Due to the improvement of luminous efficiency, LED has been applied in general lighting nowadays. However, the efficacy and life of high power LED lamps are degraded for the problem of overheat temperature of the chips. In accordance with the above reason, the thermal management has been important in LED application. The thesis aims to analyze the thermal problem of high power LED lamp by FEM. In the beginning, we analyzed the temperature curves and thermal stress curves of chips by changing the thickness of AuSn solder in 4 structures. According to the results, the better thickness range and structures were chosen. In the second step, the effect of different sizes of a vapor chamber on the different thermal conductivities of lamp system was discussed. Finally, we orthogonalized all the designed parameters by Taguchi orthogonal array method, and then found the optimal design by comparing the results with the initial analyses. In this study, we proposed a solution to improve the quality characteristics of LED lamp by Taguchi method. So the effect of each control factors on the performance was able to be determined. For different features of demand, the present study is helpful to achieve the ideal design in manufacturing. Key words: FEM, high power LED lamps, Taguchi orthogonal array method

The post-weld-shift (PWS) introduced in the butterfly laser packaging is investigated in this study. The elastic-plastic-thermal coupled finite element model is employed in the stress and deformation analyses. The temperature dependent material properties are used to calculate the residual stresses and the post-weld shift distributions during the packaging process. The finite element package ¡¥MARC¡¦ is used in this study. And the commercial optical software, i.e. ¡¥Zemax¡¦ is also employed in laser power coupling efficiency simulation. The variations of laser welding sequence, Nd-YAG pulse laser power, and initial ferrule¡¦s alignment position on PWS for butterfly laser packaging are studied and discussed in this work. The results indicated adjust the sequence and pulse laser power properly can improve the PWS in butterfly packing significantly. Besides, the PWS correction technique, i.e. the ¡¥Laser Harmering¡¦, is also illustrated in this study. The simulate results showed that proper arrange the welding processes may improve the coupling efficiency over 75¢M.

Abstract In this thesis, we have studied the post-weld-shift (PWS) in laser welding technique for laser module packaging. The joining method for packaging of laser module by laser welding technique can offer a number of significant advantages. It provides strong joint strength, therefore, the packaging has good long-term stability. It also provides high-speed and high-volume production, and hence the packaging is potential low cost. However, the laser welding process has caused PWS of laser module, would decay the coupling efficiency of laser module. We investigate the weld-spot by using metallographic method. The PWS in stainless steel (SS304L) plate is studied experimentally and numerically. The metallographic results are in good agreement with the Finite-Element-Method (FEM) results that the PWS in x-y plane can be neglected. Based on the experimentally and numerically results of PWS in SS304L, we investigate the yield improvement of laser module packaging. The laser hammer technique was used to improve the coupling efficiency of laser module. The results show displacement of the z-axis is from 1 to 9 (£gm) that equals to the angle changes of upper parts of laser module from 0.38¡Ñ10-2 to 3.4¡Ñ10-2 (degree). Therefore, the coupling efficiency of laser module can be improved from 4 to 20 (%).

Abstract The effects of residual stresses distribution and post-weld-shift on the signal coupling efficiency of an Optical Add & Drop Multiplex (OADM) are investigated in this thesis. The position variations between the two collimators in the OADM under the temperature cycling test and high temperature aging test have been simulated and studied. The finite element method package, i.e. MARC, is used for the stresses and deformation simulations of an OADM under different load cases. The coupled thermal-elastic-plastic model is employed in the analysis, and the creep effect of the solder is considered in the numerical simulations. The temperature dependent material properties of the 63Sn/37Pb and 96.5Sn/3.5Ag solder are used for the solder solidification, temperature cycling and aging tests. The effects of the OADM packaging parameters, i.e. the different offset angles between collimators, different solder are also studied. Besides, the same simulation and analysis has also applied on the soldering with and without cavity. A comparison between the simulated and measured results indicates that the proposed finite element model is feasible for analyzing the OADM packaging problems.

