search forprimary prevention of neurotrauma injuries in frontal carcrashes. However, it should only be seen as an experimentaltool, although it clearly has a potential market for transportof disabled people.

    The EHRC changed the characteristics of the response of theneck. The bending moment in the neck was shown to increase by afew percent when the EHRC was used. With available neck injurycriteria, it was not possible to determine whether this changein response is significantly negative. Therefore, there is astrong need for more advanced injury criteria for the neck inorder to optimize such a safety system.

    To improve the knowledge of injury mechanisms and injurycriteria of the neck, a research was initiated to develop adetailed finite element model of the cervical spine. The modelis aimed to predict injuries in the neck for different types ofload modes and to work as a tool to create global injurycriteria from local tissue-based failure criteria.

    The finite element model of the cervical spine excludingmuscles has been validated in compression-flexion where a goodcorrelation was found with experimental data. By the model itwas possible to predict experimentally found injuries as theHangman's fracture and the model was used to investigate a newcar roof structure.

    In the last study a new helmet design was presented with animproved protection against tangential impacts. In this worktwo new oblique helmet testing methods were used to investigatethe behavior of the helmet. This study showed thatit ispossible to reduce the rotational energy by up to 50% by addinga low friction layer between the shell and the liner.

  • 24.
    Hallström, Stefan E.
    KTH, Tidigare Institutioner                               , Flygteknik.
    A generalised fracture mechanics approach to fracture initiated at corners1997Doktoravhandling, med artikler (Annet vitenskapelig)
  • 25.
    Ireman, Tomas
    KTH, Tidigare Institutioner                               , Flygteknik.
    Design of composite structures containing bolt holes and open holes1999Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis is concerned with stress analysis and strengthprediction in composite laminates containing bolt holes andopen holes. It covers both two- and three-dimensional analyses,and experiments have been carried out to determine criteriaparameters and to validate the analysis methods.The objective of the work on two-dimensional analysismethods has been to develop accurate and cost-efficient stressanalysis and failure prediction methods valid for complexloading conditions. Both the finite element method and a methodbased on Lekhnitskii’s complex stress functions have beenused to determine the stress distribution around the hole. Inthe case of bolted laminates, the frictionless contact betweenthe bolt and the hole has been taken into account. Differentfailure criteria, including the Point Stress Criterion (PSC)and the Damage Zone Criterion (DZC) have been used to predictthe strength of test specimens subjected to complex loadingconditions. In the case of bolted laminates, simple failurecriteria for preliminary design are proposed. The validity ofthese criteria is demonstrated on multi-fastener tension- andshear-loaded test specimens. A comprehensive test programme wascarried out to establish criteria parameters and to generatedata to validate the stress analysis and strength predictionunder complex loading conditions. A special test fixture wasdesigned for this purpose. Good agreement was found betweenpredicted and measured results.The objective of the work on three-dimensional methodshas been to develop tools for three- dimensional stress andfailure analyses and to study the effect of various factors onthe strength of single-lap joints. An experimental programmewas conducted to characterize the failure mechanisms and tomeasure deformation, strain, and bending effects. Athree-dimensional finite element model of a bolted single-lapjoint has been developed to determine the non-uniform stressdistribution through the thickness of the laminate in thevicinity of the hole. The model was validated against measuredstrains and displacements from the experimental programme. Theagreement between predicted and experimental results wasgenerally good. In the failure characterisation part of theexperimental programme, it was found that the failure of thejoints was dominated by kinking. A failure analysis procedurefor the prediction of bearing failure dominated by kinking hasbeen developed. In this procedure, failure is predicted using aquadratic failure criterion evaluating fibre stress andtransverse shear stress at a characteristic distance from theedge of the bolt hole. Experimental results were used tovalidate the analysis procedure and good agreement was foundbetween predicted and experimental failure loads. The analysisprocedure were then used study the effect of eight differentparameters which affect the strength of bolted compositelaminates. The parameters studied were: laminate thickness,lay-up, bolt diameter, bolt configuration (countersunk orprotruding head), friction, clamping force, clearance andlateral support. The parametric study was organised as areduced two-level factorial test. The results from theparametric study show that laminate thickness, friction,clamping force and bolt configuration are the parameters whichhave the strongest influence on the strength of the joints.

