Licentiatavhandling Linköping : Linköpings universitet, 2007.

No description available.

In the transition from conventional to green energy production resources, steam turbines are used to satisfy the lack of energy during peaks in the demand times and the limited access of renewable resources. This type of usage for steam turbines makes them operate on a flexible schedule, which leads to unpredictable issues related to shorter component life and faster crack propagation. Thus, the steam turbine components must be examined to determine their specific life period. This will help set proper maintenance intervals and prevent unexpected failures. For that, thermo-mechanical fatigue (TMF) testing is used, where a specimen made of the same material as the turbine component is subjected to both temperature and load variation. The specimen is pre-cracked to investigate the crack propagation behavior, which is the focus of this study. This thesis work concentrates on simulating the TMF cycle for the steam turbine casing component. The material is 9%-10%Cr ferritic steel. The aim is to understand the material behavior during crack propagation and to predict a useful testing parameter. The method provided in this work discusses two cases, both are out-of-phase (OP) TMF tests with strain control. The maximum and minimum temperatures for the cycle are 600 ˚C and 400 ˚C respectively, while the maximum and minimum strain levels are 0 and  respectively. The study will investigate different , which is the maximum compressive strain level. Case 1 has a dwell time at the maximum temperature only, while case 2 has dwell times at both maximum and minimum temperatures. The method utilizes the stress intensity factor (SIF) to characterize the crack tip conditions. Also, it uses Paris' law to estimate the duration of the tests. For simplification, only the elastic behavior of the material is considered. The results obtained show no effect of using different pre-crack lengths due to the strain control condition. Minor effects can be observed by using different dwell times, however very short dwell times must be avoided to produce reliable results. A recommended dwell time of 5 minutes could be used, since longer dwell times will make the test prohibitively time-consuming. The compressive strain levels used in the work shows large effects on the results. Using low compressive strain values will produce a very long time for the tests, while very high compressive strains produce large plasticity. Thus, high compressive strains must be avoided since the SIF describes cracks for only elastic or near elastic cases. Also, small compressive strain levels in case 2 should not be used since it will lead to results like case 1. This is due to the small creep effect at the minimum temperature. Finally, compressive strain levels of 0.6 %, 0.5 % and 0.4 % are recommended for case 1, while only 0.6 % compressive strain level is recommended for case 2. This thesis contributes to the fields of solid mechanics, fracture mechanics and the use of TMF testing, where a recommended set of testing parameters are provided.

In computational fluid dynamics (CFD), the computational domain can be discretized using mesh- based methods or particle based methods. During this project; a CFD method that uses smoothed particle hydrodynamics (SPH), in which the computational domain is discretized by particles, is modelled and compared to mesh-based CFD methods, in which the domains are broken into a set of discrete volumes. The aim with this master thesis project is to determine whether the SPH method can replace mesh-based methods in cases that involve free surface flows and fluid-structure interac- tions (FSI’s) in order to avoid mesh-deformations. The comparison is done by studying a free fall of a torpedo shaped object, 500 mm in length, both experimentally and with numerical simulations. The CFD methods that are compared are mesh-based one-way FSI, mesh-based two-way FSI and the SPH method. The methods are created in the two simulation software ANSYS (one-way and two-way FSI) and LS-DYNA (two-way FSI and SPH). The comparisons are made by looking at experimental and numerical accelerations. The experiment gave uncertain results and there were difficulties in comparing experimental results to numerical results. When looking at all results, it is concluded that the mesh-based methods give reasonable maximum values while the SPH method gives too high values. For the mesh-based methods in ANSYS, air is present which is not the case for the methods mod- elled in LS-DYNA. When comparing the computation time for all methods, it is concluded that the presence of air increases the computation time considerably and based on the results in this project, air is not necessary to take into consideration. The aim of this project is reached by concluding that the mesh-based method in LS-DYNA is the most suitable method for the studied case, based on the following: acceleration behaviour, maximum acceleration values, computation time and the possibility to neglect air. The conclusion might be revised when future work on the SPH method has been done.

No description available.

No description available.

No description available.

No description available.

When a material is mechanically loaded or experience environmental changes such as for example thermal or pressure variations it is affected, in some way, due to these new conditions. In order to measure engineering properties related to these structural changes, such as for example deformation and strain, we need to gain information about them that are precise and reliable. There exist many different methods for such measurements. However, most often these methods measure the pure surface response due to the deforming mechanism, since this is what can be observed directly by use of cameras and various sensors. We therefore know a lot about how the material surface behaves but not much about how the structure beneath the surface behaves. As long as the material structure is reasonably homogeneous this may be enough but as the complexity of the material structure increase it gets more important to obtain information from the inside of the material. In this thesis two techniques with the ability to measure internal deformations in optically non-transparent materials are presented. The fundamental principle of both the techniques is the same. The techniques utilize a correlation based routine to estimate deformations from two and three dimensional image data collected with x-ray-based methods. The first technique, called Digital Speckle Radiography (DSR), measures two-dimensional deformation fields, in a single plane within the examined material. The deformations are estimated by the use of image correlation applied to two-dimensional digital x-ray images. The second technique, called Tomographic 3D-DSP, measures the three-dimensional unrestricted deformation, in every point of the examined object. Here the correlation procedure is carried out on volumetric object data collected with computed tomography (CT). Three separate experiments have been carried out, to investigate the behaviour of the two techniques. In two of the experiments the two-dimensional technique is applied. In the first of these the flow profile of an alumina powder is measured as it flows through a silo configuration. In the second experiment the motion in a thin film of glue, sandwiched between two wooden plates, exposed to shear, is measured. Finally in the third experiment the three-dimensional technique is used to measure the deformations in bone tissue when being exposed to a mechanical load. In this case two measurements have been carried out, and compared. These differ through a small damage that has been introduced to the bone tissue in the second measurement. / Godkänd; 2005; 20061221 (haneit)