Abstract In this thesis, the effect of the orientation of trussed honeycomb core design on the stiffness of a composite honeycomb plate is presented. A commercial finite element (FEM) package ¡¥MSC-MARC¡¦ is employed in the stiffness simulation. To illustrate the feasibility and accuracy of the proposed FEM model, the measured and calculated data for two different sizes regular honeycomb plates (with regular hexagonal cell) are compared. Results show that a good agreement between the simulated and the measured static deflections and dynamic characteristics is found. Numerical results indicate that different orientations of trussed honeycomb core design may improve the stiffness/density ratio of a composite honeycomb plate significantly. The effects of other design parameters of composite honeycomb plate, e.g. width and height of plate, thickness of truss, cell wall and faces, and material of truss, on the stiffness/density ratio have also been investigated in this study.

<p>Alla barn har en rättighet att känna sig trygga i skolan och inte bli utsatta för kränkande behandling eller mobbning. Mobbning är ett problem som måste uppmärksammas alltmer eftersom det inte alltid tas på allvar trots att varje skola har någon form av antimobbningsplan. Mobbning kan uttryckas i form av fysisk, psykosocial och verbal mobbning. Vårt syfte med undersökningen är att lyfta fram barns uppfattning om mobbning. Då lyder vår problemformulering som följer: Hur uppfattas mobbning av barn i årskurs fem på sex olika skolor? Vårt intresse ligger i att utföra vår undersökning i årskurs fem på sex olika skolor som aktivt arbetar med olika program mot mobbning. Undersökningen är inte avsedd som en jämförande studie. Vår metod är kvalitativ i form av en helt anonym enkätundersökning med öppna frågor då vi anser att ämnet är alltför känsligt för att använda vid intervjuer. Svaren vi får är inte ämnade att föra statistik utan syftet är att analysera och tolka barnens svar för att skapa en förståelse av deras uppfattning. Vi har valt att i analysen av enkätsvaren använda oss av symbolisk interaktionism, social identitetsteori, rollteori och aggression som gruppfenomen.</p>

Considering the hypothetical core melt down scenario for a light water reactor (LWR) a possible failure mode of the reactor pressure vessel (RPV) and its failure time has to be investigated for a determination of the loadings on the containment. Numerous experiments have been performed accompanied with material properties evaluation, theoretical, and numerical work /REM 1993/, /THF 1997/, /CHU 1999/. For pre- and post-test calculations of Lower Head Failure experiments like OLHF or FOREVER it is necessary to model creep and plasticity processes. Therefore a Fi-nite Element Model is developed at the FZR using a numerical approach which avoids the use of a single creep law employing constants derived from the data for a limited stress and temperature range. Instead of this a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. A main task for this approach is the generation and validation of the CDB. Additionally the implementation of all relevant temperature dependent material properties has been performed. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied. The validation of the numerical model is performed by the simulation of and com-parison with experiments. This is done in 3 levels: starting with the simulation of sin-gle uniaxial creep tests, which is considered as a 1D-problem. In the next level so called "tube-failure-experiments" are modeled: the RUPTHER-14 and the "MPA-Meppen"-experiment. These experiments are considered as 2D-problems. Finally the numerical model is applied to scaled 3D-experiments, where the lower head of a PWR is represented in its hemispherical shape, like in the FOREVER-experiments. This report deals with the 1D- and 2D-simulations. An interesting question to be solved in this frame is the comparability of the French 16MND5 and the German 20MnMoNi55 RPV-steels, which are chemically nearly identical. Since these 2 steels show a similar behavior, it should be allowed on a lim-ited scale to transfer experimental and numerical data from one to the other.