    Key words:Composite, laminate, bolted joints, openholes, static strength, failure characterization, damage,complex loading, stress analysis, three-dimensional analysis,contact analysis, failure prediction, factorial test

    Fulltekst (pdf)
    FULLTEXT01
  • 26.
    Isikveren, Askin T.
    KTH, Tidigare Institutioner                               , Flygteknik.
    Quasi-analytical Modelling and Optimisation Techniques for Transport Aircraft Design2002Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The research work presented here focuses on the subject oftransport aircraft design at the pre-design or conceptuallevel. The primary topics addressed are: (1) generation of avast array of new quasi-analytical expressions to permit aconceptual treatment of commercial and business transportaircraft with adequate sensitivity for more advanced tradestudies; (2) review and adoption of a method to predictstability and control characteristics (using the Mitchellmethod); (3) a study of the relative merits between variousmethods in facilitating an expedient and robust constrainedmulti-objective optimisation result within the context oftraditional conceptual design problems (Genetic Algorithms andNelder-Mead Simplex search); (4) creation of a software packageas a new and unique conceptual tool that permits the generationof design proposals in an accurate yet expeditious manner; and,(5) practical demonstration of the new conceptual designsoftware package by undertaking some actual aircraft designproposals.

    The design problem is addressed using mostly closed formsolutions but transcendental expressions with much simplifiednumerical scheme algorithms have also been adopted for sake ofaccuracy. Various new models have been proposed for atmosphericproperties, geometry, gas-turbine engine performance, low-speedand high-speed aerodynamic characteristics, minimum controlspeed limited balanced field estimation, asymmetric flight,and, en route performance characteristics including definitionof operationally permissible speed schedules and flighttechniques for payload-range/fixed sector profiles optimised interms of maximum specific air range, minimum fuel, minimumtime, minimum direct operating cost and maximum profit/returnon investment. The work was extended further to include issuesrelating to the impact of vehicular attributes to pricing themarket is willing toabsorb. Useful information regarding howthese individual computational elements of the methodology maybe integrated for the purpose of constructing coherent modularsub-spaces and formulation of a basic inter-disciplinarycoupling is also presented. The mathematical foundationsderived in this work have lead to an array of tangibleconclusions that aid the conceptual designer via implicitguidelines to achieve truly balanced design concepts.

    In an explicit demonstration of methodology effectivenessand relative simplicity, a software package called QCARD orQuick Conceptual Aircraft Research and Development was createdin the MATLAB environment. The new software system wasdeveloped to assist the designer in predicting, visualising andoptimising conceptual aircraft designs in a much moreinteractive and far-reaching manner than what is afforded withcontemporary applications whilst emphasising speed and economyof effort.

    The methodology and software was employed for a 19 passengerturbofan commuter transport design using the cost effectiveWilliams International FJ44-2 engines. To complement this, afuselage stretch version of the baseline vehicle designed toaccommodate 31-34 passengers was also undertaken utilising agrowth version of the original FJ44 power plant. The minimumgoal for both of these concepts was to afford unparalleledcomfort through speed and spaciousness with a competitive edgeagainst turboprops in terms of economics and field performance.The final design effort involved proposal of a Trans-Atlantichigh-performance executive transport employing anunconventional Twin Oblique Lifting Surfaces, or, TOLSconfiguration. The intent here was to produce a new super-largebusiness jet able to operate up to low supersonic speeds withfield performance, en route fuel burn efficiency and costcomparable to that of contemporary business aircraft for thismarket segment.

    Keywords: aircraft, conceptual, design, specifications,atmosphere, geometry, weight, aerodyanmics, propulsion,operational performance, stability and control, constrainedmulti-objective optimisation, computer aided design, regional,business, high-transonic, low-supersonic.