Företaget Cranab, i vindeln, tillverkar i stor utsräckning skotar-, och skördarkranar till skogsmaskiner i varierande storlekar. Företaget tillverkar sedan ett år tillbaka även lastbilkranar. En kran består av olika delar i varierande storlekar så som kranpelare, lyftarmar, vipparmar, mellanbommar och innerbommar. Dessa krandelar är svetsade konstruktioner och består i sig av olika komponenter, de olika komponenterna skärs ut i en lasermaskin och svetsas sedan på de olika krandelarna. När krandelarna är kompletta bearbetas de i en CNC-maskin. När den färdiga krandel ska bearbetas i CNC-maskinen placeras den i en fixtur som säkerställer en stabilare bearbetning och förhindrar främst vibrationer. I nuläget används en uppsjö av olika fixturer som är konstruerade för en esnkild krandel, vilket medför en längre ställtid och fixturerna tar väldigt stor plats på golvet. Syftet med detta arbete är att ta fram ett konstruktionsförslag till en flexibel fixtur där ett antal krandelar med varierande storlek går att spänna fast. Många faktorer är viktiga vid konstruering av fixturerna för att kunna säkerställa en optimal bearbetning av krandelarna. Cranab står inför en stor investering gällande CNC-maskin vilket påverkar fixturen då den skall roteras 90 grader under bearbetningen, de nuvarande fixturerna är inte anpassade för denna rotation och därför måste även detta tas till hänsyn under konstruktion utöver de tidigare kraven. Under detta arbete behandlades lyftarmar till skotare vilket är den mest komplicerade krandelen. Första momentet av arbetet består av informationsinsamling och analys av nuvarande fixturer, efter detta utförs konstruktionsarbetet i CAD-programmet Inventor där ett koncept till fixturen tas fram. Resultatet av arbetet är en fixtur som kan hantera åtta stycken olika varianter av lyftarmen till skotare, i nuläget kan en fixtur endast användas till maxiamalt två olika varianter. I och med den nya konstruktionen kan justeringarna som krävs för olika varianter göras på ett smidigt sätt och inga traverser eller liknande verktyg krävs för att ställa om fixturen, vilket effektiviserar fixturen ytterligare. Resultatet ses som en klar förbättring jämfört med de nuvarande fixturerna, även om det som presenteras inte är en färdigställd genomarbetad fixtur så är det en grund att arbeta vidare med. / The company Cranab, located in Vindeln, manufactures cranes in varius sizes mostly to forest machines, since a year back they also manufactures cranes to trucks. A crane consists of different components in various sizes such as crane piller, lifting arms, rocker arms, middle boom and inner boom. These components are welded constructions and consists of different details, the different details are produced in a laser cutting process and then welded on to the arm itself. When the arm is complete it is put into a CNC-machine where it is processed. When the arm is ready for the CNC-machine it is placed in a fixture to ensure a more stable processing an mostly to readuce vibrations. The current situation at Cranab is that they use one specific fixture to one specific arm. For this reason it takes a lot of time to change between arms and the fixtures itself takes a lot of place in the workshop. The purpose of this project is to construct a flexible fixture that is able to handle a couple of arms by changing the fixture in a smooth way. A lot of varius factors are important when constructing a fixture that ensures a stable and safe process in the CNC-machine. Cranab are investing a lot of money in a new CNC-machine that will process these arms, the new machine is going to rotate the whole fixture 45 degreese. The fixture that are now used are not able to handle this kind of rotation so except the current requirements the new fixture must be able to hold the whole weight of the arm. During this project the lifting arm to forwarders will be analyzed which is the most complicated part of the crane. The first part of the project will consist of collecting information about the current situation and analyzing the fixtures that are now used, after that the construction of the fixture will be done in the CAD-program Inventor where a koncept will be be developed. The project results in a fixture that can handle eight arms, the current fixtures that are used can only handle a maximum of two arms. With the new fixture, the adjustmets that are necessary when different arms needs to be mounted will be easy to implement and they won’t need a traverse to adjust the fixture. This will make the workprocess of adjusting the fixture much more time efficient. The result is, in comparison with the old fixtures, a clear improvement. Although the project resulted in a raw model of the flexible fixture it is a clear improvement of the existing ones and it is something to continue working with.