<p>The demands the automotive gear designer has to considerduring the gear design process have changed. To design a gearthat will not fail is still a challenging task, but now lownoise is also a main objective. Both customers and legalregulations demand noise reduction of gears. Moreover, thequality of the product is more in focus than ever before. Inaddition, the gear design process itself must be inexpensiveand quick. One can say that the gear designer faces a newdesign environment. The objective of this thesis is tocontribute to the answer to some of the questions raised inthis new design environment.</p><p>In order to respond to the new design situation, the geardesigner must consider new phenomena of gears that werepreviously not a matter of concern. One such phenomenon is anew gear failure type, Tooth Interior Fatigue Fracture (TIFF).As the gear teeth are made more slender in an attempt to reducethe stiffness variation during the mesh cycle, therebypotentially reducing the noise, the risk of TIFF is increased.The phenomenon of TIFF is explored in detail (paper III-VI)through fractographic analysis, numerical crack initiationanalysis using FEM, determination of residual stress by meansof neutron diffraction measurements, testing for determiningmaterial fatigue properties, fracture mechanical FE-analysis,sensitivity analysis and the development of an engineeringdesign method. The main findings of the analysis of TIFF arethat TIFF cracks initiate in the tooth interior, TIFF occursmainly in case hardened idlers, the fracture surface has acharacteristic plateau at approximately the mid-height of thetooth and the risk of TIFF is more pronounced in slender gearteeth.</p><p>Along with the more optimised gear design, there is atendency for the gear to be less robust. Low robustness, i.e.,great variation in performance of the product, implies a highincidence of rejects, malfunction and/or bad-will, all of whichmay have a negative effect on company earnings. As the use ofoptimisation decreases the safety margins, greater attentionhas to be paid to guaranteeing the products' robustness.Moreover, in order to be cost-effective, the qualities of thegear must be verified early in the design process, implying anextended use of simulations. In this thesis, two robustnessanalyses are presented in which the analysing tool issimulation. The first one considers robust tooth root bendingfatigue strength as the gear is exposed to mounting errors, thesecond one considers robust noise characteristics of a gearexposed to manufacturing errors, varying torque and wear. Bothof these case studies address the problem of robustness ofgears and demonstrate how it can be estimated by use ofsimulations. The main result from the former robustnessanalysis is that wide gears are more sensitive to mountingerrors, while the latter analysis showed that to achieve robustnoise characteristics of a gear it should have large helixangles, and some profile- and lead crowning should beintroduced. The transverse contact ratio is a trade-off factorin the sense that both low average noise levels and low scatterin noise due to perturbations cannot be achieved.</p><p><b>Keywords</b>: robust design, Taguchi method, gear, idler,simulations, Finite Element Method, Tooth Interior FatigueFracture, TIFF</p>

Kurbelwellen verfügen über konstruktive Besonderheiten - wie Versteifungen an den Hauptlagern zur Verbesserung der Steifigkeit oder Auskerbungen an den Kurbelwangen zur Reduzierung der rotierenden Massen -, deren Dimensionen, verglichen mit der Kurbelwelle selbst, sehr klein sind. Um Steifigkeitsberechnungen mit der Finite-Elemente-Methode durchführen zu können, muss die Geometrie adäquat vernetzt werden, was bei komplizierten Geometrien nur durch ein feines Startnetz erreicht werden kann. Da dessen Konstruktion aufwendig und die Verwendung nachteilig ist, werden Ersatz-Deformationsprobleme über geometrisch einfacheren Gebieten mit ortsabhängigen Materialparametern definiert, die mit Hilfe von Materialfunktionen modelliert werden. Nach einer theoretischen Darstellung werden verschiedene Materialfunktionen definiert und ihre Eigenschaften anhand von numerischen Experimenten miteinander verglichen.

Gegenstand der vorliegenden Publikation sind Festigkeitsberechnungen von Maschinen aus der Hütten- und Walzwerkstechnik mit Pro/Mechanica. Erläutert werden die Arbeitstechniken, die bei der Aufbereitung der Modelle zum Einsatz kommen, sowie die genutzten Regelwerke für den Festigkeitsnachweis. Die angeführten Rechenbeispiele stammen allesamt aus der täglichen Praxis der industriellen Nutzung von FE-Methoden im Maschinenbau.