  • 27.
    Jaafar, Mariatti
    KTH, Tidigare Institutioner                               , Flygteknik.
    The behaviour of continuous fiber impregnated thermoplastic (COFIT) woven system2001Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 28.
    Kelly, Gordon
    KTH, Tidigare Institutioner, Flygteknik.
    Load Introduction in Carbon Fibre Composites for Automotive Applications2002Licentiatavhandling, med artikler (Annet vitenskapelig)
    Fulltekst (pdf)
    FULLTEXT01
  • 29.
    Kleiven, Svein
    et al.
    KTH, Tidigare Institutioner                               , Flygteknik.
    Peloso, Paul M.
    von Holst, Hans
    KTH, Tidigare Institutioner                               , Flygteknik.
    The epidemiology of head injuries in Sweden from 1987 to 20002003Inngår i: Injury control and safety promotion, ISSN 1566-0974, E-ISSN 1744-4985, Vol. 10, nr 3, s. 173-180Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The purpose of the present study was to evaluate the variability in the annual head injury incidence rate in Sweden from 1987 to 2000. It was hypothesized that the annual incidence rate would decrease over time due to a variety of primary preventive strategies that have been introduced in Swedish society. We used the Hospital Discharge Register at the National Board for Health and Welfare and head injury codes 800-804, and 850-854 from ICD9 system and S2.0-S2.9, and S6.0-S6.9 codes from ICD-10 system. We evaluated the patterns of age, gender, external cause of injury (E-code), type of injury, length of hospital stay, and trends over time. Head injuries due to transportation collision were reduced over the 14-year period analysis. Falls persisted as the dominant cause of head injury. Overall, men had 2.1 times the incidence of head injury compared to women. There was a decline in younger ages experiencing a head injury over this interval, while the number of head injuries among elderly people increased over time. Concussion was about three times more frequent than fractures. Hematoma and diffuse or focal contusions had a much lower incidence rate than concussion. Concussions and fractures decreased over time. Diffuse or focal injuries showed a steady rate of occurrence over the study interval while hematoma increased. Although length of hospital stay varied widely from zero to more than 50 days, 73.6% of hospital days were confined to two days or less. The incidence rate is stable over this time frame. While head injuries attributable to transportation accidents decreased, falls made up an increasing proportion of head injuries. Since we observed an increase in head injuries among elderly, primary prevention strategies may need to be targeted at this age group, and at preventing falls.

  • 30.
    Kolsters, Hans
    KTH, Tidigare Institutioner                               , Flygteknik.
    Stiffness and strength of laser-welded sandwich panels2002Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 31.
    Kuttenkeuler, Jakob
    KTH, Tidigare Institutioner                               , Flygteknik.
    Aircraft composites and aeroelastic tailoring1998Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis treats various aspects of structural polymercomposites in aircraft applications. The mechanical performanceand quality of resin transfer molded (RTM) carbon fiberreinforced epoxy composites is studied. In a first part, the influence of manufacturing process parameters on the mechanicalbehavior of laminates is experimentally investigated. A number of process parameters are used as variables and performance ismeasured in terms of tensile and compressive strength as wellas interlaminar fracture toughness. The process parameters are concluded to have little affect on the measured properties. In a second part, the quality and structural performance of an entirely co-cured RTM manufactured aircraft control surfacedemonstrator is investigated. A series of quasi staticstructural tests using distributed loading is performed. Experimental results are compared with finite element analysis. Effects of impact damage on the performance are also studied.Good agreement is obtained between the predictions and the experiments.

    A nondestructive method for determination of elasticmaterial properties of orthotropic plates using naturalfrequencies is developed and verified. Finite elementcalculations of the natural frequencies of the plate are matched to experimentally determined frequencies using theelastic constants as variables. The method is successfully verified even for nontrivial specimen geometries with cornersingularities. Emphasis is on practical utilization ofknowledge about numerical and modeling errors as well asexperimental uncertainties.

    The optimal design of a thin orthotropic wing subject toaeroelastic constraints is studied using numerical methods andverified in low speed wind tunnel testing. The flutter speed ofthe wing is maximized using the laminate orientation asvariable. Further, the problem of increasing the flutter speed to a prescribed value using minimal amount of additional concentrated masses on a  fixed wing design is investigated. The main objective of the study is to verify that the performance of the optimized design can be achieved also in experiments. It is found that the optimal design is very sensitive to uncertainties in material and structural properties.Consequently, this has to be accounted for in the problemformulation. It is shown, and experimentally verified, that the robustness requirements on the optimal design can be met byreformulating the optimization problem.

  • 32.
    Kuttenkeuler, Jakob
    et al.
    KTH, Tidigare Institutioner                               , Flygteknik.
    Grenestedt, Joachim
    KTH, Tidigare Institutioner                               , Flygteknik.
    Influence of process parameters on mechanical behavior of RTM moldings1995Inngår i: Tenth International Conference on Composite Materials: III. Processing and Manufacturing; Whistler, British Columbia; Canada; 14-18 Aug. 1995., 1995, s. 261-268Konferansepaper (Annet vitenskapelig)
  • 33.
    Kuttenkeuler, Jakob
    et al.
    KTH, Tidigare Institutioner                               , Flygteknik.
    Grenestedt, Joachim
    KTH, Tidigare Institutioner                               , Flygteknik.
    Performance and quality of a resin transfer molded aircraft control surface1995Rapport (Annet vitenskapelig)
  • 34.
    Kuttenkeuler, Jakob
    et al.
    KTH, Tidigare Institutioner                               , Flygteknik.
    Ringertz, Ulf
    KTH, Tidigare Institutioner                               , Flygteknik.
    Aeroelastic design optimization with experimental verification1998Inngår i: Journal of Aircraft, ISSN 0021-8669, E-ISSN 1533-3868, Vol. 35, nr 3, s. 505-507Artikkel i tidsskrift (Fagfellevurdert)
  • 35.
    Kuttenkeuler, Jakob
    et al.
    KTH, Tidigare Institutioner                               , Flygteknik.
    Ringertz, Ulf
    KTH, Tidigare Institutioner                               , Flygteknik.
    Aeroelastic tailoring considering uncertainties in material properties1998Inngår i: Structural optimization (Print), ISSN 0934-4373, E-ISSN 1436-2503, Vol. 15, nr 3-4, s. 157-162Artikkel i tidsskrift (Fagfellevurdert)
  • 36.
    Le Moigne, Yann
    KTH, Tidigare Institutioner, Flygteknik.
    CFD simulations of delta wing pitching to high alpha2002Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 37.
    Levin, Klas
    KTH, Tidigare Institutioner                               , Flygteknik.
    Durability of Embedded Fibre Optic Sensors in Composites2001Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis concerns various aspects of the durability offibre optic sensors embedded in composite. Since repair orreplacement of embedded sensors is not generally possible, thefunctional reliability of embedded sensors is one of the mostimportant prerequisites for successful use. The main researchobjective was to investigate the interaction between the sensorand the composite, and how this is affecting the mechanical andoptical sensor response. Fibre optic sensors embedded incomposite structures induce local stress concentrations whenthe composite is subjected to mechanical loads andenvironmental changes such as temperature and moisture. Acomplex transfer of stresses through the interfaces between theembedded sensor and the composite occurs and can result inlarge local stresses in the composite and a significant changein the response of the embedded sensor. These stressconcentrations make the interfaces susceptible todebonding.

    The sensor performance was studied experimentally andnumerically. Some basic results were generated for the EFPI andBragg grating sensors. The phase-strain response was determinedduring static and fatigue loading. The results showed that thesensors were more reliable in compression than in tensilestatic and fatigue loading. Generally, the sensor reliabilityduring loading was significantly improved for the Bragg gratingsensors over that of the EFPI sensor, as an effect of thesensor geometry. This was also demonstrated in theinvestigations on impacts. Impacts do not necessarily result indamage in the composite, but might cause debonding or otherfailure modes in the sensor area. Large, local stressconcentrations occur at several positions in the EFPI sensor,which pointed out that this sensor type was not suitable forembedded applications.

    The shift in focus from the sensor concept based on the EFPIsensor to that based on the Bragg grating sensor manifesteditself in several studies. The calculated deformation fieldaround an embedded optical fibre was verified in experimentsusing a high-resolution moiré interferometric technique.Furthermore, the improvement in the coating technology wasverified. A significant higher interfacial strength wasobtained with the silane-treated glass surface. The resultsindicated that at least a twofold improvement of the shearstrength was obtained.

    To simultaneously measure the in-plane strain components andthe temperature change, embedded Bragg grating sensors werearranged in a rosette configuration. The relationship betweenthe optical response from each sensor and the strains in thelaminate was numerically and analytically established.

    Damage lead to stress redistribution in the sensor region,which may influence the output from the embedded Bragg gratingsensor. The effect was numerically evaluated for interfacialdamage, and was compared to that of a sensor with undamagedinterface. The results showed that debonding might have asignificant influence, in particular for combined thermal andmechanical loading.

    Keywords: composites, fibre optic sensor, embedded, EFPIsensor, Bragg grating sensor, durability, fatigue, impact,strain measurement, interface, stress analysis

    Fulltekst (pdf)
    FULLTEXT01
  • 38.
    Malmqvist, Johan
    et al.
    Chalmers University of Technology.
    Young, Pete Y.
    Massachusetts Institute of Technology.
    Hallström, Stefan
    KTH, Tidigare Institutioner, Flygteknik.
    Kuttenkeuler, Jakob
    KTH, Tidigare Institutioner, Flygteknik.
    Svensson, Thomas
    Linköping University.
    Lessons learned from design-build-test-based project courses2004Inngår i: Design 2004: Proceedings of the 8th International Design Conference, Vols 1-3 / [ed] Marjanovic, D, 2004, s. 665-672Konferansepaper (Fagfellevurdert)
  • 39. Mariatti, M.
    et al.
    Nasir, M.
    Ismail, H.
    Bäcklund, Jan
    KTH, Tidigare Institutioner, Flygteknik.
    Effect of hole drilling techniques on tensile properties of continuous fiber impregnated thermoplastic (COFIT) plain weave composites2004Inngår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 23, nr 11, s. 1173-1186Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The effect of hole drilling technique on tensile properties of COFIT plain weave composite using circular hole was investigated. As expected, the tensile properties of COFIT woven system decrease with increasing hole sizes. The laminate, which was drilled by orbital technique, seems to impart higher tensile properties and better damage resistance compared to those of conventional drilling technique. In order to predict the laminate strength with the presence of open hole, the Point Stress Criterion was used. Results indicate that good agreement was obtained between experimental and estimation tensile strengths.

  • 40.
    Matrat, Jérome
    KTH, Tidigare Institutioner                               , Flygteknik.
    Modelling of fibre optic sensors embedded in composites2001Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 41.
    McGarva, Lance
    KTH, Tidigare Institutioner                               , Flygteknik.
    Thermoplastic Composite Sandwich Components: Experimental and Numerical Investigation of Manufacturing Issues2002Doktoravhandling, med artikler (Annet vitenskapelig)
    Fulltekst (pdf)
    FULLTEXT01
  • 42.
    Mäkinen, Kjell
    KTH, Tidigare Institutioner                               , Flygteknik.
    Underwater shock loaded sandwich structures1999Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The effects of underwater explosions on ships have beenstudied ever since it was realised that explosions under watercould be accomplished. In order to study the response of asandwich structure in water, exposed to an underwaterexplosion, we need to have knowledge about the whole chain ofevents, i.e. THE EXPLOSION, THE FLUID-STRUCTURE INTERACTION andTHE RESPONSE OF SANDWICH STRUCTURES.

    There are several different kinds of loads generated by anunderwater explosion that might affect a vessel in water andthey are all very complex. At an explosion we have the initialshock wave that is transmitted through the water to thestructure. This initial shock wave, will give rise toadditional loads on the structure, when reflected on the watersurface and the sea bottom. The reflection on the water surfacecauses a zone of water just under the water surface to cavitateand the water surface to rise (spray dome). At the chargelocation we have the formation of the bubble, with itspulsation and migration towards the surface. At every bubbleminimum, a shock wave is generated which rapidly decreases inmagnitude for each pulsation. The bubble is also attracted tothe sea bottom and objects in the water, but rejected by thewater surface. However this is an area that is not covered inthis thesis. When the shock wave reaches a structure, thestructure moves away, but in the next instant when the pressureis applied, the structure is moving in the same direction asthe load and therefore the load pressure is decreased. As thewave hits the structure it bounces back and may causecavitation to occur at the fluid-structure interface. All thesephenomena must be taken into account when evaluating thepressure acting on a structural surface.

    Finally we have the response of the sandwich structure whichdepends on the many parameters that a sandwich structure ismade up of. We have the faces with their different properties,i.e. depending on reinforcement (fibre) material, reinforcement(fibre) direction and thickness (number of fibre layers). Thecore may vary in density and thickness. This gives us a verylarge number of possible sandwich configurations. However,since we are dealing with fast loading sequences the mass andits distribution in the structure are very important.

    Looking locally (transverse direction) at a sandwichstructure, the front face is first compressed into the corewhen hit by a shock wave. This initiates oscillation about thecore of the faces. This may cause significant transversetension in the faces and delamination may occur. This mode offailure has not been considered before and has to beinvestigated further in the future. Going from one dimension totwo dimensional problems leads to the study of sandwich beams.The change in behaviour of a sandwich beam when the parameterschange can in many cases be predicted by the use of a simpleexpression. In order to verify this, several numerical exampleswere analysed and some important conclusions were reached. Whenthe parameters of the sandwich beam change it is not only thestiffness of the beam that changes, but also the distributionof the energy between the faces and the core of the sandwich.This sometimes makes it very difficult to predict the completeresponse. For example, stiffer faces lead not only todecreasing deformation and face stress, but also to anincreasing core stress. This is due to the redistribution ofenergy between the faces and the core in the sandwich beam. Thebehaviour of three-dimensional structures, such as a sandwichpanel, is similar to that of a sandwich beam. One can use theexample of the beam to predict the change in the response of apanel when the parameters vary.This thesis does not try to cover the latest researchconcerning all the different phenomena occurring during anunderwater explosion. For some of the phenomena there are moreadvanced methods available. This is rather an attempt toprovide engineers with methods that can be used to solve thistype of problem.

  • 43.
    Norsell, Martin
    KTH, Tidigare Institutioner                               , Flygteknik.
    Optimal aircraft trajectors considering radar range constraints2001Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 44.
    Nyman, Tonny
    KTH, Tidigare Institutioner                               , Flygteknik.
    Fatigue and residual strength of composite aircraft structures1999Doktoravhandling, med artikler (Annet vitenskapelig)
    Fulltekst (pdf)
    FULLTEXT01
  • 45. Oddy, C.
    et al.
    Ekermann, Tomas
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Farkostteknik och Solidmekanik.
    Ekh, M.
    Fagerström, M.
    Hallström, Stefan
    KTH, Tidigare Institutioner (före 2005), Flygteknik.
    Evaluation of damage initiation models for 3D-woven fibre composites2019Inngår i: ECCM 2018 - 18th European Conference on Composite Materials, Applied Mechanics Laboratory , 2019Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Three dimensional (3D) fibre-reinforced composites have shown weight efficient strength and stiffness characteristics as well as promising energy absorption capabilities. In the considered class of 3D-reinforcement, vertical and horizontal weft yarns interlace warp yarns. The through-thickness reinforcements suppress delamination and allow for stable and progressive damage growth in a quasi-ductile manner. With the ultimate goal of developing a homogenised computational model to predict how the material will deform and eventually fail under loading, this work proposes candidates for failure initiation criteria. The criteria are evaluated numerically for tensile, compressive and shear tests. The extension of the LaRC05 stress based failure criteria to this class of 3D-woven composites is one possibility. This however, presents a number of challenges which are discussed. These challenges are related to the relative high stiffness in all directions, which produce excessively high shear components when projected onto potential off-axis failure planes. To circumvent these challenges, strain based criteria inspired by LaRC05 are formulated. Results show that strain based failure predictions for the simulated load cases are qualitatively more reasonable.

  • 46.
    Olsson, Robin
    KTH, Tidigare Institutioner                               , Flygteknik.
    Impact response and delamination of composite plates1998Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis covers a selection of issues associated with impact response and delarknation of composite plates. The problems include contact problems, impact response and delankration testing. The interaction between Hertzian contact stresses and flexural stresses in a plate is studied by comparing a finite element solution with superposition of closed form solutions. Indentation of sandwich panels is studied experimentally and analytically by use of a novel solution which considers core crushing and large face sheet deflections. Wave controlled impact response caused by small mass impact on onhotropic plates is studied analytically and experimentally by use of a one-parameter dimensionless equation. A separate paper describes the extension of the model to sandwich plates. Analytical and experimental aspects of delamination testing are covered by an improved beam analysis of the double cantilever beam specimen and a study of analytical and experimental sources of error in the evaluation of the mixed mode bending specimen. Finally, an extensive experimental program to study the transferability of delamination growth criteria from standard coupen specimens to simple components is reviewed.

  • 47.
    Paget, Christophe
    KTH, Tidigare Institutioner                               , Flygteknik.
    Active Health Monitoring of Aerospace Composite Structures by Embedded Piezoceramic Transducers2001Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The objectives of the thesis work were to study theinteraction between embedded piezoceramic transducers andcomposite structures as well as determine techniques tosimplify the Lamb waves analysis. Firstly, this studyconsidered the design of the embedded piezoceramic transducers.Secondly, the effect of the embedded transducer on thecomposite strength as well as the influence of the mechanicallyloaded composite on the characteristics of the embeddedtransducer were investigated. Finally, to simplify the analysisof such complex Lamb wave responses, two techniques weredeveloped. They were based on the wavelet technique and amodelling technique, respectively.

    The design of the embedded piezoceramic transducers wasimproved by reducing the stress concentrations in the compositeas well as in all components constituting the piezoceramictransducer, that is, the piezoceramic element, interconnectorand conductive adhesive. The numerical analysis showed that thethickness of the interconnector had no significant influence onthe stress state of the piezoceramic transducer. It was alsofound that a compliant conductive adhesive reduced the stressconcentration located at the edge of the piezoceramic element.The structural integrity of composites embedded with theimproved piezoceramic transducer was investigated. Theexperiments, performed in tensile and compressive staticloading, indicated that the strength of the composite was notsignificantly reduced by the embedded piezoceramic transducer.Further investigations were conducted to evaluate theperformance of the improved piezoceramic transducer used as aLamb wave generator embedded in composites subjected tomechanical loading. The tests were conducted in tensile andcompressive static loading as well as fatigue loading. Thestudy showed a large working range of the embedded piezoceramictransducer. A post processing technique based on the waveletswas further assessed in the detection of damage and in thedamage size evaluation. A new wavelet basis was developedspecially for processing the Lamb wave response. This method,focused on the wavelet coefficients from the decomposition Lambwave response, showed promising results in evaluating thedamage size. The wavelets offered a sensitive tool to detectsmall damage, compared to other detection methods, improvingthe damage detection capabilities. The other technique wasdevoted to the simplification of the generated Lamb waves bythe use of multi-element transducers. The transducers weredesigned using both a normal-mode expansion and a FE-method.This technique allowed reducing the effect of a Lamb wave modetowards another. This technique was successfully implemented ina damage detection system in composites.

    Keywords:Embedded piezoceramic, transducer, composite,structural integrity, health monitoring, damage detection, Lambwaves, wavelets, normal-mode expansion, FE-method

    Fulltekst (pdf)
    FULLTEXT01
  • 48.
    Paget, Christophe A.
    KTH, Tidigare Institutioner                               , Flygteknik.
    Damage detection in composites using embedded piezoceramic transduceers and lamb wave techniques2001Licentiatavhandling, med artikler (Annet vitenskapelig)
  • 49.
    Persson, Erik
    KTH, Tidigare Institutioner                               , Flygteknik.
    Machining and fatigue induced damage in bolted composite laminates1998Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The effects of hole machining defects on strength andfatigue life of carbon/epoxy laminates with open holes andpin-loaded holes subjected to static and fatigue loading havebeen investigated. Traditional drilling techniques causingvarying extent of damage and a novel method causing nodetectable damage were employed to machine the holes. Intrinsicdamage and propagation of damage during fatigue loading wasdetected using non destructive examination techniques. Theresults showed that intrinsic damage affect the strength andfatigue life considerably. They also show that during a largeportion of the fatigue life the growth of damage (mainlydelaminations ) do not affect the overall structural responseof the specimens.

    Several factors affecting static strength and fatigue lifeof multiple-row bolted joints in carbon/epoxy laminates wereinvestigated experimentally and ranked in order of importance.the experiments were set up according to a design ofexperiments plan. Design factors such as the ratio between holediameter and spacing between fasteners, and type of fastenerhead proved to have significant influence on the strength andfatigue life.

    The strain energy density used as a failure criterion hasbeen employed to predict delamination initiation in apin-loaded carbon/epoxy laminate. The finite element method wasused to determine the stress and strain fields in the vicinityof the pin-loaded hole. Experiments of pin-loaded specimens andsubsequent non destructive examination were used to validatethe analysis. The analytical results agree well with theexperiments.

    Design variables such as hole to pin shape configuration andhole to edge distance were investigated experimentally andanalytically. Pin-loaded specimens instrumented with straingages determined the strains far and near the hole. Twodimensional analysis using the modified mapping collocationmethod was employed to determine the stresses and strains farand near the hole. The analytical predictions and experimentalmeasurements indicate that the load carrying capacity of apin-loaded hole can be altered by changing the pin-shape.

    Key words:Composite, laminate, bolted-joints,pin-loaded, hole machining, damage, computerized tomography,fatigue, delamination, strength, strain energy density,boundary collocation method.

  • 50.
    Rajput, Moeen S
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Forsberg, Fredrik
    Hallström, Stefan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner. KTH, Tidigare Institutioner (före 2005), Flygteknik.
    Experimental and numerical study of the response to various impact energy levels for composite sandwich plates with different face thicknesses2019Inngår i: Journal of Sandwich Structures and Materials, ISSN 1099-6362, E-ISSN 1530-7972, ISSN 1099-6362, s. 1654-1682Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Composite sandwich structures find wide application in the aerospace sector thanks to their lightweight characteristics. However, composite structures are highly susceptible to low velocity impact damage and therefore thorough characterization of the impact response and damage process for the used material configurations is necessary. The present study investigates the effect of face-sheet thickness on the impact response and damage mechanisms, experimentally and numerically. A uni-directional, non-crimp fabric is used as reinforcement in the face-sheets, and a closed cell Rohacell 200 Hero polymer foam is used as core material. Low-velocity impact tests are performed in a novel instrumented drop-weight rig that is able to capture the true impact response. A range of impact energies are initially utilized in order to identify when low level damage (LLD), barely visible impact damage (BVID) and visible impact damage (VID) occur. A thorough fractography investigation is performed to characterize the impact damage using both destructive and non-destructive testing. The damage from the impacts in terms of dent depth, peak contact force, deflection and absorbed energy is measured. The results show bilinear responses in dent depth vs. impact energy and absorbed energy vs. impact energy. It is found than the BVID energy works well as an indication for the onset of excessive damage. Fractography reveals that there is a failure mode shift between the LLD and the VID energy levels, and that delaminations predominantly grow along the fiber direction and rotate in a spiral pattern through the thickness, following the laminate ply orientations. Finally, a progressive damage finite element model is developed to simulate both the impact response and the delamination extent, incorporating both intra- laminar and inter-laminar damage modes. The simulation shows good agreement with the experiments.

    Fulltekst (pdf)
    fulltext
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